2019 AS Paper 2

Question 1

Role of enzymes in protein digestion

Answer 1

Provides hydrolysis of peptide bonds

Endopeptidase acts in middle of polypeptide

Exopeptidases acts at the end of polypeptide

Dipeptidases acts between 2 amino acids

Question 2

Why is re-consumption of not fully broken down of proteins is necessary

Answer 2

Remaining/undigested protein broken down

So more amino acids absorbed

Because protein/food passes again through stomach/ileum

Question 3

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin

Answer 3

More oxygen dissociation
OR
Deceases haemoglobin’s affinity for O2

By decreasing blood pH/increasing acidity

Question 4

How can a steeper dissociation curve be adapted for exercise

Answer 4

Higher affinity for oxygen

Allows aerobic respiration when diving

Question 5

The 2 scientists who proposed models of the chemical structure of DNA of DNA replication

Answer 5

Watson and Crick

Question 6

Enzyme used in DNA replication

Answer 6

DNA polymerase

Question 7

Role of single stranded DNA fragments in semi conservative replication

Answer 7

Template

Which determines the order of bases

Question 8

Role of the DNA nucleotides in semi conservative replication

Answer 8

Forms complementary DNA strand

Question 9

Role of antibodies in stimulating phagocytosis

Answer 9

Bind to antigen

Cause clumping

Question 10

Measurements involved in rate of water movement

Answer 10

Initial and Final mass

Time taken

Number of xylem vessels

Question 11

Reason for adding a layer of oil in water practicals

Answer 11

Prevents water loss

Question 12

How to use a sharp scalpel safely in practical

Answer 12

Cut away from body

Against a flat surface

Question 13

Aseptic techniques when dealing with bacteria and agar

Answer 13

Wear gloves/apron to prevent contamination

Burning Bunsen close by to create upward current of air

Work on disinfected bench to prevent contamination

Flame instrument/equipment prevent contamination

Lift lid slightly to prevent entry of microbes

Question 14

Differences between mitosis and meiosis

Answer 14

One division in mitosis, two divisions in meiosis

Daughter cells genetically identical in mitosis, daughter cells genetically different in meiosis

Two cells produced in mitosis, four cells produced
in meiosis

Separation of homologous chromosomes only in
meiosis, not present in mitosis

Crossing over only in meiosis, not present in mitosis

Independent segregation only in meiosis, not present in mitosis

Question 15

Ways which genetic diversity between species is measured

Answer 15

Comparing measurable features

Comparing amino acid sequences

Comparing differences in the base sequence of DNA

Comparing differences in the base sequence of mRNA

Question 16

Role of iron ions, sodium ions and phosphate ions in cells

Answer 16

Iron ions:
Haemoglobin binds/associates with
oxygen

Sodium ions:
Co-transport of glucose/amino
acids

Sodium moved out by
active transport/Na – K pump

Creates a sodium diffusion gradient

Affects osmosis/water potential

Phosphate ions:
Affects water potential

Joins nucleotides/in phosphodiester bond

Used to produce ATP

Phosphorylates other compounds making them more
reactive

Question 17

How does the cell membrane affect the movement of substances

Answer 17

Phospholipid bilayer allows
movement of lipid-soluble substances

Phospholipid bilayer prevents
movement/diffusion of polar substances across membrane

Carrier proteins allow active
transport;

Channel/carrier proteins allow
facilitated diffusion/co-transport;

Shape of channel / carrier
determines which substances
move

Number of channels/carriers
determines how much movement;

Membrane surface area
determines how much
diffusion/movement

Cholesterol affects
fluidity