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.

III. Question for 3 Marks : 

Q.1. What to you mean by competition? Define intraspecific and interspecific competition. 

Ans : Competition can be defined as the struggle for existence between two closely related species or organisms who are sharing the same resources that are limiting like food, shelter and reproduction. 

Intraspecific Competition : This is the competition between two groups. of organisms or individuals of the same species for food, shelter and reproduction, eg. fight between two male dogs for mating with one female, sharing a piece of meat or living in a house. 

Interspecific Competition : When the competition is taking place between two different species for food and shelter, then it is called as interspecific competition. Struggle between tiger and deer is the example of interspecific competition. 

Q.2. Define the process of migration. What is immigration and emigration? 

Ans : The process of movement of organism from a place to another place in search of food, good climate, habitat and return to their original habitat when the stressful period is over. 

Immigration : When the individuals are coming into a population to increase the size of the population, then it is called immigration. It is called the positive factor of population. 

Emigration : When the individuals are going out of a population to decrease the size of the population, then it is called Emigration. It is called as negative factor of population.

Q.3. What are the levels of organisation. 

Ans : The levels of organization are: 

(a) Organisms (individual).

(b) Populations.

(c) Communities. and

(d) Biome.

Q.4. What is adaptation? Describe the adaptation in organisms to extreme environmental condition. 

Ans : Adaptation is any attribute of the organism which is morphological, physiological and behavioural that enables the organisms to survive and the reproduce in its habitat. 

Some adaptation in organisms to extreme environmental conditions are mentioned below : 

(i) Many desert plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits to minimise water loss trough transpiration. 

(ii) Mammal from colder climates generally have shorter ears and limbs to minimise heat loss. 

(iii) Some species are capable of burrowing into the soil to hide and escape from the above ground heat.

Q.5. In an aquarium two herbaceous species of fish are living together and feeds on phytoplankton. As per Gause theorem one of the species is to be eliminated in course of time. But it is found that both of the species are surviving in the aquarium. Give possible reasons. 

Ans : According to Gause’s theorem one of the species is to be eliminated in course of time but practically it is seen that both of the species are swimming in the aquarium. It is because in Gauss’s theorem it is also mentioned that this is true only if resources are limiting but not otherwise As we know that aquarium is an artificial ecosystem not natural so the phytoplanktons has to be supplied from the outside as it can not grow its own. So depending upon the population of the fish phytoplanktons are supplied as per need. So competition does not occur between them and both can live. 

Q.6. What are the mechanism developed by the prey to avoid predators? 

Ans : The mechanism developed by the prey to avoid predators are : 

(i) Some species of insects and frogs are cryptically colours i.e. camouflaged to avoid being detected easily by the predator. 

(ii) As plants can not escape from its predators so they have evolved an astonishing variety of morphological and chemical defenses b against herbivores. 

(iii) The monarch butterfly is highly distasteful to its predator, which is w bird, because of a special chemical present in its body.

Q.7. What is parasitism? Describe the endoparasite and ectoparasite with examples. 

Ans : The process in which the parasites live in the host body and acquire their essential food and nutrition is known as parasitism. Most of the parasites causes harm to the hosts. 

There are mainly two types of parasites : 

Endoparasite : Those organism that live inside the host body at different places and acquire their essential food from it is known as endoparasite. For example – Plasmodium 

Ectoparasite : These organisms or parasites that feed on the external surface of the host organism are called ectoparasites. For example, Mosquito, Bed bug, Leech etc. 

Q.8. Explain the different types of adaptation adopted by plants to avoid predators? 

Ans : The adaptation adopted by the plants to avoid predators are : 

(i) Cactus are those with small spines throughout the plant body, hence no herbivorous animal feed on them. 

(ii) Some plants have oxalis like alkaloid and protects from the herbivorous animals. eg. colocasia. 

(iii) Some plants having different taste and hence protected from predators, eg. Neem, Bryophyllum. 

(iv) Caffeine, nicotine, quinine, opium are the product which repels the plant predators easily. 

(v) There are some plants which are with sticky substance over the to leaf or stem and hence not feed by the herbivorous animals. 

Q.9. What role the predators play in the ecosystem? 

Ans : Predators are playing an important role in the ecosystem. Generally on the basis of predation, some animals are released in the biological control agent. Moreover predation maintains the food chain in the ecosystem. Predation keeps the population under control. So we can say that predation is most important to balance the ecological equilibrium. 

Q.10. Describe the phenomenon of mutualism with examples. 

Ans : The interaction confers benefits on both the interacting species. For example : Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria. Here the fungi helps the plant in absorption of water and minerals whereas the algae prepare the food. 

The most spectacular and evolutionarily fascinating examples of mutualism are found in plant animal relationships. Plants need the help of animals for pollinating their flowers and dispersing their seeds. Plants offer rewards in the form of pollen and nectar for pollinators and fruits for seed disperses. 

Q.11. What are the attributes of population growth?

Ans : A population has certain attributes that an individual organism does not. An individual may have birth or death but a population may have birth rate or death rate. 

Birth rate: The no. of births in a definite time periode is called the birth rate, It is a positive factor to the population.

Death rate: The no. of deaths in a population in an interval of time period is called the death rate. It is called the negative factor. Another attribute characteristic of a population is sex ratio. An individual in either a male or a female but a population has a sex ratio. Again the size of the population gives us its status in the habitat. 

Q.12. Describe the various type of positive and negative interaction between different species? 

Ans : In nature animals, plants and microbes can not live in isolation but they interact in various ways to form a biological community. Interspecific interactions arise from the interaction of populations of two different species. They could be beneficial, detrimental or neutral to one of the species or both. Assigning a ‘+’sign for beneficial interaction, ‘–’ ve sign for detrimental and ‘O’ for neutral interaction. 

In mutualism both the species benefits whereas in competition both of them lose in interaction with each other. In both parasitism and predation one species i.e. parasites and predator gets the benefit and the interaction is detrimental to the other species i.e. host and prey. The interaction where one species gets the benefit whereas the other neither benefited nor harmed is called commensalism. But in amensalism on the other hand one species is harmed and the other is unaffected.

Assigning a ‘+’ sign for beneficial interaction, ‘–’ sign for detrimental and 0 for neutral interaction, all possible outcomes of interspecific interactions are shown in the table below- 

Table : Population Interactions 

Q.13. In what ways are prey species benefited from the predators? Do scavengers which feed on the same species have the same effect? Explain. 

Ans : Prey species is benefited from the predator by : 

(i) The member is checked. 

(ii) Population is maintained. 

(iii) Maintain the food chain. 

Scavengers also playing an important role : 

(i) They clean the environment.

(ii) They maintain the food chain.

(iii) They minimize the growth of harmful organisms. 

Q.14. What is ecological niche of an organism? Why it is believed that no two species can occupy exactly the same niche? 

Ans : An ecological niche refers to animals place in the biotic environment and its relation to its food and enemies or its functional role in an, ecosystem. No two species can occupy the same ecological niche. If they do occur in the same in the geographical area, then they use different food items or are active at different times or are occupying somewhat different niches. In case, two different species found in the same ecological niche, then only one survives while other is excluded. 

IV. Long questions for 5 Marks :

Q.1. How does population interacts? Give the different types of interactions found in population. 

Ans : See Q. No. 12 (‘E’ type)

Q.2. Name and define the attributes of an individual and a population. 

Ans : See Q. No. 11 (above ‘E’ type) 

Q.3. Describe the logistic population growth curve with suitable examples. 

Ans : No population of any species in nature has its disposal unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. Here the fittest individual will survive and reproduce. In nature, a given habitat enough resources to support a maximum possible number, beyond which no further growth is possible. This is known as nature’s carrying capacity (K) for that species in that habitat. 

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 population density (N) in relation to time (t) results in a sigmoid curve. This type of population growth is called verhulst – Pearl logistic Growth and described by the following equation. 

       dN/dt = rn (N –N/k)

Where, N = Population density at time t. 

             r  = intrinsic rate of natural increase. 

             K = carrying capacity 

Q.4. Parasitism is a specific interactions in which one partner derives benefits at the expense of other. What are the evidence or facts observed due to parasitism. 

Ans : Parasitism is such type of process where between two species one gets benefited whereas,the other is harmed. Here the benefited species is known as parasite and the other is host. Parasitism has evolved in so many taxonomic groups from plants to higher vertebrates. Majority of the parasites harm the host, they may reduce the survival, growth and reproduction of the host and reduce its population density. They may render the host more vulnerable to predation by making it physically weak. 

For example : Cuscuton, a parasitic plant that is commonly found growing on hedge plants has lost its chlorophyll and leaves in the course of evolution. It derives its nutrition from the host plant which it parasitises. 

Q.5. How does abiotic factor influences the growth and development in plants? 

Ans : The abiotic factors that influences the growth and development in plants are – temperature, water, light and soil. 

Temperature : The most ecologically relevant environmental factor is temperature. The average temperature on land varies seasonally, decreases progressively from equator towards the poise and from plains to the mountain tops. The temperature tolerance in plants varies with places. As without temperature organism can not survive likewise excess temperature is also harmful for plants. 

Water : After temperature, water is the most important factor influencing the life of organism. In the process of growth and development a particular amount of water is essential which take part in the process of photosynthesis. The productivity and distribution of plant is also heavily dependent upon water. 

Light : Light is also very important factor which is very much essential for photosynthesis. Sunlight is source of energy for plants. Many plants depend on sunlight to meet their photoperiodic requirement for flowering. 

Soil : This is the part where plants anchor and keep themselves upright. The nature and properties of soil in different places vary and so the type of plant grow there also varies. The soil type also depends on soil unlike other products directly on food. 

Q.6. What is age-pyramid? Describe the pre-reproductive, reproductive and post-reproductive age pyramids with suitable diagrams. 

Ans : A population at any given period of time is composed of individuals of different ages. If the age distribution is plotted for the population, the resulting structure is called an age pyramid. The shape of the pyramids reflects the growth status of the population whether it is 

(a) growing.

(b) stable. or 

(c) declining. 

Q.7. ‘Nature has a carrying capacity for a species’. Explain the stątement with suitable examples. 

Ans : Carrying capacity can be defined as feeding capacity of an environment of an ecosystem for a population of species under provided set of conditions. It is also stated that level beyond which no major increase can occur. 

Carrying capacity is depended upon three major systems. 

(i) Productive system.

(ii) Protective system.

(iii) Assimilative system. 

For example, A crop field is enough for 1000 grass happer, if the number is increased more than 1000 then the grass happer can not feed on the grasses property. That means, the carrying capacity of the crop field is 1000 grass happers only. 

Q.8. Does light factor affect the distribution of organisms? Give a brief description with some suitable examples of living organisms. 

Ans : Light has an important role on the distribution of plants and animals. 

Light on the distribution of plants : 

(i) The decreasing light intensity at various depth determines the distribution of plants in ocean. For eg. green algae is found on the share line, brown algae found somewhat deeper and red algae in deep water. 

(ii) Some plants grow in full sunlight, they are called Halophytes eg. sunflower, poplar, pines etc. Some plants can grow only in shade and are called sciophytes. For eg. Fir, source etc. There are some plants which can grow partly in sunlight and partly in shady area. eg. Tea. 

(iii) We know the day length control various physiological processes like flowering, dormancy etc, thus playing an important role in the natural distribution of plants. 

(iv) Stratification in terrestrial communities also regulated by sunlight. 

Light and distribution of animals : 

(i) Lighted place for the diurnal animals and light philic animals. 

(ii) Nocturnal or shade loving animals are found in dark and shady areas only. 

(iii) Vesperal animals are found in the dark period only and found in that zene only. 

Q.9. Name the five key tools for accomplishing the tasks of recombinant DNA technology. Mention the function of each tool. 

Ans : Recombinant DNA technology involves the following key tools. 

(i) Isolation of DNA : It involves the enzyme lysozyme (bactering), cellulase (plants) and chitinase (fungus). 

(ii) Fragmentation of DNA : Here the DNA parts are isolated. 

(iii) Amplification of gene: Here the DNA fragments are amplified. The PCR amplify original DNA fragment into multiple copies of DNA fragments. 

(iv) Joining of DNA fragments into vector. 

(v) Transfering recombinant DNA into host. 

(vi) Culturing host cells for multiplication of recombinant DNA.

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