Mass transport in animals Flashcards – AQA A-Level Biology - (7402)

What is the quaternary structure of haemoglobin, and how does it bind oxygen?

It has four polypeptide subunits, each with a haem group that reversibly binds one oxygen molecule.

What role does haemoglobin in red blood cells play?

It transports oxygen in the blood.

How does oxygen partial pressure affect oxygen loading and unloading by haemoglobin?

Oxygen loads where partial pressure is high and unloads where it is lower.

What relationship does an oxyhaemoglobin dissociation curve show?

The relationship between oxygen partial pressure and the percentage saturation of haemoglobin with oxygen.

Why is the oxyhaemoglobin dissociation curve sigmoid?

Cooperative binding: the first oxygen molecules to bind change haemoglobin’s shape, making subsequent oxygen molecules easier to bind.

How does carbon dioxide concentration affect haemoglobin’s affinity for oxygen in the Bohr effect?

Higher carbon dioxide concentration reduces haemoglobin’s oxygen affinity; lower concentration increases it.

How does carbon dioxide concentration affect the position of the oxyhaemoglobin dissociation curve?

Higher carbon dioxide shifts the curve right; lower carbon dioxide shifts it left.

At a given oxygen partial pressure, how does increased carbon dioxide concentration affect haemoglobin saturation?

Haemoglobin is less saturated with oxygen.

How does a high carbon dioxide concentration in tissues affect oxygen unloading from haemoglobin?

It promotes oxygen unloading.

At the same oxygen partial pressure, how does haemoglobin oxygen affinity relate to saturation?

Higher affinity means greater saturation; lower affinity means lower saturation.

How does haemoglobin oxygen affinity relate to the position of its oxygen dissociation curve?

Higher affinity shifts the curve left; lower affinity shifts it right.

How can differences in haemoglobin oxygen affinity suit an animal’s environment?

They affect how readily oxygen is loaded and unloaded.

What does it mean that mammals have a double circulation?

Blood passes through the heart twice in a complete circuit.

How do the pulmonary and systemic circulations differ in their routes?

Pulmonary: heart → lungs → heart.
Systemic: heart → rest of the body → heart.

Which vessels carry blood between the heart and lungs, and in which direction does each carry it?

The pulmonary artery carries blood from the heart to the lungs; pulmonary veins return it to the heart.

Which vessels carry blood between the heart and the body, and in which direction does each carry it?

The aorta carries blood from the heart to the body; the venae cavae return it to the heart.

What are the directions of blood flow in the renal arteries and renal veins?

Renal arteries carry blood to the kidneys; renal veins carry it away.

What do the coronary arteries supply?

The heart muscle itself.

What are the four chambers of the human heart, and what is the role of each type?

The right and left atria receive blood; the right and left ventricles pump blood out.

What is the role of the heart's septum?

It separates the right and left sides, limiting mixing between them.

Where are the two types of heart valves located?

Atrioventricular valves lie between the atria and ventricles; semilunar valves lie at the exits from the ventricles.

Why do the ventricles have thicker muscular walls than the atria?

The ventricles pump blood out of the heart.

Why does the left ventricle have a particularly thick wall?

It pumps blood around the systemic circulation.

What is the cardiac cycle?

The repeating sequence of heart contraction and relaxation.

What happens to the heart muscle and blood in the chambers during diastole?

The heart muscle relaxes, and blood fills the chambers.

What completes ventricular filling during the cardiac cycle?

Atrial contraction.

Why do the atrioventricular valves close during ventricular contraction?

Ventricular contraction raises ventricular pressure, closing the valves.

When do the semilunar valves open, and what follows?

When ventricular pressure exceeds pressure in the arteries leaving the heart, the valves open and blood is ejected.

Why do the semilunar valves close as the ventricles relax?

Ventricular pressure falls below arterial pressure.

When do the atrioventricular valves open as the ventricles relax?

When atrial pressure exceeds ventricular pressure.

What flow pattern is maintained by pressure-driven movement of the heart valves?

One-way flow of blood.

How does ventricular volume change during filling and ejection?

It rises during filling and falls during ejection.

What are arterioles?

Small branches of arteries that lead towards capillary beds.

How can arterioles change the width of their lumen?

Smooth muscle in their walls contracts or relaxes, narrowing or widening the lumen.

How do changes in arteriole lumen width help regulate blood delivery to capillary beds?

They alter resistance to blood flow, helping regulate how much blood reaches particular capillary beds.

In which direction do veins carry blood?

Towards the heart.

What is the pressure of blood in veins?

Relatively low.

How do vein walls differ from artery walls?

Vein walls are thinner and contain less muscle and elastic tissue.

How does the width of a vein’s lumen affect resistance to blood flow?

Its relatively wide lumen offers low resistance to flow.

What is the function of valves in veins?

They prevent backflow of blood.

What role do surrounding skeletal muscles play in venous blood flow?

Their contraction helps move blood towards the heart.

What are capillary beds, and how do they position blood relative to body cells?

They are extensive networks of capillaries that bring blood close to body cells.

How does capillary wall structure support diffusion between blood and tissues?

The wall is one layer of endothelial cells thick, providing a short diffusion distance.

How do narrow lumens and extensive branching support capillary exchange?

They help provide a large exchange surface and allow time for exchange.

Where do substances move during capillary exchange?

Between the blood and surrounding tissue, across capillary walls.

What is the role of tissue fluid around body cells?

It provides a medium for exchange between cells and blood.

How does tissue fluid form at the arterial end of a capillary?

Blood hydrostatic pressure forces water and small dissolved substances out through the capillary wall.

Which blood components remain in the capillary during tissue fluid formation?

Blood cells and most plasma proteins.

How does blood hydrostatic pressure change along a capillary?

It falls as blood moves along the capillary.

Why does water tend to return from tissue fluid to the blood?

Plasma proteins contribute to a lower water potential in the capillary.

What happens to excess tissue fluid?

It enters lymphatic vessels and is eventually returned to the bloodstream.