Biology questions involving diagrams of a plant cell, human tooth, and human heart, with questions on cell parts, photosynthesis, cell differences, tooth anatomy, and heart structures.

Here are the answers to your Biology questions:

Section A

1. The diagram below shows a plant cell.

a) Name the parts labeled A, B, C and D.

• A: Cell wall
• B: Cell membrane
• C: Vacuole
• D: Chloroplast

b) State the function of the part labeled D.
The chloroplast (D) is the site of photosynthesis, where light energy is converted into chemical energy in the form of glucose.

c) Give two differences between the cell shown above and an animal cell.

• The plant cell has a cell wall, which is absent in animal cells.
• The plant cell has chloroplasts, which are absent in animal cells.
• The plant cell has a large, central vacuole, whereas animal cells have small, temporary vacuoles or none.

2. The diagram below shows a human tooth.

a) Name the type of tooth shown above.
Molar

b) Name the parts labeled E, F and G.

• E: Enamel
• F: Dentine
• G: Pulp cavity

c) State the function of the tooth shown above.
Molars are adapted for grinding and crushing food.

3. The diagram below shows a human heart.

a) Name the parts labeled H, I, J and K.

• H: Aorta
• I: Pulmonary artery
• J: Right atrium
• K: Right ventricle

b) State the function of the part labeled H.
The aorta (H) carries oxygenated blood from the left ventricle to all parts of the body.

c) Name the blood vessel that carries blood from the lungs to the heart.
Pulmonary vein

4. The diagram below shows a section through a flower.

a) Name the parts labeled L, M, N and P.

• L: Anther
• M: Filament
• N: Stigma
• P: Ovule

b) State the function of the part labeled P.
The ovule (P) contains the female gamete (egg cell) and develops into a seed after fertilization.

c) Name the agent of pollination for the flower shown above.
Insect (based on the visible structure of prominent anthers and stigma, suggesting adaptations for attracting insects).

5. The diagram below shows a simple reflex arc.

a) Name the parts labeled Q, R, S and T.

• Q: Sensory neuron
• R: Relay neuron (Interneuron)
• S: Motor neuron
• T: Effector (Muscle/Gland)

b) State the function of the part labeled R.
The relay neuron (R) connects the sensory neuron to the motor neuron within the central nervous system, allowing for the transmission of the nerve impulse.

c) Give one example of a reflex action.
Knee-jerk reflex (or blinking, withdrawal from a hot object).

Section B

6. The table below shows the results of an experiment to investigate the effect of temperature on the rate of enzyme activity.

a) Plot a graph of the rate of enzyme activity against temperature on the grid provided.
To plot the graph:

• Draw a horizontal axis (x-axis) for Temperature (°C) and a vertical axis (y-axis) for Rate of enzyme activity (arbitrary units).
• Label the axes clearly and choose appropriate scales.
• Plot each data point from the table.
• Draw a smooth curve connecting the plotted points. The curve should rise from 0°C, peak around 40°C, and then fall back to 0 at 70°C.

b) From your graph, determine the optimum temperature for the enzyme activity.
The optimum temperature is the temperature at which the enzyme activity is highest.
From the table, the highest activity (30 arbitrary units) occurs at 40°C.
Optimum temperature: $\boxed{\text{40°C}}$

c) Explain why the enzyme activity is zero at 0°C and 70°C.

• At 0°C, the enzyme molecules have very low kinetic energy, leading to infrequent collisions with the substrate and thus no or very low enzyme activity. The enzyme is inactive but not permanently damaged.
• At 70°C, the high temperature causes the enzyme's three-dimensional structure to break down, particularly the active site. This process is called denaturation, which permanently alters the enzyme and prevents it from binding to the substrate, resulting in zero activity.

d) Name two factors other than temperature that affect enzyme activity.

• pH
• Substrate concentration
• Enzyme concentration
• Presence of inhibitors or activators

7. a) Describe the process of gaseous exchange in humans.
Gaseous exchange in humans occurs in the alveoli of the lungs. Oxygen from inhaled air, which is at a higher partial pressure in the alveoli, diffuses across the thin alveolar and capillary walls into the blood. Simultaneously, carbon dioxide, which is at a higher partial pressure in the blood arriving from the body tissues, diffuses from the blood into the alveoli to be exhaled. This movement of gases is driven by diffusion gradients.

b) Explain how the human lung is adapted for gaseous exchange.

• Large surface area: The lungs contain millions of tiny air sacs called alveoli, providing an enormous surface area (approximately 70-100 square meters) for efficient gas exchange.
• Thin walls: The walls of the alveoli and the surrounding capillaries are extremely thin (one cell thick), minimizing the diffusion distance for gases.
• Rich blood supply: Each alveolus is surrounded by a dense network of capillaries, ensuring a constant supply of deoxygenated blood and efficient removal of oxygenated blood, maintaining steep concentration gradients.
• Moist surface: The inner surface of the alveoli is covered by a thin layer of moisture, allowing oxygen to dissolve before diffusing across the membrane.
• Ventilation: Breathing movements continuously refresh the air in the alveoli, maintaining a high oxygen concentration and a low carbon dioxide concentration, thus sustaining the diffusion gradients.

8. a) Describe the process of photosynthesis.
Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, stored in organic compounds like glucose. This process primarily occurs in the chloroplasts, using chlorophyll to capture light. It involves two main stages:

1. Light-dependent reactions: Light energy is absorbed by chlorophyll, splitting water molecules (photolysis) to release oxygen, electrons, and protons. This energy is used to produce ATP and NADPH.
2. Light-independent reactions (Calvin cycle): Carbon dioxide from the atmosphere is fixed and, using the ATP and NADPH produced in the light reactions, is converted into glucose. The overall equation for photosynthesis is:

$$6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Light Energy} \xrightarrow{\text{Chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$$

b) Explain the importance of photosynthesis to living organisms.

• Food production: Photosynthesis is the primary source of organic food (glucose) for almost all living organisms. Plants, as producers, form the base of nearly all food chains, directly feeding herbivores and indirectly feeding carnivores and omnivores.
• Oxygen production: It releases oxygen as a byproduct into the atmosphere. This oxygen is essential for aerobic respiration in most living organisms, including humans and animals, allowing them to release energy from food.
• Carbon dioxide regulation: Photosynthesis removes carbon dioxide from the atmosphere, helping to regulate Earth's climate and mitigate the greenhouse effect.
• Energy source: The chemical energy stored in photosynthetic products (like fossil fuels formed from ancient plants) is a major energy source for human activities.