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Follow water and sugars through plants and reason about transpiration with three worked examples and 12 original questions.
Original AI-assisted Readnary material. Not independently academically reviewed; answers may contain errors. Check important results against your course materials.
Selected content from Biology 0610 section 8 for 2026-2028 exams. It focuses on xylem, phloem, water uptake and transpiration factors; anatomy drawing and full experimental methods are outside this guide.
| Tissue or process | Main role | Direction or route |
|---|---|---|
| Xylem | Water and mineral ions; support | Mostly upwards from roots |
| Phloem | Sucrose and amino acids | Source to sink as needed |
| Transpiration | Water vapour loss from leaves | Through stomata to air |
Root hair cells provide a large surface area in contact with soil water. Water enters root cells by osmosis when the relevant water-potential gradient is favourable; dissolved mineral ions may need active transport, which uses energy. Water then passes through root cortex cells into the xylem. Trace the named route when answering: root hair cell, cortex, xylem and mesophyll in the leaf. Do not say all dissolved materials move by the same process or that root hairs are underground leaf structures.
Xylem vessels carry water and mineral ions from roots through stems to leaves and help support the plant. Their thick lignified walls and long hollow pathway suit this job. Phloem carries sucrose and amino acids between sources and sinks: for example, from photosynthesising leaves towards growing or storage regions. The route in phloem depends on the current source and sink; it is not simply 'always down'. A stem cross-section shows both tissues, but their positions must be read from the particular diagram supplied.
Water evaporates from moist mesophyll surfaces and water vapour diffuses through air spaces and stomata to the surrounding air. This water loss is transpiration. Continued loss helps draw water up through the xylem from the roots. Stomata allow gas exchange as well as water-vapour escape; guard cells regulate their opening. A leaf does not deliberately 'pump' water vapour out with a motor-like action. Describe evaporation inside the leaf and diffusion out when explaining the pathway.
At otherwise comparable conditions, a warmer leaf generally loses water faster because evaporation and diffusion increase. Greater air movement removes humid air around the leaf and can maintain a steeper vapour gradient. Greater ambient humidity reduces that gradient and usually reduces water loss. Light often opens stomata, increasing loss, but species and water status matter. State what is controlled in comparisons. A single wilting result does not by itself identify which environmental factor changed.
Place root hair cell, xylem, root cortex cell and leaf mesophyll cell in the order water follows from soil to leaf.
A plant loses more water on a windy than a still day at similar temperature, light and humidity. Explain.
A leaf makes sucrose while roots absorb mineral ions. Which tissue mainly carries each?
Try each question before opening its answer. Numerical answers should include your working.
Its long projection gives a large surface area in contact with soil water; water can enter by osmosis along a suitable water-potential gradient.
Root hair cell -> root cortex cells -> xylem -> leaf mesophyll cells.
Water and dissolved mineral ions, mainly upwards from roots, and it provides structural support.
Sucrose and amino acids between source and sink tissues.
No. It runs from a source to a sink, which can be above or below depending on where materials are produced and needed.
Xylem. Vessel structure and lignified walls help transport water and support the stem.
Loss of water vapour from leaves, including evaporation from moist surfaces and diffusion out through stomata.
The outside air already contains more water vapour, so the diffusion gradient away from the leaf is smaller.
Transpiration generally rises because moving air removes humid air near the leaf and maintains a steeper vapour gradient.
Evaporation and diffusion generally increase with temperature, assuming other conditions such as stomatal opening remain comparable.
They are pores through which water vapour exits and gases exchange; guard cells regulate their opening.
No. Both variables may alter water loss, so change wind while keeping light and other relevant conditions as constant as possible.
Xylem is not the main sugar-transport tissue. Phloem movement is source-to-sink rather than universally downwards. Water vapour loss involves evaporation and diffusion; environmental predictions assume other relevant conditions are comparable.
Biology · IGCSE · STUDY GUIDE
Follow water and sugars through plants and reason about transpiration with three worked examples and 12 original questions.
Read the original Readnary guide in PDF view or use the web lesson above. Try the questions before revealing their explained answers.