Science · Suggested Grade 7
Transpiration and Water Transport: Class 7 Guide
A plant can lose water through its leaves even when no droplets drip from them. Much of that water leaves as invisible vapour.
Original explanations and practice by BananaLearn · Published 1 November 2026
On a small screen, swipe across the illustration to read every label.
Trace the water route
Roots absorb water from the soil. Water moves through xylem in roots and stems to leaves. Within leaves, water evaporates from moist cell surfaces into air spaces and water vapour diffuses out, mainly through stomata. Transpiration is the loss of water vapour from a plant’s aerial parts.
This is a simplified route, not a claim that every drop follows an identical path. Stomata are small pores whose opening is regulated. Most water taken up is not simply stored forever in the plant or converted entirely into food.
Why water moves upward
Evaporation at the leaf contributes to a pulling effect through connected water in xylem. Water’s cohesion helps transmit that pull, with adhesion to vessel walls also contributing. Root uptake and other processes matter too. Avoid the picture of a tiny mechanical pump inside every leaf.
Transpiration is linked to the transport of water and dissolved mineral ions. Sugars made in photosynthesis are transported mainly in phloem, a different tissue. A labelled diagram should not place every transported substance in the same tube without distinction.
Do not confuse transpiration with photosynthesis
Photosynthesis uses light energy to make organic substances from carbon dioxide and water, releasing oxygen in the familiar school model. Transpiration describes water-vapour loss. Both involve leaves and water, but one process is not another name for the other.
Plants also respire, including at night. A statement such as leaves work only in daytime hides these differences. The rate of transpiration can vary with stomatal behaviour and environmental conditions; it is not automatically zero whenever photosynthesis slows.
Factors change rates, not just one fixed number
Warmer conditions can increase evaporation, moving air can remove moist air near a leaf, and high humidity can reduce the vapour concentration difference. Light can influence stomatal opening. These factors interact, and water shortage may cause stomata to close, limiting loss.
Therefore windy always means the same increase is too strong. The plant species, water supply and other conditions matter. A fair comparison changes one intended factor while controlling or recording the others. Rate means a quantity per unit time, not simply a final total.
Interpret a fictional mass-loss comparison
Imagine two identical planted setups with soil surfaces covered to reduce direct soil evaporation. In one hour, setup A loses 6 g and setup B loses 10 g. Their average mass-loss rates are 6 g/h and 10 g/h. The difference is 4 g/h. These are invented data for interpretation, not an actual experiment.
Even with covered soil, leaks, incomplete seals, balance error or differences between plants can affect the result. Mass loss supports a water-loss explanation under the stated controls; it does not directly count each molecule passing through stomata. Repeated measurements and appropriate controls strengthen the inference.
Observe safely and respectfully
A teacher-led demonstration may use a suitable healthy plant and clear covering around a leafy shoot to observe condensation, with an appropriate comparison and short observation period. Do not harm protected plants, leave covers on plants for long periods, or taste collected water. Follow the teacher’s chosen procedure.
For this guide, the paper model and fictional data are sufficient. Condensation inside a covering can support the presence of water vapour but does not by itself eliminate every other source. A conclusion should mention the comparison and what was controlled.
Build a complete explanation
A useful answer follows the route and names changes: water is absorbed, transported in xylem, evaporates within the leaf and diffuses out mainly through stomata. Add a condition if discussing a rate. This is clearer than saying plants sweat, which is only a loose analogy.
Use the resource to separate observation, interpretation and remaining uncertainty. Parents can ask which tissue carries water and whether the same statement describes sugars. If these are confused, revisit the transport diagram before memorising a list of environmental factors.
Observation, inference and controls
Copy the record into a notebook or use it to organise your own answer. Blank spaces are for your work.
| Record | Setup A | Setup B | What must be checked? |
|---|---|---|---|
| Mass loss in 1 h | 6 g | 10 g | Comparable plants, seals and balances |
| Average rate | 6 g/h | 10 g/h | Equal observation time |
| Conclusion | ___ | ___ | Avoid claiming an uncontrolled cause |
10 questions with explained answers
Try the questions before opening the answers. Explain the reason, then try a changed example to check your understanding.
Which tissue mainly transports water upward?
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Xylem
Distinguish it from phloem, which mainly transports sugars.What commonly leaves through stomata in transpiration?
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Water vapour
Not necessarily visible droplets.Where does evaporation occur in the simplified leaf model?
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From moist internal cell surfaces into leaf air spaces
Vapour then diffuses outward.Is transpiration another name for photosynthesis?
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No
They describe different processes.Does respiration stop in plants at night?
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No
Plants respire at night as well as during the day.6 g lost in one hour: average rate?
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6 g/h
Divide loss by time.10 g/h versus 6 g/h: rate difference?
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4 g/h
Subtract the rates.Why cover the soil in the fictional comparison?
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To reduce direct evaporation from soil
This helps isolate plant-associated water loss, without removing every possible error.Can water shortage reduce transpiration despite warm air?
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Yes
Stomatal closure can limit water loss.Should invented data be presented as a measured BananaLearn experiment?
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No
The guide labels the data as fictional.
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