AQA GCSE Biology Paper 2 ALL ANSWERS CORRECT 2024/25 EDITION GUARANTEED GRADE A+

What is homeostasis? The maintenance of a constant internal environment. What is a stimulus? A change in your environment than requires a response. e.g Light, sound, touch, pressure, pain, chemical or temperature. What do the receptors do? Detect the stimulus or change in environment. What happens after the receptors? Receptors send messages to the CNS via the sensory neurone. What makes up the central nervous system? The brain or spinal cord What is an effector? Muscles or glands that bring about a response. What do the muscles and glands do in response to stimuli? Muscles contract and glands secrete chemical substances(hormones). What is a sensory neurone? A neurone that carry information from the receptors to the CNS. What is a relay neurone? Neurones that carry impulses from the sensory neurone to the motor neurone. What is a motor neurone? Neurones that carry information from the CNS to the effectors. What is the nervous system? It is a system that allows you to react to your surroundings. How do signals travel across a synapse? The chemical or neurotransmitter diffuses across the synapse and binds to a complementary receptor on the neurone (postsynaptic). This causes an electrical impulse to travel down the next neurone. What is a synapse? A gap between two neurones. What is the thermoregulatory centre of the brain? Near the hypothalamus, monitors the temperature of blood. Describe the stages in a reflex arc. Stimulus->Receptor->sensory neurone->CNS (relay neurone) -> motor neurone -> effector -> response Name responses that reduce body temperature. Hairs lie flat, sweat and blood vessels get wider(vasodilation) What happens during vasodilation? The blood vessels supplying the skin dilate (widen). This helps to transfer energy to the environment. Name responses that increase body temperature. Hairs stand up, no sweat, shivering and blood vessels constrict(vasoconstriction) What happens during vasoconstriction? The blood vessels supplying the skin constrict to close off the skins blood supply. What is the body's core temp? 37 degrees Celsius What are hormones? Chemical messengers that travel in the blood to target organs. Compare and Contrast the endocrine (hormone) system and the nervous system. Nervous is faster acting than the endocrine system. Hormones have longer lasting effects compared to electrical impulses. Nerves act on a very specific area whereas hormones act more general. What does the thyroid gland do? Produces thyroxine which is involved in regulating metabolism. What do the adrenal glands do? Produce adrenaline which is used to prepare the body for fight or flight. What is the role of the pancreas? Produces glucagon and insulin which are involved in regulating glucose levels in the blood. Name the hormone that is released if blood sugar is too high. Insulin What does insulin do? It makes the liver convert glucose into glycogen. This causes blood glucose levels to decrease. Name the hormone that is released if blood sugar is too low. Glucagon What does glucagon do? HINT GLU-COSE-GONE It makes the liver convert glycogen to glucose. This causes the blood glucose level to increase. What is type I diabetes? When the pancreas produces little or no insulin. What is type II diabetes? When a person becomes resistant to their own insulin. Being overweight can increase your chances of type II diabetes. How can type I diabetes be treated? Insulin injections, limiting intake of foods rich is simple carbohydrates e.g. sugars and regular exercise. How can type II diabetes be treated? It can be controlled by eating a carbohydrate controlled diet and getting regular exercise. What is the role of the kidneys. Kidneys make urine by taking unwanted waste products out of your blood. They are involved in selective reabsorption. Name three things that are re-absorbed by the kidneys into the blood. Glucose, water and ions. Name three things that are removed from the body in the urine. Urea, water and ions. What is deamination? Proteins (excess amino acids) cannot be stored by the body. Excess amino acids are converted to fats and carbohydrates. This occurs in the liver. What is produced as a waste product of deamination? Ammonia is produced as a waste product. Ammonia is toxic so it is converted into urea in the liver. What hormone controls the amount of water absorbed by the kidneys? ADH What happens when the concentration of water in the blood is too low. I.e. the Blood is MORE concentrated. Receptors in the hypothalamus detects the water content is too low. The coordinator in the brain receives the information and coordinates a response. The pituitary gland produces MORE (Anti-diuretic hormone) ADH, which makes the kidney tubule MORE permeable. This means that MORE water is reabsorbed into the bloodstream. The kidneys produce a small volume of concentrated urine. What happens when the concentration of water in the blood is too high. I.e. the Blood is dilute/LESS concentrated. Receptors in the hypothalamus detects the water content is too high. The coordinator in the brain receives the information and coordinates a response. The pituitary gland produced LESS ADH, which makes the kidney tubule LESS permeable. This means that LESS water is reabsorbed into the bloodstream. The kidneys produce a large volume of dilute urine. How does a dialysis machine work? In a dialysis machine the patients blood flows between a partially permeable membrane surrounded by dialysis fluid. The dialysis fluid contains the same concentration of dissolved ions and glucose as healthy blood. This means they won't be lost from the blood during dialysis. Only wastes such as urea and excess ions and waters diffuse across the barrier. What is the purpose of the partially permeable membrane in the dialysis machine. To only allow small soluble molecules (e.g. urea, water and ions) to move into the dialysis fluid, not large molecules like proteins. What are the advantages and disadvantages of a kidney transplant over dialysis? Kidney transplants are a cure, but they can be rejected. Patients are treated with immunosuppressants. People are not always on the donor list, relatives have to agree to the donation. Transplants are cheaper than dialysis to the NHS. Long waiting lists for transplants. Patients have to spend 3-4 hours a day, 3 x a week which can have a negative impact on their quality of life. What are the four stages of the menstrual cycle? 1) Menstruation-the uterus lining breaks down 2) The uterus lining builds up again 3) Ovulation-Around day 14 a egg is released from an ovary. 4) The wall is maintained for about 14 days until day 28. If the egg has not been fertilised and implanted into the uterus lining it breaks down. What is the role of FSH (Follicle stimulating hormone) in the menstrual cycle? Made in the pituitary gland. Causes a egg to mature in one of the ovaries in a structure called a follicle. Stimulates the ovaries to produce oestrogen. What is the role of oestrogen in the menstrual cycle? Produced by the ovaries. Causes the lining of the uterus to grow. Stimulates the release of LH (which causes ovulation) and inhibits the release of FSH. What is the role of LH (Luteinising hormone) in the menstrual cycle? Produced in the pituitary gland. Stimulates the release of an egg (ovulation) at day 14. What is the role of progesterone in the menstrual cycle? Produced by the ovary by the remains of the follicle. Maintains the lining of the uterus. When the level of progesterone falls the lining of the uterus breaks down. Inhibits the release of LH and FSH. Where is testosterone produced? In the testes. How does the contraception pill work? Contains oestrogen and progesterone. Taking oestrogen every day prevents the release of an egg by inhibiting FSH. Progesterone reduces fertility by stimulating the production of thick sticky mucus at the cervix preventing the sperm getting to the egg. What are the side effects of the pill? Headaches and nausea. Still contract STIs. What is the contraceptive patch? Contains same hormones as the pill. Patch is stuck under the skin (5cm x 5cm). Each patch lasts a week. What is the contraceptive implant/injection? Implant is inserted under the skin. Releases progesterone. Can last for 3 years. Injection lasts less time 2-3 months. What is an intrauterine device? Is a T shaped device that is inserted into the uterus to kill sperm and prevent implantation of the fertilised egg. Name three barrier methods, non hormonal methods of contraception. Male and female condom, diaphragm, spermicide What is the diaphragm? A plastic cup that fits over the cervix (opening to the womb) to form a barrier. How does spermicide work? It kills or disables the sperm. Name a permanent ways to avoid pregnancy. Abstinence (not having sex), sterilisation which is having Fallopian tubes or sperm duct cut. How does IVF work to help infertile couples? FSH and LH are given to a woman to help eggs mature and release. Eggs are then collected from a woman's ovaries. The eggs are fertilised in a lab with the man's sperm. The fertilised eggs are grown into embryos in an incubator. The 1-2 embryos are then transferred to the woman's uterus to increase chance of pregancy. What are the pros and cons of IVF? PRO: Gives an infertile couple a child. CON: Multiple births, these are risky, more chance of still birth and miscarriage. CON: Success rate is low CON: Emotionally and physically stressful CON: Side effects of hormones e.g. abdominal pain What are the ethical concerns linked to IVF? IVF leads to unused embryos which are destroyed or used for medical research. (Potential life). Genetic testing could be carried out on the embryo which could lead to designed babies. What is the sclera? The tough supporting wall of the eye What is the cornea? Outer transparent layer, bends/refracts light into the eye What is the pupil? The hole in the centre where light enters What is the iris? A muscle that controls the diameter of the pupil and how much light enters. The coloured part of the eye. What is the retina? Contains receptor cells called rods and cones. These are sensitive to colour and light intensity. What is the lens? Focuses the light into the retina What is the ciliary muscles and suspensory ligaments? Control the shape of the lens What is the optic nerve? Carries impulses from the receptors on the retina to the brain Why is the iris reflex needed? To prevent light from damaging the retina. Explain the iris reflex in very bright light. In very bright light a reflex is triggered to make the pupil smaller. The CIRCULAR muscles CONTRACT and the RADIAL muscles RELAX. Explain the iris reflex in dim light. In dim light a reflex is triggered to make the pupil dilate. The CIRCULAR muscles RELAX and the RADIAL muscles CONTRACT. Define accommodation. Where the eye focuses light on the retina by changing the shape of the lens. Explain how the eye focuses on something that is near to it. The ciliary muscles contract which slacken the suspensory muscles. This causes the lens to become fat (more curved) so increases how much light is bent. Explain how the eye focuses on something that is far away. The ciliary muscles relax which causes the suspensory muscles to pull tight. This causes the lens to become thinner so refracts light by a smaller amount. What is long sightedness (hypermyopia)? How is it treated? People are unable to focus on near objects. This occurs when the lens doesn't refract the light enough or the eyeball is too short. The image is brought into focus BEHIND the retina. You can use glasses with a convex lens to treat it. What is short sightedness (myopia)? How do you treat it? People are unable to focus on FAR objects. This occurs when the lens is the wrong SHAPE and refracts the light too much. The image is brought into focus IN FRONT of the retina. You can use glasses with a concave lens to treat it. Name some of the treatments for vision defects. Contact lenses, laser eye surgery and replacement lens surgery. What is the brain made from? Millions of interconnected neurones What is the brain in charge of? It is in charge of our complex behaviours, controls and coordinates everything we do breathing, sleeping, memory etc. What is the cerebral cortex? The outer wrinkly layer of the brain, controls consciousness, memory and language What is the medulla? The base, controls unconscious activities like breathing, movement in the intestines and heartbeat What is the cerebellum? At the back, responsible for muscle contraction & balance What is the hypothalamus? controls homeostasis and pituitary gland What is the pituitary gland ? It is the master gland. It produces many hormones that regulate homeostasis e.g ADH, FSH Name some methods by which scientists study the brain. MRI, Electrical stimulation, Studying patients with damage to their brain. Evaluate the benefits and risks of procedures carried out on the brain and the nervous system. +ve- Can lead to the treatment for disorders of the nervous system -ve- The brain is complex and delicate. The treatment of brain damage is difficult. It also carries risks such as physical damage or increased problems with brain damage e.g. speech. NB: ADD A CONCLUSION. What is reaction time? The time it takes to respond to a stimulus What is reaction time affected by? Age, drugs e.g. caffeine or gender Why are computers a better way of measuring reaction time than the ruler test? Computers can give a more precise reaction time because they remove human error. Computers can record the reaction time to a millisecond so more accurate. Computers remove the possibility that a person can predict when to respond by using a persons body language. What is auxin? A growth hormone found in the roots and shoots of plants. It controls the growth of plants in response t light, gravity and water. What does phototropism mean? The movement of a plant towards light. If light is coming from one side of a plant what will happen. Auxin diffuses to the dark/shaded side of plant. This causes the cells to grow faster on that side (elongate) which causes the shoot to bend twards the light. What till happen if the tip of a shoot is removed from a plant? There will be no auxin as auxin is found in the shoot. The plant will not grow. What effect does auxin have on shoots and roots? Auxin promotes growth in shoots and inhibits growth in roots. What will happen to a shoot if it is growing sideways? Auxin moves to the lower side of the shoot and the root. This is caused by gravity. It cause the lower side of the shoot to grow faster so the shoot bends upwards towards the light. In the root the lower side grows slower meaning the root bends downwards. How can auxins be used to kill weeds? Most weeds growing in a field of crops or on a lawn are broad leaved, in contrast to grasses and cereals which are narrow leaves. Selective weedkillers have been developed using auxin to kill only broad leaf plants by disrupting their growth patterns. What does ethene do? Stimulates the ripening of fruit. What does gibberellin do? Stimulates seed germination, stem growth and flowering. Give three ways auxin is used commercially? Killing weeds, growth from cuttings using rooting powder, growing cells in tissue culture. What are chromosomes? Long molecules of DNA inside a nucleus. 23 pairs inside the nucleus of body cells. What is DNA? DeoxyriboNucleic Acid. It is a chemical that all genetic material in a cell is made from. It is a polymer. It is made up of two strands coiled together as a double helix. What is the structure of DNA? DNA strands are polymers made up of repeating nucleotides. Each nucleotide is made up of one sugar (deoxyribose) and a phosphate. The sugar phosphate molecules form the backbone to the DNA stands. One of the four bases ACTG joins to the sugar molecule. How do the bases pair in DNA? A-T and G-C How many bases code for an amino acid? Three/triplets What is a gene? Small section of DNA found on a chromosome Genes tell cells in what order/sequence to put amino acids in to make specific protein. How are proteins synthesised? DNA unwinds exposing one strand. An mRNA copy is made using the DNA as a template. U replaces T. The first stage happens in the nucleus. (Transcription). mRNA is single stranded and can leave through the DNA pore. Proteins are made in the cytoplasm. The ribosome reads the mRNA . Every three bases codes for an amino acid. The correct amino acids are brought to the ribosome by carrier molecules. tRNA. This stage is called translation. What do genes code for? A particular sequence of AMINO ACIDS put together to make SPECIFIC PROTEINS What is a genome ? The entire set of genetic material in an organism Why is it important to understand the human genome? (3) 1)Allows scientists to IDENTIFY GENES that link to different types of disease i.e Down Syndrome 2)Development of effective treatments 3)Can be used to trace migration of certain populations by tiny differences in GENOMES. How many chromosomes are in a normal body cell? 46 or 23 pairs How many chromosomes in a gamete (sex cell)? 23 Give 3 details of sexual reproduction in plants/animals -Animal gametes -egg & sperm - Plant gametes-ovule & pollen -Each gamete contains 23 chromosomes -nucleus of both gametes fuses=mixture of genetic info=variation in offspring Give 3 details of Asexual reproduction -One parent -Genetically identical offspring-clone -Happens by mitosis Give 2 examples of organisms that reproduce asexually Bacteria Some animals&plants What type of cell division are gametes (sex cells) produced by? Meiosis What are the 5 stages of Meiosis 1-Duplicate genetic info-forming 'X' chromosomes that arrange themselves into pairs 2-Chromosomes line up in centre of cell in homologous pairs 3-Pairs pulled apart so each new cell only has one copy of each chromosome-some of the father's chromosomes and some of the mother's go into each cell randomly, but each cell has an equal amount of chromosomes in total 4-2nd division-chromosomes line up in centre & separated again 5=4 gametes-each with single set of chromosomes Give 2 details about the 4 gametes produced in meiosis 1-Each contain 1 set of chromosomes 2-Each gamete genetically different Why are gametes produced in meiosis genetically different? Because chromosomes are shuffled up during meiosis and each gamete only gets half of them at random Explain how/why the cell produced by gamete fusion replicates itself (3) 1) After 2 gametes fused during fertilisation-resulting new cell divides by mitosis to make copy of itself 2)Mitosis repeats many times to make lots of new cells in an EMBRYO 3)As embryo develops-cells differentiate into diff types of specialised cell that MAKE UP WHOLE ORGANISM How many pairs of chromosomes are in a human body cell? 23 Pairs What do each of the chromosomes control? 22 pairs of chromosomes are matched/homologous pairs-control CHARACTERISTICS 23rd pair-XY or XX -Sex defining chromosomes What are the male and female chromosomes? Males: XY-The Y chromosome causes male characteristics Females:XX-combination allows female characteristics to develop Explain the chances of a child being male/female using a punnet diagram. 50% chance of male and 50% chance of female. How do you use genetic diagrams to find the probability of getting a boy or a girl? (3) 1-Put possible gametes from one parent down side, and from other parent along the top 2-In middle boxes, fill in letters from top & side (like multiplication) 3-There are 2 XX result & 2 XY results -50% chance of boy/girl What do the pairs of letters in the middle of a Punnett square show? The possible gamete combinations What do inherited genes control? The characteristics you develop. Genes code for proteins. Some characteristics controlled by single gene Most characteristics controlled by several INTERACTING GENES What are alleles? VERSIONS of genes. You have 2 versions (alleles) of every gene in your body-one on each chromosome in a pair What does it mean if an organism is Homozygous?