CBSE Class 12 Biology Organisms And Population Worksheet Set C

Very Short Answers Type Questions

Question. Species that can tolerate narrow range of temperature are called......
Answer : Stenothermal Organisms Temperature, a major abiotic factor affects the metabolism, activity and so many other physiological functions of the organism. On the basis of temperature tolerance, organism can be classified as eurythermal and stenothermal. (i) Eurythermal organisms can tolerate and thrive in a wide range of temperatures. (ii) Stenothermal organisms tolerate only a narrow range of temperatures.

Question. What is the interaction between two species called?
Answer : Interaction between two species is called interspecific interaction. These could be beneficial, detrimental or neutral to one of the species or both.

Question. Define aestivation.
Answer : Aestivation is a behavioural adaptation to avoid extreme heat and dessication in summer season. In which the organism slows down its metabolic activities. It is also known as summer sleep.

Question. What is diapause and its significance?
Answer : It is a stage of suspended development that some organisms like zooplanktons in lakes and ponds, adopt to survive under unfavourable conditions.

Question. What would be the growth rate pattern, when the resources are unlimited?
Answer : In case of unlimited resources, the pattern of growth rate is exponential.

Question. What are the organisms that feed on plant sap and other plant parts called?
Answer : The organism that feed on plant sap and other parts of plants are termed as phytophagous.

Question. What is commensalism?
Answer : Commensalism is an interaction where one species is benefitted and the other is unaffected. e.g., an orchid growing as an epiphyte on a mango branch.

Question. Name the association in which one species produces poisonous substance or a change in environmental conditions that is harmful to another species.
Answer : Parasitism is the association in which one species produces poisonous substance or a change in environmental conditions that is harmful to another species. Examples are protozoans such as Amoeba and Plasmodium vivax that lives in human body and cause diseases.

Question. What is mycorrhiza?
Answer : Mycorrhiza is a symbiotic association between a fungus and the root of higher plants like conifers i.e., Pinus and leguminous plants. Note Fungal hyphae get protection and nourishment from its symbiont, while in turn helps in absorption of organic solutes to higher plants.

Question. Emergent land plants that can tolerate the salinities of the sea are called.
Answer : Halophytes emergent land plants that can tolerate the salinities of sea and are even able to maintain their water supply from the same are called as halophytes.

Short Answer Type Questions

Question. 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?
Answer : Coral reefs are found in zone with high salt concentration (salinity), optimal temperature and with a less siltation condition which fairly facilitate to colonise corals. In case of high siltation and water flow, coral reef do not colonise.

Question. Define heliophytes and sciophytes. Name a plant from your locality that is either heliophyte or sciophyte. 
Answer : Plants growing well in bright sunlight or favour bright light are called heliophytes or sun plants. While those plants which require low intensity of light or partial shade for growing are termed as shade loving plants or sciophytes.

Question. 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 all colours of the visible components of the spectrum of light do not enter or penetrate in the depths of water.

Question. 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 : The type of association, the lianas have with the trees is commensalism because the plant gets the support of the tree without affecting harming or providing any benefit to the tree.

Question. Give the scientific names of any two microorganisms inhabiting the human intestine.
Answer : The scientific names of two microorganisms inhabiting the human intestine are Escherichia coli and Lactobacillus.

Question. What is a tree line?
Answer : Tree line is the edge of the habitat where trees are capable of growing. Due to environmental conditions such as cold temperature, high altitude or lack of moisture the trees are not found beyond this line and if found show stunted growth or form low dense matted bushes.

Question. 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.
Answer : In a sea shore, water current restrict distribution of organisms. In streamed areas of ocean, animals are strong swimmer or possess attaching organs such as peduncle, or live under stone, in burrows etc. Burrowing animals like tubeworm, Nerlies are strong swimmer. Burrowing, building cubes and holdfast or penduncle adaptation are found in sandy, muddy and rocky substratum respectively.

Question. If a freshwater fish is placed in an aquarium containing sea water, will the fish be able to survive? Explain giving reasons.
Answer : No, a freshwater fish placed in the aquarium containing sea water, will not be able to survive. Because, its body system is adapted to function normally in a narrow range of salinity and it cannot survive in the high salinity of sea water.

Question. Why do all the freshwater organisms have contractile vacuoles whereas majority of marine organisms lack them?
Answer : Contractile vacuole helps in osmoregulation. Because of the cellular environment of a freshwater organism being hypertonic, the water diffuses inside the cell constantly and gets collected in the contractile vacuole, which squeezes the extra water out of the cell periodically. Thus, keeping the internal environment constant. While in case of marine organisms, this does not occur due to high salinity, therefore no need of contractile vacuole.

Long Answer Type Questions

Question. The following diagrams are the age pyramids of different populations. Comment on the status of these poulations.
Answer : Figure A It is a ‘pyramid’ shaped age pyramid. In this figure, the base, i.e., pre-reproductive stage is very large as compared with the reproductive and post-reproductive stages of the population. This type of age structure indicate that the population would increase rapidly. Figure 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. Figure C It is ‘urn’ shaped pyramid. In this figure, the pre-reproductive and reproductive stages are less than the post-reproductive stages of this population. In this population more older people are present. This type of age structure indicates that the population definitely is declining.

Question. Comment on the growth curve given below. 
Answer : The growth curve shown above is logistic growth curve or S-shaped curve. Logistic growth curve is considered more realistic because unlimited resources are not available in an ecosystem or in a habitat, where K–stands for carrying capacity. N–indicates population density, which is the number of species of a population per unit area. r–is for intrinsic rate of natural increase.

Question. A population of Paramecium caudatum was grown in a culture medium. After 5 days the culture medium became overcrowded with Paramecium 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 : Initially, after a lag phase, the population will grow in an exponential manner as the nutrients and space will be abundant. When the food sources get depleted, the population density starts decreasing and ends in an asymptote phase, then the population density reaches the carrying capacity (maximum number of individuals of a population or species that a given environment can sustain indefinitely). The population shows a pattern of logistic growth giving an S-shaped curve. Where K = carrying capacity N= population density at time ‘t’ r = Intrinsic rate of natural increase

Question. Discuss the various types of positive interactions between species.
Answer : The interspecific interaction are of three types positive or beneficial, negative or antagonistic and last neutral interaction. Some positive interactions are scavenging, commensalism, protocooperation and mutualism. Mutualism This interaction confers benefits on both the interacting species, e.g., (i) Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria. (ii) The mycorrhizae are associations between fungi and the roots of higher plants. The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the fungi with energy-yielding carbohydrates. (iii) Plants offer nectar, juicy and nutritious fruits to animals that help pollinate their flowers and disperse their seeds. Commensalism This is the interaction in which one species benefits without affecting the other, e.g., (i) An orchid growing as an epiphyte on a mango branch. (ii) Barnacles growing on the back of a whale. (iii) The cattle egret foraging close to the cattle that stir up and flush out insects from the vegetation. (iv) Sea anemone that has stinging tentacles and the clown fish that lives among them to get protection from predators. Scavenging is the act of feeding by scavenger like bacteria, fungi on the remain of dead animals. Protocooperation in the type of relationship in which both partners mutually obtain benefits. But they associate purely to benefit from each other and can live without each other.

Question. Comment on the following figure: I, II and III, A, B, C, D, G, P, Q, R, S are species. 

Answer : Figure I It is a single population and all individuals are of the same species, i.e., a individuals interact among themselves and their environment intraspecific interaction. Figure II It is a community and it contains three populations of species A, B and C. They interact with each other and their environment and is called interspecific interaction. Figure III 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.

Question. Which element is responsible for causing soil salinity? At what concentration does the soil become saline?
Answer : Soil salinity is the salt content in soil, which is caused by improper irrigation. The process of increasing salt content is termed as salinisation. Causes of Soil Salinity The high salt concentration of soil is caused by improper irrigation method from a salt laden water table. When salt concentration in soil is increased, than it get accumulated due to evaporation. Human activities like fertilising crop is also responsible for salinity of soil. As fertiliser contain potassium, which can form a naturally occuring salt-sylvite. Salinity of soil degrades soil and vegetation. Normally the pH value of soil comprises between 2.2-9.7, while above which the soil is degrading by salt content.

           Very Short Answer

Q1)       Who formulate the first postgraduate course in ecology in India?

Q2)       Define ecology?

Q3)       What is Darwinian fitness?

Q4)       What are the major biomes of India?

Q5)       What is eurythermal?

              Short Answer

Q6)       Distinguish between commensalism and amensalism?

Q7)       How ecology is different from environment?

Q8)       What are population attributes?

Q9)       What do you mean by adaptation?

Q10)     What are the four basic processes of the population growth?

              Long Answer

Q11)     State the difference between exponential growth and logistic growth?

Q12)     State the difference between mutualism and parasitism?

Q13)     Explain the major abiotic factors?

Q14)     State the difference between biotic factors and abiotic factors?

Q15)     State the difference between predation and parasitism?

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