NCERT Exemplar: Organisms & Populations - 2 | Biology Class 12 - NEET PDF Download

SHORT ANSWER TYPE QUESTIONS 

Q.1. Why are coral reefs not found in the regions from west Bengal to Andhra Pradesh but are found in Tamil Nadu and on the east coast of India?
Ans. High salinity, optimal temperature and less siltation are essential to colonise corals. If siltation and fresh water inflow are very high, the corals don’t colonise. In contrast when the siltation and fresh water inflow by the rivers are very less, the coral do colonise.

Q.2. If a fresh water fish is placed in an aquarium containing sea water, will the fish be able to survive? Explain giving reasons.
Ans. If a fresh water fish is placed in an aquarium containing sea water, it will not be able to survive because of the osmotic problems, they would face. Sea water is hypertonic as compared to fish, so it lost water through exosmosis and die due to dehydration.

Q.3. Why do all the fresh water organisms have contractile vacuoles whereas majority of marine organisms lack them?
Ans. In majority of fresh water organisms, contractile vacuoles is present which help in osmoregulation (remove excess water from body). In marine organism there is no need of removal of water from body (due to hyptonic condition), hence contractile vacuoles are absent.

Q.4. Define heliophytes and sciophytes. Name a plant from your locality that is either heliophyte or sciophyte.
Ans. 

• Heliophytes also called sun-loving plants, are those that require for their optimum growth full exposure to the sun. Example: Mango
• Sciophytes also called shade-loving plants, are those plants that require reduced light intensity. Example: Lycopodium

Q.5. Why do submerged plants receive weaker illumination than exposed floating plants in a lake?
Ans. Submerged plants receive weaker illumination than exposed floating plants in a lake because on passing of light through water much more amount of light is lost.

Q.6. In a sea shore, the benthic animals live in sandy, muddy and rocky substrata and accordingly developed the following adaptations.
a. Burrowing
b. Building cubes
c. Holdfasts / peduncle
Find the suitable substratum against each adaptation.
Ans. 
a. Sandy,
b. Muddy,
c. Rocky

Q.7. Categorise the following plants into hydrophytes, halophytes, mesophytes and xerophytes. Give reasons for your answers.
a. Salvinia
b. Opuntia
c. Rhizophora
d. Mangifera
Ans. 
a. Hydrophyte
b. Xerophyte
c. Halophyte
d. Mesophyte

Q.8. In a pond, we see plants which are free-floating; rooted–submerged; rooted emergent; rooted with floating leaves. Write the type of plants against each of them.

Ans. 
a. Submerged
b. Rooted emergent
c. Rooted with floating leaves
d. Free- floating
e. Rooted submerged

Q.9. The density of a population in a habitat per unit area is measured in different units. Write the unit of measurement against the following:

Ans. 
a. Nos. / Vol
b. Coverage / area
c. Biomass / area
d. Nos. / area
e. Wt. / area

Q.10.

a. Label the three tiers 1, 2, 3 given in the above age pyramid.
b. What type of population growth is represented by the above age pyramid?
Ans. (a)
1. Pre-reproductive population
2. Reproductive population
3. Post-reproductive population
(b) Expanding or growing population

Q.11. In an association of two animal species, one is a termite which feeds on wood and the other is a protozoan Trichonympha present in the gut of the termite. What type of association they establish?
Ans. They shows mutualism.

Q.12. Lianas are vascular plants rooted in the ground and maintain erectness of their stem by making use of other trees for support. They do not maintain direct relation with those trees. Discuss the type of association the lianas have with the trees.
Ans. This association is called commensalism.

Q.13. Give the scientific names of any two microorganisms inhabiting the human intestine.
Ans. 
1. Escherichia coli
2. Enterococcus faecalis

Q.14. What is a tree line?
Ans. When we go up the altitude, beyond a particular height no trees are found and the vegetation comprises only of shrubs and herbs. The altitude beyond which no tree is seen is known as tree line.

Q.15. Define ‘zero population growth rate’. Draw a age pyramid for the same.
Ans. Yes. An inverted bell shaped age pyramid is obtained. The young of pre- reproductive age group individuals are less in number and both pre- reproductive and reproductive stages are in the same level.

Q.16. List any four characters that are employed in human population census.
Ans. 
1. Birth rates
2. Death rates
3. Sex ratio
4. Age distribution

Q.17. Give one example for each of the following types
a) Migratory animal
b) Camouflaged animal
c) Predator animal
d) Biological control agent
e) Phytophagous animal
f) Chemical defense agent
Ans. 
(a) Migratory animal—Siberian crane, Salmon
(b) Camouflaged animal—Frog, insects
(c) Predator animal—Tiger, sparrow
(d) Biological control agent—Moth (against prickly pear cactus)
(e) Phytophagous animal—Insects like Locusta
(f) Chemical defense agent—Cardiac glycosides produced by Calotropis

Q.18. Fill in the blanks

Ans.

Q.19. Observe the set of 4 figures A, B, C and D and, answer the following questions
i. Which one of the figures shows mutualism?
ii. What kind of association is shown in D?
iii. Name the organisms and the association in C.
iv. What role is the insect performing in B?

Ans. 
(i) Figure ‘A’ shows’ mutualism (plant-animal relationship).
(ii) Figure ‘D’ shows predation (leopard killing deer and eating it)
(iii) Figure ‘C’ shows commensalism (cattle egret and grazing cattle)
(iv) In figure ‘B’ insect is phytophagous that feed on sap of the flower.

LONG ANSWER QUESTIONS

Q.1. Comment on the following figures: 1, 2 and 3:
A, B, C. D, G, P, Q, R, S are species

Ans. 
Fig. 1: It is a single population, and all individuals are of the same species, i.e. A—Individual interact among themselves and their environment.
Fig. 2: It is a community and it contains three populations of species A, B and C. They interact with each other and their environment.
Fig. 3: It is a biome. It contains three communities of which one is in climax and other two are in different stages of development. All three communities are in the same environment and they interact with each other and their environment.

Q.2. An individual and a population has certain characteristics. Name these attributes with definitions.
Ans. A population has certain attributes that an individual organism does not. An individual may have births and deaths, but a population has birth rates and death rates. In a population these rates refer to per capita births and deaths, respectively. The rates, hence, expressed as change in numbers (increase or decrease) with respect to members of the population.

• Another attribute characteristic of a population is sex ratio. An individual is either a male or a female but a population has a sex ratio (Example: 60 per cent of the population are females and 40 per cent males).
• A population at any given time is composed of individuals of different ages. If the age distribution (per cent individuals of a given age or age group) is plotted for the population, the resulting structure is called an age pyramid. For human population, the age pyramids generally show age distribution of males and females in a combined diagram. The shape of the pyramids reflects the growth status of the population (a) whether it is growing, (b) stable or (c) declining.

Q.3. The following diagrams are the age pyramids of different populations. Comment on the status of these populations.

Ans. 
Fig. A: It is a pyramid shaped age pyramid. In this figure, the base, i.e., pre-reproductive stage is very large when compared with the reproductive and past reproductive stages of the population. This type of age structure indicates that the population would increase rapidly.
Fig. B: It is an inverted bell shaped pyramid. In this figure, the pre- reproductive and reproductive stages are same. This type of age structure indicates that the population is stable.
Fig. C: It is ‘Urn’ shaped pyramid. In this figure, the pre-reproductive and reproductive stages are less than the post reproductive stage of this population. In this population, more older people are present. This type of age structure indicates that the population definitely is declining,

Q.4. Comment on the growth curve given below.

Ans. A population growing in a habitat with limited resources show initially a lag phase, followed by phases of acceleration and deceleration and finally an asymptote, when the population density reaches the carrying capacity. A’ plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth and is described by the following equation:

(1 - N/K)  Environmental resistance

Q.5. A population of Paramoecium caudatum was grown in a culture medium. After 5 days the culture medium became overcrowed with Paramoeium and had depleted nutrients. What will happen to the population and what type of growth curve will the population attain? Draw the growth curve.
Ans.  It shows logistic growth.
A population growing in a habitat with limited resources show initially a lag phase, followed by phases of acceleration and deceleration and finally an asymptote, when the population density reaches the carrying capacity. A’ plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth and is described by the following equation:

(1 - N/K)  Environmental resistance

Q.6. Discuss the various types of positive interactions between species.
Ans. Both the species benefit in mutualism. The interaction where one species is benefitted and the other is neither benefitted nor harmed is called commensalism.

Q.7. In an aquarium two herbivorous species of fish are living together and feeding on phytoplanktons. As per the Gause’s Principle, one of the species is to be eliminated in due course of time, but both are surviving well in the aquarium. Give possible reasons.
Ans. Each species has a specific position or functional role within the community, called niche. According to the Gausse’s principle, no two species can live in the same niche. In this case, two herbivorous species are living in the same niche and feeding on phytoplanktons. It may be because of the availability of sufficient phytoplanktons and or less number of individuals of the fish species. Of the two species might have occurred and though neither of the species have been eliminated, niche overlapping may effect the growth and development of individuals of the species.

Q.8. While living in and on the host species, the animal parasite has evolved certain adaptations. Describe these adaptations with examples.
Ans. In accordance with their life styles, parasites evolved special adaptations such as the loss of unnecessary sense organs, presence of adhesive organs or suckers to cling on to the host, loss of digestive system and high reproductive capacity. The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of its primary host.

Q.9. Do you agree that regional and local variations exist within each biome? Substantiate your answer with suitable example.
Ans. Yes, regional and local variations exist within each biome. Regional and local variations within each biome lead to the formation of a wide variety of habitats. On planet Earth, life exists not just in a few favourable habitats but even in extreme and harsh habitats-^scorching Rajasthan desert, perpetually rain-soaked Meghalaya forests, deep ocean trenches, torrential streams, permafrost polar regions, high mountain tops, boiling thermal springs, and stinking compost pits, to name a few. Even our intestine is a unique habitat for hundreds of species of microbes.

Q.10. Which element is responsible for causing soil salinity? At what concentration does the soil become saline?
Ans. Soil salinity is the salt content in the soil. Salts are a natural component in soils and water. The ions responsible for salination are: Na⁺, K⁺, Ca²⁺, Mg²⁺ and Cl^–. 

Q.11. Does light factor affect the distribution of organisms? Write a brief note giving suitable examples of either plants or animals.
Ans. Since plants produce food through photosynthesis, a process which is only possible when sunlight is available as a source of energy, we can quickly understand the importance of light for living organisms, particularly autotrophs. Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesise optimally under very low light conditions because they are constantly overshadowed by tall, canopied trees. Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering. For many animals too, light is important in that they use the diurnal and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities.

Q.12. Give one example for each of the following:
i. Eurythermal plant species _______________
ii. A hot water spring organism _______________
iii. An organism seen in deep ocean trenches _______________
iv. An organism seen in compost pit _______________
v. A parasitic angiosperm _______________
vi. A stenothermal plant species _______________
vii. Soil organism _______________
viii. A benthic animal _______________
ix. Antifreeze compound seen in antarctic fish _______________
x. An organism which can conform _______________
Ans. 
(i) Eurythermal plant species—Red algae
(ii) A hot water spring organism—Thermus aquaticus
(iii) An organism seen in deep ocean trenches—Sea cucumbers
(iv) An organism seen in compost pit—Earthworm
(v) A parasitic angiosperm—Cuscuta reflexa
(vi) A stenothermal plant species—Conifers
(vii) Soil organism—Earthworm
(viii) A benthic animal—Crabs, Sponges
(ix) Antifreeze compound seen in Antarctic fish—Antifreeze glycoproteins orAFGPs
(x) An organism which can conform—Frog