Higher Biology

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Higher Biology

• Adaptation
• Part 4

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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 adaptations- reduce transpiration rate
Structural adaptations- resisting drought
Physiological adaptations
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Structural adaptations

• To reduce transpiration rate
• Leaves have a reduced number of stomata.
• Leaves have a thick cuticle.
• Leaves can be rolled and/or hairy.
• Leaves have sunken stomata in pits.
• Leaves can be small and circular.
• 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
• Long roots.
• Extensive system of superficial roots.
• Storing water in succulent tissues.
• Folded stems.

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Physiological adaptations

• To reduce water loss
• 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.
• 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
• Not required since water provides the support for
  submerged plants.
• 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
• Store O2 produced during photosynthesis for use
  in respiration.
• 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

• 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.