8. Transport in Mammals

Question 1

Can a red blood cell carry out active transport?

Answer 1

Yes. Active transport occurs across the cell surface membrane and can be fuelled by ATP produced by anaerobic respiration.

Question 2

Albumin is the most abundant plasma protein. Suggest why it is important that capillary walls should not be permeable to albumin.

Answer 2

• albumin in blood plasma decreases its water potential
• helping to draw water back from tissue fluid into capillaries
• if albumin could diffuse out of capillaries into tissue fluid, more water would accumulate in the tissue fluid (oedema)

Question 3

Explain why it is important that fetal haemoglobin and maternal haemoglobin are different.

Answer 3

• fetus gains oxygen from maternal blood
• across placenta
• partial pressure of oxygen in placenta is low
• maternal Hb releases oxygen
• fetal Hb has higher affinity for oxygen and allows it to pick up the oxygen
• oxygen needed for aerobic respiration

Question 4

After birth, the adult form of Hb gradually replaces the fetal form of Hb. Suggest why this is necessary.

Answer 4

• affinity of fetal Hb would be too high

- would not release oxygen readily enough

Question 5

Explain why the body needs to respond to high altitude by increasing the number of red blood cells. [3m]

Answer 5

• less oxygen in inhaled air
• lower saturation of Hb with oxygen
• Hb has lower affinity for oxygen
• more RBCs so MORE Hb
• compensation

Question 6

Suggest why the property of water to act as a solvent is important in the mammalian transport system. [2m]

Answer 6

• many substances need to be dissolved and transported
• ionic compounds can dissolve
• polar compounds, eg. glucose, can dissolve
• globular proteins, eg. enzymes, can dissolve

Question 7

Describe how the lymphocytes in a person with leukaemia differ from those of a healthy person. [3m]

Answer 7

• lymphocytes are immature
• as no large nuclei
• lack of function for either B- or T-lymphocytes
• difficult to distinguish between lymphocytes and monocytes

Question 8

Outline and explain the events that occur in the heart during ventricular diastole. [4m]

Answer 8

• pressure in ventricles decreases
• semilunar valves close
• blood entering atria
• bicuspid and tricuspid valves open
• atria contract (atrial systole)
• pressure in atria exceeds pressure in ventricles
• so blood enters ventricles from atria

Question 9

Explain how atheroma can lead to a heart attack. [3m]

Answer 9

• atheroma takes place in coronary arteries
• and causes uneven blood flow
• causes thrombus formation by platelets
• decreased blood flow caused by narrowed lumen
• less blood with glucose and O2 reaches heart muscle
• heart attack caused by damage to heart tissues

Question 10

Outline 4 properties of water that make it ideal as the largest component of plasma

Answer 10

1. good solvent - water dissolves polar molecules, ionic compounds
2. cohesion between water molecules - so continuous blood flow
3. high specific heat capacity - helps maintain constant blood temperature
4. high latent heat of vaporisation - in body temp, plasma stays liquid / water does not evaporate

Question 11

Describe the role of carbonic anhydrase in the transport of carbon dioxide. [3m]

Answer 11

1. catalyses the reaction (in RBC) between CO2 and water to form carbonic acid
2. carbonic acid dissociates to form hydrogencarbonate ions
3. very fast reaction
4. maintains steep [ ] gradient for diffusion of CO2 from tissues to blood
5. catalyses reverse reaction in the lungs
6. hydrogencarbonate ions diffuse into the plasma

Question 12

Explain why tissue fluid is more similar to blood plasma than it is to blood. [3m]

Answer 12

• tissue fluid and blood plasma do not have RBC
• RBC are too large to pass through gaps between endothelial cells
• tissue fluid and blood plasma similar viscosity / blood more viscous