AQA Biology A-Level - Homeostasis MS PhysicsAndMathsTutor.com
Mark schemes
Q1.
(a) (Insulin stimulates release of osteocalcin – no mark)
1. Osteocalcin causes more (release of) insulin;
2. (More) insulin causes more (inactive) osteocalcin (release);
1. and 2. Idea of more required but other words can
be used
1. and 2. Ignore ref. to further
1. and 2. Ignore ref. to more B cells / osteoblasts
stimulated
2
(b) 1. (Change in pH) changes / breaks ionic / hydrogen bonds;
Ignore ref. to peptide or sulfur-sulfur bonds
Accept polar bonds
2. Changes tertiary structure;
Ignore changes to primary structure
Reject ref. to active site / enzyme
Accept forms binding site
Ignore 3D
Accept 3o
2
(c) 1. (Insulin) leads to more transport proteins / channel (proteins) / carrier
(proteins) for glucose;
Ignore references to opening channels
Accept co-transport / GLUT 1 or 4 protein
2. More glucose (for respiration / glycolysis) enters cell;
Idea of more required once to cover both mark
points
Ignore references to glycogen formation / fat
metabolism / enzyme activation
2
[6]
Q2.
(a) 1. Binding (of interferon gamma) changes shape/tertiary structure of
receptor (protein);
2. This activates/switches on the enzyme;
3. Use of ATP (to phosphorylate STAT1);
1. Accept reference to second messenger
mechanism/process
3. Context is important
2 max
Mark schemes
Q1.
(a) (Insulin stimulates release of osteocalcin – no mark)
1. Osteocalcin causes more (release of) insulin;
2. (More) insulin causes more (inactive) osteocalcin (release);
1. and 2. Idea of more required but other words can
be used
1. and 2. Ignore ref. to further
1. and 2. Ignore ref. to more B cells / osteoblasts
stimulated
2
(b) 1. (Change in pH) changes / breaks ionic / hydrogen bonds;
Ignore ref. to peptide or sulfur-sulfur bonds
Accept polar bonds
2. Changes tertiary structure;
Ignore changes to primary structure
Reject ref. to active site / enzyme
Accept forms binding site
Ignore 3D
Accept 3o
2
(c) 1. (Insulin) leads to more transport proteins / channel (proteins) / carrier
(proteins) for glucose;
Ignore references to opening channels
Accept co-transport / GLUT 1 or 4 protein
2. More glucose (for respiration / glycolysis) enters cell;
Idea of more required once to cover both mark
points
Ignore references to glycogen formation / fat
metabolism / enzyme activation
2
[6]
Q2.
(a) 1. Binding (of interferon gamma) changes shape/tertiary structure of
receptor (protein);
2. This activates/switches on the enzyme;
3. Use of ATP (to phosphorylate STAT1);
1. Accept reference to second messenger
mechanism/process
3. Context is important
2 max
