6 (i) 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 correct answer is D: cell wall, chloroplast, large vacuole. Plant cells have a cell wall that provides structure and protection, chloroplasts for photosynthesis, and a large vacuole that stores nutrients and maintains turgor pressure, all of which are not present in animal cells.

To calculate the percentage difference, use the formula:

$ext{Percentage Difference} = \frac{|\text{Value}_1 - \text{Value}_2|}{\text{Average of Values}} \times 100$

Assuming Value 1 (potato 2 at 5 weeks) is 50 and Value 2 (potato 3 at 10 weeks) is 30, the calculation would be:

$\text{Percentage Difference} = \frac{|50 - 30|}{\frac{50 + 30}{2}} \times 100 = \frac{20}{40} \times 100 = 50\%$

Potatoes need glucose for several reasons:

1. Energy Source: Glucose is a primary source of energy for cellular processes through cellular respiration.
2. Building Blocks: It serves as a precursor for synthesizing other carbohydrates, which are vital for the potato's growth and development.
3. Storage: Glucose can be stored as starch, providing energy reserves for the plant.

1. Objective: To determine how varying light intensity affects the rate of photosynthesis in green plants.
2. Materials: potted plants of the same species, light source, light meter, timer, water, and CO2 source (sodium bicarbonate).
3. Method:
   • Place the plant under the light source at a fixed distance.
   • Use a light meter to measure the initial light intensity.
   • Start the timer and measure the rate of photosynthesis by counting the volume of oxygen produced (using a water displacement method) over a fixed time.
   • Repeat the experiment by changing the distance of the light source to vary the light intensity (e.g., 10cm, 20cm, 30cm) while keeping all other conditions constant.
4. Control Variables: Ensure temperature, water availability, and CO2 levels remain constant throughout the experiment.