Topic – 21.2
(a) Fig. 1.1 is a photograph showing different stages of bread‑making. Bread dough is made by mixing flour, water and yeast together. Bread dough A has just been mixed. Bread dough B was mixed a few hours before the photograph was taken and has increased in volume.
(i) State the name of the gas that caused bread dough B to increase in volume.
(ii) State the name of the process in yeast that produces the gas during bread‑making.
(b) State one other product that is made using yeast, apart from food or drink.
(c) Bacteria are another type of microorganism that is used in biotechnology.
Tick two boxes to show why bacteria are useful in biotechnology.
(d) Bacteria and yeast are living organisms. Table 1.1 shows descriptions of some characteristics of living organisms.
Complete Table 1.1 by writing the name for each characteristic described.
(e) State two cell structures that are found in both bacteria and plants.
▶️ Answer/Explanation
Ans:
(a)(i) Carbon dioxide is the gas produced by yeast during fermentation, causing the dough to rise.
(a)(ii) The process is respiration (anaerobic), where yeast converts sugars into CO2 and alcohol.
(b) Yeast is used to produce biofuels (e.g., ethanol) through fermentation.
(c) Bacteria are useful because they make complex molecules (e.g., insulin) and have a rapid reproduction rate.
(d) The characteristics are:
– Sensitivity (responding to stimuli),
– Excretion (removing waste),
– Growth (increase in size/mass).
(e) Common structures in bacteria and plants:
– Cell wall (provides support),
– Cell membrane (controls substance movement).
Topic – 5.1
Enzymes are biological catalysts.
(a) Describe what is meant by a catalyst.
(b) State the type of biological molecule enzymes are made of.
(c) The rates of enzyme activity of two different enzymes, A and B, were recorded at different temperatures. Fig. 2.1 shows the results:
(i) Compare the effect of temperature on the rate of enzyme activity for enzymes A and B. Use data from Fig. 2.1 to support your answer.
(ii) State the part of an enzyme that has a complementary shape to a substrate.
(iii) State one factor, other than temperature, that would affect the rate of enzyme activity.
(d) The box on the left contains the word ‘Enzymes’. The boxes on the right contain some sentence endings.
Draw three lines from the box on the left to make three correct sentences.
▶️ Answer/Explanation
Ans:
(a) A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It lowers the activation energy required for the reaction to proceed.
(b) Enzymes are made of proteins (or amino acids), which fold into specific 3D structures to catalyze biochemical reactions.
(c)(i) Both enzymes A and B show an increase in activity with temperature up to an optimum, followed by a decline due to denaturation. Enzyme A has a lower optimum temperature (~40°C) compared to B (~45°C), and A is active at lower temperatures while B remains active at higher temperatures.
(c)(ii) The active site of an enzyme binds specifically to the substrate due to its complementary shape.
(c)(iii) pH affects enzyme activity, as deviations from the optimal pH can alter the enzyme’s structure and reduce its efficiency.
(d) Enzymes are linked to:
1. are involved in all metabolic reactions,
2. are necessary to sustain life,
3. are used to make fruit juice (e.g., pectinase in juice extraction).
Topic – 3.1
(a) A student investigated how surface area affected the rate of diffusion. The student started with four agar cubes that each had a volume of \(1cm^3\). The agar cubes were dyed with a red indicator. The red indicator turned yellow when exposed to acid. The student cut the cubes into different numbers of blocks to increase the surface area. The blocks were placed in acid, as shown in Fig. 3.1. The student recorded the time taken for all of the agar blocks in each test‑tube to turn yellow. The student repeated the investigation twice and calculated a mean.
(i) Calculate the mean time for all the blocks to turn yellow in test‑tube C. Give your answer to the nearest whole number. Space for working.
(ii) Using the results shown in Table 3.1, describe the effect of surface area on diffusion.
(iii) State one factor, other than surface area, that could affect diffusion in this investigation.
(iv) Complete the sentences to describe how the acid particles diffuse to cause the colour change. The acid particles move from the acid solution into the ………. , down a …………. gradient. The energy for this process comes from the ………….. energy of random movement of the acid particles.
(b) Describe one way that osmosis differs from other types of diffusion.
(c) Substances needed for respiration diffuse into cells.
(i) Circle the two substances needed for aerobic respiration in humans.
carbon dioxide glucose glycogen oxygen protein urea water
(ii) State where aerobic respiration occurs in cells.
(iii) State the name of the part of all cells that substances pass through to enter the cell.
▶️ Answer/Explanation
Ans:
(a)(i) 82
The mean time for test-tube C is calculated as \(\frac{80 + 85 + 81}{3} = 82\) (rounded to the nearest whole number).
(a)(ii)
Increasing the surface area increases the rate of diffusion, as seen by the shorter time taken for the blocks to turn yellow.
(a)(iii)
Temperature or concentration of acid could also affect the rate of diffusion.
(a)(iv)
The acid particles move from the acid solution into the agar, down a concentration gradient. The energy comes from the kinetic energy of the particles.
(b)
Osmosis differs from diffusion as it specifically involves the movement of water molecules across a partially permeable membrane.
(c)(i)
The two substances needed for aerobic respiration are glucose and oxygen.
(c)(ii)
Aerobic respiration occurs in the mitochondria of cells.
(c)(iii)
Substances pass through the cell membrane to enter the cell.
Topic – 10.1
(a) Symptoms of the disease influenza may include sneezing. Fig. 4.1 shows a sign at a hospital.
Explain why washing your hands after sneezing can help to prevent the spread of disease.
(b) State two ways of preventing the spread of disease through water.
(c) State three ways the body defends itself against disease.
(d) Identify each disease or virus as transmissible or non‑transmissible by drawing a circle around the correct word.
- Human immunodeficiency virus (HIV) – transmissible / non‑transmissible
- coronary heart disease (CHD) – transmissible / non‑transmissible
- scurvy – transmissible / non‑transmissible
▶️ Answer/Explanation
Ans:
(a) Sneezing releases droplets containing pathogens (e.g., viruses or bacteria). Washing hands removes these pathogens, reducing the risk of transmission to others via surfaces or direct contact.
(b) Two effective methods are:
- Boiling water to kill pathogens.
- Chlorination or UV treatment to sterilize water.
(c) The body defends itself through:
- Physical barriers like skin and mucus.
- Chemical defenses such as stomach acid.
- Immune responses like white blood cells and antibodies.
(d) Classification:
- HIV: transmissible (spreads via bodily fluids).
- CHD: non-transmissible (caused by lifestyle/genetics).
- Scurvy: non-transmissible (due to vitamin C deficiency).
Topic – 14.5
(a) A student investigated the conditions needed for the germination of cress seeds. Fig. 5.1 shows the apparatus, conditions used and the results of the investigation.
(i) Identify the letters of the two test‑tubes in Fig. 5.1 that show that oxygen is needed for germination ………… and ………… .
(ii) A gardener wanted to store some cress seeds for a long time before using them. Use the information in Fig. 5.1 to identify the ideal conditions to prevent germination. Tick two boxes
(b) Tropic responses were investigated in two plants, X and Y. The plants were placed in separate boxes for 5 days. Fig. 5.2 shows plants X and Y at the start of the investigation. Both boxes had a hole on one side that let light in. Plant X was kept in the same position. Plant Y was placed on a platform that was continually rotated.
(i) Predict and explain how the shape of plant Y will differ from the shape of plant X after 5 days of growth.
(ii) State the name of the tropic response that would be seen in plant X in Fig. 5.2 after 5 days.
(iii) Suggest and explain the advantage to a plant of tropic responses in shoots.
(c) State the position plants occupy in a food chain.
▶️ Answer/Explanation
Ans:
(a)(i) C ; D / E
Test-tubes C and D/E show that oxygen is needed for germination. In C, seeds are submerged in boiled water (no oxygen), and in D/E, oxygen is absent due to displacement by another gas or vacuum.
(a)(ii) cold ticked ; dry ticked
Cold and dry conditions inhibit germination by slowing metabolic activity and preventing water absorption, respectively.
(b)(i) plant Y would be straight(er) ; all, sides / parts / leaves, of plant Y, receives light
Since Plant Y is rotated, light exposure is even on all sides, preventing directional growth (tropism).
(b)(ii) phototropism
Plant X grows toward the light due to phototropism, a directional response to light.
(b)(iii) receives more light / AW ; for photosynthesis
Tropic responses help shoots maximize light absorption, enhancing photosynthesis and growth.
(c) first trophic level / producer
Plants are producers, forming the base of the food chain by converting sunlight into energy.
Topic – 20.2
(a) Cabbages are crop plants.
Fig. 6.1 shows an area where the forest has been removed to create space for a monoculture of cabbage plants.
(i) Describe reasons for habitat destruction, other than crop production.
(ii) Describe the advantages of growing crops such as cabbages as a large‑scale monoculture.
(b) Habitat destruction can cause species extinction. State two ways that species can be conserved, other than protection of their habitat.
(c) Four islands, A, B, C and D, were surveyed to identify the different types of crop plant monocultures present. The survey identifies the percentage of each type of monoculture on each island. Fig. 6.2 shows the results of the survey.
Identify the island or islands from Fig. 6.2 that: have the greatest number of different types of monocultures ………………………. have the greatest percentage of crop 2 monocultures ………………………. have more than 50% crop 3 monocultures. ………….. and ………….. .
(d) One effect of deforestation and monocultures is a reduction in biodiversity. State what is meant by the term biodiversity.
(e) Crop 3 is a type of tree that can be used for firewood. Suggest how this resource can be managed sustainably.
▶️ Answer/Explanation
Ans:
(a)(i) Habitat destruction occurs due to urbanization, infrastructure development, mining, pollution, or climate change. These activities reduce natural habitats, leading to biodiversity loss.
(a)(ii) Monoculture advantages include higher yield, cost efficiency, easier harvesting, and uniform application of fertilizers/pesticides, making large-scale farming more profitable.
(b) Species conservation methods include captive breeding, seed banks, anti-poaching laws, and reintroduction programs to prevent extinction.
(c) Island A has the most monoculture types. Island A leads in Crop 2. Islands B and D have >50% Crop 3 monocultures.
(d) Biodiversity refers to the variety of species in an ecosystem, crucial for ecological balance and resilience.
(e) Sustainable firewood management involves replanting trees and regulating logging to prevent deforestation.
Final Answers:
(a)(i) Urbanization, mining, pollution, etc. (any three valid reasons).
(a)(ii) Higher yield, cost efficiency, easier harvesting.
(b) Captive breeding, anti-poaching laws.
(c) A ; A ; B and D.
(d) Variety of species in an ecosystem.
(e) Replant trees and regulate logging.
Topic – 7.2
(a) Fig. 7.1 is a diagram of the human digestive system.
State the letter in Fig. 7.1 that identifies:
- the gall bladder
- the organ that secretes salivary amylase
- where egestion occurs
- where most absorption occurs
- where physical digestion occurs
- where the pH is acidic.
(b) The boxes on the left show some examples of nutrients. The boxes on the right show some examples of molecules. Draw lines to link each nutrient to a molecule found in that nutrient. Draw two lines.
(c) State the vitamin deficiency that causes rickets.
(d) Describe the dietary importance of the mineral ions calcium and iron.
(e) Fat, protein, vitamins and mineral ions are all required for a balanced diet. State the names of two other components of a balanced diet.
▶️ Answer/Explanation
Ans:
(a) H (gall bladder), A (salivary amylase secretion), F (egestion), G (absorption), C (physical digestion & acidic pH).
(b) Protein → Amino acids, Fat → Fatty acids & glycerol (as shown in the diagram).
(c) Vitamin D deficiency causes rickets, leading to weak bones.
(d) Calcium strengthens bones/teeth; iron is essential for haemoglobin in red blood cells.
(e) Two other components: Carbohydrates and water/fibre.