Comprehensive Guide to Cells, Tissues, and Biological Systems for Exams

Let us now move on to our next important topic. Cell, yes cell, we often call it the basis of life, meaning

the building blocks of life, and this is a very important topic for competitive exams. Absolutely. Without this, we cannot even imagine life. This is the smallest unit. Is

n't it? Yes, the basic unit. Whether it is a small bacteria or we humans or a big tree, everything is made up of these cells. Yes, all the work of the body, meaning making energy, sending information forward, everything happens at this level,

at the level of the cell. So how was it discovered? I mean, who saw it first ? Where does the story begin? Look, the first name that comes is of Robert Hooke.

Okay. It is about 1665. Okay. He took cork, which is the bark of a tree, and looked at it through a microscope, then he saw small empty rooms like a beehive.

Empty rooms? Yes. Actually, they were dead cells whose walls were left only. But he was the one who discovered it. That is why Robert Hooke is called the father of cytology. I mean, the father of cell science. Okay. So those were dead cells. Then who saw a living

cell? The credit for seeing a living cell goes to Antonie van Leeuwenhoek. This is from 1674. Okay. He looked at the water in a pond through a microscope and

saw small moving organisms like bacteria in it. Those were living cells. And then there are many things inside a cell. Like its control center. Yes, the nucleus. It was discovered by Robert Brown in 1831. It

is a very important part of the cell. And the DNA about which we hear so much, that instruction manual, the DNA molecule, was discovered much earlier by Frederick Mishra in 1869, but its structure is like a winding staircase,

double helix. Yes, the double helical model was described by Watson and Crick in 1953. And another name worth remembering is Camillo Golgi, he discovered Golgi bodies. Okay, so now let's

go inside the cell. What are its main parts? If we consider the cell as a factory, then what are its departments? Yes, this is a good way to understand. So first of all the outer wall of the factory. In animal cells this is the cell membrane

. What is it like? It is thin, flexible and alive. It is like the gate of the factory. What do you mean? Meaning it decides which thing

will come in and which will go out. This is called selectively permeable. It does not let everyone come and go. Well, what is it made of? It is made of proteins and lipids. And in plants, they probably have another layer

. Absolutely. In plants, bacteria and fungi, there is another thick and strong wall outside this membrane. That is called the cell wall.

So how is it different from the membrane? It is non-living. And it is completely permeable. Meaning it does not stop anyone. Everyone can come and go. Its main function is to give a certain shape to the cell, to give it strength.

And it is made of different things in different organisms. Isn't it? Yes. In plants, it is made of cellulose. Bacteria have peptidoglycan and fungi have chitin. Animal cells do not have this. It is important to remember this.

Okay. The walls are done. Now the control room of the factory. You told me. Nucleus. Yes. Nucleus. This is the largest part of the cell and it is called the brain of the cell. All activities

are controlled from here. What is there inside it? No, nucleolus. What is the function of the nucleolus? It makes ribosomes which are the factory for making proteins and the most important thing is

the chromatin material. Chromatin. What is this? It is a tangled web like a thread. DNA and proteins are present in it . Okay. And chromosomes

are made from this. Absolutely. When the cell is about to divide, then these threads of chromatin get tightly wrapped and form thick structures which we call chromosomes. Okay.

These chromosomes contain DNA and small parts of DNA are called genes. All the genetic information is in them. Humans have 23 pairs of chromosomes . Okay? Now

what is there in the space between the nucleus and the outer membrane, the main floor of the factory? It is called cytoplasm. It is a jelly-like substance and in it all the small parts of the cell, called cell organelles,

float. These are the real machines of the factory. We cells are also of different types. Some are simple, some are complex. Yes. There are mainly two types of them. Prokaryotic and eukaryotic.

What is the difference between them? Prokaryotes are very simple. Like bacteria. They have neither a clear nucleus with a membrane nor other membrane-bound organelles like mitochondria etc. Their DNA just

lies in the cytoplasm. Spherical and eukaryotic Eukaryotic cells are more developed . Like our cells, plant cells. They

have a proper nucleus surrounded by a membrane and also have many membrane-bound organelles like mitochondria, Golgi bodies, lysosomes. Their DNA is organized in chromosomes inside the nucleus. So tell us a little about these organelles as well.

These are factory machines, like where does the energy come from in the factory? Mitochondria is responsible for energy. It is called the power house of the cell. Power house. Yes. It breaks down food and extracts energy from it

and stores it in the form of ATP. ATP is the energy currency of the cell. And the interesting thing is that mitochondria also have their own DNA and ribosomes . Oh wow, this is very special and

the packaging and dispatch department of the factory. That is the work of Golgi bodies. It is also called Golgi complex. It sorts out the proteins and lipids etc. made in the cell. It makes some changes in them and then

packs them and sends them to the right place. And does it make anything else? Yes, it also makes lysosomes. Consider lysosomes as the cleaners or garbage collectors of the cell. Okay. How? Or

they digest the bacteria etc. that come from outside. Sometimes if the cell gets damaged, they burst and digest the entire cell. Oh, that is why they are called suicidal bags or suicidal beds. Absolutely. That is why

and where are proteins and lipids actually made? They are made in the endoplasmic reticulum i.e. ER. It is a net-like structure. It is of two types. Rough ER and smooth ER.

What is the difference between them? Rough ER has ribosomes stuck to its surface like tiny grains. That is why it looks rough. The job of ribosomes is to make proteins. So rough ER helps in protein synthesis.

And smooth ER. There are no ribosomes on smooth ER. Its job is to make lipids i.e. fats and steroids. Okay? Plants also have some other special things, vacuoles and plastids. Yes, plant cells often

have a very large vacuole. It stores water, nutrients and waste products and keeps the cell inflated from inside, which gives support to the plant. And plastids. Plastids are found only in plants and some algae

. They are also special like mitochondria. Because they also have their own DNA and ribosomes. There are types of them too. Yes, there are three main types. Chloroplasts contain chlorophyll and

make food through photosynthesis. These are the solar panels of the plant. Then we have chromoplasts which give colour to flowers and fruits. Red, yellow, orange. And the third are leucoplasts which

are colourless and store starch, oil or protein. Got it? Now one last question. How do these cells increase their number? How does this division or cell division take place? Cell division is very important. For growth of the body

, for repairing injuries and for reproduction, there are broadly two main ways of division. Which ones? The first is mitosis. This

happens in our normal body cells which are called somatic cells. In this, two new cells exactly like the original are formed from one cell in which the number of chromosomes remains the same. This is for growth and repair. And the second

is meiosis. This happens only in the reproductive cells which form gametes. Like sperm and egg. In this, one cell divides into four cells and the number of chromosomes in each new cell is halved.

Half. Why? So that when the male and female gametes combine and fertilize, the number of chromosomes in the child formed becomes normal again. Meiosis also brings genetic diversity which is necessary for evolution.

So this was the story of the cell. A small unit but so complex and important. Absolutely. It is a matter of thought that how so many different machines, these organelles work in such perfect coordination inside a single cell. Each has its own work and

together they run life. And these methods of division are also so unique. One leads to growth, the other brings diversity and life continues from generation to generation. Yes, both mitosis and meiosis are important parts of life.

They are extremely important for continuity and evolution. Really. Ok, let's leave a question for our listeners. Which part of the cell or which process makes you think the most?

Mitochondria having its own DNA, lysosomes becoming suicide bags, or the chromosomes getting halved in meiosis. Yes, do share your thoughts in the comments below. We will be waiting. Plants have their own amazing world and

to understand their structure and how they work, it is very important to know about their tissues. Yes. So today let's talk a little more deeply about these plant tissues.

Yes, absolutely. We will especially focus on two main types of tissues. One is meristematic tissue which is responsible for the growth of the plant i.e. increasing the length and width.

And the second is permanent tissue. Yes, which perform different very specific functions in the plant . Yes and you can say that these tissues are like the foundation of a building. What is their structure? How many types are there? It is very

important to understand this. Ok. Yes. Because see, these tissues give the plant its shape. They support it and actually help it to do all its important functions.

Hmm. So let's see how all this happens. Okay. So let's start with the meristematic tissue. As you said, it is for growth. Yes.

So, it is found in those parts of the plant where there is continuous growth. Right? Like the top end of the stem or root. Exactly. And their cells are very active. Active means?

Active means that their cytoplasm is very thick. But the interesting thing is that there is no empty space between the cells, intercellular space. Okay and there are no vacuoles either? Yes, there are no vacuoles either or they are very small

. You can say that their only mission is to divide rapidly. Okay. And create new cells. This is how the plant grows. So these have become like the growth engine of the plant.

Yes. And where are they found in the plant? Depending on this, their types will also be different . Yes, yes, absolutely. There are three main types based on their location . Which ones?

The first one is the apical meristem. It is located at the apex at the very tip of the stem and the root. And what does it do? It increases the length of the plant. Both upwards and downwards in the root.

Okay? And the second one is the intercalary meristem . You will find it at the base of the leaves or in the space between the twigs, the internodes. Okay. So it increases the length of those parts

like the leaf petiole. Yes, something like that. And the third one is the lateral meristem. It is responsible for increasing the thickness of the stem and the root.

Where is this thickness increasing tissue located? You will find it just below the bark. Cambium is a good example of this. Amazing. That means the growth of both the length and thickness of the plant is controlled by different meristems. This is very systematic.

Yes. Okay. Now a question. When these meristematic cells, these growth cells, stop dividing, what happens to them then? Very good question. This is where permanent tissue comes into play.

Ok. When meristematic cells lose their ability to divide and become ready to perform a particular function, it means they become specialized. Yes, absolutely. When they become specialized,

they become permanent tissue and this process is a very important term. It is called differentiation. Differentiation, yes, okay. Yes, remember this. And

the identity of these permanent cells is that they often have a large central vacuole. Oh, so they have a vacuole. Unlike meristematic. Absolutely. And their cell wall can be thin

or thick according to the need. Yes, did you understand? So these permanent tissues must also be of many types. Yes, broadly two types. Simple permanent tissue and complex permanent tissue. Okay. So let's first understand the simple ones.

In this, parenchyma is probably the most common. Right? I have read it. Absolutely right. Parenchyma is the most common. Its cells are alive. The cell wall is thin and there is also empty space between them. And what is their main job?

Their main job is to store food. Like starch or fat and also to give some support to the plant. There are some special types in this too. Like in some aquatic plants, the parenchyma

is filled with air. Why air? So that the plant can float on water. This is called aerenchyma. Well aerenchyma is great for floating. Yes. And if chlorophyll

is present in parenchyma then it is called chlorenchyma. Chlorenchyma means it can also do photosynthesis. Absolutely photosynthesis. Wow, how many forms of the same tissue? Well what is the next one among simple tissues?

Next is collenchyma. This is also made up of living cells. Collenchyma. What is its function? It gives flexibility to the plant . Flexibility especially in the new stems or the petioles of the leaves

. Yes, when the wind blows, the branches do not break but bend. That is because of this, yes, absolutely it happens because of this collenchyma . Their cells are a little thick at the corners. Irregularly and there

is very little empty space between them. Flexibility and the third simple tissue is sclerenchyma. It gives rigidity and strength to the plant. Hardness, for example, think of the outer fibre of coconut,

the brown one, yes , or the hard shell of walnut or almond, yes, it is made of sclerenchyma. Well, it must be very strong.

Very, very strong. Its cells are actually dead. Dead cells and their walls become very thick and hard due to a chemical called lignin. Lignin. Okay.

So, in a way, it becomes the armour of the plant. Yes, we can definitely say so. It gives mechanical strength to the plant. So, these are simple permanent tissues. Parenchyma, collenchyma and sclerenchyma. The functions of all three are completely different.

Yes. Now, plants have become strong and flexible from inside, but how do they protect themselves from the external environment like sunlight, water, germs? There must be special tissues for this too. Yes, there are. We

call them protective tissues. The first name that comes in this is epidermis. Epidermis looks like skin. Yes, understand it to be something like that. It is the outermost layer of all parts of the plant, root, stem, leaf, flower, fruit.

A single layer and its job is to provide protection. Absolutely. For example, in desert plants, it is thick to reduce water loss and it is often coated with a waxy substance called cutin.

A waxy layer. Yes, it is called cuticle. It prevents water from evaporating. It protects the plant from injury and also protects against fungal infection. So, is there an epidermis in the roots as well?

Yes, it is in the roots as well. But the epidermal cells there absorb water . They form thin fiber-like structures called root hairs . Root hairs? Yes, they help absorb

water and minerals . Right. They increase the surface area for absorbing water. Okay? So the epidermis is the outer protection. Yes.

Anything else? Yes. There is one more. As the plant gets older, the stem and roots become thicker. So the epidermis is replaced by another strong layer . It is called cork. Cork. Have you heard this name?

The one with the bottle cap. Yes, the same cork. It is a part of the bark of the tree . The cells of cork are also dead like sclerenchyma. Dead? Then how does it protect? A substance called suberin

is deposited on their walls. Suberin, yes suberin. This makes the cork completely impermeable to water and gases . So neither water can come in from outside nor can gas go out from inside.

So this is an even stronger protection. Yes. It protects the mature roots and stems. Okay? So you have understood the simple and protective tissues. Now let's come to complex permanent tissues. As

the name suggests, these are a little complex. Yes, they are complex because they are made up of more than one type of cells and all these cells work together as a unit, like a team.

Like a team. Ok. Which are these? The two main complex tissues are xylem and phloem. You have heard the names xylem and phloem a lot. These are transport tissues, right? Absolutely. These are also called conducting tissues. These

are part of the plant's transport system. Xylem and phloem together form the vascular bundle . Okay? So let's talk about xylem first. What is its special function? The main function of xylem is to pull water and dissolved

minerals from the roots and transport it to the upper parts of the plant. That means from bottom to top. Yes, there is always one way traffic from bottom to top in one direction . You can think of it as the water pipeline of the plant.

Water pipeline right. And what cells is it made of? There are four types of cells in it. Tracheids and vessels. Both of these mainly transport water and minerals. Then there are xylem fibers which give strength.

Fibers this sclerenchyma like yes, this is actually sclerenchyma. And the fourth one is xylem parenchyma. What does parenchyma do here? It stores food and

also helps a little in the sideways conduction of water. And one special thing is that out of these four, only xylem parenchyma is a living cell. The other three are dead. Well only parenchyma is alive in xylem. Okay. Now let's come to phloem.

What does it do? The job of phloem is to transport the food produced in the leaves through photosynthesis, that sugar, to all those parts of the plant where it is needed. Where is it needed? Like

in the growing buds, in the fruits, in the seeds or for storage in the roots. Okay. So, it transports food. And does its transport also happen from bottom to top ? No. Phloem

can be transported in both directions. Two way traffic. From top to bottom as well as from bottom to top as per the need . Well, this is different from xylem. Yes, it can be called the food delivery network of the plant. Food delivery network, great. And

what cells are there in it? There are four types of parts in it too. Sieve tubes and companion cells. Both of these together do the main work of food transport.

Sieve tubes and companion cells. Yes. Then there is the phloem parenchyma which stores food and the phloem fibers which provide support and strength. There are fibers in it too. And are the cells of phloem alive?

Yes, unlike xylem, most of the cells of phloem are alive. Sieve tubes, companion cells, phloem parenchyma, all of them are alive. Only the phloem fibers are dead . Got it? So xylem transports water and minerals from bottom

to top and phloem transports food in both directions. Absolutely right. So see how we saw that all these different permanent tissues were formed by differentiation from meristematic tissue . Simple ones parenchyma, collenchyma, sclerenchyma

then protective epidermis and cork and finally complex xylem and phloem. Hmm. And these xylem and phloem together form the vascular bundle. And the most interesting thing is that the composition of each tissue is so perfectly

adapted to its function. How fit we are. You said it right. Absolutely. When all these tissues work together, then only a complete plant can stand. It can run its life. That means

these tissues help in everything - in growing, in making food, in drawing water, in standing upright and in protecting itself. Each one has its own important role. Yes. Here one thing makes us think . The way the work of each tissue in plants is so clearly divided and their structure

is perfect for that work. Does n't this make us think about the amazing engineering and design of nature ? Yes, it is. How simple cells together form

such a complex, so effective system. This is amazing in itself. Now my next topic is animal tissue. It is very important to understand whether it is our body or that of an animal, how it is made. Yes, and how do the different parts

perform their special functions? Have you ever thought how different is the structure of our skin from bones or muscles? That's right. All this amazingness is due to these tissues. And yes, this is a very important topic for

competitive exams like SSC or UPSC . Definitely. So we will mainly look at four types of tissues. First epithelial . Second

muscular. Third connective. And fourth nervous tissue. Okay.

Let's take a look inside them. Let's start with epithelial tissue. Epithelial. Yes. Epithelial. These form the outer or inner surface of the body and organs. A kind of covering or lining.

Yes. Meaning like a protective shield. Absolutely. Their cells are also of different shapes . They can be flat. Squamous Cuboidal or Columnar Columnar

The flat cells we have now are of two types - Squamous. Simple means just one layer. Yes, just a thin layer of cells. Like inside our mouth or food pipe. These are very delicate and

help things pass through them. Ok. The second one is stratified. Which has many layers. Yes. It has many layers of cells. Like our skin. Now think

how much rubbing the skin does. So here a strong structure with many layers is necessary. Isn't it? Yes, absolutely right. And the cuboidal cells are often found in glands. Like sweat or salivary glands from where something is secreted.

Okay. And the long pillar cells form the inner lining of our intestines and stomach. There, more absorption and secretion is done. On some of our pillar cells, we

have tiny hair-like cilia. Cilia, yes cilia, which keep moving continuously. They work to move mucus in the windpipe or the egg in the fallopian tube. Here you can see how the structure

fits perfectly according to the function. Very interesting. Okay, so this was about the covering. Now how does movement take place in the body? Here comes the use of muscular tissue. Muscular tissue. Yes, muscular tissue. It is made up of long cells

whose main function is to contract and expand. Contraction and relaxation. Which causes movement. Absolutely, which produces movement. It is of three types. Skeletal, smooth and cardiac. Okay? Skeletal muscle is the one that

is attached to our bones . Like the muscles of the arms and legs, biceps, etc. Well, no striations are visible in them.

Striations and the special thing is that their cells have many nuclei. Multinucleated. Why? Because they are formed by the joining of many cells, which gives more strength. And they

work as per our wish. Voluntary but they also get tired. Yes, they get tired quickly. The exact opposite of this is smooth muscles. These are found in our internal organs. Like the digestive tract, lungs,

walls of blood vessels. They do not have striations. There is only one nucleus in each cell. Uninucleated and most importantly, they do not work as per our wish. Involuntary. Imagine if we had to think continuously for digestion or breathing

. Yes, of course, they work slowly and do not get tired, which is necessary for the continuous functioning of these organs. And the third heart muscle is cardiac muscle, which is found only in the heart.

Yes, only and only in the heart, it is also involuntary. Involuntary, it also has striations but its cells are branched. The branches join together to form a web. Right. This structure

helps the heart to beat together. And the most amazing thing is that this muscle keeps working from birth to death without getting tired . Amazing , isn't it? Now let's come to connective tissue. Connective tissue is

the connecting tissue. Yes, as the name suggests, it works to connect, support and bind different tissues and organs of the body . There are many types of it. For example,

one is areolar tissue. It is loose. Fills the empty space between the organs. Connects the skin to the muscles. And also helps in repair. Yes. In repairing tissues. Meaning, it can be called the packing material of the body in a way.

Okay. Connected to this is adipose tissue. Fat tissue in which fat is stored. Yes, it stores fat. It stays under the skin and keeps the body warm. It

works as insulation. And also protects the internal organs from injury. Absolutely. Then comes dense connective tissue which has a lot of fibrous fibers . It must be strong.

Yes, very strong. There are two main examples of this. Tendon which connects muscles to bones like a strong rope. Muscle to bone. Yes. And the second is ligament. Which

binds bones to each other at the joints. Bone to bone. Ligament also has some elasticity. Yes. It gives flexibility along with strength. Okay. Connective tissue also includes skeletal tissue,

right? Yes. Skeletal tissue. Yes, absolutely. The first is cartilage . It is strong but flexible. Like

the outer part of our ear, the pinna. Yes. Or the tip of the nose. It also lubricates the joints. Right. And the second is bone. Asthi.

It is very hard and strong. Made of calcium and phosphorus? Yes. It gives structure to the body, helps in movement and protects delicate organs. Like the brain and lungs. Okay?

And a special type of connective tissue is fluid connective tissue. Fluid connective tissue means our blood. Yes, blood. It has a liquid matrix called plasma. Plasma

contains water, proteins, hormones etc. Yes. And in this plasma, cells float . Yes. There are three types of blood cells. Red blood cells, RBCs, these contain hemoglobin which carries oxygen.

White blood cells, WBCs, which are our body's army , fight infection . And platelets, which help in clotting of blood when there is an injury.

Another fluid involved in clotting is lymph. It is similar to plasma. But it does not contain RBCs. It also The immune system is part of the immune system. Okay. All of these together maintain

the transportation, protection and balance of the body . Very good. And now the fourth and last type of nervous tissue is nervous tissue. Which is found in

our brain, spinal cord and nerves . Yes. Its basic unit is the neuron or nerve cell. These cells are very special. How? Their job is to receive information, stimuli from the external environment like heat, cold, touch or from inside the body.

And then convert it into electrochemical signals and transmit it very quickly from one part of the body to another. Okay. This tissue is responsible for thinking, understanding, feeling

and controlling all the actions of the body. So we saw how these four main types of tissue epithelial, muscular, connective and nervous with their special structure and function form the body of a complex organism.

Each tissue is designed perfectly for its work. Absolutely. Understanding this is the foundation of biology and it shows how amazing the organization of living beings is. Right. Well, before leaving, I

leave a question for the listeners. Yes, definitely. Just think , how and what effect our diet, exercise or lifestyle would have on the health and functioning of these different tissues ?

This is something to think about. What do you think about this? Do tell us in the comments. Now my next topic is diversity in the living world. When we look around us, we see countless types of living beings.

Yes, of course. And to understand this diversity, scientists have created a system of classification. Classification, yes. So where does it start? I mean,

on what basis is the first major division? It starts from the cell. From the structure of the cell. See, broadly speaking, living beings have been divided into two main groups. Okay. Which ones? One is prokaryotes and the other

is eukaryotes. The names are a little technical but it is important to understand their basic difference. Okay? So first let's talk about prokaryotes. They are probably kept in Kingdom Monera, right? Yes, Kingdom Monera. The identity of prokaryotes

is that their cells are very simple. Understand the structure of a single room. Single room means that there is no membrane bound nucleus, no membrane bound organelle

. And neither any other membrane bound organelle. Everything is in the cytoplasm . Okay. And what do they eat? I mean how do they get nutrition? There is variety in this too. Some make their own food

from sunlight or chemicals. They are called autotrophic. Yes autotrophs. And the rest depend on others . They are heterotrophic.

And do they have a cell wall outside their cell or not? It may or may not be there. It depends on the group. Okay? So these are very simple organisms. Let me give some examples like bacteria

etc. Absolutely. Bacteria is the classic example of this . In this also there are archae bacteria which are found in very extreme conditions like hot water springs or places with very high salt.

Oh wow. And then there are the bacteria that we commonly find in soil, water and even on our bodies. Another important group is cyanobacteria. They are

also commonly called blue green algae. Yes, I have heard of it. They do photosynthesis, right? Perfect. They can do photosynthesis . So this is the basic story of prokaryotes.

Got it? Simple cell, no nucleus, autotrophic or heterotrophic, may or may not have a cell wall. And in the example bacteria, cyanobacteria. Perfect. Now let's come to the second group. Eukaryotes.

How are they different from prokaryotes? Eukaryotes? Yes. Their cells are more developed and complex . Understand it like a big house in which there are different rooms. Each room has its own work.

Good means more organized. Yes, we can say. They have a nucleus surrounded by a proper membrane in which the genetic material is protected. There are many other membrane bound organelles. Like mitochondria, Golgi body etc.

And there are different types of organisms in eukaryotes too. Some are single celled, some are multicellular like us. Absolutely. Eukaryotes can be single celled i.e. unicellular or multicellular made up of many cells.

So first let us talk about unicellular eukaryotes. They come in Kingdom Protista. Yes. Kingdom Protista. These are very interesting organisms. They live in water or moist organisms. They are mostly found in many places. What is special about them?

They often have some special structures for moving around. For example, some have cilia like small hairs. Some have flagellum like a long tail. Well, for moving around.

Yes. And they usually do not have a cell wall. There are a few exceptions like Euglena. But most do not have it. In terms of nutrition, they can also be autotrophic or heterotrophic . Some examples of protista are amoeba,

paramecium. Yes, absolutely. Single-celled algae, diatoms and protozoa like amoeba, paramecium, euglena, all come under protista. These methods of movement in protozoa are asked a lot in exams. How

does paramecium move? Paramecium has thousands of small cilia all over its body. They all move together. Like paddling, right? Okay. They have cilia and Euglena has one or two long flagella

. He moves forward using it as a whip. And amoeba does not have any fixed shape. That's right. Amoeba keeps changing its shape. It forms fake legs by extending

its cell membrane and cytoplasm. These are called pseudopods. Pseudopods. Yes, pseudo means fake. Pod means legs. With these, it moves slowly and also catches its food. This thing about pseudopods must

be remembered. Yes, this is really unique. So, these are protista unicellular eukaryotes. Now let's come to multicellular eukaryotes. Yes. Now here comes another big division. What is that?

It is based on whether there is a cell wall or not. Well, first let's see those groups which have a cell wall. Who comes in it? Plants Fungi. Yes, there are mainly two kingdoms in it . Fungi and Plantae. Let's talk about fungi first. Mushrooms, yeast,

molds, all these. Absolutely. Most fungi are multicellular. Yeast is the only exception which is unicellular. And what is their cell wall made of? Cellulose like plants.

No, this is the special thing. The cell wall of fungi is made of a complex sugar called chiton. Chiton? Oh, this is the one that is found in the outer shell of insects. That's right. The same chiton. This

is an important point. It is often asked. And how do they make their food? They are not green. You got it right. They are heterotrophic. Meaning they take nutrition from others. There are two ways of doing this.

Which ones? Either they take nutrition from dead, rotten organic matter. Such fungi are called saprophytic. Saprophytic. Okay. Like mushrooms growing on wood.

Yes. Or they live on a living host plant or animal and take their food from it. These are called parasitic. Parasitic like the fungus that causes ringworm and scabies. Yes, fungi can be harmful as well as beneficial for us.

How is it beneficial? You know that yeast is used in bread and bakery. Yes, and in fermentation as well. But antibiotics have a very big contribution. Have you heard the name penicillin? Penicillin.

Yes. The first antibiotic. Absolutely. It was found from a fungus Penicillium. And it was discovered by Alexander Fleming. This name should also be remembered. Alexander Fleming. Okay. And any

other special example of fungus? Another very interesting example is lichen. Lichens are those which look like colorful patches on stones or on the bark of trees. Yes, that one. Lichen is actually

a combination of two organisms. A fungus and an algae or cyanobacteria. Two organisms together. Yes. And they live in a symbiotic relationship . Meaning both symbiotic organisms help each other. Algae makes food through photosynthesis

and fungus provides it with a place to live, water and minerals. It is a perfect partnership. Wow, this is an amazing relationship. Isn't it? So this is about fungi. Chiton with cell wall, heterotrophic portion, and

examples like yeast penicillin, lichen. And the second group in multicellular with cell wall was Plantae. Yes. Kingdom Plantae. All plants come under this . From small mosses to big trees. They have cell wall which is mainly

made of cellulose and they are autotrophic. They make their food through photosynthesis. Okay. This is a very big topic in itself . By the way. Yes, absolutely. There can be a lot of discussion on this separately

. So now finally those multicellular eukaryotes which do not have cell wall. Yes, they are all of us from Kingdom Animalia . We animals, insects, all

of us do not have cell wall in our cells. there is only cell membrane and we all They are heterotrophic. Meaning they depend on others for nutrition. So this is the complete classification. In a way, prokaryotes are Monera. Then

in eukaryotes there are unicellular, protista and multicellular. In multicellular also there are fungi with cell wall, Plantae and without cell wall Animalia. Of course, this is a basic framework to understand this huge diversity of life,

on the basis of features like cell structure and cell wall? But here a question comes to mind, is only cell structure and cell wall enough to understand organisms or how did the deep relationships between them develop? What role do they play in the environment?

All this is not equally important. This is a very good question. And to be honest, as science is progressing, the methods of classification are also changing. Now using genetics molecular biology,

efforts are being made to understand the evolutionary relationships of organisms and their history of development in more depth. So this classification is not static. It keeps getting updated continuously. We mean this story will go further. What do you think? Do tell us in the comments.

Now my next topic is classification of the plant kingdom. We see that in competitive exams questions are often asked from this, right? Yes.

So having a basic understanding of this means it is very important. Yes, of course. We will know in which main groups the plants are divided? How to identify them? Of course.

And this is not just a matter of memorizing as you said. Understanding the classification of plants is actually understanding the story of their evolution. Well yes. I mean how simple organisms living in water gradually

became complex plants ruling on land. Yes. This is a whole journey. We are interesting. So where does one start? Which are the simplest ones?

First comes Thallophyta. Thallophyta. Their biggest identity is that their body means it is not divided into root, stem and leaves . Well. So then how is it?

There is just a bag or thallus-like structure. These mainly include algae. Oh algae, yes, which are mostly found in water . Like the green moss that grows

in ponds or on moist walls . Yes, those green algae can be Chlorophyceae. And on the basis of colour, they are divided into green, brown and red algae. Okay. And one important thing is that they

do not have vascular tissue, i.e. xylem, phloem, etc. So, they do not have a system to carry water and food up and down . Meaning, they are completely dependent on water. Yes, absolutely. Then, which plants evolved a little from them?

After this comes Bryophyta. Yes. They can be said to be among the first plants to grow on land. But they could not become completely of the land . Could not become completely of the land. That is why

they are called amphibians of the plant kingdom. Amphibians, yes. Like a frog, it needs both water and land.

Yes, yes, you understood correctly. They live on land. Especially in moist and shady places, they need water for fertilization. Okay. And they also

do not have real roots, stems, leaves and vascular tissues. Like moss, Riccia, Marchantia, all these are examples of this. They were trying to come to the land but they did not get complete independence from water. What was the next step in evolution?

The next and very important stage is Pteridophyta. What? Here we see two big changes. What? For the first time, vascular tissues i.e.

vascular tissues developed in plants . Xylem and phloem developed. Okay. And along with this, structures like roots, stems and leaves also became clearly visible in them. Oh wow, with the advent of vascular tissues, they would

be able to transport water and nutrients to the top in a better way. Absolutely. Maybe that is why they are also bigger than Bryophytes . Like those ferns, right?

Absolutely right. Vascular tissue made them more successful on land. Ferns are the most common example of this. Yes, I have seen it. But one thing was still similar to Bryophytes.

What? These also reproduced not by seeds but by spores and were dependent on water for fertilization. Well, so the seeds had still not come. No, that is why they are mostly found in cool, wet, shady places.

So where would the real game changer seeds have come from then? Certainly, the plants that form seeds are called phanerogams or spermatophytes. These are the most evolved plants.

Well. They are divided into two main groups. Gymnosperms and angiosperms. I have read that gymno means naked and sperm means seed. So what about these? Are the seeds in the open? That means they are enclosed inside the fruit,

you got it right. Their seeds are not enclosed in the ovary. That is why no fruit is formed. The seeds look straight as if they are attached to a cone. Okay. These are mostly evergreen trees or shrubs. For example, pines

, yes they are found on mountains. Yes, pines, cycas, deodar are found in abundance in cold areas. Okay. And then come the most successful and most visible plants around us, the angiosperms.

Absolutely. Angiosperms means angiosperm plants. Angiosperm means covered. So their seeds are covered. Yes, their seeds are safe inside the fruit . These are flowering plants. Meaning those in which flowers bloom.

Flowering plants and today they dominate the earth. That's right. In them, the root, stem, leaf, flower, fruit, everything is fully developed. The most advanced. So that means most of our food

items, grains, pulses, fruits, vegetables, all these are angiosperms. Yes absolutely. Wheat, rice, mango, rose, mustard all come under this. Well, are they further divided? Yes , based on the number of

cotyledons present in the seed . Okay. One is monocotyledonous (monocots) which have one cotyledon. Like wheat, rice, maize, grass, onion, garlic, okay.

And the other is dicotyledonous (dicotyledons) which have two cotyledons. Like gram, pea, mustard, mango, neem, pulses. Got it? So, this is a complete picture of the classification of plants. The journey from Thallophyta to Angiosperms. It

is really interesting to understand how life came out of water and became so successful on land. Yes, and knowing this order of evolution is not just for rote learning. It helps us understand the ecosystem. How different plants have

adapted themselves according to their environment, right? Absolutely. Another thing to think about is how this gradual evolution of plants, like coming to land, then creating the vascular system, then making seeds, would have affected the evolution of other life on earth, like animals and even us humans

? This is a deep question. Yes. What do you think about this? Do tell us in the comments below . Let's try to understand the vast world

of the animal kingdom . How are organisms divided? There are some bases for this. Like what is their physical organization? Is it at the cell level or tissue or organ level. What is the symmetry in them?

Can they be divided into equal parts? And do they have a body cavity? Understanding this classification is very important for competitive exams. Because most of the questions are made from these characteristics. Absolutely. And this classification actually

tells the story of the evolution of life. How complex organisms were formed from simple organisms. So where should we start ? The simplest ones. Yes, let's start from the Phylum Porifera. Phylum Porifera are the most basic organisms. They have only cellular level organization.

Cellular level organization means there are cells but they have not yet formed tissues together . You are right. And there are many small holes on their body through which water enters and there is a canal system.

They get food and oxygen from that. They do not have any fixed shape or symmetry. They are asymmetrical. And their structure is like a skeleton. Yes. It is made of spicules or spongin fibers. Spongilla

is a common example of this. Okay. So these are Porifera. Now one step ahead of them. Yes, the next phylum is Coelenterata or Cnidaria, Coelenterata and Cnidaria. Okay, what is special about them? Here the level of organization has increased. Now

the tissue level has come. The cells are forming tissues together and there is symmetry too. Aris samiti radial symmetry. Radial symmetry means cutting a cake from the center. Absolutely. Cut from the center in any plane and you

will get equal parts. And their biggest identity is those cnidoblast cells. Cnoblasts. What are these cnidoblasts? These are special cells that have a sting. Sting cells are used

for both prey capture and defense. Hydra and jelly fish are very good examples of this. So first there were just cells, then tissues . Now it was the turn of organs. Absolutely. The next stage is the phylum

Platyhelminthes. Here, the organ level organization is visible. And the symmetry has also changed. Now there is bilateral symmetry. Bivalve symmetry. Bivalve means that it

can be divided into two equal parts in only one way. Left and right. Exactly. Think this must have helped the organism to move in one direction . Yes. And they are flat, right from top to bottom.

Dorso ventrally flat. Yes, yes. That is why they are called flatworms or helminthes. They are called flat worms. But in these the body cavity has not been formed yet. This is an acoelomate.

There is no coelom. A parasite like tape worm comes in this group. Okay. Who comes after these flat worms? After these come round worms. Round worms. Phylum Ascaris helminthes or Nematoda.

Ascaris helminthes and Nematoda. In these the organization has become even better. At the organ system level. There is indeed butterfly symmetry at the organ system level. And in these there is that cavity like thing but not true pseudocoelomate.

Absolutely pseudocoelomate. There is no true body cavity. We Ascaris is a common example of this. The one of the stomach worms. Got it? Now let us come

to the organisms with true body cavity. True coelom. Yes. Phylum Annelida. Annelida also has organ system level. There is butterfly symmetry. But their special thing is that their body is divided into segments from inside and outside.

Metameric segmentation like earthworm, earthworm. Yes. Earthworm, leech. All of them come under this category. Earthworms also have those small thorn-like appendages for walking, right?

Yes, they do. This segmentation and true coelom were big steps in evolution. Definitely. Well, now let's talk about the phylum which has the most organisms in the world. Phylum Arthropoda.

Arthropoda. Hmm, this is the largest phylum in the animal kingdom . Oh wow, why is this group so successful ? There are many reasons. One is that their legs are jointed

. Jointed appendages, easy movement. Then outside the body there is a strong cover exoskeleton made of chitin which provides protection and their circulatory system is open.

Yes, open circulatory system. All the insects, spiders, crabs that we see, all come under this. Amazing. So then which is the second largest phylum? It is

Mollusca. Their body is very soft. And most of them have a shell made of calcium carbonate. Just like a snail or a clam. Snails, pilea, oysters

have a layer called mantle which forms that shell. And octopus also comes under this. But it does not have a shell. Yes, octopus is also a mollusc. It does not have an outer shell but it belongs to this group. It

is also very intelligent. Interesting. Okay. After Mollusca. Phylum Echino Dromata. Echino Dromata. Hmm. All of them live in the sea. And they have thorns on their skin

. Spiny skinned, like starfish. Yes. There was something unique about their symmetry, right? Yes. Very unique. Their larvae have basal symmetry like we have.

Yes. But when they become adults, they start having radial symmetry. Hey, radial in adults? This is strange,

isn't it? And another identity of theirs is the water vascular system. A system that runs on water pressure and helps in locomotion, catching food, breathing, etc. This is found only in them.

Amazing, good and now the most developed group in which we also come. Phylum Chordata Chordata. They are identified by three main things that are definitely present at some stage of life. One is the nototochord, a flexible rod-like structure.

Second is the dorsal hollow nerve cord which forms the brain and spinal cord in us. And third is the pharyngeal gill slits. Pharyngeal gill slits. And within this Chordata come the Vertebrata, that is, vertebrates. In which the

spinal cord replaces the nototochord. Of course, we broadly divide the vertebral column and Vertebrata into five classes . First is Pisces, i.e. fishes. They have two chambered heart and breathe through gills. Second is

Amphibia, amphibians like frogs. Three chambered heart in water and on land. Then Reptilia, reptiles, snakes, lizards, they also have three chambered heart . Yes. But there is an exception, crocodile, it

has four chambered heart. Well then the fourth class is Aves, i.e. birds. Feathers, four chambered heart and warm blooded. Right. And finally the fifth class is Mammalia, mammals. We all have four chambered heart, hair on the body, memory glands

and we are also warm blooded. So this is a complete classification plan of the animal kingdom. Yes, every phylum has its own identity, its own characteristics which also show the order of evolution.

Really, these characteristics and examples are very important for exams. These have to be remembered. Absolutely. And here is a question to think about. As organisms became more complex from simple, they developed new methods to remove waste from their bodies.

How did the methods of excretion change? How did the excretion organs evolve from Porifera to Chordata? It can be very interesting to think about this. Excellent question. Yes, it can be thought about. So what

are your thoughts on this classification or is any other question coming to mind? Do share in the comments below. So let us now delve into a topic which is not only interesting but also very important for many exams like SSC, UPSC.

How does the control system of humans and plants control everything, our body, our brain and how do plants respond without a brain? Today we will understand the main aspects of this. Parts of the brain, the nuances of the nervous system, the movements of plants and

yes, the magic of hormones in both. Absolutely. It is very fascinating to understand how all these different parts work together like an orchestra. The nervous system extending from the brain to the myopic cells and then those chemical messengers

i.e. hormones are all connected to each other. We will focus on those special points which are useful from the exam point of view. Yes, let's start from our control center. The brain is broadly divided into three parts. Isn't it? Forebrain

, midbrain and hindbrain. Yes, of course. In this, the forebrain is called our thinking, memory, willpower, everything is controlled from here.

Yes, to a large extent, the cerebrum is the largest part of the forebrain. This is the part that does complex work like thinking, understanding, remembering. Thalamus is also present in this. It makes us feel pain, cold, hot etc. And a very important part is

the hypothalamus. Hypothalamus. Yes, I have heard about it. It is very small but does great work. Absolutely. It controls body temperature, hunger, thirst, sleep, etc. It

also regulates our emotions like anger, happiness. And the special thing is that it works like a bridge between the nervous system and the endocrine system, that is, the system of hormones . Well, this is very interesting. And then

what are the main functions of the midbrain and the hindbrain? See, the midbrain mainly controls some involuntary actions related to sight and hearing . I mean reflex actions like the pupils of the eyes suddenly

contracting in bright light or turning the head towards a sound, all this is fine and the hindbrain includes the cerebellum,

which is responsible for maintaining the balance of the body and its posture. Like when we walk or ride a bicycle, we do not fall, it is because of this that there is the pons. You can say that it works as a relay station

between different parts of the brain, it sends messages here and there and then there is the medulla. Medulla is the most important for life . Why medulla?

Because it controls those tasks over which we have no direct control. Breathing , heartbeat, blood pressure, all these important autonomic functions are handled by the medulla. Oh my god, I mean all this goes on so automatically

. But how do these messages spread throughout the body? The brain cannot do all this alone . This is where the nervous system comes into play. Right? Absolutely right. The brain is one, or rather the most important part of this vast network. We

call it the nervous system. Its most basic unit is the neuron. These are the longest cells in our body. Think of it like electrical wires. They transmit information from one place to another very quickly.

Neuron. Yes. And the gap between two neurons. Yes. It is called synapse. This is a very small space where the signal of one neuron

often reaches the next neuron through some chemicals. This is where the exchange of information takes place and we generally divide this entire system into two parts. Central nervous system i.e. CNS which includes the brain and spinal cord.

And the other is the peripheral nervous system PNS. Which includes all those nerves that come out of the CNS and spread throughout the body and carry messages. We understood this was our point but how does all this happen in plants, they

do not have brain or nerves, yet like the Mimosa plant, it wilts away on being touched. Yes, the way of reaction is different in plants. They do not have a nervous system, but they too respond to stimuli. Mainly two types of movements

are seen in them. Nastic and tropic. Nastic and tropic. Nastic movement is that which does not depend on the direction of the external stimulus. Like you have seen Gave the example of Mimosa. The leaves close when touched.

Touch from any direction or some flowers blooming in the morning and closing in the evening, this is also a nestic movement. Ok. And tropic movement depends on the direction. Yes, tropic movement is in the direction of the stimulus or in the opposite direction. This

is very important for the growth and development of plants . For example, the stem always grows towards the light, this is called phototropism. The roots growing down in the ground in search of water is hydrotropism or the roots going down due to the pull of gravity

is geotropism. Even the pollen tube growing towards the ovule is also a kind of chemical pull. Chemotropism is amazing. Plants are so smart. Ok, now let's come to hormones. These

work as chemical messengers in animals, right? And the pituitary gland is called the master gland. Why is that? Yes. The pituitary gland is located just below the brain . It is called the master gland because it itself

produces many hormones. Along with this, it also controls many other important hormone-producing glands like thyroid, adrenal. It itself produces growth hormone. If it is produced less in childhood, then the person remains a dwarf. Dorfism and if

it starts producing more after adulthood, then the hands, legs, face become strangely large. That condition is called acromegaly. Oh and which gland produces that fight or flight hormone ? That is adrenaline. It produces the adrenal gland

which sits like a cap right above our kidney. Whenever there is any danger or stress, this hormone is released. The heart starts beating fast. Blood pressure increases. Breathing becomes fast. So that we can face that situation or run away from there

. Fight or flight response. Ok. And the thyroid is probably in the throat. Yes, of course. The thyroid gland is in the throat and produces thyroxine hormone. It controls our body's metabolism i.e. how energy will be used.

If there is a deficiency of iodine, this gland swells up and is called goiter. Because iodine is necessary to make thyroxine. Then there is the pancreas which makes insulin. Insulin controls the blood sugar level. If it is not made or does not work properly,

diabetes occurs. And yes, there are sex hormones too. Testosterone in men and estrogen progesterone in women. There is another hormone which is probably responsible for sleep.

Yes, that is melatonin. It is made by the pineal gland in the brain. It helps in controlling our sleep-wake cycle which is called circadian rhythm . It is made more when it is dark, which makes us sleepy.

Interesting. Do plants also have hormones? Meaning, like the ones in our body? Yes, plants also have similar chemical regulators which we call plant hormones or phyto hormones. Their functions are also very important for plants. Like

auxins and gibberellins. Both of these mainly help in increasing the height of the plant . They lengthen the cells. They increase the growth of the stem. There is cytokinin. It promotes cell division. It

prevents leaves from aging quickly. Then there is abscisic acid ABA. It is also called stress hormone. Stress hormone in plants. Yes, when there is any stress on the plant like lack of water then ABA stops the growth. It closes the stomata of the leaves so that water

loss is reduced. It also keeps the seeds in dormant state and a very special one is ethylene. It is in gaseous state and it plays a major role in ripening the fruits . Well, fruits ripen due to ethylene. So overall,

whether it is a human or a plant, their entire life depends on a very complex and wonderful coordination of the brain, nerves and these hormones . All these are so intimately connected. You are absolutely right. The coordination and balance of these control

systems keeps life running smoothly and it is interesting to think that if there is even a slight disturbance in any one of these systems, the entire balance can be disturbed and how big can be its impact?

Absolutely, the next time you see a plant growing towards the light or feel your heart beating fast in a stressful situation, then definitely think about these amazing internal control systems. They really run us. What

are your thoughts on this topic? Share in the comments below. Now our next topic is reproduction . This can be said to be a very important concept of biology. Yes, especially for competitive exams, questions from this

come in SSC, UPSC. Right. So, broadly understood, then living beings are divided into two groups. There are many different ways in which organisms increase their numbers. One is asexual in which only one parent is enough. And the other is sexual in which two parents are needed.

Yes, so let's talk a little more about this so that the main points for the exam become clear. Let's start with asexual reproduction. In this, as said, a new organism is formed from just one parent. There are many interesting ways of this.

In small organisms like amoeba like us, binary fission occurs. Meaning one cell directly grows into two. Very simple. Simple and also very fast for those organisms.

Exactly. Then in some, like Plasmodium which spreads malaria. There is multiple fission. Many new cells are formed from one. Okay. Then comes fragmentation. This is seen in algae like spirogyra.

The body simply breaks into pieces and the amazing thing is that each piece becomes a new organism. Wow, this seems quite efficient. Isn't it? And yes, budding is also a method. You must have seen in hydra or yeast that a small bud-like protrusion comes out.

Yes, it then separates. And a new organism is formed. Another one is regeneration. It is quite famous in planaria. If it is cut, then a completely new organism can be formed from the cut part. Regeneration is amazing and spore

formation also occurs in fungi. For example, new fungi grow from small spores in rhizopsis. All these methods are a very efficient way to increase their population i.e. their numbers rapidly for asexual organisms, especially simple organisms. It is efficient.

Hmm. Hmm. But the special thing in this is that the new organisms that are formed are genetically exactly like their parents. An exact copy. Meaning no variation. No variation. So if the environment

is stable and not changing, then it is good. But if there is a change, then there can be a problem . Absolutely right. Well, there is a special kind of asexual reproduction in plants which is called vegetative propagation. Yes,

it is quite common. Yes, in this, a completely new plant is prepared from any part of the plant like root, stem or leaf. Like we cut the branch of a rose and plant it. That is called cutting.

Yes, that is cutting or grafting. In lemon, strawberry, a part of one plant is joined to another. So that the good qualities of both can be combined or the qualities of one come in the other. Correct. And till now this

is also an advanced technique. Tissue culture. In the lab, thousands of plants can be made from a small plant tissue. The advantage of vegetative propagation is very clear. If there is a plant whose fruits are very good or flowers are very beautiful, then with this technique we can make its exact copy, a new

plant and that too quickly. It has a lot of value in agriculture and horticulture. But yes, the same problem arises here too. Lack of genetic variation. So if any disease comes, then all the plants can be affected simultaneously

because all are similar. This is a risk factor. You said it right. So asexual means speed and method of making copies. But if variation is needed to be adapted in the changing environment, then

sexual reproduction comes into play. Yes. In this, there are two parents, male and female, and their special reproductive cells , which we call gametes, meet. Let us first look at the plants.

The reproductive organ here is the flower. In the flower, the stamen is the male part. It produces pollen grains. These contain the male gametes. Okay. And the pistil

is the female part. Inside this are the ovaries and inside the ovaries are the ovules, which contain the female gametes. Okay? So when these pollen grains somehow

reach the stigma. Stigma is a part of the pistil. That process is called pollination. And how does this happen? Through air, through water. Yes, it can happen through air, through water or

through insects like bees, butterflies. Then when the male gamete comes out of the pollen grain and meets the female gamete inside the ovule, that is called fertilization. And after this,

after fertilization, the ovary becomes a fruit and the ovules become seeds. Seeds. Ok. So this is how fruits and seeds are formed. Interesting.

Yes. Now let's come to humans. In humans. Here also the male and female reproductive systems are different. In the male system, we have testes which make sperms i.e. male gametes.

And in the female system, there is ovule which makes ova or eggs female gametes. Right and usually the union of these two i.e. fertilization happens in the fallopian tube. In the fallopian tube.

Okay. There are some other things related to this which are important for the exam as well as for general awareness. For example, you must have heard of IVF . Yes, it is called invitro fertilization or test tube

baby. Exactly. It is a helpful technique for couples who are facing difficulty in conceiving naturally. It is a part of assisted reproductive technology.

Absolutely. Another important health point is cervical cancer. It is often found to be related to HPV or human papilloma virus. Yes, vaccines are also available for this. Now awareness is important.

Very important. Then there are surgical methods of birth control. Vasectomy for men and tubectomy for women. These are permanent methods of contraception. Yes. And one more unique thing is that some organisms also have parthenogenesis.

Well, what is that? In this, like in some lizards or bees, the egg develops into a new organism without fertilization, that is, without meeting with the sperm . Wow. Development without fertilization

is different. So look, the biggest feature of sexual reproduction is genetic variation. Yes, it differentiates it from asexual reproduction. Absolutely. Because in this,

genes of two different parents are meeting. So the new offspring that is born is slightly different from its parents. A unique combination is formed. And the advantage of this variation is that this variation helps the species to adapt to the changing environment

. This is the base of evolution. So this variation is necessary for survival. It is very important in the long term. And apart from this, having a correct understanding of human reproduction is also very important to increase awareness for reproductive health

. So we saw that there are two main methods of reproduction . One is asexual which rapidly creates identical copies. It is common in simple organisms or in vegetative propagation.

Yes, in which there is no variation. And the second is sexual which brings variation which increases the ability to tolerate changes in adaptation. It is common in complex organisms . Both methods

are important in their own places to maintain life in different circumstances. And from the point of view of the exam, it is important. Of course. And from this entire discussion, a question is coming to my mind which

can perhaps be thought about. These techniques of vegetative propagation and especially tissue culture, which we talked about. Yes. To what extent and how can

these change our agriculture, food security and conservation of endangered plants in the future? What are its possibilities in the future? This is a good question. What impact will technology have on agriculture and conservation?

What are your views on this subject? Do tell us in the comments. Yes, we will be happy to know. We will meet in the next part with a new topic. Now my next topic is the human digestive system.

This is very important for exams. So let's understand it properly. Yes, of course. We will see how the food we eat goes on a complete journey and how the body breaks it into small parts

so that it can be used. Yes. And this journey starts from our mouth which we call the oral cavity or buccal cavity. Well, from the mouth. Yes. As soon as we start chewing food,

our salivary glands start producing saliva. Yes, it is there but is this saliva only for wetting or is there anything special in it? No, no, not just for wetting,

it contains a very important enzyme called salivary amylase. Salivary amylase. Yes. And its job is to start digesting carbohydrates . But to break down complex carbohydrates into simpler forms

. So it is worth keeping in mind that the digestion of carbohydrates starts from the mouth itself. Oh wow, that means digestion starts so soon. And how is the medium here?

Not acidic. Here in the mouth, the medium is almost neutral or slightly alkaline. Okay. So where does the food go after the mouth ? Directly to the stomach? No. After the mouth, the food goes

to the oesophagus. You can just think of it as a food pipe. Well, just a pipe. Yes. Its job is to just take the food from the mouth down to the stomach, which is called the stomach. There

is no digestion, no digestion in it. Understood? There is just a path. Then what is the story in the stomach? I have heard that there is a lot of acid there. Yes, of course. As soon as it reaches the stomach, gastric juice is released. Gastric juice and in this

It is hydrochloric acid i.e. HCL. HCL. Yes. And this HCL is very important. It has two main functions. Firstly, if any harmful bacteria have come with the food, then it kills them. Well, in a way, cleaning.

Just like a security check. And the second function is to make the environment of the stomach very acidic. Oh, so much acid that the stomach itself is not threatened by it . And what is the benefit of this acidic environment?

Great question. Look, the inner wall of the stomach has a thick layer of mucus on it , this layer protects the stomach from strong acid. Well, it is a protection layer?

Yes and the acidic environment is important because there is another very powerful enzyme in the gastric juice of the stomach, pepsin. Pepsin for protein. Absolutely. This pepsin can work only and only in an acidic environment and it

starts breaking down the protein and converting it into simple amino acids. So the digestion of protein starts in the stomach. Amazing. That means the stomach is a kind of chemical lab and also protects itself. Ok, so now this acidic soup like food is ready.

Where will it go after the stomach? After the stomach, the food enters the small intestine . Hmm. And you can say that this is the most important part of the digestive system. Why the most important?

Because firstly its length is very long. About 7 1/2 meters. 7 1/2 meters. Yes. Imagine such a long tube inside us and secondly most of the digestion work is done here. And the absorption of the digested food

also happens here. Ok. So major digestion and absorption happens here. Does it have parts too? Yes. It has three parts. Duodenum, jejunum and ileum. But the most

important thing is that the small intestine does not work alone. It gets help from two big supporting organs. Which are the supporting organs? Liver.

And pancreas. Ok, liver and pancreas. What is their role here? See, the liver produces bile juice. This bile juice breaks the big drops of fat into small drops. This is

called emulsification. Emulsification for fat. Yes. And the second thing that bile juice does is that it makes the medium of the acidic food that has come from the stomach alkaline or basic. Because the enzymes of the small intestine

work only in a basic medium. Okay. So the liver handled the fat and changed the medium. And the pancreas. Pancreatic juice comes out of the pancreas . It contains many powerful enzymes. Such

as amylase which digests the remaining carbohydrates and trypsin. Trypsin is also for protein . Yes, it completely breaks down the protein into amino acids. But remember that

trypsin also works only in the alkaline medium which was created by the bile juice. Got it? That means the final digestion of carbohydrates, protein, fat has taken place in the small intestine with the help of the liver and pancreas

. But how will the body use it after digestion? How will it absorb? Absolutely correct point. This is where villi or rasankur come into play. These are millions of tiny finger-like projections on the inner wall of the small intestine.

Finger-like projections, villi. Yes, their job is to increase the surface area manifold for the absorption of digested food. Achcha. So that maximum nutrients

can be absorbed. Exactly. Like a very big carpet has been laid in a small room so that something can be absorbed from every corner. From here the digested food gets mixed in the blood and reaches the entire body.

Wow villi. This has to be remembered. So the small intestine is the powerhouse of digestion and absorption. Now what happens to the waste that is not digested? The food that is not digested or the water that is left, all of that now goes

to the large intestine. Achcha, how long is the large intestine? It is much shorter in length than the small intestine. About 1/2 meter. 1.5 meter. Okay. And what is its main job?

Its main job is to absorb the remaining water. Water absorption. Okay. So water absorption happens in the large intestine. Okay? And then finally after absorbing water, the solid waste material that remains which is called stool

gets deposited in the rectum and then when the time comes, it is thrown out of the body through the anus. This process is controlled by swing muscles. Swing muscles. So this was the whole journey starting from the mouth to the anus. Every organ

has its own specific role. Absolutely. Mouth, then esophagus, stomach, then Small intestine where liver and pancreas help. Then large intestine and finally outside. Amazing. And how wonderful it is to think that all these different organs, liver,

pancreas, stomach, intestines, all work together in such perfect coordination, in such harmony . Rightly said. This is a great example of biological engineering. Isn't it? This coordination is the most important. To run this whole process

successfully. Really this coordination is the most interesting thing. Well, what do our listeners think about this whole digestive system? Which part or which enzyme did they find most fascinating?

Do tell us in the comments below. Look at the respiratory system, it is not just about breathing in and out. It is about understanding how our body creates energy. How it generates power. Absolutely. And the role of oxygen is very important in this.

Yes. So broadly there are two ways. The one in which oxygen is needed is called aerobic . Yes aerobic and the other in which oxygen is not needed is anaerobic

. So let's talk about this today, right? Absolutely. Let us first look at anaerobic respiration. This happens without oxygen. Like in yeast.

Yes. Like in yeast, it breaks down glucose to form ethanol and carbon dioxide and also some energy. It does so even if it is a little. And the interesting thing is that our muscles do this too.

Okay, when? When we do a lot of intense exercise like sprinting or lifting heavy weights. Then the muscles need a lot of energy at once . And oxygen is not able to reach them that fast.

You are right. Yes, absolutely. So at that time they start breaking down glucose without oxygen. The result is the formation of lactic acid. And it is this lactic acid that causes stiffness or pain in the muscles

later. Yes, exactly that. So this is about IVA. But the main energy source of the body is VVA respiration, which is aerobic respiration. Yes. In which oxygen is used.

Yes. This process happens inside the cell. In its power house, in the mitochondria. Okay. Here glucose is completely broken down with the help of oxygen. I mean

in small parts and what is formed from it? It forms carbon dioxide, water and most importantly lots of energy, now much more than IBA. Well, I mean the main energy comes from here.

Absolutely. We get the strength to do our daily work from here. So okay. Now you understand how energy is formed? But how does this oxygen go inside the body? I mean what is the complete path of the air?

Look, it starts from the nose. From the nostrils. Yes, we breathe through the nose. And the nose is not just a path. The hair and mucus there. They clean the air. They stop dust from getting removed.

And they also make the air a little moist, right? Absolutely. Then the air moves forward. In the pharynx i.e. pharynx. So this is the place where the food and windpipe meet. Yes. This is the common path. After this the air

goes to the larynx. Which is also called voice box or Adam's apple . And then the air reaches the windpipe. Trachea.

Trachea. Is there anything special in it? Yes, very special. It has C-shaped rings made of cartilage. Rings. C-shaped. What is their function? Their function is very important. They prevent the windpipe from collapsing. Meaning, they ensure

that the passage for air always remains open. No matter how the neck is bent. Ok! Yes, this is important. Yes, then this trachea artfully divides into two parts. Which are called bronchi or bronchus. One in the right lung,

one in the left. And going inside the lungs, these bronchi keep on dividing into thin tubes. These are called bronchioles. Meaning they keep on expanding like the branches of a tree

. Understand it exactly like that. And at the end of these thinnest tubes are small pouches like balloons. Air sacs alveoli. Yes alveoli. In millions and

this is where the real work of exchange of gases takes place. So these are alveoli where oxygen goes into the blood. You got it right. These alveoli have very thin walls and around them

there is a network of very fine blood tubes i.e. capillaries. Okay. So when we breathe in, the air contains about 21% oxygen. And nitrogen 78% and

very little carbon dioxide, about 0.03%. Yes. So this 21% oxygen crosses the thin wall of the alveoli and enters the blood directly. And the carbon dioxide present in the blood, which

is a waste product of the body's metabolic activity, comes out of the blood and enters the alveoli. There is an exchange. Oxygen goes in and carbon dioxide goes out. That is why when we exhale,

there is less oxygen in it. About 16%, yes about 16% and carbon dioxide increases by about 4.4%

and nitrogen remains at 78%. It remains the same. 78% went in and 78% came out. Because our body does not use it in this process. It just keeps coming and going.

Well, now you understand this whole system of gas exchange. Hmm. But how does this breathing in and breathing out happen? I mean which muscles work? There are two main things in this. One is our

rib cage. Yes. And the other is a large dome-like muscle just below it. Diaphragm. Diaphragm. Yes, I have heard. So this is completely a mechanical process

. What happens when we breathe in ? Then our ribs move up and outwards and the diaphragm contracts and goes downwards. It becomes a little flat.

Okay. What happens is that the space inside the chest i.e. the volume of the chest cavity increases. There is more space. Yes. Due to more space,

the pressure inside the lungs becomes less as compared to outside. And the air comes in by puffing. It gets pulled in like a vacuum. Absolutely. And when we exhale,

then everything happens in reverse. Completely opposite. The ribs come back down and inwards. The diaphragm loosens and comes back up to its dome shape. So the volume of the chest cavity decreases.

Right. When the volume decreases, the pressure on the lungs increases and the air goes out. This is a continuous rhythm. Inside and outside. Yes. This is a rhythmic process that keeps going on.

So starting from the nose to the pharynx, larynx, trachea, bronchus, bronchioles, alveoli and then the diaphragm and ribs, this entire system works together . Absolutely so that the body

keeps getting oxygen continuously, and carbon dioxide keeps coming out, it is a very efficient system. It is really an amazing system. How important is it to know all this. And it also forces us to think. Like when we go to a height where

there is less oxygen in the air. Yes. Or like nowadays pollution has increased so much in the cities. So what effect would these changing conditions have on our delicate and balanced respiratory system?

How would the body adjust to these challenges? Yes, this is something to think about. What changes would take place in the body in these conditions? This is also a very deep subject in itself. That's right. What is your opinion about this

? What do you think? Do tell us in the comments. Now my next topic is the human circulatory system. Okay. What do they call it? It is an amazing network

that keeps the blood flowing continuously throughout our body. We and its main controller is our heart.

We work tirelessly like a pump. Absolutely. And the main parts of this system are the blood itself.

Absolutely. Then the vessels in which it flows, which we call blood vessels. Yes, blood vessels. Special among these are arteries and veins. We

and yes, blood groups. Well, these arteries and veins, arteries and veins sound similar. Yes. But what is the basic difference between them? See, there

is a difference. What usually happens is that arteries are those that carry clean blood, that is, oxygenated blood, away from the heart. Yes. Throughout the body, yes, and because the pressure

is high, their walls are a little thick. They are strong. On the other side are veins. What do they do? They bring back the used blood from the body, which has less oxygen, to the heart.

So their walls will be thin then? Yes, they are thinner than arteries. But I read somewhere that there is some opposite in this as well. Meaning is there any exception? Yes, yes. This is a very important point. Often people get confused here. There

are two big exceptions. The first is pulmonary artery. Pulmonary artery is called artery. The name is artery. Absolutely. But it carries dirty blood from the right side of the heart, that is, blood which does not have oxygen, to the lungs

for cleaning. Okay. Yes. And the second one is the pulmonary vein. Now the name is vein. But it carries fresh oxygenated blood from the lungs

to the left side of the heart. So this shows that the work it does is more important than the name . Well, this is really interesting. Okay, now let's come to blood pressure. What exactly does this

120/80 12080 mean when we hear it? Blood pressure. This is the pressure that the flowing blood exerts on the walls of the arteries. It has two numbers, systole and diastole. Yes, systole and diastole.

The higher number, like 120 mmAg. This is the systolic pressure. This is the pressure when the heart contracts and pumps blood forcefully into the arteries. Okay?

And the lower number, like 80 mmAg, is the diastolic pressure. This is the pressure when the heart expands, relaxes between beats. This pressure is necessary so that blood and oxygen can reach important organs like the brain.

And what is it measured with? The one that doctors tie on the hand? Yes, yes, it is called sphygmomanometer. That machine measures this question and what happens sometimes is that the heartbeat gets disturbed, so to keep it normal, a small device is installed called

a pacemaker. Well, you understood pacemaker. Let us now talk about blood groups. Who discovered them and how many types are there? The credit for discovering blood groups goes to Karl Landsteiner. He told that there

are mainly four groups A, B, AB and O. AB, AB, O. Okay? But there is one more thing in it, the Rh factor. It is a type of protein that is present on the surface of blood cells. If it is present, then the blood group

is called positive plus way. Like A positive, B positive. And if it is not present, if this protein is not present, then the blood group is called negative. A negative, B negative, etc. And what is that concept of universal donor and universal

acceptor? Yes, it is related to this. People with O negative or O minus are called universal donors. Because their blood has neither A antigen nor B, nor the protein with Rh factor. So their blood

can be given to anyone in an emergency. To anyone of any blood group? In principle, yes, in an emergency. And those with AB positive are called universal acceptors . Because they have all three antigens A, B and R. So they can take blood of any group

. But yes, matching is very important before blood transfusion. We think this is very important. Well, I also heard about a very rare blood group . What is this Bombay blood group?

Oh wow. You heard it right. Bombay blood group is very rare. As the name suggests, it was discovered in Bombay. It was discovered by Dr. Bhende in 1952. Well. What is its specialty?

Its specialty is that these people do not have A and B antigens on their red blood cells . Another antigen H antigen is also missing. Whereas everyone else has H antigen . Oho. So

because of this, these people can take blood from people with Bombay blood group and give it to them only. This shows how diverse the human body is.

Really amazing. Now tell me how the blood moves through the heart and throughout the body ? Which are the main pipelines and which parts of the heart are involved in this? Sure. See, the used blood from the body which is deoxygenated comes through two big veins

called venacava. They come to the first chamber of the heart. The right atrium . Right? From there, the blood passes through a valve called tricuspid valve and goes to the lower chamber. The right ventricle. This valve

prevents the blood from going back up. Then the right ventricle pumps this blood into the pulmonary artery. Remember that exception artery? Yes, which takes the dirty blood to the lungs. Absolutely. The blood is cleaned in the lungs. It

gets oxygenated. Then this clean blood goes through the pulmonary vein, the second exception. Yes, it enters the left atrium of the heart through the pulmonary vein . The upper left chamber. From there,

the blood goes into the left ventricle through another valve, the mitral valve. The left ventricle is probably the strongest part. Yes, it is the strongest chamber of the heart because it

has to pump blood throughout the body. So this left ventricle contracts strongly and pumps the clean blood into the largest artery, the aorta. Aorta and then from the aorta. From the aorta. Then a network of small arteries delivers blood throughout the body and this

cycle continues without stopping. Amazing. So in short, this The circulatory system delivers oxygen and nutrients to every cell and removes impurities like carbon dioxide from there. A transport system.

You said it right. A nonstop transport system. And that is why it is so important to keep an eye on blood pressure and know your blood group. Especially in emergencies or at the time of blood donation. Just think how complicated this network of the body

is and how perfectly it works every second without stopping. It is so amazing in itself. Isn't it? Or think how having such a rare group like Bombay blood group teaches us so much about the diversity of human biology

? What are your thoughts about this circulatory system or if you have any question in your mind, please tell us in the comment section below. Hello, from the perspective of competitive exams, the excretory

system of the human body is a very important topic. Absolutely. Let's talk about this today. How does our body remove these useless substances, waste materials, and what

is the role of kidneys in this? We will understand this in a little more depth. Yes, it is important to understand how this whole system, this cleaning system works? What are the organs in it? What is their function? These details can be very important for exams.

So where do we start? From the kidneys? Yes. Yes. Kidneys are the main players here. Let's start with the kidneys. Okay. So as you said, kidneys are the main organs and their working unit, the smallest

unit, is called nephron. Right. And I was surprised to know that there are lakhs of such nephrons in each kidney. Yes, lakhs. These are the ones that actually do the work of cleaning the blood. These small filters.

One more thing about their structure. Yes. The right kidney is a little lower than the left one. Okay. Why is that? This is mostly because of the liver above to give it space.

Anyway, their most important function, as I said, is to continuously filter the blood. We filter and there is also a special vein connected to the kidney, the renal vein. It takes back the blood which has less oxygen. That means

deoxygenated blood. And sometimes there are problems in it like stones etc. Yes, absolutely. Kidney stones can form. It is mostly formed due to the accumulation of a chemical called calcium oxalate.

And if for some reason both the kidneys stop working then it is a serious situation. Then one has to resort to dialysis. There is a machine which does the same work that the kidneys do. Cleaning harmful things from the blood.

This is a life saving process. Absolutely. Well, now let's go inside the nephron. You said that it is the life of the kidney. What happens in it? There are two main parts which are important to understand. Glomerulus and Bowman's capsule.

This is where the first and you can say tremendous cleaning of the blood takes place. This is called ultrafiltration. Ultrafiltration means that almost all the small things like water, glucose, salt, urea

are filtered out from the blood. Think of it like a very fine sieve. Hey, so then the useful things also got removed. Like glucose and water. Excellent question, you got it right. This is where the nephron shows its second magic. Reabsorption

. Okay. Yes. What happens in this process is that whatever is necessary for the body from the filtered liquid like glucose, amino acids, most of the water, some essential salts, all of them

are absorbed back. They are sent back to the blood. Meaning first remove everything and then take back the useful ones. Absolutely. And the real waste that is left behind like urea, extra water, extra salt

moves forward. Do you have any idea that our kidneys filter about 180 liters of liquid every day . 180 liters every day. Yes. But how much urine is formed from that? Only 1.5 to 2 liters. The rest, that is

more than 99% goes back to the body. Due to this reabsorption. Amazing. So this remaining liquid is urine. Yes, absolutely. Urine is formed at the end of this process. If we look at normal urine

, it contains about 95% water and the remaining 5% mainly contains urea and some other dissolved wastes like creatinine, uric acid, salt, etc. Its pH value also keeps changing.

Between 4.5 to 8. And why is its colour light yellow? That is due to a pigment. It is called urobilin or urochrome. This is what gives it its light yellow colour. Okay, one more question, where is this urea

formed in the body from? I mean, where does it come into the blood from? See, when protein metabolism takes place in our body, that is, when protein breaks down, ammonia is formed. Ammonia.

Yes. And ammonia is very toxic for the body. It cannot be kept like this. So our liver very quickly converts this ammonia into urea. Urea is less toxic. So the liver makes urea from ammonia.

Yes, the liver converts ammonia into urea. Then this urea gets mixed in the blood and reaches the kidneys. The kidneys filter it out from the blood. So even though urea is the main excretory product, the job of making it is of the liver and removing it is of the kidneys.

Got it? So urine is formed in the kidneys. Then how does it go out of the body? Thin tubes come out from the kidneys. These are called ureters or ureta. These take the urine down to the urinary bladder.

Where it gets collected. Absolutely. The urinary bladder is a pouch-like organ where urine collects and when it is full, we get a signal and then it is expelled from the body. Okay. This is about liquid waste.

Yes, through urine. But the body also expels waste in other ways . For example, solid waste means feces. The food that we do not digest

comes out in the form of feces through the anus after the digestion process. Yes, right. And its yellow color is due to a pigment called cat rubin. It

is formed by the breakdown of old red blood cells. This also comes from the liver. Okay. So it became solid, it became liquid. And there is also gaseous waste. Like carbon dioxide.

Oh yes. We expel that through the lungs while exhaling. Absolutely. So the lungs are also an excretory organ in a way. And yes, our skin also excretes in the form of sweat. Through sweat?

What is there in it? Sweat mainly contains water and salt . But a very small amount of urea and other wastes are also released. So the skin also helps a little in cleaning the body. So that means the kidneys are the main ones. But the liver,

lungs, skin, all work together to keep the body clean. So today we understood the excretory system in great detail. How the kidneys filter the blood with the help of nephrons . How urea is formed and excreted? What is the composition of urine? And

how do other organs of the body help in this work. Yes, and it is important to remember how important these organs are for us. How important it is to take care of their health. Another thing to think about is that our daily habits like how much water we drink, what we

eat? How much impact it must have on this entire system, especially the kidneys. Of course, we should definitely think about this. What is your opinion about this? If you want, you can tell in the comments. We will meet again next time with another important topic. Hello.

Hello. Hello. All the friends preparing for competitive exams are welcome. Today we will talk in depth about diseases and some important aspects related to them . This is a very important topic for exams like SSC, UPSC

. So let's start with the classification of diseases. See, some diseases are acute like cold, flu. They come and go away in a few days. On the other hand, there are some long-term chronic diseases

like diabetes or TB. They affect the body for a long time. Absolutely. And there is another important way to understand them. Infectious and non-communicable. Infectious means communicable diseases as the name suggests

. They can spread from one person to another. Like Covid, we have seen, chicken pox or AIDS also come under this. Okay. And on the other hand, there are non-communicable non-communicable diseases. These

do not spread by touching or contact. Hmm. Like diabetes, arthritis or polio. So it becomes important to know what are the reasons behind them? What are the factors ? So let's start with

one of these factors i.e. virus. They are very interesting, aren't they? They remain lifeless outside the body. But as soon as they reach a living cell i.e. host cell, they become active immediately. The genetic material in them is usually RNA

. Not DNA. And yes, one question is why antibiotics are not effective on them? This is a very good question. Look, antibiotics affect the cell wall of bacteria or their metabolism.

Viruses do not have these things. That is why antibiotics are completely ineffective in viral infections . Viruses cause many serious diseases. Take polio for example. Yes, polio. It

is caused by the poliomyelitis virus and directly attacks our nervous system. The good news is that India has been declared polio-free in 2023. And yes, if we talk about the polio vaccine, the first injectable IPV was made

by Dr. Jonah Salt and the drops OPV, which we call oral polio vaccine, was developed by Dr. Albert Saban. Well, hepatitis is also caused by a virus. It affects the liver, right? Yes, absolutely. Hepatitis directly

affects the liver . It also has many types but the main ones are A, B and C. Type A is spread through contaminated food or water. Type B is transmitted through bodily fluids such as blood or semen. Meaning it can also be sexually transmitted

and type C is mainly transmitted by coming in contact with infected blood. For example, suppose an infected needle has been used. The good news is that India has made its first indigenous hepatitis A vaccine Heavyshore.

Oh wow heavy noise this is great news. Well AIDS is also a serious viral disease. It is important to know about it. Absolutely. AIDS means Acquired Immunodeficiency Syndrome. It is Human Immunodeficiency

Virus from HIV. It is a special type of virus, retro virus. Meaning it can make DNA from its RNA in the host cell and it directly weakens our immune system. How does it spread?

The main ways of its spread are unsafe sex, transfusion of infected blood or from an infected mother to a child at the time of birth or by breastfeeding. The main test to detect it is ELISA test. World AIDS Day is also celebrated every year on 1 December for awareness

. Okay? Apart from these, dengue, measles, swine flu, H1 N1 and bird flu H5 N1 are also caused by viruses. Dengue is spread by female, Aedes, Egypt mosquito. And it is also interesting to know that smallpox

has been eradicated from the world in 1979 itself. You are absolutely right. So this was about viruses. Now let's come to bacteria. These are prokaryotic organisms. This means that the nucleus in their cells

is not surrounded by a membrane and they are unicellular. As we said earlier, antibiotics affect them. Yes. So what are the major diseases caused by them? There are many well-known diseases

that are caused by bacteria. Like TB, tuberculosis, which is also called tuberculosis. It is caused by a bacteria called Mycobacterium tuberculosis and mostly affects the lungs. It was also earlier called white plague.

BCG vaccine is given for prevention. Then cholera. It is caused by Vibrio cholerae bacteria. It spreads through dirty water, so it is a waterborne disease. The death caused by it is also sadly called blue death.

Typhoid and plague are also related to bacteria. Right. Yes, absolutely. Typhoid is caused by Salmonella Typhi bacteria and its test is called Widal test and plague is caused by Yersnia pestis bacteria.

It has caused a lot of devastation in history and the deaths caused by it were called Black Death. Oh my God. Apart from these, there are many more such as leprosy, tetanus, whooping cough, diphtheria, pneumonia, gonorrhoea, syphilis and anthrax which

can spread from animals to humans. All these are bacterial diseases. Right? So apart from viruses and bacteria, some diseases are also caused by fungus and protozoa . Some common skin problems like ringworm, ringworm or athlete's foot or sometimes

even baldness can be caused by fungus. Yes, absolutely. And talking about protozoa, the most well-known disease caused by it is malaria. It is caused by a protozoa called Plasmodium

and is spread by female Anopheles mosquito. For its treatment, we use quinine medicine which is obtained from the bark of the Sakona tree. We test for malaria with the vivax test

and 25 April is World Malaria Day. Apart from this, there is sleeping sickness which is caused by Trypanosoma protozoa and is spread by the TC fly.

And there is Kala Azar which is caused by Leishmania protozoa and is spread by the sand fly. Finally, we talk about those disorders which are not caused by any external organism but due to a problem in our own genes.

These are called genetic disorders. Yes, these are caused by a defect or change in the gene, say mutation. And these can also go on from generation to generation. Like Down syndrome, thalassemia, sickle cell anemia and albinism.

That is, color blindness. These are some examples. Some are related to the sex chromosomes. Like Turner syndrome. It occurs only in women. It has one less chromosome. Ok.

And there is Klinefelter syndrome which occurs in men. It has an extra X chromosome. Albinism which is called colorlessness. That too is a genetic condition. So this was a brief but important discussion on diseases, their different

types, the factors that spread them and some genetic disorders . All these facts are very important in terms of competitive exams . Very important. Of course, today we

understood different pathogens like viruses, bacteria, fungi, protozoa and the diseases associated with them and also talked about genetic disorders. Now a thing worth thinking about here is that after having so much information about diseases, what role can every member

of the society play in improving public health, making preventive measures effective and spreading awareness ? What do you think? Do tell in the comments. So let's come to the next topic. Nutrients. These are really amazing things. Isn't it? Without which

life cannot go on. Neither of plants nor of us. Yes, understand that this is petrol and diesel of the car like a statue. In a way, it is fuel. The information we have

sees them broadly in two parts. Micronutrients means those which are needed more. Yes, and micronutrients which are needed in less quantity but are very important.

Yes, absolutely. And the purpose of this discussion is to understand the story of these nutrients in simple language . What are they? How many types are there? Where do they come from? And most importantly, their deficiency. Yes, what can their deficiency do to the body

? Especially for those preparing for competitive exams, it is very beneficial to understand this. Yes, because questions are made from here. Well, first let's talk about plants in brief.

Yes, let's do it. They also need micronutrients. See in MAC, carbon, hydrogen, oxygen are obtained from air and water . Yes, that is basic. Then come primary nitrogen,

phosphorus, potassium. We know them as NPK fertilizers. Yes, NPK. And secondary includes calcium, magnesium, sulfur. And micro includes iron,

manganese, zinc, etc. Although only a pinch is needed, without these, plants become sick . Ok. How? For example, if there is less iron, the leaves start turning yellow. This is called chlorosis because chlorophyll is not formed properly

. Due to lack of iron or zinc, the leaves remain small. Little leaf disease occurs. Got it? Now let us come to the nutrition of humans and other animals. There

are three big players in macronutrients here. Carbohydrates, fats and proteins. Yes, carbohydrates are an instant energy source for the body . Like petrol for a car. Meaning instant energy.

Yes, the simplest form is glucose. Hmm. And when many glucoses are combined, starch is formed in plants or glycogen in animals. This works as stable energy.

Ok. And the interesting thing is that these complex carbohydrates like starch are generally not sweet. Ok. And fats. Fats not only provide energy but

also store energy. Like the body's power bank. Yes, you can say so. Also, they help in keeping the body warm and protecting the delicate organs from injury. Oil, ghee, butter, nuts are good sources of this.

There are types of fats too. Yes, there are two main types of it too. Saturated and unsaturated. It can be easily understood that those which solidify at normal temperature like ghee or butter are saturated

okay and those which remain liquid like most oils are unsaturated. Okay? And then come proteins which are often called body building blocks. Why so?

Because they are very important for repairing the wear and tear of the body and making new cells. Okay. Proteins are actually made up of small links called amino acids. Just like a garland is made from beads. Some of these amino acids

are essential. Meaning our body cannot make them. They have to be taken from food only. Like leucine, lysine etc. and the rest of the non-essential ones are made by the body itself. Such as

glycine, protein, pulses, eggs, meat, fish are excellent sources of protein. We are talking about micro nutrients. Now let us come to those micro nutrients which are required in small quantity, but

the deficiency of which can cause big problems. Vitamins and minerals. This part is very important for exams, isn't it? You said it right. Very much. Vitamins were discovered by Kaiser Funk. They help in

proper functioning of many internal functions of the body, i.e. metabolism . They are divided into two groups on the basis of solubility. One is those which dissolve in fat. Vitamin A, D, E and K.

These can be stored in the body. Oh, these can be stored. Yes. And the other ones which dissolve in water, Vitamin B complex and Vitamin C. These usually do not get stored in the body and

have to be taken daily. Okay. Let us quickly see some special vitamins and the diseases caused by their deficiency. These are often asked in exams. Sure.

Vitamin A, its chemical name is probably retinol. Yes, retinol. Its deficiency causes night blindness. Meaning less vision at night

. Yes. Source: Carrot and Mango. Yes. Then Vitamin C Ascorbic Acid. Its deficiency causes Scurvy in which gums become weak and start bleeding. Yes. And its sources are citrus fruits like

Amla, Lemon, Vitamin D, Calciferol. Its deficiency causes rickets in children and osteomalacia in adults which weakens the bones . Absolutely. Sunlight is a very good source of this and

so is fish oil. Vitamin B12, Cyanocobalamin Its deficiency causes a type of anemia. It is called Perseus anemia. Yes. And it is mostly found in animal foods.

And Vitamin K Phyllonone Its deficiency causes problems in blood clotting. Bleeding does not stop easily when there is an injury. Green leafy vegetables are a good source of this. Okay. These

are vitamins. What about minerals? Minerals are equally important along with vitamins . Like calcium which is needed for strengthening bones and teeth. Everyone knows? Yes, milk, curd. Yes. Its deficiency

makes bones weak and brittle, which is called osteoporosis. And iron is necessary for making hemoglobin in the blood. It is hemoglobin that carries oxygen to the body. Deficiency causes anemia

i.e. lack of blood. And iodine is present in salt. Yes, iodine is necessary for the proper functioning of the thyroid gland. Its deficiency can cause goiter. That is why it is advisable to take iodised salt.

Overall, a balanced diet containing all these macro and micronutrients in the right amount is very important for staying healthy. Definitely. And from the perspective of competitive exams, vitamins and

minerals, their sources and diseases caused by their deficiency are such topics from which direct questions are often asked. Yes, it will be beneficial to memorise these by making a table. Absolutely. Remembering them well

can be scoring. Absolutely. Before leaving, a question comes to mind . Ask. In today's fast-paced life and the kind of processed or ready-to-eat food we are eating,

are we able to fulfill all the nutritional needs of the body? Are we unknowingly getting away from essential nutrients? This is really a matter to think about. What

do you think? Are we really able to take a balanced diet or is the dependence on supplements increasing? What are your thoughts on this? Do share in the comments. So let's talk today

about two very important topics - teeth and genetics. Yes and both of these are such that questions are made from them in competitive exams. This is an important part of general science. Absolutely. So let's start with teeth.

I mean everyone knows that there are teeth but it is important to know their structure, their types. Yes, like the first thing, the hardest part of the body. That is the enamel of the teeth. Isn't it? Which is on top of the crown.

Absolutely right. Crown means the tooth that we can see and this enamel is made of calcium phosphate which is very strong. Okay. And below this, there is dentin and then inside there is pulp cavity which contains nerves etc.

The part of the tooth which is buried in the gum is called root. And where the crown and root meet near the gum, that part is called neck.

Okay? This is the structure. Yes. Now, there are types according to their function. Yes, absolutely. There are four main types. The ones in the front which

are used for cutting. Incisors. Yes. Incisors. There are eight in total. Four on top, four below. Then next to them are those pointed ones. Canines?

Yes. Probably used for tearing. Absolutely. There are four canines. Then come the premolars. There are eight of them. And the last ones are the molars, a total of 12. Their and

the premolars' job is to chew and grind food. Well, the wisdom teeth are also included in these. Yes, yes. That is the third molar. The 12 molars counted include the four wisdom teeth.

So in total, an adult has 32 teeth? Yes, 32. But in children, that is, milk teeth, there are only 20. Oh yes, why this difference? Which teeth are not there in children?

They do not have premolars. This is something to remember. Straightaway comes the incisors, canines and then molars. Well, that is why the dental formula they write must also be different. Yes, absolutely. The formula for adults is 2123/2123,

which means in one jaw, two incisors, one nine, two premolars, three molars. And for children, there is zero in place of premolars. The correct formula for children is 2102/2102 . Two incisors, one canine, zero premolar, two molars.

This is quite logical to understand. Well, any other interesting thing related to teeth, like elephant's teeth. Yes, that is a common misconception. The big teeth of an elephant that are visible outside are actually its incisors. Not canines.

Oh wow. And the beak of birds. That is also interesting. The beak of birds is a modified form of teeth. They do not have teeth in their mouth like us. What a thing. That means the story of teeth is also quite deep. Now let's move a little further from here

. These physical characteristics like how the teeth will be? How many will they be? How is all this decided ? Genetics comes into play here. Isn't it? Yes, absolutely. Genetics is considered to be the father of Gregor John

Mendel. He was the one who conducted experiments on pea plants . Yes, it was his work on Picea sativum that taught us the laws of inheritance. And what

is the basis of inheritance in humans? Chromosomes. Yes, chromosomes. Every cell has 23 pairs, that is, a total of 46 chromosomes. Out of these, 22 pairs are autosomes that determine the rest of the characteristics of the body. And the 23rd pair is

called the sex chromosome. It determines the sex. XX in women and X-Y in men. And sometimes there is a mistake in the number of these chromosomes. There are some syndromes etc.

Yes, it can happen. These are called chromosomal abnormalities. For example, one is Turner syndrome. What happens in Turner syndrome? It occurs in women when they have one less X chromosome. That means

there is only X instead of X. So a total of 45 chromosomes remain. 44 autosomes plus X. Okay. And I have also heard of Down syndrome. As per our knowledge, this occurs in men when an extra X chromosome comes. That means XXV instead of XV.

Yes, as per the information available, the sex chromosome status of men becomes XXV. So there are a total of 47 chromosomes. 44 autosomes plus XXV. Okay? This was about chromosomes. Now

let us look at it from the perspective of evolution. So, some patterns are seen in the organs of living beings as well. Like those analogous and similar organs. Yes, this is also a very important concept. Homologous organs. What are these?

These are those organs whose basic structure or origin is the same. But their functions can be different. Any example? Like a human hand, a dog's front leg and a bird's wing. If you

look at the structure of their bones, the basic pattern will be the same. But the function of the hand is to grasp, the legs are for running, and the wings are for flying. Got it? Structure same, function different and homologous would be the opposite. Yes, homologous organs.

Their origin and structure are different. But their function is the same. Okay. For example, butterfly wings, bat wings and bird wings. All three are used for flying. But butterfly wings are made of chitin.

Bats have skin spread between the fingers and bird wings have bones and feathers. So the structure is completely different but the function is the same, flying. Wow, this is very clear. Homologous means structure same but function different. Homologous means

structure different but function same. Absolutely. This helps in understanding the process of evolution . So today we covered a lot. Complete detailing of teeth, their structure, type, number, dental formula, some interesting facts.

And then we touched the basics of genetics. Mendel, chromosomes, sex determination, some syndromes and these homologous and analogous organs. All these points are very useful for competitive exams.

Definitely. And before leaving, he leaves a question for the listeners. Think about what these similar and rich organs found in living beings indicate about the story of evolution? Yes, definitely think about it. What

are your thoughts on this? Do tell us in the comments below.