BY4-June 2012

Question 1

What is meant by the term exponential growth?

Answer 1

Population grows at an increasing rate/doubles in unit time.

Question 2

Give two reasons which could lead to a decline in population growth in this culture. (Anaerobic bacteria)

Answer 2

Competition for nutrients.
Build-up of waste products.
Oxygen supplied.

Question 3

What conditions would be needed for the growth of the bacteria in this experiment? (Anaerobic bacteria)

Answer 3

Optimum temperature.
Optimum pH.
Source of carbon and nitrogen or nutrients.
Absence of oxygen.

Question 4

Describe two precautions which should be carried out to ensure aseptic conditions in this experiment. (Serial dilution)

Answer 4

Sterile equipment.
Flame loop.
Disinfectant bench.
Flame neck of tube.
Work next to flame.

Question 5

Explain why the white matter is white and the grey matter is grey.

Answer 5

White matter made of myelin sheath.

Grey matter made of cell bodies.

Question 6

What is the difference in function between an axon and a dendrite?

Answer 6

Dendrite conducts impulse towards cell body.

Axon conducts away from cell body.

Question 7

Explain how it is possible for the three metabolic pathways (Glycolysis, Calvin Cycle and Krebs Cycle) to take place independently of each other in the same cell.

Answer 7

Different places within cell.
Different enzymes.
Glycolysis takes place in cytoplasm.
Calvin Cycle takes place in chloroplast.
Krebs Cycle takes place in mitochondria.

Question 8

Where do the light dependant reactions take place?

Answer 8

The Grana of the chloroplast.

Question 9

What does the light dependant reactions produce which enable the Calvin Cycle to occur?

Answer 9

Reduced NADP and ATP.

Question 10

Explain why photosynthesis is essential for the survival of animals on this planet.

Answer 10

Produces oxygen as a bi-product.
Organic materials.
Fixing carbon.

Question 11

State a use for nitrates in pants.

Answer 11

Synthesise amino acids.
Synthesise nucleic acids.
Synthesise DNA and RNA.

Question 12

Why is magnesium required by plant cells?

Answer 12

Used in chlorophyll so important to photosynthesis.

Question 13

Define what is meant by the term photoperiodism.

Answer 13

Response controlled by relative length of light and dark periods.

Question 14

Explain the change in potential difference shown by the micro electrode after light pressure was applied.

Answer 14

Stimulation causes sodium ions to move in/diffuse.
Inside becomes less negative.
Threshold not reached(all or nothing law).
Sodium voltage gated channels remain closed/no action potential.

Question 15

Explain the change in potential difference across the membrane shown by the microelectrode when heavy pressure was applied.

Answer 15

Sodium ions in.
Threshold reached.
Sodium (voltage gated) channels open.
Depolarisation.
Inside becomes -ve.
Action potential occurs.
Sodium (gated) channels close and potassium channels open.
K+ move down concentration gradient.
Repolarised.
Refractory period.
Sodium potassium pump restores resting potential.

Question 16

Suggest two ways by which exciting drugs could change activity at the synapse and two ways by which chemicals could inhibit activity at the synapse.

Answer 16

Excitatory drugs:
-Mimic normal transmitter.
-Inhibit breakdown of of transmitter.
-Blocks uptake back into presynaptic knob.
-Increases number of receptors on post synaptic membrane.
Inhibitory drugs:
-Prevent exocytosis/realise of transmitter substance.
-Bind with receptors on post synaptic membrane and block it.
-Prevents Ca2+ entry into presynaptic knob.

Question 17

What is the general name given to glands which produce hormones?

Answer 17

Endocrine glands.

Question 18

The maintenance of a constant, stable internal environment is known as what?

Answer 18

Homeostasis.

Question 19

What do osmoreceptors in the hypothalamus measure?

Answer 19

The solute potential of the blood.

Question 20

Where is ADH stored?

Answer 20

Posterior pituitary gland.

Question 21

Describe how the different regions of the nephron and associated blood supply are adapted to their function.

Answer 21

Afferent vessel wider than efferent.
Increase in blood pressure.
Gaps in endothelial cells.
Gaps in basement membrane.
Podocytes feet.
Ultrafiltration into Bowman’s capsule from glomerulus.
Water and salts can, RBC’s can’t.
Proximal convoluted tubule cells have microvilli to give large surface area.
Large no. of mitochondria for active transport.
Selective re-absorption in proximal convoluted tubule.
Descending limb permeable to water/water moves out, decreasing potential in the nephron.
Ascending limb loop of Henle pump out Na+ but impermeable to water.
Decreases water potential in medulla.
Collecting duct walls receptors for ADH.
Permeability varies depending on how much ADH is released.

Question 22

How do you explain for the low rate of population growth in the first three hours of the experiment?

Answer 22

Getting used to new medium.
Replication of DNA.
Synthesis of enzymes.
Genes switched on.
Digestion.