The whole of AQA Biology Paper 1 in only 63 minutes! 17th May 2022 | Science exam revision

– Hey, guys, here is
your whole topic summary for the first paper in AQA Biology. Now remember, this is just
a summary of everything. If you want a full checklist of absolutely everything you need to know
with thousands of questions, keywords; long, long lists
of things you need to know for chemistry and
physics, you can get them. The free version (mumbles)
which is over my website, or if you wanna ease, have
Amazon print it out for you, you can get it over there. (upbeat music) Here we have our beautiful plant cell with a cell membrane. That's responsible for
determining which bits going in and out of the cell. Cell wall, important for structure. The vacuole, important for structure. The cytoplasm, where most
of the reactions take place. The tiny little dots are the ribosomes, which are responsible
for protein synthesis.

The green bits are the chloroplasts. The pink ones are the mitochondria, where energy is produced. And then last but not
least, we have our nucleus. Here we have our animal
cell with our cell membrane. Again, controlling what goes in and out are mitochondria. Where energy is produced, ribosomes, which are responsible
for protein synthesis; cytoplasm where most of
the reactions take place; and our nucleus, that's
where the DNA's hold, that's the control center of the cell. You'll notice there are several
features of a plant cell that an animal cell doesn't share. For example, the cell wall, the vacuole, the chloroplasts. If you look up at these pages yourself, you can download them,
the free-version guide from my website. Here we have our bacterial cell which has its cell membrane controlling what goes in and out; the cytoplasm, where most of the reactions take place; the chromosome… The DNA not in a nucleus.

The flagella, which is
used for locomotion. Ribosomes for protein synthesis, and then on the outside,
you have the cell wall. Even though you have
to learn the structure of a typical plant cell
or a typical animal cell, there isn't really a typical type of cell because there are a wide range of differentiated specialized cells. We can see here in our cross-section leaf, it has lots of different types cells in. Here we have a neuron
which looks very different to a muscle cell, which is going to look very different to a skin
cell or very different to a set of cells in the gut. They're going to specialize
to do their jobs. So here we have villi, which
give us long surface area. Here cells are very tall
to provide structure.

Here the cells have a very long body so that the neurons can
travel a long distance. And the muscle cells are
going to stretch and contract. All cells start off looking the same. So they have your basic cell structure. And then various different
genes will be turned on and turned off. And that's when it will
start to specialize, that's when differentiation
will take place, and it will grow this
really, really long axon or it'll grow the villi, or it will turn into a leaf cell. Microscopy techniques have varied wildly over the time, from the
very, very basic starts where you had your lenses and you had to use the focus
to see what was going on.

These were all generally hand done, very, very basics. To ones that you're probably
more familiar with in school which have slightly more
sophisticated lenses, to the massive ones
that I used to work on, electron microscopes, where they're all controlled by computer. If you want to work out image heights, object heights or
magnification from an image you've taken from a microscope, the calculation if magnification equals image height over object height. DNA is a long strand of
deoxyribonucleic acid, made of lots of letters:
As, Ts, Cs and Gs.

And these twist round into a double helix. This double helix is
still ridiculously long, so it further twists round
so that it's in a chromosome. And this chromosome is located
in the nucleus of a cell. In mitosis, we go from one parent cell to two identical daughter cells. The first thing that
needs to happen is that the DNA in the nucleus needs to condense into chromosomes, and
then they need to line up down the middle. Once they're all lined up down the middle, and all the checks have
taken place to make sure the chromosomes aren't gonna go astray, they can start to be pulled
apart to either end of the cell. New nuclei will form, and
then they will separate into two identical daughter cells. Stem cells are fantastic
things because they are things that have the
potential to turn into any other type of cell.

They have a number of different uses. For example, if you're
treating Parkinson's disease, they can be used to grow new brain cells. If we're talking about
brain or spinal injury, bone injuries, then
they can be used to grow new bones to fill the gap. If we have organ failure,
we can grow new organs or parts of organs instead of waiting and making someone wait
on the incredibly long transfer waiting list. If you want to make stem cells, then we take a nuclei out of an egg cell, we take nuclei from the patient's cell and insert that into the empty egg. The egg can then start to
develop into an embryo. From this embryo, the stem
cell are then removed, and stem cells are turned into new cells. This does come with quite
a lot of controversy because human embryos
are going to be created and then destroyed. And there were lots of
religious objections to this, people just saying that life starts when embryos are created, and people who object to
the destruction of embryos. When we're talking about
diffusion, we are talking about things moving from
a high concentration down the diffusion gradient to an area of low concentration.

This could be things moving from an area inside a cell where they've
been made to another area, or it could be things
moving out of a cell. For example, it could be
happening in the lungs, these the alveoli, the air spaces. And this is the capillary
traveling around it. There's very, very thin walls only one cell thick. And carbon dioxide is going to diffuse from the blood into lungs
so they can be breathed out, and oxygen is going to
diffuse from the lungs into the blood so it can
be taken around the body.

Or this can be in the gut, these are the villi of the gut. This is the gut cavity here. When you notice, again,
they are one cell thick, and just like the alveoli, they have very large surface area. We're going to get digested food moving from the gut cavity into the blood so that it could be taken
around the rest of the body. So diffusion is the movement of gases or any particles that
dissolved in solution moving down our concentration gradient from a high concentration to
an area of low concentration. Osmosis is specifically
the movement of water through a partially-permeable membrane from the area of high water concentration to an area of low water concentration.

So you'll notice this
partially-permeable membrane, the pools in it aren't large enough for the solute to move through. So the water is going to be the
one that moves through here. This sort of thing can
happen in root hair cells where we're looking at
the uptake of water. Active transport, again,
is a movement across a membrane, but it is from, this time, a low concentration to
a high concentration against the concentration gradient. So our channel, our
active transport channel is going to pick up
something that it wants. It is then going to move that through the channel to the outside. This could happen, for
example, when we're talking about glucose in the gut
or minerals in roots. You need to know the
difference between a tissue, an organ, and organ system. A tissue is one type of cell
carrying out one function. An organ is made up from
lots of different types of cells carrying out a joint function.

And an organ system are a group of organs that work together to
carry out a function. So our hierarchy is cells, tissues, organs, organ systems. For example, we could have muscle cells which are part of muscle tissue
which, together, contract, which form part of the
stomach, churning food; and this forms part of
the digestive system. Here we have an overview
of our digestive system. The mouth which is mechanically
gonna break down food; the salivary gland which
is gonna produce amylase; the liver which produces bile. Bile is something that emulsifies fat, so increases its surface area of fats turning them from a big
blob into a small blob and neutralizes stomach acid. The gall bladder that stores bile; the small intestine
that moves glucose, ions and other things into the blood and has a very large surface area; the stomach which churns out food. The stomach acid, hydrochloric
acid kills bacteria. And it provides an
environment proteases to work. Your pancreas which produces enzymes; your large intestine which
removes excess water; and your rectum and anus
which gets rid of waste food.

There a number of different
enzymes in the digestive system that you need to be aware of. Lipase breaks down fats into fatty acids and glycerol. It is made in the pancreas and small intestine. And works in a small intestine. Protease breaks down proteins into amino acids. It is made in the stomach, pancreas and small intestine. And works in the stomach and small intestine. Amylase breaks down starch into sugars. It is made in the salivary glands, pancreas and small intestine. And it works in the mouth and small intestine. Amylase, protease and
lipase are all enzymes and work with the lock and key mechanism. We have our enzyme which has a very specifically-shaped active site. So only one substrate, or
a couple of substrates, are going to fit in there, the ones that have the
complementary sites. They're gonna form an
enzyme substrate complex, and then the enzyme is either
going to break apart things or it is going to join together things.

It is then going to release the products, and then the enzyme is unchanged and can be used again. You need to know how temperature
affects enzyme activity, and it is this kind of lopsided curve. When we have really,
really low temperatures, there is not enough energy. At the peak, this is
the optimal temperature. And then after the peak,
the enzymes get denatured, which means their links between them holding everything together
are being destroyed. The enzyme is not killed. I know the temptation is to say this, but the correct term is denatured. Our curve for pH is much more symmetrical. We still have an optimal pH. But when it is too high or too low, the bonds aren't going to be in place. So the active site of
the enzyme is going to be breaking down, so again,
it is going to be denatured. Here we have our respiratory system. Air goes in through the mouth or the nose down into the trachea, which is also known as the windpipe. Then into the bronchus which
is branch of the trachea into the bronchiole which is
the branch of the bronchus, and into the little grape or
cauliflower-shaped alveoli.

This is where gas exchange happens. And they have incredibly
large surface area. The diaphragm moves up and
down to bring air in and out. The heart pumps blood around the body. The intercostal muscles
allow the ribcage to expand. And the ribs, the last part
that makes up everything, protects the lungs. Here we have a cardiovascular system, and it is a double system. The blood gets pumped from
the heart to the lungs, goes back to the heart
and then gets pumped around the rest of the body. If you see a picture of the heart, the first thing you do is write right and left on there. We have our vena cava
where the blood enters. It goes into the right atrium down through a valve
into the right ventricle. From the right ventricle, it goes up and to the lungs via the pulmonary artery.

It comes back into the heart via the pulmonary vein, into the left atrium, into the left ventricle, and then is pumped to the rest of the body via the aorta. If you want to check you
have the path of blood right, then we need to be looking
at capital letters. It goes through the vena cava, the atrium, the ventricle, then the artery, back through the vein into the atrium to the ventricle, and then the aorta. So it goes vena cava, atrium, ventricle, artery, vein, atrium, ventricle, aorta. V-A-V-A-V-A. If you don't have that pattern, you've made a mistake somewhere. Other features of the
heart that you need to know are here, these are valves
that will only allow blood to flow.

And this side has a much larger muscle than this side. The right side only needs to pump blood to the lungs which aren't very far away. But this side has to pump blood to the rest of the body,
a much longer distance. The majority of the time,
veins carry deoxygenated blood apart from the pulmonary
vein which carries oxygenated blood back into the heart. And the majority of the time, arteries carry oxygenated blood apart from the pulmonary vein which carries deoxygenated blood from
the heart to the lungs. If the heart isn't functioning properly, pacemakers, artificial pacemakers can be introduced to
help the heart keep time. Or if somebody has cardiovascular disease, then these tubes can get blocked up. Arteries have very thick walls because they are carrying
blood under high pressure, which means they have a thin lumen; that's the gap in the middle.

Capillaries are very, very small. They are only one cell thick, or very, very think I should say. They're only one cell thick, this is to allow for diffusion. They generally, they're
around in this kind of like mesh network around things like the gut, around the villi in the gut, around the alveoli in the lungs, so they have a large surface area. The veins carry deoxygenated blood, they carry back to the heart, so they have valves. And they have thin walls and a thick lumen because they're carrying blood under low pressure. Blood is made up of several components. The actual color of blood
is this pale yellow color. This is the serum, that's the
liquid component of the blood. The cells give it its actual color. Red blood cells, the cells
that give blood its color, have no nuclei. And this is so they have more space to carry oxygen, which is
the their main function.

White blood cells are
part of the immune system. And platelets of fragments of cells, and they are important
for things like clotting. When we have cardiovascular disease, we have fatty deposits… building up in the coronary arteries, the arteries around the heart. This can lead to the
formation of blood clots. This blood clot can block an artery. This is going to restrict the oxygen… to some cells. These cells are then going to die. If too many cells die, this can then lead to a heart attack. If so many cells die that the
heart can't function properly or can't pump blood properly. Risk factors for this
are going to be smoking, high blood pressure, or having too much salts or fat in your diet. We are about halfway through. Well done, guys, we can keep going; we can do this. I do wanna say thank you to a few people who have supported me, helped me to add captions to the video. Captions are gonna make your
revision so much easier. Beth, Hannah, and Nicola
have been fantastic in their support, and
Narinder and Izzy are awesome, awesome teachers who are
supporting me as well.

Health is a complicated concept. It is going to be overall state of physical and mental wellbeing. This is gonna be affected
by a number of things. It is going to be affected by your diet, exercise, community, whether you feel lonely, whether you have friends; and in part by your genes. Epidemiology studies are
going to be looking at the levels of health and illness in a population. We need to do it in a wide population so we can look for different risk factors. For example, we can't force people, we can't ask people to eat a high-fat diet or to do lots of exercise or to drink lots so we can compare them to other people who don't do those things
or do do those things. But there are people
within a wide population that do do those things already. So if we wanted to look at the
affect of exercise on health, we could take our population, we could look at people
that do lots of exercise and compare them to people
that didn't do any exercise.

And because we have such large population of people we're looking at, then we can compare the two groups. And we can follow these
groups for years and years to see what the affects are going to be. Cancer is when cells begin
to divide uncontrollably. This is going to lead to lumps, which for most people, some people is the first sign that something is wrong. And these lumps can be
divided into two groups: benign tumors and malignant tumors. Benign tumors are slow and
are generally harmless.

Things like warts or moles are benign tumors. And having a lump on your skin generally doesn't do you much damage. The problem is when they
are malignant tumors. These are fast growing,
they are aggressive, and they are mobile. So I don't mean the wart in your arm or the mole in your arm is gonna get up and start moving around. I mean cells are gonna
move throughout your body. Cells from the initial
lump are gonna jump into the blood stream, move somewhere else, and they could set up tumors,
lumps, in other places. And while a lump on your
skin generally won't do you much damage, a lump in your brain, a lump in your liver
or a lump in your lungs can do you quite a lot of damage. There are also risk
factors involving cancer, and there are lot of things
that we are in control of. Smoking has large
implications in lung cancer. Diet, a good diet, can reduce your risk of bowel cancer, whereas if you don't eat
much fruit and vegetables, then you are putting your
bowel at risk of cancer.

The amount of time you spend in the sun can affect your
susceptibility to skin cancer. And unprotected sex can leave you at risk of cervical cancer. Here we have a cross-section
of a typical leaf. Our palisade mesophyll
where photosynthesis is going to take place; cuticle which is the waxy layer; upper and lower epidermis
which cover the plant; spongy mesophyll which is
the space for gas exchange; and the guard cell and stomata which is where transpiration takes place. Inside the plant, we have
the xylem and the phloem. The phloem is going to carry water, this is generally going to
be an upwards direction, from the roots where it's collected to the leaves where it can
be used for photosynthesis, and the phloem which carries ions and food, and this is generally
in a downwards direction; from the leaf where food can
be made in photosynthesis to the roots where it can be stored in, for example, potatoes. There are several factors that affect the rate of transpiration, and transpiration not only involve water moving out of the stomata but also moving up through the xylem. So if we have bright light, that is going to lead
to more transpiration.

More light means more photosynthesis which means it's going
to need to be more water brought up into the cell. If we have a high temperature, that is going to lead
to more transpiration… because the rate of reaction
is going to happen faster. If we have high wind, that is going to lead
to more transpiration… because wind is going to be brushing against the leaf or the
flowing against leaf moving thing out of the way, so diffusion is going to play a part here. And if we have high humidity, this is going to lead
to lower transpiration. Water is going to
struggle to leave the leaf because there is a very
high concentration of water, it's very humid outside. A pathogen is a microorganism that causes disease. For example, we can have viruses, bacteria, fungi, or protists. And these can be spread in
a number of different ways. They can be spread in the
air, for example, by coughing. They can be spread by touch, for example, if you have
bacteria on your hands or you have bacteria virus on your hands and you touch a table
and someone else then touches that same table.

They can be spread though blood, sexual fluids. Or they can be transferred via a vector like via mosquito. Bacteria are going to make you feel ill because they produce a lot of toxins, so they'll give you things
like food poisoning. Viruses will make you feel ill
because when they reproduce, they cause massive cell death. Measles is a virus. It is spread by liquid droplets in the air or on surfaces. For example, if you sneeze or coughed and the liquid droplets
that come out of your mouth and out of your nose go into the air, and if somebody breathes that
in, they can get the virus.

Or if it goes onto a piece of furniture or like say the train
or bus that you're on, then you touched that, and
then you touched your mouth; that's how it can go in. The virus will quite happily
sit around for a few hours waiting for someone else to infect. This is very common in children, and they're going to feel very ill. It's going to be like having
a bad cold or a bad cough, there's gonna be coughing and sneezing; red eyes, high temperature, and a nasty rash. These days there is very little damage, because there's a widespread
vaccination program the MMR, which prevents a lot of people getting it, and there are very few serious
complications with measles. HIV is a virus. It can be spread in a number of ways, that is unprotected sex, sharing needles, child birth; that's from mother to child,
not just general child birth, infected blood, breast feeding from an infected mother.

The implications are
devastating for someone, although outcomes have
rapidly improved recently due to the development of new drugs. So HIV attacks the white blood cells. White blood cells are an important part of your immune response. So if your white blood
cells are being attacked, then you have little immune response. The damage is widespread
and HIV can develop into AIDS where, that's Acquired
Immune Deficiency response which can lead to even
the smallest infection having devastating
consequences because you have no immunity against it. Tobacco mosaic virus is,
unsurprisingly, a virus. It is spread from plant to
plant by direct contact. The implications are a
reduced level of chlorophyll, which is why you can see the
mosaic pattern on the leaves.

Some areas have a different level of chlorophyll than others. Now if they have reduced chlorophyll, that's gonna be reduced photosynthesis which is going to lead to reduced sugars. Meaning that there's
going to be a lower yield from the plants, whether
that's tobacco plants; this also affects tomato plants. So it's gonna affect the
commercial side of a business. Salmonella is caused by bacteria. It's spread by eating infected foods. It lives in the gut of farm animals, so infected foods are
going to be things like eggs, meat, milk or poultry. However, it's very, very rare in the UK. We have eggs that have a
little line mark on them which means they are salmonella free. And I don't think there's been a case of salmonella poisoning from eggs in years. The implications are going to be diarrhea, stomach cramps, vomiting and fever. Not very pleasant at all. And if severe hydration sets in, then it can be life threatening. Gonorrhea is a bacteria which has a very long complicated name. It is spread via contact
with penile or vaginal fluid. It can also be passed from
a mother to a newborn baby.

The implications are a thick green smelly discharge from the penis or vagina, thoroughly unpleasant; pain in urinating and bleeding. While the symptoms are
thoroughly unpleasant, about one in 10 infected
men and around half of infected women won't
actually show any symptoms. Because the symptoms are so unpleasant, and because quite a large number of people don't actually show any symptoms, it is very, very important
that you always wear a condom. Apart from being smelly and offputting, the main damage here is
going to be to (mumbles), apart from if you're a newborn baby where it can lead to blindness. Rose black spots is caused by a fungus. Fungus is spread by spores. You're going to see large
areas of discoloration… which can actually lead
to quite a lot of damage. It is going to be a loss of vigor, the plant's not going to be very happy because it won't be able
to produce enough sugars. The leaves are going to appear black, they're going to appear yellow. They could all potentially fall off and then the plant might die.

Malaria is a parasite. It is spread by female mosquitos drinking your blood at night. It's not quite as sexy as
(mumbles) made it out to be. The implications are
going to be a high fever, sweats and also chills, headache, vomiting, chest and muscle pains, and diarrhea. And this can be lethal in severe cases. The body is rather good
at protecting itself against pathogens. The stomach is full of
acid which kills bacteria. Your respiratory system,
your nose, trachea, bronchi are full of mucus and
hairs which trap bacteria. Your skin acts as a barrier
which stops things getting in. And your eyes have tears
which wash them out clean. Your immune system is brilliantly
clever at protecting you.

It consumes pathogens,
so your white blood cells will engulf, they will
eat anything that they see as unfamiliar and dangerous, and then it will destroy it. They produce antitoxins
to counteract the toxins that the bacteria produce. And they produce antibodies
so they can recognize pathogens faster. I imagine most of you
have been vaccinated, or if you haven't, at least
you've heard about vaccinations. Vaccinations are given
generally to children or people that (mumbles) gone
holiday to different places. And the childhood
vaccination program in the UK has prevented millions
and millions of deaths, and further, millions and
millions of serious illnesses. In this country, it has
wiped out a large number of debilitating diseases. It is very rare to hear
of anyone getting polio these days in the UK because
we are all vaccinated against it at a young age. The polio vaccine isn't
too bad because they give it to you on a sugar cube, but it is quite painful taking
your eight-week-old baby to be injected by the nurse. A vaccination is going
to contain small amounts of dead or inactive pathogens.

This allows your immune
system to develop antibodies. So if you get infected with
a disease at a later point, your body already had antibodies to it, it can recognize it, it
knows it's a pathogen, it knows how to deal with,
and it can be dealt with quickly before you get ill. The advantages are that a
large number of diseases has been wiped out. For example, nobody gets smallpox anymore or polio. And we have herd immunity
which means if a large percentage of the
population are vaccinated against disease, even the small percentage that have decided to not be vaccinated or can't be vaccinated for medical reasons are going to be protected as well because the disease will
find it very hard to spread. The disadvantages is
they don't always work. The polio vaccine, (mumbles) vaccines are very, very efficient, but things like the flu vaccine doesn't always work.

And it can be painful, and there can be side effects. You may heard about a controversy where somebody linked the
MMR vaccine and autism. This is completely untrue. There is absolutely no
link between these two. Because bacteria divide so quickly, in good conditions, they can
divide once every 20 minutes, they are going to be
very, very susceptible to mutations in their DNA. Completely random changes, which means completely
randomly one tiny bacteria could develop a resistance
to an antibiotic. And it only needs one bacteria
out of a large collection to become resistant to the antibody for it to become a problem. Here we can see an
antibiotic sensitivity test. These are the disk with antibiotics on, and you can see the
bacteria's grown all the way up to these disks, but not all the way up to this disk here.

So the role of antibiotics
is to kill bacteria. Because divides so quickly, mutations can quickly develop. If (mumbles) of any antibiotics, any non-resistant bacteria
will be killed off, and any resistant bacteria
will survive and grow. This is natural selection in action, and soon, only resistant
bacteria will be left. This is a problem because
we are running out of antibiotics which treat common complications with, for
example, tonsillitis. It is easily treated these days, small infections are
easily treated these days, which previously they
might've been lethal. We use antibiotics far too much. They are given to animals daily, habitually in their feed, and this is driving natural selection, driving the bacteria to mutate.

You are doing such fantastic work. Well done for making it this far. We're just gonna take
another little mind pause, another little break for
you to gather yourself, to refresh yourself, and
then we're gonna start again. New drugs need to be
tested for new things: toxicity, efficacy and dose. Toxicity tells us the level
or the amount of the drug that we can take before the
side effects are too bad. All drugs that we take on a
daily basis have side effects, but since we know how toxic they are, we know which safe or reasonable
level we can take them at without suffering too badly
from the side effects. Efficacy is like how efficient it is. You can see the similarities
in the two words. Does it work better or
worse than what's already on the market? Are the side effects better or worse than what's already on the market? Is it worth developing
or taking this drug? And dose: how much do you need to take for the drug to be effective? Penicillin has saved millions
and millions of lives.

It's potentially saved your life and you probably haven't even realized. When Alexander Fleming
discovered penicillin in 1928, it really was revolutionary
because before that, people were dying of things that now we take for granted. If you've ever been in
hospital and had an operation, you've probably been given
antibiotics afterwards to stop you getting an infection. Or if you've ever had tonsillitis, you've probably been given penicillin, and it cleared up any infection
without many complications. But before we had penicillin, people died of operations, people died to
common things all the time. But this was an accidental discovery. He went away, left his bacterial plates, and some of them went moldy. And he noticed that the
bacteria didn't grow all the way up to the mold. Something in the mold
was stopping the growth of the bacteria. And this is when we
realized it was penicillin, and that penicillin could
stop bacterial growth. And the discovery of aspirin is down to a traditional ancient medicine. It's been known for
ages that people used to chew on willows, willow bark, when they had a headache, when they had a toothache,
when they weren't feeling very well.

So the willow, the willow bark was taken, it was distilled, and it was discovered it has aspirin in it, and that's how we got
our major pain killer. These beautiful, beautiful
flowers are foxgloves, but they are highly, highly toxic. Because from this flower we get digitalis, which is a heart drug,
saved millions of lives, but the flowers probably
killed hundreds of children. You may have seen plants in the summer covered with thousands, millions of tiny little black or green aphids devouring the plant as they go.

They will go, they will
suck all of the water, all the nutrients, all of
the ions out of the plant, effectively killing it. However, good news is
that ladybirds and ants love to eat aphids. So this is a way that we could
have natural pest control. You can go on the
internet and you can order a box of ladybirds, and you can use these to control the aphids in your garden.

Photosynthesis is going to take water, carbon dioxide, and turn it into oxygen and glucose. We can take light and we can
put it above the equation, but do not put it in the
equation because it is not a reactant. It's just a condition that's needed. You also need to know
the symbols for these. So water is H2O plus carbon dioxide which is CO2, goes to oxygen, O2 plus glucose, which is C6H12O6. This needs to be balanced,
but this is a nice easy one to balance because it is six, six, six; so you can just
remember that it's six, six, six.

And when you're writing our your formula, make sure your numbers are little and are in the correct place. Because if you write this, that's wrong, that's wrong, and you will lose the marks. In photosynthesis, we are
taking energy from here, we're taking energy from light and we are locking it up in glucose. This is an endothermic reaction. It takes in energy. There are certain requirements
of photosynthesis. First of all, we are
going to need chlorophyll. That is our green pigment in leaves, we are going to need water and carbon dioxide because
they are our reactants, and then we're going to need sunlight. And the levels of these can greatly affect how much photosynthesis takes places. The rate of photosynthesis
is going to depend on the percentage level of carbon dioxide. As the percentage level of
carbon dioxide increases, so the rate of photosynthesis
is going to increase, but only after a point. After this point, there are going to be other limiting factors. Past this point, we need
to increase something like the water, light, or the temperature if we want more
photosynthesis to take place.

We could easily switch
this out to represented level of water, and the
graph would look the same. Light intensity is important
for the rate of photosynthesis. When it's night time, when it's dark, we do not have lots of
photosynthesis going on. As we get further through the day, as we get more light intensity,
the rate of photosynthesis will increase until we get to a point where it was no longer
the limiting factor, and other things like the
reactants or temperature need to be increased. After this point, we need to think about increasing other things. Now even though the graph is flat here, it looks like it might have stopped, it hasn't; there is still a steady rate of photosynthesis, it's
just not increasing as much as it was down here.

It's just a steady rate. When plants are very, very cold, everything acts very, very slowly. Not a lot happens. It slowly increases until a nice point where the enzymes are
happy and there's lots and lots of photosynthesis going on, until it gets too hot and
they start to be denatured, and the the rate will
fall off very rapidly. So we have our rate of reaction
increasing with temperature and our optimal temperature and our enzymes getting denatured. It's really important that
you remember that the enzymes are denatured; they are not
killed, they are denatured. The actual rate of
photosynthesis that takes place is much more complicated than
depending on just one thing. It's going to depend on
lots of different things all at once. The glucose from
photosynthesis is going to be stored as starch. The most obvious example
of starch is going to be… potatoes. For respiration, we are
going to take glucose, add it to oxygen and come out with water and carbon dioxide. You need to know the symbols for these, so oxygen is O2; water, H2O; carbon dioxide, CO2; and glucose, C6H12O6.

This needs to be balanced,
but it's a nice and easy one. Six, six, six. You have to make sure your
numbers are in the right side and in the right place,
so these ones need to be little numbers, and these
ones need to be big numbers. Respiration is an exothermic reaction, which means energy is given out. The best example we can see of respiration is (mumbles) jelly baby demo, where we take potassium chlorate,
that's our liquid oxygen, add in our glucose, that's our jelly baby, and you can see the
massive amount of energy that comes off it.

Anaerobic means without oxygen. So for anaerobic
respiration, we take glucose and we turn it into energy and lactic acid. Not as much energy as aerobic respiration. Because the glucose
isn't fully broken down. The lactic acid is going
to build up in muscles, causing an oxygen debt. This build up is gonna be quite painful, so you'll get it when you're
doing things like sprinting or when you run out of oxygen. So after you've finished sprinting, after you finish running, to
get rid of this oxygen debt, you're going to need to
breathe really, really hard, that's why you pant. You keep breathing hard after (mumbles) to pay back this oxygen debt, to get the blood flowing,
to remove the lactic acid from your muscles. Anaerobic respiration can
also take place in yeast.

So yeast will take the glucose and will convert it into carbon dioxide and ethanol. Ethanol is used in drinks
and cleaning products. And carbon dioxide is used
for a variety of things. We're gonna talk about context of yeast, that is what is going to make your cakes or your bread rise. Metabolism is the rate
that chemical reactions take place in your body. For example, glucose
being turned into starch, cellulose or glycogen. Fatty acids and glycerol are
being turned into lipids. Amino acids being made into proteins. Glucose and nitrate ions
forming amino acids. Proteins breaking down to form urea. And all of this is
going to involve energy. The energy is gonna come from
respiration involving glucose. That's going to take
place in the mitochondria of our cells. Amino acids, they're important
for building proteins. Proteins make up all of our hormones, all of our enzymes. These are the bits that actually carry out all of the reactions within our body. Lipids are important for
maintaining our cell structure and for storing energy. Well done, guys, excellent work for making it this far.

The rest is biology only. So if you're doing combined
science, well done. You can go and have a relax or try some quick work questions, or go through the revision guide. Bacteria divide very, very quickly from one into two into four into eight into 16. A good bacteria, a happy bacteria, a bacteria that's got lots of nutrients and is happy with what it's doing will divide roughly every 20 minutes. So that very, very quickly you'll go from one bacteria
to millions of bacteria. So that you can become
very ill from ingesting, from getting in a cut,
from getting your skin, just a single bacteria, because they divide very, very rapidly. If you want to produce
an uncontaminated culture of bacteria, moving your bacteria
from one place to another, you first need to flame
your inoculation loop so that it is red hot.

This makes sure it kills
everything that is on there. You need to make sure
that you open your bottles near the flame so that
no further contamination can get in there. Open the lid as little as possible, flaming the lid as you go. Work as quickly as possible to transfer the sample of bacteria
that you've picked up into your uncontaminated broth, and working as quickly as possible so that you don't get any
other bacterial contamination.

You can then leave the
sample at 37 degrees if you've got an incubator, or just leave it on
the bench at 25 degrees for a few days, and
your bacteria will grow. I've done a much longer
video explaining this, as you can see into here. If you want to go and have a look at that, it's in the playlist with all of the other required practicals. When we're going to be
looking at the effect of antibiotics or antiseptic
on how bacteria grow, we need to make sure that our work area and our hands are clean. Because even though these
bacteria are relatively safe to use, we have to assume
they're going to pathogenic. You need to make sure you've
labeled the underside, not the lid of the agar plate. And these plates will
probably already be seeded for you by the technician. You can put your little
filter paper disks on there, use forceps to do this, and then incubate them for
at 25 degrees for 48 hours.

We can then measure the clear zones in two different directions. Here the clear zone is
slightly hard to see, but hopefully if you look
close enough, you can see it. It's better if you measure the diameter, but in this case, the
only thing that I could do was to measure the radius 'cause the clear film was so large. Here we have our lovely little mouse. He's going to be vaccinated
and this is what's going to start the
formation of antibodies. After a while, cells from
the spleen of the mouse where the antibodies
will form, are collected. We can take a known cell
line, a cancerous cell line, blame a cells, and we
can fuse them together.

After the antibodies
and the cancer cell line have been fused together, we end up with a hybrid cell. These hybrid cells can be grown in culture in a laboratory, and here we
have lots and lots of them. After they've grown up,
the cells can be taken, and the cells and the
antibodies can be separated. The antibodies can then be used
for various different things like pregnancy tests or cancer detection. Plant diseases can be
identified in a number of different ways. This could be due to
discoloration of the leaves, so here we have the tobacco mosaic virus, where you can see the
leaves going colored. Or they could be a black color developing as in rose black spots. The leaves could fall off. It could have a loss or a vigor, which basically means it falls over and looks a bit pathetic. The flowers could either develop wrong or they could not develop at all. Or it could die. However, a poorly looking
plant doesn't necessarily have a disease, it might
have an ion deficiency. If it has low nitrates, it
is going to have poor growth plus yellow leaves. If there are low phosphates,
it is going to have poor root growth plus discolored leaves.

A low potassium is going to lead to poor flower and fruit growth. And low magnesium is going to be yellow leaves. This crosses over into chemistry. This is why your NPK
fertilizers are important. (upbeat music).

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