Class 12 Biology Chapter 13 Organisms and Populations

Class 12 Biology Chapter 13 Organisms and Populations The answer to each chapter is provided in the list so that you can easily browse through different chapters Assam Board HS 2nd Year Biology Chapter 13 Organisms and Populations Question Answer.

Class 12 Biology Chapter 13 Organisms and Populations

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Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given Assam Board Class 12 Biology Chapter 13 Organisms and Populations Solutions for All Subjects, You can practice these here.

Organisms and Populations

Chapter – 13


Very Short Answer Type Questions

Q.1. What do you mean by population? 

Ans : The group of organisms of one or more species that are living in a particular area in a particular time period is called the population of that species in that area. 

Q.2. What is organism? 

Ans : Plants, animals and microbes which by the process of growth and development increase their number is called as organism. 

Q.3. Explain the meaning of community. 

Ans : When more than one populations occupy the same ecosystem through the close relationship or interdependence among themselves are known as organisms. 

Q.4. Name the two major factors that affect population. 

Ans : The two major factors which affect the population are: 

(a) Immigration. and

(b) Emigration

Q.5. Name the biotic components of ecosystem.

Ans : The biotic components of an ecosystem are : 

(a) Parasitism.

(b) Predation.

(c) Commensalism.

(d) Mutualism.

(e) Nutralism. and

Q.6. What is xerophyte? 

Ans : The plants which grow in the area where scarcity of water is found i.e. in desert are called the xerophyte. They have long roots but without the leaf but stem can perform the function of leaf. 

Q.7. What is mesophyte? 

Ans : The plants which grow in area where moderate amount of water is found, are called as mesophyte. 

Q.8. Mesophyte prefer what type of habitat? 

Ans : Mesophyte always prefers the medium watery condition i.e. neither aquatic nor desert. 

Q.9. What is hydrophyte? 

Ans : The plants that abundance of water i.n. aquatic condition, is called as hydrophyte. 

Q.10. If the condition is dry what type of plant will develop in that region. 

Ans : If the condition is permanently dry then xerophytic plant can grow and if it is temporally dry then mesophyte plants can also survive. 

Q.11. Explain the term carrying capacity of a habitat. 

Ans : Carrying capacity can be explained as maximum number of individuals of a population that can be sustained by a given habitat or ecosystem. 

Q.12. What do you mean by migration? 

Ans : Migration can be defined as the mass movement of organisms from a place to another place temporarily in regular basis in search of food, shelter or other biological need. Generally in migration the animals follow the same route as followed by their forefathers. 

Q.13. What is mimicry of nature? Give one example of it. 

Ans : The organisms which copy the appearance of some dangerous animals to keep away themselves from their natural enemy is called mimicry. For example, Natrix, a non poisonous snake. 

Q.14. Define ecotone species of nature. 

Ans : The transitional zones between trua adjacent biomes are called ecotone. The species found in this area are called ecotone species.

Q.15. When and why do some animals like frogs hibernate? 

Ans : They can not adjust their body temperature by the change of environmental temperature, hence they like frog, lizard hibernate.

Q.16. What is zero population growth? 

Ans : When birth rate and death rate becomes equal then the population growth is called zero population growth. 

(B). Fill up the blanks : (1 Mark) : 

Q.1. A large biogeographic region consisting of a major vegetation type and associated animals in a specific climatic zone is called ____

Ans : Biome. 

Q.2. Every individual of a species is called ____

Ans : Organism. 

Q.3. Any place in the world, any specific location ranging from equator to polar region, hot spring, compost and even the human intestine are ______ of organisms.

Ans : Habitat.

Q.4. _____ which live on dead organic matters are responsible for decomposition. 

Ans : Decomposers. 

Q 5. Hydrophytes prefer ____habitat.

Ans : Aquatic. 

Q.6. Soil is the source of all _____ compounds essential for life. 

Ans : Inorganic.

Q.7.  ____ and ___ regions receive more intense light and there temperature is more.

Ans : Equatorial, tropical.

Q.8. Altitude, slope, depression and other physical features of earth is called _____

Ans : Geographical factors.

Q 9. ____ is the phenomenon in which body temperature changes with the temperatures outside. 

Ans : Conform.

Q.10. ___ is a photosynthetic pathway in which the stomata remain open during night instead of daytime. 

Ans : CAM. 

Q.11. ____ shows association of both algae and fungi. 

Ans : Lichen.

Q.12. _____ bacteria fix atmospheric nitrogen in a leguminous plant. 

Ans : Rhizobium.

Q.13. _____ is an assemblage of homogenous interbreeding individuals occupying a geographical location and interact among themselves and with others in the habitat forming a ecological unit. 

Ans : Species.

Q.14. Population growth that depends upon carrying capacity of the habitat and showed log, lag and steady phase of growth forming a ___ curve is called logistic growth. 

Ans : Sigmoid. 

Q.15. The aggregation of individuals of a species is called _____

Ans : Population.

Q.16. The relationship where one organism is benefited, while the other is neither benefited nor harmed is referred as ____

Ans : Commensalism. 

Q.17. Desert plants can tolerate water stress by forming_____

Ans : Spies. 

(C). Select true or false statements: 

Q.1. Natality means birth rate. 

Ans : True.

Q.2. All organisms other than green plants prepare their own food. 

Ans : False.

Q.3. Mortality is increase in number of population. 

Ans : False.

Q.4. The organism is required to generate heat to maintain temperature suitable for its body which is called thermo regulation. 

Ans : False.

Q.5. Some organisms hibernate to escape extreme conditions of environment. 

Ans : True. 

Q.6. Population increase due to migration of individuals from an area is called emigration. 

Ans : False.

Q.7. The potential to support a certain number of organisms in a habitat is called carrying capacity of the habitat. 

Ans : True.

Q.8. Fungal association of roots of higher plant is called mycorrhiza. 

Ans : True.

Q.9. Soil water available to plant is surface water. 

Ans : False.

Q.10. Exponential population growth is d N/dt = rn. 

Ans : False.

Q.11. Competition is most acute between individuals of same species. 

Ans : True.

Q.12. Symbiosis is that when the interaction is useful to both the populations. 

Ans : True.

Q.13. An association of animals when both partners are benefited called commensalisms. 

Ans : False.

II. Short type questions 2 marks : 

Q.1. How does strong wind affect a plant? 

Ans : Strong wind accelerates the rate of transpiration and increases the rate of evaporation of water for which plants need more water to absorb. 

Moreover strong wind may tear off the large leaf which will affect the rate photosynthesis. 

Q.2. What is log and lag phase? 

Ans : Log phase : It is the period of rapid growth or rise in population due to availability of food and requirements of life in plenty. 

Lag phase : It is the growth phase in population in which the individuals adapt themselves to the new environment, sot there is no or very little growth is found in population due to limited resources. 

Q.3. What is commensalism? Give example of commensalism. 

Ans : Commensalism is the interaction of two species in which one species gets the benefit and the other is neither harmed nor benefited. 

Orchid live in some trees where orchid is benefitted but the hosting plant neither benefited nor harmed. 

Q.4. Define the phenomenon of antibiosis and allelopathy. 

Ans : Antibiosis : Antibiosis is the inter-relation between two or more animals where one get harmed. 

Allelopathy : It is the process where a plant secretes a chemical substance called Hormone which is used to control the growth of another plant or another species. 

Q.5. What is amensalism? Give example of amensalism.

Ans : Amensalism is the process of interaction of two species where one species is harmed but the other is unaffected. 

Growth of penicillium causes harm to the growth of bacteria but penicillium remains unaffected.

Q.6. What are the biotic and abiotic factors? 

Ans : Biotic factors : The interrelationship between the plants, plants and animals, microorganisms and plants are called biotic factor. Parasitism, symbiosis, epiphytes are the example of biotic factors. 

Abiotic factors : The non-living factors like temperature, light, wind, precipitation, humidity etc. are called abiotic factors. 

Q.7. How light influences the growth and development in plants? 

Ans : Light is essential abiotic factor for the growth and development of plants. Generally plants can prepare their food in presence of light by the process of photosynthesis. Moreover, some plants are called short day plant (eg. tobacco), long day plant (eg. beet) and day neutral plant (eg. tomato) where growth and development is directly depend upon the duration of light. Again quality of light and intensity of light may play an important role in the growth and development of plant. 

Q.8. What is meant by homeostasis? 

Ans : The mechanism by which organism can maintain a constant environmental condition despite of varying external environmental condition is known as homeostasis. 

Q.9. What is eurythermal and stenothermal? Give example of each type. 

Ans : Eurythermal : The organisms which can tolerate a wide range of temperature is called as eurythermal, eg. cockroach. 

Stenothermal : The organisms which are restricted to a narrow range of temperature, are called as stenothermal, eg. fish. 

Q.10. What is Biome? Give examples of Biome. 

Ans : Biome can be defined as the community where different types of plants and animals can live i.e. multiplication of ecosystem is called the biome, eg. Tundra, Desert etc. 

Q.11. Define the Gause competitive exclusion principle. 

Ans : According to the Gause’s competitive exclusion principle when two closely related species competing for the same resources can not co- exist indefinitely and the competitively inferior one will be eliminated eventually. This can be possible only if the resources are limiting. 

For eg. Mc Arther showed that 5 closely related species of warblers on the same tree were able to avoid the competition and co-exist due to their different behavioural activities. 

Q.12. Distinguish between.

(a) Hibernation and Aestivation.

(b) Hibernation and Aestivation.

Ans : (a) Hibernation and Aestivation.

(i) It is the condition of passing the winter in a resting or dormant condition.(i) It is the state of inactivity during hot and dry summer.
(ii) The animal rests in a warm place.(ii) The animal rests in a cool, shady and moist place.
(iii) It lasts for the whole duration of winter.(iii) In generally lasts for hot dry day time because nights are often cooler.

(b) Ectotherms and Endotherms 

Ans :

(i) They are also called cold- blooded animals.(i) They are also called warm blooded animals.
(ii) They are unable to regulate their body temperature and it changes with temperature of environment.(ii) They can regulate their body temperature.
(iii) They exhibit both hibernation and aestivation.(iii) Their activities are uncommon.
(iv) They are less active animals.(iv) They are more active animals.

Q.13. Define the following terms. 

(a) Predations.

Ans : The process where predators directly or indirectly depend on prey for their food is known as predation. This is natural way of transferring to higher trophic levels the energy fixed by plants. Ifa predator is too efficient and overexploits its prey, then the prey might become extinct and following it, the predator will also become extinct for lack of food. Besides acting as ‘conduits’ for energy transfer across trophic levels, predators play other important roles. They keep prey population under control. For example : Tiger and deer. Here Tiger acts as a predator and deer as prey. 

(b) Camouflage.

Ans : Prey species have evolved various defensive mechanism to lessen the impact of predation. One among these mechanism is camouflage. Here the prey to safeguard themselves from the predator changes its body colour so that predators can not recognise them. For example : some species of insects and frogs are cryptically coloured to avoid being detected easily by the predator. Their colour resembles like colour of tree, leaf etc. 

(c) Amensalism.

Ans : Amensalism is the relation between two species where one species in harmed and on the other hand other is unaffected. It is also called antibiosis in which one species secretes antibiotics and inhibits growth of other organism. For example penicillium secretes antibiotics which inhibits the growth of harmful bacteria. Again roots ofblack walnut secrete Juglone chemical which inhibits the growth of seedlings of apple, tomato etc. 

Q.14. Distinguish between camouflage and mimicry. Give one example from each. 

Ans : In camouflage the organisms change their colour to match with the surrounding. So that their predator can not and leaf insect exhibit the camouflage. 

In mimicry, the non poisonous animals and plants try to copy the shape, size and colour of the poisonous one to keep away their enemies. Non poisonous snakes looks like more dangerous, sometimes flowers appear like some animals etc.

Q.15. Write the special characteristics feature of a parasitic organism. 

Ans : The special characteristic features of parasitic organisms are: 

(i) They are smaller than the host. 

(ii) They may be endoparasite a may be ectoparasite. 

(iii) They suck the nutrients from the host body only. 

(iv) They are completely dependent on the host or partially depend upon the host. 

Q.16. What is symbiosis? Give one example each from plant and animal kingdom. 

Ans : Symbiosis is a relationship between two organisms where both are benefited and helping each other. 

For example Fungus are found in the root of some plants developing a symbiotic relationship which is called mycorrhiza. Again hermit crab and Algae are found together having symbiotic relationship.

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