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Plants and water loss (under the microscope)

About this lesson

Students will examine leaf samples to identify stomata and learn how different plants adapt to retain water.


Year level: 3, 4, 5, 6

Theme: Water and the natural environment


Learning objectives

Students can:
  • gain an understanding of how plants lose water through transpiration
  • examine leaf samples and identify how plants adapt to retain water
  • use a microscope to view adaptation characteristics and locate stomata in leaves.

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

  • Microscopes fact sheet
  • A variety of fresh leaf samples of plants from home or the school grounds (it is best to pick leaves mid-morning after exposure to sunlight, which opens their stomata, making them easier to see. Geranium leaves give a good result).
  • Scissors
  • Microscope
  • Plastic gloves

Lesson description

Discuss

  • Explain how a plant loses water through its leaves (transpiration).
  • Brainstorm some of the common features of leaves that help plants retain water (see teacher background for pointers).
  • Watch the video Transpiration (2:08).

Activity

  • In groups have students discuss the adaptation characteristics of the leaves in front of them. Draw and record observations. The follow questions may aid the discussion:
    • Does it feel furry or hairy? (E.g. lavender or geranium leaf)
    • Is it a small leaf? (E.g. Geraldton wax)
    • Is the surface of the leaf tough? (E.g. eucalypt)
    • Does it store water? (E.g. cactus leaf)
  • Students examine each leaf under the microscope and add any extra details.
  • Set the microscope on the maximum magnification (100X). Have students look at the underside of a geranium leaf. Can they find some stomata? (Students should see pinpricks of light on a darker background and each dot of light is a stoma).
  • Instruct students to move the leaf sample so that they can see the edge of the leaf. Are there any noticeable differences in the leaf edge? Try to explain why certain leaves display these adaptations (e.g. serrated edge versus smooth leaf hairs).
  • Students draw and describe what they see.
  • Examine other leaves under the microscope.

Reflect & summarise

  • What kind of adaptation characteristics did students observe on the various leaf types?
  • Did anyone identify stomata on the leaves? What did this look like?

Extension activities

  • Will transpiration in a plant be greatest on a warm, sunny day, a cold, damp day or at night?
  • Explain why only some of the water that rises up a plant from the roots escapes through the leaves.
  • Why is transpiration important to plants?
  • Describe a method of collecting clean drinking water that uses transpiration in plants. Draw and label a diagram to explain your method.

Teacher background information

What is transpiration?

A plant loses water vapour through its leaves in a process called transpiration. There are a number of factors that contribute to the amount of water a plant loses, these include:

  • Size of the plant
  • Type of plant – plants transpire at different rates depending on their ability to adapt to their surroundings (e.g. cacti in arid climate will save water and transpire less)
  • Temperature – transpiration increases as the temperature rises
  • Humidity – as humidity rises the transpiration rate drops (it is harder for water to evaporate in these conditions)
  • Wind speed – more movement in the air around a plant will cause a higher transpiration rate
  • Soil moisture – plants that lack water in the soil will deteriorate and as a result transpire less water \

The function of stomata

Water vapour escapes through tiny holes (pores) found primarily on the underside of leaves called stomata. The stoma (single pore) consists of cells known as guard cells. These cells are responsible for opening and closing the stomata, which provides plants with the ability to conserve water. Stomata also assist in allowing carbon dioxide and oxygen in and out – necessary for the process of photosynthesis.

Plant adaptations

All plants have different and distinct features that allow them to adapt and survive in certain environmental and climatic conditions. Leaves have many structures that help prevent water loss in plants and some of these include:

  • Small leaves – less evaporative surface per leaf. It also won’t get as hot as a large leaf which is likely to receive more sun exposure
  • Hairy leaves – insulate/ provide shade against heat, cold and dry wind, reflect sunlight
  • Thick, waxy layer – keeps plant cooler and therefore reducing loss of water
  • Succulent – help store water (e.g. cacti)

Did you know?

Stomata means mouth in Greek as it assists in the exchange between the internal and external environments of a plant.

Key vocabulary

  • Adaptation: A form or structure modified to fit a changed environment.
  • Stomata: Tiny openings in the epidermis of a plant (plant leaves) through which gases and water vapour pass.
  • Transpiration: The emission of water vapour from the leaves of plants.