Topic: 2.1 (Cell Structure)
Fig. 1.1 shows a diagram of an animal cell and a bacterial cell.
(a) Complete Table 1.1 by identifying the structures labelled B to J in Fig. 1.1.
Some structures may not be present in both cells.
One row has been completed for you.
(b) State the function of mitochondria.
(c) Egg cells and sperm cells are examples of specialised animal cells.
Place ticks (✓) in Table 1.2 to show the correct adaptive feature for each type of cell.
▶️ Answer/Explanation
(a)
Explanation: The labels B-J are identified based on their structures. B is the cell membrane (present in both), C is the cytoplasm (both), D is the ribosome (both), E is the nucleus (animal cell only), F is the mitochondrion (animal cell only), G is the plasmid (bacterial cell only), H is the flagellum (bacterial cell only), I is the cell wall (bacterial cell only), and J is the capsule (bacterial cell only).
(b) Aerobic respiration.
Explanation: Mitochondria are the powerhouse of the cell, generating ATP through aerobic respiration. This process involves breaking down glucose in the presence of oxygen to release energy.
(c)
Explanation: Egg cells are large with stored food (✓ in row 1), while sperm cells have a tail for motility (✓ in row 3). The other features are either not applicable or incorrect for these specialised cells.
Topic: 19.2
(a) Topic- 19.2 (food web)
(b) Topic- 19.2 (food web)
(d) Topic- 18.3 (selection)
Fig. 2.1 shows part of a food web for a coral reef. Algae and plankton are producers.
(a) Using the information in Fig. 2.1, identify:
- an organism that feeds at the third trophic level,
- a herbivore,
- a carnivore,
- an organism that is a primary consumer and a secondary consumer.
(b) (i) State what the arrows in Fig. 2.1 represent.
(ii) Using the information in Fig. 2.1, construct a food chain containing five organisms. Do not draw the organisms.
(iii) State the name of the process used by some producers to convert energy from light into chemical energy.
(iv) State the name of the type of organism that gets its energy from dead or waste organic material.
(c) The large fish in the food web is the coral grouper, Cephalopholis miniata.
Fig. 2.2 is a photograph of a coral grouper on a coral reef. Coral groupers are a popular food fish for humans.
Overharvesting of the large fish would cause the turtle population to decrease.
Using the information in Fig. 2.1, explain why the turtle population would decrease.
(d) Coral groupers developed over time from a species of fish with very few spots on their bodies.
Complete the sentences to explain how coral groupers developed.
The fish species with few spots had genetic variation in their population.
When these fish ………………………………………….., some of the offspring were born with more spots than others.
Fish with more spots were better adapted to the ………….. because predators were less likely to see them.
Fish with more spots had a greater chance of passing on the ………….. for more spots to the next generation.
This process is called ……………. selection.
▶️ Answer/Explanation
(a)
Third trophic level: turtles / large fish / sea urchins / sharks / starfish
Herbivore: sea cucumbers / small fish / sea urchins
Carnivore: sea urchins / turtles / large fish / starfish / sharks
Primary & secondary consumer: sea urchin
(b)
(i) The arrows represent energy transfer/flow.
(ii) Example food chain: algae/plankton → small fish → starfish → large fish → shark
(iii) The process is photosynthesis.
(iv) Organisms that get energy from dead matter are decomposers.
(c)
Overharvesting large fish reduces their population, forcing sharks to eat more turtles. Additionally, fewer large fish mean more small fish survive, leading to overgrazing of algae. This reduces food for sea cucumbers, which turtles depend on, causing their population to decline.
(d)
When these fish reproduced, some offspring had more spots. Fish with more spots were better adapted to the environment/coral reef as predators couldn’t see them easily. They passed on the alleles for more spots, leading to natural selection.
Topic: 6.2
(a) Topic- 6.2 (leaf structure)
(b) Topic- 6.2 (leaf structure)
(c) Topic- 6.2 (leaf structure)
Fig. 3.1 shows a photograph of some leaves on a tree.
(a) State two features of the leaves, visible in Fig. 3.1, that are adaptations for photosynthesis.
(b) Fig. 3.2 is a diagram of part of a cross-section of a leaf.
(i) Explain how the parts of the leaf labelled A, B, C and D in Fig. 3.2 adapt the leaf for gas exchange during photosynthesis.
(ii) State the name of the mineral ion that plants need to make chlorophyll.
(c) Complete the sentences about transport in plants.
Leaves contain ………….. bundles.
The xylem in the bundles provides plants with support and transports water and ………… from the …………. to the leaves.
Phloem in the bundles transports ………….. and amino acids.
▶️ Answer/Explanation
(a) Any two from:
• Large surface area (to maximize light absorption).
• Thin structure (to allow efficient gas exchange and light penetration).
• Presence of chlorophyll (visible as green color, essential for photosynthesis).
(b)(i) Explanations for parts A, B, C, D:
• A (Spongy mesophyll): Loosely packed cells create air spaces for gas diffusion.
• B (Stomata): Openings allow CO2 to enter and O2 to exit.
• C (Guard cells): Regulate stomatal opening to control gas exchange.
• D (Air space): Facilitates movement of gases within the leaf.
(b)(ii) Mineral ion for chlorophyll:
Magnesium (Mg2+), as it is a central component of the chlorophyll molecule.
(c) Transport in plants:
Leaves contain vascular bundles.
The xylem transports water and minerals from the roots to the leaves.
Phloem transports sucrose and amino acids.
Topic: 16.4
(a) Topic- 16.5 (male reproductive system)
(b) Topic- 16.5 (male reproductive system)
Fig. 4.1 is a diagram of part of the human male reproductive system.
(a) Identify the letter in Fig. 4.1 for the structure that:
- produces sperm,
- places sperm into the vagina,
- carries urine out of the body,
- holds the testes outside the body.
(b) Scientists investigated the link between testis size and length of sperm in bird species. Fig. 4.2 shows the results.
Using the information shown in Fig. 4.2:
(i) Describe how the length of the sperm changes as the testis size increases.
(ii) Calculate the difference in length between the longest sperm and the shortest sperm.
(iii) State the testis size that has the longest sperm.
▶️ Answer/Explanation
(a)
Ans: U; S/T; T; R
Explanation: In the male reproductive system, the testes (U) produce sperm, the penis (S/T) places sperm into the vagina, the urethra (T) carries urine out of the body, and the scrotum (R) holds the testes outside the body.
(b)
(i) Ans: It increases and then decreases.
Explanation: The graph shows that sperm length rises as testis size increases up to a certain point (6 arbitrary units) and then declines.
(ii) Ans: 58 µm
Explanation: The longest sperm is ~90 µm (at testis size 6), and the shortest is ~32 µm (at testis size 1). The difference is \(90 – 32 = 58\) µm.
(iii) Ans: 6 arbitrary units
Explanation: The peak sperm length occurs when the testis size is 6 arbitrary units, as seen in Fig. 4.2.
Topic: 11.1
(a) Topic- 11.1 (gaseous exchange in humans)
(b) Topic- 11.1 (gaseous exchange in humans)
(c) Topic- 13.1 (excretion in humans)
Fig. 5.1 shows part of the human gas exchange system.
(a) Identify the structures labelled F and G on Fig. 5.1.
(b) Write the words in the correct order in the boxes to show the structures inspired gases move through to get from outside the body to the blood.
alveoli bronchiole bronchus trachea
(c) The composition of air changes between inspiration and expiration.
(i) Complete the table about how expired air differs from inspired air. Choose the word or phrase from the list.
Each word or phrase may be used once, more than once or not at all.
higher lower the same
(ii) State the name of the substance used to test for the presence of carbon dioxide gas.
(d) The lungs excrete waste gases.
(i) State the name of one other organ that excretes waste substances.
(ii) Circle three other substances that humans excrete.
amino acids mucus glycerol starch haemoglobin urea ions water
▶️ Answer/Explanation
(a)
F: larynx (voice box) ;
G: capillary (tiny blood vessel where gas exchange occurs) ;
(b)
Inspired air travels from the trachea → bronchus → bronchiole → alveoli, where oxygen diffuses into the blood.
(c)(i)
Carbon dioxide: higher (produced as a waste product of respiration) ;
Oxygen: lower (used up in cellular respiration) ;
Water vapour: higher (added during gas exchange in the lungs) ;
(c)(ii)
Limewater turns cloudy in the presence of carbon dioxide.
(d)(i)
Kidney (filters blood to remove urea and excess ions/water).
(d)(ii)
Circled substances: urea (nitrogenous waste), ions (excess salts), water (maintains balance).
Topic: 18.1
(a) Topic- 18.1 (variation)
(b) Topic- 18.1 (variation)
(a) (i) State the meaning of the term variation.
(ii) Table 6.1 shows some statements about variation.
Place ticks (✓) in the boxes to show which statements describe continuous and
discontinuous variation.
Place one tick in each row.
(iii) Fig. 6.1 shows graphs of two types of variation.
On Fig. 6.1, state an example of a phenotype for each type of variation shown.
(b) Complete the statements about mutation.
Mutation is a ………… change in which new …………. are formed.
The rate of mutation is increased by some chemicals and by ……….. radiation.
▶️ Answer/Explanation
(a)(i) Variation refers to the differences between individuals of the same species. These differences can be due to genetic or environmental factors.
(a)(ii) 
(a)(iii) The top graph (discontinuous variation) represents traits like blood groups (A, B, AB, O) or seed shape in peas, which have distinct categories. The bottom graph (continuous variation) represents traits like body length or mass, which show a range of values.
(b) Mutation is a genetic change in which new alleles are formed. The rate of mutation is increased by some chemicals and by ionising radiation.
(a) Topic- 20.2 (Habitat destruction)
(b) Topic- 20.2 (Habitat destruction)
(c) Topic- 20.3 (pollution)
Fig. 7.1 shows how some uses of land have changed from the year 1500 to the year 2000 in one country.
(a) Using the data in Fig. 7.1:
(i) Identify the years when there was the largest increase in the percentage of land used for farming.
(ii) State the trend for the percentage of land used for housing.
(iii) State the year when the percentage of land used for forests and wild plants was equal to the percentage of land used for farming.
(b) Deforestation is one of the consequences of using land for farming.
Outline the undesirable effects of deforestation.
(c) State one way humans can damage aquatic environments.
▶️ Answer/Explanation
(a) (i) From 1800 to 1900
The largest increase in farming land occurs between these years, as seen in the steepest rise in the graph.
(a) (ii) The percentage of land used for housing increases.
The graph shows a consistent upward trend in housing land use over time.
(a) (iii) 1970
The graph intersects at this year, indicating equal percentages for forests/wild plants and farming.
(b) Undesirable effects of deforestation include:
– Loss of biodiversity and habitat destruction.
– Soil erosion and increased flooding.
– Higher carbon dioxide levels in the atmosphere.
(c) One way humans damage aquatic environments:
– Pollution (e.g., sewage, plastics) or overharvesting of aquatic species.
Topic: 12.3 (Anaerobic Respiration) & 21.2 (Biotechnology)
(a) Yeast can respire anaerobically.
The box on the left shows the beginning of a sentence. The boxes on the right show some sentence endings. Draw three straight lines from the box on the left to the boxes on the right to make three correct sentences.
(b) State two ways anaerobic respiration in yeast is used in biotechnology.
(c) A student investigated the effect of different glucose solution concentrations on the volume of gas produced by yeast. The results are shown in Table 8.1.
The rate of gas production can be calculated using the formula:
\( rate = \frac{1}{time} \)
Calculate the rate of gas production for the glucose solution concentration of 0.4 mol per dm3. Give your answer to two decimal places.
▶️ Answer/Explanation
(a) Anaerobic respiration in yeast is linked to:
- Breaks down nutrient molecules.
- Is a chemical reaction.
- Releases less energy than aerobic respiration.
(b) Two uses of anaerobic respiration in yeast (Biotechnology):
- Bread making (fermentation causes dough to rise).
- Production of ethanol/alcohol (used in biofuels and beverages).
(c) Calculation of gas production rate:
From Table 8.1, for 0.4 mol/dm3, time = 50 seconds.
Using the formula \( rate = \frac{1}{time} \),
\( rate = \frac{1}{50} = 0.02 \, cm^{3} \) per second.
Final Answer: 0.02 \( cm^{3} \) per s