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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 were the same to prevent any osmotic movement of water in or out of the chloroplasts or the solution. If the water potentials were different, osmosis could occur, leading to either swelling or shrinking of the chloroplasts. This would affect their ability to function properly during the photosynthetic process.
Step 2
Explain why the student set up Tube 1.
Answer
The student set up Tube 1 to demonstrate that light alone does not affect the DCPIP colour change without the presence of chloroplasts. This serves as a control to show the necessity of chloroplasts for the reduction of DCPIP in the presence of light.
Step 3
Step 4
Explain the results in Tube 3.
Answer
In Tube 3, the DCPIP turned colourless after exposure to light due to the presence of chloroplasts. The chloroplasts were able to perform photosynthesis, driving the reduction of DCPIP, which indicates that light-dependent reactions occurred successfully.
Step 5
Explain the advantage of the student using the IC50 in this investigation.
Answer
Using IC50 provides a standard measure that allows for comparison between different chemicals or concentrations. It indicates the effectiveness of a chemical in halting the decolourisation of DCPIP at a specific concentration, aiding in determining which weed-killer is more effective.
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 disrupt the electron transport chain in chloroplasts, consequently affecting the photosynthetic process. By limiting photosynthesis, these chemicals reduce the energy available for plant growth, ultimately stunting the weeds' development.