The structures found in plant cells but not in animal cells are:

• Cell wall
• Chloroplast
• Large vacuole

Thus, the correct answer is option D: cell wall, chloroplast, large vacuole.

To find the percentage difference, first calculate the mean length of starch grains:

For potato 2: Mean length = 50 µm

For potato 3: Mean length = 30 µm

The difference in mean length is:

$50 - 30 = 20\,\text{µm}$

Now, calculate the percentage difference relative to the mean length of potato 2:

$\text{Percentage difference} = \left( \frac{\text{Difference}}{\text{Initial}} \right) \times 100 = \left( \frac{20}{50} \right) \times 100 = 40\%$

1. Temperature of the environment where potatoes are stored.

2. Humidity or moisture levels in the storage conditions.

The potatoes need glucose for energy and respiration. Glucose is a vital source of energy for cellular processes, enabling the plant to grow and maintain its cellular functions.

Plan for the Investigation

1. Set up the experiment: Place a light source at varying distances from a pondweed in water.
2. Measurement: Measure the amount of oxygen produced, which can be assessed by counting the number of bubbles released or measuring the volume of oxygen collected in a syringe.
3. Repeat: Conduct the experiment multiple times at different distances from the light source to gather sufficient data.

Variables and how to control them

• Ambient Light: Ensure the room is completely dark before starting, closing curtains or turning off other light sources.
• Temperature: Use a thermometer to maintain a consistent temperature of the water.
• Carbon Dioxide Concentration: Add sodium hydrogen carbonate to the water to keep the carbon dioxide levels consistent.
• Amount of Pondweed: Use the same amount of pondweed in each trial to ensure consistency.