2nd PUC Biology Question Bank Chapter 13 Organisms and Populations

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Karnataka 2nd PUC Biology Question Bank Chapter 13 Organisms and Populations

2nd PUC Biology Organisms and Populations NCERT Text Book Questions and Answers

Question 1.
How is diapause different from hibernation?

Diapause Hibernation
(i) Dormant stage in development of an organism (i) State of inactivity in a mature organism.
(ii) Occurs in summers and winters (ii) Only during winters
(iii) Reduction in free water (iii) No such adaptations

Question 2.
If a marine fish is placed in a freshwater aquarium, will the fish be able to survive? Why or why not?
If a marine fish is placed in a freshwater aquarium, the fish will not be able to survive because of osmoregulation problems. The marine fish is adapted to live in saline water, so, if it is kept in freshwater, it will not be able to cope with the outside hypotonic environment and it would face death.

Question 3.
Define phenotypic adaptation. Give one example.
Phenotypic adaptations are non-genetic changes occurring in living organisms due to various extreme environmental conditions, such as stress, extreme temperature, change of habitat. These include acclimatization, behavioural changes, etc.

KSEEB Solutions

Question 4.
Most living organisms cannot survive at temperatures above 450C. How are some microbes able to live in habitats with temperatures exceeding 1000C?
Archaebacteria (Thermophiles) are ancient forms of bacteria found in hot water springs and deep-sea hydrothermal vents. They are able to survive in high temperatures because their bodies have adapted to such environmental conditions. These organisms contain specialized thermo-resistant enzymes, which carry out metabolic functions that do not get destroyed at such high temperatures unlike other enzymes.
Most living organism can not survive above 45° because:

  • Above 45° C enzymes get denatured
  • Protoplasm precipitates at high temperatures.

Question 5.
List the attributes that populations but not individuals possess.
the population has some attributes which are not shown by its individual members. An individual born and dies, whereas the population has a birth rate (natality) and a death rate (mortality). Each population has certain characteristics, such as age distribution, genetic composition, growth models. An individual is either male or female but a population has a sex ratio.

Question 6.
If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?
2nd PUC Biology Question Bank Chapter 13 Organisms and Populations 1

Question 7.
Name important defence mechanisms in plants against herbivory.
There are various defence measures for animals against predators. But plants, as they cannot move away, have certain defence mechanisms against herbivory. Their main defences are chemical toxins, such as strychnine, a poison produced by tropical vine, morphine by opium poppy, nicotine produced by tobacco plant. Apart from these chemicals, the common defence measure is presence of spines (modified leaves) on the leaves, stems of the plant, modifications of leaves into thorns, development of sharp silicated edges in leaves which prevent them from damage caused by herbivores.

Question 8.
An orchid plant is growing on the branch of the mango tree. How do you describe this interaction between the orchid and the mango tree?
An orchid growing on the branch of a mango tree is an epiphyte. Epiphytes are plants growing on other plants which, however, do not derive nutrition from them. Therefore, the relationship between a mango tree and an orchid is an example of commensalisms, where one species gets benefited while the other remains unaffected. In the above interaction, the orchid is benefited as it gets support while the mango tree remains unaffected.

Question 9.
What is the ecological principle behind the biological control method of managing pest insects?
The ecological principle behind the biological control method of managing pest insects is a predator-prey relationship. It is based on the ability of the predator to regulate the prey population.

KSEEB Solutions

Question 10.
Distinguish between the following:
(a) Hibernation and Aestivation
(b) Ectotherms and Endotherms

Hibernation Aestivation
(i) Condition of passing the winter in a resting or dormant condition. (i) State of inactivity during hot and dry summer.
(ii) Animal rests in a warm place (ii) Animal rests in a cool, shady, moist place.
(iii) Lasts for the whole winter. (iii) Lasts for the hot dry day because nights are often cooler


Ectotherms/Cold Blooded Entotherms/Warm Blooded
(i) Unable to regulate their body temperature. (i) Able to regulate their body temperature.
(ii) Lives in areas with favourable body temperature as they change their body temperature with respect to environmental temperature (ii) Live in all places as there is only little effect on their body temperature by environmental temperature.
(iii) They show hibernation, aestivallon and are less active. (iii) More active and no such inactive states are expressed

Question 11.
Write a short note on
a. Adaptations of desert plants and animals
b. Adaptations of plants to water scarcity
c. Behavioural adaptations in animals
d. Importance of light to plants
e. Effect of temperature or water scarcity and the adaptations of animals.
(a) Desert plants have developed various adaptations to increase absorption of water and to reduce water loss. They have well developed root system that penetrates deep into soil surface to absorb water, leaves have thick waxy covering and are mostly reduced into spines to reduce rate of transpiration. Stems are green (carry out photosynthesis) and fleshy (to store water and mucilage). Animals in arid areas have the ability to tolerate dry conditions. During daytime desert animals move to burrows and seldom come out. They minimize loss of water by producing dry feces and concentrated urine. Some of them have special physiological adaptations to cope with scarcity of water and hot arid desert conditions. E.g., kangaroo rat seldom drinks water and 90% of its water requirements are met from metabolic water produced by respiratory breakdown of fats. Likewise, camel does not sweat till body temperature rises upto 55° – 66°C. Its body cells are capable of tolerating upto 40% dehydration, etc.

(b) The xerophytes have special adaptations to withstand prolonged period of drought. These are of four types – ephemerals (drought escapers), annuals (drought evaders), succulents (drought resistants) and non-succulent perennials (drought endurers). Ephemerals are xerophytes which evade dry conditions by remaining in the form of seeds but live for a brief period and complete their life cycle during the rains. Common examples are Euphorbia prostrata, Tribulus terrestris, etc. Annuals are the xerophytes which continue to live for a few months even after rains in hot dry conditions. They have modifications to reduce transpiration. A common example is Echinops echinatus. Succulents have fleshy organs to store large amounts of water. Plants like Opuntia, Euphorbia, Asparagus have fleshy stems which are green and photosynthetic. Non-succulent perennial plants have many morphological modifications to withstand dry conditions. These have an extensive root system that spreads deep in the soil and may reach water table to absorb the maximum amount of water. They also possess waxy coatings or hairs on leaves, sunken stomata, reduced leaf blades etc. to reduce transpiration, Examples include Acacia nilotica, Calotropis procera, etc.

(c) Some organisms show behavioral adaptations to cope with variations in their environment. E.g., desert lizards. They lack the physiological ability that mammals have to deal with high temperature. They keep their body temperature fairly constant by behavioral means. They enjoy in the sun and absorb heat when their body temperature drops below the comfort zone, but move into shade when the surrounding temperature starts increasing. Some species are capable of burrowing into the soil to hide and escape from too much heat.

(d) Light is the visible part of the electromagnetic spectrum. It is an important ecological factor as it affects different physiological processes of plants, e.g., photosynthesis, transpiration, movements, flowering, seed germination, etc.

  • Photosynthesis: Light is essential for photosynthesis. The amount of photosynthesis depends upon the quality, intensity and duration of light.
  • Growth: It is favoured by increased availability of food, moderate light intensity and red light. UV radiations favour rosette habit in plants. Blue light favours moderate but normal growth.
  • Transpiration: Stomata generally open in light and close in darkness. Because of it light promotes transpiration. Transpiration is further enhanced by heating effect of light.
  • Germination: A number of seeds are sensitive to light. They are called photoblastic seeds. Positively photoblastic seeds germinate only in the presence of light, e.g., Vtscum, Lactuca, Rumex.
  • Movements: Small photosynthetic organisms show positive phototaxis in moderate light, e.g., Chlamydomonas, Euglena, Volvox. Plant shoots bend towards the source of light. It is positive phototropism. Flowers of some plants open or close in response to light and darkness.
  • Photoperiodism: Different plants require different periods of light for flowering which is known as photoperiod and the response of the plant to photoperiod in terms of flowering is called photoperiodism.

(e) Animals facing water scarcity have ability to tolerate arid conditions and reduce water loss. For example kangaroo rat seldom drinks water; 90% of its water needs are met from v metabolic water i.c., water produced by respiratory breakdown of fat and the remaining 10% is fulfilled from food. It is nocturnal in habit and seldom comes out of its burrow during the daytime. It has a thick body covering to minimise water loss due to evaporation. The kangaroo rat excretes nearly solid urine and faeces. Another example is that of camel, commonly called the ‘ship of desert’. Camel being very economical in water consumption, tolerates fluctuations in temperature, maintains blood stream moisture with body cells capable of tolerating extreme heat stress, does not sweat till body temperature rises to 55°-66°C, produces dry faeces and concentrated urine. During periods of non-availability of water, the animal does not produce urine and stores urea.

Question 12.
List the various abiotic environmental factors.

  • Atmospheric factors: Light, temperature, wind and water.
  • Lithosphere: Rock, soil.
  • Hydrosphere: Pond, river, lake and ocean.
  • Edaphic factors: Soil texture, soil water, soil air, soil microorganism, soil pH, minerals.
  • Topographic factors: Slope, altitude, valley.

Question 13.
Give an example for:
(a) An endothermic animal
(b) An ectothermic animal
(c) An organism of benthic zone
(a) An endothermic animal – Monkey (mammal)
(b) An endothermic animal Frog (amphibian), snake (reptile)
(c) An organism of the benthic zone – Angle Fish

Question 14.
Define population and community.
The population can be defined as the total number of individuals of a species or any other class of an organism in a defined area or habitat or a group of individuals of the same species within a community.
The community can be defined as a naturally occurring assemblage of species living within a defined area or habitat.

Question 15.
Define the following terms and give one example for each:
a. Commensalism
b. Parasitism
c. Camouflage
d. Mutualism
e. Interspecific competition
(a) Commensalism is the interaction between two living individuals of different species in which one is benefited while the other is neither harmed nor benefited except to a negligible extent. For example, the pilot fish (Naucrates) always accompanies the shark without getting attached to its body. It feeds on falling pieces of food when the shark is eating the prey.

(b) Parasitism is an interaction between two living organisms of different species in which one organism called a parasite obtains its food directly from another living organism called the host. The parasite spends a part or whole of its life on or in the body of the host. Thus it is an interaction between two individuals wherein the parasite gets the benefit at the expense of the host.

(c) Camouflage (Cryptic appearance) is the ability to blend with the surrounding or background. It is the most common type of adaptation by animals to remain unnoticed for protection or aggression. Camouflage is protective to animals which are preyed upon by others. It is advantageous in predation for predators like praying mantis (Mantis religiosa) which are green coloured, resembling a thin stem, and remain unnoticed till the prey comes within their striking range.

(d) Mutualism is an interaction between two species in which both species benefit. (The term symbiosis is often used synonymously with mutualism.) A well-known example of mutualism is the association between termites and the specialized protozoans that inhabit their guts. The protozoans, unlike the termites, are able to digest the cellulose of the wood that the termites eat and release sugars that the termites absorb. The termites benefit by being able to use wood as a foodstuff, while the protozoans are supplied with food and a suitable environment.

(e) In interspecific competition two or more populations usually belonging to the same trophic level or feeding habit compete with one another for the available natural resources. For example, in a forest area trees, shrubs, herbs, and vines compete with one another for sunlight, nutrients, water, pollinators, and dispersal agents.

Question 16.
With the help of a suitable diagram describe the logistic population growth curve.
2nd PUC Biology Question Bank Chapter 13 Organisms and Populations 2
Logistic growth occurs because of natural selection. Here nature selects the filter (Survival of the fittest). Nature has resources to support a maximum number of people (Carrying Capacity (K)) beyond which resources won’t support them due to their lock. This explains that the log-phase follows a phase of acceleration. So we get the sigmoid curve.

This growth is Verhulst-pearl Logistic Growth
\(D=\frac { dN }{ dt } =rN\left( \frac { K-N }{ K } \right) \)

N=Population density at time
K = Carrying capacity
r = Intrinsic rate of natural increase

Question 17.
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,
(d) Parasitism is an association of two organisms of different sizes and species in which one is benefited and the other is harmed. The organism which is benefited is called a parasite, and the organism that suffers is termed host. The parasite is weaker and smaller than host and gets nourishment and often shelter also from the host. The host can live without the parasite, but the parasite cannot survive without the host.

Question 18.
List any three important characteristics of a population and explain.
The three important characteristics of a population are:

1. Population density: The number of individuals of a species per unit area, or a volume is called population density.
PD=\(\frac { N }{ s }\)

Where, PD = Population density
N = Number of individuals in a region
S = Number of a unit area in a region.

2. Birth rate: It is expressed as the number of births per 1000 individuals of a population per year.

3. Death rate: It is expressed as the number of deaths per 1000 individuals of a population per year.

2nd PUC Biology Organisms and Populations Additional Questions and Answers

2nd PUC Biology Organisms and Populations One Mark Question

Question 1.
Define the term ecology.
It is the study of the relationships of living organisms with the biotic and abiotic components of the environment.

Question 2.
Name the factors essential for the formation of major biomes

  • The annual variation in the intensity and duration of temperature
  • The annual variation in precipitation accounts for the formation of major biomes.

Question 3.
Which one of the two stenothermals or eurythermal, shows a wide range of distribution, on earth and why? (CBSE 2008)
Eurythermal shows a wide range of distribution as they can tolerate and thrive in a wide range of temperatures.

Question 4.
Between amphibians and birds, which will be stable to cope with global warming? (AI2008)
Birds will be stable because they are eurythermal, which can tolerate a wide range of temperatures.

KSEEB Solutions

Question 5.
Why many freshwater animals cannot live for long in seawater or vice versa. (Delhi 2008)
This is because of the osmotic changes in the body.

Question 6.
Define homeostasis
It is the self-regulatory mechanism to maintain the internal environment constant despite changes in the external environment.

Question 7.
How do herbs and shrubs survive under the shadow of big canopied trees in the forest? (AI 2008)
They are adapted to photosynthesis optimally under very low light conditions and hence survive under the shadow of big canopied trees.

Question 8.
Why is the polar region not a suitable habitat for tiny hummingbirds? (AI 2008)
The small birds have a larger surface area to body volume ratio and tend to lose heat fast when it is cold outside; consequently, they have to spend more energy to generate body heat.

Question 9.
Define the term migration
Migration is the temporary, long-distance, or short-distance movements of animals from the stressful movement to a less stressful or comfortable environment and returns to the original habitat when the stressful period is over.

Question 10.
Define the term hibernation.
It is the process in which animals spend the winter in an inactive/dormant state,
eg: Frogs, the polar bear.

Question 11.
When and why do some animals (frog, polar bear) go into hibernation (Delhi 2008)
When the animals (like frogs) are not able to migrate from unfavorable or stressful conditions/habitats during the very cold conditions, they hibernate to avoid the stress by escaping in time.

Question 12.
Define the term aestivation?
It is the process in which animals spend the dry, hot summer period in an inactive state,
eg: Snails.

Question 13.
When and why do some animals undergo aestivation?
When the snails are not able to migrate from stressful habitats in summers they undergo aestivation to avoid stress by escaping in time.

Question 14.
Define the term adaptation.
The development of certain features in an organism in response to a particular environment which may improve the chances of survival is called adaptation.

Question 15.
What is Allen’s rule?
Allen’s rule refers to the minimising of heat loss in animals by possessing shorter ears and limbs.

Question 16.
Why do people living at high altitude have a higher red blood cell count or total hemoglobin
To compensate for the low atmospheric pressure and low oxygen content of air prevailing at high attitudes, people have higher, RBC count or total haemoglobin.

KSEEB Solutions

Question 17.
List any 2 physiological responses that help you to gradually get acclimatized to high altitudes when you go from the plains (Delhi 2008)

  • Increasing in breathing rate
  • Decreasing in binding capacity of haemoglobin.
  • Increase in RBC production.

Question 18.
Define Population density.
The total number of individuals of a species present per unit area or volume at a given time.

Question 19.
Give an example where population estimation of an organism is done indirectly without actually counting the organism. (AI2008)

  • The number of fish caught in a trap indicates the total population density in a lake
  • The tiger census is based on the pug marks or faecal pellets.

Question 20.
When does a population growth curve become sigmoid?
Sigmoid growth curve represents logistic growth where growth is slow initially and then becomes rapid the curve becomes steady due to resources become tending.

2nd PUC Biology Organisms and Populations Two Marks Questions

Question 1.
Why is thermoregulation more effectively achieved in larger animals than in smaller ones?
Larger ones achieve thermoregulation more effectively than smaller ones because of less surface area/volume ratio in larger ones, hence lose body heat slowly.

Question 2.
Name the specialty of any population.
Any population has some specialty these are:

  1. Population density
  2. Growth rate
  3. Death rate
  4. Age distribution
  5. Biotic capacity
  6. Population growth form
  7. Changes of population
  8. Population dispersion.

Question 3.
Study 3 representative figure of age pyramids
2nd PUC Biology Question Bank Chapter 13 Organisms and Populations 3
(a) Mention names were given to the 3 kinds of age profiles (i), (ii), (iii).
(i) Expanding population (Triangular)
(ii) Stable population (Bell-shaped)
(iii) Declining population (Cube-shaped)

(b) Which one of them is ideal for the population and why?
We take a stable population pyramid as ideal because our aim is to stabilize the population.

(c) How do such age profile studies help policymakers get concerned about the growing population?
Age pyramid/profile can indicate

  • Rate of growth of population
  • Increase in the elderly population and reproductive-aged people.

These features help prepare for future planning on:

  • The stress of family planning
  • To help elderly and needful people to live comfortably.

Question 4.
(a) Write eg: for Verhulst Pearl logistic growth
\(\frac { dN }{ dt } =rN\left( \frac { K-N }{ K } \right) \)
r=intrinsic rate of natural increase
N = Population density at time (t)
K = Carrying capacity.

KSEEB Solutions

(b) Draw graph for a population whose population density has reached the carrying capacity.
2nd PUC Biology Question Bank Chapter 13 Organisms and Populations 4

(c) Why is the logistic growth model considered a more realistic one for most animal populations?
The logistic growth model is considered realistic in animals because each area has a carrying capacity beyond which environmental resistance grows and restricts their growth. It decreases natality and increases mortality.

(d) Draw a growth curve where resources are not limiting the growth of the population?
2nd PUC Biology Question Bank Chapter 13 Organisms and Populations 5

Question 5.
In adjacent population growth curves
2nd PUC Biology Question Bank Chapter 13 Organisms and Populations 6
Curve (a) – Non-limiting
curve (b) – Limiting and has reached carrying capacity.

(ii) In absence of predators which curve will be demonstrated?
Curve (a) because of the absence of a controlling factor.

Question 6.
Write the differences:

  1. Species and Population
  2. Population growth and Population density
  3. Mono-specific and Polyspecific Population
  4. Competition and Scattering.


  1. Species and Population: Population on defined as organisms that belong to identical species and identical geographical niche or area. The said area should enable these species to interbreed with each other.
  2. Population growth and Population density: In biology, Population growth is the increase in the number of individuals in a population but the population density is a measurement of population per unit area, it is a quantity of type number density.
  3. Monospecific or Polyspecific population: Monospecific population is the population of individuals of only one species but the polyspecific or mixed population is the population of individuals of more than one species and it is generally referred to as a community.
  4. Competition and Scattering: Competition is in general a contest between two or j more rivalry between two or more entities, organisms, animals, economic groups or social groups, etc. Population scattering is a method which shows equilibrium by the interaction of population. In population, scattering seeds away from the parent plant.

Question 7.
List any two adaptive features evolved in parasites enabling them to live successfully on their hosts. (Delhi 2008)
The adaptive features of parasites include

  • Loss of unnecessary sense organs
  • Presence of adhesive organs or suckers to cling on to the host.
  • Loss of digestive system
  • High reproductive capacity.

Question 8.
Explain, The formation of new species.
Although all life on earth shares various genetic similarities, only certain organisms combine genetic information by sexual reproduction and have offspring that can then successfully reproduce. Scientists call such organisms members of the same biological species.

Question 9.
Write the influence of temperature on the life of the organism.

  • The temperature affects the enzyme reaction in the bur body.
  • The thermal tolerance of organisms determines their geographical distribution.

Question 10.
Differentiate between Euryhaline and ‘ Stenohaline animals.
Euryhaline animals Animals which can tolerate a wide range of salinity. Stenohaline animals Animals which can tolerate a narrow range of salinity.

Question 11.
What is the effect of light on the life of animals?

  • Intensity and duration of light influence the activities like foraging, migratory activities, and reproduction.
  • light influences the temperature and thereby the metabolism of animals.

Question 12.
How does human beings maintain constant body temperature?

  • In summer we sweat profusely; the evaporation of the sweat cools the body and brings the body temperature down.
  • In winter, we shiver and that produces more heat, to raise the body temperature.

Question 13.
Mention 2 adaptations the mammals of the colder regions have, to minimize the loss of body heat.

  • Mammals of colder regions have shorter ears and limbs.
  • Aquatic mammals of colder seas have a thick layer of fat called blubber below the skin which acts as an insulator reduces the loss of body heat.

Question 14.
Differentiate between Population Size and Population Density.

  • Population size: The number of individuals of a species, in a given area at a given time.
  • Population density: The number of individuals of a population per unit area at a given time.

Question 15.
Biomass is a more meaningful measure of population size. Explain.

  • If the population is huge, the total number is not as easily adaptable measure as the counting takes a very long time or counting becomes practically impossible.
  • For some ecological investigations, there is no need to know the absolute population size/density.

Question 16.
Define carrying capacity.
Carrying capacity is the maximum number of individuals of a population that can be sustained by a given habitat.

Question 17.
What is the role of predators in maintaining species diversity in an ecosystem?
Predators help in maintaining species diversity in an ecosystem or community by reducing the intensity of competition among the competing prey species.

Question 18.
In what ways the prey species are adapted to escape from predators? Explain with example.

  • Some species of frogs and insects are cryptically coloured or camouflaged to avoid being detected easily by predators.
  • Some prey species are poisonous and are avoided by the predators.

Question 19.
(a) How is Cuscuta adapted to be a parasitic plant?
(b) Why do cattle avoid browsing on Calotropis plants? Explain. (CBSE foreign 2009)

  • Cuscuta has no chlorophyll and leaves.
  • It develops haustoria to derive nutrition from the host its parasites.

(b) Calotropis plants possess a highly poisonous cardiac glycoside, which is fatal to animals.

Question 20.
Name two basic types of competition found amongst organisms. Which one of these is more intense and why?
The two types of competitions are

  • Interspecific competition and
  • Intraspecific competition

This intraspecific competition is more intense because it is an interaction among individuals of the same species for similar requirements.

Question 21.
Explain interference competition with an example.
In interference competition, even if the resource is abundant, the feeding efficiency of one species is reduced by the interfering and inhibitory presence of other species.
Eg: The Abingdon tortoise in Galapagos islands become extinct within a decade due to the introduction of a goat on that island.

KSEEB Solutions

Question 22.
Differentiate between commensalism and Amensatism.

  • Commensalism:- It is the interspecific interaction in which one species is benefited while the other is neither benefited nor affected.
  • Amensatism:- It is an interspecific interaction in which one species is affected, while the other species is neither benefited nor affected.

Question 23.
What is resource partitioning? Give an example.
It is the phenomenons in which two species competing for the same resource could avoid competition by choosing different patterns of foraging and different times of feeding. Eg:- Five closely related species of warblers living on the same tree has been shown to co-exist and avoid competition by behavioural differences.

Question 24.
Give the interaction present in each.

  1. The cuckoo lays her eggs in the crow’s nest
  2. Orchid grows on a mango tree
  3. Cuscuta growing on a shoe flower plant
  4. Clownfish living among the tentacles of sea anemone
  5. Ticks live on the skin of dogs
  6. Mycorrhizae living on the roots of higher plants
  7. Sea anemone is often found in the shells of hermit crab (CBSE-Delhi 2008)


  1. Brood parasitism
  2. Commensalism
  3. Commensalism
  4. Commensalism
  5. Parasitism
  6. Commensalism
  7. Commensalism.

Question 25.
Name and explain the interaction between fig trees and certain species of wasps.
The interaction between fig trees and certain species of wasp is the mutualism.

  • The female wasp uses the ovary of flowers as a site of oviposition (egg-laying) and the developing seeds as a flood for the larvae.
  • The flower is pollinated when the wasp is searching a place for oviposition.

Question 26.
What type of interaction is there between clownfish and sea anemone. Why? (AI 2008)
The interaction between clownfish and sea anemone is commensalism. In this, one is benefitted and the other is neither benefitted nor harmed.
In this relation
(i) The sea anemone has stinging tentacles which keep away the predators of clownfishes in this clownfish are getting benefit and the sea anemone is not getting any benefit or not harmed.

Question 27.
\(D=\frac { dN }{ dt } =rN\left( 1-\frac { N }{ K } \right) \)
(a) Which type of growth curve does it represents,
(b) What do the following notations represent
(i) \(\frac { dN }{ dt } \) (ii) r (iii) N (iv) K (CBSE 2005)
(a) It represents logistic or Verhulst-Pearl logistic growth
(b) \(\frac { dN }{ dt } \) = rate of change in population size
r – intrinsic rate of natural increase
N – Number of existing individual
K – Carrying capacity.

Question 28.
Study the population growth curves shown in the diagram.
2nd PUC Biology Question Bank Chapter 13 Organisms and Populations 7
(1) Identify curves ‘a’ and ‘b’
(2) Mentions the conditions responsible for the curves ‘a’ and ‘b’ respectively
(3) Give the equation for the curve ‘b'(CBSE 2006)
(1) a – Exponential curve
b – logistic or sigmoid curve

a – Unlimited food and other resources
b – Limited food and other resources

\(\frac { dN }{ dt } =rN\left( \frac { K-N }{ K } \right) \)

Question 29.
Study the table given below in regard to population interactions and the questions given below.
2nd PUC Biology Question Bank Chapter 13 Organisms and Populations 8
[(+) plus – beneficial interaction; (-) minus – detrimental interaction; 0 (zero) – neutral interaction.
(a) Identify the interactions a to e
(b) Explain each one. (CBSE 2008 comptt)
A – B
(a) Amensalism – Species A harmed species B unaffected
(b) Predation/parasitism – Species A benefited species B harmed
(c) Competition – Species A and B mutually inhibited
(d) Mutualism – Both A and B benefitted
(e) Commensalism – Species A is benefitted Species B is unaffected.

Question 30.
Is the statement in correctly matched ? If it is incorrect, rewrite the correct form Camoflague: An organism showing resemblance with external environment animals or plants for the purpose of protection
Incorrect:- Camoflague is blending with the background or surroundings due to similar colours, shape, or marketing so as to remain unnoticed by predators (for protection) and prey (advantage).

2nd PUC Biology Organisms and Populations Three Marks Questions

Question 1.
What are Conformers? Why they haven’t evolved mechanisms for temperature regulation or osmoregulation.
Conformers are that organism, which change their body temperature, osmolarity etc. according to the external ‘environmental conditions.
(1) During the course of evolution, the costs and benefits of maintaining a constant internal environment are taken into consideration, when it is not advantageous, the organisms have not evolved mechanisms to maintain homeostasis.

(2) Heat loss or gain is a function of surface area and hence very small animals are not found in polar region i.e. they have become distributed according to the external conditions.

(3) Similarly aquatic animals, that are conformers can change the osmolarity of their body fluid according to the surroundings.

KSEEB Solutions

Question 2.
Explain population fluctuation.
Population is generally a group of individuals of a particular species occupying a particular area at a specific time.
Population fluctuation: Any increase or decrease in number of individuals in a population from its equilibrium state is known as population fluctuation. It may occur due to various reasons, such as due to change in climate or due to change in physical environment or due to predators.

Question 4.
What do you mean by biotic community? Describe characteristic features of any biotic community.
Biotic community: A biotic community is a localized association of several populations of different species living in a given geographic area of habitat. It represents heterogeneous assemblage of different groups of organisms both plants and animals. Biotic community is composed of smaller units of intimately associated members belonging to different species.

The different species of a community share a common environment and their relationships are based on direct or indirect functional interactions. The nature of the relationship is determined by the requirements of the members of a community.

Characteristics of a community: Each community has its own characteristics which are not shown by its individual component species.

  1. Species diversity: Each community is made up of many different organisms: Plants, animals, microbes, which differ taxonomically from each other. The number of species and population abundance in the community also vary greatly.
  2. Growth form and structure: Each community has a definite growth form. This different growth form determines the structural pattern of a community.
  3. Dominance: In each community, all the species are not equally important. There are relatively only a few of these, which determine the nature of the community. These few species exert a major controlling influence on the community. Such species are known as dominants.
  4. Succession: Each community has its own development history. It develops as a result of a directional change in it with time.
  5. Trophic structure (Self-sufficiency): Nutritionally, each community, a group of autotrophic plants as well as heterotrophic animals exists as a self-sufficient, perfectly balanced assemblage of organisms.

Question 4.
Differentiate between ectoparasite an endoparasite.

Ecto parasite Endo parasite
Those organisms which live on the surface of the other living organism and derive food from it eg: lice on human Those organisms which live inside the body of other living organisms and derive food from it eg: Plasmodium and liver fluke in man.

Question 5.
What is brood parasitism? Give an example of what adaptation has evolved in this phenomenon
Brood parasitism is a phenomenon in which one species (parasite) lays eggs in the nest of other species (host) of bird and lets the host incubate them, eg: Cuckoo lays eggs in crow’s nest Cuckoo’s eggs shows resemblance with the eggs of crow in colour size etc which failed to identify by the crow with their eggs.

Question 6.
Name and explain the kind of interaction in the following
(1) Algae and fungi in lichens
(2) Head louse and humans
(3) Hermit crab and sea anemone.
(1) Algae and fungi in lichens:-

  • This is an example of mutualism in which both are benefited
  • Fungi provide protection and help in absorbing water and minerals whereas the algae prepare food for the fungus.

(2) Head louse and human: This is an example of ectoparasitism the parasite gets shelter as well as food from the human’s head.

(3) Hermit crab and sea anemone:- This is an example of commensalism in which sea anemone gets a benefit for moving to places rich in nutrients while the hermit crab neither benefitted nor harmed.

Question 7.
2nd PUC Biology Question Bank Chapter 13 Organisms and Populations 9
The above graph shows the organisms response to abiotic environmental factors. Name the categories of animals. Which show the pattern a, b, and c respectively and define each of them.
(a) Conformers:
These are organisms which cannot maintain a constant internal environment but change the body temperature and osmolarity of their body fluids according to the external conditions.

(b) Regulators:
These organisms which maintain a relatively constant environment called homeostasis.

(c) Partial regulators:
These are organisms which have evolved the capacity to regulate the internal environment of the body to a limited range of external factors beyond which they become conformers.

Question 8.
Explain the following
(i) Predators are conducts of energy transfer
(ii) Predators are prudent in nature

  • A predator in a food chain feeds on the prey and obtains energy
  • When the predator becomes a prey to another animal in the food chain, it transfers the energy obtained from ‘its’ prey.

(ii) If a predator is too efficient and overexploits the prey, the prey population becomes extinct. As a result predator will also become extinct due to the lack of food and hence predator are said to be prudent in nature.

KSEEB Solutions

Question 9.
The Mediterranean orched Ophrys employs a method called sexual deceit to get the flowers pollinated. Explain the phenomenon.
In the flower of Ophrys, one petal resembles the female of a bee species in size, colour markings etc.

  • The male bee perceives it as a female and pseudo copulates with it.
  • During the process the pollengrains from the anthers become dusted on the body of bees. When this bee is attracted to another flower of this orchid species, the process is repeated and the pollen grains falls on the stigma hence pollination is achieved.

Question 10.
Mention any 4 adaptations seen is Xerophytic plants to cope up with water scarcity.

  • Xerophytes (Desert plants) have thick cuticle on their leaf surface.
  • Leaves are absent or reduced to spines to prevent transpiration.
  • Presence of sunken stomata to reduce water loss.
  • The photosynthetic function is taken up by green flattened stems.
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