Paper 3 (Practice based)

Question 1

Nerve impulse arriving at synapse

Answer 1

Nerve impulse causes calcium ion channels to open, calcium ions enter by facilitated diffusion. Causes synaptic vesicles to fuse with presynaptic membrane. Leads to the release of neurotransmitters

Question 2

Nitrogen containing biological molecules

Answer 2

Amino acids, nucleic acid, DNA, RNA, ATP, NAD, cyclic AMP, chlorophyll

Question 3

Method of determining plant species richness at one site

Answer 3

Assign numbers to sites and spin a wheel to randomly select sampling sites, use of quadrant and identify the plant species in each quadrant

Question 4

Enzymes involved in semi-conservative replication of DNA

Answer 4

DNA helicase, DNA polymerase

Question 5

Phosphorylation

Answer 5

Phosphorylation makes a substrate more reactive so the activation energy needed for the reaction is lowered

Question 6

Insulin increases rate of respiration

Answer 6

Insulin leads to more carrier proteins for active cotransport of glucose. More glucose for glycolysis enters the cell

Question 7

Binding one oxygen molecule to haemoglobin makes it easier for another to bind

Answer 7

Binding first oxygen changes the tertiary shape of haemoglobin. This uncovers another binding site/haem group for the second oxygen to bind to

Question 8

Why is detergent used to break open cells and organelles

Answer 8

Cell membranes are made from phospholipids, detergent dissolves phospholipid bilayer

Question 9

How does ultrafiltration occur in glomerulus

Answer 9

High hydrostatic pressure. Water, glucose, ions and urea pass out through small pores in capillary endothelium and through capillary basement membrane

Question 10

Role of saprobionts in nitrogen cycle

Answer 10

They use enzymes to decompose proteins, producing ammonia.

Question 11

Competitive inhibitor

Answer 11

Same shape as substrate, competes with the substrate for binding at the active site on the enzyme. Fewer enzyme-substrate complexes are formed

Question 12

Sympatric speciation

Answer 12

Not geographically isolated, but reproductively isolated. Changes in allele frequency as they face different selective pressures. Alleles become so different that they cannot breed to produce a fertile offspring

Question 13

Effects of high sodium concentration on blood volume

Answer 13

Sodium ions lower water potential of the blood. Water would move into the blood by osmosis from tissue fluid. This increases the volume of blood

Question 14

Advantage of Bohr effect during exercise

Answer 14

Increases the dissociation of oxygen for aerobic respiration at the tissues. Anaerobic respiration delayed so less lactate at tissues

Question 15

Effects of activating AMPK and developing slow twitch muscle fibres

Answer 15

More acetyl coenzyme A would enter the Krebs cycle, so Krebs cycle generates more reduced coenzymes. So more ATP would be produced. Developing slow twitch muscle fibres would increase endurance

Question 16

HIV replication inside helper T cells

Answer 16

RNA converted into DNA using reverse transcriptase. The DNA is incorporated into the helper T cell’s DNA. DNA transcribed into HIV mRNA. HIV mRNA translated by the helper T cell into new HIV proteins for assembly into viral particles

Question 17

Effects of anaerobic conditions in waterlogged marshes on ammonium compounds and nitrite, nitrate ions

Answer 17

Fewer active nitrifying bacteria because they require aerobic conditions. Less oxidation of ammonium ions to nitrite ions and nitrate ions. More denitrification, because denitrifying bacteria do not require oxygen. So more nitrate ions reduced to nitrogen gas

Question 18

Exopeptidases and endopeptidases

Answer 18

Exopeptidases hydrolyse peptide bonds at the ends of a polypeptide. Endopeptidases hydrolyse internal peptide bonds within a polypeptide. Creates more ends, so more surface area

Question 19

Use of a radioactively labelled DNA probe

Answer 19

Extract DNA and add restriction enzymes. Separate the fragments using gel electrophoresis. Treat the DNA to form single strands. The probe will bind to the complementary gene, this can be viewed using autoradiography