The Circulatory System: Edexcel International AS Biology Review

Comprehensive practice questions covering the circulatory system, cardiac cycle, haemoglobin function, and cardiovascular diseases based on Edexcel International AS Biology notes.

What are two reasons large organisms require a mass transport system instead of relying solely on diffusion?

The diffusion distances are too great for substances to reach every cell quickly enough, and large organisms often have high energy requirements.

What is the definition of mass transport?

The bulk movement of gases or liquids in one direction, typically through a system of vessels and tubes.

What characterizes a double circulatory system in mammals?

Blood travels around the body in two separate circuits: the pulmonary circulation and the systemic circulation.

Which blood vessels transport blood away from the heart at high pressure?

Arteries.

How does the endothelium of an artery adapt to cope with high pressure?

It is highly folded, allowing the vessel to expand as blood is pumped through.

What is the function of collagen in the outer wall (tunica adventitia) of an artery?

It is a strong protein that protects the blood vessel from damage caused by over-stretching.

Why do veins contain valves?

To prevent the backflow of blood and ensure it returns to the heart given the low blood pressure.

What is the significance of capillary walls being only one cell thick?

It reduces the diffusion distance for substances like oxygen and carbon dioxide between the blood and body tissues.

In a closed circulatory system, where is the blood contained?

It is always contained within a network of blood vessels.

What is the function of the septum in the human heart?

It is a wall of muscular tissue that separates the left and right sides of the heart to prevent oxygenated and deoxygenated blood from mixing.

Which specific valve separates the right atrium from the right ventricle?

The tricuspid valve (an atrioventricular valve).

What are the two major blood vessels that bring blood into the heart?

The vena cava and the pulmonary vein.

During which stage of the cardiac cycle do the atrioventricular (AV) valves close?

Ventricular systole.

What formula is used to calculate heart rate in beats per minute if the length of one cardiac cycle is known?

$$\text{Heart rate} = (1 \div \text{length of one cycle in seconds}) \times 60$$

How many haem groups are found in a single molecule of haemoglobin?

$4$ haem groups.

What is cooperative binding in the context of haemoglobin?

The conformational change that occurs after the first oxygen molecule binds, making it easier for subsequent oxygen molecules to bind.

In what form is the largest percentage of carbon dioxide transported in the blood?

As hydrogen carbonate ions ($HCO_{3}^{-}$).

What effect does a high partial pressure of carbon dioxide ($pO_{2}$) have on haemoglobin's affinity for oxygen?

It reduces the affinity, causing the oxygen dissociation curve to shift to the right (the Bohr effect).

How does foetal haemoglobin differ from adult haemoglobin on a dissociation curve?

The curve for foetal haemoglobin is shifted to the left because it has a higher affinity for oxygen.

What is the primary cause of atherosclerosis?

Damage to the endothelium of an artery followed by an inflammatory response.

What is an atheroma?

A plaque formed by the accumulation of cholesterol, lipids, macrophages, and platelets under the endothelium.

During blood clotting, which enzyme catalyses the conversion of soluble fibrinogen into insoluble fibrin?

Thrombin.

What is a myocardial infarction?

A heart attack caused when blood flow to the heart muscle is restricted, reducing oxygen delivery and leading to cell death.

What is the term for a blood clot that forms within a blood vessel and obstructs flow?

A thrombus.