5. Why do submerged plants receive weaker illumination than exposed floating plants in a lake?
Answer. 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.
6. In a sea shore, the benthic animals live in sandy, muddy and rocky substrata
and accordingly developed the following adaptations.
b. Building cubes
Find the suitable substratum against each adaptation.
Answer. a. Sandy, b. Muddy, c. Rocky
7. Categorise the following plants into hydrophytes, halophytes, mesophytes and xerophytes. Give reasons for your answers.
a. Salvinia b. Opuntia
c. Rhizophora d. Mangifera
Answer. a. Hydrophyte, b. Xerophyte, c. Halophyte, d. Mesophyte
8. In a pond, we see plants which are free-floating; rooted-submerged; footed emergent; rooted with floating leaves. Write the type of plants against each of them.
Answer. a. Submerged, b. Rooted emergent, c. Rooted with floating leaves, d. Free- floating, e. Rooted submerged
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:
a. Bacteria …………..
b. Banyan …………..
c. Deer …………..
d. Fish …………..
Answer. a. Nos. / Vol; b. Coverage / area; c. Biomass / area; d. Nos. / area; e. Wt. / area
. 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?
1. Pre-reproductive pogulation
2. Reproductive population
3. Post-reproductive population
(b) Expanding or growing population
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?
Answer. They shows mutualism.
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.
Answer. This association is called commensalism.
13. Give the scientific names of any two micro organisms inhabiting the human intestine.
Answer. 1. Escherichia coli
14. What is a tree line?
Answer. 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.
15. Define ‘zero population growth rate’. Draw an age pyramid for the same.
Answer. 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.
16. List any four characters that are employed in human population census.
Answer. 1. Birthrates
2. Death rates
3. Sex ratio
4. Age distribution
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
Answer. (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
18. Fill in the blanks:
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?
Answer. (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 Type Questions
1. Comment on the following figures 1, 2 and 3:
A, B, C, D, G, P, Q, R, S are species
Answer. 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.
2. An individual and a population has certain characteristics. Name these attributes with definitions.
Answer. 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 (e.g., 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.
3. The following diagrams are the age pyramids of different populations. Comment on the status of these populations.
Answer. 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,
4. Comment on the growth curve given below.
Answer. 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:
5. A population of Paramoecium caudatum was grown in a culture medium. After 5 days the culture medium became pvercrowded with Paramoecium and had depleted nutrients. What will happen to the population and what type of growth curve will the population attain? Draw the growth curve.
Answer. It shows logistic growth. (See Ans no. 4)
6. Discuss the various types of positive interactions between species.
Answer. Both the species benefit in mutualism. The interaction where one species is benefitted and the other is neither benefitted nor harmed is called commensalism.
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.
Answer. 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.
8. While living in and on the host species, the animal parasite has evolved certain adaptations. Describe these adaptations with examples.
Answer. 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.
9. Do you agree that regional and local variations exist within each.biome? Substantiate your answer with suitable example.
Answer. 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..
10. Which element is responsible for causing soil salinity? At what concentration does the soil become saline?
Answer. 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–.
11. Does light factor affect the distribution of organisms? Write a brief note giving suitable examples of either plants or animals.
Answer. 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.
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 antarcticfish ………………
(x) An organism which can conform ………………
Answer. (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