CBSE Class 12 Biology Organisms And Population Worksheet Set A

MULTIPLE CHOICE QUESTIONS

Question. Obligate parasites live on 
(a) living host only
(b) living host and dead organic matter
(c) dead organic matter only
(d) artificial liquid medium
Answer : A

Question. A population has more young individuals compared to the older individuals. What would be the status of the population after some years?
(a) It will decline
(b) It will stabilize
(c) It will increase
(d) It will first decline and then stabilize 
Answer : C

Question. Ecotone is
(a) a polluted area.
(b) the bottom of a lake.
(c) a zone of transition between two communities.
(d) a zone of developing community. 
Answer : C

Question. Which of the following is a partial root parasite?
(a) Sandal wood
(b) Mistletoe
(c) Orobanche
(d) Ganoderma
Answer : A

Question. According to Allen’s rule, the mammals from colder climates have
(a) shorter ears and longer limbs
(b) longer ears and shorter limbs
(c) longer ears and longer limbs
(d) shorter ears and shorter limbs
Answer : D

Question. If a population of 50 Paramecium present in a pool increases to 150 after an hour, what would be the growth rate of population?
(a) 50 per hour
(b) 200 per hour
(c) 5 per hour
(d) 100 per hour
Answer : D

Question. Select the statement which explains best parasitism.
(a) One organism is benefited
(b) Both the organisms are benefited
(c) One organism is benefited, other is not affected
(d) One organism is benefited, other is affected. 
Answer : D

Question. Biosphere is
(a) a component in the ecosystem.
(b) composed of the plants present in the soil.
(c) life in the outer space.
(d) composed of all living organisms present on earth which interact with the physical environment. 
Answer : D

Question. Lichens are the associations of
(a) bacteria and fungus
(b) algae and bacterium
(c) fungus and algae
(d) fungus and virus
Answer : C

Question. Mycorrhiza help in absorption of 
(a) calcium
(b) nutrients
(c) metals
(d) none of these
Answer : B

Question. The plants which can withstand narrow range of temperature tolerance are called
(a) stenothermal
(b) eurythermal
(c) mesothermal
(d) monothermal
Answer : A

Question. Abundance of a species in a population, within habitat is called 
(a) niche density
(b) absolute density
(c) relative density
(d) geographic density
Answer : A

Question. The great barrier reef along the east coast of Australia can be categorised as 
(a) population
(b) community
(c) ecosystem
(d) biome
Answer : C

Question. Within biological communities, some species are important in determining the ability of a large number of other species to persist in the community. Such species are called 
(a) keystone species
(b) allopatric species
(c) sympatric species
(d) threatened species
Answer : A

Question. Presence of flagellated protozoans in the gut of termites are the example 
(a) Symbiosis
(b) Parasitism
(c) Antibiosis
(d) Commensalism
Answer : A

Question. The formula for exponential population growth is
(a) dN/rN = dt
(b) rN / dN = dt
(c) dN / dt = rN
(d) dt / dN = rN
Answer : C

Question. The salinity in sea water in parts per thousand (ppt) ranges between 
(a) 5-15%
(b) 30-35%
(c) 50-75%
(d) more than 100%
Answer : B

Question. In Urn shaped age pyramid of the population the trend of growth is 
(a) Rapid
(b) Stable
(c) Declining
(d) Stationary
Answer : C

ASSERTION REASON QUESTIONS

Directions : These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following five responses.
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.
(e) If the Assertion is incorrect but the Reason is correct.

Question. Assertion : Leaf butterfly and stick insect show mimicry to dodge their enemies.
Reason : Mimicry is a method to acquire body colour blending with the surroundings. 
Answer : A

Question. Assertion : Animals adopt different strategies to survive in hostile environment.
Reason : Praying mantis is green in colour which merges with plant foliage. 
Answer : A

Question. Assertion : The sex ratio of Kerala is highest in India.
Reason : In countries like India the population is increasing at a rapid rate.
Answer : B

Short answer type questions:

Question. What is interference competition? Define competitive exclusion principles.
Answer: (i) Feeding efficiency may be reduced due to interference of another species. E.g. –Tiger and deer.
(ii)Two closely related species need same resource can not co-exist indefinitely.

Question. Name and explain the kind of interaction in the following.
Answer: 1. Algae and Fungi in Lichens
2. Head Louse Humans
3. Hermit Crab and Sea Anemone
(i) Interaction of mutualism where the two species are equally benefited. Fungus provides protection, helps in absorption of water and minerals, Algae provide food for the Fungus.
(ii) This is case of Parasitism where the louse is an ectoparasite. Parasite takes shelter on humans and also derives nutrition.
(iii) It is commensalisms where one species is benefited and the other is neither benefited nor affected. Sea Anemone is benefited as it does not have to move to places rich in nutrients, while hermit crab is neither benefited nor harmed.

Question. Biomass is a more meaningful measure of population size. Explain with an example.
Answer: (i) Population large Total number is not an easily adoptable measure. Counting takes long time or practically impossible
(ii) There is no need to know the absolute population size for some investigations.
(iii) Number may sometimes be misleading e.g. In a given area there are 200 Parthenium plants and a single banyan tree. Here biomass size of the banyan tree is much more than those of 200 Parthenium plants.

Question. With the help of age pyramids explain the nature of a population.
Answer: a. Pre-reproductive/ re-productive/ post-reproductive

Question. What are the different types of population growth pattern? Mention their differences.
Answer: a. Logistic and Exponential growth
b. S Shaped curve, J shaped curve. Limiting Factors, No-limiting Factors

Question. How does Ophrys get pollinated by bees?
Answer: 1. Sexual deceit.
2. One petal resembles female.
3. Male pseudocoupulates with the flower.
4. Pollen grain transferred from one flower to another.

Question. What is brood parasitism? Give an example. What adaptation has evolved in this phenomenon?
Answer: One species lays eggs in the nest of another bird, lets the host incubate them. e.g. Cuckoo lays eggs in the nest of a crow.
The Eggs of the parasite resemble the eggs of the host in colour, size. Reduce chances of the host bird detecting the foreign eggs and ejecting them from nest.

Question. Name the interspecific interaction in which one is detrimental while the other is neutral.
Answer : Amensalism.

Question. Write what do phytophagous insects feed on.
Answer : Phytophagous insects feed on plant sap and other parts of plants.

Question. What is an interaction called when an orchid grows on a mango plant? 
Answer : Commensalism

Question. Pollinating species of wasps show mutualism with specific fig plants. Mention the benefits the female wasps derive from the fig trees from such an interaction.
Answer : Many species of fig trees have mutual relationship with the pollinator species of wasp. A given fig species can be pollinated only by its partner wasp species and not by other species. The female wasp uses the fruit not only as an oviposition (egg laying) site but also uses the developing seeds within the fruit for nourishing its larvae. The wasp pollinates the fig inflorescence while searching for suitable egg- laying sites. In return the fig offers the wasp some of its developing seeds as food for the developing wasp larvae.

Question. Why are cattle and goats not seen browsing on Calotropis growing in the fields?
Answer : Cattle and goats are never seen grazing on Calotropis, because Calotropis is a weed that produces highly poisonous cardiac glycosides. It is a harmful chemical that makes herbivores sick, inhibits feeding or digestion, disrupts reproduction or even kills them.

Question. If 8 individuals in a laboratory population of 80 fruitfiies died in a week, then what would be the death rate for population for the said period?
Answer : Death rate of fruitfly population for given time period will be :
8/80 = 0.1 individuals per fruitfly per week.

Question. Name the interaction that exists between Cuscuta and shoe-flower plant.
Answer : Parasitism

Question.Name the interaction that exists between sucker fish and shark.
Answer : Commensalism

Question. Name the type of interaction that exists between barnacles and whale.
Answer : Commensalism

Question. Name the type of interaction seen between fig and wasps. 
Answer : Mutualism

Question. In a pond there were 20 Hydrilla plants.Through reproduction 10 new Hydrilla plants were added in a year. Calculate the birth rate of the population. 
Answer : Birth rate is calculated as 10/20 = 0.2 offspring per Hydrilla per year.

Question. Comment on the interaction between a clown fish living among the tentacles of a sea anemone. 
Answer : Mutualism is the interaction between clown fish and sea anemone. The clown fish lives among the stinging tentacles of sea anemone and gets protection from its predators. Clownfish has a slimy mucus covering that protects it from the poisonous tentacles of sea anemone. Also clownfish makes its meals from the anemone’s leftover. In return clownfish helps anemone in catching its prey by luring other fish towards it. It also eats the dead tentacles keeping the anemone and the area around it clean.

Question. List any two adaptive features evolved in parasites enabling them to live successfully on their hosts. 
Answer : Adaptive features evolved in parasites that enable them to live successfully on their hosts are :
(i) Well developed reproductive system enabling excessive multiplication.
(ii)   Presence of adhesive organs or suckers to cling on to the host.

Question. Give one example where population estimation of an organism is done indirectly without actually counting the organism.
Answer : Sometimes population size is indirectly estimated without actually counting them, for example, tiger census in our National parks and tiger reserves is often based on pug (animal’s foot print) marks and faecal pellets.

Question. Give an example where percentage cover is a more meaningful measure of the population size. 
Answer : The percentage cover or biomass is a more meaningful measure of the population size in a forest area, where only a single huge banyan tree is accompanied by large number of Parthenium plants.

Question.What is mutualism? Mention any two examples where the organisms involved are commercially exploited in agriculture. 
Answer : Mutualism is an interaction between two organisms of different species where both the partners are benefitted and the association is obligatory. E.g., : nitrogen fixation in root nodule of legume by Rhizobium bacteria and pollination of orchid flower Ophrys by bee

Question. Differentiate between parasitism and competition, giving one example of each. State the common characteristic they share.
Answer : Differences between parasitism and competition are as follows: 

Parasitism	Competition
It is relationship between two living organisms of dierent species in which one organism obtains food from another living organism.	It is rivarly between two or more organi sms of same or different species for obtaining the same resources.
E.g., lice, an ectoparasite sucks blood of animals and Trypanosoma, an endoparasite feeds on body fluid.	E.g., in forest areas, trees shrubs, herbs and vines compete with each other for sunlight, nutrients, water, pollinators etc.

 

Question. Explain Verhulst-Pearl Logistic Growth of a population. 
Answer : According to Verhulst-Pearl logistic growth, population increases in size in sigmoid fashion. S-shaped growth form is found in stable population. It shows population growth in a habitat with limited resources. Population shows initially a lag phase, followed by phases of increase and decrease and finally 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 as explained by the following equation :

dN /dt rN ( rN K-N)/K
Where N = population density at a time t; r = intrinsic rate of natural increase and; K = carrying capacity

Question. Differentiate between commensalism and mutualism by taking one example each from plants only. 
Answer : 

Mutualism	Commensalism
It is an association between two organisms in which both are benefitted.	It is an association between two organisms in which only one is benefitted. The second is neither benefitted nor harmed.
Contact between the two organism is obligatory. Nitrogen fixing blue -green alga or cyanobacterium called Anabaena is associated with water fern Azolla in a mutualistic interaction.	Contact between commensal and its benefactor may be periodic or continuous. Many epiphytes,e.g., orchids, are found growing on the branches and in the forks of trees. These epiphytes use the trees only for attachment and manufacture their own food by photosynthesis.

 

Question. Name the type of association that the genus Glomus exhibits with higher plants. 
Answer : Members of fungal genus Glomus often form symbiotic association with the roots of higher plants. These associations are termed as mycorrhizae. Fungus helps the plant root in absorption of water and minerals and also helps the plants to increase tolerance to salinity and drought. In return plant
provides food to the fungus.

Question. Describe the mutual relationship between fig tree and wasp and comment on the phenomenon that operates in their relationship. 
Answer : Many species of fig trees have mutual relationship with the pollinator species of wasp. A given fig species can be pollinated only by its partner wasp species and not by other species. The female wasp uses the fruit not only as an oviposition (egg laying) site but also uses the developing seeds within the fruit for nourishing its larvae. The wasp pollinates the fig inflorescence while searching for suitable egg- laying sites. In return the fig offers the wasp some of its developing seeds as food for the developing wasp larvae.

Question. Name the interaction that exists between Cuscuta and shoe-flower plant.
Answer : Parasitism

Question.Name the interaction that exists between sucker fish and shark.
Answer : Commensalism

Question. Name the type of interaction that exists between barnacles and whale.
Answer : Commensalism

Question. Name the type of interaction seen between fig and wasps. 
Answer : Mutualism

Question. Explain mutualism with the help of an example.
Answer : Mutualism is an interaction between two organisms of different species where both the partners are benefitted and none of the two are capable of living separately. E.g., lichen is a composite entity which is formed jointly by an alga (phycobiont) and a fungus (mycobiont). The main body of the lichen is formed of fungus. The fungus also provides fixation, water, minerals and shelter to the alga. The alga manufactures food not only for itself but also for the fungus. This interaction or relationship allows the lichen to grow in highly hostile environment like bare rock.

Question. Explain brood parasitism with the help of an example. 
Answer : Brood parasitism in birds is a fascinating example of parasitism in which the parasitic bird lays its eggs in the nest of its host and lets the host incubate them. During the course of evolution, the eggs of the parasitic bird have evolved to resemble the host’s eggs in size and colour to reduce the chances of the host bird detecting the foreign eggs and ejecting them from the nest. Laying eggs by koel in crow’s nest is an example of brood parasitism.

Question. How does the floral pattern on Mediterranean orchid Ophrys guarantee cross pollination?
Answer : The Mediterranean orchid Ophrys employs sexual deceit to get pollinated by a species of bee. One petal of its flower bears an uncanny resemblance to the female of the bee in size, colour and markings. The male bee is attracted to what it perceives as a female, pseudocopulates with the flower, and in that process pollinates the flower. Thus, it brings about cross pollination in the Ophrys species.

Question. Mention the changes the koel must have undergone in order to achieve brood parasitism, during the course of evolution. 
Answer : Brood parasitism in birds is a fascinating example of parasitism in which the parasitic bird lays its eggs in the nest of its host and lets the host incubate them. During the course of evolution, the eggs of the parasitic bird have evolved to resemble the host’s eggs in size and colour to reduce the chances of the host bird detecting the foreign eggs and ejecting them from the nest. Laying eggs by koel in crow’s nest is an example of brood parasitism.

Question. Explain the two defense mechanisms evolved in preys to avoid overpopulation of their predator.
Answer : Prey species have evolved various defenses to lessen the impact of predation. Some species of insects and frogs are cryptically-coloured (camouflaged) to avoid being detected easily by the predator. Some mimic poisonous insects in design, colour and pattern and therefore are avoided by the predators.

Question. Write the importance of measuring the size of a population in a habitat or an ecosystem.
Answer : It is important to measure population size of habitat because it indicates that whether population is flourishing or declining.

Question. (a) Explain “birth rate” in a population by taking a suitable example.
(b) Write the other two characterstics which only a population shows but an individual cannot.
Answer : (a) Birth rate refers to per capita births, i.e., average number of individuals produced per unit time. For example, if in a pond there were 20 lotus plants last year and through reproduction 8 new plants are added, then taking the current population to 28, we calculate the birth rate as 8/20 = 0.4 offspring per lotus per year.
(b) Other attributes of population which individuals cannot show include -
(i) Death rate - An individual dies but a population has death rate. It refers to per capita deaths, i.e., average number of individuals that die per unit time. If 4 individuals in a laboratory population of 40 fruitflies died during a specified time interval (say a week), the death rate in the population during that period is 4/40 = 0.1 individuals per fruitfly per week.
(ii) Sex ratio - An individual has sex but a population has sex ratio, i.e., number of females and males per 1000 individuals. E.g., 60% of population are females and 40% are males.

Question. (a) List any three ways of measuring population density of a habitat.
(b) Mention the essential information that can be obtained by studying the population density of an organism. 
Answer : (a) Population density means number of individuals present per unit area or per unit volume of the environment in which the population exists. We can find out population density of a habitat by determining the population size.
The different methods to study population size are as follows:
– Quadrat method : It is a method which involves the use of square of particular dimension to measure number of organisms. For example the number of Parthenium plants in a given area can be measured using the quadrat method.
– Direct observation: It involves counting of organisms. For example, in order to determine the number of bacteria growing in a petri dish, their colonies are counted.
– Indirect method : The number of fishes caught per trap gives the measure of their total density in a given water body.
(b) Population has attributes that individual organisms do not. These include birth rate, death rate, sex ratio and age distribution. The proportion of different age groups of males and females in a population is often presented graphically as age pyramid; its shape indicates whether a population is stationary, growing or declining. Ecological effects of any factor on a population are generally reflected in its size (population density), which may be expressed in different ways (numbers, biomass, percent cover, etc.) depending on the species. The size of the population tells us a lot about its status. By studying the population of an organism, we can also know how population grows through births and immigration and declines through deaths and emigration.

Question. List two advantages that a mycorrhizal association provides to the plant.
Answer : Mycorrhizal association is mutualistic interaction between fungus and roots of higher plant.
Two advantages of this association to the plant are : (i) Fungus solubilises the minerals present in soil and helps the plant in absorption of minerals.
(ii) It protects plant against pathogenic fungi.

Question. How are ephemeral plants adapted to withstand hot and dry environment? Explain.
Answer : Ephemerals are xerophytic plants of hot and dry habitat where environment favours higher rate of transpiration than the rate of absorption. Ephemerals live for a brief period during the rains and rest of the year is passed in form of seeds.

Question. What does ecological niche of an organism represent? 
Answer : The ecological niche of an organism represents the status or role of the organism in its environment. Niche is defined by the types of food it consumes, its predators, temperature tolerance, etc.

Question. During a school trip to ‘Rohtang Pass’, one of your classmates suddenly developed ‘altitude sickness’. But, she recovered aer sometime.
(a) Mention one symptom to diagnose the sickness.
(b) What caused the sickness?
(c) How could she recover by herself after sometime? 
Answer : (a) Heart palpitation
(b) Sickness is due to low atmospheric pressure of high altitudes, as body does not get enough oxygen. (c) After sometimes, body compensates for low oxygen availabilty by increasing red blood cell production, decreasing binding capacity of haemoglobin and by increasing breathing rate.

Question. Why the plants that inhabit a desert are not found in a mangrove? Give reasons.
Answer : Plants inhabiting desert (xerophytes) are not found in mangroves, because xerophytic plants are adapted to dry and hot environment. They possess various physical modifications to tolerate extreme water scarcity and heat, like extensive root system, succulent organs, leaf reduced to spine, etc. Mangrove swamp is a region of vegetation where soil is highly saline and water logged. Only halophytes can survive in such regions as they possess aerial roots called pneumatophores through which gaseous exchange occurs. Roots of xerophytes are positively geotropic and will suffocate and die in such badly aerated soil ultimately leading the whole plant to death.

 

1 Name the type of association that the genus Glomus exhibits with higher plants. 

 

2 How biome and ecological niche terms differ from each other? Give examples of each. 

 

3 If a population of 50 Paramecium present in a pool increases to 150 after an hour, what would be the growth rate of population?

 

4 A population has more young individuals compared to the older individuals. What would be the status of the population after some years?

 

5 Describe the mutual relationship between fig tree and wasp and comment on the phenomenon that operates in their relationship.

 

6 Discuss the interactions of following with their hosts :

a) an epiphyte (with example)

b) a parasite ( with example)

c) a mycorrhizae fungus

 

7 If a fresh water fish is placed in an aquarium containing sea water, will the fish be able to survive? Explain giving reasons.

 

8 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.

 

9 Give the scientific names of any two microorganisms inhabiting the human intestine. 

 

10 An individual and a population has certain characteristics. Name these attributes with definitions.

 

11 Name the interaction in each of the following:

a. Cuckoo lays her eggs in the crow’s nest

b. Orchid grows on a mango tree

c. Ticks live on the skin of dogs.

d. Sea anemone is often found on the shell of hermit crab. D’2008

 

12 Describe any three adaptations that are shown by animals to resist and sur vive under unfavourable conditions.

 

13 Give the equation for exponential growth curve. What does ‘‘r’’ represent in the equation ?

 

Write its importance in population growth.

(b) Explain the principle of carrying capacity by using population Verhulst-Pearl logistic growth curve.

 

14 Give one example for each of the following:

i. A hot water spring organism _______________

ii. An organism seen in deep ocean trenches _______________

iii. A parasitic angiosperm ______________

iv. An organism which can conform_____________________