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AIMS:
1. What are some desert plants?
2. What are some desert plant
adaptations?
MOTIVATION:
Show students pictures of different types
of desert plants. The following pictures were taken from http://ontheline.org.uk/explore/nature/deserts/plants.htm (picture 1),
pictures 2 through 5 are from http://mbgnet.mobot.org/sets/desert/index.htm and picture 6 is from http://xeri.com/xeriscape/palms/palm6.htm
Ask the following questions about the pictures:
What do you notice about these plants? What are their leaves like?
Why do you think some of the plants have such thick stems? What do you
think is stored in those stems? What do you think is the purpose of the spikes?
PROCEDURE:
1. After showing the students the different desert
plants, elicit the names of various plants, such as cactus, succulents, palm
trees, Joshua trees, creosote, mesquite, shrubs, bushes, mosses, lichens.
Students can link to http://mbgnet.mobot.org/sets/desert/index.htm to see the different plants.
Students can work in small groups and research each plant mentioned and
illustrate them.
2. Introduce vocabulary related to desert plants:
cactus, succulent, saguaro, adaptation, yucca, roots, palm tree, Joshua tree, creosote bush, stomata |
Students can look up the words from the following
websites: http://m-w.com (Merriam-Webster online) or http://dictionary.com
2. Initiate a discussion based on the following
questions- What conditions do the plants need to adapt to? and What adaptations
do you think the desert plants have to make in order to survive in the harsh
desert climate? From this discussion you should be able to come up with
enough adaptations to have students look up the information online and fill in a
database. You can choose a variety of plants that have adapted in different
ways. A few good sites to link to are http://cotf.edu/ete/modules/msese/earthsysflr/biomes.html and http://library.thinkquest.org/28855/species.html (where the pictures were
imported from). Click here for a
student copy.
ADAPTATION |
EXAMPLE |
Capturing Water |
1. Long roots to tap
into underground sources. 2. Short horizontal roots that collect
water as soon as it falls to the ground. |
Water Storage |
Plants store water either
in their stems, leaves, roots, or fruits. These plants are
called succulents and include cacti. |
Water Loss |
1. The size, sheen,
or texture of the leaf helps to minimize water loss. Small leaves or
spines limit the amount of surface area exposed to the drying heat. Glossy
leaves reflect the Sun's radiant heat reducing leaf temperatures and
evaporation rates. Waxy leaves prevent moisture from escaping.
2. Some plants only open their leaf pores at
night when air temperatures are cool and the evaporation rate is low. |
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LAB ACTIVITY:
To show how waxy leaves prevent moisture from escaping
this simple experiment can be performed:
Problem: How can we show how waxy leaves reduce
moisture loss in plants?
Hypothesis: We think if waxy leaves reduce
moisture loss, then a leaf coated in Vaseline should show less moisture
produced.
Materials: two identical plants, Vaseline, two
plastic bags.
Procedure: 1. On one plant, coat the
undersides of the leaves with a layer of Vaseline. 2. Place both
plants completely into the plastic bags and tie tightly. 3. Observe
the moisture build up on the inside of the bags over a few days.
Observations: After a few days, moisture beads
will have formed on the plant whose leaves were not coated in Vaseline.
There should be little or no moisture formed on the plastic bag with the
Vaseline coated leaves.
Conclusion: The Vaseline acts as a waxy coating on
the leaf. The fact that moisture is not forming proves that this prevents
the loss of moisture.
ASSESSMENT: Purchase a few different types of cactus and
succulents. Examine the root system on the plants. Are the roots
long? Are the roots shallow? Where is each plant searching for
water? Deep underground or on the surface? Have the students cut
open the stems. Have them notice if there is water stored in the stems?
Are the stems hollow? Do the same with the leaves. Are the leaves
fleshy? Why? What do you think is stored in the leaves? Are
the leaves waxy? Ask who remembers why some cactus have waxy leaves?
Continue in this manner until the children have figured out why this type of
plant is well adapted to desert conditions.
FOLLOW-UP: This lesson will
lead into the next lesson "What are
some desert animals?" |