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Question 1

Topic: 1.2

(a) Fig. 1.1 is a photograph of an insect. Insects are arthropods.

(i) Arthropods belong to the animal kingdom. State the name of one other kingdom.

(ii) State one feature visible in Fig. 1.1 that is present in insects but not in the other groups of arthropods.

(iii) Complete Table 1.1 by writing:

the names of two groups of arthropods other than insects
one identifying feature for each named group.

(b) (i) Complete the description of an adaptive feature.

An adaptive feature is an …… feature that helps an organism to survive and …… in its environment.

(ii) Fig. 1.2 is a photograph of a leaf insect.

State one adaptive feature visible in Fig. 1.2 and suggest how the adaptive feature helps the animal to survive.

▶️ Answer/Explanation

Solution

(a)(i) Plants / Fungi / Protoctista / Prokaryotes

Explanation: The five kingdoms of living organisms are Animals, Plants, Fungi, Protoctista (protists), and Prokaryotes (bacteria). Any one of these except Animals would be correct here.

(a)(ii) 6 legs / 3 pairs of legs OR 3 main body parts (head, thorax, abdomen) OR wings

Explanation: Insects are distinguished from other arthropods by having exactly 6 legs (3 pairs), three distinct body parts (head, thorax, abdomen), and often wings in adult forms. Other arthropods like arachnids have 8 legs, crustaceans have 10 or more legs, and myriapods have many legs.

(a)(iii)

Alternative answers could include:

Myriapods: many pairs of legs (more than 16 legs)

Explanation: The major arthropod groups besides insects are arachnids (spiders, scorpions), crustaceans (crabs, lobsters), and myriapods (centipedes, millipedes). Each has distinct identifying features.

(b)(i) An adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment.

Explanation: Adaptive features are traits passed down through generations (inherited) that enhance an organism’s survival and reproductive success in its specific environment.

(b)(ii) Feature: Shape/pattern resembles a leaf

Suggestion: This camouflage helps the insect avoid detection by predators by blending in with its leafy environment.

Explanation: The leaf insect’s remarkable resemblance to leaves (including vein-like patterns and leaf-shaped body) is an excellent example of protective mimicry. This adaptation makes it extremely difficult for predators to distinguish the insect from real leaves, significantly increasing its chances of survival.

Question 2

Topic: 2.1

(a) Fig. 2.1 is a labelled diagram of an animal cell.

(i) The boxes on the left show the functions of some of the structures shown in Fig. 2.1. The boxes on the right show the letters of the structures labelled in Fig. 2.1. Draw lines to link each function to the correct letter. Draw four lines.

(ii) State two letters shown in Fig. 2.1 that identify structures which are also found in bacterial cells.

(b) Respiration is a characteristic of living organisms. State three other characteristics of all living organisms.

▶️ Answer/Explanation

Solution

(a)(i)

Explanation: The cytoplasm (A) is the jelly-like substance that contains and supports all other cell organelles. The nucleus (B) controls all cellular activities as it contains the genetic material. The cell membrane (C) is selectively permeable and regulates what enters and leaves the cell. Ribosomes (D) are the sites of protein synthesis where amino acids are assembled into proteins.

(a)(ii) A and C (or D)

Explanation: Bacterial cells, like animal cells, contain cytoplasm (A) and a cell membrane (C). Some bacteria also have ribosomes (D), though bacterial ribosomes are slightly smaller (70S compared to 80S in eukaryotes). The nucleus (B) and other membrane-bound organelles are absent in bacterial cells.

(b) Any three from: movement; sensitivity; growth; reproduction; excretion; nutrition

Detailed Explanation:

Movement: All living organisms show some form of movement, whether it’s locomotion in animals or growth movements in plants.
Sensitivity: Organisms can detect and respond to changes in their environment (stimuli).
Growth: Living things increase in size and complexity through cell division and cell enlargement.
Reproduction: Organisms produce offspring, either sexually or asexually, to continue their species.
Excretion: The removal of toxic waste products of metabolism like carbon dioxide and urea.
Nutrition: All organisms need to take in nutrients to provide energy and materials for growth and repair.

These characteristics, along with respiration, are often remembered by the acronym “MRS GREN” (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition).

Question 3

Topic: 7.4

(a) State the meaning of the term chemical digestion.

(b) Enzymes are involved in chemical digestion. Table 3.1 shows some information about enzymes used for chemical digestion.

(i) Complete Table 3.1.

(ii) State where amylase, lipase and protease are made in the human body.

(ii) State two functions of the acid found in gastric juice.

▶️ Answer/Explanation

Solution

(a) Chemical digestion is the breakdown of large molecules into smaller molecules or the conversion of insoluble substances into soluble ones through enzymatic reactions.

Explanation: This process involves enzymes that catalyze the hydrolysis of complex food molecules (like starch, proteins, and fats) into simpler, absorbable forms (like sugars, amino acids, and fatty acids). It occurs in the mouth, stomach, and small intestine.

(b)(i)

Explanation: Amylase breaks down starch into sugars (e.g., maltose), lipase hydrolyzes fats into fatty acids and glycerol, and protease digests proteins into amino acids.

(b)(ii)

amylase: salivary glands and pancreas

lipase: pancreas

protease: stomach (as pepsin) and pancreas

Explanation: Amylase is secreted in saliva (mouth) and pancreatic juice (small intestine). Lipase is primarily produced by the pancreas. Protease enzymes like pepsin are made in the stomach, while others (trypsin) come from the pancreas.

(c)(i) Hydrochloric acid (HCl)

Explanation: Gastric juice in the stomach contains HCl, which creates an acidic environment (pH ~2) essential for digestion and pathogen control.

(c)(ii)

1. Kills harmful microorganisms/pathogens in food, preventing infections.

2. Provides the optimum pH for pepsin (a protease) to break down proteins effectively.

Explanation: The acidic environment denatures proteins (aiding digestion) and activates pepsinogen into pepsin. It also inhibits bacterial growth, protecting the digestive system.

Question 4

Topic: 9.1

(a) Complete the sentences about the circulatory system.

The heart …… blood around the body.

Blood is carried away from the heart in blood vessels called …… .

Blood is carried to the heart in blood vessels called …… .

Nutrients are delivered to cells by blood vessels called …… .

One-way flow of blood is ensured by the presence of …… .

(b) Fig. 4.1 shows ECG traces of the activity of a student’s heart.

An ECG trace was produced while the student was at rest and while the student was exercising.

The ECG trace shows the number of heart beats in 2.8 seconds.

There were four heart beats in 2.8 seconds at rest.

(i) State the number of heart beats in 2.8 seconds during exercise.

(ii) Calculate the percentage increase in heart beats between at rest and during exercise.

Describe other ways of reducing a person’s risk of developing coronary heart disease.

(d) Fig. 4.2 shows a stethoscope which is used to listen to the heart.

State the cause of the heart sounds detected by the stethoscope.

▶️ Answer/Explanation

Solution

(a)

The heart pumps blood around the body.

Blood is carried away from the heart in blood vessels called arteries.

Blood is carried to the heart in blood vessels called veins.

Nutrients are delivered to cells by blood vessels called capillaries.

One-way flow of blood is ensured by the presence of valves.

Explanation: The circulatory system is a closed system where the heart acts as a pump. Arteries carry oxygenated blood away from the heart (except pulmonary artery), while veins return deoxygenated blood back to the heart (except pulmonary vein). Capillaries are tiny vessels where exchange of nutrients and gases occurs. Valves prevent backflow of blood, especially in veins and between heart chambers.

(b)(i) 6 beats

Explanation: By counting the peaks in the ECG trace during exercise, we can observe there are 6 complete heartbeats in the same 2.8 second period.

(b)(ii) 50%

Explanation: The calculation is done as follows:
At rest: 4 beats in 2.8 seconds
During exercise: 6 beats in 2.8 seconds
Increase = 6 – 4 = 2 beats
Percentage increase = (Increase/Original) × 100 = (2/4) × 100 = 50%

(c) Any three from:
– Maintaining a balanced diet
– Reducing consumption of saturated fats
– Reducing salt intake
– Maintaining healthy body weight
– Avoiding smoking
– Managing stress levels
– Getting adequate sleep

Explanation: Coronary heart disease is often caused by lifestyle factors. A balanced diet helps maintain healthy cholesterol levels. Reducing saturated fats prevents plaque buildup in arteries. Salt reduction helps control blood pressure. Healthy weight reduces strain on the heart. Smoking damages blood vessels. Stress management and proper sleep contribute to overall cardiovascular health.

(d) (Heart) valves closing

Explanation: The characteristic “lub-dub” sounds heard through a stethoscope are caused by the closing of heart valves. The “lub” sound occurs when the atrioventricular valves close at the start of ventricular contraction (systole). The “dub” sound occurs when the semilunar valves close at the end of ventricular contraction.

Question 5

Topic: 12.2

(a) Fig. 5.1 is a diagram of a cell carrying out one type of respiration. The arrows show the direction of movement of the substances involved in respiration in this type of cell.

(i) State the type of respiration shown by Fig. 5.1.

(ii) Identify the substances involved in respiration that are represented by the letters A and B in Fig. 5.1.

(iii) State the process by which oxygen moves into the cell.

(b) State three processes that require energy from respiration.

(c) Some students investigated the effect of temperature on respiration in yeast.
-The students put a beaker containing 20 cm³ of a yeast suspension into a water-bath at different temperatures.
-They collected the gas released by the yeast cells in a gas syringe.
-They recorded the volume of gas released after 15 minutes.

Table 5.1 shows the results.

Using the data in Table 5.1, describe the effect of temperature on the rate of respiration in yeast.

▶️ Answer/Explanation

Solution

(a)(i) Aerobic respiration.

Explanation: The diagram shows oxygen entering the cell and carbon dioxide leaving, which are characteristics of aerobic respiration. This process occurs in the presence of oxygen and is more efficient than anaerobic respiration.

(a)(ii) A: Glucose; B: Water.

Explanation: In aerobic respiration, glucose (A) is broken down to release energy, and water (B) is produced as a byproduct. The chemical equation for aerobic respiration is: \( C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy} \).

(a)(iii) Diffusion.

Explanation: Oxygen moves into the cell by diffusion, which is the passive movement of molecules from an area of higher concentration (outside the cell) to an area of lower concentration (inside the cell). This process does not require energy.

(b) Three processes that require energy from respiration:

Active transport: Movement of molecules against their concentration gradient, such as the absorption of nutrients in the gut.
Muscle contraction: Energy is needed for muscle fibers to contract, enabling movement.
Protein synthesis: Building proteins from amino acids requires energy, especially for growth and repair.

(c) Effect of temperature on the rate of respiration in yeast:

The rate of respiration increases as the temperature rises from 0°C to 40°C, peaking at 40°C. This is because higher temperatures increase the kinetic energy of molecules, leading to more frequent enzyme-substrate collisions. Beyond 40°C, the rate decreases sharply due to enzyme denaturation, which alters their active sites and reduces their efficiency. At very high temperatures (70°C and above), respiration nearly stops as most enzymes are denatured.

Key observations:

Optimum temperature for yeast respiration is around 40°C.
Respiration is very slow at low temperatures (0°C–10°C).
Enzyme activity is destroyed at temperatures above 60°C.

Question 6

Topic: 14.5

A seedling is a seed which has just started to grow a small root and a small shoot.

(a) State the environmental conditions that a seed requires to grow into a seedling.

(b) Fig. 6.1 shows a drawing of a seedling at the start of an investigation into plant growth responses.

The seedling was attached to a piece of card so that the root and shoot were horizontal.

The card and seedling were placed inside a box that excluded all light. The box was placed on the ground for three days.

Fig. 6.1 shows the apparatus at the start of the investigation.

(i) On Fig. 6.2 draw the expected appearance of the root and shoot after three days in the box.

(ii) State the name of the response shown by the root and the shoot in this investigation.

▶️ Answer/Explanation

Solution

(a) Water; oxygen; suitable temperature; space (or any other valid condition).

Explanation: Seeds require specific environmental conditions to germinate and grow into seedlings. Water is essential to activate enzymes that break down stored food in the seed. Oxygen is needed for aerobic respiration to provide energy for growth. A suitable temperature is necessary as it affects enzyme activity – too cold and reactions slow down, too hot and enzymes may denature. Space allows for root and shoot expansion and access to resources.

(b)(i)

Answer for Fig. 6.2

Expected drawing: root pointing down, shoot pointing up

Explanation: After three days in the dark box, the root would grow downward (positive gravitropism) and the shoot would grow upward (negative gravitropism). This occurs because plant roots are positively gravitropic – they grow in the direction of gravity, while shoots are negatively gravitropic – they grow against gravity. This response ensures the root grows into the soil to absorb water and minerals, while the shoot grows upward to reach light for photosynthesis.

(b)(ii) Tropism (or specifically gravitropism/geotropism).

Explanation: The response shown by both the root and shoot is called tropism, which is a growth response to directional external stimuli. In this case, it’s specifically gravitropism (also called geotropism) as the response is to gravity. The root shows positive gravitropism (growing with gravity) while the shoot shows negative gravitropism (growing against gravity). This differential growth response is controlled by the distribution of auxins (plant hormones) in response to gravity.

Question 7

Topic: 16.4

(a) Fig. 7.1 is a diagram of part of the male reproductive system.

Complete Table 7.1 by writing in the letter of the structure identified in Fig. 7.1 that carries out each function.

Each letter can be used once, more than once or not at all.

(b) State the name of the hormone that controls development of secondary sexual characteristics in females.

Identify the cells and the process labelled in Fig. 7.2.

▶️ Answer/Explanation

Solution

(a)

Explanation: The male reproductive system has specialized structures with specific functions. The vas deferens (D) carries sperm only. The scrotum (B) contains and protects the testes while keeping them at the right temperature. The seminal vesicle (E) produces fluid that helps sperm swim. The testes (C) have dual functions – producing both sperm and testosterone, the male sex hormone.

(b) Oestrogen

Explanation: In females, oestrogen is the primary hormone responsible for the development of secondary sexual characteristics during puberty. These include breast development, widening of hips, and the growth of pubic and underarm hair. Oestrogen also regulates the menstrual cycle and prepares the body for reproduction.

(c)

cell A: egg (cell)/ovum

cell B: sperm (cell)

process C: fertilisation

cell D: zygote

Explanation: The diagram shows the process of human fertilization. Cell A is the female gamete (egg or ovum), which is large and contains nutrients for the developing embryo. Cell B is the male gamete (sperm), which is specialized for motility to reach the egg. Process C represents fertilization, where the sperm nucleus fuses with the egg nucleus. The result is cell D, the zygote, which is the first cell of the new individual containing genetic material from both parents.

Question 8

Topic: 19.3

(a) State one source of methane gas.

(b) Fig. 8.1 is a graph showing the estimated change in methane concentration in the atmosphere over a thousand-year period.

Complete the sentences to describe the changes in methane concentration shown in Fig. 8.1.

The general trend is for methane concentration to ……

The concentration of methane was the same in the year 1000 and in the year ……

Over the thousand-year period shown in the graph, the concentration of methane has increased by …… parts per billion.

(ii) State two effects on the environment of increasing carbon dioxide and methane concentrations in the atmosphere.

(iii) State one natural process that removes carbon dioxide from the atmosphere.

(d) Yeast can be used to produce ethanol for use as a biofuel.

(i) State the name of the process used by yeast to produce ethanol.

(ii) Large amounts of ethanol are required as a biofuel.

Maize is a food plant that is also used to produce ethanol as a biofuel.

Maize grown for ethanol production is grown in large-scale monocultures.

Describe the disadvantages of growing crop plants such as maize in a large-scale monoculture.

▶️ Answer/Explanation

Solution

(a) Rice fields / wetlands / cattle / livestock / melting permafrost / termites / wildfires / burning fossil fuels / natural gas / fracking

Explanation: Methane is produced naturally through various biological processes like decomposition in wetlands (rice fields), digestion in ruminant animals (cattle), and by termites. Human activities like fossil fuel extraction (natural gas, fracking) and burning also release methane.

(b)

The general trend is for methane concentration to increase.

The concentration of methane was the same in the year 1000 and in the year 1600.

Over the thousand-year period shown in the graph, the concentration of methane has increased by 1100 parts per billion.

Explanation: The graph shows a general upward trend in methane concentration over time. There are periods where concentrations plateau (like around 1600 AD) before continuing to rise. The difference between the starting and ending concentrations is approximately 1100 ppb.

(c)(i) Combustion / decomposition / decay

Explanation: Besides respiration, carbon dioxide is released when organic matter burns (combustion) or when it decomposes through the action of microorganisms.

(c)(ii)

1 Enhanced greenhouse effect

2 Climate change / global warming / sea level rise / extreme weather events

Explanation: These gases trap heat in the atmosphere, leading to the greenhouse effect. Increased concentrations intensify this effect, causing global temperatures to rise (global warming), which in turn leads to climate change, melting ice caps, rising sea levels, and more frequent extreme weather events.

(c)(iii) Photosynthesis

Explanation: Plants and other photosynthetic organisms naturally remove CO₂ from the atmosphere during photosynthesis, converting it into oxygen and organic compounds.

(d)(i) Anaerobic respiration / fermentation

Explanation: Yeast produces ethanol through fermentation, a type of anaerobic respiration where sugars are broken down without oxygen, yielding ethanol and carbon dioxide as byproducts.

(d)(ii)

Reduces soil nutrients / requires more fertilizers – Monocultures deplete specific nutrients from the soil, requiring artificial fertilizers.

Encourages pests / requires more pesticides – Large areas of single crops attract specific pests, leading to increased pesticide use.

Increases soil erosion / water pollution – Lack of crop diversity makes soil more vulnerable to erosion, and fertilizer/pesticide runoff contaminates water.

Reduces biodiversity – Monocultures create ecological deserts that don’t support diverse wildlife.

Competes with food production – Land used for biofuel crops isn’t available for growing food, potentially raising food prices.

Explanation: Large-scale monoculture farming for biofuels has multiple environmental drawbacks. The lack of crop diversity makes the system ecologically unstable, requiring more chemical inputs (fertilizers, pesticides) which can pollute waterways. The practice also reduces habitats for wildlife and can contribute to deforestation when new land is cleared for cultivation.

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