CP11 Investigate photosynthesis using isolated chloroplasts (Hill Reaction)

Devise an investigation to compare the rate of the light-dependent reaction in shade tolerant and shade intolerant plants grown at different light intensities. (6 marks) write indicative content points:

-use shade tolerant and intolerant plants

-plants grown in same conditions, e.g. temp and humidity

-plants grown in either 5% or 25% light

-take same masses of leaf

-add to equal volume of isolation medium

-grind in pestle and mortar for same length of time

-filter suspensions of plant material through muslin

-centrifuge to isolate chloroplasts

-resuspend chloroplast pellet

-expose suspensions to 5% and 25% light intensity

-keep temperature controlled

-add DCPIP and record time for it to decolourise

-carry out repeats to calculate mean time

-If difference is due to LDR, shade tolerant would decolourise more quickly at lower LI

How could you produce quantitative data in this practical?

time taken to decolourise DCPIP, use of a colorimeter

Why is a cold solution containing sucrose and a buffer used in this investigation to grind the cut leaves into? (2)

-buffered/cold to stop enzyme denaturation

-sucrose to stop osmotic loss of water from chloroplasts

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