core pracs

Question 1

Hill reaction

Answer 1

Change: combination of leaf extract, isolation medium, DCPIP
Organism: same species, same part of plant, same age
Repeat: 4x at each condition, mean, anomalies, calculate s.d.
Measure: time to decolorise DCPIP in each tube, use t-test
Same: distance from light, time in light, volume of filtrate, volume of isolation fluid.

Question 2

Explain the results:
Tube 1: leaf extract + DCPIP - colour changes until it is the same colour as tube 4 (leaf extract + distilled water)
Tube 2: Isolation medium + DCPIP - no colour change
Tube 3: leaf extract + DCPIP in the dark - no colour change
Tube 4: leaf extract + distilled water - no colour change
Tube 5: supernatant + DCPIP - no colour change

Answer 2

Tube 1: Light independent reaction reducing DCPIP
Tube 2: DCPIP does not decolourise when exposed to light
Tube 3: No photosynthesis in the dark - tube 1 results due to effect of light on extract
Tube 4: Leaf extract does not change colour in light
Tube 5: supernatant does not have chloroplasts, so no reduction of DCPIP so chloroplasts are needed to release electrons.

Question 3

Explain why a cold solution is used in the Hill reaction

Answer 3

Cold - stop enzyme denaturation