AQA GCSE Combined Science: Trilogy Biology Paper 1 (Higher), 2021: Question 6

Key topics

• Water transport: osmosis, xylem, stomata, transpiration
• Sugar transport: translocation in phloem
• Phloem structure: sieve tubes and companion cells
• Why plants move sugars around the plant

How marks are awarded

• 1 mark questions need the exact term
• 2-mark questions usually need a point plus a reason
• 4-mark descriptions need a clear sequence of events
• Use correct plant transport vocabulary

✅ Correct answer

Water is absorbed from the soil by osmosis through root hair cells. It moves through the xylem vessels to the leaves. Water then evaporates from the leaf surfaces and exits through the stomata into the atmosphere. This movement is driven by transpiration.

💡 Key knowledge

• Osmosis is the movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
• Xylem carries water and mineral ions upward through the plant.
• Stomata are tiny pores in the leaves where water vapour leaves the plant.
• Transpiration is the loss of water vapour from the leaves.

🧠 Exam technique

• Write the water pathway in order: soil → root hair cell → xylem → leaf → stomata → atmosphere
• Include the process name transpiration to show what drives the movement.
• You do not need a full long explanation; 4 clear linked points can earn all 4 marks.

❌ Common errors

• Saying water is transported by phloem instead of xylem.
• Mixing up osmosis and diffusion.
• Forgetting that water leaves through the stomata.
• Not mentioning evaporation/transpiration as the reason water is pulled through the plant.

✅ Correct answer

Translocation

💡 Key knowledge

Translocation is the movement of dissolved sugars, such as sucrose, through the phloem from where they are made or stored to where they are needed.

🧠 Exam technique

For a 1-mark “name the process” question, the exact word matters. If you write “transport” or “movement,” that is too vague.

❌ Common errors

• Writing transpiration instead of translocation.
• Writing diffusion because the sugars are dissolved.
• Using a general word like “transport” with no specific process name.

✅ Correct answer

Sieve tube cells have pores in their end walls, so dissolved sugars can move from cell to cell. They also have few or no sub-cellular structures, such as no nucleus, which leaves more space for the movement of sugars.

💡 Key knowledge

• Sieve tubes are adapted for moving dissolved food materials.
• Pores in the end walls let sap flow through the tube.
• Few organelles / no nucleus means more room for transport.
• Thick, rigid cell walls can also help the tube withstand pressure.

🧠 Exam technique

• To get both marks, give the feature and explain how it helps.
• Use Figure 6: the pores and lack of nucleus are the easiest visible adaptations to mention.
• Answers like “it is hollow” can be too vague unless explained.

❌ Common errors

• Describing the companion cell instead of the sieve tube cell.
• Only naming the feature with no explanation.
• Saying “it has no nucleus because it is empty” — that is not the scientific wording needed.

✅ Correct answer

The process requires energy, so it is an active process / uses active transport. This is because companion cells have many mitochondria, which provide energy for the process.

💡 Key knowledge

• Many mitochondria = lots of respiration = lots of energy.
• Active transport is needed when substances move against a concentration gradient.
• Companion cells help load sugars into the sieve tube cells.

🧠 Exam technique

• For 2 marks, give one idea about the process and one reason.
• Good process words: energy , active process , active transport .
• Good reason: many mitochondria .

❌ Common errors

• Just writing “companion cells have mitochondria” with no link to energy.
• Saying the movement is passive or diffusion.
• Missing the idea that the cells are adapted to support sugar movement in the sieve tube.

✅ Correct answer

Sugars are made in the leaves by photosynthesis, but all cells need sugar for respiration. Moving sugars both upwards and downwards means sugars can be transported to meristems for growth and cell division, and to storage organs where they can be stored as starch, fat or oil.

💡 Key knowledge

• Leaves make sugars by photosynthesis.
• Respiration needs sugar in all living cells.
• Meristems need sugars for growth and cell division.
• Some sugars are transported to storage organs for later use.

🧠 Exam technique

• To score 3 marks, give three separate points.
• Think: made in leaves, needed by all cells, used for growth or storage.
• Use both directions: sugars travel to different parts of the plant depending on need.

❌ Common errors

• Saying sugars only move upwards.
• Forgetting that sugars are needed for respiration.
• Only mentioning storage, with no explanation of growth or respiration.
• Confusing sugar transport with water transport.

Key facts to remember

• Water: osmosis into root hair cells
• Water moves in xylem
• Water leaves through stomata
• Water loss is driven by transpiration
• Sugar movement in phloem is called translocation

📐 Memory tip

For transport questions, always ask:

• What is moving?
• Which tissue carries it?
• What is the process called?
• How is the structure adapted?

How to secure full marks

• Use the correct scientific word, not a general description.
• Link structure to function when asked about cells.
• For longer answers, write the steps in order.
• Don’t repeat the same idea in different words — add a new point each time.

Most common slips

• Mixing up xylem and phloem
• Writing diffusion instead of translocation
• Forgetting that companion cells have many mitochondria
• Not explaining why sugars must move to different parts of the plant