The Whole of AQA Biology Paper 2 | 15th June 2022 | GCSE science exam revision

– Hello my lovely
kittens, this video covers everything you need for your
second biology exam for AQA. If you want to follow along
everything we do in this video, get all the student for any
specification statements, make sure there's nothing
that you've missed out, you can get that in my free
written guide over on my website, loads and loads of
specification statements, loads and loads of pictures for you to fill it in as we're going through. Pages and pages and pages
of keywords for biology, crosswords to make sure
you know all of those.

All of your units of
physics are also in there. Good luck guys. If there's anything you
need, just let me know. (relaxed guitar music) Homeostasis is the maintenance of a constant internal environment and to keep your body
functioning properly, we need to control our
blood glucose levels, our water levels and our temperature. The brain is the control center and that's gonna be sending signals to various parts of the body.

For example to the pancreas, which is responsible for producing insulin And the effectors-muscles
are gonna do things like moving, for example shivering and then glands are
going to be responsible for the production of our hormones. The nervous system is incredibly complex and is overlaid on our
spinal and muscular system. It consists of the brain, spinal cord, which together are going to make the central nervous system or CNS and all the neurons, the
receptors and effectors. When you pick up stimuli,
that signal needs to travel from wherever you picked
it up, say your fingers, all the way up to your nervous system, your central nervous system, sometimes just stopping
at your spinal cord and then coming straight back again. That is going to be a reflex. This is gonna happen when
you touch something hot, so you move your hand away
without even thinking about it. Other times something is going to happen, the signal will go up to your brain, you'll think about it and
then you'll decide to move.

The nerve cells involved
in this are very long. So this cell body here is incredibly long and this can send a fast electrical signal, however when we come to transfer the signal from one nerve
cell to another nerve cell, things slow down a bit because
they have to cross a synapse. This is going to be a slow chemical signal, as the chemical has to be released, diffuse across the channel
and then be picked up and then initiate another
electrical signal.

Here we have a male and
female endocrine system. the pituitary gland is in the brain. Thyroid is in the neck. The adrenal glands are in the kidneys. The pancreas is hiding behind the stomach, The ovaries are kind of like hip level and then testes hang below the penis. The testes produce testosterone, which has the effects of growing muscles and making the balls and
penis drop and grow larger, increasing the rate of hair growth. Estrogen is produced in the
ovaries, that is responsible for the maturation of eggs
and the menstrual cycle. The pancreas produces insulin which is important for regulating
blood glucose levels. The adrenal glands produce adrenalin which is important for our
fight-or-flight response. The thyroid produces thyroxine which is important in regulating our metabolism. The pituitary gland is very busy, among other things it produces
the follicle-stimulating hormone FSH and the
luteinizing hormone LH.

Control of blood glucose
is very complicated. After a meal has been eaten, blood glucose levels start to rise. This is picked up by the pancreas. The pancreas produces insulin which is sent out into the blood. The insulin in the
bloodstream is gonna cause body cells to start to remove
glucose from the blood. Liver and muscle cells
can take the glucose and convert it into glycogen and store it. Removing glucose from the blood will cause blood glucose levels to fall. If blood glucose levels get too low, this is also picked up by the pancreas. The pancreas will start
to produce glucagon. The glucose that has
previously been stored in muscle and liver cells starts
to return to the blood. The most complicated part of this is getting all the names right. The stored form of glucose is glycogen. Glucagon will covert that into glucose and this return into the glucose will cause blood glucose levels to rise again.

There are two different types of diabetes, type one and type two. In type one diabetes, the
pancreas doesn't work properly. So it doesn't produce the
right amount of insulin. In type two diabetes, cells start to become
insensitive to insulin. Symptoms for both are
going to be loss of weight, an increased need to wee, being very thirsty, blurry vision, fatigue, so being very sleepy and hunger. Treatment for type one
diabetes is going to involve insulin injections. Type two diabetes, it's
gonna be controlling diet, exercise. One of the reasons
periods feel so rubbish is because your hormones are
literally all over the place.

Starting with follicle-stimulating
hormone, it rises, peaks and its job is to make the small egg grow up to a larger egg
and then be released. Luteinizing hormone is only active for a very, very short period. Its job is to release the egg. Estrogen builds up until it
stimulates luteinizing hormone. Progesterone builds up
slowly as it builds up the lining of the uterus
and if there is no egg or if there is no embryo
implanted in it, that will decrease and the lining of
the uterus will break down. There are a number of different
methods of contraception, some hormonal, some non-hormonal that will stop you getting pregnant. But not all of these will protect against sexually transmitted diseases. So it is always very, very
important that you wear a condom. This is a barrier method of contraception. This will stop the sperm
getting the woman pregnant and it will also stop
any nasty STDs from being transmitted from her to
him or from him to her.

The pill and the coil,
IUD, intrauterine device are hormonal methods of
stopping getting pregnant. They are going to stop the egg being released or the egg being implanted. The diaphragm is a barrier method because it will stop sperm entering the vagina. But the semen will still
be transferred into the vaginal entrance,
so that you can still get sexually transmitted
diseases this way. If you're sure that you
don't want to have children, you can go to be sterilized,
you can have a vasectomy.

You can have your tubes
tied, which will mean that no sperm will get from the testes out to the penis or for the woman,
no egg will be released. Around one in six people will find themselves in the unfortunate position where they can't have children naturally. About half of this is due
to male-related reasons and half of this is due
to female-related reasons. As you can see, I am one of
those people and last year, in 2016 we did IVF and this is my massive bump. So the obvious advantages for IVF are you get a baby out of it and if you've been in the situation where you can't have something that
you really really want, you know it's very, very sad and it affects your mental health quite a lot. So having a baby is
gonna be good for people that want to have a baby,
their mental health. However the disadvantages are you have to take a large, large number of drugs for a very, very long period of time.

These have very nasty side effects as well as the daily injections which leave you horribly bruised. There are long term consequences for this because taking these IVF drugs increases your chance of various
different types of cancer. It is very, it's very, very expensive. I had to have it twice. That's twice as expensive. It doesn't always work. There is about a 40%
success rate with IVF, with each round of IVF costing at a minimum, 5,000 pounds with a 40% success rate. Here were the large number of drugs that I had to take day by day. It's a very costly, time
consuming, painful process. Mitosis will lead to two identical daughter cells. Whereas myosis will lead to four different daughter cells. You can remember mitosis goes to two because it has a T in it. Mitosis is used for things like growth or repair whereas myosis is used for sexual reproduction. So these are going to be gametes. In mitosis, we are going to
end up with diploid cells and in myosis we are going to end up with haploid cells, haploid cells having half the number of DNA as the original cell.

In women, the gametes are eggs and in men, the gametes are sperm. In a plant, we have eggs still and that is in the stigma and then the male gametes in plants are pollen and that is on the stamen. In myosis, we are going
to have two divisions. So our chromosomes will line up, they will sort themselves down the middle. There will be a little bit
of crossing over going on. So they will swap chunks
of their chromosome to increase the genetic diversity. They will divide into two. Then they will line up
and divide into two again and you'll notice that
each of the cells have half of the number of
DNA as the parent cell. Asexual reproduction is very
common in the plant world, strawberry plants and
in bacteria and fungi. You are going to get a
genetically identical population, as these are dividing by mitosis. So all of the daughter cells
are going to be the same.

Let us just pause for
a moment, look at these beautiful pictures and
then we can start again. A gene is a stretch of DNA that codes for a characteristic. A genome is all the genes in a body or all of the genes that you have. A gamete is going to be a sex cell. So in humans, that is
the sperm or the egg. Chromosome is bundled up DNA. Alleles are different versions of genes. Dominant means you only need one gene to express a characteristic. Recessive means you need two identical recessive genes to
express a characteristic.

Homozygous means your genes are the same. Heterozygous means your
genes are different. Genotype is what genes you have. Phenotype is the collection of characteristics that you have. We can work out the
chances of a disease or a phenotype being passed on
by doing a genetic cross. These are things that I think should be laid out very formally
and very properly. So mother genotype, big R, little r, mother's phenotype, the carrier. Father's phenotype, big R, little r, father's phenotype, the carrier. Mother's gametes, R, r. R, r. Now we can move the mother's
gametes over here, R, r and the father's down here, R, r and then fill in these ones down and these ones across and so the mother, R, r. Then this one down. R, r. The father, this one across. R, r and then for the father, this one across. R, r. Then the offspring are going
to have dominant-dominant. So they're going to be
homozygous in a non-sufferer. Two of the potential offspring
or half the potential offspring are going to be
heterozygous in a carrier and then out of the
offspring, one in four of them has a chance of being double homozygous to recessive and being a sufferer.

Polydactyly is a condition
where people get one, two, three, four, five, six
little adorable baby fingers and it is dominant. So here we have a mother
who has two homozygous recessive and five fingers
and a father who has a dominant and a recessive
and has six fingers. We can fill in the genetic
cross, mother, mother, mother. Father, father, father, father and we can see somebody who
has this dominant disease. If they have one gene, they will pass it on or their offspring has 50% chance
of also having polydactyly. Cystic fibrosis is a recessive disease. So as we saw in the first example, if we have two parents that are carriers, there is a one in four chance of an offspring having the disease. If only one parent is a carrier, then the chances of the baby having cystic fibrosis are virtually nothing apart from a brand new mutation and chances of them
being a carrier are 50%. If your family has a known genetic disease or if you had a child that
had a genetic disease, you could opt to have IVF
and before your embryo was implanted back into you,
you could have it screened.

So embryo screening or
pre-implantation genetic diagnosis. The advantages to this
are that you can test the embryo so you only
put back healthy embryos. So the chances are the baby born is going to be healthy and
is going to survive. Or you can have an embryo
implanted which could help be a match, a genetic match
for a sibling already born. The disadvantages of this is that embryos are going to be created
and destroyed and some people have religious objections to this. Your chromosomes are in the
nucleus and you have 23 pairs. So there is 46 in total. I say 23 pairs because you're going to get one copy from the mother and
one copy from your father. So you'll have two
copies of chromosome one, two copies of chromosome
two, two copies of chromosome three, two
copies of chromosome four. One from your mother and
one from your father. This will allow for
you to be homozygous or heterozygous for dominant
or recessive genes. If you have inherited two X chromosomes, you're gonna be genetically female. If you have inherited
an X and a Y chromosome, you're gonna be genetically male.

If you know a pair of identical twins, you'll know that they
are not exactly the same even though their genotypes are the same. While they have identical
genes, their phenotypes, their characteristics
and how they look are going to be very different
because your phenotype is influenced by lots of different things. Firstly, your genotype. So that's your DNA, your genetic information
and your environment. This is going to lead to natural variation in a population. Things that are going
to lead to variation in a population are going to
be influences like diet, exercise and personal choice. Making new copies of cells involves copying DNA over and over again and if you try copying
something down thousands, millions of times, eventually
there will become a mistake and this mistake might
just happen once and then get forgotten or this
mistake might be copied over and over and over again and if
it gets copied over and over again, we've got a mutation and
we've got natural selection.

All of these changes added together, these small changes, these big changes, this is our theory of natural
selection of evolution, of gradual change happening over time, this theory thought up by Charles Darwin that means we are more
suited to our environment. Darwin's theory is that
life, all life that we know these days has evolved over
the past three billion years from the first life, the
very, very simple unicellular organisms that were in that slushy puddle and the way this evolution
happens is by natural selection. So random mutations in genes lead to natural variation in a population. So that can be small things
like different hair color, different eye color or big
things like how tall people are.

So for giraffes, being tall
is quite an important thing because it means they have
access to a larger range of food sources and
individual characteristics which make them better
suited to the environment are more likely to survive and reproduce, whether this is tall giraffes
or finches with different shaped beaks or moths that
have gone black or gone white and the genes for these
useful, these desirable characteristics will be passed
on to the next generation. Evidence for evolution comes from fossils.

Not everything leaves fossils because fossils come from the hard parts, the bones. The soft bits are just
going to decay away, so it won't leave fossils. And we can see evolution happening with bacteria because they
multiply very quickly, 20 minutes in some circumstances. So we can see changes,
adaptations for natural selection being passed on and
happening very, very quickly. Fossils can show us
changes that have happened and how different animals are related. From these, we can use or
draw an evolutionary tree showing us how closely things are related.

Things on one branch
means they're very closely related and the point
where they branch off, that's where they became
genetically distinct. When a single species of animals gets geographically separated, and this could be because they were on different islands or there could be a mountain range that
pops up in between them, then we end up with a situation
where we have speciation, where one species leads to
various different species and this is called speciation. Darwin saw this when he was
over in the Galapagos Islands. The finches, small little
birds always started off as one population, one species
but as they separated out onto the islands and as they
got separated from each other, they became quite different. The main difference was
in the shape and length of their beaks as they
became more adapted to the food sources on
those different islands. So whether they had to
dig down deep to get their food or whether
the food was on leaves, whether the food was hard to reach or whether the food was easy to reach. I think we can take a
second to appreciate how adorably cute these little
guys are before we start to talk about the serious
issue of selective breeding.

Selective breeding is breeding an animal for a particular characteristic. It happens with dogs,
it happens with cows, with horses, with cats, with chickens. Any animals that we keep and
we're looking for a particular characteristic have probably
undergone selective breeding and the advantages of this are you get animals which have the
desired characteristic, whether it's the very flat
face of a pug or horses that run fast or cows that
produce a lot of milk. It is important commercially that dairy farmers have cows that
produce a lot of milk, that dog breeders have
dogs that look cute. However the disadvantage to
this is if you have a healthy animal who doesn't display
the desired characteristics, for dairy farmers they are
looking for cows that produce a lot of milk, these are
obviously going to be female cows.

So any male calves that are born, they are healthy animals
but they do not share the desired characteristic,
so they are killed. Dogs that don't share the
desired characteristic can be put to sleep even though they
are perfectly healthy animals. Thousands of dogs, cats
each year are killed just because they are not cute enough or do not look like the industry standard. The desired characteristic can lead to long term health
problems for the animals. I've chosen the pug as the example here. Because of the large number
of folds on their face, it squashes their little nose and it gives them long term breathing problems. Dogs like Labradors are
very susceptible to things like arthritis and dogs
like Rhodesian Ridgebacks, the desired characteristic
is a mutation and new dogs that are born without the
Ridgeback can be put to sleep and then lastly we have a lack of genetic diversity within the population. So when we're talking about breeding, this can lead to a lot of
inbreeding where brothers and sisters are bred to get
the desired characteristic, which is going to lead to
recessive bad mutations coming out more often in the population.

It also means they're
gonna be more susceptible to any diseases that
are going to be around because they don't have
the genetic immunity. Genetic engineering has brought around some fantastic advances. One of the most useful of this is the way we produce insulin these days. Previously insulin used
to be harvested from pig cells and that's what
people had to inject. It wasn't very good and
it wasn't very efficient. These days we've taken
the gene for insulin, we've taken a bit of bacterial DNA with the original DNA characteristic and bacterial DNA
reproduces really quickly.

The insertion of the gene for
insulin into the bacterial DNA means that the bacteria
are now producing insulin. So we are now producing large
amounts of human insulin, which is a really important
point, quickly and safely. This is much, much better for people than having to inject pig insulin. It's made things much cheaper,
much faster and much safer. We can genetically modify plant DNA.

So we can take DNA with our
required characteristic, whether that is a drought resistance gene, say there are countries
that don't get much rain and are very, very susceptible
to droughts can survive that better, so their crops
are gonna grow better. Whether that's a gene
which produces a vitamin. So there are countries that
don't have good food security, where food is shortage,
where people are dying because they're not getting
the right amount of vitamins, we can engineer the food,
the rice that they're growing so that it produces more
vitamins so it's healthier so that less people are going to die.

Or whether it's just pesticide resistance or the ability to resist
being eaten by pests, being eaten by bugs so
that yields are higher. We can take that gene and
put it into our original plant's DNA, producing a
genetically modified plant. We can add in the new
gene to the plant DNA, we can produce seeds and then the farmers can grow those seeds and the plants will have this new desired characteristic. Some people don't like
genetically modified plants because they think
it's interfering with nature. Another mental break,
let us all just pretend for a moment we are
Instagram travel bloggers. Bacteria divide very, very rapidly. Bacteria that is happy, has lots of food, has lots of space and nutrients is going to divide roughly every 20 minutes. This allows a single mutation to spread through the
population really quickly. This is gonna allow antibody
resistance to really easily develop and spread
due to branching mutations.

Those branching mutations mean that the bacteria that don't
get killed by antibiotics, they're going to be selected
for by natural selection and bacteria easily pass
from person to person or from animal to person
or from animal to animal which means antibiotic-resistant bacteria is going to spread really easily. Penicillin has saved
many millions of lives, probably yours at some
point, definitely mine. Because before Penicillin,
before the widespread use of antibiotics, people died
of very, very common things. Going into the hospital to have a simple operation most of the time was lethal before the widespread use of antibiotics. The smallest infection could kill you. MRSA is bacteria that is
resistant to most antibiotics. Now this happens on your skin, it's there on your skin on the time. If you go into a hospital
to have an operation, you will get swabbed for it
to find out if you have it. But if you do have it and then
you get an infection with it, there are very few antibiotics
they can use to treat it.

The development of new
antibiotics is very slow, partly because we've looked for a lot of these in a lot of places
and partly because developing new drugs is
very, very expensive. So companies are gonna spend their time, spend their effort and
their resources looking at drugs that are gonna
make them lots of money, drugs that people have to take every day for heart disease or diabetes. Antibiotics you take once for maybe seven days and then you
don't need them again. So they don't necessarily
make pharmaceutical companies lots of money but they will
cost lots of money to develop.

Carl Linnaeus developed taxonomy, which is the study of grouping
living things together. We can see on our
evolutionary tree here that some things are very
closely grouped together and for other things, you actually have to go quite a long distance. He developed a naming system where each organism has a two part
Latin name and this will tell us how closely related they are. It's a bit like them having a
first name and a second name, a genus and then a species.

The genus will be the wide
overarching type of thing and then the species will
be exactly what thing it is. With each new development in biology, with each new development in genetics, we understand more and
more about classifications. So our taxonomy and our evolutionary tree is evolving all the time. The three-domain system
divides everything in life into three groups, eukaryotes,
bacteria and archaea. Eukaryotes are things that have nuclei. An ecosystem are the animals, plants, everything living within a certain area. The community are the plants
and animals that live there and they're all dependent
upon one another. They cannot survive without each other. For example, the animals eat the plants. They can't survive without
doing that and the plants rely on the animals to
distribute their seeds. To survive and reproduce,
a species needs food, water, air and sometimes but not always a mate. Abiotic and biotic factors are things that are going to affect any organism.

Abiotic are non-living factors
such as light intensity, temperature, water levels, pH, ion levels, wind, carbon dioxide levels and oxygen levels. Biotic factors are going to be
living factors such as food, predators and pathogens. An increase or reduction or
removal or introduction of any of these factors can have a
dramatic impact on a community. For example, the introduction
of a new predator or a new pathogen could
wipe out a community. An increase or a decrease
in the temperature could mean that an organism's
food source is gone or an organism can't
survive in that environment and plants and animals aren't
going to be able to survive without sufficient levels of
carbon dioxide and oxygen. Animals need to adapt to their environment so that they can survive. Cacti are well-adapted to a desert environment because
they have shallow roots. They have spines to
prevent them being eaten and they can store water in their leaves. Snow foxes are white so that they blend in. They have small ears so
that they don't lose heat due to the surface area and
they have a very thick coat.

All food chains start in the same place, with the sun providing energy and then from this energy,
things are going to grow. Mainly plants and they
get eaten by other things. Whether it's grass being eaten by cows and then going on to be
eaten by us or whether we eat the plants directly or
whether the plants, here the corn is being turned into corn
syrup which is used in ketchup. Whether we eat them
directly or process them, we are a top consumer whereas
other things like cows are gonna be herbivores
because they just eat plants. The direction of the arrow is really important in food chains. The direction of the arrow means eaten by. If you want to investigate
what grows in a field, you can use a quadrat which is going to be say a meter square, you throw that on the ground and count what is in there, randomly moving it around the field so that you get a wide coverage.

You're going to need to
estimate the size of the field so that you can work out
how much area there is. Work out your plant population
per area that you've measured and then multiply that up
to cover the entire field. A transect is a bit more ordered. You start at a point,
take a line and then take measurements at every single
point along that line. This could be say from a hedge moving away so that you are varying things like the light intensity or
distance from water. So for the carbon cycle, I'm
referring a lot to organic compounds and if you haven't
heard this phrase before, it can be a bit confusing.

Organic compounds are just any compound that has carbon in it and just to remind you,
a compound is two or more elements that are
chemically bonded together. So here are all the different
locations that carbon can be. It can be carbon dioxide in the air or carbon dioxide can
be dissolved in oceans. It can be as organic compounds
in plants or in animals. These organic compounds can
also present in the dead plants or animals and
they are in fossil fuels. Now you need to know the
various different ways that they change from all
these different locations and what the process is called. So let's start with fossil fuels. When we have fossil
fuels, we can burn them so that the carbon in them goes into the air and the fancy
name for this is combustion and when the carbon dioxide is in the air, it can be taken up by plants and this is the process of photosynthesis and the opposite can occur as well because plants will also
undergo respiration.

Plants get eaten by animals and then plants and animals both die. From the organic compounds
that are in the dead plants and animals, they
can turn into fossil fuels by either being buried or being sedimented or they can just go straight back up into the air by the process of decay and then lastly, animals are also undergoing respiration. So carbon isn't a static thing. It is constantly moving around, from carbon dioxide in the air to carbon compounds that are in animals, plants, in dead animals
and then being turned into fossil fuels which can then be burned and put the carbon
dioxide back in the air. This is a very, very
complicated involved process that happens over millions of years and you need to know all of these steps. The water cycle is much more complicated than you think it is going to be.

Here energy from the sun comes down, warms the surface of
the water on the earth and this is gonna cause
the water to evaporate. As the water evaporates,
it's gonna become less dense. It's gonna rise up and then it's going to condense when it starts to cool down. This is when we're going
to get clouds formed. When the clouds are
heavy when the water is accumulated so much, it
is going to start to rain and the fancy word for
rain is precipitation. After it's rained, the water is going to
do a number of things. It can go into mountains where
it will sink in or percolate deep into the mountains
where it's then gonna pick up stuff like irons,
salts which is gonna affect the taste and the
chemistry of the water. This will then come out somewhere as a little stream and go into the river. Some of it's going to go into the soil, moving slowly back towards a river or a lake as free flow. Some of the water will go
straight onto the ground. If the rock or the mud
is already saturated, if it is full of water or
the rock is impermeable, then that will just run off into the nearest river or
stream or lake or reservoir.

All of it ending up at some
point in a large collection of water, whether that is
in the sea again or whether that's in a reservoir or
whether that's in a lake. Some of that water will get taken up by plants and used in photosynthesis. It will also come out of plants in the process of transpiration and then go up in to make clouds and then the cycle can
start all over again. Microorganisms are part
of the system of biotic and abiotic factors that
help break down old things, for example old food
so that the components can be recycled back through the system.

Biodiversity is the range of plants and animals that live within a habitat and humans have a massive
impact on biodiversity. Whether it is chopping down
loads of natural fields so that we can plant the same type
of crop over and over again, reducing the biodiversity
of that environment because we're replacing it
with the same type of crop or whether we are chopping down fields or forests so that we can
replace it with cities.

There are a wide range of
different types of pollution, whether it's air pollution from smog, water pollution where oil
or rubbish is getting into the water or plastic pollution
where we're just leaving rubbish all over the place
and this can have a dramatic impact on the plants and
animals that live there. If we change the chemistry of
the water they're living in, if you bring in nitrates on fertilizer or if you bring in too much oil, the fish and the plants are going
to struggle to survive. With plastic, it is being eaten by animals and the chemicals in there
are moving up the food chain and air pollution is
having a massive effect on the animals, not just their breathing but their ability to camouflage.

Large parts of the world are
suffering from deforestation at the moment where the trees
are being cut down either for logging so that the
trees, the wood can be used or so that the land can be
used to grow things like crops. The problem with deforestation
is that it destroys habitats for the plants
and animals and if this is happening in a rainforest
where there are lots of rare animals or animals that
have yet to be discovered, then these animals are
losing their habitat, so they can't be protected.

It leads to soil erosion. So the soil that was held
together by the roots isn't held together
anymore, so when it rains, that just washes away and
there's the loss of nutrients. Peat is basically mud. It is complicated fancy
mud but it's basically mud and this can be used for
burning and what they do is they chop it out of the
ground in square chunks. It needs to be left in the sun to dry and then it can be used as a fuel. The problem with chopping
this out of the ground to use as fuel is that
it has taken millions of years for this to grow, so
it's a non-renewable resource and it provides a fantastic
habitat for plants and animals and once it is chopped up and
burnt, that habitat is lost.

There are a number of gases that contribute to global warming. We have carbon dioxide, water and methane being the main ones and global warming might
be a slightly confusing term because not everywhere
is getting hotter. Some places are getting
colder, some places are getting drier, some
places are getting windier. This is climate change going on. So while Australia may be having
its hottest Christmas ever, we could be having our coldest
Christmas ever here in the UK and this is all due to global
warming or climate change.

This is gonna have a
massive impact on animals, predominantly on their habitat
and their food sources. Polar bears live on ice
caps, they hunt, they fish and then they need to go and
rest on floating blocks of ice. If the poles are getting
warmer and the ice isn't there, it's gonna melt, polar bears after a long time fishing won't have anywhere to rest and are at significant risk of drowning. Habitats are also spreading. For example as the top
of a mountain warms up, mosquitoes can move
further up the mountain, changing the location of
where plants can grow, where animals can live.

If a region is too hot or too cold, food may not grow there anymore, the plants or the animals
that another animal survives on, which is
going to leave a species vulnerable if their food
source has been wiped out. Well done for making it this far guys. Excellent, excellent work. Those of you doing combined science can go and have a break now, the
rest of this is biology only. The brain is the control
center of the body. It makes sure everything
functions properly and tells various
different parts what to do. We have the cerebral cortex,
the cerebellum and the medulla. The brain is an incredibly
complicated thing to study because for it to be functioning properly, it needs to be inside a living person. Doctors can work on
mapping various different things by using MRI
scanning and CT scanning, giving their person different stimuli to see which parts of the brain light up.

Here we have our beautiful
picture of the eye. The sclera which is the white bit. The retina, which is where
the image is focused. The optic nerve, which
sends message to brain. The ciliary muscles, which
change the shape of the lens. The cornea, which is
a protective covering. The pupil lets light in. The lens is responsible for focus and the suspensory ligaments
hold the lens in place. If you are short-sighted, you can't see distant objects and if
you are long-sighted, you can't see close objects. In an eye that can see
correctly, the lens will take the light and will focus
the image on the retina. Whereas someone that is short-sighted, the image focuses before
the retina and someone that is long-sighted, the image
focuses behind the retina.

To correct short-sightedness,
we need a diverging lens and to correct long-sightedness,
we need a converging lens. Body temperature is going to
be regulated by the thermo- regula- tory, thermoregulatory center in the brain. If you are too cold, the hairs
on your body will stand up. This is to trap a layer of air. You're going to stop sweating. Vasoconstriction will start. So your blood vessels will constrict so that they are further
away from the skin. Less blood is going to
flow close to the surface of the skin, so less heat
is going to be lost from it and your muscles are going to start to shiver and movement is
gonna produce energy. If you are too hot, your hairs are going to lie flat so they're not trapping any air. You're going to start
sweating and the water is going to evaporate, leading
to heat and energy loss and your blood vessels
are going to undergo vaso- dilation, meaning they are going to get wider so that blood can flow closer to the surface of the skin
so that heat can be lost.

The kidneys have three
functions, they remove urea, they control the iron content and they control the water
content of the blood. There are three ways we can
lose water from our body. In urine, in sweat and when we breathe out. It's important to control the
level of water in the body because if there is too
much water taken up by cells by osmosis, then they
might pop or if there's not enough water, then the
enzymes, the functions, the reactions won't be able to take place. There are three steps in the
way that the kidneys function.

Ultrafiltration, reabsorption
and then the release. Blood enters the kidneys
under high pressure and water ions, urea and sugar
are gonna be squeezed out into the capsule, which is
at the start of the nephron. As this all flows along the nephron, useful things will be absorbed. All of the sugar is going to be absorbed via active transport. Some ions, the amount
of ions that we need, the type of ions that we need are gonna be reabsorbed by active transports and enough water that we need
is going to be reabsorbed.

The hormone that controls how much water is going to be absorbed is ADH, which is antidiuretic hormone and then anything that isn't reabsorbed is going to come out as wee. If the kidneys aren't working properly, a person can undergo kidney dialysis. The dialysis machine will
take over the function of the kidneys but it
is very time-consuming. It takes about four hours and has to be done three times a week. So this has a huge impact on someone's life and is not a lot of fun. An alternative to dialysis
could be kidney transplants but these come with
very long waiting lists and there is always the risk of rejection. Phototropism means something is gonna grow towards the light. Geotropism or gravitropism means something is gonna grow towards gravity. Meaning your roots are
always gonna go downwards and your chutes are
always gonna go upwards.

Gibberellins are important for growth. Ethene is important for ripening plants and auxins are important for growth and diagonal growth in
the right direction. The advantages of sexual reproduction is that you'll get a genetically
diverse population, which means they're going to be better protected from diseases. The counter to that is that
a disadvantage of asexual reproduction is that you're
going to get a genetically identical population. So that if a disease
comes along and one plant is susceptible, changes are all plants, the whole population or
animals are going to be susceptible and they're all
going to be wiped out at once.

An advantage of asexual
reproduction is that there is only one parent, meaning that the plant
or the animal doesn't have to wait around for a mate to turn up. Whereas with sexual reproduction, a mate is required and sometimes this can
be quite hard to find, especially in sparsely
populated locations. Another advantage of asexual reproduction is that their energy is conserved and what I mean
by that is that the parent is putting all of its energy
into conserving its own genes.

So this is like the selfish gene, it wants its genes, its
genetics to be continued as opposed to continuing putting energy into something that only
has half of its genes. DNA is made from different
bases that fit together. So we are always going
to have A connecting to T and we are always going
to have C connecting to G. This is always, always,
always going to be the case. It has a sugar phosphate backbone and there are two of those which stretch all the way around the outside. There are two of those,
it is a double helix. You see that the green is
always connected to the yellow, A to T, C to G, the blue is
always connected to the orange and it's going around in a helical or a double helical structure. Each three letter sequence of DNA is gonna code for an amino acid. So here we have A, G, A. We start off with A, find G, then find A. So that DNA sequence is going
to code into the amino acid, arginine. The next three along, CTG, are going to code into leucine and this will keep going until eventually we have a long amino acid chain.

This can then fold up in
very complicated ways until we get a protein that will
look something like that and proteins are responsible for basically everything that happens in your body. They're the hormones, they're the enzymes, they're the cell walls,
everything is a protein or dependent upon a protein and these proteins are
very, very specific. An enzyme substrate's active site is going to be very, very specific
to the substrate. So if there is a mistake
in our amino acid chain, if something is missing
or if something is wrong, we put the wrong amino acid in there, then our enzyme, our protein
is going to fold up wrong. The mutation is going to have caused a change in the protein, which can then have a massive impact on how it functions.

Meaning that it might not
work properly, meaning that it might not break down what
it's supposed to break down, meaning that it might not
function in the correct way. There is a massive amount of DNA in each of our cells and only
some of it is useful. So say this section here
might be non-coding, which basically means it's like junk DNA just getting in the way. There is a number of different ways that cloning can take place. We can do it with a plant where we just chop a little bit off,
pop that into something like rooting hormone,
put it into the soil, put it into the new pots and
it will grow into a new plant. This works really well with things like lavender or strawberries. We can do it by tissue
culture where we can let one cell divide,
then we can take that, put it into further Petri dishes until we have lots of dishes of the same. We can clone animals by embryo transfer. So an animal, a sheep, a cow, anything that the farmer wants to have, wants his animal to have lots
and lots of genetic babies, more than they can
naturally have at one time, the egg is removed from this animal.

This is gonna be mixed with sperm from the desired other parent. The embryo is then allowed
to develop and at this point, they can do pre-implantation
genetic diagnosis to test for the sex of the animal. So it's important for dairy farmers that the cows that are born are female. Or if they're looking for particular characteristics, they can test for those. They can only do this in animals, it is illegal to do this in humans. So it is perfectly safe to
take that embryo, remove a cell to do the genetic
diagnosis and then divide it up. So you would have eight, 12 identical embryos developing. Once these embryos have developed, the embryos can be implanted
into surrogate mothers so that more genetically
identical animals with desirable genetic characteristics
can be born at once.

Many more than the natural
mother, the biological mother would actually
be able to carry safely. If there is one particular
animal that you want to clone, you can remove a body
cell from that animal, take the DNA out of that body cell, take a different female
animal and remove an egg cell, remove the nucleus from that egg cell. DNA from the animal that you want to clone is inserted into the egg cell. It is stimulated to make it divide and then an embryo will develop. The embryo can then be implanted into a surrogate mother who
gets very, very pregnant with a clone of the original animal. The baby born will be genetically identical to the first animal. The surrogate mother may also be the animal that the egg was taken
from but it doesn't have to be, it can be a third
completely different animal and then the baby animal
that is born is not going to be genetically
related to the surrogate mother or the mother that donated the egg.

When Darwin proposed
his theory of evolution, it was very controversial. There were lots of religious objections. This is because he was saying
that the earth was billions of years old, whereas that's
not what it says in the Bible. He was saying that we were evolved from monkeys who evolved from primordial soup and that's not what it says in the Bible. An alternative theory at the time is that of acquired characteristics, say for example if you dyed
your hair blond during your lifetime and you had a baby
while your hair was blond, your baby would have blond hair. Wallace worked with Darwin, they published a paper together and Wallace was very important when we're talking about speciation due to geography. Mendel worked with sweet
peas and he was the precursor to discovering genes
or units of information that inherited units of information.

Decay and decomposition are
breaking down of organic matter and this generally
happens by microorganisms. Microorganisms are alive and
this is something we need to think about when we are
looking at how temperature, water and oxygen affect
the levels of decay. They are not going to work at
very, very low temperatures. They are going to have
a rather narrow set of temperatures which they're
going to want to work in. They rely on enzymes to break things down. They are going to slowly be increasing how well they work as the
temperature increases.

But then at a certain point
the enzymes are gonna mature, so it's gonna come quite
steeply down and if it gets too hot, the whole
thing's gonna catch on fire. Very similar with the level of water, it's gonna be slowly increasing as it gets wetter and then past a certain point, the bacteria just aren't
going to be able to cope. They need to have oxygen, they
need to be able to respire and if there's too much water,
they just can't do that. Oxygen, there is a very narrow amount of oxygen that they will be able to use. Without oxygen, they can't do
anything and too much oxygen, then it starts to become toxic. In the garden, gardeners
can compost things so that they can get rid
of their unwanted things and then take the nutrients,
the goodies in there and put them back onto the garden.

Compost is gonna get
rather hot as this goes on and it's gonna get rather
smelly and gas is going to be released and this gas
can be harvested and used. When we are looking at food chains, we can also think about
construction pyramids. Either pyramids of numbers
or pyramids of biomass. Each of these are tropic
levels and when we're doing numbers, you just
need to look at the number of things that eat the
thing below and biomass, we need to take into account the number and the mass of the
stuff that's being eaten. As we jump between tropic levels, roughly 10% of energy is
transferred from one to the other. It is going to be lost in
a number of different ways. Respiration, waste as in urea and feces, movement, running around, jumping, doing normal animal things. Food security is how sure that we are going to have food on our table. So how sure we are that our supermarkets are going to be full of
things for us to buy.

If as a country we don't produce much of our own food, we have to
buy it from other places. Which means we depend on other countries, other people's climates, trade agreements with these other countries
and transport arrangements, getting the food across borders. Increasing our own food
production in this country will help to ensure our food security. If we are producing our own food, we're not reliant on other people. We need to take into account
ways to increase yield, for example using
fertilizer but then we also need to take into account the impact that might have on the wider environment and we need to take into account
production methods. Are they land-intensive? Are they good for the environment or not? As we are an island, sustainable fishing is one way we can help to
secure our food security. But we need to take into
account things like net size.

Are we catching fish
before they are too old, before they've had a chance to reproduce? Are we catching too many? Do we maybe need to move to line-caught fish so we don't catch endangered species? And we need to look at fisheries quotas. We can also look at new
ways of developing food. For example, culturing microorganisms which we can use as a food source. (relaxed guitar music).

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