Nutrition

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Question 26

A student investigates how light availability affects the rate of photosynthesis in the green unicellular alga Scenedesmus. To make the microscopic algae easier to handle, the student immobilises them into calcium alginate beads.

The student uses the following method:

Step 1: Place $cm310\text{ cm}^3$ of red-orange hydrogen-carbonate indicator solution into each of three test tubes, A, B, and C.
Step 2: Place 20 algae-containing beads into tube A and another 20 algae-containing beads into tube B.
Step 3: Place 20 alginate beads containing no algae into tube C.
Step 4: Wrap tube B completely in aluminium foil to exclude all light.
Step 5: Seal all three tubes with airtight rubber bungs.
Step 6: Place the tubes $cm15\text{ cm}$ away from an LED light source in a water bath maintained at $22∘C22^\circ\text{C}$ for four hours.

(i) Explain the purpose of tube C in this investigation. (ii) Why is it necessary to keep the temperature of the water bath constant? (iii) Name the independent variable in this investigation.

[3]

The table shows the student's results:

Test tube	Algae present	Light conditions	Colour of indicator at start	Colour of indicator after four hours
A	Yes	Light	Red-orange	Purple
B	Yes	Dark	Red-orange	Yellow
C	No	Light	Red-orange	Red-orange

(i) Explain the change in colour of the indicator in tube A. (ii) Explain the change in colour of the indicator in tube B.

[4]

Suggest a different method using these algae beads that the student could use to quantitatively determine how light intensity affects the rate of photosynthesis.

[3]

Nutrition

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Question 26

The student uses the following method:

Step 1: Place $cm310\text{ cm}^3$ of red-orange hydrogen-carbonate indicator solution into each of three test tubes, A, B, and C.
Step 2: Place 20 algae-containing beads into tube A and another 20 algae-containing beads into tube B.
Step 3: Place 20 alginate beads containing no algae into tube C.
Step 4: Wrap tube B completely in aluminium foil to exclude all light.
Step 5: Seal all three tubes with airtight rubber bungs.
Step 6: Place the tubes $cm15\text{ cm}$ away from an LED light source in a water bath maintained at $22∘C22^\circ\text{C}$ for four hours.

(i) Explain the purpose of tube C in this investigation. (ii) Why is it necessary to keep the temperature of the water bath constant? (iii) Name the independent variable in this investigation.

[3]

The table shows the student's results:

Test tube	Algae present	Light conditions	Colour of indicator at start	Colour of indicator after four hours
A	Yes	Light	Red-orange	Purple
B	Yes	Dark	Red-orange	Yellow
C	No	Light	Red-orange	Red-orange

(i) Explain the change in colour of the indicator in tube A. (ii) Explain the change in colour of the indicator in tube B.

[4]

Suggest a different method using these algae beads that the student could use to quantitatively determine how light intensity affects the rate of photosynthesis.

[3]

Nutrition

Question 26

Nutrition Questions

Nutrition

Question 26

Nutrition Questions