Transport of water from roots to leaves during transpiration

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The **loss of water vapour** from the leaves of a plant, mostly through the **stomata**.

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Plant tissue made of long, **hollow, dead tubes** that carry **water** (and minerals) **upwards** from roots to leaves.

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**Upwards only** — roots → stem → leaves. It never carries water back down.

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The continuous, one-way flow of water from the **roots, up the xylem, to the leaves**, driven by transpiration.

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Water molecules **stick to one another**, forming one **continuous, unbroken column**.

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The **pull** on the water column created when water **evaporates** at the leaf; it is transmitted down the xylem.

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Evaporation at the leaf creates **tension**; **cohesion** keeps the column unbroken, so water is **pulled up** the xylem from the roots.

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They are **hollow dead tubes with no end walls** (one continuous pipe), and have **lignified walls** that stop them collapsing.

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Lignin makes the wall **strong**, so the vessel does **not collapse** under the tension (pull) of the water column.

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In the **xylem** — the water-carrying tubes (the central stele), where the strengthened walls show up.

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**Hot, dry, windy and bright** conditions — like drying washing on a line.

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It **slows it down** — moist surrounding air means a smaller difference, so less water diffuses out.

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Light **opens the stomata**, so more water vapour escapes and the rate **increases**.

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At the **root hair cells**, which have a large surface area for absorbing water from the soil.