7 Mass Transport

Question 1

What is the function of haemoglobin?

Answer 1

Transports oxygen to the tissues

Question 2

Describe the structure of haemoglobin

Answer 2

Quaternary Structure
Four polypeptide chains
prosthetic group- iron ion that associated with an oxygen molecule.

Question 3

Describe the binding of oxygen to haemoglobin

Answer 3

First molecule struggles to bind due to the structure, second and third don’t struggle due to positive cooperation (quaternary structure changes). Last one struggles again due to a lower chance of an oxygen molecule hitting that binding site

Question 4

Describe the human oxygen dissociation curve.

Answer 4

it demonstrates the relationship between the percentage saturation of oxygen and the partial pressure of oxygen. therefore the affinity- closer to the left the higher the infinity.

Question 5

What causes the Bohr Shift?

Answer 5

Increase in carbon dioxide concentration leads to lowered PH and therefore the Hb changes shape, lowering its affinity.

Question 6

Describe the main events of the cardiac cycle.

Answer 6

Diastole- the heart is relaxed and the atrium fills up with blood.
Atrial systole- atrium contracts and the AV valves are forced open, blood goes into the ventricles.
Ventricular systole- ventricle contracts, AV valves shut and semi lunar valves are forced open, blood leaves the heat through the aorta and pulmonary artery.

Question 7

cardiac output formula

Answer 7

heart rate x stroke volume

Question 8

What is tissue fluid?

Answer 8

A watery liquid that contains glucose, amino acids, fatty acids, ions in solution and oxygen. These are all supplied to the tissues and it receives carbon dioxide and other waste products.

Question 9

What is tissue fluid formed from?

Answer 9

The blood plasma

Question 10

Describe the formation of tissue fluids.

Question 11

How does tissue fluid return to the circulatory system?

Question 12

Describe the cohesion-tension theory

Answer 12

1. Water evaporates from the mesophyll cells due to heat from the sun leading to transpiration.
2. Due to the hydrogen bonds between water molecules (cohesion), water forms a continuous, unbroken column of water across the mesophyll cells and down to te xylem.
3. The transpiration pull occurs due to the constant evaporation of water into the stomata and out of the leaf.
4. This puts the xylem under tension- negative pressure.

Question 13

Describe evidence for the cohesion tension theory

Answer 13

1. Change in diameter of tree trunks according to rate of transpiration. (xylem vessels suck in when under tension)
2. If xylem vessel is broken and air enters it, the tree can no longer draw up water (the continuous stream)
3. When xylem vessel is broken, water doesn’t leak out.

Question 14

Mass-flow hypothesis

Answer 14

Sucrose diffuses down a concentration gradient by facilitated diffusion from photosynthesising cells into companion cells.
Hydrogen ions are actively transported from companion cells into the spaces within cell walls using ATP. They then diffuse down a concentration gradient through carrier proteins into sieve tube elements.
Co transport occurs with hydrogen ions and sucrose.
The sieve tubes therefore have a lower (more negative) water potential.
The xylem has a much higher (less negative) water potential, so water moves into the sieve tubes, creating a hydrostatic pressure.
At the sink (respiring cells), sucrose is used up or converted for storage.
…

Question 15

What are ringing experiments?

Answer 15

A section of outer layers of the tree are stripped away leaving mostly the xylem. Shows that the phloem is responsible for translocating sugars.