Comprehensive GCSE Biology Paper 1 Revision Guide: Key Concepts & Practicals

Let's see how quickly we can cover everything you need to know for GCSE biology paper one. This is good for

higher and foundation tier, double combined and triple separate science. I'll tell you when some of the bigger

concepts are for triple, but not what's for higher in foundation as there's not a lot of difference honestly. And don't

forget to check out the science shorts app to help you test your knowledge. Let's go. All life consists of cells. We

can see cells with a normal light microscope and maybe the nucleus, but the subcellular structures won't really

be visible. Using an electron microscope, however, allows us to see far finer details. So, we can see an

image of these organels. As such, these microscopes have a better resolving power and a higher resolution. We say we

can calculate the actual size of a cell by knowing the magnification of the microscope. Magnification is equal to

image size divided by object size. We put cells into two main groups. Ukarotic cells have a nucleus in which their DNA

is found. That's your plant and animal cells, for example. Proarotic cells don't have a nucleus. The cell membrane

keeps everything inside the cell, but they're also semi or partially or selectively permeable, which means they

allow certain substances to pass through. Plant cells have an extra cell wall made of cellulose, providing a

rigid structure for them. Bacteria also have a cell wall, but it's not made of cellulose. Cytoplasm is the liquid that

makes up the cell in which most chemical reactions take place. Mitochondria is the site of respiration. That's where

energy is released for the cell to function. Ribosomes are the site of protein synthesis. That's where proteins

are assembled. That's where amino acids are assembled into proteins. Plant cells also contain chloroplasts. That's the

site of photosynthesis. They contain chlorophyll. Plant cells also have a permanent vacule in which sap is stored.

Bacteria multiply by binary fision. We can do a practical on this by producing a culture on agar in a petri dish using

aseptic technique. That is making sure nothing else contaminates the culture. We lift the lid of the dish towards a

flame which causes other microbes in the air to move upwards and away from the dish and it destroys them too. Using

sterilized equipment, we can either put a drop of bacteria culture in the middle or spread it all around to create a lawn

and put spots of different antibiotics on top instead. We put a few bits of tape around the dish to hold the lid on,

but not all the way round, otherwise air won't get in and the bacteria will respire anorobically. We don't want

that. We incubate it at 25° for a couple of days, say. Once the culture has grown, we can either calculate the size

of the culture from an initial drop or the area in which bacteria did not grow or were killed by an antibiotic to then

compare with others. In both cases, we use p<unk> r^ 2 or p<unk> d^ 2 over 4 to calculate the area of these circles.

Ukarotic cell nuclei contain DNA which is stored in several chromosomes. Humans have 23 pairs of these in every nucleus.

So we call them diploid cells. That's not the case for gametes though, sperm and egg cells. They have just 23, not 23

pairs. They have half the amount. So therefore, we call them hloid cells. New cells must constantly be made for growth

and repair. They do this by duplicating by mitosis. Here's the process, the mitosis process. The genetic material is

duplicated. The nucleus breaks down and one set of each chromosome pair is pulled to opposite sides of the cell. A

new nucleus forms in each of these to house the copied chromosomes. And we now have two identical cells. By the way,

you might hear that the nucleus divides, which isn't quite right, but you'll get the mark if you put that. Cells

specialize or differentiate depending on the function they need to fulfill. For example, nerve, muscle, root hair,

xyllem, and phenom cells. Stem cells are those that haven't yet specialized. They're found in human and animal

embryos and the merry stems of plants. That's the top of the chute. Stem cells are also made in your bone marrow

throughout your life as well, but these ones only specialize into blood cells. We can use stem cells to combat

conditions like diabetes and paralysis. In fact, right out of the movie The Island, people are now getting clones of

themselves made, then harvesting the stem cells, as these won't be rejected by the person. Personally, I think this

is a dystopian man-made horror beyond comprehension. You have to weigh up the ethical arguments for yourself. Cloning

plants can be used to prevent species from becoming extinct or produce crops with specific characteristics.

Diffusion is the movement of molecules or particles from an area of high concentration to an area of low

concentration. We say they move down the concentration gradient. Like a ball just rolling down a hill, it'll do it by

itself. That doesn't require any energy input. So, we say it's passive. This will happen across a semi or partially

or selectively permeable membrane if the holes in the membrane are large enough for the molecules to move through. For

example, for most cells, water molecules can pass through, but glucose molecules will not, at least not by diffusion

anyway. Osmosis is the name specifically given to the movement, we could say diffusion, but we say movement of water

across such a membrane. For example, if there's a higher concentration of glucose outside a cell, the glucose

can't diffuse in to balance the concentration. So instead, the water moves out of the cell, resulting in a

decrease in its mass. The rate of diffusion and osmosis can be increased by increasing the difference in

concentrations, increasing the temperature or increasing the surface area of the membrane across which this

happens. This is why the villi cells in your small intestine are lumpy as well as alvioli, the air sacks in your lungs

and root hair cells for example too. They all have a very high surface area to volume ratio. The practical for

osmosis goes as follows. Cut equalsized cylinders from a potato or another vegetable, weigh them and place them in

test tubes with varying concentrations of sugar solution. After a day or so, we remove them, dab the excess water off

their surface and reweigh. We calculate percentage change in mass. If it's lighter than it was before, this is a

negative change in mass. We plot these percentages against sugar concentration and we draw a line of best fit. Where

this crosses the x-axis is the concentration at which no change in mass should have occurred. So no osmosis. So

this means this must be the same as the concentration inside the potato itself. Glucose and other nutrients and minerals

can move through a membrane by active transport whereby carrier proteins in the membrane use energy to move

substances through the membrane. As there's energy used in this case, this can actually move them against the

concentration gradient. For example, moving mineral ions into plant root hair cells. It's when cells get organized

together that things get interesting though. When similar cells are connected, we call this a tissue. Say

heart tissue for example. Tissues form organs. For example, your heart and organs work together in an organ system

like your circulatory system. Your digestive system breaks down food you eat into useful nutrients for your body

to use. Acid in your stomach breaks it down. Bile and enzymes work together in your small intestine to break it down

further. Bile is made in the liver and stored in the gallbladder before being used. What it does is neutralize the

acid from the stomach and it also emulsifies fats to form droplets that increase the surface area of these

exposed to the enzymes so they're broken down faster. Enzymes are biological catalysts, some of which break down

larger molecules into smaller ones that can then be absorbed by the villi in your small intestine into the

bloodstream to be transported to every part of your body. For example, amalayise is the enzyme that breaks down

starch into glucose. Well, moltos first but eventually glucose. Enzymes are specific that is they only break down

certain molecules. For example, carbohydrases break down carbohydrates into simple sugars. Ama is one of these.

Proteazes break down proteins into amino acids and lipases break down lipids, that's fats, into glycerol and fatty

acids. They're specific because they work on a lock and key principle. The substrate, for example, the starch binds

to the enzyme's active site. We then call this a complex. However, this can only happen if the substrate is the

right shape in order to fit the active site. In reality, they're incredibly complex shapes, no pun intended. These

shapes here are just there to represent them. Much like a lock and key, though, it only works if they're the right shape

for each other. The rate of enzyme activity increases with temperature due to the molecules having more energy.

That is, until the active site changes shape, and so the substrate no longer binds to it. We say the enzyme has

denatured. This maximum rate occurs at the optimum temperature. Optimum meaning best. This is similar for pH as well

except it can denature at too high or too low pH. The practical on this involves mixing amalayise with starch at

different temperatures or with different pH buffer solutions. Once mixed, we start a timer. Then every 10 seconds, we

remove a couple of drops and put them into a spot in a tile dimple with iodine solution in. To begin with, the iodine

solution will turn black due to there being starch present, but eventually it will stay orange, showing that all of

the starch has been broken down. Calculate the time taken to do that. And then we plot these times against pH or

temperature. Draw a curved line of best fit, and the lowest point is where the starch would have taken the shortest

time to be broken down. That's the optimum temperature or pH. However, in true biology fashion, we're technically

not allowed to interpolate between points for some reason. So, we must only say that the optimum pH or temperature

is between the two lowest points. Shrug. Food tests allow us to identify what nutrients are in our grub. IN solution

turns from orange to black in the presence of starch. Benedict solution turns from blue to green to orange to

brick red in the presence of sugars. We say it's semi-quantitative. Biruet reagent turns from blue to purple with

proteins. And cold ethanol will go cloudy with lipids, that is fats. Breathing isn't respiration, but it does

provide the necessary oxygen for respiration to happen in our cells. Air moves down the trachea into the bronchi,

then the bronchioles, and it ends up in the alvioli, the air sacks, where it diffuses into the blood vessels around

it. Alvoli are lumpy, so they have a large surface area. So this diffusion happens at a fast rate. The oxygen then

binds to the hemoglobin in your red blood cells. They then transport it to every cell in your body to be used for

respiration. Carbon dioxide made from respiration is dissolved into the plasma of the blood where it diffuses into the

lungs and is exhaled. Some water is also excreted this way too. As you know when you breathe on a cold mirror for

example, the heart is at the center of the circulatory system, the transport system of your body. We call it a double

circulatory system because blood enters the heart twice every time it's pumped around the body. Deoxxygenated blood

from the body enters in the right side of your heart. By the way, you always look at the heart or any diagram as if

it's yours and it enters through the vennea, the main vein into the right atrium of the heart. The valve between

the right atrium and the right ventricle stops back flow just like all valves to stop deoxxygenated blood from going back

into the body. The heart muscles contract and the blood goes through the pulmonary artery to the lungs to be

oxygenated. It then comes back to the heart through the pulmonary vein into the left atrium. It then goes into the

left ventricle then out to the body through the aorta. The left side of the heart has thicker walls as the left

ventricle has to pump blood to the whole body whereas the right ventricle only has to pump it to the lungs. A group of

cells in the wall of the right atrium create electrical pulses that cause the heart muscles to contract and the heart

to beat. If these aren't working properly, you can be given an artificial pacemaker to do the same job. Blood

vessels that go away from the heart are always arteries veins towards that means the arteries carry oxygenated blood

apart from the pulmonary artery and vice versa for veins. Arteries have thicker walls to withstand the higher pressure

and so that means they have a thinner lumen the hole in the middle that the blood travels through. Veins have

thinner walls due to the lower blood pressure but have valves to stop backflow. Arteries split and get smaller

and smaller until they end up as tiny capillaries with one cell thick walls to allow the fast diffusion of molecules in

and out of cells. The heart is a muscle, so it needs its own supply of oxygen and therefore blood to keep the muscle

pumping. This is delivered by the coronary artery. If this is blocked by the buildup of fatty deposits, a heart

attack can occur. This is CHD, coronary heart disease. Stances are little tubes inserted into blood vessels to keep them

open so blood can flow in this case. Statins are drugs that reduce cholesterol which in turn reduces the

fatty deposits. Faulty heart valves result in backflow occurring. These can be replaced with artificial ones. Along

with plasma and red blood cells, blood also carries white blood cells which combat infection and platelets which

clump together to clot wounds and stop bleeding. CBD, cardiovascular disease, is an example of a non-communicable

disease as the cause comes from inside your body. Other examples of such diseases include conditions like

allergic reactions and cancer. A communicable disease must be caused by a pathogen that enters your body that will

cause a viral, bacterial, or fungal infection. Back to non-communicable diseases, though, obesity and too much

sugar can cause type 2 diabetes. A bad diet, smoking, and lack of exercise can affect the risk of heart disease.

Alcohol can cause liver diseases. Smoking, lung disease, or lung cancer. Cancer is the result of damaged cells

dividing uncontrollably, leading to tumors. A carcinogen is the term given to anything that increases the risk of

cancer, for example, the tar in cigarettes. Benign tumors don't spread through the body, and they're relatively

easy to treat. However, malignant tumors are when these cancerous cells spread through the body, much worse. BMI stands

for body mass index. It's an indication of how healthy a person's weight is relative to their height. Whatever

number you end up with will put you into bands that determine if you're underweight, a healthy weight,

overweight, or obese. Plants also have organs. Leaves are where photosynthesis takes place, producing food for the

plant. Water also leaves the plant through them, allowing transpiration to take place. the diffusion of water into

roots and up the xyllem. We say it's unidirectional as it only goes in one direction. The rate of transpiration can

be increased by the following. Increasing the temperature, decreasing the humidity, and increasing the air

movement around the plant. All of these result in water evaporating from the leaves at a faster rate. Roots are where

water and mineral ions enter the plant. The merist stem are where new cells are made. Flowm on the other hand are the

conveyor belts of cells that transport sugars, food, and sap up and down the plant. We call this transllocation.

That's a birectional. A lack of nitrate ions means a plant can't synthesize proteins effectively and that stunts

growth. Chlorosis is the scientific term for the yellowing of leaves. This can be due to magnesium deficiency as it's

needed to make chlorophyll. The cross-section of a leaf looks like this. Every layer has its own function. At the

top, we have the waterproof waxy cuticle. That's not there to stop water from entering the leaf, but to stop it

from evaporating from the top and causing the leaf to dry out. The upper epidermis. Epidermis just means outer

layer consists of transparent cells that allow light to pass through to the palisade meaphil layer. Mesophil just

means a layer in the middle. These are chalk full of chloroplasts. So this is where the majority of photosynthesis

takes place. Below that is the spongy meaphil layer that has lots of gaps around the cells to increase the surface

area across which gas exchange can occur. Carbon dioxide diffuses into the cells while oxygen and water diffuse

out. We also have the vascular bundle that includes the xylem and phe. The lower epidermis is the bottommost layer

of the leaf and it has holes in it called stmata which is where gases enter and exit the leaf. The size of a stor is

controlled by the guard cells that flank the hole. They change size to control the rate at which gases enter and leave.

For example, they close the stomata at night to reduce the rate of water loss as less water is needed for

photosynthesis. Communicable diseases are caused by pathogens. That can be viruses, bacteria, fungi, or protests.

Protests are single cell parasites. They all reproduce in your body and cause damage to it. But viruses can't

reproduce by themselves. A virus, in fact, is just a protein casing that surrounds genetic code that it injects

into your cells, which causes the cell to produce more copies of a virus. The cell explodes, and the virus goes on to

infect more cells. Creepy, right? Measles is a virus that causes a rash and it can actually be pretty deadly,

too. It's spread by droplets from sneezes or coughs. HIV is an STD or STI, sexually transmitted disease or

infection that compromises your immune system. That's called AIDS for short. It can also be spread by people sharing

needles. Bacteria on the other hand release toxins that damage your body's cells like salmonella in undercooked

food or gonorrhea another STD that causes a yellow discharge from the genitalia. Not nice. Fungi do something

similar like athletes foot while protests do all sorts of different things. For example, malaria is caused

by a protest that burrows into red blood cells to multiply. Then they burst out destroying the red blood cell in the

process. It's spread by mosquitoes. So we say mosquitoes are the vector for this disease. It's not only animals

though. Plants are particularly susceptible to fungal infections like rose black spot. Purple black spots

appear on the leaves and then they fall off. Such infections can be treated with fungicides. Tobacco mosaic virus affects

plants by discoloring leaves due to inhibiting chlorophyll production. Less photosynthesis occurs and that causes

stunted growth. Our bodies are excellent at protecting us from these pathogens though. Thank goodness. Skin is the

first barrier to them entering. And if they do enter your nose and trachea, they can be trapped by mucus. Acid and

enzymes in your digestive system will destroy them, too. If they still manage to enter the bloodstream, though, white

blood cells are ready to combat them. One type of these are called lymphosytes. They produce antitoxins to

neutralize the poisons pathogens produce and they also make antibodies which stick to the antigen on a pathogen and

this stops them from being able to infect more cells and it makes them clump together. Fagasites are then able

to ingest them and destroy them. An antigen on the surface of a pathogen will have a specific shape. So that

means only an antibbody that fits it will neutralize it. If pathogens are unknown to the immune system,

lymphosytes will start making all sorts of different shapes until one fits. Miraculously, your immune system will

then store a copy of this antibbody next to a copy of the antigen so it's ready to stop it from causing an infection

next time you're exposed to it. You now have immunity. A vaccine is a dead or inert version of a pathogen, usually a

virus, that exposes your immune system to the pathogen, so it can produce the antibbody without it infecting you. For

example, the flu vaccine, you're injected with the virus that has been radiated, so the DNA has been damaged in

sight, so it can't do the job. Incidentally, the CO jab, however, was intended to work differently. Instead,

you're injected with the DNA, or technically mRNA, needed to trick your cells into making part of the virus,

including the antigen. It was the first widely used jab that used this mRNA technology.

Antibiotics kill bacteria. They don't kill viruses. Penicellin was the first one discovered. There are good bacteria

in our bodies as well. So, antibiotics are designed to be as specific as possible because you don't want to

damage those or your body's cells either. Problem is, as bacteria mutate, they can become resistant to

antibiotics. So the more you use them, the less effective they become. Drugs used to be extracted from plants and

other organisms. For example, aspirin comes from willow trees, penicellin from a mold. Now synthesizing drugs is one of

the biggest industries on the planet. They have to be trial to see how effective they are and to check for side

effects. First we do lab trials on cell tissue, then trials on animals, and then human trials. We give the drug to a

group of people, but also we give a placebo to a control group without telling them. Say a pill that's just a

sugar pill, not the actual drug. This is what we call a blind trial because the test subjects don't know what they're

taking. A double blind trial is when even those analyzing the results from the tests aren't aware of which group is

which, and that's to eliminate any bias. This is a crazy one. Monoconal antibodies. These are made from clones

of a cell which is able to produce a specific antibbody to combat a disease. This is achieved by combining

lymphosytes from mice with tumor cells and this makes a hybrid cell. This is then cloned to produce a lot of

antibodies ready to treat a patient. These are monoconal antibodies can also be used for medical diagnosis, pathogen

detection in a lab, or even just identifying molecules in tissue by binding them to a dye. So, they glow

when grouped together because they'll be designed to bind to a specific molecule. The downside to these is that the side

effects are turning out to be worse than scientists expected. Photosynthesis happens in chlorophyll in chloroplasts

in plant cells to provide food for a plant. Here's the word and balanced chemical equation for it. And as energy

is needed in the form of light to make this reaction happen, this is an endothermic reaction. The glucose made

from photosynthesis is used for respiration or is turned into starch or fat as a store of energy. Cellulose is

used to produce cell walls and amino acids are used for synthesizing proteins. The rate of photosynthesis

increases with higher temperature unless it's so high that enzyme denaturing occurs. Increasing light intensity or

increasing CO2 concentration. Any one of these can be a limiting factor, by the way. For example, even if there's lots

of carbon dioxide and it's warm, if there's not enough light, the rate of photosynthesis will be limited by this.

In other words, it doesn't matter how much you increase the other two, it won't get any faster. A graph might look

like this. Before the graph plateaus, levels out, the variable on the x-axis has to be the limiting factor. After it

isn't, it must be one of the other two instead. Sometimes you'll have two lines, for example, for different

temperatures, and that shows that temperature must be the limiting factor. Here's the practical on this. We can

measure the rate of photosynthesis by submerging pondweed in an inverted measuring cylinder. We measure the

volume of oxygen made over time. We can instead count the bubbles, but that's less accurate. The independent variable

could be the light intensity, and that's changed by varying the distance from the light source, for example, a lamp.

However, light intensity follows an inverse square relationship. In other words, if you double the distance, the

light intensity quarters, three times further, 1 nth of the intensity. So therefore, the rate of photosynthesis

should also follow suit. Every cell bar red blood cells has mitochondria, the site of respiration. Respiration takes

place in every organism to provide energy for other chemical reactions to take place and also for movement and

warmth. Aerobic respiration means with oxygen. Here's the word and balanced chemical equations. As you can hopefully

see, it's the opposite of photosynthesis. During exercise, your breathing rate and heart rate rise to

increase the rate at which oxygen is delivered to your cells for respiration. Anorobic respiration occurs when there's

a lack of oxygen. Glucose is instead converted straight into lactic acid, which releases some energy, but less

than aerobic respiration does. This is what you feel when your muscles ache during intense exercise. This poison

can't stay in your body. So, there is an oxygen debt built up. That means more oxygen is needed afterward to break down

this lactic acid in the liver where it's turned back into glucose. That's why your breathing rate and heart rate take

some time to return to normal after exercise. Plant and yeast cells can respire anorobically, but slightly

differently. Instead, glucose is turned into ethanol and carbon dioxide. That's why yeast is used when baking. The CO2

bubbles made cause the bread or cake to rise. This is also called fermentation. It's also used to make alcoholic drinks

as ethanol is produced. Metabolism is defined as the sum of all reactions in a cell or organism. These can include

respiration, conversion of glucose into starch, glycogen, and cellulose. Fatty acids and glycerol are built up into

lipids and also the breakdown of excess proteins. So, I hope you found that helpful. Leave a like and a comment if

you did and click on the card to take you to the playlist for all of the papers. And don't forget to check out

the quiz shorts app to help you test your knowledge. And I'll see you next time.