How do desert plants prevent loss of water ?

Adaptations of desert plants to prevent loss of water are-:

1.  Presence of thick cuticle on stem and leaf surfaces. This reduces the rate of transpiration.

2. Some desert plants develop succulent organs (stems, leaves and roots) e.g. Asparagus, Begonia, Bryophyllum.

3. Presence of extensive root system to absorb water.

4. Either leaves are absent or small-sized leaves or transformed into spines to minimize the rate of transpiration.

5. The stomata get sunken to reduce the rate of transpiration.

6. Some xerophytes remain dormant either as seeds or as roots and  they sprout up during rains e.g. Cassia, Argemone

 

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To live in groups is beneficial because :
  • feeling of security
  • can obtain food easily
  • Partner is available for mating
  • All the above


D.

All the above
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What is competition ? Explain competitive release and Gause’s competitive exclusion principle. Write contribution of Mac Arthur.

 Competition is an interaction between organisms of the same species (intra-specific) or different species (inter-specific) for the same resources (nutrition, shelter, sunlight, etc.). It harms both the species.

Gause’s competitive exclusion principle states that two closely related species competing for the same resources cannot exist together indefinitely as the competitively inferior one will be eliminated eventually.

Mac Arthur had shown that five closely related species of warblers living on the same tree were able to avoid competition and co-exist to behavioural differences in their foraging activities. He gave an example of 'competitive release'.

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Name the major abiotic factors and state their importance.

Environmental factors. These include :

1. Light. 2. Temperature. 3. Water. 4. Soil. 

1. Importance of light. It is important for photosynthesis, flowering in plants, plant growth, metabolism, and periodicity.

2. Effect of temperature. It is the most important factor affecting almost all activities of organisms. 

3. Effect of Water- Water is essential for life. It covers more than 70% of the earth’s surface and forms the most extensive habitat for the organisms. Types of plants and animals distributed in water bodies greatly depends upon the nature of water (fresh-water or sea water). Land plants derive water from the soil while the land animals derive water from pools, ponds, lakes, rivers, springs etc.

4.Effect of Soil - Soil provides the necessary nutrition and minerals for the growth of plants and also provides shelter to anumber of organisms. 

 

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Explain J-Shaped pattern of population growth.


J-shaped Growth curve. Population grows exponentially and after obtaining peak value the population may abruptly decrease. It is shown by small population of reindeer experimentally reared in a natural environmental with plenty of food but no predators. It has only two phases :

1. Lag phase. It is period of adaptation of animals to new environment so is characterized by slow or no growth in population.


J-shaped Growth curve. Population grows exponentially and after obtai

â–² Fig. 5.2. J-shaped growth curve.

2. Logarithmic or Exponential phase. It is characterized by rapid growth in population which continues till enough food is available. But with the increase in reindeer population, there is corresponding decrease in the availability of food which finally becomes exhausted, which leads to mass starvation and mortality. This sudden increase in mortality is called population crash.

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