Extra Questions for Class 12 Biology Chapter 13 Organisms and Populations

Extra Questions for Class 12 Biology Chapter 13 Organisms and Populations

Q.1. Name the interaction between sea anemone and the hermit crab that grows on it.
Ans. Commensalism

Q.2. Why are green algae not likely to be found in the deepest strata of the ocean?
Ans. The wavelength of light at the deepest strata is unsuitable for growth of green algae.

Q.3. Species that tolerate wide range of salinity are called __.
Ans. Euryhaline.

Q.4. What is the interaction called between Cuscuta and shoe flower bush?
Ans. Parasitism

Q.5. What is an interaction called when an orchid grows on a mango plant?
Ans. Commensalism

Q.6. Give one function of aerenchyma in aquatic plants.
Ans. Aerenchyma gives buoyancy to the aquatic plants due to presence of air chambers.

Q.7. Write the basis on which an organism occupies a space in its community/natural surroundings.
Ans. Feeding relationships with other organisms.

Q.8. What do phytophagous insects feed on?
Ans. Phytophagous insects feed on plant sap and other parts of plant.

Q.9. Between amphibians and birds, which will be able to cope with global warming? Give reasons.
Ans. Birds being eurythermals can tolerate a wide range of temperature and thus will be able to cope with global warming more efficiently.

Q.10. Why are some organisms called as eurythermals and some others as stenohaline?
Ans. Eurythermals are organisms that can tolerate and thrive in a wide range of temperature, whereas stenohalines can tolerate a narrow range of salinities.

Q.11. Name the interaction between a whale and the barnacles growing on its back.
Ans. Commensalism

Q.12. Name a ‘photoperiod’ dependent process, one each in plants and in animals.
Ans. In plants, flowering and in animals, migration/foraging are photoperiod dependent processes.

Q.13. Which one of the two, stenothermals or eurythermals, shows wide range of distribution on earth and why?
Ans. Eurythermals show a wide range of distribution on earth, as they show tolerance for wide range of temperatures.

Q.14. Why are mammals the most successful animals on earth?
Ans. The mammals are most successful animals on earth because they can maintain a constant body temperature with high range of tolerance whether in Antarctica or in Sahara desert.

Q.15. What are ectotherms?
Ans. Ectotherms are those animals whose body temperature changes and matches with that of the environment in which they are living. They are also called cold-blooded animals.

Q.16. Mention the effect of global warming on the geographical distribution of stenothermals like amphibians.
Ans. Due to global warming, stenothermals would either migrate or die due to change in the temperature.

Q.17. When and why do some animals go into hibernation?
Ans. When the animals are not able to tolerate the stressful conditions like low temperature, they hibernate to avoid the stress by escaping in time since they can not migrate.

Q.18. What is mycorrhiza?
Ans. Mycorrhiza is a symbiotic association between a fungus and the roots of higher plants.

Q.19. When and why do some animals like snails go into aestivation?
Ans. Snails undergo aestivation if they are unable to migrate in order to avoid stressful condition of high temperature.

Q.20. Why do people living in high altitude have more haemoglobin/high RBC count?
Ans. To acclimatise at high altitude, the people have more haemoglobin/high RBC count to compensate for the low oxygen availability.

Q.21. State Gause’s Competitive Exclusion principle.
Ans. Gause’s Competitive Exclusion Principle states that two closely related species competing for same resources, cannot coexist indefinitely, (the inferior will be eliminated) by the superior one.

Q.22. What is a tree line?
Ans. When we go up the altitude, beyond a particular height no tree are found and the vegetation comprise only of shrubs and herbs. The altitude beyond which no tree is seen is known as tree line.

Q.23. Why has life history of variation evolved?
Ans. (a) Life history of variation has evolved.
(b) In order to maximise reproductive fitness of individual.

Q.24. Why are cattle and goats not seen browsing on Calotropis growing in the fields?
Ans. Calotropis produces highly poisonous cardiac glycosides. Therefore, cattle and goats do not
browse on them.

Q.25. What does nature’s carrying capacity for a species indicate?
Ans. In nature, a given habitat has enough or limited resources to support a maximum possible number of population and nature’s carrying capacity indicates that how much growth is possible in a population.

Q.26. Pollinating species of wasps show mutualism with specific fig plants. Mention the benefits the female wasps derive from the fig trees from such an interaction.
Ans. The wasp uses the fruit as oviposition, i.e., egg laying and the developing seeds for nourishing its larvae.

Q.27. Name two organisms (one plant and one animal) which breed only once in their life time.
Ans. Pacific salmon fish and bamboo.

Q.28. If 8 individuals in a laboratory population of 80 fruit flies died in a week, then what would be the death rate of population for the said period?
Ans. Death Rate = Number of individuals dead / Total number of individual = 8/80 = 0.1. The death rate will be 0.1 individuals per week.

Q.29. What is Allen’s rule?
Ans. According to Allen’s rule, mammals in colder climate have shorter ears and shorter limbs to minimise heat loss.

Q.30. Why do predators avoid eating Monarch butterfly? How does the butterfly develop this protective feature?
Ans. The Monarch butterfly is highly distasteful to its predator (birds) because of a special chemical present in its body. It acquires this chemical during its caterpillar stage by feeding on a poisonous weed.

Q.31. Give an example of an organism that enters ‘diapause’ and why.
Ans. Many species of Zooplankton under unfavourable conditions enters diapause which delay overall development and hence they can pass unfavourable conditions.

Q.32. Give two reasons as to why a weed such a Calotropis flourishes in abandoned fields.
Ans. Calotropis flourishes in abandoned fields because of:
(i) It has dry hairy seeds which help in dissemination (ii) Its have xerophytic adaptations like thick hair on leaves and stems. (iii) It is not grazed by animals as it produces poisonous substances like
cardiac glycosides. (Any two)

Q.33. What does J-shaped growth curve of a population indicate?
Ans. The J-shaped growth curve indicates the minimum or absence of environmental resistance.

Q.34. Name the type of association that the genus Glomus exhibits with higher plants.
Ans. Symbiosis/Mycorrhizae/Mutualism.

Q.35. What does sigmoid growth curve of a population indicate?
Ans. Sigmoid growth curve of a population indicates following characteristics:
(i) Initially the growth is slow.
(ii) The growth becomes rapid and the curve becomes steady due to environmental resistance.

Q.36. In a pond there were 20 Hydrilla plants. Through reproduction 10 new Hydrilla plants were added in a year. Calculate the birth rate of the population.

Ans. Birth rate = Number of individuals born / Total number of individuals = 10/20 = 0.5. Birth rate is 0.5 plants per year.

Download Books – Exam Special

CBSE Books	ICSE Books
OLYMPIAD Books	FOUNDATION Books
JEE Books	NEET Books

➡ Click below titles to expand