AQA GCSE Biology Biology Paper 1 (Higher), 2024: Question 7

✅ Correct answers

• Leaf 1: covered with black paper, so no light reached the leaf.
• Without light, no photosynthesis happened.
• So no glucose was made, and therefore no starch was present.
• Leaf 2: covered with transparent plastic, so light could get in, but the leaf had no carbon dioxide.
• Without carbon dioxide, no photosynthesis happened.
• So no glucose was made and no starch was present.
• Leaf 3: not covered, so it had light and carbon dioxide.
• Therefore it could photosynthesise and make glucose, which was stored as starch.

💡 Key knowledge

• Photosynthesis needs light and carbon dioxide.
• Starch is made when glucose is produced and then stored.
• Black paper blocks light completely.
• Transparent plastic lets light through, but in this question it was used to remove carbon dioxide.

🧠 Exam technique

• Link each treatment to the missing factor.
• Then explain the consequence: no photosynthesis → no glucose → no starch.
• For Leaf 3, make the positive explanation: conditions allow photosynthesis, so starch is present.
• Use the exact wording “no starch present” or “starch present” for the test result.

❌ Common errors

• Saying only “it had no water” is not needed and does not score here.
• Writing “no photosynthesis because no starch” is backwards.
• Mixing up the roles of light and carbon dioxide.
• For Leaf 2, some students wrongly said the plastic blocked light. The question says transparent plastic.

✅ Correct answers

• Green part: starch present / positive test / blue-black colour.
• White part: no starch present / negative test / no blue-black colour.

💡 Key knowledge

• Green parts contain chlorophyll, so they can photosynthesise.
• White parts do not contain chlorophyll, so they cannot photosynthesise.

🧠 Exam technique

• This is a 1-mark table completion question.
• Write a clear starch test result for each part.

❌ Common errors

• Giving one answer for both rows.
• Writing only “yes” or “no” without saying starch.
• Confusing green with white parts.

✅ Correct answer

• The green part contains chlorophyll and the white part does not.
• So light is absorbed by the green part, photosynthesis occurs, and starch can be formed.
• The white part cannot photosynthesise, so no starch is made there.

💡 Key knowledge

• Chlorophyll is the green pigment needed for photosynthesis.
• Without chlorophyll, the leaf cannot capture light energy effectively.

🧠 Exam technique

• You get one mark for chlorophyll in the green part and one for linking that to photosynthesis and starch.
• Use “because” or “so” to show cause and effect.

❌ Common errors

• Saying “white areas are covered by chloroplasts” — the mark scheme focuses on chlorophyll.
• Forgetting to connect chlorophyll to photosynthesis.

✅ Correct answer

Magnesium (also allow Mg or Mg²+ ).

💡 Key knowledge

• Magnesium is needed to make chlorophyll.
• Without enough magnesium, leaves can become yellow.

❌ Common errors

• Writing “nitrate” or “iron” when the question specifically asks for yellow leaves.
• Giving a description instead of the ion name.

✅ Correct answer

Chlorosis

💡 Key knowledge

Chlorosis is the yellowing of leaves, often caused by a lack of chlorophyll due to mineral deficiency.

❌ Common errors

• Writing “necrosis” — that means tissue death, not yellowing.
• Giving “yellowing” only, without the scientific term.

✅ Correct answer

Measure the volume of oxygen produced in a given time, or count the number of bubbles produced in a given time.

🧠 Exam technique

• Always include time in the answer.
• Examples: “cm³ of oxygen per minute” or “bubbles per minute”.

❌ Common errors

• Only writing “measure oxygen” — too vague.
• Leaving out the time, so it is not a rate.

✅ Correct answer

A factor that, if increased, would increase the rate of photosynthesis, or a factor that stops the rate increasing further.

💡 Key knowledge

• Limiting factors can include light intensity, carbon dioxide concentration, and temperature.
• Only one factor limits the rate at a time.

❌ Common errors

• Saying “anything needed for photosynthesis” — too vague.
• Not showing that the factor affects the rate.

✅ Correct answer

• Increasing the temperature while keeping carbon dioxide concentration constant increases the rate of photosynthesis.
• This is because higher temperature increases the movement/kinetic energy of molecules and the frequency of collisions, so enzyme activity increases.
• Increasing the carbon dioxide concentration while keeping temperature constant also increases the rate of photosynthesis.
• This is because carbon dioxide is a reactant, so more of it increases the rate until another factor becomes limiting.
• All the curves plateau because another factor becomes limiting.

💡 Key knowledge

• Photosynthesis is controlled by several limiting factors.
• Temperature affects enzyme activity.
• Carbon dioxide is a raw material used in photosynthesis.
• When the line levels off, something else is limiting the rate.

🧠 Exam technique

• To get full marks, describe both trends and explain both using biology.
• Use the graph evidence: higher curves are above lower curves.
• Finish by stating why the curves level off.

❌ Common errors

• Saying the plateau happens because “light becomes limiting” in every case — the mark scheme does not accept that here.
• Forgetting to mention enzyme activity or collisions for temperature.
• Saying “carbon dioxide is a catalyst” — it is not.

✅ Correct answer

light intensity ∝ 1 / distance²

📐 Calculations / formula reading

1. Remember the inverse square law means intensity gets smaller very quickly as distance increases.
2. The correct relationship is:

light intensity ∝ 1 / distance²

❌ Common errors

• Writing 1 / distance instead of 1 / distance² .
• Reversing the relationship.
• Forgetting the square.

🧠 Exam technique

• Use the exact science words: chlorophyll, photosynthesis, starch, carbon dioxide, enzyme activity.
• For explain questions, write in a chain: cause → process → result.
• When a graph is involved, refer to what happens at low and high values, and mention the plateau.
• For one-mark answers, keep it short but precise.

💡 Key knowledge

• Light and carbon dioxide are needed for photosynthesis.
• Green parts have chlorophyll; white parts do not.
• Magnesium deficiency causes chlorosis.
• Rates are often measured per unit time.

❌ Common errors to avoid

• Mixing up “starch present” with “glucose present”.
• Forgetting that transparent plastic still lets light through.
• Giving vague answers like “it changed the rate” without saying how.
• Missing the square in the inverse square law.