Transcript adaptation-42

Higher Biology
Adaptation
Part 4
Adaptation 4
By the end of this lesson you should be
able to:
 Know what a xerophyte is.
 Describe the problems that xerophytes face.
 Describe how xerophytes are adapted to survive in
 their environment.
 Know what a hydrophyte is.
 Describe the problems that hydrophytes face.
 Describe how hydrophytes are adapted to survive in
their environment.
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Xerophytes


Moorlands- exposed and
windy
Xerophytes are plants
that have become
adapted to survive in
habitats where
transpiration rates are
very high.
Examples of habitats
are:
Deserts- hot and dry
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Xerophytes

There are 3 categories of xeromorphic
adaptations:
Structural adaptationsreduce transpiration rate
Structural adaptationsresisting drought
Physiological adaptations
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Structural adaptations
To reduce transpiration rate:
1. Leaves have a reduced number of
stomata.
2. Leaves have a thick cuticle.
3. Leaves can be rolled and/or hairy.
4. Leaves have sunken stomata in pits.
5. Leaves can be small and circular.
6. Leaves are reduced to spines.
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Structural adaptations
To reduce transpiration rate:
Marram Grass (T.S.)
Rolled leaf
Hairs
Thick cuticle
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Structural adaptations
To reduce transpiration rate:
Cactus surface
Sunken stomata
in pits
Thick cuticle
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Structural adaptations
To resist drought:
1. Long roots.
2. Extensive system
of superficial
roots.
3. Storing water in
succulent tissues.
4. Folded stems.
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Physiological adaptations
To reduce water loss:
1. Reversed stomatal rhythm- closed during
the day and open at night. They take in
CO2 during the night and store it for use
in photosynthesis during the day.
2. Ceasing vegetative activity during dry
times- e.g. existing in a desiccated state
(seed) and only germinating when water
becomes available.
 Insert and complete the “Xerophytes”
summary sheet .
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Hydrophytes

Partially submerged
e.g. water lily
Hydrophytes are
plants that live
either partially or
completely
submerged in
water.
Completely submerged
e.g. water milfoil
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Hydrophytes

These have evolved adaptations to help
them survive in an aquatic environment.
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Hydrophytes- adaptations
Specialised leaves
 Submerged leaves have no stomata.
 Floating leaves have all their stomata on
the upper surface.
 Floating leaves have long leaf stalks
(petioles) to enable the leaves to move up
and down in response to changes in water
level.
 Submerged leaves are narrow or finely
divided.
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Hydrophytes
Floating leaves- stomata
on top surface
e.g. water lily
Narrow, finely divided leaves
e.g. water milfoil
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Hydrophytes adaptations
Reduced Xylem:
1. Not required since water provides the
support for submerged plants.
2. Any xylem is found at the centre of the
stem- to allow flexibility in response to
water movements.
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Hydrophytes adaptations
Extensive air spaces:
1. Store O2 produced during photosynthesis
for use in respiration.
2. Provide buoyancy for leaves- keeps them
near the surface for maximum exposure
to light.

Insert and complete the “Hydrophytes”
summary sheet.
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Practice Questions

1.
2.
Torrance
TYK page 183 Q1-5
AYK page 184 Q4-6
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Adaptation 4
Can you do it?
 Know what a xerophyte is.
 Describe the problems that xerophytes face.
 Describe how xerophytes are adapted to survive in
 their environment.
 Know what a hydrophyte is.
 Describe the problems that hydrophytes face.
 Describe how hydrophytes are adapted to survive in
their environment.
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