PS Exps. 17/11/22

Question 1

b) Explain why the student set up Test tube 1

c. Explain the results in test tube 3.

Answer 1

a.
- so osmosis does not occur
- chloroplast doesn’t shrink (flaccid)

b.
- to show that light doesn’t affect the DCPIP.
- to show chloroplasts are required

c.
- Reduction of DCPIP by electrons
- Electrons from LDR

Question 2

d. The student evaluated the effectiveness of different chemicals as weed-killers by assessing their ability to prevent the decolourisation of DCPIP in chloroplast suspensions.

He added different concentrations of each chemical to illuminated chloroplast T suspensions containing DCPIP.
He then determined the IC↓50 for each chemical.
The IC↓50 is the concentration of chemical which inhibits the decolourisation of DCPIP by 50%.

Explain the advantage of the student using the IC↓50 in this investigation.

Answer 2

Provides a standard reference point

OR

can compare (different concentrations) weedkillers

Question 3

Explain how chemicals which inhibit decolourisation of the DCPIP could slow the growth of weeds.

Answer 3

1. Less ATP produced
2. Less NADP produced
3. Less GP reduced/ converted to TP

Question 4

1. The scientists used a control group in this trial. Explain why.
2. Suggest how the control group would have been treated.
3. Describe the effect of taking the drug on acid secretion.

Answer 4

1. To make sure any change in the dependent variable was due to the effect of the independent variable (amount of H+ ions).

→ to make sure the effect of the drug was not due to anything else in the tablet.

b. No drug given/ placebo

c.
Decrease for 3 hrs
(accept 1-4 hrs)

Question 5

Describe the part played by the inner membrane of a mitochondrion in producing ATP.

Answer 5

1. e- s transferred down ETC
2. Some E from the ETC used to take protons into space between membranes
3. Energy used to combine ADP and Pi to produce ATP.

Question 6

A scientist investigated ATP production in a preparation of isolated mitochondria. He suspended the mitochondria in an isotonic solution and added a suitable respiratory substrate together with ADP and phosphate. He bubbled oxygen through the preparation.

1. Why was the solution in which the mitochondria were suspended isotonic?
2. Explain why the scientist didn’t use glucose as the respiratory substrate.
3. Explain why the oxygen concentration would change during this investigation.

Answer 6

1. Prevent damage to the mitochondrion caused by osmosis. Shrink/ lysis
2. Glucose is broken down during glycolysis in the cytoplasm. It’s not in the mitochondrion.
   Can’t cross mitochondrial membrane, only pyruvate can.
3. Final e- acceptor
   Respiration makes water.