Reproduction, Ecosystems & Genetics

What is the main function of the testes in the human male reproductive system?

• ATo produce eggs, released for fertilisation
• BTo produce sperm cells, the male gametes✓
• CTo store urine before it leaves the body
• DTo carry the developing foetus during pregnancy

Answer: The testes are the male reproductive organs, and their main job is producing sperm cells, the male gametes, throughout adult life. Producing eggs is the role of the ovaries, not the testes, so that option names the wrong organ. Urine is stored in the bladder and a foetus develops in the uterus, so neither of those distractors describes what the testes actually do.

What is the main function of the uterus in the human female reproductive system?

• AIt produces the eggs that are released each month
• BIt produces the sperm cells needed for fertilisation to take place
• CIt is where a fertilised egg implants and develops into a foetus during pregnancy✓
• DIt filters waste products out of the mother's blood

Answer: The uterus is the organ in which a fertilised egg implants and grows into a foetus throughout pregnancy. Eggs are produced and released by the ovaries, not the uterus, so that option confuses the two organs. Sperm production happens in the testes of the male body, and filtering waste from blood is a job done by the kidneys, so neither distractor describes the uterus.

What normally happens to the lining of the uterus during the menstrual cycle if an egg is not fertilised?

• AIt thickens permanently to protect the ovaries
• BIt breaks down and is shed from the body as a period✓
• CIt hardens to form the placenta ready for the next cycle
• DIt is absorbed back into the ovary for reuse

Answer: Each month the lining of the uterus thickens in preparation for a possible pregnancy, and if the egg released that cycle is not fertilised, the lining breaks down and is shed from the body as a period. The lining does not thicken permanently, since it is renewed and shed on a monthly cycle rather than staying in place. It is not absorbed back into the ovary, and the placenta only forms after fertilisation and implantation have occurred, not as a routine part of every cycle.

What happens during fertilisation in human reproduction?

• AThe placenta forms directly from the sperm cell alone
• BA sperm cell divides in two to form twin embryos
• CA sperm cell and an egg cell join together to form a new single cell✓
• DAn egg cell splits into several smaller eggs inside the uterus

Answer: Fertilisation happens when a sperm cell and an egg cell join together, combining their genetic material to form a new single cell that can develop into an embryo. A sperm cell dividing to form twins is not how fertilisation works, and an egg cell does not split into several smaller eggs inside the uterus. The placenta develops from tissue formed after fertilisation and implantation, not from the sperm cell alone.

How can a mother's lifestyle, such as smoking during pregnancy, affect her developing foetus?

• AHarmful substances are too large to cross the placenta into the foetus
• BHarmful substances can pass from the mother's blood, across the placenta, to the foetus✓
• CHarmful substances are removed from the blood by the umbilical cord before reaching the foetus
• DHarmful substances are filtered out by the mother's uterus, not the placenta, before reaching the foetus

Answer: The placenta is the organ that lets nutrients and oxygen pass from the mother's blood to the foetus, but harmful substances such as those from smoking can cross it too, which is why maternal lifestyle affects the foetus. It is not true that the umbilical cord removes harmful substances, since it simply carries blood between the placenta and the foetus. The uterus is the muscular organ that holds the foetus rather than the exchange organ, so it does not perform this filtering role, and harmful substances are known to cross the placenta rather than being too large to do so.

Which feature would you expect to find in a flower that is pollinated by insects rather than by wind?

• ASmall, dull petals and large amounts of light, feathery pollen
• BNo petals at all, since insects do not respond to colour or scent
• CBrightly coloured, scented petals and nectar to attract pollinators✓
• DAnthers that hang far outside the flower to release pollen into moving air

Answer: Insect-pollinated flowers typically have brightly coloured, scented petals and produce nectar, all of which attract insects that then carry pollen between flowers. Small, dull petals with light, feathery pollen are features of wind-pollinated flowers, which rely on air currents rather than insects. Anthers hanging outside the flower to catch the wind is also a wind-pollination adaptation, and insect-pollinated flowers usually have petals precisely because insects do respond to colour and scent.

How can recreational drugs affect a person's body and behaviour?

• AThey change a person's appearance but leave the internal organs unaffected
• BThey improve concentration and physical fitness with no risks
• CThey can alter behaviour and interfere with normal life processes such as reaction time✓
• DThey have no measurable effect on the nervous system

Answer: Recreational drugs can act on the nervous system, which can alter a person's behaviour and interfere with normal life processes such as reaction time. It is not true that they improve concentration and fitness with no risks, since many recreational drugs carry health risks and can impair performance. They do have measurable effects on the nervous system, and their effects go well beyond appearance, often reaching internal organs such as the liver, heart or brain.

What is meant by 'substance misuse' in relation to recreational drugs?

• AStoring drugs safely, away from children, in a locked cabinet
• BReading the dosage instructions on a medicine label
• CUsing a drug in a way, or amount, that causes harm to health or behaviour✓
• DUsing any medicine exactly as prescribed by a doctor

Answer: Substance misuse describes using a drug in a way, or in an amount, that causes harm to a person's health or behaviour, rather than any use of drugs at all. Taking a medicine exactly as a doctor prescribes it is the opposite of misuse, since it is following safe medical guidance. Storing drugs safely away from children and reading dosage instructions are both sensible safety habits, not examples of the drug itself being misused.

Why might regular recreational drug use damage a person's life processes over time?

• ADrugs can interfere with the normal functioning of organs such as the liver, heart or brain✓
• BDrugs act on a person's sense of taste and smell rather than on organs
• CDrugs affect the body during sleep but wear off as soon as a person wakes
• DDrugs gradually strengthen organ systems, including the heart and lungs, over time

Answer: Recreational drugs are chemicals that circulate in the bloodstream and can interfere with the normal functioning of organs such as the liver, heart or brain, which is why regular use can be damaging. Their effects reach far beyond taste, since drugs act on organ systems throughout the body. Drugs do not strengthen organ systems over time, and their effects do not wear off as soon as a person wakes, since many recreational drugs act while a person is awake and active.

Which two substances are the reactants used by a plant during photosynthesis?

• AOxygen and glucose
• BCarbon dioxide and water✓
• CCarbon dioxide and oxygen
• DNitrogen and water

Answer: Photosynthesis uses carbon dioxide, taken in through the leaves, and water, absorbed by the roots, as its two reactants. Oxygen and glucose are actually the products of photosynthesis, not the starting materials, so that option reverses the process. Nitrogen is not a reactant in photosynthesis, and oxygen is a product rather than a reactant, so it should not appear alongside carbon dioxide in this list.

What are the two main products formed during photosynthesis?

• AStarch and carbon dioxide
• BCarbon dioxide and water
• CWater and nitrogen
• DGlucose and oxygen✓

Answer: During photosynthesis, a plant produces glucose, which it can use or store as an energy source, and releases oxygen as a by-product. Carbon dioxide and water are the reactants that are used up to start the reaction, not the substances made at the end of it. Nitrogen is not involved in photosynthesis, and although starch can later be made by joining glucose molecules together, carbon dioxide is a reactant rather than a direct product of the reaction.

Why is photosynthesis so important for almost all life on Earth?

• AIt allows plants and algae to use sunlight to build organic molecules as an energy store, and it helps maintain atmospheric oxygen and carbon dioxide levels✓
• BIt allows plants to absorb oxygen directly from the soil through their roots instead of from the air
• CIt produces every single drop of the water that a growing plant needs for all of its other life processes
• DIt lets plants break down glucose to release energy for growth, but only when sunlight is unavailable

Answer: Photosynthesis lets plants and algae use light energy to build organic molecules that store energy, and because almost all food chains ultimately depend on these organisms, this also helps maintain the balance of oxygen and carbon dioxide in the atmosphere. Plants take in carbon dioxide through their leaves rather than absorbing oxygen from the soil, so that option describes the wrong gas and the wrong route. Breaking down glucose to release energy is respiration, not photosynthesis, and it happens continuously rather than only when sunlight is unavailable. Photosynthesis uses water as a reactant rather than producing it, so it is not the source of a plant's water supply.

Which adaptation helps a leaf carry out photosynthesis efficiently?

• AA dense network of muscle fibres that pump carbon dioxide into the cells
• BA broad, thin shape with stomata that lets gases diffuse in and out easily✓
• CA thick, waxy structure with no openings to prevent any gas exchange at all
• DA narrow, rolled shape designed to keep sunlight away from the chloroplasts

Answer: A broad, thin leaf shape gives a large surface area for light to be absorbed, while tiny pores called stomata let carbon dioxide and oxygen diffuse in and out easily. A thick, waxy structure with no openings would actually block gas exchange, which would prevent photosynthesis rather than support it. A narrow, rolled shape that keeps sunlight away from the chloroplasts would reduce light capture, and leaves have no muscle fibres, since gas movement into leaves happens by diffusion, not pumping.

Almost all other organisms in a food web ultimately depend on which group for their energy?

• AFungi, since they absorb energy directly from the soil
• BDecomposers, since they release energy stored in dead material
• CCarnivores, since they are at the top of most food chains
• DPhotosynthetic organisms, such as plants and algae✓

Answer: Photosynthetic organisms, such as plants and algae, capture light energy and store it in organic molecules, which is why almost every other organism in a food web ultimately depends on them for energy. Decomposers recycle energy already stored in dead material rather than being the original source of it. Carnivores sit near the top of food chains and rely on other organisms for energy rather than producing it themselves, and fungi obtain their energy from organic matter rather than absorbing energy directly from the soil.

What are the reactants of aerobic respiration in a cell?

• AWater and oxygen
• BCarbon dioxide and water
• CWater and glucose
• DGlucose and oxygen✓

Answer: Aerobic respiration uses glucose and oxygen as its reactants, breaking them down inside cells to release energy for life processes. Carbon dioxide and water are the products released at the end of the reaction, not the substances used to start it. Water paired with glucose, and water paired with oxygen, both wrongly swap in water, a product of respiration, for oxygen, the actual reactant, so neither pairing is correct.

What are the products of aerobic respiration, besides the release of energy?

• AEthanol and carbon dioxide
• BGlucose and oxygen
• CLactic acid and water
• DCarbon dioxide and water✓

Answer: Aerobic respiration breaks down glucose using oxygen and produces carbon dioxide and water as waste products, alongside the release of energy. Glucose and oxygen are the reactants that get used up, not the products left behind, so that option describes the start of the reaction instead of the end. Lactic acid is produced by anaerobic respiration in humans, and ethanol together with carbon dioxide is produced by anaerobic respiration in yeast, so neither belongs to the aerobic pathway.

What happens during anaerobic respiration in human muscle cells, for example during intense exercise?

• AGlucose is broken down into lactic acid without using oxygen✓
• BOxygen is combined with lactic acid to release large amounts of energy
• CGlucose is broken down into ethanol and carbon dioxide without oxygen
• DGlucose reacts with carbon dioxide to produce extra oxygen for the muscles

Answer: When muscle cells cannot get enough oxygen during intense exercise, they respire anaerobically, breaking glucose down into lactic acid without using oxygen. Producing ethanol and carbon dioxide is what happens during anaerobic respiration in yeast, not in human muscle cells. Anaerobic respiration by definition does not use oxygen, so combining oxygen with lactic acid describes the wrong process, and glucose does not react with carbon dioxide to make oxygen in either type of respiration.

What happens during anaerobic respiration in yeast, such as in fermentation?

• AOxygen reacts with ethanol to produce glucose and water
• BGlucose is broken down into ethanol and carbon dioxide without using oxygen✓
• CGlucose is broken down into lactic acid without using oxygen
• DCarbon dioxide is combined with water to make glucose

Answer: In yeast, anaerobic respiration breaks glucose down into ethanol and carbon dioxide without using oxygen, which is the basis of fermentation. Breaking glucose down into lactic acid is what happens in human muscle cells during anaerobic respiration, not in yeast. Oxygen reacting with ethanol to reform glucose and water reverses the true process, and combining carbon dioxide with water to make glucose describes photosynthesis, not respiration.

How does anaerobic respiration differ from aerobic respiration in terms of energy release?

• AAnaerobic respiration does not use oxygen and releases much less energy from each glucose molecule✓
• BAnaerobic respiration breaks glucose down fully into carbon dioxide and water
• CAnaerobic respiration and aerobic respiration release exactly the same amount of energy from each glucose molecule
• DAnaerobic respiration uses more oxygen and releases far more energy overall

Answer: Anaerobic respiration takes place without oxygen and only partly breaks down glucose, so it releases much less energy from each glucose molecule than aerobic respiration does. It cannot use more oxygen than aerobic respiration, since by definition it uses none at all. Fully breaking glucose down into carbon dioxide and water is a feature of aerobic respiration, not anaerobic respiration, and the two processes release very different amounts of energy rather than exactly the same amount.

What does a food web show about the organisms in an ecosystem?

• AThe order in which different types of rock form during the rock cycle
• BA network of overlapping food chains that shows how organisms in an ecosystem feed on each other✓
• CThe exact number of individual organisms living in a habitat
• DThe precise chemical formula of every substance that each organism in the ecosystem eats as its main food source

Answer: A food web is a network of overlapping food chains that shows the feeding relationships between the many organisms living in an ecosystem. It does not state the exact number of individual organisms present, since it shows feeding links rather than a population count. The order in which rocks form belongs to the rock cycle in geology, and food webs show feeding relationships rather than the chemical formulae of foods.

Why is insect pollination important for human food security?

• AInsects add nitrogen directly to the soil around growing crops
• BInsects remove pests from crops without pollinating any flowers
• CInsects pollinate the flowers of many food crops, allowing them to produce seeds and fruit✓
• DInsects break down harvested crops in storage after they have already been picked, releasing nutrients

Answer: Many food crops rely on insects to pollinate their flowers, and without this pollination those crops cannot produce the seeds and fruit that humans harvest for food. Insects breaking down harvested crops in storage would spoil food rather than help produce it, so that describes damage, not pollination. Insects do not add nitrogen directly to soil, since that role is played by decomposers and certain bacteria, and this question is specifically about pollination, not general pest control.

What can happen when toxic materials, such as some pesticides, enter a food chain?

• AThey are passed out of the body each time an organism reproduces
• BThey can build up in the bodies of organisms and become more concentrated at higher levels of the food chain✓
• CThey stay in the producers at the start of the chain and are not passed on
• DThey break down instantly as soon as they are eaten and have no effect once they enter a living organism in the chain

Answer: Toxic materials that enter a food chain can build up in the bodies of organisms, and because predators eat many prey organisms, these toxins can become more concentrated at higher levels of the food chain. It is not true that they break down instantly with no effect, since many toxic substances persist in the body for a long time. Their effects are not limited to the first organism in the chain, since they can pass along it, and reproduction does not automatically remove toxins that have built up in an organism's tissues.

What does it mean to say that organisms in an ecosystem are interdependent?

• AOrganisms compete with each other for resources, but are unaffected by other species
• BOrganisms living in the same ecosystem do not interact with each other, even when sharing a habitat
• COrganisms rely on each other, for example for food, shelter or pollination✓
• DPlants depend on other organisms to survive, but animals do not

Answer: Interdependence means that organisms in an ecosystem rely on each other in various ways, for example for food, shelter or pollination, so changes affecting one species can affect many others. Saying organisms do not interact contradicts the whole idea of interdependence, which is built on organisms affecting each other. It is not only plants that depend on other organisms, since animals also rely on food sources, and organisms that compete for resources are still affected by other species, not isolated from them.

How might pollution in a habitat affect the organisms that live there?

• AIt has no effect on organisms unless they eat the polluting substance directly
• BIt affects organisms that photosynthesise, such as plants and algae, but leaves animals unharmed
• CIt tends to increase the population sizes of the organisms in that habitat over time
• DIt can harm organisms directly or reduce the food and resources available to them✓

Answer: Pollution can harm organisms directly, for example by poisoning them, or indirectly by reducing the food and resources available in a habitat. It does not tend to increase population sizes, since pollution more commonly reduces the numbers of organisms that can survive in an affected habitat. Pollution can harm organisms that never eat the polluting substance, and it affects animals as well as photosynthesising organisms, since both can be harmed by contaminated air, water or soil.

What is meant by 'heredity' in genetics?

• AThe breakdown of food molecules to release energy inside an organism's body cells
• BThe passing of genetic information from parents to their offspring✓
• CThe way that a single species changes its own habitat during just one lifetime
• DThe process by which an organism repairs its own damaged skin cells after an injury

Answer: Heredity is the passing of genetic information from parents to their offspring, which explains why offspring often resemble their parents. Repairing damaged skin cells is a healing process within an individual organism, not a description of how traits pass between generations. A species changing its habitat during one lifetime is not heredity, and breaking down food to release energy describes respiration, not the inheritance of genetic information.

Where in a cell are chromosomes, made of DNA, normally found?

• AIn the vacuole
• BIn the cell wall
• CIn the nucleus✓
• DIn the chloroplast

Answer: Chromosomes, made of tightly coiled DNA, are normally found in the nucleus of a cell, which acts as the control centre containing the cell's genetic information. The cell wall is a rigid outer layer that supports and protects plant cells, not a location for chromosomes. The vacuole stores cell sap and helps keep the cell firm, and the chloroplast is the site of photosynthesis, so neither structure stores chromosomes.

Which scientists are usually credited with contributing to working out the structure of DNA?

• AMendeleev, Newton, Darwin and Hooke
• BWatson, Crick, Wilkins and Franklin✓
• CLinnaeus, Lavoisier, Faraday and Dalton
• DPasteur, Fleming, Curie and Priestley

Answer: Watson, Crick, Wilkins and Franklin are the scientists usually credited with contributing to the discovery of the structure of DNA, with Franklin's X-ray images providing crucial evidence for the double helix model. Mendeleev, Newton, Darwin and Hooke made major contributions to other areas of science, such as the Periodic Table, gravity, evolution and cell discovery, rather than to the DNA model. Pasteur, Fleming, Curie and Priestley are linked to germ theory, antibiotics, radioactivity and gas chemistry, and Linnaeus, Lavoisier, Faraday and Dalton are linked to classification, chemistry and atomic theory, so none of these groups match the DNA discovery.

What is meant by continuous variation within a species, such as human height?

• AA characteristic that falls into a few separate categories, such as blood group, with nothing in between
• BA range of measurements across the population, with no sharp division between groups✓
• CA characteristic that stays exactly identical in each member of the species, with no differences
• DA characteristic that skips one generation, then reappears again in the next generation

Answer: Continuous variation describes a characteristic such as height, which shows a range of measurements across a population with no sharp division between groups. A characteristic that falls into a few separate categories, such as blood group, is an example of discontinuous variation instead. A characteristic cannot show continuous variation if it is identical in every member of the species, since variation requires some difference between individuals, and continuous variation is about a spread of measurements rather than a trait appearing or disappearing across generations.

How does variation within a species contribute to natural selection?

• ANatural selection removes the variation from a whole population within just a single generation
• BVariation between individuals appears after an organism has already finished reproducing successfully
• CIndividuals in a species are equally likely to survive and reproduce, regardless of their characteristics
• DSome individuals have characteristics that help them compete more successfully and survive to reproduce✓

Answer: Because individuals within a species vary, some have characteristics that help them compete more successfully for resources, survive and go on to reproduce, passing those characteristics to their offspring. If every individual were equally likely to survive regardless of its characteristics, there would be no natural selection at all. Variation exists before an organism reproduces rather than only appearing afterwards, and natural selection acts gradually over many generations rather than removing all variation within a single one.

Why might environmental change lead to a species becoming extinct?

• AIndividuals may become less well adapted to the changed conditions and fail to survive and reproduce✓
• BExtinction is caused by gene banks failing to store enough seeds or other hereditary material
• CEnvironmental change improves the survival chances of the species living in that particular habitat
• DSpecies automatically evolve brand new adaptations within a single generation, without natural selection

Answer: When an environment changes, individuals that are less well adapted to the new conditions may fail to survive and reproduce, and if too few individuals succeed, the whole species can become extinct. Environmental change does not generally improve survival chances, since it often makes conditions harder for a species that was suited to the old environment. Species do not automatically evolve new adaptations within a single generation, since evolution by natural selection happens gradually over many generations, and extinction can occur regardless of whether a gene bank exists, since gene banks are a way of preserving hereditary material rather than the cause of extinction.