Mass transport

Question 1

Why do large organisms need a transport system?

Answer 1

• Diffusion alone is too slow because they have a low SA:V ratio.
• Transport systems deliver oxygen and nutrients efficiently.
• To remove waste products like carbon dioxide and urea.

Always mention SA:V ratio when explaining why transport systems are needed.

Question 2

How does SA:V ratio affect transport?

Answer 2

1. Small organisms (e.g., amoeba) have a high SA:V ratio, so diffusion is sufficient.
2. Large organisms (e.g., mammals) have a low SA:V ratio, making diffusion too slow, so they require a mass transport system.

Saying ‘small organisms have a small SA:V ratio’ is incorrect. They actually have a high SA:V ratio.

Question 3

What are the key features of a mass transport system?

Answer 3

1. A transport medium (e.g., blood) to carry substances.
2. A system of vessels (e.g., arteries, veins) for movement.
3. A pump (heart) to generate pressure.
4. Mechanisms for controlling flow (e.g., valves).

Always mention pressure and control mechanisms when describing a transport system.

Question 4

What is the difference between open and closed circulatory systems?

Answer 4

• Open – Blood flows freely in the body cavity, under low pressure, found in insects.
• Closed – Blood is fully enclosed in vessels, under higher pressure, found in fish and mammals.

Saying ‘insects have no circulatory system’ is incorrect. They have an open circulatory system.

Question 5

What is the difference between single and double circulation?

Answer 5

• Single circulation – Blood passes through the heart once per circuit (e.g., fish).
• Double circulation – Blood passes through the heart twice per circuit (e.g., mammals).

Double circulation maintains high pressure for efficient oxygen delivery.

Question 6

Why do mammals have a double circulatory system?

Answer 6

1. Higher metabolic demand.
2. They need more oxygen for respiration.
3. Maintains high pressure, allowing faster delivery of oxygen and glucose.
4. Prevents oxygen mixing, keeping oxygenated and deoxygenated blood separate.

Saying ‘double circulation makes blood move faster’ is incorrect. It’s about maintaining high pressure.

Question 7

What is the function of the heart?

Answer 7

• The heart is a muscular pump responsible for circulating blood throughout the body.
• It maintains the flow of blood through two circulations: the pulmonary circulation (to the lungs) and the systemic circulation (to the rest of the body).

Mark Scheme Point: “The heart has a right side for pulmonary circulation and a left side for systemic circulation.”

Question 8

What are the heart chambers and their functions?

Answer 8

1. Right Atrium: Receives deoxygenated blood from the vena cava.
2. Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary artery.
3. Left Atrium: Receives oxygenated blood from the pulmonary vein.
4. Left Ventricle: Pumps oxygenated blood to the body via the aorta.

Mark Scheme Point: “The left side of the heart pumps oxygenated blood, while the right side pumps deoxygenated blood.”