Samacheer Kalvi 12th Bio Zoology Guide Chapter 10 Organisms and Population

Tamilnadu State Board New Syllabus Samacheer Kalvi 12th Bio Zoology Guide Pdf Chapter 10 Organisms and Population Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 12th Bio Zoology Solutions Chapter 10 Organisms and Population

12th Bio Zoology Guide Organisms and Population Text Book Back Questions and Answers

Question 1.
All populations in a given physical area are defined as
(a) Biome
(b) Ecosystem
(c) Territory
(d) Biotic factors
Answer:
(a) Biome

Question 2.
Organisms which can survive a wide range of temperature are called
(a) Ectotherms
(b) Eurytherms
(c) Endotherms
(d) Stenotherms
Answer:
(b) Eurytherms

Question 3.
The interaction in nature, where one gets benefit on the expense of other is …………………
(a) Predation
(b) Mutualism
(c) Amensalism
(d) Commensalism
Answer:
(d) Commensalism

Question 4.
Predation and parasitism are which type of interactions?
(a) (+,+)
(b) (+, O)
(c) (-, -)
(d) (+, -)
Answer:
(d) (+, -)

Question 5.
Competition between species leads to
(a) Extinction
(b) Mutation
(c) Amensalism
(d) Symbiosis
Answer:
(a) Extinction

Question 6.
Which of the following is an r-species?
(a) Human
(b) Insects
(c) Rhinoceros
(d) Whale
Answer:
(b) Insects

Question 7.
Match the following and choose the correct combination from the options given below.

Column I	Column II
A. Mutalism	1. Lion and deer
B. Commensalism	2. Round worm and man
C. Parasitism	3. Birds compete with squirrels for nuts
D. Competition	4. Sea anemone on hermit crab
E. Predation.	5. Bernacles attached to Whales

Dispersal
(a) A – 4, B – 5, C – 2, D – 3, E – 1
(b) A – 3, B – 1, C – 4, D – 2, E – 5
(c) A – 2, B -3, C – l,D – 5, E – 4
(d) A – 5, B – 4, C – 2, D – 3, E – 1
Answer:
(a) A- 4, B – 5, C – 2, D -3, E – 1

Question 8.
The figure given below is a diagrammatic representation of response of organisms to abiotic factors. What do A, B and C represent respectively.

A	B	C
a. Conformer	Regulator	Partial Regulator
b. Regulator	Partial Regulator	Conformer
c. Partial Regulator	Regulator	Conformer
d. Regulator	Conforme	Partial Regulator

Answer:
(a) Conformer, Regulator, Partial Regulator

Question 9.
The relationship between sucker fish and shark is ………………..
(a) Competition
(b) Commensalism
(c) Predation
(d) Parasitism
Answer:
(b) Commensalism

Question 10.
What type of human population is represented by the following age pyramid?
(a) Vanishing (a) Vanishing population
(b) Stable population
(c) Declining population
(d) Expanding population
Answer:
(b) Stable population

Question 11.
Which of the following is correct for r-selected species?
(a) large number of progeny with small size
(b) large number of progeny with large size
(c) small number of progeny with small size
(d) small number of progeny with large size
Answer:
(a) large number of progeny with small size

Question 12.
Animals that can move from fresh water to sea called as ………………..
(a) Stenothermal
(b) Eurythermal
(c) Catadromous
(d) Anadromous
Answer:
(c) Catadromous

Question 13.
Some organisms are able to maintain homeostasis by physical means …………………
(a) Conform
(b) Regulate
(c) Migrate
(d) Suspend
Answer:
(b) Regulate

Question 14.
What is a Habitat?
Answer:
A habitat can be considered as the ‘address’ of the organism. Organisms in a habitat interact with each other and can be part of trophic levels to form food chains and food webs.

Question 15.
Define ecological niche.
Answer:
Niche of an organism can be defined as the total position and function of an individual in its environment.

Question 16.
What is Acclimatisation?
Answer:
Animals are known to modify their response to environmental changes (stress) in reasonably short time spans. This is known as Acclimatization. This is observed when people who have moved from the plains to higher altitudes show enhanced RBC count within a few days of settling in their new habitat. This helps them cope with lower atmospheric oxygen and higher oxygen demand.

Question 17.
What is Pedogenesis?
Answer:
Pedogenesis is the process of formation of soil (embryonic soil) from the rock materials by weathering.

Question 18.
What is Zero Stress?
Answer:
Stress refers to any environmental factor causing a change in the biological system which is potentially injurious.

Question 19.
What is soil permeability?
Answer:
The characteristic of soil that determines the movement of water through pore spaces is known as soil permeability. Soil permeability is directly dependent on the pore size. Water holding capacity of the soil is inversely dependent on soil porosity.

Question 20.
Differentiate between Eurytherms and Stenotherms.
Answer:

Eurytherms	Stenotherms table
Organism that can tolerate wide range of temperature. E.g.: Human beings	Organism that can tolerate narrow range of temperature. E.g.: Fish

Question 21.
Explain hibernation and aestivation with examples.
Answer:
In certain conditions, if the organisms is unable to migrate, it may avoid the stress by becoming inactive. This is seen commonly in bears going into hibernation during winter. Some snails and fish go into aestivation to avoid summer related problems like heat and desiccation.

Question 22.
Give the diagnostic characters features of a Biome.
Answer:

• Location, Geographical position (Latitude and Longitude)
• Climate and physiochemical environment
• Predominant plant and animal life
• Boundaries between biomes are not always sharply defined. Transition or transient zones are seen.

Question 23.
Classify the aquatic biomes of Earth.
Answer:

• Freshwater (Lakes, ponds and rivers)
• Brackish water (Estuaries / Wetlands)
• Marine (Coral reefs, pelagic zones and abyssal zones)

Question 24.
What are the ways by which organisms respond to abiotic factors?
Answer:
The ways by which organism respond to abiotic stress are Regulate, Conform, Migrate and Suspends, etc.

Question 25.
Classify the adaptive traits found in organisms.
Answer:
The adaptive traits may be structural adaptation, behavioural adaptation and physiological adaptation.

Question 26.
Differentiate Natality and Mortality?
Answer:

Natality	Mortality
1. Natality refer to the birth rate.	Mortality refers to the death rate.
2. Birth rate is calculated as: Number of births per unit time average population	Death rate is calculated as: Number of deaths per unit time average population

Question 27.
Differentiate J and S shaped curve.
Answer:

J-shaped growth	S-shaped growth table
1. Population increase rapidly and exponentally and stops suddenly due to environmental stress.	Population increases slowly at first then more rapidly and then slows down due to this environmental stress.
2. Population declines due tmaso s mortality. E.g: Insects	Population is maintained. E.g: Small mammals

Question 28.
Give an account of population regulation.
Answer:
The inherent tendency of all animal populations is to increase in number. But it does not increase indefinitely. Once the carrying capacity of the environment is reached, population numbers remain static or fluctuate depending on environmental conditions. This is regulated by many factors which are

• Density independent – Extrinsic factors
• Density dependent – Intrinsic factors
  Extrinsic factors include availability of space, shelter, weather and food, etc. Intrinsic factors include competition, predation, emigration, immigration and diseases.

Question 29.
What is ecological density, crude density and population density?
Answer:

Indices of Density	Keys
1. Population density	It is usually expressed as the number of individuals per unit area or volume. E.g. 100 trees per acre.
2. Crude density	It is the size of a population in relation to the numbers per unit of total space. E.g. 1000 fish in a pond.
3. Ecological density	It is the size of a population in relation to the numbers per unit of habitat space. (Available area or volume that can be colonized by a population). E.g. 1000 fish in the volume of water in the pond.

Question 30.
Give an account of the properties of soil.
Answer:

• Texture of soil – The texture of soil is determined by the size of the soil particles. The types of soil include sand, silt and clay on the basis of their size differences.
• Porosity – The space present between soil particles in a given volume of soil are called pore spaces. The percentage of soil volume occupied by pore space or by the interstitial spaces is cal Ted porosity of the soil.
• Permeability of soil – The characteristic of soil that determines the movement of water through pore spaces is known as soil permeability. Soil permeability is directly dependent on the pore size. Water holding capacity of the soil is inversely dependent on soil porosity.
• Soil Temperature – Soil gets its heat energy from solar radiation, decomposing organic matter, and heat from the interior of Earth. Soil temperature effects the germination of seeds, growth of roots and biological activity of soil-inhabiting micro-and macroorganisms.
• Soil water – In soil, water is not only important as a solvent and transporting agent, but also maintains soil texture, arrangement and compactness of soil particles, making soil habitable for plants and animals.

Question 31.
Differentiate between Tundra and Taiga Biomes.
Answer:

Tundra Biome	Taiga Biome
1. Tundras are Treeless plains with grasses.	Taiga biome is composed of conifers with needle shaped leaves and scaly leaves.
2. Precipitation is less than 250 mm per year.	Precipitation is about 380-1000 mm per year

Question 32.
List the adaptations seen in terrestrial animals.
Answer:

• Earthworms, land Planarians secrete a mucus coating to maintain a moist situation for burrowing, coiling and respiration, etc.
• Arthropods have an external covering over the respiratory surfaces and well – developed tracheal systems.
• In vertebrate skin, there are many cellular layers besides the well-protected respiratory surfaces that help in preventing loss of water.
• Some animals obtain their water requirement from food as partial replacement of water lost through excretion.
• Birds make nests and breed before the rainy season as there is availability of abundant food. But during drought birds rarely reproduce.
• Camels are able to regulate water effectively for evaporative cooling through the-skin and respiratory system and excrete highly concentrated urine, and can also withstand
  dehydration up to 25% of their body weight.

Question 33.
Describe Population Age Distribution.
Answer:
The proportion of the age groups (pre-reproductive, reproductive and post reproductive) in a population is its age distribution attribute. This determines the reproductive status of the population at the given time and is an indicator of the future population size. Usually a rapidly growing population will have larger proportion of young individuals. A stable population will have an even distribution of various age classes. A declining population tends to have a larger proportion of older individuals.

Question 34.
Describe Growth Models/Curves.
Answer:

Populations show characteristic growth patterns or forms. These patterns can be plotted and termed as J-shaped growth form and S-shaped growth form (Sigmoid form). Their growth is represented by S shaped growth curve.
J shaped growth form: When a population increases rapidly in an exponential fashion and then stops abruptly due to environmental resistance or due to sudden appearance of a limiting factor, they are said to exhibit J-shaped growth form. Many insects show explosive increase in number during the rainy season followed by their disappearance at the end of the season. S-Shaped growth form (sigmoid growth) Some populations, as in a population of small mammals, increase slowly at first then more rapidly and gradually slow down as environmental resistance increases whereby equilibrium is reached and maintained. Their growth is represented by S shaped growth curve.

12th Bio Zoology Guide Organisms and Population Additional Important Questions and Answers

12th Bio Zoology Guide Organisms and Population One Mark Questions and Answers

Question 1.
The study dealing with animal behaviour is called as
(a) Euthenics
(b) Ethology
(c) Ecology
(d) Pedogenesis
Answer:
(b) Ethology

Question 2 .
Identify the proper sequence in increasing order of population
(a) Species → Population → Community → biome
(b) Population → Community → Species → biome
(c) Biome → Species → Community → Population ‘
(d) Community → Population → Biome → Species
Answer:
(a) Species → Population → Community → biome

Question 3.
Functional status of an organism in its community is ………………….
(a) Biome
(b) Niche
(c) Species
(d) Population
Answer:
(A) Niche

Question 4.
Pick out the eurythermal organism
(a) Fish
(b) Frog
(c) Tiger
(d) Lizards
Answer:
(c) Tiger

Question 5.
Locomotary speed of an organism changes due to light. This phenomenon is referred as ……………….
(a) Photonasty
(b) Photokinesis
(c) Phototropism
(d) Phototaxis
Answer:
(b) Photokinesis

Question 6.
Identify the incorrect statement
(a) Water is a universal solvent
(b) Water has less surface tension
(c) Water is heavier than air
(d) When freezes water contracts
Answer:
(b) Water has less surface tension

Question 7.
The soil zone is known as …………………..
(a) Pedosphere
(b) Atmosphere
(c) Hydrosphere
(d) Stratosphere
Answer:
(a) Pedosphere

Question 8.
Assertion (A): Snake is a stenotherm.
Reason (R): Organism can tolerate narrow temperature fluctuations.
(a) Both A and R are correct R explain A
(b) A is correct R is incorrect
(c) R does not explain A
(d) Both A and R are incorrect
Answer:
(a) Both A and R are correct R explain A

Question 9.
Assertion (A): Diapause is carried out to overcome abiotic stress.
Reason (R): Animals become inactive during winter.
(a) Both A and R are correct R explain A
(b) A is correct R is incorrect
(c) R does not explain A
(d) Both A and R are incorrect
Answer:
(b) A is correct R is incorrect

Question 10.
Assertion (A): Movement of organism from one place to another and back is called migration.
Reason (R): Eel is an example for aradromous migration.
(a) Both A and R are correct R explain A ‘
(b) A is correct R is incorrect
(c) R does not explain A
(d) Both A and R are incorrect
Answer:
(a) Both A and R are correct R explain A

Question 11.
Which is not a feature of Tundra?
(a) Large population oscillation
(b) Short season of growth and reproduction
(c) Low biotic diversity
(d) Extremely hot climate
Answer:
(d) Extremely hot climate

Question 12.
Pick out the correct statement regarding K-selected species
(a) Produce many offsprings
(b) Only few reach adulthood
(c) Unstable environment
(d) Long life expectancy
Answer:
(d) Long life expectancy

Question 13.
Maximum reproductive capacity of an organism under favourable condition is referred as ………………..
(a) Carrying capacity
(b) Biotic potential
(c) Natality
(d) Fecundity
Answer:
(b) Biotic potential

Question 14.
During breeding season, Salmon migrates from sea to fresh water. This is an example for……………
Answer:
Anadromous migration.

Question 15.
Exponential growth shows ……………. growth patterns.
Answer:
J-shaped

Question 16.
Interaction between Ascaris in human gut is an example for……………..
Answer:
Parasitisim

Question 17.
If both the species of an interaction is benefitted then it is said to be………………….
Answer:
Mutualism

Question 18.
Match the following

Column I	Column II
a) Stenotherm	Human
b) Eurytherm	Lizards
c) Phototaxis	Salmon
d) Anadromous migration	Earthworm

(a) a – ii, b – i, c – iv, d – iii
(b) a – iii, b – ii, c – i, d – iv
(c) a – iv, b – iii, c – ii, d – i
(d) a – i, b -iv, c – iii, d – ii
Answer:
(a) a – ii, b – i, c – iv, d – iii

Question 19.
As altitude increases ……………….
(a) O₂ density increases
(b) Precipitation decreases
(c) Temperature increases
(d) Snowing decreases
Answer:
(b) Precipitation decreases

12th Bio Zoology Guide Organisms and Population Two Marks Questions and Answers

Question 1.
What is ecosphere?
Answer:
The largest and most nearly self-sufficient biological system is often designated as the Ecosphere, which includes all the living organisms of the Earth, interacting with the physical ~ environment to regulate their distribution, abundance, production and evolution.

Question 2.
List out the adaptation of fish to survive in aquatic environment.
Answer:
Fishes possess fins for locomotion, streamlined body (aerodynamic) sensory lateral line system, gills for respiratory purpose and air sacs for floatation.

Question 3.
Define niche.
Answer:
Niche of an organism can be defined as the total position and function of an individual in its environment.

Question 4.
Name few abiotic factors that influence organisms in an environment.
Answer:
Temperature, light, water, soil, humidity and altitude, etc.

Question 5.
State Allen’s rule and Bergmann’s rule.
Answer:
Allen’s rule: Warm blooded animals living in cold climates have shorter limbs, ears and other appendages than the same species in warm climates.
Bergmann’s rule: Birds and mammals have larger body size in cold regions than warmer regions.

Question 6.
What does Jordon’s rule state?
Answer:
In some aquatic environments, an inverse relationship between water temperature and fish meristic characters is observed – lower the temperature, more the vertebrae.

Question 7.
State Van’t Hoff’s rule.
Answer:
Van’t Hoff’s rule states that with the increase of every 10°C, the rate of metabolic activity is doubled or the reaction rate is halved with the decrease of 10°C.

Question 8.
What is Q₁₀ value? How it is calculated?
Answer:
The effect of temperature on the rate of reaction is expressed in terms of temperature coefficient or Q₁₀ value. The Q₁₀ values are estimated taking the ratio between the rate of reaction at X°C and rate of reaction at (X-10°C).

Question 9.
Differentiate between Eurytherms and Stenotherm
Answer:

Eurytherm	Stenotherm
Organism that can tolerate narrow range of temperature. E.g: Fishe	Organism that can tolerate wide range of temperature. E.g: Human beings

Question 10.
Snakes are stenotherms. Why?
Answer:
Snakes are stenotherms since they can tolerae only a narrow range of temperature fluctuation.

Question 11.
Define phototaxis.
Answer:
The movement of organism in response to light, either towards the source of light as in Moths (positive phototaxis) or away from light (Earthworm (negative phototaxis).

Question 12.
What is photokinesis?
Answer:
A change in the speed of locomotion (or frequency of turning) in a motile organism or cell which is made in response to a change in light intensity is called photokinesis. It involves undirected random movement in response to light.

Question 13.
What is pedosphere and soil profile?
Answer:
Pedosphere: The outer soil zone of the Earth.
Soil profile: Soil is formed by many horizontal layers called soil profile.

Question 14.
Point out the major functions of soil.
Soil has four major functions

• medium for plant grbwth .
• means for water storage and purification
• modifier of Earth’s atmosphere
• habitat for many organisms, which in turn modify the soil

Question 15.
Define humidity and mention its types.
Answer:
Moisture in the form of invisible vapor in the atmosphere is called humidity, which is generally expressed in terms of absolute humidity, relative humidity or specific humidity.

Question 16.
What is a Biome?
Answer:
Biomes are large regions of Earth that have similar or common vegetation and climatic conditions. They play a crucial role in sustaining life on Earth. They are defined by their soil,climate, flora and fauna. Biomes have distinct biological communities that have been formed in response to a shared physio-chemical climate.

Question 17.
Enumerate the characters of a Biome.

• Location, Geographical position (Latitude and Longitude)
• Climate and physiochemical environment
• Predominant plant and animal life ‘
• Boundaries between biomes are not always sharply defined. Transition or transient zones are seen.

Question 18.
Which is the largest biome on Earth? Classify it.
Answer:
Aquatic biome is the largest biome occupying 71% of biosphere.
The aquatic biomes on Earth are:
a) Fresh water biome (Lakes and Ponds)
b) Brackish water biome (Estuaries / Wetlands)
c) Marine biome (Coral reefs and abyssal zones)

Question 19.
Define alpine zone.
The alpine zone between timber line and snow zone includes in the descending order, a sub¬snow zone immediately below the snow zone, a meadow zone in the centre and a shrub zone which gradually merges into the timber zone.

Question 20.
What is a forest? Name the major forest biomes.
Answer:
Forest is a broad term used to describe areas where there are a large number of trees. The major forest biomes are the Tropical forests and the Temperate forest.

Question 21.
What are the types of tropical forest?
Answer:
(a) Evergreen rain forest
(b) Seasonal rain forest
(c) Semi evergreen forest
(d) Dry deciduous forest

Question 22.
How the cold deserts are characterized? Give an example.
Answer:
Cold deserts are characterized by cold winters with snowfall and high overall rainfall throughout the winter and occasionally over the summer.
E.g.: Ladakh region in India.

Question 23.
Fishes are said to be conformers Justify.
Answer:
In fishes, the osmotic concentration of the body fluids changes with that of surrounding water osmotic concentration. Hence they are called conformers.

Question 24.
When and why do snails go into aestivation?
Answer:
Snails undergo aestivation during summer to avoid heat and overcome dessication.

Question 25.
How do animals like fishes and bears avoid unfavourable climatic conditions?
Answer:
Fishes undergo aestivation to avoid summer related problems.
Bears undergo hibernation to avoid winter related problems.

Question 26.
What are cryptic animals? How cryptic adaptation helps them?
Answer:
Cryptic animals are those which camouflage perfectly with their environment and are almost impossible to detect. Certain reptiles and insects such as chameleons and stick insects show this type of adaptation, which helps in prey capture or to evade from predators.

Question 27.
Explain any two behavioural adaptations?
Answer:
The two most characteristic forms of behavioral adaptations are migration and courtship. Migration allows the animals to find better resources or evade threat. Courtship is a set of bhavioral patterns to find a mate to reproduce.

Question 28.
Define population.
Answer:
Population is defined as any group of organisms of the same species which can interbreed among themselves, and occupy a particular space and function as part of a biotic community.

Question 29.
What are the attributes of population?
Population density, Natality, Mortality, Age distribution, dispersion . (immigration and emigration)

Question 30.
Camels are well adapted to xeric conditions, how?
Answer:
Camels are able to regulate water effectively for evaporative cooling through the skin and respiratory system and excrete highly concentrated urine, and can also withstand dehydration up to 25% of their body weight.

Question 31.
How natality and mortality can be calculated?
Answer:

Question 32.
Define biotic potential.
Answer:
It is the maximum reproductive capacity of an organism under optimum environmental conditions.

Question 33.
Which type of species interaction is noticed between a) Cat and Rat (b) Crocodile and birds
Answer:
(a) Amensalism
(b) Mutualism

Question 34.
Define Commensalism.
Answer:
Commensalism is species interaction in which one species (the commensal) is benefitted whereas the host is neither benefitted nor affected.
Eg: Sucker fish on Shark.

12th Bio Zoology Guide Organisms and Population Three Marks Questions and Answers

Question 35.
Define the terms (a) guilds (b) ecological equivalents
Answer:
Groups of species with comparable role and niche dimensions within a community are termed ‘guilds’. Species that occupy the same niche in different geographical regions, are termed ‘ecological equivalents’.

Question 36.
Define temperature. How it impacts the life of an organism?
Answer:
Temperature or degree of hotness and coldness is an essential and variable factor in any environment. It influences all forms of life by affecting many vital activities of organisms like metabolism, behaviour, reproduction, development and even death in the Biosphere.

Question 37.
Light is essential for life. Why?
Answer:
Light influences growth, pigmentation, migration and reproduction. The intensity and frequency of light influences metabolic activity, induce gene mutations (UV, X-rays). Light is essential for vision. This is proved by the poorly developed or absence of eyes in cave dwelling organisms. Diapause is also influenced by light in animals. Gonads of birds become more active with increasing light in summer. Light influences the locomotion and movement of lower animals.

Question 38.
What is Acclimatization? Explain with example.
Answer:
Animals are known to modify their response to environmental changes (stress) in reasonably short time spans. This is known as Acclimatization. This is observed when people who have moved from the plains to higher altitudes show enhanced RBC count within a few days of settling in their new habitat. This helps them cope with lower atmospheric oxygen and higher oxygen demand.

Question 39.
Enlist the characteristics of Tundra.
Answer:

• Extremely cold climate
• Low biotic diversity
• Simple vegetation structure
• Limitation of drainage
• Short season of growth and reproduction
• Energy and nutrients in the form of dead organic material
• Large population oscillations

Question 40.
Name the major biomes of the Earth.
Answer:
Tundra biome, Taiga biome, Grassland biome, Alpine biome, Forest biome and Desert biome.

Question 41.
Why do organisms migrate? Give example.
Answer:
Organisms tend to move away temporarily from a stressful habitat to a new, hospitable area and return when the stressful period is over. Birds migrate from Siberia to Vedanthangal in Tamilnadu to escape from the severe winter periods.

Question 42.
Define (a) Diapause (b) Ethology
Answer:
Diapause: Some lower animals suspend a certain phase of their life cycle, which is referred to as diapause.
Ethology: The study of animal behaviour, under natural conditions.

Question 43.
Comment on the J-shaped growth form.
Answer:
When a population increases rapidly in an exponential fashion and then stops abruptly due to environmental resistance or due to sudden appearance of a limiting factor, they are said to exhibit J-shaped growth form. Many insects show explosive increase in number during the rainy season followed by their disappearance at the end of the season.

Question 44.
Explain sigmoid growth.
Answer:
Some populations, as in a population of small mammals, increase slowly at first then more rapidly and gradually slow down as environmental resistance increases whereby equilibrium is reached and maintained. Their growth is represented by S shaped growth curve.

12th Bio Zoology Guide Organisms and Population Five Marks Questions and Answers

Question 45.
Enumerate the properties of water.
Answer:

• Water is one of the main agents in Pedogenesis (soil formation).
• It is the medium for several different ecosystems.
• It is present as moisture in the atmosphere and the outer layers of the lithosphere and is uneven in distribution on the Earth.
• Water is heavier than air and imparts greater buoyancy to the aquatic medium. This enables organism to float at variable levels.
• Water has high heat capacity and latent heat, due to which it can withhold large amounts of heat. Thus, oceans and lakes tend to maintain a relatively constant temperature, and the biosphere is relatively thermostable.
• Water is physically unique because it is less dense as a solid (ice) than as a liquid.
• When water freezes (0°C), it contracts. The maximum density of liquid water occurs at 4°C. Below that, it expands markedly. This enables ice to float on the top of water bodies. Hence, only the surface of water bodies will freeze, while below the surface, water will be in liquid form, sustaining life.

Question 46.
Give an account of grass land biome.
Answer:

• Grasslands occur in temperate and in the tropical regions.
• They have hot summers, cold winters, and irregular rainfall.
• Often they are characterized by high winds.
• The low irregular rainfall is the factor which makes the difference between a temperate deciduous forest and a temperate grassland.
• Herbivores like antelope, bison, wild horse, jack rabbit, ground squirrel and prairie dogs are abundant.
• Predators include coyotes, foxes, hawks and snakes.
• In India, fauna of grasslands includes Elephant, Gaur, Rhino and Antelope.
• Flora of grasslands include purple needle grass, wild oats, foxtail, ryegrass and buffalo grass.

Question 47.
Write in detail about Temperate forest and its types.
Answer:

1. These forests occur in eastern North America, northeastern Asia and western and central Europe.
2. Have well-defined seasons with a distinct winter. Moderate climate and a growing season of 140-200 days during 4-6 frost-free months distinguish temperate forests.
3. Annual temperature varies from -30° C to 30° C.
4. Precipitation (750-1500 mm) is distributed evenly throughout the year.
5. Soil is fertile, enriched with decaying litter.
6. Canopy is moderately dense and allows light to penetrate, resulting in well-developed and richly diversified understorey vegetation and stratification of animals.
7. Flora is characterized by 3-4 tree species per km2. Trees have broad leaves that are lost annually such as oak, hickory, beech, hemlock, maple, basswood, cottonwood, elm, willow, and spring-flowering herbs.
8. Fauna consists of squirrels, rabbits, skunks, birds, deer, mountain lion, bobcat, timber wolf, ~ fox, and black bear. Based on seasonal distribution of rainfall, the types of temperate forests are:

• Moist conifer and evergreen broad-leaved forests: wet winters and dry summers.
• Dry conifer forests: dominate higher elevation zones; low precipitation.
• Mediterranean forests: precipitation is concentrated in winter (<1000 mm /year).
• Temperate coniferous forests: mild winters, high annual precipitation (> 2000 mm /year).
• Temperate broad-leaved rainforests: mild, frost-free winters, high precipitation (> 1500 mm/year), evenly distributed throughout the year.

Question 48.
Point out the adaptive traits of aquatic animals.
Answer:

• The pectoral fins and dorsal fins act as stabilizers or balancers and the caudal fin helps in changing the direction as a rudder.
• Arrangement of body muscles in the form of bundles (myotomes) help in locomotion.
• Stream lined structure helps in the swift movement of the animals in water.
• Respiration by gills making use of gases dissolved in water.
• Presence of air-bladders filled with air for buoyancy.
• Presence of lateral-line system. They function as rheoreceptors which is helpful in echolocating objects in water.
• Integuments rich in mucous glands are protected by scales.
• Maintain water and ionic balance in its body with excretory structures.

Question 49.
Differentiate between r-selected species and k-selected species.
Answer:

r-selected species	k-seleced species
Smaller sized organisms	Larger sized organisms
Produce many offspring	Produce few offspring
Mature early	Late maturity with extended parental care
Short life expectancy	Long life expectancy
Each individual reproduces only once or few times in their life time	Can reproduce more than once in lifetime
Only few reach adulthood	Most individuals reach maximum life span
Unstable environment, density independent	Stable environment, density dependent

Question 50
Describe in detail on population interaction.
Answer:
Organisms belonging to different populations interact for food, shelter, mating or for other