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Biology · Grades 8–11

Transport in plants

Distinguish xylem, phloem and water loss.

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Learn the idea

Xylem

Xylem transports water and dissolved mineral nutrients in the usual plant model.

Phloem

Phloem transports sugars and other solutes between sources and sinks.

Transpiration

Evaporation from leaves and diffusion through stomata contribute to water loss.

Conditions

Temperature, humidity, air movement and stomatal behavior can affect water loss.

Worked examples

Which tissue is associated with water and mineral transport?

Xylem provides a water-transport pathway.

Xylem.

Which tissue moves sugars between sources and sinks?

Phloem transports organic solutes.

Phloem.

Check your understanding

  1. What are stomata?

    1. Small chromosomes.
    2. Adjustable pores involved in leaf gas exchange.
    3. Only roots.

  2. A model shoot loses 8 g of water in 4 hours. Find the average mass-loss rate.

  3. Why might greater humidity reduce transpiration under otherwise similar conditions?

Answers and marking notes

Answers and marking notes
  1. Adjustable pores involved in leaf gas exchange.

    Stomata connect internal leaf spaces with the atmosphere.

  2. 2 g/hour

    8/4 = 2 g per hour.

  3. It reduces the water-vapor gradient from leaf air spaces to the surrounding air.

    State the gradient explanation and that other conditions matter.

Further reading and review references

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Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.