A* Notes

Question 1

Explain an advantage of the Bohr effect. (3)

Answer 1

1) More dissociation of oxygen.
2) Faster aerobic respiration.
3) More ATP produced.

Question 2

Explain the effect of carbon dioxide concentration on the dissociation of oxyhaemoglobin. (4)

Answer 2

1) Increasing blood carbon dioxide e.g. due to increased rate of respiration.
2) Lowers blood pH (more acidic)
3) Reducing Haemoglobin’s affinity for oxygen as tertiary structure changes shape.
4) So faster unloading of oxygen to respiring cells.

Question 3

Describe the structure of Haemoglobin. (3)

Answer 3

1) Quaternary structure protein.
2) Made up of 4 polypeptide chains.
3) Each chain contains a haem group which contains a ferrous ion.

Question 4

Describe the unloading of oxygen. (5)

Answer 4

1) At low partial pressures of oxygen.
2) e.g. respiring tissues.
3) Haemoglobin has a low affinity for oxygen.
4) So oxygen readily unloads with haemoglobin.
5) So percent saturation of haemoglobin with oxygen is low.

Question 5

Describe the loading of oxygen. (5)

Answer 5

1) At high partial pressures of oxygen.
2) e.g. gas exchange surfaces.
3) Haemoglobin has a high affinity for oxygen.
4) Oxygen readily loads with haemoglobin.
5) So percent saturation of haemoglobin with oxygen is high.

Question 6

Explain how the co-operative nature of oxygen binding results in an S shaped oxyhaemoglobin dissociation curve. (2)

Answer 6

1) Binding of the first oxygen changes quaternary structure of haemoglobin.
2) This uncovers haem group binding sites making further binding of oxygen easier.

Question 7

Explain why different types of haemoglobin can have different oxygen transport properties. (3)

Answer 7

1) The polypeptide chains are made with different amino acid sequences.
2) This results in a different tertiary structure.
3) So they have different affinities for oxygen.

Question 8

Describe what occurs when the oxyhaemoglobin dissociation curve shifts to the left. (4)

Answer 8

1) Haemoglobin has a higher affinity for oxygen.
2) More oxygen associates with haemoglobin more readily.
3) At gas exchange surfaces where pO2 is higher.
4) e.g. organisms in low oxygen environments such as high altitudes or foetuses.

Question 9

Describe what occurs when the oxyhaemoglobin dissociation curve shifts to the right. (3)

Answer 9

1) Haemoglobin has a lower affinity for oxygen.
2) More oxygen dissociates with haemoglobin more readily.
3) At respiring tissues where oxygen is needed.

Question 10

Describe atrial systole. (5)

Answer 10

1) Atria contract.
2) Volume decreases and pressure increases.
3) AV valves open when pressure in atria exceeds pressure in ventricles.
4) Semi lunar valves remain shut since pressure in arteries exceeds pressure in ventricles.
5) So blood is pushed into the ventricles.

Question 11

Describe ventricular systole. (5)

Answer 11

1) Ventricles contract.
2) Volume decreases and pressure increases.
3) AV valves shut since pressure in ventricles exceeds pressure in atria.
4) Semi lunar valves open since pressure in ventricles exceeds pressure in arteries.
5) So blood is pushed out of the heart through the arteries.

Question 12

Describe diastole. (5)

Answer 12

1) Atria and ventricles relax.
2) Volume increases and pressure decreases.
3) Semi lunar valves remain shut since pressure in arteries exceeds pressure in ventricles.
4) Atrioventricular valves remain open since pressure in atria exceeds pressure in ventricles.
5) So blood fills the atria via veins and flows passively to ventricles.

Question 13

Explain how the structure of the arteries relate to the function. (5)

Answer 13

1) Narrow lumen to maintain high blood pressure.
2) Thick wall to withstand high blood pressures.
3) Thick smooth muscle tissue to withstand blood flow.
4) Thick elastic tissue to maintain high pressure.
5) Smooth endothelium to reduce friction.

Question 14

Explain how the structure of the arterioles relate to the function. (3)

Answer 14

1) Thicker smooth muscle layer than arteries so when it contracts, the lumen narrows and reduces blood flow to capillaries.
2) Thicker smooth muscle layer than arteries so when it relaxes, the lumen widens and increases blood flow to capillaries.
3) Thinner elastic layer so pressure surges are lower.

Question 15

Explain how the structure of the capillaries relate to the function. (4)

Answer 15

1) Wall is a one cell layer of endothelial cells to reduce diffusion distance.
2) Large network of capillaries increases surface area for diffusion.
3) Narrow lumen to reduce blood flow rate so there is more time for diffusion.
4) Pores in walls to allow larger substances through.

Question 16

Explain how the structure of the veins relate to the function. (4)

Answer 16

1) Valves prevent backflow of blood.
2) Wider lumen than arteries so there is less resistance to blood flow.
3) Very little elastic and muscle tissue since blood pressure is lower.

Question 17

Explain the formation of tissue fluid. (4)

Answer 17

1) At the arteriole end of the capillaries.
2) Higher hydrostatic pressure inside capillaries than tissue fluid.
3) Forcing water out of capillaries.
4) Large plasma proteins remain in capillary.

Question 18

Explain the return of tissue fluid to the circulatory system. (4)

Answer 18

1) At the venule end of capillaries.
2) Hydrostatic pressure reduces as fluid leaves capillary.
3) An increasing concentration of plasma proteins in the capillary lowers water potential in capillary below that of the tissue fluid.
4) Water enters capillaries from tissue fluid by osmosis down a WP gradient.
5) Excess water is taken up by lymph capillaries and returned to the circulatory system by veins.

Question 19

Suggest and explain causes of excess tissue fluid accumulation. (3)

Answer 19

1) Low concentration of protein in blood plasma.
2) Water potential in capillary is not as low.
3) More tissue fluid is formed at the arteriole end.

Question 20

Describe the arrangement of the components of a cell membrane. (5)

Answer 20

1) Phospholipids form a bilayer - fatty acid tails face inwards, phosphate heads face outwards.
2) Integral proteins span bilayer.
3) Peripheral proteins are on the surface of the membrane.
4) Glycolipids found on exterior surface.
5) Glycoproteins found on exterior surface.

Question 21

Explain the role of cholesterol in cell membranes. (2)

Answer 21

1) Restricts movement of the molecules making up the membrane.
2) So decreases fluidity.

Question 22

Suggest how cell membranes are adapted to their functions. (2)

Answer 22

1) Phospholipid bilayer is fluid so membrane can bend for phagocytosis.
2) Glycoproteins act as receptors and are involved in cell recognition.

Question 23

Describe simple diffusion. (5)

Answer 23

1) Small, lipid-soluble substances.
2) Move from an area of higher concentration to an area of lower concentration.
3) Down a concentration gradient.
4) Across phospholipid bilayer.
5) Passive process - doesn’t require ATP.

Question 24

Describe facilitated diffusion. (4)

Answer 24

1) Polar substances
2) Move down a concentration gradient.
3) Through specific channel and carrier proteins.
4) Passive process - doesn’t require ATP.

Question 25

Explain the role of channel and carrier proteins in facilitated diffusion. (3)

Answer 25

1) Shape of protein determines which substances move. 2) Channel proteins facilitate diffusion of water-soluble substances. 3) Carrier proteins facilitate diffusion of larger substances. Complementary substance attaches to binding site. Protein changes shape to transport substance.

Question 26

Describe osmosis. (4)

Answer 26

1) Water moves 2) From an area of high water potential to an area of low water potential. 3) Down a water potential gradient. 4) Passive process - doesn't require ATP

Question 27

Describe how movement across membranes occurs by active transport. (4)

Answer 27

1) Substances move from an area of lower to higher concentration. 2) Against a concentration gradient. 3) Requiring hydrolysis of ATP. 4) And specific carrier proteins.

Question 28

Describe the role of carrier proteins and the importance of the hydrolysis of ATP in active transport. (4)

Answer 28

1) Complementary substance binds to specific carrier protein. 2) ATP hydrolysed into ADP + Pi releasing energy. 3) Carrier protein changes shape. 4) Pi released -> protein returns to original shape.

Question 29

Describe how movement across membranes occurs by co-transport. (2)

Answer 29

1) Two different substances bind to and move simultaneously via a co-transporter protein. 2) Movement of one substance against its concentration gradient is coupled with the movement of another down its concentration gradient.

Question 30

Explain how AIDS is caused by HIV. (4)

Answer 30

1) HIV infects and kills helper T cells. 2) So helper T cell can't stimulate cytotoxic T cells, B cells or phagocytes. 3) So B plasma cells can't release as many antibodies for agglutination and destruction of pathogens. 4) Immune system deteriorates and the person is more susceptible to infections.

Question 31

Explain how monoclonal antibodies can be used in medical treatments. (4)

Answer 31

1) Monoclonal antibodies have a specific tertiary structure. 2) Complementary to antigen found only on a specific cell type. 3) Therapeutic drug attached to antibody. 4) Antibody binds to specific cell forming antibody-antigen complex delivering drug.

Question 32

Explain how monoclonal antibodies can be used in medical diagnosis. (4)

Answer 32

1) Monoclonal antibody has a specific tertiary structure. 2) Complementary to antigen. 3) Dye attached to antibody. 4) Antibody binds to receptor forming antigen-antibody complex.

Question 33

Suggest the purpose of a control well in the ELISA test. (2)

Answer 33

1) To show only enzyme caused colour change. 2) To show all unbound antibodies have been washed away.

Question 34

Suggest why failure to thoroughly wash the well in an ELISA test can cause a false positive. (2)

Answer 34

1) Antibody with enzyme remains. 2) So substrate is converted into colour product.