Water uptake
Introduced| English | Meaning |
|---|---|
| root hair cells/ruːt heə selz/ | A specialised root epidermal cell with a long extension that increases the surface area for absorbing water and mineral ions. |
| osmosis/ɒzˈməʊsɪs/ | The net movement of water molecules through a partially permeable membrane from higher to lower water potential. |
| active transport/ˈæktɪv ˈtrænspɔːt/ | The movement of substances across a cell membrane against their concentration gradient using energy and carrier proteins. |
| transpiration/trænspəˈreɪʃn/ | The loss of water vapour from a plant's aerial parts, mainly through its stomata. |
| transpiration stream/trænspəˈreɪʃn striːm/ | transpiration stream |
Drinking through roots
- A plant takes in all its water through its roots — then moves it up to every leaf.
- It starts at specialised root hair cells 根毛细胞.
Water enters a root hair cell by:
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Water moves in by osmosis down the water gradient.
Minerals are taken into root hair cells by:
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Minerals are scarce in soil, so active transport pulls them in.
A root hair cell's long shape gives it a large:
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Large surface area speeds water and mineral uptake.
Root hair cells
- Root hair cells have a long, thin extension giving a large surface area.
- Water enters them by osmosis 渗透; minerals enter by active transport 主动运输.
Water is taken up by root hairs, carried up the xylem, and lost from the leaves
Water uptake by root hairs
Root hair cells take in water by osmosis — water moves from the dilute soil into the more concentrated cell.
After crossing the root, water enters the ______ to travel up the plant.
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Xylem carries water up to the leaves.
The path of water
- Water passes from the soil → root hair cell → across the root → into the xylem.
- From there it travels up to the leaves.
A tree moves water up from its roots through xylem vessels
Evaporation of water from the leaves helps pull water up the plant.
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This creates the transpiration stream.
The pull from above
- Water is pulled up because it evaporates from the leaves (transpiration 蒸腾作用), creating a pull.
- This continuous column of water is the transpiration stream 蒸腾流.
Worked example. A root hair cell sits in dilute soil water. Water moves in by osmosis (down the water gradient), while scarce minerals are pulled in by active transport (against their gradient, using energy).
You've got it
- root hair cells (large surface area) take in water by osmosis, minerals by active transport
- water travels: soil → root → xylem → leaves
- evaporation from leaves pulls water up — the transpiration stream