SS2 Biology Lesson Note on Adaptation of Plants

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ADAPTATION OF PLANTS

Plants are grouped into three on the basis of the environmental conditions under which they grow, especially on availability of water in the soil. The three groups are hydrophytes, mesophytes and xerophytes.

Adaptation of Hydrophytes

Hydrophytes are plants that have adapted to living in the aquatic environment. They are either submerged of floating on the water surface. The plants can also grow in the soil that is permanently saturated with water. Their adaptive features include the following:

1. Possession of large air cavities called parenchyma that serve as a means of buoyancy and storing gases for respiration.
2. Possession of photosynthetic chloroplast that make use of less light in water for photosynthesis.
3. Possession of breathing roots (pneumatophores) by some of the hydrophytes, which grows above the water level to get enough oxygen for respiration.
4. Possession of hairy leaves and thin and waxy cuticle to repel rain water as they do not meet it.
5. Surface plants float on water have broad leaves that contain numerous stomata on the upper side of the leaf, which trap maximum light for photosynthesis.
6. Possession of small feathering roots.
7. Less rigid structure because water pressure support them.
8. They have succulent stem.
9. Numerous stomata are opened at all times.

Examples of hydrophytes include water lily, water lotus and water hyacinth.

Adaptation of Mesophytes

Mesophytes are terrestrial plants that grow in areas of moderate water supply. They are the large ecological group of terrestrial plants. Their adaptive features are:

1. Possession of well developed root system.
2. Presence of well developed vascular bundle.
3. Possession of large thin leaves.
4. Presence of large number of stomata on the under surface of the leaves.
5. Presence of erect and branded stem.
6. Possession of mesophyll layer that is well differentiated with many intercellular spaces.

Examples include maize, sunflower, cassava, hibiscus, mango and orange.

Adaptation of Xerophytes

Xerophytes are plants that grow in dry areas with little water or moisture such as desert. Their adaptive features are:

1. Reduced leaves that are reduced to spines and tiny scales to reduce water loss.
2. Reduced number of stomata to reduce water loss.
3. Sunken stomata reduce transpiration.
4. Large hairs on surface to reduce water loss.
5. Succulent leaves and stems to store water.
6. Deep root system to absorb water from depth.
7. Possession of thick, waxy cuticle that reduces water loss through cuticular transpiration.
8. Shedding of leaves during day season to prevent water loss through transpiration.
9. Possession of ability to fold their leaves during the day to decrease the number of stomata that is exposed, thus reducing the rate of transpiration.

Examples are cactus, euphorbia, Aacia, pine and opuntia.

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