BY4-Jan2013

Question 1

Identify the chemical that acts as a photoreceptor in plants.

Answer 1

Photochrome.

Question 2

The part of the plant that detects changes in day length.

Answer 2

Leaves.

Question 3

Identify two forms in which nitrogen can be absorbed by plant roots.

Answer 3

Ammonium and nitrate.

Question 4

Identify the stage in the nitrogen cycle that would be slowed by ploughing and drainage of soils.

Answer 4

Denitrification.

Question 5

Identify free-living bacteria involved in the fixation of atmospheric nitrogen.

Answer 5

Azotobacter.

Question 6

State the colour of the bacteria following the application of the counter stain.

Answer 6

Gram +ve = purple

Gram -ve = red

Question 7

Explain the differences in the appearance of the two types of bacteria when stained with the frame staining technique.

Answer 7

Gram +ve - thick peptidoglycan cell wall. Retains crystal violet stain.
Gram -ve - lipopolysaccharide layer external to peptidoglycan cell wall. Does not retain crystal violet stain. Stains red with counter stain.

Question 8

What’s the advantage of having the lipopolysaccharide layer to gram -ve bacteria?

Answer 8

Lipopolysaccharide layer protects against some antibiotics.

Question 9

Suggest why this number in a viable count is likely to be an underestimate of the actual number of bacteria present.

Answer 9

Does not include dead/non-viable bacteria.

Cannot be sure each colony has grown from a single bacterium.

Question 10

Explain what is meant by the term carrying capacity.

Answer 10

Maximum number of a population that can be sustained by a particular environment.

Question 11

Describe two density dependant factors and one density independent factors that would affect population growth.

Answer 11

Density dependent:
Nutrient/food, oxygen level, disease, waste products, pH.
Density independent:
Temperature, size of particular environment.

Question 12

What is interspecfic competition?

Answer 12

Competition for nutrients, space, resources between two different species.

Question 13

Explain intraspecific competition.

Answer 13

Competition between individuals of the same species.

Question 14

Explain how interspecfic competition would result in a population decrease.

Answer 14

Competition for the same food source.
Competition for the same niche.
More successful species outcompetes.

Question 15

Explain the importance of ATP in cells.

Answer 15

ATP needed for active transport and protein synthesis.
Different types of energy can be transferred into a common form.
Only 1 molecule needed to transfer energy to chemical reactions.
Energy can be supplied in small amounts/less energy wasted.
Single bond needed to be broken to release energy.

Question 16

Explain why ATP is sometime called the universal energy currency.

Answer 16

Used by all organisms.

To provide energy for nearly all biomechanical reactions.

Question 17

Explain how opening and closing ion channels results in depolarisation of the axon membrane.

Answer 17

Sodium channels open.
Na+ flood into axon.
Inside axon becomes positively charged.

Question 18

Explain how opening and closing ion channels results in repolarisation of the axon membrane.

Answer 18

Sodium channels close and potassium channels open.
Sudden influx of K+ ions flooding out of axon.
Inside axon becomes negatively charged.

Question 19

Explain why an action potential was not generated by stimuli 1 to 4.

Answer 19

Threshold potential not reached.
Stimuli not enough to open Na+ ion channels.
‘All or nothing’

Question 20

Explain what is meant by quaternary structure.

Answer 20

2 or more polypeptide chains.
Bonded together.
To form functional protein.

Question 21

Name the substance you would expect to find around the outside, covering the axon.

Answer 21

Myelin.

Question 22

Name the cell that produces the substance myelin.

Answer 22

Schwann cell.

Question 23

Explain how the substance secreted by these cells and their arrangement along the neurone affect the speed of transmission of a nerve impulse.

Answer 23

Myelin inhibits movement of ions from axon/insulates axon.
Gaps between Schwann cells called nodes of Ranvier.
No myelin present at gaps.
Depolarisation only possible at modes of Ranvier.
Action potential jumps from node to node-saltatory conduction.
Nerve transmission faster.

Question 24

Where does glycolysis occur?

Answer 24

Cytoplasm.

Question 25

Where does the link reaction take place?

Answer 25

Matrix of mitochondria.

Question 26

Where in the cell does the Krebs Cycle occur?

Answer 26

Matrix of the mitochondria.

Question 27

Which stage of respiration will operate in the absence of oxygen?

Answer 27

Glycolysis.

Question 28

Name the enzyme responsible for the production of CO2 during respiration.

Answer 28

Carboxylase.

Question 29

Explain how the light independent stage of photosynthesis (Calvin Cycle) leads to the production of triose phosphate.

Answer 29

Occurs in the stroma.
5C compound-Ribulose bisphosphate.
CO2 fixed to 5C compound.
Reaction catalysed by RuBisco.
Forms hexose bisphosphate.
Unstable and breaks down into two glycerate 3 phosphates.
Converted into triose phosphate.
G3P is reduced by reduced NAD which supplies H.
ATP broken down to ADP and Pi, supplying energy for conversion.

Question 30

Indicate the origin of the raw materials required for this stage of photosynthesis and the possible uses of the triose phosphate produced.

Answer 30

ATP and reduced NADP from light dependent stage.
CO2 from environment.
RuBP regenerated from triose phosphate.
Phosphate from ATP needed for this.
Triose phosphate starting point for synthesis of: glucose, lipids, amino acids, starch etc.

Question 31

Explain how the kidney is involved in osmoregulation in mammals.

Answer 31

Antiduretic hormone(ADH).
ADH is released by the pituitary gland.
ADH carried in the bloodstream to the collecting duct.
When the blood is more concentrated it is detected by osmoreceptors in the hypothalamus.
More ADH is released.
ADH levels increases the permeability of the cells lining the collecting duct/aquapourine channels opening.
Water moves out of the collecting duct by osmosis.
Into the tissue fluid which it is rapidly removed by the capillary network.
This occurs because the medulla of the kidney has a high solute concentration.
Due to the counter current multiplier system operating in the loop of Henle.
This conserves water and produces concentrate urine.
Most water absorbed in the proximal convoluted tubule.
Length of loop affects volume of urine produced.
Long loop results in more water reabsorbed eg kangaroo rat lives in dry environment with little water.

Question 32

Identify the name given to the process by which flowering plants are affected by the relative periods of dark and light they are exposed to.

Answer 32

Photoperiodism.