Friday, 10 September 2021 07:58

Plants - class 8 science revision notes

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Adaptations of plants to their environment.

Adaptations are mechanisms that enable a plant to survive in a habitat. Plants habitats include:-

  • Dry areas
  • Wet areas.
  • Normal soil and water condition

Plants adapted to dry area.

Plants that are able to survive in dry area are called xerophytes.

Examples include: Cactus, acacia, euphorbia, baobab, sisal, marram grass, pricky pears, desert
shrubs, sun dune grass, jacaranda, thorn tree, cassava, casuarinas and candelabra.

Characteristics of xerophytes.

  1. They have deep and widespread root system to obtain waterfrom a wider area.
  2. They have stemsthat can store water; their stems are thick, fleshy and succulent. They also have waxy cuticle to reflect sunlight which may cause overheating.
  3. They have needle-like leaves which reduces water loss by transpiration and evaporation.
  4. Some have few leaves to reduce water losslike acacia.
  5. Some shed leaves in dry seasonsto reduce water loss eg jacaranda.
  6. Some fold their leaves to trap moisture for the plant eg sun dune grass.
  7. Some are covered with a thick waxy cuticle which reduces water loss through evaporation eg sisal.
  8. Some become inactive during dry seasons.
  9. Some have sunken stomata that are hidden in small depression.
  10. Some have reversed stomatal rhythm i.e. open their stomata during the night and close during the day.
  11. Some have more stomata on the lowersurface than on the upper surface to reduce water loss through evaporation.

Plants adapted to wet areas.

They are called hydrophytes.

Most they grow in equatorial forests, swamps, marshes, lakes and rivers.

They include: water lily, butter cup, mangroves, bladderwort, water lettuce, duck weed, aquatic
ferns, rice plants and water hyacinth.

Adaptations of hydrophytes.

  1. They have broad or wide flat leaves which enables them to float on water and encourages water loss by transpiration eg water lily
  2. They have shallow roots which reduce the rate of absorption
  3. They have leafy shoots which encourages water loss by transpiration, they also have more stomatas on the upper surface than on the lowersurface
  4. They have numerous stomata which remain open to allow gas absorption for photosynthesis.
  5. They have flexible stemsthat cannot be broken by water currents.
  6. They have thin cuticle to encourage water loss through transpiration.
  7. They have air sacs to enable them to float on water.
  8. They have waxy and hairy leaf surface to prevent water from standing on the leaf surface.
  9. They have floating flowers to allow for the cross pollination by small animals.

Adaptations to normal soil and water conditions.

Plants which grow in normal soil and water conditions are called mesophytes.

They includes maize, beans, potatoes and bananas.

Signs of unhealthy crops.

  1. Leaf discoloration.
  2. Stunted or stranded growth.
  3. Curled leaves.
  4. Spots or streaks
  5. Wilting.

Effects of crop diseases.

  1. Lower yields.
  2. Reduces quality of produce.
  3. Reducesincome or economic loss.
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