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A student isolated chloroplasts from spinach leaves into a solution to form a chloroplast suspension - AQA - A-Level Biology - Question 4 - 2017 - Paper 2
Question 4
A student isolated chloroplasts from spinach leaves into a solution to form a chloroplast suspension. He used the chloroplast suspension and DCPIP solution to invest... show full transcript
Worked Solution & Example Answer:A student isolated chloroplasts from spinach leaves into a solution to form a chloroplast suspension - AQA - A-Level Biology - Question 4 - 2017 - Paper 2
Step 1
04.1 Explain why it was important that these water potentials were the same.
Answer
It is crucial for the solution used to produce the chloroplast suspension to have the same water potential as the chloroplasts to prevent osmosis from occurring. If the water potentials were different, osmosis would lead to either the chloroplasts bursting due to water intake (if the surrounding solution is hypotonic) or shriveling (if the surrounding solution is hypertonic). This would ensure that the chloroplasts remain intact, preserving their functionality for the experiment.
Step 2
04.2 Explain why the student set up Tube 1.
Answer
The student set up Tube 1 to show that light does not affect the DCPIP, as it contains no chloroplasts. This serves as a control in the experiment, helping to compare the results of the other tubes where chloroplasts are present and investigating their light-dependent reactions.
Step 3
04.3 Explain the results in Tube 3.
Answer
In Tube 3, the DCPIP turns from blue to colourless after 30 minutes, indicating that the chloroplasts are engaged in photosynthesis. The reduction of DCPIP in the presence of light suggests that electrons are being transferred from the chloroplasts during the light-dependent reactions, thereby reducing DCPIP and demonstrating the functionality of the chloroplasts in light.
Step 4
04.4 Explain the advantage of the student using the IC50 in this investigation.
Answer
Using the IC50 provides a standardized measure to determine the effectiveness of different chemicals as weed-killers, allowing the student to compare the potency of various substances. It helps identify the concentration at which each chemical inhibits DCPIP reduction by 50%, establishing a benchmark for the effectiveness of weed-killers.
Step 5
04.5 Explain how chemicals which inhibit the decolourisation of DCPIP could slow the growth of weeds.
Answer
Chemicals that inhibit the decolourisation of DCPIP interfere with the photosynthetic processes in weeds. By preventing the reduction of DCPIP, these chemicals can essentially inhibit the light-dependent reactions of photosynthesis, leading to reduced ATP and NADPH production. This lack of essential energy molecules can slow growth, impair plant respiration, and ultimately affect the overall health and vitality of the weeds.