GCSE AQA Biology Paper Two – Complete Topic Summary with Model Answers – Secondary School, Exams of Biology

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GCSE AQA Biology Paper two

"Natural Selection - CORRECT ANSWER A theory for evolution put forward by natural selection. It is where species have naturally evolved over time in order to survive:

1. there is a struggle for existence.
2. more organisms are born that can survive.
3. the ones that survive breed and pass on their characteristics to their offspring.
4. over long periods of time the characteristics of the population change." "Reasons Why Darwin's Theory for Evolution Took Along Time for People to Accept. - CORRECT ANSWER - it challenged Christianity.

• there was little evidence at the time.
• inheritance and variation were discovered 50 years later." "Darwin's Theory of Evolution - CORRECT ANSWER Those individuals that are best adapted to the environment will survive and reproduce; those traits that help them, become more common in a species and maladaptive traits die out. This is called natural Selection." "Lamarck's Theory About Giraffes - CORRECT ANSWER They have longer necks because they were constantly stretching to reach food off the trees. They then passed this characteristic onto the next generation." "Different Fossil Formations - CORRECT ANSWER - hard parts of animals have not decayed.
• parts of animals have not decayed as conditions needed were absent.
• parts of organisms are replaced by other materials as they decay.
• as preserves traces. E.g. footprints." "Reasons why there is a Gap in the Fossil Record - CORRECT ANSWER - many early forms of life were soft bodied so they leave behind few traces.
• traces may have been destroyed by geological activity." "Selective Breeding - CORRECT ANSWER The process of selecting a few organisms with desired traits and characteristics then breeding them together to form offspring with these features." "Genetic Engineering - CORRECT ANSWER This involves changing the characteristics of an organism by introducing a new gene:

1. enzymes are used to isolate the required gene.
2. the gene is inserted into a vector.
3. the vector is used to insert the gene into the require cells." "Genetically Modified Crops - CORRECT ANSWER Crops that have been modified for desired characteristics using genetic engineering. E.g. to increasing fruit productivity, or to become resistant to diseases, etc."

"Ovulation - CORRECT ANSWER The process in which an egg is released from the ovary." "FSH - CORRECT ANSWER This is secreted by the pituitary and causes eggs in the ovaries to mature and stimulates the ovaries to produce oestrogen." "Oestrogen - CORRECT ANSWER This is secreted by the ovaries and inhibits FSH releases and stimulates LH release and makes the lining of the uterus grow again after menstruation." "Menstruation - CORRECT ANSWER The monthly shedding of the uterine lining." "LH - CORRECT ANSWER This is secreted by the pituitary gland and stimulates ovulation." "Progesterone - CORRECT ANSWER This is secreted by the empty follicle in the ovaries and maintains the lining of the uterus during the second half of the cycle and inhibits FSH and LH release." "Methods of Contraception & How They Work - CORRECT ANSWER - The Pill - contains oestrogen and progesterone which inhibits FSH production so that no eggs are released.

• An Injection, Implant or Skin Patch - slowly releases progesterone to stop the release of eggs.
• Condoms and Diaphragms - prevent sperm from reaching the egg.
• Intrauterine Devices - prevent embryos from implanting in the uterus.
• Spermicidal Creams - kills sperm." "Methods to Increase Fertility - CORRECT ANSWER - Fertility Drug - contains FSH & LH to stimulate eggs to mature.
• I'm Vitro Fertilisation:

1. giving a FSH and LH to stimulate the growth of many eggs.
2. collect eggs from women.
3. fertilise eggs with dads sperm in a laboratory.
4. insert one or two embryos into the woman's uterus." "Tropism - CORRECT ANSWER A growth response of a plant toward or away from a stimulus controlled by auxins." "Tropism When Gravity is the Stimulus - CORRECT ANSWER - Growth of Shoots = negatively gravitational.

• Growth of Roots = positively gravitropic." "Tropism When Light is the Stimulus - CORRECT ANSWER - Growth of Shoots = positively phototropic.

• Growth of Roots = negatively phototropic." "Auxins - CORRECT ANSWER Plant hormones that lead to phototropism by elongating the dark side of the plant." "Gibberellins - CORRECT ANSWER A hormone which is important in initiating seed germination." "Germination - CORRECT ANSWER the process where seeds sprout and begin to grow." "Ethene - CORRECT ANSWER A hormone which controls cell division an ripening of fruits." "Effect of Light on Growth Required Practical - CORRECT ANSWER 1) take a number of small plastic boxes and make a hole on one side of each container, which is the same size.

2. put some soil in the containers and plant 10 cress seeds in each.
3. put a lid on each box.
4. put the containers in even lighting with the holes pointing in different directions.
5. water the soil and leave for several days.
6. come back every day and record growth of cress." "Uses of Auxins - CORRECT ANSWER - weed killers.

• rooting powders.
• promoting growth." "Uses of Ethene - CORRECT ANSWER - In the food industry to control the ripening of fruit during storage and transport." "Uses of Gibberellins - CORRECT ANSWER - end seed dormancy and makes seeds germinate.
• promote flowering.
• increase fruit size." "Asexual Reproduction - CORRECT ANSWER This involves only one parent and no fusion of gametes, meaning no mixing of genetic information so the production of a genetically identical offspring. It uses mitosis." "Sexual Reproduction - CORRECT ANSWER This involves the fusion of a male and female gamete. This leads to the mixing of genetic information so variation of offspring is found. It uses meiosis." "Gamete - CORRECT ANSWER Specialised cell involved in sexual reproduction." "Meiosis - CORRECT ANSWER 1) in a diploid cell, each chromosome replicated itself.

"The Thermoregulatory Centre - CORRECT ANSWER This is in the brain and it monitors and controls body temperature, blood temperature via impulses from temperature receptors." "Effects when Body Temperature is too High - CORRECT ANSWER - Vasodilation.

• Swear more.
• Transfer of energy form the skin to the environment." "Effects when Body Temperature is too Low - CORRECT ANSWER - Vasoconstriction
• Stop sweating
• Piloerection
• Shiver" "The Nervous System - CORRECT ANSWER This enables humans to react to their surroundings and coordinate their behaviour. It stimulates a reflex arc." "Types of Neurones - CORRECT ANSWER Sensory Neurone, Motor Neurone, Relay Neurone." "Reflex Arc - CORRECT ANSWER 1) the pain stimulus is detected by receptors.

2. impulses from the receptor pass along a sensory Neurone to the CNS.
3. an impulse then passed through a relay Neurone.
4. a motor neurone carries an impulse to the effector.
5. the effector (muscle or gland) responds" "Synapse - CORRECT ANSWER The connection between neurones. When an electrical impulse reaches this, a chemical is released that diffused across the gap. This causes an electrical impulse to be generated in the second one." "Human Reaction Time Required Practical - CORRECT ANSWER 1) the experimenter holds a meter rule from the end.
6. the subject had their finger and thumb a small distant apart either side of the ruler on the 50cm line.
7. the experimenter lets go of the ruler and the subject has to trap it.
8. the distance the ruler travels from the 50cm line is noted.
9. the experiment is repeated on the subjects that have just drunk coffee and the subjects that have not." "Parts of the brain - CORRECT ANSWER - Medulla

• Cerebellum
• Cerebral Cortex" "Medulla - CORRECT ANSWER controls automatic actions such as heartbeat and breathing." "Cerebellum - CORRECT ANSWER coordinates movement and balance"

"cerebral cortex - CORRECT ANSWER responsible for consciousness, intelligence, memory and language." "Parts and Functions of the Eye - CORRECT ANSWER - Retina - contains receptor cells that are sensitive to brightness and colour of light.

• Optic Nerve - carries impulses from the retina to the brain.
• Sclera - forms a tough outer layer.
• Cornea - transport region.
• Iris - controls the size of the pupil and the amount of light reaching the retina.
• Ciliary Muscles & Suspensory Ligaments - change the shape of the lens to focus light onto the retina." "Accommodation - CORRECT ANSWER The process of changing the shape of the lens to focus on near or distant objects." "Myopia - CORRECT ANSWER Shortsightedness." "Hyperopia - CORRECT ANSWER Long sightedness." "The Endocrine System - CORRECT ANSWER This is made up of glands that secrete hormones directly into the bloodstream." "Hormones - CORRECT ANSWER Chemical messengers that are carried in the blood." "Pituitary Gland - CORRECT ANSWER This is a master gland in the brain that secretes several hormones in response to body conditions." "Adrenaline - CORRECT ANSWER This is produced by the adrenal glands in times of fear or stress to increase the bodies heart rate." "Thyroxine - CORRECT ANSWER This is produced in the thyroid gland and increases metabolic rate to control growth and development in young animals." "Allele - CORRECT ANSWER Different forms of a gene." "Genotype - CORRECT ANSWER An organism's allele combinations." "Phenotype - CORRECT ANSWER Physical characteristics of an organism." "Homozygous - CORRECT ANSWER An organism that has two identical alleles for a trait." "Homozygous Recessive - CORRECT ANSWER Both alleles for a trait are the same and are both recessive (E.g. aa)."

• CO2 levels.
• O2 levels." "Population Size Required Practical - CORRECT ANSWER 1) place a quadrat on the ground at random.

2. count the number of individual plants of one species in the quadrat.
3. repeat a number of times and calculate the mean number of plants.
4. work out the mean number of plants in 1m squared.
5. measure the area of the whole area of the habitat and estimate the number of plants in the whole area." "Plant Distribution Required Practical - CORRECT ANSWER 1) stretch a long tape called a transect line across the area.
6. place a quadrant down at regular intervals along the line.
7. count the plants in the quadrat each time." "Decomposers - CORRECT ANSWER These are the organisms that break down the waste products or dead material from other organisms secreted by enzymes. They are a type of bacteria and fungi and they need oxygen, moisture, a suitable temperature and pH." "Rate of Decay Required Practical - CORRECT ANSWER 1) take a sample of fresh milk.
8. place in a beaker and cover.
9. keep warm.
10. measure the pH of the milk at regular intervals over several days." "The Carbon Cycle - CORRECT ANSWER This describes how carbon is recycled in nature. It relies on decomposed to return the carbon to the atmosphere as carbon dioxide through respiration." "The Water Cycle - CORRECT ANSWER This describes how fresh water circulated between living organisms, rivers and the sea." "Producer - CORRECT ANSWER An organism that makes its own food. E.g a green plant." "Primary Consumers - CORRECT ANSWER animals that feed on producers - herbivores." "Secondary Consumers - CORRECT ANSWER Animals that eat herbivores - carnivores." "Tertiary Consumers - CORRECT ANSWER Carnivores that eat other carnivores." "Tropic Level - CORRECT ANSWER A step in a food chain or food web."

"Linnaeus System of Classification. - CORRECT ANSWER Kingdom ~> Phylum ~> Class ~> Order ~> Family ~> Genus ~> Species." "Binomial System - CORRECT ANSWER Identifying organisms by their genus and species names." "3 Domain System - CORRECT ANSWER Dividing organisms into 3 domains:

• Archaea - primitive bacteria which usually live in extreme conditions.
• Bacteria - true bacteria.
• Eukaryota - protists, fungi, plants and animals." "Extinction - CORRECT ANSWER This is where a species is completely eradicated. It is caused by:
• new predators.
• new diseases.
• new competitors.
• a catastrophic event.
• changes in the environment." "Evolutionary Trees - CORRECT ANSWER A model used to explain the evolutionary links between groups of organisms." "Speciation - CORRECT ANSWER This is a theory suggesting how new species develop:

1. populations become physically isolated from each other.
2. genetic variation is present between the 2 populations.
3. natural selection occurs differently in the 2 populations.
4. the populations become so different that successful interbreeding is no longer possible - they produce undertake offspring." "Levels in an Ecosystem - CORRECT ANSWER - individual organisms.

• populations - groups of individuals of the same species.
• communities - made up of many populations living together." "Things Species Compete For - CORRECT ANSWER - water.
• space.
• territory.
• food.
• light.
• mates." "Ecosystem - CORRECT ANSWER All the organisms living in a habitat and the non living parts of the habitat."

"Causes of Loss in Biomass - CORRECT ANSWER - faeces, urine and excretion

• respiration. This usually means there are fewer organisms in the ecosystem." "Ways to Prevent Fish Numbers Decreasing - CORRECT ANSWER - controls the size of the nets used so only older fish are caught.
• set fishing quotas do only a certain number of fish can be caught." "Biotechnology - CORRECT ANSWER This allows microorganisms to be grown in large quantities for food. They are grown in fermenters where conditions are controlled carefully." "Mycoprotein - CORRECT ANSWER This is a fungus that is rich in protein, low in fat, high in fibre and suitable for vegetarians. Quorn contains this." "