AQA GCSE Biology Biology Paper 1 (Higher), 2024: Question 4

✅ Correct answers

• The leaf tissue that contains the most chloroplasts is the palisade mesophyll.
• The leaf tissue that contains many air spaces is the spongy mesophyll.
• The plant tissue that can differentiate throughout the life of the plant is the meristem.

💡 Key knowledge

• Palisade mesophyll is packed with chloroplasts for photosynthesis.
• Spongy mesophyll has air spaces to allow gases to move quickly through the leaf.
• Meristem contains unspecialised cells that can divide and become different cell types.

🧠 Exam technique

• These are one-word / one-phrase recall marks.
• Write the exact tissue name in the right order.
• Do not describe the tissue unless asked — the mark is for the correct term.

❌ Common errors

• Writing just chloroplast instead of palisade mesophyll.
• Writing spongy cell or one cell only — the mark scheme wants a tissue, not a single cell.
• Confusing meristem with mature tissues that are already specialised.

✅ Correct answer

Lignin

💡 Key knowledge

Lignin is deposited in xylem walls and makes them thick, strong, and waterproof. This helps xylem vessels transport water and resist collapse.

🧠 Exam technique

If the question asks for one other substance, give just the named substance. The mark scheme accepts lignin.

❌ Common errors

• Writing cellulose — this was already given in the question.
• Writing vague phrases like “strong wall material”.

✅ Correct answer

Translocation

💡 Key knowledge

Translocation is the movement of dissolved sugars in the phloem around the plant.

🧠 Exam technique

Use the plant-transport word translocation, not the general term “transport”.

❌ Common errors

• Answering active transport — the mark scheme says ignore this.
• Writing transpiration — that is water movement in xylem, not sugar movement in phloem.

✅ Correct answer

(Permanent) vacuole

💡 Key knowledge

Plant cells often contain a large permanent vacuole, which helps maintain turgor and can be seen in cell diagrams or micrographs.

🧠 Exam technique

When a figure is used, match the label to a visible sub-cellular structure. Here, the mark scheme accepts vacuole or permanent vacuole.

❌ Common errors

• Writing cell membrane or cell wall without checking the label.
• Giving a description instead of the structure name.

✅ Correct answer

• Cell X contains mitochondria.
• Mitochondria carry out aerobic respiration.
• Respiration releases energy.
• This energy is needed to move dissolved sugars against the concentration gradient from a low concentration to a high concentration.
• The sugars are moved by active transport.

💡 Key knowledge

• Active transport uses energy from respiration.
• It moves substances from low concentration to high concentration.
• Mitochondria are the site of aerobic respiration, so cells with lots of active transport need many mitochondria.

🧠 Exam technique

• To get full marks, link the ideas in a chain: mitochondria → respiration → energy → active transport → against concentration gradient.
• Each linked idea earns a mark when clearly stated.
• Use the phrase against the concentration gradient for top credit.

❌ Common errors

• Writing anaerobic respiration — this is not accepted.
• Saying “mitochondria make energy” — the mark scheme rewards releases energy, not “make/produce”.
• Forgetting to mention the concentration gradient.
• Talking about diffusion alone — this question is about active transport because sugar moves from low to high concentration.

✅ Correct answers

• Loss of cytoplasm
• Loss of nucleus
• Loss of mitochondria
• Loss of ribosomes
• Loss of sub-cellular structures
• End walls become perforated

💡 Key knowledge

When a plant cell differentiates into a phloem cell, it becomes specialised for transport. Some internal structures are lost, and sieve plates form to help sugars move through the phloem.

🧠 Exam technique

Only one correct structural change is needed. Give a clear feature seen in mature phloem cells, such as loss of nucleus or perforated end walls.

❌ Common errors

• Describing a phloem cell in general without stating a change.
• Writing “bigger” or “different shape” — the mark scheme does not accept size/shape changes here.
• Giving xylem features instead of phloem features.

✅ Must-know terms

• Palisade mesophyll
• Spongy mesophyll
• Meristem
• Lignin
• Translocation
• Active transport
• Mitochondria
• Permanent vacuole

🧠 How to get full marks

• Use exact biology terms.
• For explanations, link structure to function.
• For transport questions, mention energy and concentration gradients.
• Keep answers concise and focused on the mark scheme.