Study of plants found in xerophytic and aquatic conditions/habitats. And comment on their adaptations

 Practical Notebook Biology Standard XII

Biology 

Answeres

Practical Notebook
Standard XII

Class-12th

science

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8. Study of plants found in xerophytic and aquatic conditions/habitats.  And comment on their adaptations 

Introduction: 

Adjustment (acclimatization) of plants and animals for their survival and perpetuation, to their environment by means of special structures or functions, is known as adaptation The plants that can grow and survive in deserts, dry conditions of soil, and high temperature, are called xerophytes.  All xerophytes show adaptations to reduce the loss of water due to transpiration.  Some xerophytes show the presence of stored mucilage in the plant parts that help in retaining water.  Some plants have latex, that helps retain water and seal the place of injury.  E.g.  Euphorbia, Calotropis, Acacia, Opuntia. 

 The plants that grow in abundance of water are, called hydrophytes.  They are generally adapted to remain buoyant and avoid the decaying and tearing effects of water.  They have developed aerenchyma tissue for buoyancy.  e.g.  Hydrilla, Vallisneria, Eichhornia, Pistia, Nelumbo (Lotus), Typha. 

 Calotropis Procera (Race): 

1 Comment: 

1. It is a non-succulent, drought enduring, a wild shrub of arid, desert, and wastelands.  
2. The leaves and young branches are covered by a mealy coating along with hair which acts as an insulating covering.  
3. The leaves are thick and somewhat leathery 
4. The plant possesses latex.  

 2. Acacia arabica (Babhool) Comments:

1. It is a non-succulent xerophyte.  
2. The leaves are bipinnately compound.  Leaflets are very small in size to reduce transpiration.
3. The stipules are modified into spines to reduce transpiration and also to protect plants against marauding / grazing animals.  .  The older parts of the stem are covered over by thick, brown bark.  Fig.  Acacia arabica 

3. Opuntia dillenii (Nagphani) Comments:

1.  It is a succulent (drought resisting or enduring) xerophyte.  
2. The stem is flattened, jointed, green, and is called phylloclade.  It takes over the function of photosynthesis because the leaves are modified into spines.  (water storage tissue).  
3. The stem i.c.  phylloclade is fleshy succulent due to the presence of mucilage that retains water 
4. Phylloclades are with many nodes (areoles) and internodes.  The areoles have one or more spines which represent the modified leaves of an axillary branch.  
5. Bristles (Trichomes) provide protection against grazing animals.  Fig.  Opuntia

4. Hydrillo Comments: 

1. It is a submerged hydrophyte 1. e. 
2. grows entirely underwater.  It is attached to the substratum by poorly developed adventitious roots in freshwater.  
3. The stem is slender and soft.  It is without mechanical tissue, hence it limps when taken out of water.  
4.  Leaves are very thin, membranous, and are arranged in whorls.  They lack cuticles and stomata.  
5.  The entire plant is covered by mucilage that protects it from the rotting effect of water.  

5 . Vallisneria is another submerged hydrophyte.  & Eichhornia (Water Hyacinth) Comments

Fig.  Hydrilla It is a free-floating hydrophyte that grows in freshwater ponds, lakes, etc.  2 The stem is short and spongy due to the aerenchyma that stores air.  It is the offset that grows prostrate just below the water surface and serves as means for vegetative reproduction.  3 Leaves show swollen, spongy, petioles and arise in clusters at a node.  They have a waxy coating in addition to cuticle to prevent wetting and rottening.  4. Adventitious roots are also produced in clusters at nodes.  They act as balancers.  They have Toot pockets.  Root hair is absent.  Pistia is another free-floating hydrophyte, while Nelumbo (lotus) is anchored or rooted hydrophyte with floating leaves.

6. Typha (Cattail) Comments: 

Fig.  Eichhornia 

1. t is an amphibious and anchored hydrophyte that grows in marshy places or shallow waters 
2. The stem is a rhizome with adventitious roots and emergent leaves, coming out of the water surface 
3. The leaves are long, linear, soft, spongy, thick, and subcylindrical.  They have aerenchyma tissue.  
4. The leaves show the presence of mechanical tissue also and hence they are able to stand creat They have cuticles and stomata on the emergent part.  (Actually, Typha is a hygrophyte) Fig.  Typha