Biology Transport in Mammals

Why do mammals need a transport system?

Mammals are large with a small surface area to volume ratio and high metabolic rates, so diffusion alone is too slow to supply oxygen and nutrients and remove wastes efficiently.

What is meant by a closed circulatory system?

A closed circulatory system is one where blood is contained within vessels and circulates around the body, allowing for efficient transport of oxygen, nutrients, and waste without direct contact with tissues.

What is double circulation?

Blood passes through the heart twice in one complete circuit (pulmonary and systemic circulation).

Name the four chambers of the mammalian heart.

Right atrium, right ventricle, left atrium, left ventricle.

Why is the left ventricle wall thicker than the right?

It must generate higher pressure to pump blood around the entire body.

What is the function of the septum?

To separate oxygenated and deoxygenated blood.

What are atrioventricular (AV) valves?

Valves between atria and ventricles that prevent backflow into atria.

Name the AV valves.

Tricuspid (right) and bicuspid/mitral (left).

What are semilunar valves?

Valves at the base of the aorta and pulmonary artery preventing backflow into ventricles.

What is the role of coronary arteries?

To supply oxygenated blood to heart muscle.

What does myogenic mean?

Heart muscle initiates its own contraction without nervous input.

Why does cardiac muscle have many mitochondria?

To supply ATP for continuous contraction.

What is the role of the sinoatrial node (SAN)?

Acts as the pacemaker and initiates the wave of excitation.

Why is there a delay at the atrioventricular node (AVN)?

To allow ventricles to fill before contracting.

What is the function of the Bundle of His and Purkinje fibres?

To conduct excitation rapidly to the ventricles from the apex upwards.

What is atrial systole?

Contraction of atria pushing blood into ventricles.

What is ventricular systole?

Contraction of ventricles forcing blood into arteries.

What is diastole?

Relaxation of both atria and ventricles.

Why do AV valves close during ventricular systole?

Ventricular pressure becomes higher than atrial pressure.

Why do semilunar valves open during ventricular systole?

Ventricular pressure exceeds arterial pressure.

What causes the second heart sound (“dub”)?

Closure of semilunar valves.

What features adapt arteries to high pressure?

Thick walls, elastic tissue, smooth muscle, narrow lumen.

What is elastic recoil?

Stretching and recoiling of artery walls to maintain blood flow between heartbeats.

What is the function of arterioles?

Control blood flow to tissues via vasoconstriction and vasodilation.

Why are capillary walls one cell thick?

To minimise diffusion distance.

Why do capillaries have narrow lumens?

To slow blood flow and allow efficient exchange.

Why do veins contain valves?

To prevent backflow of low-pressure blood.

What are the main components of blood?

plasma, RBC, WBC, platelets

What is plasma?

Liquid portion of blood containing dissolved substances.

Why do mammalian red blood cells lack a nucleus?

To allow more space for haemoglobin.

Why are red blood cells biconcave?

Increased surface area to volume ratio for oxygen diffusion.

How many oxygen molecules can one haemoglobin carry?

Four

What is cooperative binding?

Binding of one O₂ increases affinity for the next.

Why is the oxygen dissociation curve sigmoid-shaped?

Due to cooperative binding of oxygen to haemoglobin.

What is partial pressure of oxygen (pO₂)?

The pressure exerted by oxygen in a mixture of gases

What is the Bohr effect?

Increased CO₂ lowers haemoglobin’s affinity for oxygen.

Why is the Bohr effect useful?

More oxygen is released to respiring tissues.

Which direction does the dissociation curve shift with high CO₂?

To the right.

How is most CO₂ transported in blood?

As hydrogencarbonate ions (HCO₃⁻) in plasma.

What enzyme converts CO₂ to carbonic acid in RBCs?

Carbonic anhydrase.

What is the chloride shift?

Movement of chloride ions into RBCs as hydrogencarbonate ions leave.

Why does the chloride shift occur?

To maintain electrical neutrality.

How is tissue fluid formed?

By pressure filtration at the arteriole end of capillaries.

What causes fluid to leave capillaries?

High hydrostatic pressure.

What causes fluid to re-enter capillaries?

Osmotic pressure due to plasma proteins.

What happens to excess tissue fluid?

It enters lymphatic vessels and becomes lymph.

State two functions of the lymphatic system.

Return tissue fluid to blood and transport lymphocytes.

What is the role of platelets in clotting?

Form a platelet plug and release clotting factors.

Why is blood clotting important?

Prevents blood loss and entry of pathogens.

How does blood contribute to immunity?

Transports phagocytes, lymphocytes, and antibodies.

How does lymph contribute to immunity?

Carries antigens and lymphocytes to lymph nodes.