CIE iGCSE Co-Ordinated Science B9.1 Circulatory systems Exam Style Questions Paper 4
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B8.3 — Transpiration (Part (a)(i), (a)(ii))
• Topic B8.1 — Xylem and phloem (Part (b)(i))
• Topic B8.4 — Translocation (Part (b)(ii))
• Topic B9.1 — Circulatory systems (Part (c)(i), (c)(ii))
▶️ Answer/Explanation
(a)(i) High wind speed increases the rate of transpiration because:
- Wind removes water vapour from around the leaf.
- This maintains a steep concentration gradient of water vapour between the leaf and the outside air.
- Increased diffusion of water vapour from the stomata occurs.
Transpiration is the loss of water vapour from the leaves. Wind increases the transpiration rate by removing the layer of humid air that builds up around the leaf surface. This maintains a steep concentration gradient between the water vapour inside the leaf (high concentration) and the air outside (low concentration), which increases the rate of diffusion of water vapour out through the stomata.
(a)(ii) Effect on distance: Increases (for 25°C compared to 15°C).
Explanation (any two from):
- Increase in the rate of transpiration.
- Increased rate of water evaporating from the mesophyll cell surfaces.
- Increased rate of diffusion of water vapour out of the leaf through the stomata.
Higher temperature increases the kinetic energy of water molecules, causing them to evaporate more rapidly from the surfaces of mesophyll cells inside the leaf. This increases the concentration of water vapour in the air spaces, leading to a greater diffusion gradient and a faster rate of transpiration, so the air bubble moves a greater distance.
(b)(i) Mineral ions.
Xylem vessels transport water and dissolved mineral ions (such as nitrates, phosphates, and potassium ions) absorbed from the soil by root hair cells, up the plant to the leaves.
(b)(ii) Translocation is the movement of sucrose and amino acids from sources to sinks through phloem vessels.
Translocation is the transport of sucrose (produced during photosynthesis) and amino acids (produced from nitrate ions) in the phloem. Sucrose and amino acids are transported from sources (where they are made or stored, e.g., leaves) to sinks (where they are used or stored, e.g., roots, fruits, growing tips).
(c)(i) In a single circulatory system, blood only goes through the heart once during each complete circuit of the body.
Path: Heart → Gills (for oxygenation) → Body (for delivery of oxygen and nutrients) → Heart.
In fish, blood is pumped from the heart to the gills where it is oxygenated. It then flows directly to the rest of the body where oxygen is delivered and carbon dioxide is picked up, before returning to the heart. This means blood passes through the heart only once per complete circuit.
(c)(ii) Any one from:
- Allows faster metabolism because blood can be pumped at higher pressure to the body.
- Allows different blood pressures in the pulmonary circulation (low pressure to lungs) and systemic circulation (high pressure to body).
- Oxygenated blood and deoxygenated blood are kept separate, making oxygen delivery more efficient.
The double circulation in mammals has two separate circuits: pulmonary circulation (heart to lungs and back) and systemic circulation (heart to body and back). This separation allows blood pressure to be lower in the lungs, preventing damage to delicate capillaries, while maintaining higher pressure for efficient delivery of oxygen and nutrients to the rest of the body, which supports a faster metabolic rate.
Question
Explain the advantages of a double circulation compared to the circulation in a fish.
(i) Tick \((\checkmark)\) one box to identify which statement explains why capillaries have thin walls.
(ii) Fish gills have a good blood supply as they have many capillaries with thin walls. Suggest one other feature that makes the gills a good gas exchange surface.
An \(8\text{ mm}^3\) sample is taken from a patient.
The sample contains \(1.022\times 10^{6}\) platelets.
(i) Calculate the number of platelets per mm³ in the sample.
(ii) Suggest how this number of platelets may affect the patient if they cut themselves.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B9.1 — Circulatory systems (Parts (a) & (b))
• Topic B9.3 — Blood vessels (Part (c)(i))
• Topic B11.1 — Gas exchange in humans (Part (c)(ii))
• Topic B9.4 — Blood (Part (d)(i) & (d)(ii))
▶️ Answer/Explanation
(a) X should be placed on the right-hand side of the circulatory system (the region after the gills).
In fish, blood becomes oxygenated as it passes through the gills. The right side of the diagram shows oxygenated blood flowing from the gills to the organs.
(b) Three advantages of double circulation:
• Blood is circulated more quickly in the mammalian system.
• Higher blood pressure is maintained to supply the body tissues.
• Lower blood pressure is maintained for the lungs, preventing damage to delicate capillaries.
• More effective delivery of oxygen and nutrients to body cells.
• Oxygenated and deoxygenated blood are kept completely separate.
(c)(i) ✓ to allow movement of substances in and out of blood
Thin capillary walls (single cell layer thick) create a short diffusion distance, allowing efficient exchange of oxygen, carbon dioxide, nutrients, and waste products between blood and tissues.
(c)(ii) Large surface area / good ventilation with water.
Gills have many lamellae which increase surface area, and water flows continuously over them maintaining a steep concentration gradient for efficient gas exchange.
(d)(i) Number of platelets per mm³:
\(\frac{1.022 \times 10^6}{8} = 127750\) platelets per mm³
(Alternative: \(1.278 \times 10^5\) platelets per mm³)
(d)(ii) The platelet count is below the healthy range (127750 < 150000).
This may cause:
• Reduced blood clotting ability.
• Increased risk of pathogens entering the wound.
• Increased blood loss from the cut.
• Slower wound healing.