The Variety Of Life

Question 1

What is the role of haemoglobin, and how is it efficient at doing this?

Answer 1

To transport oxygen. To be efficient, it readily associates with oxygen at gaseous exchange site, and dissociates at respiring tissues

Question 2

What is the structure of a haemoglobin molecule?

Answer 2

4 polypeptide chains (primary) coiled into helixes (secondary), folded into a specific shape (tertiary) associated with a haem group containing Fe2+ ion which combines with a single O2.

Question 3

Why do different organisms have different types of haemoglobin?

Answer 3

Different factors effect affinity for oxygen required; a high altitude environment requires high affinity, an organism with a fast metabolism requires low affinity.

Question 4

Why does haemoglobin have a reduced affinity for oxygen at the gas-exchange surface?

Answer 4

CO2 is present, which is acidic. The low pH changes the shape of haemoglobin, reducing its affinity

Question 5

Describe the process of oxygen being transported from the lungs to the tissues

Answer 5

1. In lungs, there is low CO2, so high pH, haemoglobin changes shape and readily loads oxygen
2. Affinity is increased, is not released while transporting
3. At respiring tissues there is high CO2, so low pH, haemoglobin changes shape and readily releases oxygen

Question 6

What do Oxygen Dissociation Curves show?

Answer 6

How much oxygen combines with haemoglobin at different partial pressures (kPa) of oxygen

Question 7

Why is an Oxygen Dissociation Curve always the same shape?

Answer 7

At low conc, polypeptide chains are closely united soo it is hard to absorb 1st oxygen molecule. Once one is loaded, it is easier to absorb other 3, curve increases steeply.

Question 8

What may cause an Oxygen Dissociation Curve to shift to the left?

Answer 8

If CO2 conc is low, the affinity for oxygen increases, so will associate with oxygen more readily.

Question 9

Where is starch found?

Answer 9

In many parts of a plant

Question 10

Give the basic structure of a starch molecule

Answer 10

Made up of chains of alpha-glucose monosaccharides linked by glycosidic bonds, formed by condensation reactions. It is then coiled, making it very compact.

Question 11

How is starch suited to its function of energy storage?

Answer 11

• it is compact; lots can be stored in a small place
• it is insoluble; does not draw water in by osmosis, or diffuse out of cells easily
• hydrolyses to form glucose which is easily transported and used in respiration

Question 12

How does the structure of glycogen differ from that of starch?

Answer 12

Glycogen is made up of alpha-glucose but in shorter chains and is more highly branched

Question 13

How is cellulose different from starch and glycogen?

Answer 13

It is made up of beta-glucose monosaccharides, which means to form glycosidic bonds each molecule must be rotated 180 compared to its neighbour

Question 14

What other bonds are found in cellulose, apart from glycosidic?

Answer 14

Hydrogen bonds form cross linkages between adjacent parallel chains. They are weak but numerous

Question 15

What is the major function of cellulose?

Answer 15

To provide rigidity to plant cell wall, and prevent cell bursting by exerting inward pressure to stop influx of water

Question 16

What is a leaf palisade cell’s function and how is it suited to this role?

Answer 16

To carry out photosynthesis. It is adapted by;

• long, thin cells to absorb sunlight
• contain many chloroplasts that position themselves to maximise absorption
• large vacuole pushes chloroplasts to edge of cell

Question 17

What are the main features of chloroplasts?

Answer 17

• stroma; fluid filled matrix that contains starch grains and enzymes needed for LDR
• grana; stacks of disc-like structures called thylakoids
• thylakoid; contain chlorophyll
• envelope; double membrane that is selective in what can enter

Question 18

How are chloroplasts adapted to their function?

Answer 18

• stroma has enzymes required to carry out LIR
• grana provide large SA for attachment of chlorophyll, electron carriers and enzymes in LDR
• contain DNA and ribosomes so can readily manufacture proteins needed for photosynthesis

Question 19

Give 2 features of a plant cell wall

Answer 19

• consist of microfibrils of cellulose, giving mechanical strength
• contain middle lamella, which joins adjacent cell walls

Question 20

What is the function of the plant cell wall?

Answer 20

• provide mechanical strength to cell and prevent cell bursting by reducing osmotic effect
• give strength to plant
• allow water to pass along it