Bihar Board - Class 12 Biology - Chapter 13: Organisms and Populations Short Answer Question

1. Why are calotropis plants not browsed by herbivores?

Ans: Calotropis plants are not browsed by herbivores because calotropis plants produce a highly poisonous glycoside that is a cardiac poison & thus, directly kills the predator.

2. Differentiate between stenohaline and euryhaline organisms.

Ans: Euryhaline: Organisms tolerant in a wide range of salinities. Stenohaline: Organisms tolerant to a narrow range of salinities.

3. List four features that enable the Xeric plants to survive in desert conditions.

Ans:

(i) Thick cuticle

(ii) Stomata in deep pits

(iii) Stomata closed during daytime

(iv) Leaves are reduced to spines (CAM photosynthetic pathway).

4. Differentiate between stenothermal and eurythermal organisms.

Ans: Eurythermal: Organisms that can tolerate and thrive in a wide range of temperatures.

Stenothermal: Organisms restricted to a narrow range of temperature.

5. Distinguish between ectotherms & Endotherms?

Ans: Ectotherms are those animals whose body temperature changes & matches with that of the environment in which they are living whereas Endotherms are those animals whose body temperature is maintained relatively constant by physiological regulation.

6. “Lichens are considered good examples of obligate mutualisms”. Comment?

Ans: Lichens show an intimate mutualistic relationship between a fungus & algae or cyanobacterium where the fungus helps in the absorption of nutrients & provides it to bacteria while the algae or cyanobacterium prepares the food.

7. Give any two examples of defense mechanisms in plants against herbivory?

Ans:

i) plants develop certain morphological means of defense e.g. thorns in bougainvillea & spines in cactus.

ii) plants produce & store certain chemicals which function by directly killing them or by inhibiting them from feeding.

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

Ans: Orchids grow as epiphytes on mango trees. This is an example of commensalism in which orchids are benefited by getting shelter while the tree is neither benefited or harmed.

9. State Gauss’s competitive exclusion principle?

Ans: Gause’s competitive exclusion principle states that two closely related species competing for the same resources cannot exist together as the competitively inferior one will be eliminated but this is true only when resources are limited & not otherwise.

10. What is migration? Why do animals show this phenomenon?

Ans: Migration is a phenomenon in which organisms can move away temporarily from the stressful conditions in the habitat with hospitable conditions e.g. birds undertake long-distance migration during winter.

11.  How do desert lizards maintain a fairly constant body temperature?

Ans: Desert lizards manage to deal with high temperatures by keeping their body temperature fairly constant by behavioral means. They bask in the sun & absorb heat when their body temperature is below the comfort level & move into the shade when it is higher.