AS Paper 2 2017

Question 1

Why starch is a good storage molecule

Answer 1

Insoluble- doesn’t affect water potential
Branched/coiled alpha helix makes it compact
Polymer of alpha glucose so provides glucose for respiration
Branched/more ends for faster breakdown by enzymes
Large molecule so cannot cross cell surface membrane

Question 2

The student put the same volume of water in each tube. Explain why?

Answer 2

If too much water the concentration of pigment solution will be lower/solution will appear lighter/more light passes through than expected

If too low/concentration of pigment in solution will be greater/ solution will appear darker/less light passes through than expected

So results from different temperatures are comparable

Question 3

Describe a method student could have used to monitor temperature?

Answer 3

Take readings using a thermometer/temperature sensor

Question 4

Temperature causing leakage of red pigment?

Answer 4

Damage to cell surface membrane
Membrane proteins denature
Increased fluidity tonphospholipid bilayer

Question 5

What causes non disjunction

Answer 5

An extra chromosome caused by meiosis, homologous chromosomes are not separated leads to one extra

Question 6

Explain why all cells of the body have mutation for patau syndrome

Answer 6

Mutation/extra chromosome in gamete/egg/sperm (that formed zygote)
All cells derived from a single zygote by mitosis
Or
All cells derived from a single cell by mitosis
Mitosis produces genetically identical cells

Question 7

Describe cohesion-tension theory

Answer 7

Water evaporates from mesophyll cells in the leaf
This causes a lower water potential of mesophyll cells. owater is taken up by neighbouring cells. Water potential in the leaf lowers/establishes water potential gradient between leaf and xylem
Causes water to enter roots by osmosis, water pulled up xylem as a continuous column due to hydrogen bonding between water molecules. Adhesion to the xylem walls. Water causes xylem to pull onwards creating tension.
Causes mass flow in plant

Question 8

Describe how mRNA is produced

Answer 8

The DNA strands are separated by breaking the hydrogen bonds
H bonds broken between complementary base pairs
Only one strand acts as a template/template strand used to make mRNA
And is transcribed
RNA nucleotides join by RNA polymerase
Pre MRNA formed
Splicing removes introns to form mRNA