A slide of potato cells was viewed using a light microscope - Edexcel - GCSE Biology - Question 9 - 2020 - Paper 1

The correct answer is D: cell wall, chloroplast, large vacuole. These structures are characteristic of plant cells and are not present in animal cells.

The mean length of starch grains in potato 2 after 5 weeks is 50 µm, and in potato 3 after 10 weeks is 30 µm. The percentage difference can be calculated using the formula:

$ext{Percentage Difference} = \frac{\text{Value 2} - \text{Value 1}}{\text{Value 1}} \times 100$

Substituting in the values:

$\text{Percentage Difference} = \frac{50 - 30}{50} \times 100 = \frac{20}{50} \times 100 = 40\%$

Thus, the percentage difference is 40%.

1. Temperature of storage - the temperature should be kept constant to eliminate its effect on starch grain length.

2. Type of potato - using the same variety of potato ensures that any differences in starch grain size are due to the storage conditions rather than inherent differences in the potatoes.

Potatoes convert starch into glucose for energy. Glucose is essential for cellular respiration, which provides the energy necessary for growth and cellular activities.

To investigate the effect of light intensity on photosynthesis, follow these steps:

1. Setup: Place a light source at varying distances from a sample of pondweed in water to change light intensity.

2. Measure oxygen production: Count the number of bubbles produced or measure the volume of oxygen released over a fixed time period.

3. Repeat: Conduct the experiment multiple times at each distance to ensure reliable results.

Variables to control:

• Temperature: Use a water bath to maintain a constant temperature during the experiment.
• Carbon Dioxide Levels: Add sodium hydrogen carbonate to the water to keep carbon dioxide levels consistent.
• Type of Pondweed: Use the same species and size of pondweed for each trial.