In This Post we are providing Chapter- 13 ORGANISMS AND POPULATIONS NCERT MOST IMPORTANT QUESTIONS for Class 12 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter
NCERT MOST IMPORTANT QUESTIONS ON ORGANISMS AND POPULATIONS
1. How does the shape of age pyramid reflect the growth status of a population?
Ans.Shape of pyramids reflects growth statusof the population (a) growing (b) Stable (c) declining.
2. Darwin showed that even a slow growing animal like elephant could reach enormous number in absence of checks. With the help of your understanding of growth models, explain when is this possible? Why is this notion unrealistic?
Ans. Possible if the growth model is Exponential, i.e., having unlimited resources. Its an unrealistic situation because resources are limited. Hence, it follows logistic growth model.
3. How will you measure population density in following cases?
(i) fish in a lake
(ii) tiger census in a national park
(iii) single huge banyan tree with large canopy .
Ans. (i) fish caught per trap.
(ii) number per unit area
(iii) percentage cover in biomass.
4. Species facing competition might evolve mechanism that promotes coexistence rather than exclusion. Justify this statement in light of Gause’s competitive exclusion principle, citing suitable examples.
Ans.State Gause’s competitive exclusion principle.Mechanisms is resource partitioning. E.g., experiment of Mac Arthur on Warblers (Refer page 325, NCERT book, Biology – XII).
5.Describe the specific adaptation of xerophytes with respect to root system, stem & leaves.
Ans. i) ADAPTATIONS INROOTS :- Xerophytes have well developed & extensively branched long rootsystem. While some perennial xerophytes of succulent nature possess extensive but shallow root system.They can absorb water from dew drops & small rain droplets.
ii) ADAPTATION IN STEM:- stems of woody xerophytes are comparatively stunted hard & rigid. Theymay be covered with thick e.g. Acacia main stem & branches may occur as think, fleshy, flattened & greenmodified structure called phylloclade.
iii) ADAPTATION IN LEAVES:- Leaves are usually short sized which decreases the chances of gettingover – heated when exposed to solar radiation & thus by reducing rate of transpiration. Leaves ofssxerophytes are usually thick, fleshy green & leathery which are known to store water.
6.List the important characteristics of a population & Explain?
Ans.A population has following four major characteristics :-
i) Population Density :- The size of a population in relation to a definite unit of space is termed aspopulation density. The maximum limit of density depends upon energy flow in an ecosystem, nutritionalstatus of trophic level & metabolic equilibrium. Population density can be mathematically calculatedas : D=N/atD=N/at
ii) Birth Rate / Natality :- The birth rate or natality denotes the produced number of new individuals byany natural method in per unit time. The birth can be expressed lay formula B=NntB=Nnt
iii) Death Rate / Mortality :- It refers to death rate of individuals in the population. It is expressed in asnumber of individual dying in a given period.Death Rate = no of death in population Timeno of death in population Time
iv) Carrying Capacity:- Each habitat or ecosystem has a certain space which can accommodate a finitenumber of organisms depending on its size & productivity. This is called carrying capacity
7.Describe the specific adaptations of hydrophytes with respect to roots, stem & leaves?
Ans. i) ADAPTATIONS IN ROOTS:- Root system is feebly developed &unbranched some floating plants orsubmerged plants lack roots Root hairs are absent except rooted floating hydrophyte. True root caps areabsent.
ii) ADAPTATIONS IN STEM :- In submerged hydrophytes, stems are long slender & flexible whereas inthe free – floating hydrophytes stem are modified as thick, stout, stoloniferous& occur horizontal onwater surface.
iii) ADAPTATIONS IN LEAVES:- Leaves are thin, long, ribbon shapes submerged forms. In free floatingplants, the petioles of leaves show indefinite power of growth.
8.Name& explain the bind of interaction in the following.
i) Algae & fungi in
ii) Head louse & humans
iii) Hermit crab & sea anemone.
Ans. i) Algae & fungi in lichens :- Lichens shows an intimate mutualistic interaction in with both fungushelps in absorption of nutrients & provides protection, while algae or cyanobacterium prepares the food.
ii) Head louse & humans:- Head louse shows ectoparasitism on humans in which head louse is gettingnutrition from human body & is thus benefited while human beings are harmed.
iii) Hermit crab & sea anemone:- Hermit crab & sea anemone shows commensalism as hermit crab isbenefited because it gets protection from predators which stays away from stinging tentacles of the seaanemone.
9.Mention the different defense mechanism to reduce the impact of predation?
Ans.plant species evolved various defense mechanism to reduce impact of predation :-
i) Certain insect species & frogs have camouflage or cryptic colouration to avoid detection by their predators.
ii)Some animals like monarch butterfly are highly distasteful to their predators because they accumulate a certain chemical by feeding on poisonous weeds during its caterpillar stage.
iii)Some prey are poisonous & hence are avoided by predators .
iv)Plants have evolved certain morphological, or chemical defense mechanism against herbivores e.g. thorns in bougainvillea.
v)plants also produce certain chemicals which functions as :-
- They make animal feel sick.
- They may inhibit them from feeding.
- They may interfere with digestion.
- They may directly kill them.
10.Mutualism often involves co-evolution of mutualists. Describe taking the example of animal plant (wasp-fig) relationship.
Ans.Plants need the help of animals for pollination their flowers & dispersing their seeds. Animals obviously have to be paid fees for the services that plants expect from them. Plants offer rewards or fees in the form of seed dispersers “plant – animal interactions often involve co-evolution of the mutualists that is, the evolution of the flower & its pollinator species can be pollinated only by its partner wasp species & no other species. The female wasp uses the fruit not only as an oviposition site but uses the developing seeds within the fruit for nourishing its larvae. The wasp pollinates the fig inflorescence while searching for suitable egg-laying sites. In return for the favors of pollination the fig offers the wasp some of its developing seeds as food for the developing wasp larvae.
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