Plant transport: water loss draws water through xylem
مُقدَّم| English | المعنى |
|---|---|
| transpiration/trænspəˈreɪʃn/ | النتح |
| translocation/trænsləʊˈkeɪʃn/ | الانتقال |
What would explain this observation?
- A potometer bubble moves when a shoot takes up water. This is useful evidence about transpiration 蒸腾作用, but uptake and evaporation are not exactly the same quantity.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Roots, stem and leaves form a transport system. Root hairs absorb water and mineral ions. Xylem consists of hollow dead vessels strengthened by lignin and carries water and ions from roots toward leaves. Phloem uses living tissue to move dissolved sugars from producing or storing regions to where they are needed; this is translocation 运输.
- transpiration: Loss of water from a plant by evaporation; translocation: Transport of dissolved sugars in phloem.
Which change generally reduces transpiration with other conditions matched?
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Transpiration is driven by evaporation, which slows when the surrounding air is already humid - the diffusion gradient for water flattens. Moving air and higher temperature both speed evaporation and increase transpiration.
Match each technical term to its precise meaning.
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Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Transpiration is water loss by evaporation from leaf surfaces, mainly through stomata after water evaporates from moist internal tissues. Guard cells control stomatal opening. Higher temperature and greater air movement generally increase loss; greater humidity reduces the water-vapour gradient. More light usually opens stomata, increasing loss under comparable conditions.
- Use a school-approved potometer or provided data with an airtight setup, an acclimatized shoot and matched leaf area. Change one environmental factor at a time, repeat, and plot mean uptake against that factor. If calculating volume from tube distance, use cross-sectional area×distance. Some absorbed water is used or stored, so interpret uptake as an estimate of transpiration.
Which two habits make the investigation or model in this case more defensible?
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Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a bubble moves 18 mm in 6 min, giving 3 mm/min. If tube area is 0.50 mm², volume uptake=0.50×18=9.0 mm³, and volume rate=9.0/6=1.5 mm³/min. Distance rate and volume rate are different measures and must not be mixed.
A potometer has tube area 0.40 mm² and bubble distance 20 mm over 4 min. Calculate volume uptake rate. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A potometer has tube area 0.40 mm² and bubble distance 20 mm over 4 min. Calculate volume uptake rate.
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The result is 2 mm³/min. Known: tube area 0.40 mm^2; bubble moves 20 mm in 4 min. Volume uptake = area x distance = 0.40 x 20 = 8.0 mm^3. Rate = 8.0/4 = 2 mm^3 per minute. Distance rate and volume rate are different measures.
Check the conclusion and its limits
- Phloem and xylem do not both carry only water upward. A faster bubble can reflect a leak or unmatched leaf area. Closing stomata conserves water but also affects carbon-dioxide entry and therefore photosynthesis.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Water uptake measured by a potometer is always exactly equal to water evaporated. This claim is false: A potometer measures water UPTAKE by the shoot. Some water is used in photosynthesis and kept in tissues, and leaks bias the bubble, so uptake is an estimate of - not exactly equal to - evaporation.
Plant transport: water loss draws water through xylem: Transpiration is water loss by evaporation from leaf surfaces, mainly through stomata after water evaporates from moist internal tissues. Guard cells control stomatal opening. Higher temperature and greater air movement generally increase loss; greater humidity reduces the water-vapour gradient. More light usually opens stomata, increasing loss under comparable conditions.
Water uptake measured by a potometer is always exactly equal to water evaporated.
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A potometer measures water UPTAKE by the shoot. Some water is used in photosynthesis and kept in tissues, and leaks bias the bubble, so uptake is an estimate of - not exactly equal to - evaporation.
Loss of water from a plant by evaporation: write the technical term.
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transpiration means Loss of water from a plant by evaporation.