Transpiration and Translocation
Revise Transpiration and Translocation for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Transpiration moves water up through the xylem while translocation moves dissolved sugars through the phloem — a classic pair students mix up.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Transpiration is the loss of water vapour from the leaves, which pulls water up through the plant from the roots. Translocation is the movement of dissolved sugars through the phloem.
Water is absorbed by root hair cells, travels up the xylem, and evaporates from the leaves through the stomata. This continuous flow is called the transpiration stream, and it also carries mineral ions to where they are needed.
Four environmental factors increase the rate of transpiration: higher temperature, increased air movement, increased light intensity and lower humidity. Each works by increasing evaporation or by steepening the concentration gradient of water vapour.
Revision notes
The transpiration stream
Water is absorbed by root hair cells by osmosis, moves up the xylem, and evaporates from the leaf through the stomata.
The loss of water from the leaves pulls more water up behind it, creating a continuous stream that also transports dissolved mineral ions.
Factors affecting the rate
Temperature: higher temperature increases evaporation. Air movement: wind removes water vapour, maintaining a steep gradient.
Light intensity: brighter light opens the stomata wider for photosynthesis, increasing water loss. Humidity: lower humidity means a steeper gradient, so faster transpiration.
Translocation
Translocation is the movement of dissolved sugars made in the leaves to where they are needed for respiration or to storage organs.
It occurs in the phloem, moves in both directions, and requires energy — unlike transpiration, which is driven by evaporation.
Key points
- Transpiration is water loss from the leaves.
- Water travels up the xylem in the transpiration stream.
- Translocation moves dissolved sugars in the phloem.
- Higher temperature increases the rate of transpiration.
- Air movement and light intensity increase the rate.
- Higher humidity decreases the rate.
Worked examples
Example 1
Explain why transpiration increases on a windy day. [2 marks]
Model answer
Wind removes water vapour from around the leaf (1 mark), maintaining a steep concentration gradient so water diffuses out of the stomata more rapidly (1 mark).
Example 2
Explain why the rate of transpiration decreases when humidity increases. [2 marks]
Model answer
High humidity means there is already a lot of water vapour in the air around the leaf (1 mark), so the concentration gradient between the leaf and the air is shallower and less water diffuses out (1 mark).
Example 3
State two differences between transpiration and translocation. [2 marks]
Model answer
Transpiration moves water in the xylem, whereas translocation moves dissolved sugars in the phloem (1 mark). Transpiration moves upwards only and needs no energy, whereas translocation moves in both directions and requires energy (1 mark).
Common mistakes
Saying humidity increases transpiration.
Higher humidity reduces the gradient, so it slows transpiration down.
Confusing transpiration with translocation.
Transpiration moves water in xylem; translocation moves sugars in phloem.
Naming a factor without explaining the mechanism.
Say wind maintains a steep concentration gradient, not just that wind increases the rate.
Saying transpiration requires energy from the plant.
It is driven by evaporation, not by respiration. Translocation does require energy.
Exam tips
- Explain each factor through evaporation or the concentration gradient.
- Keep transpiration and translocation clearly separate.
- Name the tissue involved in each process.
- Remember light intensity works by opening the stomata.
Key terms
- Transpiration
- The loss of water vapour from a plant's leaves.
- Transpiration stream
- The continuous flow of water from roots to leaves.
- Translocation
- The movement of dissolved sugars in the phloem.
- Humidity
- The amount of water vapour in the air.
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Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.