6 Practical 5
Investigating leaves of xerophytes
Apparatus and materials
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stem and leaves of cultivated bell heather
(Erica cinerea)
prepared slide of TS of a leaf of Erica
prepared slide of TS of a leaf of marram grass
(Ammophila arenaria)
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microscope
hand lens
calibrated eyepiece graticule
Introduction
Xerophytes are plants that have adaptations for survival in dry conditions. In this practical, you will
observe some of the adaptations shown by the leaves of two plants, heather and marram grass.
Procedure
1
Use a hand lens to look at the stem and leaf structure of bell heather (Erica cinerea).
Remove a leaf and observe its shape and colour with a hand lens.
2
Use a hand lens to look at the prepared slide of a transverse section (TS) of a leaf of Erica.
3
Use the lower power of your microscope to examine a transverse section of a leaf of Erica.
Draw a low-power plan to show the distribution of the tissues. Use a ruler or calibrated eyepiece
graticule to measure the length and width of the leaf and include this information on your drawing.
4
Use the high power of your microscope to examine the epidermis on each side of the leaf.
Make high-power drawings to show the structure of three adjacent epidermal cells from each
epidermis. Labels are not required. Use a calibrated eyepiece graticule to measure the size of the
cells. State the size of the cells on your drawing.
5
Use a hand lens to look at the microscope slide showing a transverse section of a leaf of marram
grass (Ammophila arenaria). Compare this section with Figure 6.13 on page 96 of Biology 1.
Also observe fresh leaves of marram grass, if these are available.
COAS Biology 1 Teacher Resources
Original material © Cambridge University Press 2008
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6 Practical 5
6
Study the diagram, which is a plan drawing of a transverse section of a leaf of marram grass.
Use the low power and high power of your microscope to find the areas that correspond with the
structures listed below. Indicate the position of each on the plan drawing using label lines.
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outer epidermis
inner epidermis
epidermal hair
vein
thin-walled mesophyll cells containing chloroplasts
thick cuticle
area of thick-walled cells providing support
Read the following information about marram grass.
Marram grass, Ammophila arenaria, grows on sand dunes around the coasts of western
Europe. It is the dominant species on young dunes where sand is deposited by the wind. Small
heaps of sand build up around marram plants and fresh shoots grow up through the sand that
collects over them. In fact, marram does not grow well where sand is not frequently deposited
by the wind.
Sand drains very well and retains very little water. This means that only plants well adapted to
dry conditions can survive on sand dunes that are often exposed to strong winds. Rates of
transpiration are very high. Marram grass is well adapted to such dry, windy conditions.
Marram grass is a xerophyte. It grows in a dry habitat and can decrease its transpiration to a
minimum under conditions of water shortage.
In common with other grasses, marram grass has long, narrow leaves. In wet weather, the leaf
is flat and looks like many other grass leaves. In dry weather, cells located at the base of each
furrow lose water and shrink. These cells are called hinge cells because, when they shrink, the
furrows become narrower, making the leaf roll up to form a tube. When fully rolled-up, there
is just a narrow slit along one side of the tube to allow the entry of air.
COAS Biology 1 Teacher Resources
Original material © Cambridge University Press 2008
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6 Practical 5
8
Study Figure 6.13 on page 96 of Biology 1, which shows part of a transverse section of a rolled
leaf of marram grass. The inside of the leaf has deep furrows that are lined by thin mesophyll cells
full of chloroplasts. Much of the rest of the leaf is made of large, thick-walled cells, which support
the leaf, and veins that carry water, nutrients and sugars. When rolled like this, the leaf has a small
ratio of external surface to its volume. The outer epidermis has a thick cuticle and no stomata. All
the stomata are on the inner epidermis where additional protection is provided by stiff interlocking
hairs that reduce the flow of air inside the leaf.
9
Using your observations and the information above, answer the following questions.
a Draw up a table to show the differences between the upper and lower epidermis of Erica.
b Explain how and why the epidermal cells from opposite sides of the leaf of Erica are different.
c State three ways in which leaves of marram grass are adapted to survive in dry weather.
Explain how each of the methods you describe is effective in helping the plant to survive.
COAS Biology 1 Teacher Resources
Original material © Cambridge University Press 2008
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