Photo AI
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
The water potential being the same ensures that there is no net movement of water into or out of the chloroplasts during the experiment. This stability prevents osmotic stress, such as bursting or shrinking of the chloroplasts, which could affect their ability to carry out photosynthesis accurately.
Step 2
Explain why the student set up Tube 1.
Answer
Tube 1 was set up as a control to show that DCPIP does not get reduced in the absence of chloroplasts. It demonstrates that light does not affect DCPIP in solutions without chloroplasts, ensuring any observed changes in color in other tubes can be attributed to the chloroplasts' activity.
Step 3
Explain the results in Tube 2.
Answer
In Tube 2, the DCPIP remained blue after 30 minutes because it was in darkness and chloroplasts need light to facilitate the reduction of DCPIP. The absence of light prevents the light-dependent reactions of photosynthesis from occurring, so no electrons are transferred to reduce DCPIP.
Step 4
Explain the results in Tube 3.
Answer
In Tube 3, the DCPIP changed from blue to colourless after 30 minutes because chloroplasts were present and exposed to light. This exposure facilitates the light-dependent reactions, allowing electrons from chlorophyll to reduce DCPIP, causing the color change.
Step 5
Explain the advantage of the student using the IC₅₀ in this investigation.
Answer
Using the IC₅₀ provides a standardized reference point to compare the effectiveness of different chemicals or weed-killers. It allows the student to determine the concentration at which these chemicals inhibit DCPIP reduction by 50%, helping to evaluate the strength and efficacy of each chemical.
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 photosynthetic process, reducing the ability of chloroplasts to produce energy and organic compounds. By disrupting photosynthesis in weeds, these chemicals limit their growth and hinder their ability to thrive in their environment.