Biology Paper 2

Question 1

What is epistasis?

Answer 1

When one allele masks another

Question 2

What are the principles of epigenome?

Answer 2

Have tags that respond to environmental factors, chemical tags formed around DNA and histones so that it can be unwrapped to express active genes and determines the shape of the DNA histone complex, also ensures inactive genes are not read

Question 3

What and why do they use the specific DNA polymerase in the thermocycler?

Answer 3

Thermophilic aquaticus and because it denatures at 95 degrees C so it does not denature

Question 4

describe the phosphorus cycle

Answer 4

phosphates from rocks are eroded into oceans and running water that is absorbed by plants and excreted into the soil via death that then taken up by water to form new rocks

Question 5

describe the light dependent reaction starting with Photolysis

Answer 5

chlorophyll absorbs light energy, excite electrons, move along carriers etc releasing energy, used to join ADP and pi to form ATP, photolysis of water produces protons electrons oxygen, NADP reduced by electrons

Question 5

How is the gradient of sodium maintained in the loop of Henle?

Answer 5

Sodium diffuses out of ascending limb into interstitial space between ascending and descending, sodium moves into descending limb and water moves out of it into blood capillaries, thus as filtrate moves through loop of Henle it lowers its water potential until it reaches the bottom of the ascending limb that where sodium diffuses out and so water potential increases, then there’s a higher water potential gradient in the interstitial space between ascending and collecting duct so water moves out of collecting duct into blood vessels

Question 6

what is biomass?

Answer 6

the dry weight of the total mass of living material in a specific area at a given time

Question 7

What is glycogenesis?

Answer 7

Conversion of glucose to glycogen

Question 8

three advantages of the structure of a chloroplast

Answer 8

contain both DNA and RNA so proteins can be manufactured quickly, thylakoid membrane has a large SA for rapid DF and a network of proteins in the Grana to maximise the absorbance of light

Question 8

Describe the transmission across a cholinegenic synapse?

Answer 8

Calcium ions open because of AP that move into synaptic knob via FDF, this causes vesicles to fuse with the presynaptic neurone membrane that release acetylcholine into the synaptic cleft, acetylcholine then binds to protein receptors on the sodium ion channels on the post synaptic neurone that diffuse across a concentration gradient that causes a influx of sodium ions in the post synaptic neurone that causes an AP, acetylcholine then broken by acetylcholinerase into choline and Ethanoic acid and diffuses back across the synaptic cleft but does not cause an action potential in the pre synaptic neurone as it is not in its acetylcholine form

Question 9

What are the functions of a synapse?

Answer 9

Combine multiple impulses at the same synapse so Brain is not overloaded with info + can stimulate multiple impulses in different neurones at the same time

Question 10

three advantages of mesophyll in a leaf

Answer 10

air spaces between them = rapid diffusion, long and narrow and are packed with chloroplast the thin tissue of the leaf allows light to reach mesophyll

Question 11

where does the light independent reaction

Answer 11

stroma in the fluid filled matrix

Question 12

describe the electron transport chain

Answer 12

electron is oxidised that reduces NADP, carries out series of redox reactions along the electron transport chain that is then accepted by oxygen that is the terminal electron receptor which oxidises NADPH back to NADP

Question 13

describe the process of the light independent reaction

Answer 13

CO2 combines 5 carbon ribulose-bi-phosphate to make 6 carbon molecule that is then catalysed by rubisco to create two 3 phosphate glycerate molecules that are then reduced via NADP and energy from ATP from LDR to triose phosphate that will eventually turn into glucose, NADP reformed and goes back to LDR

Question 14

what is glycolysis and where does it happen?

Answer 14

phosphorylated glucose is broken down in two 3 carbon molecules called pyruvate. happens in the matrix mitochondria

Question 15

what happens in the link reaction after Glycolysis?

Answer 15

pyruvate is decarboxylated and dehydrogenated to acetate NAD is reduced

Question 16

what happens in the Krebs Cycle after the link reaction?

Answer 16

acetyl coenzyme A combines with oxaloacetate to form citrate which is decarboxylated and dehydrogenated to form 5 carbon molecule which is then dehydrogenated and decarboxylated to form 4 carbon ATP made by substrate-level phosphorylation and FAD is reduced, oxalacetate is then regenerated to restart the cycle

Question 17

state where the Krebs cycle occurs

Answer 17

in the matrix of the mitochondria

Question 18

explain the mechanism that allows ATP concentration to control the Krebs cycle

Answer 18

ATP binds away from the active site
causes the active site to change shape
can no longer bind to the substrate/cycle cannot continue as no substrate
less/no more ATP produced

Question 19

describe how ammonium ion concentration increases in the soil when organisms die

Answer 19

protein/amino acids broken down by saprobionts

Question 20

explain how Schwann cells help the neurone to carry out its function

Answer 20

insulates the axon only occurs at the node
allows faster transmission of impulse along axon

Question 21

describe how the mark-release-recapture method could be used to estimate number of spawning age fish in the population

Answer 21

capture and count
carefully mark to avoid detection by predators
recapture, count marked and unmarked

Question 22

describe genetic diversity

Answer 22

the variation of different alleles within a species