Lesson Twenty Three: Adaptations of Plants

• Outcome
• Starter Activity (5-7 minutes)
• Procedure for Leaf Coverings
• Assessment Questions / Assignment

Outcome

• Classify pictures of habitats as deserts, tropical rain forests, or other areas.
• Infer that leaves which shed water quickly keep plants healthy in very damp climates.
• Observe the different types of shapes the plants exhibit.
• Explore the roles of succulence and tough outer coverings in preventing water loss

Materials (for each group)

• 3 sponges (4¾ x 3 x 11/16)
• 1 sponge (4¾ x 3 x 1½)
• Plastic bag
• 2 dishes large enough to hold sponges
• 2 measuring cups or graduated cylinders
• Water

Starter Activity (5-7 minutes)

Begin the lesson by posing focus questions

• What is adaptation?
• How are plants adapted to different habitats?

Adaptations are special features that allow plants and animals to live in particular habitats. The teacher is expected to provide students with pictures of local, desert, and tropical rain forest habitats and plants. Ask students to separate them by the places they come from. Let the students create a bulletin board panel for each habitat.

Activities:  Investigation of plant adaptations to different habitats  

Students will explore the roles of succulence and tough outer coverings in preventing water loss. Students will infer that leaves like these help plants survive in dry places.
Procedure

1. Give each group one large and one small sponge. Have them put each sponge in a dish. Have students pour equal amounts of water over each sponge. Allow the sponges to sit  in the water for a minute or so.
2. Have students squeeze the thin sponge into a cup. How much did it hold?

Repeat with the thicker sponge. Put the measuring cups next to each other. Which one has more water? (Older children can subtract to measure how much more the thick sponge holds.) Which sponge will dry out faster?

Remind the class that some plants live in places with lots of water, while others live in places with very little water.

Where would thick leaves be better? Thin leaves? Why?

Thick leaves like thick sponges can hold a large amount of water. In places where rain falls infrequently, plants with thick, sponge-like succulent leaves survive the droughts.

Procedure for Leaf Coverings

1. Give each group two thin dry sponges and let they place each in a dish.
2. Pour 250 ml of water over each sponge. Allow the sponges to sit in the water for a minute.
3. Students should carefully place one sponge in a plastic bag.
4. Now squeeze each sponge over measuring cups. Compare the amount of water which comes. In this demonstration, the bag acts like a tough waxy outer coating on a leaf, keeping moisture inside. Discuss the role of leaf shape and covering in keeping plants from loosing water in dry places.

For example, The Desert

The desert is very dry and often hot.  Annual rainfall averages less than 10 mm per year, and that rain often comes all at the same time.  The rest of the year is very dry.  There is a lot of direct sunlight shining on the plants.  The soil is often sandy or rocky and unable to hold much water.  Winds are often strong, and dry out plants.  Plants are exposed to extreme temperatures and drought conditions.  Plants must cope with extensive water loss. Plant Adaptations

• Some plants, called succulents, store water in their stems or leaves;
• Some plants have no leaves or small seasonal leaves that only grow after it rains.  The lack of leaves helps reduce water loss during photosynthesis.  Leafless plants conduct photosynthesis in their green stems.
• Long root systems spread out wide or go deep into the ground to absorb water;
• Some plants have a short life cycle, germinating in response to rain, growing, flowering, and dying within one year.  These plants can evade drought.
• Leaves with hair help shade the plant, reducing water loss.  Other plants have leaves that turn throughout the day to expose a minimum surface area to the heat.
• Spines to discourage animals from eating plants for water;
• Waxy coating on stems and leaves help reduce water loss.

Spine leaves of cactus

Waxy coating on its leaves

Light colored hair that helps shade the plant. 

Fig. 23.1: Plant Adaptations

Plants are classified according to where they grow:

Hydrophytes: Hydro means waterplants that grow in water, e.g., elodea, water lilies, seaweeds, algae.

• Mesophytes: Meso means middle/in between- plants that need moderate amounts of water, light and temperature, e.g., the plants in your garden.
• Xerophytes: Xero means dry / waterless-plants that grow in very dry regions, e.g., cacti and aloes.

Assessment Questions / Assignment

The students should be organized into groups of 8-10 and write a short note on the following.

1. Adaptations of desert plants and animals.
2. Adaptations of plants to water scarcity.
3. Behavioral adaptations in animals.
4. Importance of light to plants.
5. Effect of temperature or water scarcity and the adaptations of animals.