Exercise Solutions

Important Questions

1. How is diapause different from hibernation?


Diapause is a period of suspended growth or development

It occurs both in summers and winters

Examples, zooplanktons undergo diapause in lakes and ponds under unfavourable conditions

Hibernation is a sleep like state in which a few animals

It occurs usually in winters

Example, bear goes into hibernation during winter.

2. If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?

Ans: When a marine fish is placed in a fresh water aquarium, the fish will not be able to survive because;

  1. Water will enter the body of fish by endosmosis.

  2. Marine fishes do not have mechanism of salt absorption as in freshwater fishes.

  3. Their drinking water habit will cause excess of water to enter the body.

So, marine fish will fail to maintain the osmolarity and hence will die.


3. Define phenotypic adaptation. Give one example.

Ans: Phenotypic adaptations are non-genetic changes

occurring in living organisms due to various extreme environmental conditions, such as stress, extreme temperature, change of habitat. These includes acclimatization, behavioural changes, etc.


4. Most living organisms cannot survive at temperature above 45°C. How are some microbes able to live in habitats with temperatures exceeding 100°C?

Ans: Most living organisms cannot survive at temperature above 45°C because

  1. Above 45oC enzymes get denatured.

  2. Protoplasm precipitates at high temperature.

However, some microbes (Archaebacteria) are found at 100oC because od

  1. Reduced fluidity of cell membrane due to presence of branched chain lipids in their cell membranes.

  2. Presence of heat-tolerant enzymes.


5. Last the attributes that populations but not individuals possess.

Ans: Some significant attributes that populations but not individual possess are –

(i) Natality

(ii) Mortality

(iv) Population density

(v) Population dispersion

(vi) Population age distribution

(vii) Sex ratio


6. If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?

Ans: If the population growing exponentially double in size in 3 years, the intrinsic rate of increase of this population will be towards maximum.

7. Name important defence mechanisms in plants against herbivory.

Ans: There are various defence measures for animals against predators. But plants, as they cannot move away, have certain defence mechanisms against herbivory. Their main defences are chemical toxins, such as strychnine, a poison produced by tropical vine, morphine by opium poppy, nicotine produced by tobacco plant. Apart from these chemicals, the common defence measure is presence of spines (modified leaves) on the leaves, stems of the plant, modifications of leaves into thorns, development of sharp silicated edges in leaves which prevent them against damage caused by herbivores.


8. An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?

Ans: An orchid plant is growing on the branch of a mango tree is called epiphyte, i.e., plants growing on other plants or trees. This type of interaction is known as commensalism, where in orchid / derives benefit of interaction whereas mango tree is not affected. The orchid growing on the branch of mango tree get more light to grow and also, the mango is not harmed in any way.

Commensalism can be defined as an interaction between two animal or plant species that habitually live together in which one species benefits from the association while the other is not significantly affected.


9. What is the ecological principle behind the biological control method of managing with pest insects?

Ans: The ecological principle behind the biological control method of managing with pest insects is predator – prey relationship. It is based on the ability of the predator to regulate prey population.


11. Write a short note on


(a) Adaptations of desert plants and animals :

Desert plants have very small leaves or no leaves at all, and carrying out photosynthesis through the stems. Their stem could become succulent, and can store and retain water. Animals living in hot climatic region tend to be smaller than those living in cold climates. This can be explained by the fact that the amount of heat gained from the environment is approximately proportional to the body surface area. The majority of animals living in desert are small, like kangaroo rat. It feed on dry seeds and other dry plant material and does not drink,


(b) Adaptations of plants to water scarcity :

The evergreen trees such as Rhododendron, show water scarcity by an inward curling of the leaves. A more significant response is the closure of stomata, which reduces transpiration, but raises the internal temperature of die leaf affecting the rate of synthesis of proteins and photosynthesis. Deciduous trees of the temperature region drop their leaves in autumn, avoiding winter drought. Some water stressed plant’s accumulate excessive amounts of inorganic ions.


(c) Behavioural adaptations in animals : 

Migrating temporarily to a less stressful habitat forms a more stressful habitat is a kind of behavioural adaptation in animals which enables them to survive in better environmental conditions. Desert lizards regulate their body temperature constant by behavioural means. They bask in the sun and absorb heat when their body temperature decreases below the optimum, but move into shady or underground places when the temperature of the surrounding area starts increasing.


(d) Importance of light to plants : 

Light affects plants through its quality, intensity and duration. Duration of light affects phenology, photosynthesis, growth, reproduction, flowering. Quality of light influences flowering, seed germination and movements. Light is required for the production of chlorophyll in chloroplasts. Plants germinated under insufficient illumination causes the destruction of chlorophyll.


(e) Effect of temperature or water scarcity and the adaptations of animals : 

Animals mai