Comprehensive Guide to CIE IGCSE Biology: Key Concepts and Study Tips

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welcome to my all-in-one cie igcc biology video I'm so excited that I've made this video cie is something that

I've been determined to work on recently and now I finally have time so I really hope you guys find it helpful so yes cie

people only now as always my perfect answers pop up throughout the video and they will be the wording that I think

you should be including your answers in the exam to score maximum marks now if you want me to do all the hard work for

you remember I have perfect answer revision guides available on my website so go check that out and there's also

details about any revision courses I might be running however enough about that let's get

started we're going to start by looking at features that all living organisms have in common and lots of people call

that Mrs nerg or Mrs Gren so remember if they say give some features that all living organisms share you're going to

say movement respiration sensitivity you're going to say nutrition

excretion uh reproduction and growth and that just means getting bigger so if it's non-living like a virus you can

easily say it does not move it does not respire it does not excrete so just list any of the Mrs nug factors and you will

get the marks now classification there are billions of organisms that

exist on our planet and naming them has become a bit of a nightmare because the more species we discover the more names

they need to be assigned and the whole thing gets into a huge mess which is why we need classification systems and this

is just a way of classifying organisms into groups based on common features or features that they share now the system

we currently use is the binomial naming system and that names all organisms according to two names that is both the

spe species and the genus EG myobacterium tuberculosis and that's the bacteria

that causes TB we do need to discuss what a species is just to make sure you understand that and this is where groups

of organisms can be produced to produce fertile offspring and this is the crucial thing so dogs belong to the same

species because they can breed and produce puppies and these puppies should be able to breed with other puppies and

produce fertile offspring and so on and so forth remember what happens if a horse and a donkey reproduce

well they do reproduce to produce what's called a mule but this does not count as a species because mules are sterile that

means that they're infertile so two mules can't breed because they won't produce anything because of the fact

that they're sterile so a mule is not a species so the traditional classification system so not Ones based

on the binomial method we use now was based on evolutionary similarities and it grouped organisms based on their

morphology and Anatomy so effectively leave the bones which made them up a more accurate way of classifying these

organisms is to look at greater detail so actually look at their structures and that means looking at the sequence of

bases in their DNA and now how these sequence of bases determine which amino acids form which proteins so that's a

more accurate way of determining how we should group organisms more similar sequences of DNA so more similar amino

acids and proteins are more likely to be closely related right we now need to go over the

dichotomous Keys part of the specification now I think the easiest way here is to

show you past exam question to work out how you're going to approach it because really I can't just explain it without

an example so figure one figure 1.1 shows five different insects um yeah cool those insects are really nicely

drawn actually use the key to identify the insects in figure 1.1 and write the letter for each insect in table 1.1 so

the easiest way to approach this is from the animal point of view not the table so that is my first recommendation so

I'm going to look at insect a first of all you can see it's quite squat it's short and fat it has two antenna poking

out the top which are here so make sure you know that those are antenna and it has a striped casing so now let's have a

look at how a fits into this table so 1 a body is long and thin that definitely doesn't apply to insect a so I'm going

to go to B body is short and rounded yes it is short and rounded so as the table tells me I'm going to go to number three

so number 3 a no visible antenna well I can see the antenna I've marked them off so we go to B visible antenna which

tells us to go to step four step four body has a striped pattern or body has a dotted pattern I think we can safely say

a has a striped pattern which means that a is and excuse my pronunciation graphosoma

latum so I'm going to put a in here let's go to B now so B looks like a ladyb actually has very small antenna it

has a small round body with spots so one body is long and thin no body is short and rounded yes go to three no visible

antenna that's not true we can see it has antenna so B is correct it has visible antenna so we've been told to go

to four body has a stripe pattern no and we know that belongs to a anyway body has a dotted pattern yes so B needs to

be written here looking at C we've got a fairly rounded body not as round as the first two but fairly we can't see any

antenna and it seems to have quite a uniform black color so going in at one body is long and thin no body is short

and rounded yes so we're going to go to three three no visible antenna I think we can safely say it has no visible

antenna so C goes in here copris lunaris moving on to D so it's long and skinny it has some blobs on it it has

antenna so 1 a a body is long and thin yes that's true so we need to go to two 2 a body has a spotted pattern it does

have a spotted pattern which is why allais oculatus is D and then never just assume you need to work it out properly

and make sure that you agree don't just put e in as that missing Gap so e we can see it's long and thin it's gray it has

antenna so we go in at one it body is long and thin yes so we're going to go to two body has a plain pattern I think

it's safe to say it is plain which is why I'm going to put e there if we're going to use the correct

Nom clature when we're talking about naming things we can talk about the five kingdoms and that consists of plants

animals protus bacteria and fungi so what is a vertebrate well it is an animal containing a backbone a vertebrae

so your spine is made up a vertebral column so a vertebrate contains a backbone now there are several groups of

birs you need to know about and you need to know their distinguishing features so for the mammals their most notable

points is that they have furry skin and they have mamory glands which means they produce milk used to feed their

offspring moving on to birds they obviously have feathers which you find on their wings and then they have scales

on their legs with reptiles so we're talking about lizards and snakes here the most notable thing here is that they

have dry scaly skin for fish again lots of scales here they have fins which help them to swim so they have gills where

they filter water and remember they have like a flap of skin which covers the gills and we call that the ulum and

lastly they have a lateral line containing sense organs for amphibians we're talking about things like frogs

they have moist skin I tried to bribe Lyra into sitting on my lap so she's on a cushion princess Lyra has anyone seen

that episode of Friends where Rachel brings in the cat without fur on a cushion it's basically Lyra now look

what I have to do to convince her to be my friend she likes the cushion so we know what a vertebr is it

is an animal no Lyra a she's gone already we know what a v is it is an animal containing a

backbone so obviously an invertebrate is something which doesn't have a backbone and now we're going to look at the

arthropods which is a group of animals without backbones so they're all invertebrates and they have what's

called an exoskeleton which means that their skeleton is found on the outside of their bodies so things like crabs

whereas as humans we have endoskeletons because our skeletons are found within our bodies cuz look my bones aren't

sticking out unless I've had a horrible horrible accident so starting by looking at the different arthopods we're looking

at the myria pods they have antenni which are the things that stick out they have bodies made up of many segments and

they have a hard exoskeleton so something like a milipede when you're doing this try and name the different

like numbers of wings numbers of legs that sort of thing to help your answer plop out and and state whether they have

antenna or not so the insects now well obviously insects have antenna they have bodies made out of three parts which is

the thorax which is here and we know this because our lungs are found within the thorax the abdomen is further down

and then obviously at the top they have a head they have compound eyes two pairs of wings three pairs of legs so you'll

see they have six legs and the last thing to notice which is weird is that they have mouth Parts with arachnid so

spiders they have simple eyes they don't have compound eyes they can't see as well as things like flies their head and

their thorax are combined we know that spiders have eight legs which means they have four pairs of legs they have

powerful jaws because arachnids are predators they kill and eat other animals and they have what's and I love

this word they have a spinette which is the place where their spider silk comes out of so the crustacean now lots of

people are eating these we're talking about lobsters and crabs for example so what do you think of when you think of a

lobster and a crab or you think of their hard outer casing which we actually call a carpes they have claws with serrated

edges which is why you don't want to get your finger stuck because that could hurt they obviously have eyes they have

jointed Limbs and lastly you may not know this they have gills under their shell we now need to look at plants so

starting with flowering plants whose proper name is the angia spms again you just need to list a load of features so

first of all they can produce flowers they produce fruits and seeds they have extensive root systems for obtaining

water and mineral ions and coupled with this is transport system such as the xylm and florum the stamata allows

carbon dioxide into the leaves and oxygen and water out and lastly they can be monoc calans or dians and that's to

do with how many leaves they produce initially mono meaning one so a single leaf dellons produce too FRS are

extremely different even though they have leaves we have to call the leaves frons and that means that they're long

and thin these frons contain sporangia and it's these sporangia that really spores which is how the ferns reproduce

they also have what's called underground ryes now this is because they have nodules which are like small blobs which

exist underground and what these do is they send out roots and shoots helping our Fern to reproduce they also have

very simple root systems so compared with the angiosperms which have extensive root systems we say that ferns

have simple true root systems lastly viruses nice and simple here just state that they consist of a protein coat

which surrounds genetic materials such as DNA or RNA so we now need to take lots of different types of cell in turn

and know quite a lot of information about them so I'm going to start with the bacterial cell we can see from the

DI diagram that a bacterial cell has a cell wall sometimes it has a slime capsule around the edge sometimes it has

a fella which is a tail that helps the bacteria to move as I've already said it doesn't have a distinct nucleus instead

it has a circular chromosome which we call a nucleoid it has other small rings of genetic material we call these

plasmids and that remember is important when we talk about genetic engineering then you find more typical things such

as cytoplasm and cell membranes in terms of things like whether they're pathogenic or

non-pathogenic remember that they can be both so pathogen is a microorganism that causes disease it makes sense therefore

that some bacteria are pathogenic such examples include pacus which is responsible for pneumonia tuberculosis

remember that's gives people TB where they cough up blood very horrible disease however some bacteria very

useful like those used in yogurt making the example here is lactobacillus bulgaricus you remember lastly that

bacteria are unicellular which means that they're made of one cell only looking at viruses now because that

leads on quite nicely from bacteria these are very very small things they're much smaller than bacteria they're far

more simple because they're simply made out of a protein coat which arounds either DNA or RNA they don't have any of

the typical organal you would find in other types of cell crucial thing here as I've already said is that they're

non-living they do not excrete they do not respire they do not grow they're always pathogenic there's no such thing

as a good virus they're always out to hurt you and examples here include the flu virus the cold virus HIV which is

very famous because it causes AIDS next up we're looking at the Proto tests this is known as the Dustbin Kingdom lots of

of various organisms which don't fit into the other categories fit into protus some of them have animal cell

properties some of them have plant cell properties starting with algae and also Corella these both have chloroplast

which means they're more plant-like things like amoeba are more animal likee you'll see that they don't have

chloroplast they don't have a cell wall as such and they all use diffusion in order to obtain their nutrients and get

their oxygen one key one you need to know about is plasmodium this is pathogenic

because it causes the disease malaria and the plasmodium is the small protus that lives in the female mosquito's

bodies and that's what she injects when she bites you so that's actually what gives you malaria do note that they can

either be unicellular or multicellular so made up of one cell or many cells fungi now now fungi they're quite easy

because you can draw literally a plant cell but just make it slightly more circular so it has the same organ you

would find in a plant cell apart from the fact it obviously doesn't have chloroplast but it does have a cell wall

this is made out of chitin you do need to know that has a cell membrane cytoplasm it has a

vacuum now there are lots of different examples of fungi including mucco and mushrooms do notice that fungi carry out

saprotrophic nutrition and that means that they extracellularly secrete enzymes onto dead matter which it breaks

down and then absorbs as its food crucial words here are extracellular secreting enzy

which break down dead matter and that's how they actually obtain their food there are some useful examples of fungi

including yeast now remember that's used in beer and bread making why because when yeast under goes anerobic

respiration that means respiration without oxygen it breaks down glucose into ethanol which is clearly used in

beer making and also carbon dioxide and it's those bubbles of carbon dioxide that actually help that bread to rise

now we're going to look at the plant and animal cell very basic biology here first of all let's start by the listing

the organal that both animal and plant cells share so remember they both have cell membranes cytoplasm nuclei or

nucleus they have ribosomes mitochondria now in terms of the plant cell there's a few extra organal you

need to list that's the cell wall the vacu and also chloroplasts we now need to look at the

role of each of those organ and turns so because it's so key that you get these really basic questions right in your

exam because if they say what does the nucleus do you need to be able to write that so what does the nucleus do it

controls the activities of the cell what does the cytoplasm do it's where chemical reactions take place what is

the role of the cell membrane it controls what enters and leaves the cell what is the role of ribosomes it's where

protein synthesis takes place I.E where proteins are made which organisms do not contain mitochondria looking more

closely at the plant cell now what is the role of the cell wall first of all state that the cell wool is made out of

cellulose and that it protects and supports the cell the vacu remember that's filled with cell sap which also

helps to maintain the structure of the cell lastly chloroplast remember they're full of a green pigment called

chlorophyll it gives leaves the green color and that's where photosynthesis takes place a couple of tricky words you

may have come across is UK carots and procaryotes don't worry it's just a very Posh way of describing the type of cell

we're talking about ukar are all animal cells as we know it and that's because they contain membrane bound organel such

as nuclei mitochondria Etc so an animal cell like I said is an example of a eukariotic cell

procariota here because they contain no membrane bound organal so they contain no nuclei which we know because they

contain strands of DNA instead so specializ cells this is a nice topic I would get into the habit of drawing

out each cell and then labeling it and then hopefully it'll be easier to learn than just a list of separate points so

starting with the red blood cell clearly that transports oxygen around the body it does this because it contains a

protein pigment called hemoglobin which binds to the oxygen forming oxyhemoglobin in order to improve its

efficiency it has a very distinct shape so it is a biconcave dis shape which means it has an increased surface area

to volume ratio so it can transport more oxygen and it has no nucleus to allow for more hemoglobin it's also extremely

flexible allowing it to pass through the smallest spaces and along the narrowest of capillaries the muscle cell this is

adapted so that it can contract and relax in order to move the muscles cells here are very long and contain protein

fibers and the protein fibers can shorten when there is energy available which means that the muscle contracts

the ciliated cell we find lining the trachea so we're looking at our respiratory system and remember the

trachea is actually the windpipe so the cated cell contains Celia these are small hairs which waft and what they do

is they waft mucus ladened with bacteria out of the Chia into the mouth where it can be swallowed and destroyed by the

hydrochloric acid in the stomach and this is a really good defense system against microorganisms the motor nerve

cell remember there are lots of different nerve cells this is the motor so it transports signals from the

central nervous system to the affector so its real role is to conduct electrical impulses the long part of

that motor cell is called the axon and that carries the electrical impulse don't forget that it is surrounded by a

fatty sheath which we call the myin sheath and that increases the speed at which the impulses may be conducted they

have lots of branched endings so that they can reach lots of other cells the sperm cell now remember these are made

by the testes of males so the whole point of a sperm cell is reproduction remember it fuses with the ovam in

fertilization to produce a zygote so its real role is reproduction now it has to swim through the vagina through the

cervix through the uterus to the overd duct where fertilization takes place and it has a flagellum a tail to enable this

it has a whiplash tail to help it to swim its middle section contains many mitochondria which makes sense because

they release lots of energy required to power that sperm on its long journey in its head it contains an acrosome which

is full of digestive enzymes which help to digest the outer layer of that egg so it can actually penetrate it and don't

forget that its nucleus is hloy which means it contains only one set of chromosomes which makes sense because

the ovam also contains only one set of chromosomes so when they fuse at fertilization a diploid cell is made

which makes sense because we want our zygote to be deployed because it will then go on and become our baby so the

ovam now we've already said it's involved in reproduction we said it contains a hloy number of chromosomes in

its nucleus the only thing to notice here that it has a outer layer which is like a jelly coat that changes once the

sperm has penetrated through moving on to plants now so the root hair cell has a very distinctive shape why because

remember its primary role is to absorb water and mineral ions so it has an root hair which will increase the surface

area for absorption and this absorption occurs by osmosis in terms of water and mineral ions are absorbed by active

transport I've already touched on the xylm and the flo let's look at them in more detail now so the xylm transports

water and it transports the water from the roots up the plant to the leaves to the shoots where it's required now it is

made out of dead cells which form a continuous column the end of the cells has broken down so there's no cytoplasm

and that means you effectively have a drain pipe to transport that water do notice that its walls are made out of

ligin and that helps to strengthen the xylem and stop it collapsing the florum transports sugars when we look at the

structure of the leaf and we look at the layers we know that is the palisade layer which is the Palisade misail and

these are what your regular plant cells look like so do remember that they just contain lots of chloroplast which absorb

sunlight for photosynthesis which means they make sugar or they make glucose for the

plant now we're going to look at organization within organisms so we're looking at Key definitions The crucial

thing here is to just learn one definition and then just use it as a template for all your other definitions

so I'll explain what I'm talking about right now so if we start we look at a cell now remember cells are full of

organal which I've just listed nucleus cell membrane Etc so what is a cell well it's a group of organal working together

to perform the same function we're going up a step further so we're now looking at tissue what is a tissue it's a group

of cells working together to perform the same function then we're going to look at organs so what is an organ it's a

group of tissues working together to perform the same function and lastly what is an organ system it's a group of

organs working together to perform the same function and lastly what is an organism well it's a group of organ

systems working together to perform the same function now I need to list all the various organ systems within the body

which I've always been really bad at remembering all of them so I'm going to try there's the digestive system there's

the endocrine system reproductive system circulatory system respiratory system nervous system and excretory system but

if we focus in on the digestive system for example we could first of all take the fact that the digestive system is

obviously the system so what organs make up that digestive system that organ system well it's things like the stomach

esophagus pancreas small intestine large intestine then we look can look at the tissues so for example in the stomach

you've got glandular tissue which secretes Hydrochloric acid you've got muscular tissue which helps churn the

food don't worry too much about this detail by the way I just want you to get the full picture so you're not thrown

off if a question slightly strange in the exam and then you can obviously look at the cellular level within the stomach

and the organ naels so it's a big hierarchy really so lots of people struggle with

converting units and I wanted to give you a really straightforward way of doing this so let's have a look down

here we've got lots of different scientifically approved units so we've got the Pico meter which most of you

won't come across but I've just added it there for completeness sake then we have the nanometer here which is far more

likely to come up micrometer millimeter which you'll be familiar with because you'll have that on your rulers meter

which is obviously much larger than that you might have wooden meter long rulers in your science lab but you won't really

come across them apart from there kilometers that's very straightforward because we know kilometers how many

kilometers is it to the beach five and then lastly Mega meter here which you probably haven't come across so what I'm

trying to show you here is you can use this simple expedient of timesing by a th to convert between the various steps

so to get from millimeters to micrometers simply Times by thousand to get from micrometers to nanometers Times

by a th000 it obviously works the other way around if you need to get from nanometers here to micrometers here

divide by a th000 but I didn't want to make this diagram too complicated so as long as you know what you're doing you

can obviously reverse it and I'm going to show you some examples right now so let's start by converting 5 m to

micromet so let's have a look in our table and we need Times by a th000 twice and then just write out your

answer now so it becomes 5 million micromet we're now converting 3 mm to micromet so we're going from here to

here so we just need to Times by a th so we're just timesing by 1,000 WS next up converting 10 cm to

nanometers this is more complicated because we've got centimeters which isn't included here so let's first of

all convert cm to millim hopefully that's really straightforward for you because again you have a ruler it says

10 cm on it and you'll be able to work out from your ruler that 1 cm is 10 mm so therefore 10 cm is going to be a 100

mm and then we're just looking back at our little table thing and we need to see how we're getting from millimet to

nanometers and we're timesing by 1,00 twice and let's just add some little commas to try and make that make more

sense so that's 100 million nanom and now we're going to go the other way so we're converting 22 m m 2

mm so this time we need to divide by a th so 22 micromet is 0.022 millet so now we're going to practice

what we've just learned and we're going to start by looking at question one on the right hand side the diagram below

shows the general structure of an animal cell as seen under an electron microscope calculate the magnification

of the image and show you're working so let's start by writing our formula triangle out that does not look like a

triangle so it's I am which means that magnification equals the image size over the actual size the easiest way to do

this is not actually measure the diameter of the cell you need to use this scale bar here we can see from the

scale bar that its size is five micrometers so we're going to put that there as the actual size in terms of the

image size you're going to use your ruler to measure the length of that line here I know it's hard cuz I'm doing on

the iPad but let me tell you that it is 17 mm now the important thing with these calculations is to get all the units

being the same so remember I just taught you how to convert so if you actually look back in the video you can see this

but to get from millimeters to micrometers remember you times by a th000 so let's convert 17 mm to

micrometers by adding 3s / it by 5 and you get a magnific which is 3,400 time as big the

photograph shows parts of the cytoplasm of a cell the magnification of this image is 200,000 calculate the actual

width of the organal X show you're working so as always using our triangle I am we're looking for the actual length

so that's going to be image size over magnification so let's substitute in the magnification first of all cuz that's

nice and straightforward you're going to use your ruler now to work out the width it's the

width not the length of organal X so do that in millim and you'll get an answer which is 20

mm I like to keep my units in so I know what's going on we're converting that to micrometers as per usual so that becomes

20,000 ID 200,000 giving us a value which is 0.1 micromet now we're moving on to

transport so let's first of all touch on the three types of transport so we're looking at diffusion osmosis

and active transport so you need to know the definitions of these terms in great amount of detail now remember with

diffusion it's the net movement of particles from an area of high concentration to an area of low

concentration so that's the reason why you spray perfume in one side of the room where there's a high concentration

of perfume particles and it moves across to the other side of the room where you can smell it that is by diffusion it is

a passive process it does not require energy osmosis is very similar to diffusion however it involves the

movement of water which is why our definition this time is osmosis is the net movement of water from an area of

high water potential to an area of low water potential across a partially permeable membrane now potential is just

a really Posh way of saying concentration so someone where there's lots of water to somewhere where there's

little water and do add that it's across a partially permeable membrane if there's no partially permeable membrane

it's not osmosis it's just diffusion so notice when water leaves the stomata from that leaf that is by diffusion CU

stas is a whole not a partic the permeable membrane lastly active transport as the

name suggests it's an active process this means it requires energy the reason being is because it's the net movement

from an area of low concentration to an area of high concentration so against the concentration gradient so we need to

go into slightly more detail about how active transport actually works so remember that there are carrier proteins

within the membrane these carrier proteins recognize the particle to be transported the particle is transported

across the membrane using the Caro protein and this process requires energy from ATP particles then obviously

released into the cell and lastly the carry protein returns to its original position let's touch on amoeba now

remember LBA is an example of a protus this is a single celled organism which can use diffusion in order to obtain all

the nutrients it needs so oxygen diffuses from outside that amoeba into the amoeba from an area of high

concentration surrounding the amoeba to a low concentration inside the amoeba the reason why diffusion is appropriate

is because because it occurs very quickly because the amra is single CED which means it has a large surface area

to volume ratio and therefore the speed of diffusion is fast enough to allow oxygen in as and when it is required

larger organisms which are multicellular have a much smaller surface area to volume ratio diffusion is not suitable

it is too slow which is why they develop the need for circulatory system so we need to look at biological

molecules starting with Organic comp compounds and organic means relating to the element carbon and we're including

in our organic compounds carbohydrates lipids and proteins so starting with carbohydrates look at the name to work

out which elements exist within it so carbo meaning containing carbon hydrated meaning containing the elements found in

water so they contain hydrogen and oxygen also proteins also contain the elements nitrogen and sulfur and nucleic

acids contain the elements phosphorus and also sulfur we look at carbohydrates we can divide them broadly into two

groups these are monosaccharides and polysaccharides polysaccharides contain many sugars key examples here include

cellulose which is the sugar found in cell walls and also starch which remember is the storage compound found

within plants and glycogen which is found within animals and fungi so looking at proteins now so what is a

protein well it's a chain of amino acids whose order has been determined by genes this sequence of amino acids determines

the protein shap shape and the protein shape and structure give the protein its particular function so for example amino

acids found within keratin which is a protein give its very structural support function whereas amino acids found in

hemoglobin give it a very different role which is to do with the transport of oxygen looking more closely at DNA now

so we need to first of all know what the structure of DNA is remember looks like a ladder we call this a double helix

which winds itself up it's made up of a sugar phosphate backbone and remember that the sugar here is deoxy ribos why

because DNA stands for deoy deoxy ribos nucleic acid so the sugar here is deoxy ribos there's a phosphate and sugar

backbone and then linking the two backbones the rungs of the ladder are bases and remember the names of these

bases adenine thymine ganine and cytosine looking more in depth the various names involved nucleotide a

nucleotide is simply just three units made up of a deoxy VI sugar a phosphate and L A base so it could be either one

of those bases I've just mentioned so Adine thyine cytosine or ganine sorry are you is

that you I said it gu I got guine really but it sounds weird now he's saying

it M's telling me that I'm pronouncing guine wrong my biology teacher said ganine and I don't know how to say it

any other way apparently he says guanine H so he's like what an idiot um so we are need to now look at complimentary

based pairing that's when the various bases pair up in a very specific way try and remember the shape of the letters

match so guanine or guanine always pairs with cytosine because they're both curly in terms of the G and the C adamine and

thyine always pair up and that's because they're the straight so use that to help you

remember enzymes are key proteins which we need to know lots about that an enzyme is a biological catalyst this

means that it speeds up the rate of a chemical reaction without being used up now an enzyme has a very special part on

it called an active site and that's the biologically active part of the molecule and what happens is the substrate

molecule binds to that active side it forms an enzyme substrate complex which then splits up to form the useful

product that we're after now we need to just touch on enzyme activity so the two things you can alter is both the

temperature and the pH so if you look at this graph you can see at low temperatures the enzyme activity is low

the reason for this is all to do with chemistry it's to do with Collision Theory because at low temperatures

enzymes have very little kinetic energy as do the substrate molecules so it means that the enzymes and substrate

aren't coming into contact very often that means they obviously can't bind at the active site and so the reaction

can't be catalyzed catalyzed catalyzed as we increase the temperature you can see the enzyme activity increases that's

because those molecules are coming together more often and at 37° as is the case with most animals you will find the

enzyme activity has reached its peak it is at its Optimum temperature the best temperature and that means the enzymes

and substrates are coming together very frequently after this temperature and above this temperature we see a massive

decrease in in enzyme activity and that's because the enzyme has become denatured never say the word killed

they're not living they can't be killed you need to say they're denatured and what that means is that the enzyme

active site has changed shape meaning that the substrate can no longer fit if we take a look at pH now you can see a

very distinctive graph shape here and that's because enzymes have different Optimum phes and if the pH is either too

high or too low around that optimum pH you'll find that the enzyme D Natures which is why you have that cone shape

because let's look at the enzyme which has an optimum pH of s if you go to 6.5 or 7.5 the enzyme will denat and this is

true for all enzymes some enzymes prefer different phes to other ones so proteases in the stomach for example

because they're surrounded by hydrochloric acid they'll have an optimum pH of approximately three

whereas throughout the rest of the digestive system you find a slightly alkaline optimum pH so of around eight

which is why you can't take stom stomach proteas and put it in this one intestine and expect it to be

okay right we're going to be talking about all things to do with plants starting with that key plant process

photosynthesis remember photosynthesis is carried out in the chloroplast of plant cells they contain chlorophyll

which absorbs that sunlight and actually carries out the process of photosynthesis and this is the method by

which green plants make their own food so let's start by looking at the word equation for photosynthesis remember

that it's carbon dioxide plus water forms glucose and oxygen this is why it's such a great process because of the

huge volume of oxygen photosynthesis releases in terms of the balanced symbol equation try and learn this sof by heart

and remember that 6 is very important so you've got 6 CO2 plus 6 H2O forms C6 h126 + 62

now unfortunately there are lots of different factors which can act to reduce or limit the rate of

photosynthesis and we call these limiting factors you need to know the definition of a limiting factor it's a

factor which in a reaction is in the shortest Supply and a lack of this factor is the reason why rate of

reaction no longer increases now in terms of photosynthesis there are three limiting factors you need to know about

these are carbon dioxide light intensity and temperature so any one of these may act to limit how much photosynthesis can

take place and we're going to talk about each of these in turn in a different situation so let's think about early

morning we have a green plant and it's trying to photosynthesize in early morning but what could be limiting how

much photosynthesis takes place well it's early morning so it's quite cold so obviously temperature is going to be a

limiting factor here another limiting factor will most likely be light intensity because it's not as light

early morning as it is at midday day so despite carbon dioxide levels increasing you will find that low light levels low

temperatures limit the rate of photosynthesis the reason being is that in the morning low temperatures

obviously mean low kinetic energy so all those enzymes involved in those chemical reactions involved in photosynthesis

can't actually come together they don't Collide as frequently with their substrate molecules and that's all

because of lth or kinetic energy if we take midday now we know that the temperature will have increased ined we

know that the light levels will increase so neither of these things will be limiting factors the most likely

limiting factor in midday will be Caron Dark Side levels and be sure that you can look at grass on all of these

factors and make sure you understand what is going on let's quickly look at the role of

diffusion in gas exchange in plants so remember that carbon dioxide is needed by plants in photosynthesis so it will

diffuse into the leaf through through the stamata oxygen is released by photosynthesis so that will diffuse out

of the leaf also by diffusion however don't forget that plants are living organisms so that they respire which is

a bit confusing which means they need some oxygen obviously in order to carry out respiration so if you look at it

over the course of the day you will find during the night because the plant can't photosynthesize because obviously

there's no light it will just be respiring which means that more oxygen will enter the then will exit the leaf

during the day photosynthesis tends to occur at faster rate than respiration so in this case more oxygen will leave the

leaf compared with diffusing into the leaf so we know photosynthesis is the method by which plants make food and

they make that in the form of glucose so what do they do with that glucose well remember that glucose contains carbon

hydrogen oxygen so obviously contains components that can be used to make other biological molecules and this

includes fats and proteins so that glucose is used to make fats and proteins it's used to make storage

compounds such as starch which the plant can call upon in lean times and it's also used to make the sugar cellulose

which is an important component of plant cell walls because it gives it its structural Integrity relating to the

plant mineral ions luckily you don't need to know too much just learn the role of nitrates and magnesium so the

mineral ions are present in the soil of around the roots of the plant and the plant obviously needs them to be healthy

so it absorbs both magnesium and nitrates by active transport so against the concentration gradient and it uses

the nitrates to build proteins and it uses the Magnesium to manufacture the chlorophyll found in chloroplast you

need to know some deficiency signs so with magnesium clearly you won't be able to manufacture chloroplast or

chlorophyll anymore so you see yellow leaves and if you've got a lack of nitrates you will see a stunted poorly

grown plant so it's very short carrying on with the plant theme we're now going to look at the structure

of a leaf and how it is adapted for photosynthesis let's make some generic comments at the beginning by stating

that a leaf has a large surface area which is obvious so that it can absorb more light it's thin so the gases don't

have to diffuse too far looking very closely now at the structure of the leaf you need to be able to label all those

layers and discuss which each of them do and you need to be very specific here so we're going to start with the waxy

cuticle the waxy cuticle is there to prevent transpiration and remember that transpiration is the loss of water from

the leaf so a nice thick waxy cuticle prevents excess water loss next up we have the upper epidermis remember this

is transparent and it allows light to enter the leaf you don't need to say anything more than that the layer

beneath this is the Palisade misail misil is just a FY we same tissue the palis maphil is what your generic plant

cell looks like so it's your rectangle Block it's crammed full of chloroplast so it contains lots of chloroplast for

photosynthesis and this is where photosynthesis takes place under this you have the spongy misil the important

thing to note here is the presence of plenty of air spaces which allow Gases such as carbon dioxide and oxygen to

diffuse you'll also find the vein here and the vein contains the and the flum the xylm brings water into the leaf the

flum transports sugar away from the leaf then we have the lower idamis not a lot to say here the next layer is the most

important layer and that contains the guard cells and the stamata now the guard cells control whether the stamata

are open or closed and the stomata allow carbon dioxide into the leaf and oxygen and water to leave the

leaf balanced diet so what is a balanced diet well it's one which provides all the nutrients in the correct proportions

which are needed to carry out life processes moving on to humans now we're looking at balanced diet so we need to

look at the various nutrients that you need for a balanced diet their roles within the body the foods that they're

found in and any deficiency diseases so let's have a look and start by listing these nutrients so we're looking at

carbohydrates fats proteins minerals vitamins water and fiber I hope I've listed them all so starts with

carbohydrates foods which contain lots of carbohydrates include things like bread and rice and pasta carbohydrates

are an important source of energy proteins now now you find lots of protein in meat such as chicken and beef

protein is important for the growth and repair of muscles now remember lots of people take protein shapes to the gym

why because they're trying to build their muscles at the same time so that they like to take a source of protein so

try and remember it from that point of view if you have a lack of protein you get a

really horrible disease called quoco people are seem very distinctive all like stomach where your stomach comes

out super far and that's the symptom of quoco fats foods which contain a lot of fat include dairy foods such as butter

and cream I'm just giving you a few examples it's not exhaustive now fats are a very concentrated source of energy

and they provide insulation I.E they help to keep you warm moving on to some specific examples of vitamins so vitamin

C you find this in citrous fruits such as oranges and lemons vitamin C is important for the repair of tissues so

it helps to stick together the cells in the lining of your mouth and if you don't have enough vitamin C you get a

disease called scurvy which was um Infamous in the 1500s when sailors used to go out to seea they never got enough

oranges and lemons and then you'd see very characteristic mouth bleeds so scurvy is the deficiency disease and the

way way to get rid of that is by eating lots of oranges and lemons vitamin D now now vitamin D is important for strong

bones you find it in fish liver oils which is gross I hate cold liver oil but it's also manufactured by the action of

the sun on the skin so you can get a lot of vitamin D sunbathing but obviously not too much don't get burnt that's not

a good idea either and lack of vitamin D leads to rickets in children now we're going to move on to minerals such as

iron iron is found in red meat and spinach it's important for healthy blood it's a really important component of

hemoglobin which is found in red blood cells lack of iron leads to anemia which is when you feel really tired and

exhausted all the time and lastly calcium calcium is a mineral which is important for strong teeth and bones

it's found in dairy products such as milk lack of calcium will also lead to rickets last two things fiber so fiber

is essential to help food move through your digestive system without fiber you're liable to get constipation

vegetables and fruit contain a lot of fiber and water water we know we need to survive without it we would die very

quickly and that's because it supports all the chemical reactions that take place in our bodies and just be aware of

a deficiency in energy and protein is known as marasmus and that's when you see muscle wasting on limbs now an

important side not is to notice that we need a balanced diet full of all these nutrients in order to stay healthy but

obviously our requirements will vary depending on our age so older people will need less food less of each of

these nutrients compared with teenagers for example pregnant women they'll need more because they're supporting the

growing fetus teenage girls will need more iron because they've started their periods people who exercise will need

more protein to help them with the growth and repair of their muscles and lastly pregnant women will need more

dietary energy compared with people who are not pregnant so it's a bit of a Common Sense part of the specification

but just be aware that there are differing requirements now we need to look at

digestion let's first of all discuss the definition of digestion which is that it's the breakdown of large insoluble

molecules into small soluble ones the reason being that we need to take our food into our mouth and we need to break

it down into teeny tiny pieces change its structure so that it can be absorbed through the walls of the small intestine

so that's what we're on about when we're talking about digestion so there are various enzymes you need to be aware of

firstly amalay and notice the enzymes tend to end in ASE so A's amalay is made in the salivary glands in your small

intestine and your pancreas and what amalay does is it catalyzes the breakdown of starch into

glucose now we need to look at proteas this is more straightforward because as the name suggests it breaks down

proteins so protein is the substrate and it breaks down proteins into amino acids these are the products and proteases

found in your stomach in your small intestin and your pancreas slightly more detail on proteas enzymes then so we

know these break down proteins however there are two you need to know the name of and that is pepsin and Trin pepsin is

simply the proteas found within the stomach whereas Trin is found within the small intestine the last enzyme you need

to be aware of is lipase lipase breaks down lipids or fats as they're more Lo your name and lipids are broken down

into fatty acids and glycerol so do try and remember that's the most complicated one now I've already told you about

chemical digestion which relates to enzymes entirely because that's totally altering the structure of the food

molecule we need to also look at mechanical digestion which is a far more physical process that involves just

chopping that food up into smaller pieces but doesn't alter the structure of that food so if we you think about

where mechanical digestion takes place it will be in the mouth your teeth chew it'll also be in your stomach where your

muscular walls turn that food up and break it up into smaller chunks so the teeth right we need to be able to name

all the teeth and talk about what they do remember the teeth are very important in mechanical digestion they actually

alter the size of the food to make it more easily digestible by enzymes so let's name our various teeth so the

front teeth here are known as the incizors their job is simply to to cut or slice food the canines which in

humans has become hugely reduced but in animals like dogs you see that they're very long and pointed this grips the

food so it holds it in place then you have larger teeth behind that which we call the pre molers their job is to

crush and chew the food and then the larger teeth at the back they're the MERS they provide the Grinding Service

surface to actually grind that food up so so what causes teeth tooth decay so very painful when we have cavities

now that's all to do with the bacteria because obviously the bacteria feed on any excess food in your mouth which is

why it's so important that you clean your teeth properly so the bacteria stick to your teeth and they make that

plaque which the dentist can sometimes scrape off the bacteria respire and while they're doing this they produce an

acid and it's actually that acid which RADS away your teeth so particularly the enamel and the dentine of your teeth so

how can we actually protect our teeth well clearly we need to eat diet low sugar because we know sugar speeds up

the rate of Decay we need to brush our teeth regularly and ideally after a meal rinse to remove any excess food that

might be stuck between your teeth and I've even read that you can eat crunchy vegetables cuz they effectively help

remove that food too so we'll start at the mouth so I've already said we've got physical

digestion from the teeth chemical digestion comes from Amal which digests starch into glucose the food that then

passes down the food pipe which we're going to have to call the esophagus and peristalsis is a process whereby the

muscular contractions of the esophagal wall force that bolus that ball of food down into your stomach here muscular

contractions of the stomach lining help churn the food you've got the secretion of hydrochloric acid this has two jobs

it breaks down the food and also destroys pathogens and that's the reason why you don't get sick all the time if

you eat some slightly dodgy food sometimes the Fuji vant is so dodgy that you still get sick but for the most part

you'll find your stomach acid will destroy those pathogens remember a pathogen is a microorganism which causes

disease proteas is secreted that breaks down proteins into amino acids at this point the stomach empties and the food

flows into the small intestine well there'll be further peristaltic contractions I don't know if that's the

exact version of the word peristalsis it's similar enough which force the food along we've got more enzymes being added

here lipase protease and amalay and note that they'll have a differing optimum pH from the proteas in the stomach they'll

have a much higher optimum pH we need to mention bile now now bile is an interesting substance I think it's green

it's made in the liver you must remember that it's stored in the ghl bladder and it's released into the small intestine

and it has two main Jobs first of all is an emulsifier and what that means is that it breaks up large fat droplets

into smaller fat droplets why because it creates much larger surface area because small droplets have a much larger

surface area than large droplets and that means that lipas can work more easily on the lipid molecules on the fat

molecules but if you can't be bother to write all that just say that it multiplies it second role is to

neutralize stomach acid it brings up the pH to an alkaline pH approximately 7 or eight and what that does is it means

that those enzymes that have been released into the small intestine don't get denatured by all the acidic food

coming along so that's B's two main jobs to emulsify and to neutralize so at this point we've done

lots of digesting our food molecules are very small they're very soble which means they can now pass through the

walls of the small intestine into the bloodstream they often ask you what the adaptations are of the small intestine

lining so you're going to talk about Vine primarily so remember V are these structures shaped like this and they

provide a very large surface area for absorption and that's also maximized by the presence of micro this video is so

um detailed it's making me lose my voice so yeah micro help increase the surer further you've got a short diffusion

distance you've got a plentiful supply of blood capillaries and you've also got the presence of Lacs which are for fat

absorption so the small intestine is extremely adapted for for its role going into more detail to do with

the microvillus therefore so we know it increases the surface area for absorption the epithelium is one cell

thick which provides a short diffusion pathway goblet cells produce mucus like in the trachea and what this does is

protects the lining of the small intestine good blood supply from within the micro to transport those digested

food stuffs away from the small intestine to elsewhere in the body and lastly the L transports fatty acids and

glycerol so once all that food has been absorbed and you've just got the leftover undigestible food it passes

into the large intestine and here water is reabsorbed into the blood lastly the feces because we're now at the feces

stage that's the fancy word for poo the fees are stored in the rectum before they pass out of your body via the anus

we call this egestion the removal of feces from the anus not to be confused with excretion you do not excrete feces

you e Gest them excretion has a different definition it is the removal of waste products of metabolism and just

to touch on a couple more definitions ingestion is the taking in of food into the body and metabolism is the rate at

which chemical reactions take place in the body let's look at transport in plants so

we're going to start by looking at two vessels two tissues you need to know lots about that is the zym and the floam

make sure you can label these both inside the root at cross-section and inside the stem note that in the root

the X matches with the xylm which is why the X in the middle of the root is xylm that's a nice way of remembering whereas

the circles around that X are the FL inside the stem it's slightly different the outer layer of tissue is the flum

the inner layer is the xylm try and remember this because the flum transports sugar and aphids are little

insects which bite into that stem in order to steal some food so they're biting in so that they can reach that

flow and they take the food so the FL is on the outside of the stem so looking more closely at the RS as I've already

told you FL transports glucose and it transports it from the leaves where it's made in photosynthesis to other parts of

the plant so to Growing regions such as flowers in the tops of stems and to storage regions such as the roots and

that's where it's stored to starch xylm transports water this time and mineral ions from The Roots where it's absorbed

through the root hair cells up the plant to the leaves in various places so this is an important thing for you to note

xylm only transports water upwards flow and transports both up and down the Plant in terms of the structures because

is transporting water and minerals ions it needs to be very strong and notice that it's made out of dead cells which

are stacked on top of each other so there's no organes in there obstructing the flow of water there's also lignin

which helps to reinforce those walls further Flo has a different structure just list some keywords here don't talk

too much about it it has C plates tubes and it has companion cells and those companion cells contain lots of

mitochondria so that they can release energy so that Sugar can be actively transported in and out of the FL we're

now going to look at how the mineral ions enter the plant so I think I've already told you this that they enter by

active transport they enter against the concentration gradient the reason being is there's far fewer mineral ions in the

soil compared with what's inside the plant the plant is greedy it wants as many mineral ions as possible so because

it's against the concentration gradient from a low concentration in the soil to the high concentration in the plant it

absorbs it using active transport into that root hairell looking at how water is absorbed again through the root hael

this is by osmosis so it's from an area of high water potential in the soil to an area of low water potential inside

that root hair cell lastly how does water move up through the plant well just to give you a bit of chemistry

background here remember that water leaves the leaf at the stomata by transpiration so as the stomata open the

first droplet leaves but because water molecules are all attracted to each other due to the

presence of hydrogen bonding this forms a continuous column within the xylm so it's a huge chain of water molecules so

as one leaves the stomata another one is drawn up from below and we call this transpiration

stream you need to know about how the rates of transpiration may be increased and decreased so transpiration let's

remind ourselves it's the loss of water vapor from the surface of the leaf I.E through the stamata so we're looking at

how that water is leaving the leaf so how might we increase the rate at which that occurs and I always say think about

washing drying outside what sort of conditions would you want for your washing to make it dry nice and quickly

so first of all we want it to be dry and the same here this increases transpiration rates when it is dry why

is this and that's because because there are very few water molecules in the air surrounding the leaf there's far more

water inside the leaf therefore water will diffuse out through the stomato very quickly when it is dry if we look

at when it's humid so when there's lots of water in the a it feels really yucky on your skin there's a lot of water in

the air surrounding the leaf lots of water in the leaf there's not a lot of difference between the water molecules

inside and outside of the leaf so diffusion is going to occur very slowly when it is humid next next up what's

going to make our washing dry nice and quickly high temperatures we know this in hot countries our beach towels dry

nice and quickly same with transpiration increased temperature leads to increased transpiration this is because the water

molecules have more kinetic energy and therefore they can simply diffuse faster out of the

leaf next up we want wind for our washing and again windiness will increase transpiration rate the reason

being that the wind blows those water molecules away from the surface of the leaf effectively increase in the

concentration gradient so diffusion will occur nice and quickly and then the last point which has nothing to do with

washing drying is Sun so when it is sunnier you will find that there is more transpiration the reason being that

because it's sunny the plant wants to photosynthesize a lot so it opens its tomato in order to leten that carbon

dioxide which is needed for photosynthesis and clearly because the tomato is now open water can

automatically leave so what is the actual purpose of transpiration why is it a good thing

because at the end of the day we're just seeing water leaving the plant which seems like a bit of a waste firstly the

water flowing in the xylem helps to support the plant it keeps it upright and this is why when the plant doesn't

have enough water it starts to wilt it just doesn't have enough water to make its cells tured secondly it cools the

plant thirdly it provides a method for delivering mineral ions around the plant and number four IT Supplies water for

photosynthesis this let's now look at transport in animals now we're going to talk about

the circulatory system so we need to look at the heart I've already talked a little bit about multicellular versus

unicellular organisms the reason why organisms such as ourselves humans require circulatory system is because

our surface area to volume ratio is too small and diffusion is too slow so we need a circulatory system which actually

acts to transport oxygen around our bodies so that's the reason why we have a circulatory system the heart forms the

epicenter of our circulatory system it is the pump which delivers oxygen around our bodies and you've got to know

detailed information about how this actually happens so we're going to divide the heart into four do remember

that we switch over the left and right sides when we're looking at a diagram why because we're picking up the heart

and pting it into to our bodies so it is the opposite way around if you actually think about it so the four chambers are

the left atrium right atrium they form the top two Chambers left ventricle and right ventricle form the bottom two

Chambers now do remember that pulmonary means relating to the lungs so if you have used the word pulmonary it means

that blood must be flowing either to or from the lungs so we're going to start by picking up oxygen in the lungs it's

going to be delivered to the heart to the left atrium via the pulmonary vein remember that veins bring blood to the