Nutrition

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Question 44

A student investigates how light affects the rate of gaseous exchange in photosynthesising organisms using immobilized green algae (Chlorella vulgaris) beads and hydrogen-carbonate indicator.

The student uses the following method:

Step 1: Place $cm38\text{ cm}^3$ of red hydrogen-carbonate indicator solution into three separate glass vials, A, B, and C.
Step 2: Place 20 active algae beads into vial A, and 20 active algae beads into vial B.
Step 3: Place 20 blank alginate beads (containing no algae) into vial C.
Step 4: Wrap vial B completely in aluminium foil to exclude all light.
Step 5: Seal all three vials with airtight rubber bungs.
Step 6: Place the vials $cm15\text{ cm}$ away from a bright light source. A large transparent container filled with cold water is positioned between the light source and the vials.
Step 7: Leave the setup undisturbed for four hours.

(i) Explain the purpose of vial C in this investigation. (ii) Explain why a transparent container of water is placed between the light source and the vials. (iii) Identify the independent variable in this experiment.

[3]

The table below shows the results obtained by the student:

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

(i) Explain the colour change observed in vial A. (ii) Explain the colour change observed in vial B.

[4]

Suggest an alternative experimental setup using an aquatic plant that would allow the student to quantitatively determine how varying light intensity affects the rate of photosynthesis.

[3]

Nutrition

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Question 44

A student investigates how light affects the rate of gaseous exchange in photosynthesising organisms using immobilized green algae (Chlorella vulgaris) beads and hydrogen-carbonate indicator.

The student uses the following method:

Step 1: Place $cm38\text{ cm}^3$ of red hydrogen-carbonate indicator solution into three separate glass vials, A, B, and C.
Step 2: Place 20 active algae beads into vial A, and 20 active algae beads into vial B.
Step 3: Place 20 blank alginate beads (containing no algae) into vial C.
Step 4: Wrap vial B completely in aluminium foil to exclude all light.
Step 5: Seal all three vials with airtight rubber bungs.
Step 6: Place the vials $cm15\text{ cm}$ away from a bright light source. A large transparent container filled with cold water is positioned between the light source and the vials.
Step 7: Leave the setup undisturbed for four hours.

[3]

The table below shows the results obtained by the student:

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

(i) Explain the colour change observed in vial A. (ii) Explain the colour change observed in vial B.

[4]

Suggest an alternative experimental setup using an aquatic plant that would allow the student to quantitatively determine how varying light intensity affects the rate of photosynthesis.

[3]

Nutrition

Question 44

Nutrition Questions

Nutrition

Question 44

Nutrition Questions