- 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)
