Calculate the mean number of starch grains in potato cells P, Q and R - Edexcel - GCSE Biology: Combined Science - Question 6 - 2020 - Paper 1

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

• D cell wall
• chloroplast
• large vacuole.

These components are essential for the photosynthetic process and for maintaining turgor pressure in plant cells.

To calculate the percentage difference, use the formula:

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

Assuming the mean lengths are:

• Potato 2 at 5 weeks: 50 units
• Potato 3 at 10 weeks: 30 units

Calculation: (\text{Percentage Difference} = \frac{50 - 30}{50} \times 100 = \frac{20}{50} \times 100 = 40%)

Therefore, the percentage difference is 40%.

The potatoes need glucose because it serves as an essential energy source for cellular respiration. Glucose is crucial for converting sunlight into chemical energy during photosynthesis and is also necessary for various biochemical processes required for growth and development.

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

1. Set up the experiment:

   • Use a water plant, such as Elodea, in a beaker filled with water.
   • Place a light source at a measured distance from the plant.

2. Control Variables:

   • Control temperature, carbon dioxide concentration, and water availability to ensure a fair test.

3. Vary Light Intensity:

   • Change the distance of the light source from the plant at different intervals (e.g., 10 cm, 20 cm, 30 cm).

4. Measure Photosynthesis Rate:

   • Count the number of oxygen bubbles produced over a fixed time period or measure the volume of oxygen produced.

5. Repeat:

   • Repeat the experiment multiple times for accuracy and to obtain reliable results.

6. Record and Analyze Data:

   • Collect data to determine how the rate of photosynthesis varies with light intensity.