Please refer to Organisms And Populations Class 12 Biology Important Questions with solutions provided below. These questions and answers have been provided for Class 12 Biology based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 12 Biology for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 12.
Class 12 Biology Important Questions Organisms And Populations
Question. What are the key elements that lead to so much variations in the physical and chemical conditions of different habitats?
(a) Temperature and water
(b) Light and soil
(c) Only temperature
(d) Temperature, water, light and soil
Question. A few organisms can tolerate and thrive a wide range of temperature. Such animals are called
Question. Organisms that are restricted to a narrow range of salinity, are called
Question. Percolation and water holding capacity of soil is dependent upon
(a) soil composition
(b) grain size
(d) all of these
Question. The process in which the body’s internal environment is kept stable is known as
Question. To avoid summer – related problems such as heat and dessication fish undergoes
(d) none of these
Question. Seals have a thick layer of fat (blubber) below their skin that acts as an
Question. If the age distribution (per cent individuals of a given age or group) is plotted for the population, the resulting structure is called a/an
(a) population density
(b) ecological pyramid
(c) population growth
(d) age pyramid
Question. Which of the following parameter is not a part of population growth?
Question. Interspecific interaction arise from the interaction of
(a) individuals of a community.
(b) populations and their regulatory factors.
(c) populations of two different species.
(d) none of the above
Question. Which of the following secondary compounds are produced by plants for the purpose of defences against grazers and browsers?
(d) All of these
Question. Cuscuta is an example of
(d) brood parasitism
Question. Which of the following is not an example of commensalism?
(a) Sea anemone and clown fish
(b) Epiphyte / Orchid on mango branch
(c) Liver fluke and fleas
(d) Cattle egret and grazing cattle.
Question. A wasp pollinating a fig flower is an example of
Very Short Answer Questions
Question. Name two organisms (one plant and one animal) which breed only once in their life time.
Ans. Pacific salmon fish and bamboo.
Question. Species that tolerate wide range of salinity are called ____________.
Question. Why do predators avoid eating Monarch butterfly? How does the butterfly develop this protective feature?
Ans. The Monarch butterfly is highly distasteful to its predator (birds) because of a special chemical present in its body. It acquires this chemical during its caterpillar stage by feeding on a poisonous weed.
Question. How is diapause different from hibernation?
|(i)||Under unfavourable conditions, the animals that fail to migrate, avoid the stress by escaping in time and showing winter sleep is called hibernation.||Under unfavourable conditions, many species in lakes and ponds are known to enter a stage of suspended development called diapause.|
|(ii)||It occurs usually in winters.||It occurs both in summers and winters.|
|(iii)||Example, bear goes into hibernation during winter.||Example, zooplanktons undergo diapause in lakes and ponds under unfavourable conditions.|
Question. Give two reasons as to why a weed such a Calotropis flourishes in abandoned fields.
Ans. Calotropis flourishes in abandoned fields because of:
(i) It has dry hairy seeds which help in dissemination (ii) Its have xerophytic adaptations like thick hair on leaves and stems. (iii) It is not grazed by animals as it produces poisonous substances like cardiac glycosides. (Any two)
Question. What is the interaction called between Cuscuta and shoe flower bush?
Question. If 8 individuals in a laboratory population of 80 fruit flies died in a week, then what would be the death rate of population for the said period?
Ans. Death rate
Number of individuals dead /Total number of individual =8/80 = 0.1
The death rate will be 0.1 individuals per week.
Question. What are ectotherms?
Ans. Ectotherms are those animals whose body temperature changes and matches with that of the environment in which they are living. They are also called cold-blooded animals.
Question. What does J-shaped growth curve of a population indicate?
Ans. The J-shaped growth curve indicates the minimum or absence of environmental resistance.
Question. Write the basis on which an organism occupies a space in its community/natural surroundings.
Ans. Feeding relationships with other organisms.
Question. What does sigmoid growth curve of a population indicate?
Ans. Sigmoid growth curve of a population indicates following characteristics:
(i) Initially the growth is slow.
(ii) The growth becomes rapid and the curve becomes steady due to environmental resistance.
Question. What does nature’s carrying capacity for a species indicate?
Ans. In nature, a given habitat has enough or limited resources to support a maximum possible number of population and nature’s carrying capacity indicates that how much growth is possible in a population.
Short Answer Questions
Question. An organic farmer relies on natural predation for controlling plant pests and diseases. Justify giving reasons why this is considered to be a holistic approach.
Ans. Besides acting as ‘conduits’ for energy transfer across trophic levels, predators are used in biological control of plant pests. This ability of the predator is based on its regulating the prey population. The natural predators reduce interspecific competition and do not harm the crop plants. For example, in an area the invasive cactus can be brought under control by cactus-feeding predator (a moth). Using natural predation, the ecosystem is kept stable without harming any of the trophic levels.
Question. Construct an age pyramid which reflects an expanding growth status of human population.
Question. Explain the response of all communities to environment over time.
Ans. Environmental factors like temperature, water, light, soil, etc., may influence the members of communities in varying degrees. Organisms in response to these factors try to adapt according to their capacities, by maintaining a constant internal environment through homeostasis or migration to a less stressful environment or suspending activities till favourable conditions return.
(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 represents Pre-reproductive age group
2 represents Reproductive age group
3 represents Post-reproductive age group
(b) Expanding population.
Question. Bear hibernates whereas some species of zooplanktons enter diapause to avoid stressful external conditions. How are these two ways different from each other?
Ans. Hibernation is the winter sleep, seen in cold-blooded animals in polar regions, in which theysuspend their metabolic activities when external temperature becomes unfavourable. Whereas, diapause is the phenomenon seen in insects during their developmental stages, in which metabolic activities are suspended due to unfavourable conditions.
Question. (a) What is “r” in the population equation given: dN/dt = rN?
(b) How does the increase and the decrease in the value of ‘r’ affect the population size?
Ans. (a) ‘r’ is called intrinsic rate of natural increase.
(b) Population size increases with increase in ‘r’ and it decreases with decrease in ‘r’.
Question. How does our body adapt to low oxygen availability at high altitudes?
Ans. Our body adapts to low oxygen availability by increasing red blood cell production, decreasing the binding capacity of haemoglobin and by increasing breathing rate.
Question. Identify the curves ‘a’ and ‘b’ shown in the graph given below. List the conditions responsible for growth patterns ‘a’ and ‘b’.
Ans. Curve ‘a’ is exponential growth curve. When the resources (food + space) are unlimited, this type of growth curve appears. Curve ‘b’ is logistic growth curve. When the resources become limited at certain point of time, this type of growth curve appears.
Question. If a marine fish is placed in a freshwater aquarium, will the fish be able to survive? Why or why not?
Ans. A marine fish if kept in freshwater aquarium will not be able to survive because:
(a) water will enter the body of fish through endosmosis.
(b) it does not have mechanism of salt absorption as in freshwater fishes.
(c) its drinking water habit will cause excess of water to enter the body. So, the marine fish will fail to maintain the osmolarity and hence will die.
Question. Egrets are often seen along with grazing cattle. How do you refer to this interaction? Give a reason for this association.
Ans. The interaction between them can be referred to as commensalism. Egrets always forage close to where the cattle are grazing because the cattle, as they move stir up and flush out insects from the vegetation which otherwise might be difficult for the egrets to find and catch.
Long Answer Questions
Question. Water is very essential for life. Write any three features both for plants and animals which enable them to survive in water scarce environment.
Ans. Plants: Ephemeral mode (complete life cycle in short period); deep tap roots; deciduous leaves; waxy cuticle; sunken stomata; succulence to store water; C4 or CAM pathway of photosynthesis. (Any three)
Animals: No sweating; uricotelic; deposition of fat in sub-epidermal layer; burrowing nature; thick skin; body covered with scales. (Any three)
Question. (a) Following are the responses of different animals to various abiotic factors. Describe each one with the help of an example.
(i) Regulate (ii) Conform
(iii) Migrate (iv) Suspend
(b) If 8 individuals in a population of 80 butterflies die in a week, calculate the death rate of population of butterflies during that period.
Ans. (a) (i) Regulate
• Some organisms maintain homeostasis by physiological and behavioural means, such organisms are called regulators. All birds and mammals and few lower vertebrate and invertebrate species maintain homeostasis by thermoregulation and osmoregulation.
• The success of mammals is largely due to their ability to maintain a constant body temperature.
• In summers, when outside temperature is more than our body temperature, we sweat profusely and the resulting evaporative cooling brings down the body temperature.
• In winters, when temperature is lower we shiver, a kind of exercise that produces heat and raises the body temperature.
(b) Death rate = Number of individuals dead /Total population
= 8/80 = 0.1 individuals per butterfly per week
Question. Describe the specific adaptation of xerophytes with respect to root system, stem and leaves.
Ans. (i) The root system is deep-rooted, that help to reach up to the level of water table.
(ii) Stem become modified into fleshy, spongy flat and green structure called phylloclade. Stem can perform photosynthesis and store water.
(iii) Leaves have waxy layer called cuticle, contain sunken stomata and leaves are modified into hard pointed spines to reduce transpiration. Leaves become fleshy in suc culents.
Question. Differentiate between commensalism and mutualism by taking one example each from plants only.
|(i)||It is an interspecific interaction in which one species is benefited and other is neitherharm ed nor benefited.||It is an interspecific interaction in which both the species (individuals) are mutuallybe nefited.|
|(ii)||The two individuals may be physically associated.||The two individuals may be physically or physiologically associated.|
|(iii)||E.g., Sucker fish and shark.||E.g., Rhizobium and the legume plants.|
Question. Study the population growth curves in the graph given below and answer the questions that follow:
(i) Identify the growth curves ‘a’ and ‘b’.
(ii) Which one of them is considered a more realistic one and why?
(iii) If dN/dt = rN [K-N/K] is the equation of the logistic growth curve, what does K stand for?
(iv) What is symbolised by N?
Ans. (i) a is exponential growth curve or J-shaped curve.
b is logistic growth curve or S-shaped curve.
(ii) Logistic growth curve (b) is considered more realistic because unlimited resources are never available in an ecosystem or in a habitat.
(iii) K stands for carrying capacity.
(iv) N indicates population density, which is the number of species of a population per unit area.
Question. “Analysis of age-pyramids for human population can provide important inputs for long-term planning strategies.” Explain.
Ans. • The shape of the pyramids reflects the growth status of the population and is of three types:
(a) Expanding (Triangular shaped pyramid): Number of prereproductive individuals is very large, reproductive individuals moderate in no. and postreproductive are fewer. Population is
growing and show rapid increases.
(b) Stable (Bell shaped pyramid): Population size remains stable, neither growing nor diminishing i.e., all the age group are evenly balanced.
(c) Declining (Urn shaped pyramid): Population is declining or diminishing population showing negative growth.
Through analysis of the age pyramids of a population proper planing of health, education, transport, infra-structure, finance, food and employment can be done.
Thus, long-term management of resources can be done so that maximum benefits can be provided to the population.
Question. When do you describe the relationship between two organisms as mutualistic, competitive and parasitic? Given one example of each type.
Ans. Mutualism is referred to as the interspecific interaction in which both the interacting species are benefited from each other. For example, lichens represent close association between fungus and Algae.
Competition is a type of interaction due to limited resources between closely related species where they compete for the same resource and both species suffer. For example, In South American lakes, visiting flamingos and resident fishes compete for zooplanktons.
Parasitism is the mode of interaction between two species, in which one species (parasite) depends on the other species (host) for food and shelter, and in the process damages the host. For example, human liver fluke depends on two hosts, a snail and a fish, to complete its life cycle.
Question. (a) Write the importance of measuring the size of a population in a habitat or an ecosystem.
(b) Explain with the help of an example how the percentage cover is a more meaningful measure of population size than mere numbers.
Ans. (a) By measuring the size of a population, following can be predicted:
(i) Status of the population in a habitat.
(ii) Outcome of competition with other species.
(iii) Impact of predator or pesticides.
(iv) Increase or decrease of population size .
(iv) Effect of pesticide application (Any two)
(b) Example: Banyan tree and Parthenium plants.
When 1 banyan tree is compared with 100 Parthenium plants, the population of banyan in terms of number is very much low as compared to Parthenium. But in terms of percentage cover or biomass, the banyan tree provides a much larger cover in comparison to 100 Parthenium plants. Thus, the percentage cover or biomass is a more meaningful measure of
Question. Name the type of interaction seen in each of the following examples:
(i) Ascaris worms living in the intestine of humans
(ii) Wasp pollinating fig inflorescence
(iii) Clown fish living among the tentacles of sea-anemone
(iv) Mycorrhizae living on the roots of higher plants
(v) Orchid growing on a branch of a mango tree
(vi) Disappearance of smaller barnacles when Balanus dominated in the coast of Scotlan(d)
Ans. (i) Parasitism (ii) Mutualism
(iii) Commensalism (iv) Mutualism
(v) Commensalism (vi) Competition
Question. Explain co-evolution with reference to parasites and their hosts. Mention any four special adaptive features evolved in parasites for their parasitic mode of life.
Ans. If the host evolves special mechanism for rejecting or resisting the parasite. The parasite has
to (simultaneously) evolve/co-evolve the mechanism to counter act and neutralise them & i.e.
(a) Parasitic adaptation in Animals
QU It is the mode of interaction between two species in which one species (parasite) depends on the other species (host) for food and shelter, and in this process damages the host. In this process one organism is benefited (parasite) while the other is being harmed (host).
QU Adaptation of parasite:
(b) Loss of unnecessary sense organs as they do not interact with external environment [For example, eyes as they are found in an environment that lacks light.)
(c) Presence of adhesive organs or suckers to cling to host
(a) The parasite have evolved to be host-specific in such a manner that both host and parasite tend to co-evolve.
(b) Parasitic adaptation in plants
(i) Haustoria in Cuscuta
(ii) Loss of chlorophyll
(iii) Loss of leaves/foliage