All of AQA BIOLOGY Paper 2 in 25 minutes - GCSE Science Revision

Summary

This video script offers a rapid overview of AQA Biology Paper 2, covering topics 5 to 7 including homeostasis, response, inheritance, variation, evolution, and ecology. It explains the body's regulatory mechanisms, nervous system functions, and hormone roles, while also delving into eye function, thermoregulation, and reproductive processes. The script touches on genetics, meiosis, and DNA's role in evolution and adaptation. It concludes with ecology, discussing ecosystems, biodiversity, and environmental impact, providing a comprehensive review for exam preparation.

Takeaways

• 🌡️ Homeostasis is the process by which organisms maintain internal balance despite external changes, crucial for optimal enzyme activity and chemical reactions.
• 🧠 The nervous system, including the CNS and PNS, plays a key role in detecting changes and initiating responses, with reflexes providing rapid, subconscious reactions.
• 🔬 Hormones, produced by the endocrine system, are chemicals that regulate various body functions through slower signals via the bloodstream compared to the nervous system.
• 👀 The eye's structure allows for accommodation, adjusting the lens to focus light on the retina, and different cells in the retina respond to light, enabling vision.
• 🌡️ Thermoregulation involves the body's mechanisms to control internal temperature, such as sweating and shivering, to maintain a stable environment for bodily functions.
• 🚰 Kidneys maintain water and nitrogen balance in the body, filtering blood and regulating water levels, with antidiuretic hormone (ADH) influencing water reabsorption.
• 🌱 Plant hormones, like gibberellins and ethylene, influence growth, germination, and fruit ripening, and can be utilized in agriculture for various purposes.
• 🔬 Inheritance involves the creation of gametes through meiosis, introducing variation in offspring, which can be beneficial for survival and adaptation.
• 🧬 The human genome project mapped out genes in the DNA, which is crucial for understanding genetic diseases and inherited disorders.
• 🧬 Epigenetics shows that DNA can respond to the environment, influencing gene expression without changing the DNA sequence itself.
• 🌿 Ecology examines the interactions among organisms within an ecosystem, considering both biotic and abiotic factors, and the importance of biodiversity for ecosystem stability.

Q & A

What is the main concept of homeostasis in biology?

Homeostasis is the process by which an organism maintains a constant internal environment despite changes in external conditions, allowing optimal rates for crucial chemical reactions, such as those involving enzymes.

How does the nervous system contribute to homeostasis?

The nervous system, consisting of the central nervous system (CNS) and the peripheral nervous system (PNS), helps regulate internal conditions by sending electrical signals in response to stimuli, which can trigger actions like moving away from a hot surface to maintain body temperature.

What is a reflex arc and how does it differ from a conscious decision?

A reflex arc is a neural pathway that allows for a rapid, automatic response to a stimulus without the involvement of the brain. This is different from a conscious decision, which involves the brain processing the signal and making a deliberate choice before acting.

Can you explain the role of hormones in the endocrine system?

Hormones are chemical messengers produced by glands in the endocrine system. They travel through the bloodstream to various effectors in the body, influencing functions such as growth, metabolism, and the body's response to stress.

How does the body regulate blood glucose levels?

The body regulates blood glucose levels through the actions of insulin and glucagon, hormones produced by the pancreas. Insulin promotes the uptake of glucose into cells, while glucagon stimulates the conversion of glycogen into glucose when levels are too low.

What is the significance of the different parts of the brain in terms of function?

The cerebral cortex is responsible for higher-level functions like memory and problem-solving. The cerebellum controls motor skills and coordination. The medulla oblongata manages unconscious actions such as heart rate and breathing, and it also controls the release of adrenaline.

How does the eye accommodate to different distances?

The eye accommodates to different distances by changing the shape of the lens, controlled by the ciliary muscles and the suspensory ligaments. For distant objects, the muscles relax, making the lens thinner and less refractive, while for close objects, the muscles contract, making the lens thicker and more refractive.

What is the process of meiosis, and why is it important for sexual reproduction?

Meiosis is a type of cell division that results in four haploid cells, each with half the number of chromosomes of the original cell. It is crucial for sexual reproduction because it produces genetic variation in offspring, which can lead to traits that are better suited to the environment.

Can you describe the role of the pituitary gland in the endocrine system?

The pituitary gland is often referred to as the 'master gland' because it produces hormones that regulate other glands in the endocrine system. It responds to various stimuli and releases hormones that trigger other glands to produce specific chemicals, such as insulin from the pancreas or thyroxin from the thyroid.

What is the difference between type 1 and type 2 diabetes?

Type 1 diabetes occurs when the pancreas cannot produce enough insulin, often requiring insulin injections for management. Type 2 diabetes is a condition where the body's cells become resistant to insulin, often requiring dietary changes and, in some cases, medication to help manage blood glucose levels.

How does the concept of negative feedback relate to homeostasis?

Negative feedback is a biological process that helps maintain homeostasis by counteracting changes and bringing conditions back to normal. For example, if body temperature rises, the body responds by sweating and vasodilation to dissipate heat and restore the normal temperature.

Outlines

00:00

🔬 Homeostasis and Nervous System

The first paragraph introduces the concept of homeostasis, which is an organism's ability to maintain internal balance despite external changes. It discusses the role of the nervous system, including the central nervous system (CNS) and peripheral nervous system (PNS), in regulating conditions like blood glucose, temperature, and water levels. The paragraph explains the process of sensory input, signal transmission through synapses, and reflex actions. It also covers the impact of stimulants and depressants on reaction times and the structure and function of the human eye, including accommodation and the roles of different cells in vision. Additionally, it touches on thermoregulation, the importance of the brain's parts, and the use of MRI scans for brain imaging.

05:01

🌡 Endocrine System and Thermoregulation

This paragraph delves into the endocrine system, highlighting its role in hormone production and the influence of hormones on the body's functions. It explains how the pituitary gland acts as the 'master gland' and discusses the functions of other glands like the pancreas, thyroid, adrenal glands, and reproductive organs. The paragraph also covers the regulation of blood glucose levels through insulin and glucagon, the conditions of type 1 and type 2 diabetes, and the importance of water and nitrogen balance. It further explains the kidney's role in maintaining water balance through the production of urine and the function of antidiuretic hormone (ADH).

10:03

🌱 Hormones and Plant Growth

The third paragraph focuses on the hormonal responses in plants, including the effects of gibberellins, ethylene, and auxins on seed germination, fruit ripening, and plant growth direction. It describes how these hormones can be used in agriculture and as weed killers, and how they influence plant growth through processes like phototropism and geotropism. The paragraph also suggests a mini-investigation using a Petri dish to demonstrate geotropism and concludes with an introduction to the topic of inheritance, variation, and evolution.

15:04

🧬 Inheritance, DNA, and Genetic Variation

This section explores the principles of inheritance, starting with the process of meiosis in creating gametes and the role of genes in producing variation in offspring. It explains the concepts of genotype and phenotype, the structure of DNA, and the process of transcription and translation. The paragraph discusses the significance of nuclear bases and how they code for amino acids to form proteins. It also touches on harmful mutations, epigenetics, and how characteristics can be controlled by single or multiple genes, including the use of Punnett squares to predict genetic outcomes.

20:05

🐯 Evolution, Species, and Genetic Modification

The fifth paragraph examines Charles Darwin's theory of evolution and how random variation can lead to better adaptation and survival. It discusses Lamarck's theory and its relation to epigenetics, the concept of species and reproductive compatibility, and the use of selective breeding and genetic modification in producing desired traits in organisms. It also covers the process of genetic engineering, the importance of biodiversity for a stable ecosystem, and the impact of human activities on the environment and biodiversity.

25:06

🌿 Ecology, Biomass, and Environmental Impact

The final paragraph discusses the field of ecology, which studies the interactions among organisms within an ecosystem. It covers the concepts of competition, interdependence, and the roles of abiotic and biotic factors. The paragraph explains the use of quadrats and transects for population studies, the structure of food chains and trophic levels, and the importance of biomass and energy flow. It also addresses issues like deforestation, biodiversity loss, and the environmental impact of human activities, including waste management and greenhouse gas emissions. The paragraph concludes with a discussion on food security, sustainable fishing practices, and the challenges faced by modern agriculture.

Keywords

💡Homeostasis

Homeostasis is the process by which an organism maintains a constant internal environment despite changes in external conditions. It's crucial for ensuring that chemical reactions, such as those involving enzymes, occur at optimal rates. In the video, homeostasis is mentioned in relation to the body's efforts to regulate blood glucose concentration, temperature, and water levels, highlighting its importance in maintaining life processes.

💡Nervous System

The nervous system is a complex network that includes the central nervous system (CNS), which comprises the brain and spinal cord, and the peripheral nervous system (PNS), which consists of nerves throughout the body. It plays a vital role in homeostasis by detecting changes and responding to them through a series of neurons, as illustrated in the script when discussing the reflex arc and the response to a hot hob.

💡Receptor

A receptor, in the context of the video, is a structure in an organism that detects changes due to a stimulus. For example, skin receptors can detect heat, triggering a response like moving away from a hot surface. Receptors are integral to the body's ability to sense and react to its environment, which is a key aspect of maintaining homeostasis.

💡Neurotransmitter

Neurotransmitters are chemical messengers that transmit signals across a synapse, the gap between neurons. They are essential for communication within the nervous system. The script mentions neurotransmitters in the context of the signal transmission process from sensory neurons to the spine and then to the brain or effectors.

💡Hormones

Hormones are chemical messengers produced by glands in the endocrine system. They travel through the bloodstream and influence various physiological processes, including growth, metabolism, and reproduction. The video discusses hormones such as insulin, glucagon, and adrenaline, emphasizing their role in regulating body functions.

💡Thermoregulation

Thermoregulation is the body's ability to maintain a stable internal temperature despite external conditions. The script explains how the body achieves this through mechanisms like sweating, vasodilation, and shivering, which are all aimed at either losing or conserving heat.

💡Meiosis

Meiosis is a type of cell division that results in the formation of gametes, which are the sex cells—sperm and eggs in animals. It involves two rounds of division to produce cells with half the number of chromosomes, allowing for genetic variation in offspring. The video script describes meiosis in the context of sexual reproduction and its role in creating genetic diversity.

💡Genotype and Phenotype

Genotype refers to the genetic makeup of an organism, specifically the sequence of nucleotides in its DNA, while phenotype refers to the observable characteristics of an organism, such as its physical traits and behaviors. The video script explains how genotype and phenotype are related and how they influence each other, using eye color as an example.

💡Dominant and Recessive Alleles

Dominant and recessive alleles are versions of a gene that determine the expression of a particular trait. A dominant allele will mask the effect of a recessive allele when both are present. The script uses eye color as an example to illustrate how dominant (Big B) and recessive (little b) alleles interact to determine an individual's phenotype.

💡Evolution

Evolution is the process by which species of organisms change over time through genetic variation and natural selection. The script references Charles Darwin's theory of evolution, which posits that random variations in offspring can lead to traits that are better suited to the environment, thus increasing the likelihood of survival and reproduction.

💡Genetic Modification

Genetic modification is a technique used to alter the genetic makeup of an organism by adding, deleting, or changing genes. The video mentions genetically modified organisms (GMOs) such as bacteria engineered to produce insulin and crops like golden rice, which is fortified with vitamin A, demonstrating applications of genetic modification in medicine and agriculture.

💡Ecology

Ecology is the study of the relationships between organisms and their environment, including both biotic (living) and abiotic (non-living) factors. The script discusses various ecological concepts such as food chains, biodiversity, and the impact of human activities on ecosystems, emphasizing the importance of understanding these interactions for environmental conservation.

💡Food Chain and Trophic Levels

A food chain illustrates the sequence of organisms through which nutrients and energy pass as one organism eats another. Trophic levels are the positions that organisms occupy in a food chain. The video script explains how energy and biomass are transferred between these levels, from producers like plants to primary consumers, and up to apex predators.

💡Biodiversity

Biodiversity refers to the variety of life in an ecosystem, including the number of different species and their genetic diversity. The script mentions that high biodiversity contributes to a stable ecosystem and discusses the negative impacts of human development on biodiversity, such as habitat destruction and pollution.

💡Genetic Engineering

Genetic engineering is a precise method of genetic modification where specific genes are inserted, removed, or altered in an organism's DNA. The video script describes the process of genetic engineering, from the isolation of a gene to its insertion into a vector and subsequent incorporation into another organism, highlighting its potential applications and ethical considerations.

💡Cloning

Cloning is the process of creating a genetically identical copy of an organism. The video script differentiates between plant cloning, which can be done through simple techniques like taking cuttings, and animal cloning, which is more complex and involves techniques such as splitting embryo cells or transferring a nucleus from a somatic cell into an egg cell.

Highlights

Homeostasis is an organism's ability to regulate internal conditions despite external changes, essential for optimal enzyme activity.

The nervous system, including the CNS and PNS, plays a crucial role in detecting changes and responding to maintain homeostasis.

Reflexes are faster responses that bypass the brain and are mediated by the spinal cord.

Glands can act as effectors, producing chemicals needed by the body in various situations, such as saliva production.

Reaction times can be investigated by measuring the distance a ruler falls before being caught, potentially affected by stimulants or depressants.

The brain has three main parts: the cerebral cortex for higher functions, cerebellum for motor skills, and medulla oblongata for unconscious actions.

MRI scans provide a safe way to observe brain activity, but treating brain issues can be challenging.

The eye's accommodation allows it to focus light from objects at varying distances by changing the lens shape.

Thermoregulation involves the body controlling its temperature through various mechanisms, such as sweating and shivering.

The endocrine system uses hormones to regulate various body functions, with the pituitary gland being considered the 'master gland'.

Type 1 and type 2 diabetes are conditions related to insulin production and glucose absorption, respectively.

Water and nitrogen balance are critical for the body, with kidneys playing a key role in maintaining these balances.

Reproduction involves a complex hormonal cycle in females, with menstruation marking the maturation of eggs.

Inheritance, variation, and evolution are central to understanding how traits are passed down and how species adapt over time.

Genetic modification and selective breeding are methods used to introduce desired traits in organisms, with applications in medicine and agriculture.

Ecology examines the interactions between organisms in an ecosystem, considering both biotic and abiotic factors.

Food chains and webs illustrate the flow of energy and biomass through an ecosystem, with producers, consumers, and decomposers.

Biodiversity is crucial for ecosystem stability, and human activities can have significant impacts on it.

Food security and sustainable fishing practices are important for maintaining healthy ecosystems and ensuring long-term food availability.

Transcripts

let's see how quickly we can cover

everything you need to know for AQA

biology paper 2 this video is good for

higher and Foundation Tier double

combined Trilogy and triple or separate

biology that is topics 5 to 7 that's

homeostasis and response inheritance

variation in evolution and ecology I'll

tell you when something is just for

triple but not when something's just for

higher tier because there's not much

difference to be honest we're going to

be moving hecking fast so pause the

video if you need a bit more time to get

your head around something you see let's

go homeo stasis is the term given to an

organism's ability to regulate internal

conditions even when external conditions

change this is important so that 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 for example one way

that our body achieves this is with our

nervous system it consists of the CNS

that's central nervous system that's the

brain and spinal cord and the pns

peripheral nervous system the nerves

that go through the rest of the body a

receptor for example skin detects a

change due to a stimulus like a hot hob

an electrical signal travels to the

spine through sensory and relay neurons

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 affector 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 affector this is a reflex

arc this of course is much faster than a

conscious decision glands can also be

effectors which produce specific

chemicals your body needs depending on

the situation for example your salivary

glands in your mouth making saliva when

you eat food you can investigate into

reaction Times by holding the bottom of

a ruler between a person's finger and

thumb and drop it without warning then

you measure the distance it falls before

they catch it do this multiple times and

take 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 think of any ones that

are legal for you at the minute to see

how they decrease or increase Reaction

Time respectively you could calculate

the reaction time from the distance

using suat S equal half 80 squ but

you'll never be expected to do that in

this paper but it's something you could

mention if you were asked a six mark on

this quite a bit that's just for triple

biology now that's the brain eye and

Thermo regulation skip to hormones if

you're doing combined Trilogy that is

double science there are three 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 onata

controls unconscious actions your body

takes you don't think about them like

your heart and breathing rates it's also

what controls the release of adrenaline

MRI scans 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 or impossible to treat without

damaging important parts of it your eyes

are the most mind-bogglingly designed

cameras ever conceived of accommodation

is the ey's 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 that are

far away the ciliary muscles relax and

the suspensory ligaments Titan they're

both connected to the lens this results

in the lens becoming thin and that means

that 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 sary muscles

contract the suspensory ligaments

slacken and the lens becomes fatter or

thicker and so that means that it

becomes more powerful actually so light

is refracted more which means that the

light coming from the object still

converges meets focuses on the retina so

you can see a clear image the pupil 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 is

called the Scara the light is focused

then on the retina at the back of the

eye which consists of Rod and Cone

Styles which respond to light rods can

only detect light intensity so no color

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 shortsightedness you can't focus on

Far object hyperopia is long-sightedness

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 aims

to change the shape of the cornea to

achieve the same effect Thermo

regulation is your body controlling its

internal temperature by the brain

sensing blood temperature then sending

nervous and hormonal signals to various

effectors 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 this

evaporates taking heat away from your

body quickly blood vessels also dilate

widen we call this vasod dilation to

increase blood flow to the skin to

increase the rate of heat loss too cold

we have Vaso constriction instead hence

why you go pale you also shiver which

causes your muscles to produce more heat

okay back to science goodness which is

for everyone the endocrine system is a

system of glands that produce or secrete

hormones that travel to effectors 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 that they start then

producing certain chemicals examples are

the pancreas which produces insulin

we'll talk more about that in a bit the

thyroid controls all sorts of things

like growth heart muscle and digestive

function and more the adrenal glands

produce adrenaline and the ovaries in

testes release eggs or produce sperm

depending on which you have speaking of

the pancreas then it's involved in

making sure that your blood glucose

levels aren't too high or too low too

high and 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 too low on

the other hand and the pancreas produces

another hormone called glucagon which

causes the liver and muscles to turn

glycogen back into glucose ready to be

used type one 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

water and nitrogen balance are triple

only so skip to the next topic reprodu

if youj just double 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 is made from ammonia

which is produced from excess proteins

broken down into amino acids by the

liver if that wasn't the case too much

water builds up in your body and too

much water would go into your cells by

osmosis and then they' become turgid and

burst too little water however and they

become flaccid didn't stop working

kidneys do a good job of keeping the

water balance just right kidneys also

filter your blood to absorb useful

substances like glucose and some ions

bit more detail about how the kidneys

work then antidiuretic hormone or ADH is

produced in the pituitary gland which

travels to the kidneys and it causes the

tubules in the kidney to reabsorb more

water into the bloodstream so less then

go to the bladder 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 we call this negative feedback

the term negative feedback might sound

like it's bad 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 will poison you okay

reproduction is for everybody well you

know what I mean menstruation occurs in

females after puberty eggs start to

mature first FSH that's follicle

stimulating hormone made by the

pituitary gland causes an egg to mature

in the ovary this also causes the

ovaries to produce estrogen which causes

the uterous lining to thicken it also

inhibits or stops the production of FSH

so that no more eggs mature in that

cycle very clever it also causes the

pituitary gland to produce LH lutenizing

hormone which causes the egg to be

released and it starts to travel towards

the uterus via the UCT over several days

finally progesterone is also produced by

the 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 meeting an egg cell

contraception options include pills that

inhibit FSH production so no eggs mature

progesterone injections that stop any

eggs being released you can also 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 or 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

UCT where a sperm can meet it clamping

the UCT sometimes refer to having your

tubes tide or cutting the sperm ducts

either of these will obviously stop the

cells 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 injects 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 fertilize 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 however

is very low but there is also the risk

that there could be more than one baby

born which might not be desirable we've

already mentioned it adrenaline is the

hormone that increases heart and

breathing rate in stressful situations

to prepare the body for fight or flight

thyroxin is another hormone that's

secreted by the thyroid and it controls

metabolic rate if thyroxin levels are

too low the hypothalamus in your brain

releases a hormone called TR you don't

need to know the full name and that

causes the pituitary gland to produce

another hormone called TSH so the

thyroid releases more thyroxin this

again is an example of negative feedback

the last triple content in B5 plants

also have their own hormones which we

can utilize when growing plants

gibberellins 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

orins control chot and root growth it's

destroyed by sunlight so it gathers on

the Shaded side of a chute causing more

growth and elongation of cells on the

Shaded side so the Chute bends toward

the Sun or light source this is what we

called phototropism in however orins

inhibit growth the hormone gathers on

the bottom of a root and so that means

the top side grows more quickly causing

the root to grow downwards this is

called geotropism we can also use orins

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 for a few days

then turn 90° and you should see that

the roots have bent in that time proving

that geotropism is true for roots next

big topic B6 that's inheritance

variation and evolution in order to

reproduce sexually gametes sex cells

must be made this happens by meiosis for

example in the testes to make sperm the

chromosomes in a diploid cell that is 23

pairs for us are copied similar

chromosomes then pair up and the 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 haid

cells ready to fuse with another gamt

which in this case would be an egg this

is one way that variation occurs in

Offspring the resulting diploid cell

then starts to divide via mitosis which

is covered in paper one plants do this

with pollen and egg cells but they can

also reproduce asexually but as it

doesn't evolve gametes the daughter

cells will be genetically identical so a

clone of the parent is made by mitosis

an advantage of sexual reproduction is

that variation occurs which can result

in organisms becoming better suited to

their environment more in this in a bit

so more likely to survive an advantage

for asexual is that only one parent is

needed so for example a plant on its

Lonesome can still reproduce in order

for the species to survive another thing

that can do both is the parasite that

causes malaria as can 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 code is stored in your DNA

specifically while phenotype is how that

code is expressed in your

characteristics what proteins are made

it affects your physiology for triple

you need to know that the monomers

between the two strands are called

nuclear es and they're made from a sugar

and phosphate group of which there are

four types A T C and G you don't need to

know what the names are but a and t

always match to each other in the

sequence as do C and G every three of

these bases we can 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 His function they

need to be folded as well first 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 it influences how other

genes are expressed this is the realm of

epigenetics and it's changing the way

that we view DNA quite drastically back

to double some characteristics are

controlled by just one gene like color

blindness these different types of the

same gene are called alal

usually characteristics are dependent on

two or more genes though and them

interacting dominant alals are those

that result in a characteristic being

expressed even if there is another alil

present a recessive alil for example if

you have the Al's Big B little B for I

color Big B be brown little B be 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 be little B Big B Big B or little

B little be are called homozygous as

they only have one type of alil whereas

Big B little B is what we call

heterozygous we can use a punet square

to predict the probability of a certain

phenotype my parents have brown eyes but

they both have heterozygous Al for eye

color there are three different outcomes

of these combining with a 25% chance of

making me that's little be little be so

I'm not so much one in a million more

one in four my sister has brown eyes but

her son has blue eyes so she must be Big

B little B eye color is by the by but

some alals can result in disorders being

inherited for example polya extra

fingers or toes which is caused by a

dominant alil or cystic vibrosis which

is caused by a recessive alal even if

two parents don't have cystic fibrosis

they could still be carrying the

recessive alal so their child could have

the disorder human DNA is containing 23

pairs of chromosomes but only one pair

determines sex if you have XX

chromosomes you are female XY you're

male the expression of these genes

affects every cell in your body every

aspect of your physiology we can also

make a punet square for these 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 states 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 but like

see we know that our DNA is able to

respond to the environment in order to

turn genes on and off depending on

whether they're needed or not for

example there were some blind

translucent skin mackerel that were

found in a dark cave when they were bred

with normal mackerel in sunlight they

regained fully working eyes and opaque

skin within a few Generations John

Baptist Lamar's Theory asserted that

adaptation of variation is Guided by DNA

in response to a changing environment

this was scoffed at but we now know that

there is some truth to this thanks to

the discoveries made in epigenetics

bacterial resistance is largely

considered to be evidence of darwinian

evolution bacteria divides mutations

occur and inevitably a bacterium with an

increased resistance to antibiotics will

be produced that's why we only want to

use them when absolutely necessary it

also means you have to complete the

whole course of antibiotics if you don't

weaker bacteria will have been killed

off but more resistant ones will still

be there and then they'll 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 lier

Offspring but as they're infertile we

don't consider tigers and lions to be

the same species we can selectively

breed living things with desired

characteristics to enhance these for

example breeding dogs to produce breeds

like labador colleagues and if you're

into undesirable characteristics pugs

too advancements in biology over the

last few decades mean that we can also

genetically modify organisms if we don't

want to wait for selective breeding to

do the job or when it can't actually

achieve what we want it to 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 one 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

other GM crops have been modified to be

more resistant to diseases for example

the 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 bacteria plasmid or virus that in

turn inserts the gene into another

organism say a bunny rabbit but it must

be done in the early stage of its

development say just after the YK has

been fertilized as this is the only way

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 Rock in

exactly the same shape as the bone

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 cloning is triple only making

exact copies of plants is easy just take

cuttings off a plant put them in the

ground and that does the job you can

also go the slightly harder route by

cloning from a tissue culture that is

cloning from a small group of cells this

can be helpful for preserving some

species from going extinct cloning

animals is more difficult you can split

embryo cells up just after fertilization

than put them into surrogate mothers

essentially you're forcing identical

twins but you won't know exactly what

you're getting until they've developed

so if you have a fully grown animal that

you want to clone you take the nucleus

from one of its cells say in its skin

then insert that into another's 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 womb where it continues to

develop classification caraus classified

organisms into King om phm class order

family genus and species a good

pneumonic for this is King Philip came

over for good soup the binomial a Latin

name for an organism is just the genus

and species combined as time went on it

turned out that another level above

kingdom was needed domain the three

domains are ARA that's primitive

bacteria normal or true bacteria and

ukaria that's everything else of course

with DNA and nucleus of the cells you

should know about UK carotic cells from

paper one ARA by the way are often found

in extreme Environ on the earth they can

therefore be called

extremophiles final big topic ecology is

a study of how lots of organisms

interact in an ecosystem 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 around other organisms pathogens

breeding behavior and more we can use

quadrats to estimate the size of a

population of an organism in a certain

area by sampling around say 10% of the

area taking a mean and then multiplying

up for the whole area using a quadrat

with a transect allows us to observe how

population distribution changes over a

distance the food chain shows the

direction that biomass and therefore

energy Flows In an ecosystem from one

organism to another producers are any

organism that uses sunlight to produce

biomass that's usually plants or algae

primary consumers eat the producers

herbivores that eat only plants or

omnivores that eat both meat and plants

then Predators known as secondary

consumers that could be Carnival or

omnivores they prey on them and then we

can have tery consumers as well apex

predators are those at the top of the

food chain they have no natural predator

above them these levels are called

trophic levels by the way the 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 do eat foxes all life is carbon

based which means that when an organisms

die the carbon is recycled which

ultimately can be used to make more

organisms one way of course is when CO2

is produced which plants then used to

grow bacteria also release CO2 when an

organism undergoes decomposition water

follows a cycle rain falls then runs

into rivers into the sea then it's

evaporated and the cycle continues for

triple you need to know that farmers

utilize decomposition to produce natural

fertilizers that can then be used on

crops it can also be used to produce

methane gas to be used as fuel back to

double biodiversity is one of those Buzz

words that's very much in Vogue at the

minute basically it means how many

different types of organisms you have in

an ecosystem High biodiversity generally

makes for a stable ecosystem as

organisms don't have to depend on on one

species for a resource for example sadly

human development usually results in

lower biodiversity this development also

poses problems when it comes to waste

we're having to find more ways of

disposing of 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 Peete bogs to make

compost which affects the habitat of

many organisms and microorganisms

burning pce also releases CO2 now going

off piece for a second for your exams

you need to say that carbon dioxide and

methane contribute to global warming

personally I'm not so sure especially

seeing that carbon dioxide only accounts

for 0.04% of the atmosphere while

methane is

0.18% you decide who's telling porkys

incidentally water vapor is responsible

for 95% of the greenhouse effect but you

never hear about that do you anyway

deforestation bad on a big scale

flattening forests reduces biodiversity

and it's often done to create Farmland

the Pyramid of biomass is a food chain

that 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

percentage is equal to the bit divided

by the lot time 100 of course this shows

that biomass is lost at each level

because it's not just a rectangle as not

all biomass is absorbed or consumed into

the next organ organism some is lost due

to the organisms living for some time

before being eaten by a predator for

example it's also lost as water Ura and

CO2 food security is a big thing

especially in these uncertain days food

is becoming more scarce 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 of 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

important 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 in that catch

adult fish but are big enough to let the

little ons out if young fish aren't

caught then they go on to breed so there

we go you find it helpful leave a like

if you did click on a card and it'll

take you to the playlist for all six

papers once you've done the exam come

back here and tell us all how you did

we'd love to know good luck