Anatomy
State the difference between breathing and respiration in humans.
Breathing is the mechanical process of moving air into and out of the lungs (ventilation).
Respiration is the chemical process in cells that releases energy from nutrients such as glucose.
A)State the role of chlorophyll in photosynthesis.
B) Which mineral deficiency would lead to lack of chlorophyll in the plant.?
A) Chlorophyll absorbs light energy. This energy is used to convert carbon dioxide and water into glucose during photosynthesis.
B) Mg
This is a simple food chain from a grassland:
grass → grasshopper → frog → snake
a) State the term used for the grass in this food chain.
b) Name the trophic level of the frog.
c) Explain why the length of food chains is usually limited in ecosystems.
a) Grass is the producer.
b) The frog is a secondary consumer.
c) At each trophic level, 90% energy is lost (e.g. as heat from respiration, in undigested material, in movement), so less/ 10% energy is available to the next level; eventually there is not enough energy to support another trophic level, limiting the length of food chains.
State what is meant by a gene and an allele.
A gene is a length of DNA that codes for a specific protein.
An allele is a different form/version of the same gene.
State what is meant by diffusion.
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of random movement of particles.
a) State two differences in the structure of an artery and vein.
b) Explain why the left ventricle has a thicker wall than the right ventricle.
a) Any one:
Arteries have thicker muscular, elastic walls than veins.
Arteries have a smaller lumen than veins.
Veins contain valves, arteries generally do not.
b)
The left ventricle pumps blood at higher pressure to the whole body via the systemic circulation.
The right ventricle only pumps blood to the lungs, which are nearby and require lower pressure, so its wall is thinner.
Describe two differences (structure and function) between xylem vessels and phloem tissue in plants.
Structure:
Xylem vessels are made of dead cells with hollow, lignified walls; phloem is made of living cells (sieve tube elements and companion cells).
Function:
Xylem transports water and mineral ions from roots to leaves and provides support.
Phloem transports sucrose and amino acids in both directions between source and sink (translocation)
In the carbon cycle.
a) Name the process by which green plants remove carbon dioxide from the atmosphere.
b) Name two processes that return carbon dioxide to the atmosphere.
c) Explain how deforestation can affect the concentration of carbon dioxide in the atmosphere.
a) Photosynthesis.
b) Any two:
Respiration of plants, animals or decomposers.
Combustion of fossil fuels or wood.
c) Deforestation reduces the number of trees, so less carbon dioxide is removed by photosynthesis; trees are often burned or left to decay, and both combustion and decomposition release additional carbon dioxide, increasing atmospheric CO₂ concentration.
In pea plants, yellow seed colour (Y) is dominant to green seed colour (y).
A heterozygous yellow plant is crossed with a homozygous green plant.
a) State the genotypes of the parents.
b) Use a genetic diagram to show the genotypes of the F₁ offspring.
c) State the phenotype of all the F₁ offspring.
a) Yellow - Yy Green- yy
b) Gametes: Y and y from one parent; y and y from the other
Offspring genotypes: Yy, yy
c) Phenotype of F₁: 2 yellow seeds: 2 green seeds
A plant cell is placed in a solution with a lower water potential than its cytoplasm.
a) Name this type of solution relative to the cell.
b) Describe and explain what happens to the plant cell.
a) The solution is hypertonic to the cell.
b)
Water moves out of the cell by osmosis through the partially permeable cell membrane.
The cytoplasm and cell membrane shrink away from the cell wall; the cell becomes plasmolysed.
The cell becomes flaccid because it loses turgor pressure.
Describe how fats (lipids) in food are digested and absorbed in the human digestive system.
In the small intestine, bile from the liver emulsifies fats into small droplets, increasing surface area.
Lipase enzymes (from the pancreas) break fats into fatty acids and glycerol.
These products diffuse into the epithelial cells of the villi; many are reformed into fats and enter the lacteals.
Fats are then transported in the lymphatic system/lacteal duct before entering the blood circulation.
A student investigates the effect of light intensity on the rate of photosynthesis in a pondweed by counting bubbles of gas released per minute.
a) Name the gas released.
b) State two variables that the student should keep constant.
c) Explain why the rate of photosynthesis stops increasing at very high light intensities, even if light intensity continues to rise.
a) Oxygen.
b) Any two:
Temperature.
Carbon dioxide concentration.
Type / size / mass of plant or pondweed.
Volume of water.
c) At high light intensities, another factor becomes limiting (e.g. carbon dioxide concentration, temperature, enzyme activity), so increasing light further does not increase the rate of photosynthesis.
A student investigates the effect of trampling on the distribution of a plant species in a field.A square shaped quadrant is the apparatus used to sample the distribution of plants in the field.
a) Describe how the student could use this apparatus to obtain reliable results when comparing trampled and untrampled areas.
b) State one abiotic factor the student could measure that might also affect the distribution of these plants
c) How would extinction of one plant species impact the ecosystem?
a) For example:
Place quadrats randomly in trampled and untrampled areas (e.g. using random coordinates).
Count the number of the plant species in each quadrat.
Use the same size quadrat in both areas.
Take a large number of readings in each area and calculate a mean.
b) Any one: light intensity, soil pH, soil moisture, soil temperature, mineral ion concentration.
c) Without a producer, the primary consumers would reduce in population, ripple effect on the food chain, less energy available in the food web/ trophic levels,
a) Explain two differences between continuous and discontinuous variation.
b) Give one human example of each type of variation.
a) Difference:
Continuous variation shows a full range of values with no clear categories. Affected by genes and the environment/external factors.
Discontinuous variation has distinct categories with no intermediates. Affected by genes ONLY.
b) Examples:
Continuous: height or body mass in humans.
Discontinuous: blood group or ability to roll the tongue.
A student tests a food sample using Benedict’s solution and Biuret solution.
a) State the colour change that shows a reducing sugar is present.
b) State the colour change that shows protein is present.
c) Name the biological molecules detected by:
i) ethanol emulsion test
ii) iodine solution.
a) Benedict’s test: blue → brick-red (or orange/yellow/green for lower amounts).
b) Biuret test: blue → purple/lilac.
c)
i) Ethanol emulsion test: detects lipids (white emulsion forms).
ii) Iodine solution: detects starch (yellow-brown → blue-black).
The kidney helps to maintain the internal environment of the body.
a) Name two substances that are present in blood plasma entering the kidney but not present in the glomerular filtrate in Bowman’s capsule.
b) Name one substance that is present in glomerular filtrate but not in urine.
c) Explain the importance of selective reabsorption in the kidney tubules.
a) Any two:
Plasma proteins.
Blood cells (red or white blood cells).
b) Any one:
Glucose.
Some amino acids.
c)
Selective reabsorption returns useful substances such as glucose, some ions and most water from the filtrate back into the blood.
This prevents the loss of important materials and helps maintain constant blood composition and water potential (homeostasis).
a) Define transpiration.
b) Suggest two leaf adaptations of a plant living in a dry habitat, and explain how each adaptation works.
c) Explain how transpiration pull helps to move water from roots to leaves.
a) Transpiration is the loss of water vapour from the surfaces of a plant, mainly through the stomata of the leaves.
b) Any two adaptations with explanations, for example:
Small / needle-shaped leaves → smaller surface area so less evaporation.
Thick cuticle → waxy barrier reduces evaporation from leaf surface.
Sunken stomata or stomata on lower surface only → humid air trapped, reduces water potential gradient, so less diffusion of water vapour.
Hairy leaves → layer of still, moist air around leaf reduces diffusion of water vapour.
c) Water diffuses from mesophyll cells, out through stomata, lowering the water potential/volume of water of mesophyll cells; water is drawn from xylem to replace it, creating a tension in the xylem column; cohesion and adhesive forces help the water to be pulled up from roots to leaves (transpiration pull).
A lake near farmland receives runoff containing fertilisers.
a) Name the two main ions in fertilisers that cause eutrophication.
b) Describe the process of eutrophication in the lake from the arrival of fertiliser to the death of fish.
c) Suggest one way farmers could reduce the risk of eutrophication without greatly reducing crop yield.
a) Nitrate ions and phosphate ions.
b)
Fertilisers are washed into the lake, increasing the concentration of nitrate and phosphate ions.
These nutrients cause rapid growth of algae and aquatic plants (algal bloom).
The dense growth blocks light; submerged plants die because they cannot photosynthesise.
Dead plants and algae are decomposed by bacteria; bacteria carry out aerobic respiration, using up dissolved oxygen.
The concentration of dissolved oxygen falls; fish and other organisms that require oxygen die.
c) Any one suitable measure, e.g.:
Use less fertiliser or apply only when needed.
Use slow-release or organic fertilisers.
Maintain buffer strips / grass margins between fields and waterways to reduce runoff.
Describe in detail how bacteria can be genetically modified to produce human insulin.
Basic sequence:
Identify and isolate the human insulin gene from human DNA using a restriction enzyme.
Cut open a bacterial plasmid with the same restriction enzyme to produce sticky ends.
Insert the human insulin gene into the plasmid; join using DNA ligase to form recombinant plasmid.
Insert the recombinant plasmid into bacteria (e.g. by mixing with calcium salts or using an electric shock).
Select bacteria that have successfully taken up the plasmid.
Grow these bacteria in a fermenter, controlling temperature, pH, oxygen and nutrient supply.
Bacteria express the insulin gene and produce human insulin, which is then harvested and purified
An enzyme-catalysed reaction is carried out at different temperatures. The rate increases as temperature rises from 20 °C to 40 °C, then decreases rapidly above 50 °C.
a) Explain why the rate of reaction increases between 20 °C and 40 °C.
b) Explain why the rate decreases at temperatures above 50 °C.
c) State two properties that show enzymes are biological catalysts.
a)
Increasing temperature gives particles more kinetic energy.
Enzyme and substrate molecules collide more frequently and with more energy, so more enzyme–substrate complexes form per unit time, increasing the reaction rate.
b)
High temperatures denature the enzyme.
The active site changes shape so it is no longer complementary to the substrate; fewer or no enzyme–substrate complexes form, so the rate falls.
c) Any two:
They speed up reactions.
They are not used up in the reaction.
They are specific to their substrate.
They work best at an optimum temperature and pH.
A person suddenly sees a dangerous situation (for example, a car moving quickly towards them) and responds by jumping out of the way.
a) Describe the pathway of a reflex arc involved in a rapid response to such a stimulus.
b) Explain two differences between nervous and hormonal (endocrine) control in humans.
c) Describe the role of adrenaline in helping the body to respond to this situation.
a)
Receptors (in the eye) detect the stimulus and generate impulses in sensory neurones.
Sensory neurones carry impulses to the central nervous system (spinal cord/brain).
Impulses are transmitted across synapses to relay neurones and then to motor neurones.
Motor neurones carry impulses to effector muscles, which contract to move the body away.
b) Any two differences:
Nervous control uses nerve impulses transmitted along neurones; hormonal control uses chemicals (hormones) carried in the blood.
Nervous responses are very fast and usually short-lived; hormonal responses are slower but longer-lasting.
Nervous control acts on specific target cells via particular neurones; hormones can affect many organs via the bloodstream.
c)
Adrenaline is released from the adrenal glands and prepares the body for “fight or flight”.
It increases heart rate and breathing rate, causes blood to be diverted to muscles, increases blood glucose concentration, and thus provides more oxygen and energy for rapid muscular activity.
A flowering plant reproduces sexually.
a) Explain pollination
b) Describe the events that occur from pollination to the formation of a seed.
c) Explain one advantage and one disadvantage of cross-pollination compared with self-pollination.
a) Pollination is the transfer of pollen grains from the anther to the stigma.
b) After pollination:
Pollen grain germinates on the stigma and grows a pollen tube down the style.
The male nucleus travels down the pollen tube to the ovule in the ovary.
The male nucleus fuses with the female nucleus in the ovule to form a zygote (fertilisation).
The zygote develops into an embryo plant; the ovule becomes a seed (containing embryo, food store and seed coat); the ovary develops into a fruit.
c)Advantage of cross-pollination:
Produces genetic variation, increasing chances of adaptation and survival in changing environments.
Disadvantage of cross-pollination:
Depends on pollinating agents (insects, wind, etc.), so if these are absent or unreliable, fewer seeds may be produced; it can also be less energy-efficient than self-pollination.
Intensive farming practices are used to increase food production.
a) Explain how the use of greenhouses or polytunnels can increase crop yield.
b) Describe two negative environmental effects of intensive livestock production.
c) Evaluate how modern farming can be managed to increase food production while minimising damage to ecosystems.
a) Greenhouses/polytunnels:
Allow control of temperature, light and carbon dioxide concentration, keeping them near optimum for photosynthesis.
Protect plants from pests and adverse weather, reducing losses and increasing yield.
b) Any two, with brief explanation, for example:
Large amounts of animal waste can wash into rivers, causing water pollution and eutrophication.
Overuse of antibiotics in livestock can lead to the spread of antibiotic-resistant bacteria.
Methane released from cattle contributes to the enhanced greenhouse effect.
c) Points for evaluation (any suitable combination):
Use of integrated pest management (biological control plus limited pesticides) to reduce chemical input.
Careful fertiliser application (correct amount, timing, placement) and buffer zones to reduce pollution.
Rotating crops and maintaining hedgerows/woodlands to preserve biodiversity.
Legal controls, monitoring and conservation schemes to balance high yields with habitat protection.
Red–green colour blindness is caused by a recessive allele Xr carried on the X chromosome. The dominant allele for normal vision is XR.
A carrier woman for colour blindness marries a man with normal colour vision.
a) Use a genetic diagram to show the genotypes of all possible children.
b) Calculate the percentage of their sons that are colour blind and the percentage of their daughters that are colour blind.
a) Genetic diagram (any clear layout):
Offspring genotypes:
XRXR – daughter, normal vision
XRXr – daughter, carrier, normal vision
XRY – son, normal vision
XrY – son, colour blind
b) Probabilities:
Sons colour blind: 1 out of 2 sons = 50%.
Daughters colour blind: 0 out of 2 daughters = 0%; daughters can only be normal or carriers.
Multicellular organisms have specialised cells and systems for exchange.
a) State the levels of organisation in organisms, from cell up to organism.
b) Explain why large multicellular organisms need specialised exchange surfaces instead of relying only on diffusion through their outer surface.
c) Describe two structural features of a good exchange surface and explain how each increases the efficiency of diffusion.
a) Cell → tissue → organ → organ system → organism.
b)
Large organisms have a small surface area to volume ratio, so diffusion across the outer surface would be too slow to supply all cells with oxygen and nutrients or remove waste.
Many cells are far from the body surface, so diffusion distances are large; specialised exchange surfaces and transport systems are needed to maintain an adequate supply.
c) Any two features with explanation, for example:
Large surface area (e.g. folding, villi, alveoli) → more area for diffusion, so more substances can cross per unit time.
Thin barrier (one-cell thick) → short diffusion distance, increasing rate.
Rich blood supply or movement of fluid/ventilation → maintains a steep concentration gradient by rapidly removing absorbed substances or bringing more.