GCSE Biology Paper 2 – Complete Revision Guide

Name: All of AQA BIOLOGY Paper 2 in 25 minutes - GCSE Science Revision
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Description: Summary and key takeaways on GCSE Biology Paper 2 – Complete Revision Guide, covering Homeostasis & the Nervous System Homeostasis: the ability of an organism

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Feb 23, 2026

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Homeostasis & the Nervous System

Homeostasis: the ability of an organism to keep internal conditions stable despite external changes (e.g., blood glucose, temperature, water balance).
Nervous system split into CNS (brain + spinal cord) and PNS (all other nerves).
Receptor → sensory neuron → relay neuron → spinal cord → brain (conscious decision) → motor neuron → effector (muscle).
Reflex arc: signal bypasses the brain, travelling only through the spinal cord for a faster response.

Measuring Reaction Time

Drop a ruler from the thumb, record the distance before it is caught.
Convert distance to time (s = √(2d/g)).
Variables: stimulants (coffee) speed up, depressants slow down.

Brain Regions to Know

Cerebral cortex – memory, speech, problem solving.
Cerebellum – coordination, balance, motor skills.
Medulla – involuntary actions (breathing, heart rate) and adrenaline release.
MRI scans show brain activity non‑invasively.

The Eye & Vision

Accommodation – lens shape changes via ciliary muscles & suspensory ligaments.
Pupil size adjusts to light intensity.
Cornea refracts light; retina contains rods (light intensity) and cones (colour – red, green, blue).
Vision problems: myopia (far‑sightedness), hyperopia (near‑sightedness); corrected with glasses, contacts, or laser surgery.

Thermoregulation

Body temperature sensed by the brain → nervous & hormonal signals.
Too hot: sweat glands evaporate water, vasodilation increases blood flow to skin.
Too cold: vasoconstriction, shivering generates heat.

Endocrine System & Hormones

Glands release hormones into the bloodstream (slower than nerve signals).
Pituitary gland – master gland; controls thyroid, pancreas, adrenal, gonads.
Pancreas: insulin lowers blood glucose; glucagon raises it.
Diabetes types: Type 1 (no insulin production) and Type 2 (cells resistant to insulin).

Water Balance & Kidneys

Water lost via breath, sweat, urine.
Kidneys filter blood, re‑absorb glucose & ions, excrete excess water as urine.
ADH (antidiuretic hormone) from pituitary tells kidneys how much water to re‑absorb – classic negative feedback loop.
Dialysis replaces kidney function when kidneys fail.

Reproduction, Menstruation & Contraception

FSH → egg maturation & estrogen production → uterine lining thickens.
LH triggers ovulation; progesterone maintains lining.
Contraception options: hormonal pills, injections, implants, condoms, diaphragms, IUDs, tubal ligation, vasectomy.
Infertility can be treated with hormone therapy or IVF (in‑vitro fertilisation).

Plant Hormones

Gibberellins: seed germination, flowering, fruit size.
Ethylene: fruit ripening.
Auxins: phototropism (bends toward light) & root geotropism (grow downwards).
Applications: rooting powders, weed control, tissue‑culture growth.

Cell Division & Genetics

Meiosis produces four haploid gametes → genetic variation.
Mitosis creates identical diploid cells (asexual reproduction).
DNA: double helix of nucleotides (A‑T, C‑G). Every three bases code for an amino acid.
Gene expression → protein → phenotype.
Dominant vs recessive alleles; homozygous vs heterozygous; Punnett squares predict offspring ratios.
Human genome: 23 chromosome pairs; sex chromosomes (XX female, XY male).

Evolution & Antibiotic Resistance

Darwin: random variation + natural selection.
Lamarck: acquired traits (now linked to epigenetics).
Antibiotic resistance arises from mutation & selection – complete courses are essential.

Classification & Taxonomy

Hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
Mnemonic: “King Philip Came Over For Good Soup”.
Domains: Archaea (extremophiles), Bacteria, Eukarya.

Ecosystems, Energy Flow & Biodiversity

Abiotic factors: light, temperature, moisture, pH, CO₂, O₂.
Biotic factors: food, predators, competitors, pathogens.
Quadrats & transects estimate population size & distribution.
Food chain levels: producers → primary consumers → secondary → tertiary → apex predators.
Biomass pyramids illustrate energy loss at each trophic level.
High biodiversity → ecosystem stability; human development often reduces it.

Environmental Challenges & Food Security

Deforestation, peat‑bog loss, pollution, waste management threaten biodiversity.
Sustainable fishing uses mesh sizes that let juveniles escape.
Food security pressures: growing population, climate change, conflict (e.g., Ukraine wheat supply).
Strategies: improve crop yields, reduce waste, adopt sustainable practices.

Genetic Engineering & Cloning

Gene cutting (restriction enzymes) → vector (plasmid/virus) → insertion into target organism.
Applications: insulin‑producing bacteria, Golden Rice (vitamin A), disease‑resistant crops.
Cloning: plant cuttings, tissue culture, animal somatic‑cell nuclear transfer (e.g., Dolly the sheep).

Fossils & Evolutionary Evidence

Fossils can be mineralised bones, footprints, or trace fossils.
Provide historical record of life and evolutionary change.

This guide covers every major topic required for GCSE Biology Paper 2, from cellular processes to ecosystem dynamics, giving you a concise yet comprehensive revision resource.

Mastering the interconnected systems of the human body, genetics, and ecosystems—and understanding how they are regulated—provides the foundation needed to excel in GCSE Biology Paper 2.

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Full Transcript YouTube

Let's see how quickly we can cover
everything you need to know for GCSE
biology paper 2. This is good for higher
and foundation tier double combined and
triple separate science. I'll tell you
when some of the bigger concepts are for
triple but not what's for higher in
foundation as there's not a lot of
difference honestly. And don't forget to
check out the science shorts app to help
you test your knowledge. Let's go.
Homeostasis is the term given to an
organism's ability to regulate internal
conditions even when external conditions
change. This is important so crucial
chemical reactions involving enzymes can
happen at an optimum rate. Amongst other
things, our bodies work hard to regulate
blood glucose concentration,
temperature, and water levels. One way
that our body achieves this is with our
nervous system. It consists of the CNS,
the central nervous system, which
includes the brain and spinal cord, and
the PNS, the peripheral nervous system,
the nerves that go through the rest of
the body. A receptor, for example, in
your skin detects a change due to a
stimulus, like a hot hob. An electrical
signal travels to the spine through
sensory and relay neurons, that's nerve
cells. The signal travels across the gap
between these neurons called the sinapse
by a neurotransmitter chemical. Once at
the spine, the signal can go to the
brain where you can make the conscious
decision to act. The signal then goes
back to an aector like the muscle in
your arm via relay and motor neurons so
that you move your arm. A reflex is when
the signal bypasses the brain and goes
straight through the spine to the
aector. This is a reflex arc. This of
course is much faster than you making a
conscious decision. Glands can also
beectors which produce specific
chemicals your body needs. For example,
your salivory glands in your mouth make
saliva when you eat food. You can
investigate reaction times by holding
the bottom of a ruler between a person's
finger and thumb and dropping it without
warning. Then you can measure the
distance it falls before they catch it.
Do this multiple times and take the mean
average. Not too many times though, as
their nervous systems will start to get
a bit better at reacting to this. You
can introduce an independent variable
like a stimulant for example coffee or a
sugary drink or a depressant which will
have the opposite effect although I
can't really think of anybody illegal
for you guys at the minute. Then you can
see how they decrease or increase
reaction time respectively. You could
calculate the reaction time from the
distance using s=/80 squ but you'll
never be expected to do that in a paper
but it is something you could mention if
you were asked a six marker on this
maybe. These are the parts of the brain
you need to know. The cerebral cortex is
responsible for higher level functions
like memory, speech, and problem
solving. The cerebellum is responsible
for your motor skills, movement,
balance, and coordination. The medulla
controls unconscious actions your body
takes. You don't think about them like a
heartbeating or breathing. It's also
what controls the release of adrenaline.
MRI scans, that's magnetic resonance
imaging, are a way of seeing the
activity in your brain safely. If
something goes wrong with your brain,
though, it can be very difficult to
treat without damaging important parts
of it. Your eyes are the most genius
cameras ever made. Accommodation is the
term given to the eyes ability to change
the shape of the lens in order to focus
light that comes from objects that are
different distances away on the retina.
To focus light that comes from objects
far away, the siliary muscles relax and
the suspensory ligaments tighten.
They're both connected to the lens. This
results in the lens becoming thinner and
that means the light is only refracted a
little bit and that focuses the light on
the retina. To focus on near objects,
the opposite is true. The siliary
muscles contract, the suspensory
ligaments slacken and the lens becomes
fatter or thicker. That means it becomes
more powerful. So light is refracted
more which means that the light coming
from the object still converges. That
means meets focuses on the retina. So
you see a clear image. The pupil, the
hole in the iris, can change size
depending on the light intensity hitting
the eye. The cornea is the transparent
outer layer where light enters the eye.
It has a slight lensing effect itself,
while the white surface that covers the
rest of the eye is called the scara. The
light is focused on the retina at the
back of the eye, which consists of cells
that respond to light. Some of these
cells only detect light intensity, not
color. These are called rods. While
there are three different types of cones
which detect green, blue or red
wavelengths of light, a mix of which
will produce the colors we then perceive
when the signal reaches our brain via
the optic nerve. Myopia is the medical
term for short-sightedness. You can't
focus on far objects. Hyperopia is
long-sightedness, the opposite. Glasses
or contact lenses are usually used to
mitigate this by slightly converging or
diverging the light before it enters the
eye. Laser eye surgery changes the shape
of the cornea to achieve the same
effect. Thermore regulation is your body
controlling its internal temperature by
the brain sensing blood temperature,
then sending nervous and hormonal
signals to various aectors around your
body in order that your body loses heat
to its surroundings more slowly or
quickly. For example, if you're too hot,
sweat glands in your skin cause water to
cover the surface. It evaporates, taking
heat away from your body quickly. Blood
vessels also dilate, widen to increase
blood flow to the skin to increase the
rate of heat loss. We call this vaso
dilation. If you're too cold, we have
vasoc constriction instead, hence you go
pale. You also shiver which causes your
muscles to produce more heat. The
endocrine system is a system of glands
that produce or secrete hormones that
travel to affect us via the blood. This
is of course slower than any signal
carried by the nervous system. The
pituitary gland in your brain can be
considered the main or master gland as
it produces hormones in response to
stimuli that travel to other glands in
your body in order to make them start
producing certain chemicals. Examples
are the pancreas which produces insulin,
the thyroid which controls all sorts of
things like growth and heart muscle and
digestive function and more. the adrenal
glands which produce adrenaline and the
ovaries or testes which release eggs or
sperm depending on which you have.
Speaking of the pancreas, then it's
involved in making sure your blood
glucose levels aren't too high or low.
If they're too high, the pancreas
secretes insulin, which causes glucose
to move from the blood into your cells
to be used for respiration. Any excess
glucose can be converted into glycogen
to store energy, and that's done by the
liver. If these levels are too low, on
the other hand, the pancreas produces
another hormone called glucagon, which
causes the liver and muscles to turn
glycogen back into glucose, ready to be
used. Type 1 diabetes is what you have
when your pancreas can't produce enough
insulin, and you have to take insulin
injections to do the job instead. Type
two is when your cells no longer absorb
the glucose as they should. So, you have
to be careful with your diet. And if
you're overweight or obese, you have a
much higher risk of developing this.
Your body loses water when you exhale,
sweat or urinate. If your body has too
much water, let's say for example, you
drink too much, your kidneys remove it
from your blood at a faster rate where
it's mixed with ura to become urine. URA
contains ammonia which is produced from
excess proteins broken down into amino
acids by the liver. Kidneys do a good
job of keeping the water balance just
right. They also filter your blood to
reabsorb useful substances like glucose
and some ions. A bit more detail about
how they work then. Antidiuretic hormone
or ADH is produced in the pituitary
gland which travels to the kidneys and
causes the tubules in your kidney to
reabsorb more water into the
bloodstream. So less then goes to the
bladder. If the water level is too high,
less ADH is produced. So the kidneys
cause more water to be lost in urine. In
both cases, the water level returns to
normal. So this is an example of
negative feedback. Negative feedback
might sound like it's a bad thing, but
all it means is that the body responds
in such a way as to return things to
normal. If your kidneys aren't working
properly, dialysis is required.
Essentially, your blood is sent through
a machine that does the same job as your
kidneys. If this doesn't happen, the
buildup of ura can poison you.
Menstruation occurs in females after
puberty. First, FSH made by the
pituitary gland causes an egg to mature
in the ovary. This also causes the
ovaries to produce estrogen which causes
the uterus lining to thicken. It also
inhibits or stops the production of FSH
so no more eggs mature in that cycle.
Very clever. Estrogen also causes the
pituitary gland to produce LH
luteinizing hormone which causes the egg
to be released and it starts to travel
towards the uterus via the ovduct over
several days. Finally, progesterone is
also produced by the ovaries which
maintains the uterus lining. This is
great news if you're looking to get
pregnant. If not, you need to find some
way of stopping a sperm cell from
meeting an egg cell. Contraception
options include pills that inhibit FSH
production so no eggs mature,
progesterone injections that stop any
eggs from being released, or you can
just have an implant that slowly
releases this over months or years if
needed. Condoms for men and diaphragms
for women are simple barriers to stop
sperm from reaching an egg. An IUD, an
intrauterine device like a copper coil,
prevents a fertilized egg from
implanting in the lining. You could
quite simply just avoid sex for some
time after the egg has been released, as
that's when it travels slowly down the
ovduct where a sperm can meet it.
Clamping the ovducts, sometimes referred
to as having your tubes tied or cutting
the sperm duct. Either of these will
obviously stop the cells from meeting.
Some couples, however, would love to
have children but can't due to
infertility. Sometimes it's something
fairly simple like not enough FSH or LH
produced which injections can fix. The
most expensive solution to bigger issues
is IVF in vitro fertilization. Eggs are
harvested from the woman after inducing
their release and will then be
fertilized in the lab with the
prospective father's sperm. Any embryos
that develop are inserted back into the
uterus where they will hopefully embed
in the lining and grow normally. The
success rate sadly is very low, but
there's also the risk that there could
be more than one baby born, which might
not be desirable.
Adrenaline is the hormone that increases
heart and breathing rate in stressful
situations to prepare the body for fight
or flight. Thyroxine is secreted by the
thyroid. This controls metabolic rate.
Plants also have their own hormones
which we can utilize when growing them.
Gibberelins cause seed germination to
occur which we can add to seeds to give
them a wakeup call. It also promotes
flowering and increases the size of
fruits. Ethine induces ripening of
fruits. Orxins control chute and root
growth. It's destroyed by sunlight, so
it gathers on the shaded side of a
chute, causing an unequal distribution,
causing more growth and elongation of
cells on the shaded sides, so the chute
bends toward the sun or light source.
This is what we call photo tropism. In
roots, however, orxins inhibit growth.
The hormone gathers on the bottom of a
root. That means the top side grows more
quickly causing the root to grow
downwards. This is called geotropism. We
can also use oxins as weed killers,
rooting powders and for promoting growth
in tissue cultures. We can do a mini
investigation. We can put some seeds on
damp cotton wool in a petri dish for
example. Stand the petri dish on its
side, leave it for a few days, then turn
it 90° and you should see that the roots
have bent in that time demonstrating
geotropism in roots. In order to
reproduce sexually, gametes, that's sex
cells, must be made. This happens by
meiosis, for example, in the testes to
make sperm. Chromosomes in a diploid
cell, that is 23 pairs for humans, are
copied. Similar chromosomes then pair up
and genes are swapped between them. The
cell then divides to make two diploid
cells, which then divide again along
with the chromosomes themselves to make
four hloid cells, ready to fuse with
another gamet. This is one way that
variation occurs in offspring. By the
way, the resulting diploid cell then
starts to divide via mitosis. Plants can
also reproduce asexually. As this
doesn't involve gametes, the daughter
cells will be genetically identical. So,
a clone of the parent is made by
mitosis. An advantage of sexual
reproduction, of course, is that
variation occurs, which can result in
organisms becoming better suited to
their environment, so they're more
likely to survive. However, an advantage
for asexual reproduction is that only
one parent is needed. Though for
example, if a plant is on its lonesome,
it can still reproduce in order for the
species to survive. Examples of other
organisms that can do both are the
parasite that causes malaria and some
fungi.
Genome is the term given to all the
genetic material in an organism. This
code is stored in DNA, of course, which
is a two stranded polymer in a double
helix shape. A gene is a section of DNA
that codes for a specific protein. The
human genome project completed its
initial goal in 2003 when scientists
mapped out what every gene is
responsible for coding. This is powerful
because it can help us identify what
genes cause diseases or inherited
disorders. Genotype is the term given to
what specific code is stored in an
organism. While phenotype is how that
code is expressed in your
characteristics, what proteins are made
and that affects your physiology. The
monomers between two strands of DNA are
called nucleotides. And they're made
from a sugar and phosphate group. There
are four types, A, T, C, and G. You
don't need to know what the names are,
but A and T always go together in the
sequence, as do C and G. Every three of
these bases, as we call them, are a code
for an amino acid. The sequence is
copied by mRNA. This copy is then taken
out of the nucleus to a ribosome in the
cell where amino acids are connected in
the order needed which makes a protein
the shape of which affects its function.
They also need to be folded into the
right shape as well. Harmful mutations
can change a gene so much that it
results in a protein being synthesized
that doesn't do the job it's supposed
to. We now know that some DNA, however,
doesn't directly code for proteins but
influences how other genes are
expressed. This is the realm of
epigenetics and it's completely changing
the way that we view DNA.
Some characteristics are controlled by
just one gene like color blindness.
These different types of the same gene
are called alals. Usually
characteristics are dependent on two or
more genes and how they interact. But
keeping things simple, dominant alals
are those that result in a
characteristic being expressed even if
there's another alil present, a
recessive alil. We say if you have the
alals big B little B for eye color, big
B being brown, little B being blue, you
will have brown eyes. It's only when
there's no dominant alil in this case
that the recessive alil is expressed. So
me having blue eyes, I must have the
gene little B little B. Big B, big B or
little B, little B are homozygous genes
as they only have one type of alil.
Whereas big B, little B is what we call
hetererozygous. We can use a petit
square to predict the probability of a
certain phenotype. My parents have brown
eyes, but they both have hetererozygous
alals for eye color. There are three
different outcomes of these combining
with a 25% chance of making me. That's
little B, little B. So, I'm not so much
one in a million, more one in four. Eye
color is by the by, but some alals can
result in disorders being inherited. For
example, polactylene, extra fingers or
toes, is caused by a dominant alil,
while cystic fibrosis is caused by a
recessive alil. Even if two parents
don't have cystic fibrosis, they could
still be carrying the recessive alil.
So, their child could have the disorder.
Human DNA contains 23 pairs of
chromosomes, but only one pair of these
determines sex. If you have XX
chromosomes, you're female. If you have
XY chromosomes, you're male. The
expression of these genes affects every
cell in your body, every aspect of your
physiology. We can also make a punit
square to show this. As you can see,
there's a 50/50 chance of a child being
male or female. Variation is a result of
the genes inherited from an organism's
parents and also environmental factors.
Charles Darwin's theory of evolution
claims that random variation in
offspring will result in some being
better suited to their environment than
others and so are more likely to survive
and reproduce. Jean Baptiste Lamar,
however, asserted that adaptation and
variation is guided by DNA in response
to a changing environment. This was
scoffed at for a long time, but we now
know there's some truth to this thanks
to the discoveries made in epigenetics.
Like we mentioned, bacterial resistance
to antibiotics is largely considered to
be evidence of Darwinian evolution.
Bacteria divide, mutations occur, and
inevitably a bacterium with an increased
resistance will be produced. That's why
we only want to use antibiotics when
absolutely necessary. It also means you
have to complete the whole course of
antibiotics. If you don't, weaker
bacteria will be killed off, but more
resistant ones will still be there, and
then they're able to reproduce and make
you even more ill. If organisms are able
to produce fertile offspring, we say
they're of the same species. Tigers and
lions have been known to make liger
offspring, but as they're infertile, we
don't consider tigers and lions to be of
the same species. We can selectively
breed living things with desired
characteristics to enhance these. For
example, breeding dogs to produce breeds
like Labradors, collies, and if you're
into undesirable characteristics, bugs,
too. Advancements in biology mean that
we can also genetically modify organisms
if we don't want to wait for selective
breeding to do the job or when we can't
actually achieve what we want to with it
for good or ill. For example, scientists
have genetically modified bacteria to
produce insulin, which can be harvested
and used to treat people with diabetes.
Genetically modifying crops is a way of
boosting their yields or nutritional
value. For example, golden rice has a
gene inserted into it that produces
vitamin A. It was developed to combat
diets in certain areas that were lacking
in this vitamin. Other GM crops have
been modified to be more resistant to
diseases, for example. Process of
genetic engineering goes as follows. A
gene is chemically cut from the organism
that has the desired characteristic.
This is done using enzymes, for example,
the gene from a jellyfish that causes it
to glow in the dark. This is then
inserted into a vector like a bacterial
plasmid or virus that in turn inserts
the gene into another organism, say a
bunny rabbit. But this must be done in
the very early stages of its
development. Say just after the egg has
been fertilized, as this is the only way
that you can be sure that the gene will
be present in every cell of the bunny as
it grows. By the way, I didn't make up
this example. This has actually been
done. Fossils are the remains of
organisms that died a very long time
ago. The classic fossils we think about
are the bones that we dig up, but
they're not strictly speaking bones
anymore. In fact, minerals have replaced
the organic material to effectively
leave rocks in the shape of the bones.
Sometimes there can still be organic
tissue left behind if the conditions for
decay are not present. Footprints left
in mud that have hardened over time, for
example, are also considered fossils, as
well as any other trace of an organism.
It doesn't have to be the organism
itself. Making exact copies of plants is
easy. Just take cutings off a plant,
plop them in the ground, and that does
the job. You can also go the slightly
harder route by cloning from a tissue
culture. This can be helpful for
preserving some species from going
extinct. Cloning animals is more
difficult, however. One way is splitting
embryo cells up just after
fertilization, then putting them into
surrogate mothers. Essentially, you're
forcing identical twins. But you don't
know exactly what you're getting until
they're developed. If you have a fully
grown animal that you want to clone,
take the nucleus from one of its cells,
say in its skin, then insert that into
another egg cell. It's essentially now a
fertilized egg. Shocking. The egg jump
starts the development process and it
starts to divide. It's then inserted
into another female's womb where it
continues to develop. Carl Lanaeus
classified organisms into kingdom,
filmm, class, order, family, genus, and
species. A good pneummonic for this is
King Phillip came over for good soup.
The binomial or Latin name for an
organism is just the genus and its
species combined. As time went on, it
turned out that another level above
kingdom was needed. Domain the three
domains are archa that's primitive
bacteria, true bacteria and ukarot.
That's everything else of course with
DNA and a nucleus in the cells. Ara by
the way are often found in extreme
environments on the earth. They can
therefore be called extreophiles.
Organisms generally compete for food,
water, space and other things like CO2
and light for plants, shelter and mates
for animals. Interdependence is the term
given to the fact that organisms can
rely on each other for these things and
they can form a community. Abiotic
factors in an ecosystem are the
non-living aspects. For example, light,
temperature, moisture, soil pH, CO2, and
O2 levels in the air. Biotic factors are
due to organisms and things like food
that's available, predators, prey, other
organisms around, pathogens, breathing
behavior, and more. We can use a quadrat
to estimate the size of a population of
an organism in an area by sampling say
around 10% of the area taking a mean and
then multiplying up for the whole area.
Using a quadrat with a transct allows us
to observe how population distribution
or density changes over a distance. A
food chain shows the direction that
biomass and therefore energy flows in an
ecosystem from one trophic level to
another. Producers are any organisms
that use sunlight to produce biomass.
That's usually plants or algae. Primary
consumers eat the producers. That's
herbivores that only eat plants or
omnivores that eat both meat and plants.
Then predators known as secondary
consumers, that could be carnivores or
omnivores, prey on these. And then we
can have tertiary consumers as well.
Apex predators, they're at the top of
the food chain. They have no natural
predator above them. Population numbers
of all of these will fluctuate in an
ecosystem over time. By the way, this
food chain is possible. I looked it up.
Bears have been known to eat foxes. All
life is carbon based, which means that
when organisms die, the carbon is
recycled, which ultimately can be then
used to make more organisms. One way, of
course, is when CO2 is produced, which
plants then use to grow. Bacteria also
release CO2 due to respiration when an
organism underos decomposition.
Temperature and other factors can affect
rate of decomposition. Water also
follows a cycle. Rain falls,
precipitation, then runs into rivers,
then into the sea, then it's evaporated,
and the cycle continues. Farmers utilize
decomposition to produce natural
fertilizers that can then be used on
crops. Can also be used to produce
methane gas to be used as fuel. Biod
diversity is one of those buzzwords
that's very much in vogue at the minute.
Basically, it just means how many
different types of organisms you have in
an ecosystem. High biod diversity
generally makes for a stable ecosystem
as organisms don't have to depend on one
species for a resource. For example,
human development usually results in
lower biod diversity. Such development
also poses problems when it comes to
waste. We're having to find more ways of
disposing sewage, fertilizers, toxic
chemicals, atmospheric pollution, and
more to reduce our impact on the
environment. One factor is the land that
we need for building, quarrying,
farming, and disposing of waste. An
example of this is the destruction of
pete bogs to make compost which affects
the habitat of many organisms and
microorganisms. Burning pete also
releases CO2. Deforestation, bad on a
big scale, flattening forests reduces
biod diversity and it's often done to
create farmland. A pyramid of biomass is
a way of viewing a food chain which
shows us how much mass enters the next
trophic level relatively. You need to be
able to draw one on graph paper using
numbers supplied in the question and
also calculate the percentage absorbed
by the next level. As per usual, any
percentage is equal to the bit divided
by the lot times 100. Of course, it's
always a pyramid and that shows us that
biomass is lost at each level. As not
all biomass is absorbed or consumed into
the next organism. Some is lost due to
the organisms living for some time
before being eaten by a predator, for
example. They have to move, they have to
excrete. It's also lost as water, ura,
and CO2. Food security is a big thing at
the minute, especially in these
uncertain days. Food is becoming scarcer
due to increasing world population,
changing diets, food being transported
around the world, which requires huge
amounts of energy, changing growing
environments, the cost of farming,
that's a big one in the minute, and
conflicts. For example, around 40% of
the world's wheat comes from Ukraine, or
at least it used to. Farmers are
constantly trying to find more efficient
ways of farming, largely by maximizing
biomass input to crops and animals while
also reducing biomass lost by them.
Fishing sustainably is also a big thing.
If a species is fished at a greater rate
than its breeding, then its population
can disappear in those areas. One way of
sustainably fishing is by having nets
with holes that catch adult fish, but
are big enough to let the little ones
out. These escape to then go on and
breed. So, I hope you found that
helpful. Leave a like and a comment if
you did and click on the card to take
you to the playlist for all of the
papers. And don't forget to check out
the quiz shorts app to help you test
your knowledge. And I'll see you next
time.