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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 1
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 1
Step 1
Explain why it was important that these water potentials were the same.
Answer
It is crucial that the water potentials are the same to prevent osmosis. If the water potentials were different, the chloroplasts could either gain or lose water, leading to turgor changes. This would impact the integrity of the chloroplasts, possibly causing them to burst or shrivel, and thus affecting their ability to effectively conduct photosynthesis.
Step 2
Step 3
Step 4
Explain the results in Tube 3.
Answer
In Tube 3, the DCPIP turned colourless after 30 minutes, indicating that the chloroplasts were able to undergo photosynthesis when exposed to light. This shows that light is required for the reduction of DCPIP, confirming the role of light in the light-dependent reactions.
Step 5
Explain the advantage of the student using the IC₅₀ in this investigation.
Answer
Using the IC₅₀ provides a standard reference point, allowing for the comparison of different chemicals or concentrations with a consistent measure of effectiveness in inhibiting DCPIP decolourisation. This aids in identifying the most efficient weed-killer.
Step 6
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 processes of photosynthesis in weeds. By disrupting electron transport and reducing the efficiency of light-dependent reactions, these chemicals can limit the production of ATP and NADPH, ultimately slowing down the growth and vitality of the weeds.