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All 14 Flashcards — Plant transport: xylem & transpiration
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Question
What is transpiration?
Answer
The **loss of water vapour** from the leaves of a plant, mostly through the **stomata**.
Question
What is the xylem?
Answer
Plant tissue made of long, **hollow, dead tubes** that carry **water** (and minerals) **upwards** from roots to leaves.
Question
In which direction does the xylem carry water?
Answer
**Upwards only** — roots → stem → leaves. It never carries water back down.
Question
What is the transpiration stream?
Answer
The continuous, one-way flow of water from the **roots, up the xylem, to the leaves**, driven by transpiration.
Question
What does 'cohesion' mean in the xylem?
Answer
Water molecules **stick to one another**, forming one **continuous, unbroken column**.
Question
What is the 'tension' in cohesion-tension?
Answer
The **pull** on the water column created when water **evaporates** at the leaf; it is transmitted down the xylem.
Question
Explain how transpiration pulls water up.
Answer
Evaporation at the leaf creates **tension**; **cohesion** keeps the column unbroken, so water is **pulled up** the xylem from the roots.
Question
Give two adaptations of xylem vessels.
Answer
They are **hollow dead tubes with no end walls** (one continuous pipe), and have **lignified walls** that stop them collapsing.
Question
Why are xylem walls lignified?
Answer
Lignin makes the wall **strong**, so the vessel does **not collapse** under the tension (pull) of the water column.
Question
Where is lignin found in a root cross-section?
Answer
In the **xylem** — the water-carrying tubes (the central stele), where the strengthened walls show up.
Question
Which conditions speed up transpiration?
Answer
**Hot, dry, windy and bright** conditions — like drying washing on a line.
Question
How does high humidity affect transpiration?
Answer
It **slows it down** — moist surrounding air means a smaller difference, so less water diffuses out.
Question
How does light affect transpiration?
Answer
Light **opens the stomata**, so more water vapour escapes and the rate **increases**.
Question
Where does water enter the plant?
Answer
At the **root hair cells**, which have a large surface area for absorbing water from the soil.
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Full study notes for Plant transport: xylem & transpiration
Topic 2.7 hub
Transport
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