RP8 Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts.

Method

- Remove leaf stalks, grind sample, and place in chilled isolation solution.

- Filter sample into a beaker using muslin cloth and funnel. Keep beaker in an ice water bath.

- Centrifuge chloroplasts at high speed for 10 minutes to obtain pellet.

- Discard supernatant and add pellet to fresh isolation medium. Keep on ice.

- Set colorimeter to red filter, zero with chloroplast extract and distilled water.

- Place test tube 30cm from light source, add DCPIP, and immediately measure absorbance in cuvette.

- Measure absorbance every 2 minutes for 10 minutes.

- Repeat at different distances from lamp up to 100 cm to vary light intensity.

Risk Assessment

- DCPIP: Wear eye protection and wash skin/eyes immediately with cold water in case of contact.

- Biohazard: Wash hands after use and seek assistance if needed.

- Lamps: Avoid looking directly at lamp, wait for afterimage to disappear, and seek assistance if needed. - Electrical appliances: Keep liquids away from appliances and avoid touching lamp/wires with wet hands. Seek assistance if needed.

Conclusion

- Decreasing light intensity reduces photosynthesis rate as it slows photoionization of chlorophyll, resulting in slower light-dependent reaction.

- Decreased electron release by chlorophyll leads to less DCPIP reduction, prolonging the color change from blue to colorless

- Higher absorbance while DCPIP is blue indicates higher enzyme activity, shown by a steeper gradient on the graph, suggesting increased dehydrogenase activity.

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