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How plants drink (under the microscope)

About this lesson

Students will take a closer look at how water moves from a plant's roots up to other parts of the plant.


Year level: 3, 4, 5, 6

Theme: Water and the natural environment


Learning objectives

Students can:
  • understand the process of how water is transported through the stems of plants
  • carry out an experiment and use a microscope to examine the movements of water in plants.

Curriculum links

Science

  • Living things can be grouped on the basis of observable features and can be distinguished from non-living things ACSSU044
  • Living things, including plants and animals, depend on each other and the environment to survive ACSSU073
  • Living things have structural features and adaptations that help them to survive in their environment ACSSU043
  • The growth and survival of living things are affected by the physical conditions of their environment ACSSU094 

Things you will need

  • A head of celery (stem with leaves)
  • A thin slice of celery (called a cross-section)
  • 2 jars or plastic cups
  • Water
  • 2 different food colourings
  • Microscope

Lesson description

Discuss

This lesson should follow from Plants and water supply (under the microscope).

Explain to students how water pipes bring water from dams and underground supplies to our homes and school. Stems simulate this, as they are essentially a plant’s water pipeline. Describe how this is so.

Activity

Part 1 – Experiment

  • Explain to students they will use their microscope to look at the water transport system in the stems of a plant.
  • Have students look at the cross-section of the celery under the microscope. Get them to draw and describe what they see (students should be able to see vascular bundles – visible with the naked eye, as clusters of cells near the outer edge of the stem).
  • Students half fill both containers with water. Add one food colour to one container and the other food colour to the second container.
  • Split the celery stem halfway up to the leaves. Place one half of the stem in one container and the other half in the second container.
  • Have students label their containers with their name and then put them away in a safe place.
  • Get students to predict how they think water will travel up the celery stem and what they expect to see after the coloured dye has had time to move up the stem to the leaves (the vascular bundles should be clearly visible as this is where most of the dye will be absorbed).

Part 2 – Observations

  • Students come back to their containers after an hour or two or even the next day. The coloured water should have moved up the celery stems to the leaves. Have students draw and describe what they see. Get them to explain their observations.
  • Help students cut a thin slice of celery from each of the different coloured stems. Have students observe each slice under the microscope and then draw and describe what they see.

Reflect & summarise

  • As a class discuss students’ observations – were their predictions correct?
  • Discuss why only some parts of the stem changed colour. What do students think these parts are?
  • Watch the following video to recap the activity (optional).

Extension activities

  • Stems have special vessels that transport water and minerals from the roots to other parts of the plant. Find out the name of these vessels. These vessels also help to support the plant. How are they able to do this?
  • Plants also have vessels that carry glucose (sugar) made during photosynthesis to every part of the plant. What are these vessels called?
  • What is photosynthesis?
  • Why do plants need glucose?
  • Draw and label a diagram showing how water moves from the roots to the leaves of a plant. Next to the plant, draw another diagram showing how water is supplied from a bore to the kitchen tap at home. Discuss the similarities and differences.

Teacher background information

Much like water pipes bring water from dams and underground supplies to our homes and schools, stems are a plant’s water pipeline. Inside the stems are lots of thin tubes (xylem vessels), some of which carry water and minerals up from the roots while others (phloem) transport sugars from the leaves to all parts of the plant.

The pulling forces, which transport water up the plant is referred to as capillary action. The attraction of the water molecules and the molecules of the xylem is what causes the water to be drawn up, much like the action of sucking a straw. The process of transpiration (evaporation of water vapour from the leaves) also aids in the transportation of water, resulting in more water being pulled up from the roots.

Did you know?

On a dry, warm day a leaf can evaporate 100% of its water weight in just an hour.

Key vocabulary

  • Root: The part of a plant or tree that grows underground and obtains water from the soil.
  • Vascular bundles: A strand of conducting vessels in the stem or leaves of a plant, typically with phloem on the outside and xylem on the inside.
  • Xylem vessels: Hollow tube-like cells responsible for transporting water from the roots. They may be seen as light cylindrical structures in the centre of the root.