RBSE Class 12 Biology Important Questions Chapter 13 Organisms and Populations

Rajasthan Board RBSE Class 12 Biology Important Questions Chapter 13 Organisms and Populations Important Questions and Answers.

RBSE Class 12 Biology Chapter 13 Important Question Organisms and Populations

Multiple Choice Questions

Question 1.    
Ecological niche is :
(a) an ecological adapted zone
(b) the surface area of the ocean
(c) the physical position and functional role of a species within the community
(d) formed of all plants and animals living at the bottom of lake
Answer:
(c) the physical position and functional role of a species within the community

Question 2.
Which of the following forest plants controls the light conditions of the ground?
(a) Lianas and Climbers 
(b) Shrubs
(c) Tall trees    
(d) Herbs
Answer:
(c) Tall trees    

Question 3.    
Which of the following would necessarily decrease the density of a population in a given habitat?
(a) Natality > Mortality
(b) Immigration > emigration
(c) Mortality and emigration
(d) Natality and immigration 
Answer:
(b) Immigration > emigration

Question 4.    
Lichens are the association of:
(a) Bacteria and fungus
(b) Algae and bacterium
(c) Fungus and algae
(d) Fungus on virus
Answer:
(c) Fungus and algae

Question 5.    
Which one of the following is a xerophyte?
(a) Camparis    
(b) Lotus
(c) China rose    
(d) Casuarina
Answer:
(a) Camparis    

Question 6.    
Barnacles growing on the back of whale is an example of:
(a) mutualism    
(b) commensalism
(c) parasitism    
(d) predation
Answer:
(b) commensalism

Question 7.    
Plants grown on sandy soil, are grouped under :
(a) lithophytes    
(b) psamophytes
(c) hydrophytes    
(d) xerophytes
Answer:
(b) psamophytes

Question 8.    
The association of animals when both partners are benefited is :
(a) commensalism
(b) amensalism
(c) mutualism
(d) parasitism
Answer:
(b) amensalism

Question 9.    
Which one is the edaphic factor in biosphere?
(a) Light    
(b) Temperature
(c) Water
(d) Soil
Answer:
 (d) Soil
 
Question 10.    
Competion results in :
(a) extinction
(b) mutation
(c) larger number at niche
(d) symbiosis
Answer:
(c) larger number at niche

Question 11.    
Two species occupying same or overlapping area are called:
(a) sympatric    
(b) allopatric
(c) parapatric    
(d) ring species
Answer:
(a) sympatric

    

Question 12.    
The soil, which is transported by wind is known as:
(a) colluvial 
(b) eolin
(c) alluvial    
(d) glacial
Answer:
(b) eolin

Question 13.    
Avicenia, Rhizophora and Atriplex are :
(a) xerophytes    
(b) mesophytes
(c) halophytes    
(d) hydrophytes
Answer:
(c) halophytes    

Question 14.    
Roots of highter plants develop mycorrhiza for obtaining:
(a) nitrogen    
(b) sulphate
(c) phosphate    
(d) all of these
Answer:
(c) phosphate    

Question 15.    
An orchid resembling the female of an insect so as to be able to get pollinated is due to phenomenon of:
(a) mimicry
(b) pseudo-capulation
(c) pseudo-pollination
(d) pseudo-parthenocarpy
Answer:
(a) mimicry

Question 16.    
In commensalism :
(a) both partners are harmed
(b) weaker partner is benefitted
(c) both partners are benefitted
(d) none of the partner benefitted
Answer:
(c) both partners are benefitted

Question 17.    
Praying mantis is a good example of:
(a) camouflage    
(b) multerian mimicry
(c) warming calouration
(d) social insect
Answer:
(a) camouflage    

Question 18.    
Which plant is found in mangrove zone?
(a) Rhizophora    
(b) Pinus
(c) Acacia    
(d) Mangifera
Answer:
(a) Rhizophora    

Question 19. 
Sunken stomata are found in :
(a) xrophytes    
(b) hydrophytes
(c) mesophytes    
(d) halophytes
Answer:
(a) xrophytes    

Question 20. 
The interaction of species with the environment is called as:
(a) community
(b) environment
(c) ecosystem    
(d) autecology
Answer:
(c) ecosystem    

Very Short Answer Type Questions

Question 1. 
What is meant by habitat?
Answer: 
The place where an organism lives is called its habitat. It may also refer to the place occupied by an ontire biological community. For example, a large number of species are found in a forest habitat.

Question 2. 
Define microclimate.
Answer: 
The microclimate represents the climatic conditions that prevail at a local scale, or in areas of limited size, such as the immediate surroundings of plants and animals.

Question 3. 
What is biome? Give one example.
Answer: 
A biome is a large regional unit characterised by a major vegetation type and associated fauna found in a specific climatic zone. Example : Tropical rain forest biome. 

Question 4. 
Define ecology. Who coined the term ecology?
Answer: 
Ecology is the branch of biology that deals with the sludy of interactions between organisms and their environment.
The term ecology was coined by German biologist Ernst Haeckel in 1869.

Question 5. 
Many fish thrive in Antarctic waters where the temperature is always below zero. How do they manage to keep their body fluids from freezing?
Answer: 
Because of the presence of special proteins like glycoproteins in the body fluids that prevent freezing in these fishes and allow them to survive at subzero temperature.

Question 6. 
What does sigmoid curve of a population mean?
Answer: 
There is an initial gradual increase in population size, followed by an exponential increase and then a gradual decline to a near-constant level,

Question 7. 
Give an Example of a facultative mutualism. 
Answer: 
Sea anemone, which gets attached the shell of hermit crab.

Question 8. 
How do prickles help cactus to survive in desert? Give one example.
Answer: 
The two methods by which prickles help cactus to survive in desert are :

• By reducing and altering outer surface, they reduce evaporation and transpiration of water.
• By providing defence against grazing animals. Example: Opuntia.

Question 9. 
Why are. green plants not found beyond a certain depth in the ocean?
 Answer: 
 Beyond a certain depth, green plants are not found, because light is unavailable in that zone.

Question 10. 
Mention how do bears escape from stressful time in winter?
Answer: 
Bears escape from stressful time in winter by going into hibernation.

Question 11. 
State Gause’s competitive exclusion principle.
Answer: 
Gause’s competitive exclusion principle states that two competiting species for same resources cannot coexist, if all other ecological factors are constant.

Question 12. 
In a pond, there were 200 frogs, 40 more were born in a year. Calculate the birth rate of the population.
Answer: 
The birth rate of frog population
= \(\frac{400}{200} \) = 0.2 per iroe/year
or 200 per thousand/year.

Question l3. 
State the type of interaction that exists between ticks and dogs.
Answer: 
The type of interaction that exists between ticks and dogs is parasitism. Ticks are ectoparasite.

Question 14.
Name the type of interaction seen between fig and wasps.
Answer: 
Mutualism is the interaction that exists between fig and wasps.

Question 15. 
Name the interaction that exist between sucker fish and shark.
Answer: 
Sucker fish and shark show comme salism.

Question 16. 
Define population.    
Answer: 
Population can be defined as the total number of individuals of a species in a specific geographical area, which can interbreed under natural conditions to produce fertile offspring and function as a unit of biotic community.

Question 17. 
Why are mango trees unable to grow in temperate climate.
Answer: 
Mango trees are unable to grow in temperate climate because low temperature affects the kinetics of enzymes functioning and through this basal metabolism, activity and other physiological functions of the organism get affected.

Question 18. 
Provide an instance where the population size of species can be estimated indirectly, without actually counting them or seeing them. 
Answer: 
Tiger population in National Parks is calculated on the basis of pugmarks and faecal matter. 

Question 19. 
Mention the term used to describe, a population interaction between an orchid growing on a forest tree.
Answer: 
An orchid growing on the branch of a mango tree is an epiphyte. They are the plants, growing on other plants which however, do not derive nutrition from them and use them only for support. Hence, the relationship between a mango tree and an orchid is an example of commensalism.

Question 20. 
What do you understand by predation?
Answer: 
Predation is an interspecific interaction, where an animal called predator kills and consumes other weaker animal called prey.

Short Answer Type Questions - I

Question 1. 
Explain brood parasitism with the help of an example.
Or 
Koel is clever enough to lay eggs in a crow’s nest. Write the reason for this peculiar behaviour. Name the type of interaction.
Answer: 
The phenomenon in which one organism (parasite) lays its egg in the nest of another organism is called brood parasitism.
For example, Cuckoo (parasite) lays egg which resemble the host’s (crow) egg in size and colour in crow’s nest and let it he incubated by them till they hatch and grow.

Question 2. 
Draw the labelled diagrams of stable and declining age pyramids of human population.
Answer: 
For stable and declining age pyramids of human population diagram is :

Question 3. 
What is mutualism? Mention any two examples where .the organisms involved are commercially exploited in agriculture.
Answer: 
Mutalism is an interaction that confers beenfits to both the interacting species. Two examples where organisms involved are commercially exploited in agriculture are:

• Mycorrhizae : Represent a close mutual association, between fungi and the roots of higher plants. Fungi help the plants in absorption of  nutrients, specially phosphorus while the plants provide food for the fungus.
• Lichens : Represent an intimate mutualistic relationship between a fungus and photosynthe- sizing algae or cyanobacteria. Here, the fungus helps in absorption of nutrients and provides protection, while algae prepare the food.

Question 4. 
What is mutualism? Mention any two examples where the organisms involved are commercially exploited in agriculture?
Answer: 
Mutualism is an interaction that confers benefits to both the interacting species.
Examples:

• Mycorrhizae represent a close mutual association between fungi and the roots of higher plants. Fungi help the plants in absorption of nutrients, specially phosphorus, while the plants provide food for the fungus.
• Lichens represent an intimate mutualistic relationship between a fungus and photosynthesing algae or cyanobacteria. Here, the fungus helps in the absorption of nutrients and provide protection, while algae prepare the food.

Question 5. 
Why are certain organisms called regulators or conformers? Explain with the help of one example of each.
Answer: 
Some organisms are called conformers because they cannot maintain constant internal environment, e.g., lower organisms. On the other hand, certain organisms are called regulators as they can maintain their internal environment in response to external conditions, e.g., humAnswer:

Question 6. 
Heat loss or heat gain depends upon the surface area of the organisms body. Explain with the help of a suitable example.
Answer: 
Small animals have a large surface area relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this, smaller animals are rarely found in polar regions.

Question 7. 
Name and explain the type of interaction that exists in mycorrhiza and between cattle egret, and grazing cattle.
Answer: 
Mycorrhiza : It is an association between fungi and roots of higher plants. It is called mutualism. The fungi help plant in the absorption of essential nutrients from the soil, while in turn it provides the fungi with energy yielding carbohydrates. Both partners are benefitted.

The cattle egret and grazing cattle share commensalism type of relationship. The grazing cattle flush out insects from grass while grazing. So, it becomes easier for egret to catch and feed on them. In this, one partner gets benefit, while other remains unaffected.

Question 8. 
What is adaptation? Explain physiological adaptation taking an example of altitude illness.
Answer: 
Adaptation : It is any attribute of an organism, i,e., morphological, physiological or behavioural that enables the organism to survive and reproduce in its habitat.

At high altitude places like Rohtang Pass near Manali (> 3500 m) and Mansarovar, in China occupied Tibet, people suffer from Altitude sickness. This is because of low atmospheric pressure at high altitude, body does not get enough oxygen. Its symptoms are nausea, fatigue and heart palpitations. The relief occurs gradually due to acclimatisation. The body cope up with this low oxygen stress by increasing red blood cells production, decreasing the binding affinity of haemoglobin and increasing the breathing rate.

Question 9. 
Give four attributes of a population. Explain in detail the process of Mutualism.
Answer: 
Population Attributes : These are certain characteristics of a population. Four of them are as follows :

1. Population size or density.
2. Population interaction.
3. Due to natality or birth rate, population increases continuously. It is the production of new individual by birth, hatchingkor by asexual mode, etc. It is expressed as the number of birth per 1000 individuals.
4. Death rate or mortality, is the number of deaths in the population during a given period.

Mutualism : It is an interaction that confers benefits to both the interacting species. For example :
Mycorrhizae : Represent a close mutual association between fungi and the roots of higher plants. Fungi help the plants in absorption of nutrients, especially phosphorus' while the plants provide food for the fungus.

Question 10. 
How do plants benefit from having mycorrhizal symbiotic association?
Answer:
Benefits to plants having mycorrhizal symbiotic association are:

• The fungus absorbs nutrients from the soil and passes it into the plant.
• Plants show increased tolerance to salinity and drought.
• Mycorrhiza provides resistance to root-borne pathogens.
• Ail overall increase occurs in plant growth and development.

Question 11. 
State Gause’s ‘competitive exclusion principle’. How have the recent studies modified this principle?
Answer: 
Gause’s ‘competitive exclusion principle’ states that two closely related species competing for the same resources cannot coexist indefinitely and the competitively inferior on will be eliminated eventually (true if resources are limiting). This principle has been modified to ‘complete competitors cannot coexist’ one of the primary ways niche-sharing species can coexist is the competition-colonisation trade-off. In simple terms, species that are better competitors will be specialists, whereas species that are better colonisers are more likely to be generalists.

Question 12. 
Name and explain the interaction that is seen between clown fish and sea anemones.
Answer: 
Clown fish maintains commensalism with the sea anemone. In this interaction one species is benefitted and the other is neither harmed nor benefitted. Sea anemone has stinging tentacles that provide protection to clown fish from predators. The anemone does not appear to derive any benefit from the clown fish.

Question 13. 
Explain the two defence mechanisms eyolved in preys to avoid overpopulation of their predator. 
Answer: 
Defence mechanism evolved in preys are :

• Some species of insects and frogs are eryptically coloured (cimoufluged).
• Some plants have thorns are spines for defence mechanism, e.g., Acacia.

Question 14. 
Why are herbivores considered similar to predators in a ecological context? Explain.
Answer: 
In ecological context, herbivores are considered similar to predators because they feed on plants and their products to meet their food requirements, just like predators, e.g., they feed on prey for their food.

Short Answer Type Questions - II

Question 1. 
What is mutualism? Mention any two examples where the organisms involved are commercially exploited in agriculture.
Answer: 
Mutalism is an interaction that confers benefits to both the interacting species. Two examples where organisms involved are commercially exploited in agriculture are : 

1. Mycorrhizae : Represent a close mutpal association, between fungi and the roots of higher plants. Fungi help the plants in absorption of nutrients, specially phosphorus while the plants provide food for the fungus.
2. Lichens : Represent an intimate mutualistic relationship between a fungus and photosynthe-sizing algae or cyanobacteria. Here, the fungus helps in absorption of nutrients and provides protection, while algae prepare the food.

Question 2. 
Why do tribes who live in high altitude of Himalayas experience discomfort in respiration? How do you get adapted to survive in such a situation?    
Answer: 
The tribes who live in the high altitudes of Himalayas, experience discomfort in respiration because of the low atmospheric pressure prevailing there. Due to this, the body gets deprived of sufficient oxygen. The body copes up with the low oxygen stress by the following adaptations :

• Increasing red blood cell production.
• Decreasing the binding affinity of haemoglobin.
• Increasing the breathing rate.

Question 3. 
How do snails, seeds, bears, zooplanktons, fungi and bacteria adapt to conditions unfavourable for their survival?
Answer: 
Ways to adapt to unfavourable conditions are :

1. Snails undergo aestivation (summer sleep) to avoid summer related problems.
2. Bears undergo hibernation during winter.
3. Zooplanktons enter a stage of suspended development called diapause.
4. Bacteria and fungi slow down their metabolic rate and form a thick-walled spores to overcome stressful conditions. These spores germinate after the Onset of suitable environment.
5. Seeds undergo a state of dormancy during unfavourable conditions and germinate under favourable conditions.

Question 4. 
Describe the responses found in organisms against the environmental abiotic factors (any three).
Answer: 
These are following responses of different animals to various abiotic factors :

• Regulate
• Conform
• Migrate
• Suspend 

1. Regulate : Some organisms can maintain their internal environment in response to external conditions, e.g., humans.
2. Conform : On the other hand, some organisms can not maintain constant internal environment, so these are called conformers, e.g., lower organisms, 
3. Migrdte : The organisms can move away temporarily from the stressful habitat to a more favourable one. They return back when the unfavourable (stressful) period is over, e.g., migratory birds from Siberia move to Bharatpur (Rajasthan).

Question 5. 
Write down the adapatations found in organism to face the extreme conditions of environmental factors. (Any three)
Answer: 
Adaptations in organisms to face the extreme conditions :

• Kangaroo rat meets the water requirement through internal oxidation of fats. They concentrate their urine, so that minimum volume of water is excreted.
• Snails undergo aestivation during summers to survive in water source environment.
• In polar seas, aquatic mammals like seals have a thick layer of fat (blubber) below their skin that acts as an insulator and reduces loss of body heat.

Question 6. 
Explain coevolution with reference to parasites and their hosts. Mention any four special adaptive features evolved in parasites for their parasitic mode of life.
Or 
Explain parasitism and coevolution with the help of one example of each.
Answer: 
Coevolution is a phenomenon where many parasites have evolved to be host-specific in such a way that both the host and parasite tend to coevolve. If the host develops special mechanism to resist the parasite, the parasite also has to evolve the mechanism to counteract the host’s resistance.
Many living organisms live as a parasite on host (plant or animals). Parasite ensures free-loading and meals from the host and for this it evolves mechanisms to encounter and neutralise the resistance coming from host. This can be understood by the following examples: 

1. Parasites evolve special adaptations, like :

• loss of unnecessary sense organs.
• presence of adhesive organs like suckers.
• loss of digestive system.
• high reproductive capacity. 

2. The host in turn evolves special mechanism for rejecting or resisting the parasite. So, when the parasite is not able to complete its life cycle on single host it finds alternative host or secondary host to complete their life cycle in order to perpetuate its species and ensures its own reproduction. Two examples are :

• Liver fluke : hosts are man and snail.
• Malaria parasite : hosts are man and mosquito.

Question 7. 
What is ‘predation’? Explain with the help of suitable examples why- is it required in a community with rich biodiversity.
Or 
Predation is usually referred to as a detcimental association. State any three positive roles that a predator plays in an ecosystem.
Answer:
Predation is an interspecific interaction, where an animals, called predator, kills and consumes the other weaker animal called prey. Predation is natures way of transferring the energy fixed by plants to higher trophic level, e.g., a tiger (predator) eating a deer (prey), a sparrow (predator) eating fruit or seed (prey) etc. Requirement of Predators:    

1. Predators keep prey population under control. This is called biological control.
2. Predators also help in maintaining species diversity in community by reducing the intensity of competition among prey species.
3. Acts as ‘conduits’ for energy transfer across trophic level.
4. Predators play other important roles, i.e., in the absence of predator species, prey species could achieve very high population densities and cause ecosystem5instability, i.e., the biological control of pests affected by predation.

Question 8.    
(i) Organisms may be conformers or regulators. Explain this statement and given on example of each.
(ii) Why are there more conformer than regulators in the animal world?
Answer:
(i) Organisms may be regulators or conformers depending upon the response they show against abiotic stresses.
Regulators are organisms that have the ability to maintain a relatively constant internal environment by physiological and behavioural means. These organisms ensure a constant body temperature (thermoregulation), constant osmotic concentration (osmoregulation), etc., for example, in all birds, mammals etc., sweating occurs profusely and the evaporation brings down the temperature of the body during summers.

Conformers : Some organisms cannot maintain a constant internal environment, i.e., their, osmotic concentration and body temperature changes with the ambient surrounding. Such organisms are called as conformers. In aquatic animals such as Asterias, the osmotic concentration of body fluids changes according to the osmotic concentration of the surrounding water.

(ii) In the animal world, conformers are more than the regulators because thermoregulation is energetically expensive for many organisms. This is especially true for small animals like shreus and humming birds. Heat loss and heat gain is a function of surface area. Since, small animals have a larger surface area relative to their volume, they tend to lose body heat very fast.

Question 9. 
Differentiate between population and community.
Answer:

Population	Community
1. It represents a group of individuals of a single species found in an area.	It is a group of individuals of different species found in an area.
2. All the individuals of a population are similar in shape and size and behaviour.	Members of a community are different in shape and size and behaviour.
3. Members of a population do not prey upon each other.	Different members of a community do not have any relationship of eating and being eaten.
4. It is a smallar unit of organisation.	It is a large area of organisation.
5. Members of a population interbreed freely.	Different members of a community do not interbreed.

Question 10. 
Differentiate between the following :
(a) Ecosystem and Biome.
(b) Biome and Biosphere.
Answer:
(a) Difference between Ecosystem and Biome.

Ecosystem	Biome
1. It comprises a single self sustaining unit of ecological organisation.	It comprises a number'of
2. It may be natural or artificial and temporary or permanent.	It is
3. Comparatively smaller.	Comparatively larger.
4. Example: Pond.	Example : Tropical rain forest.

(b) Difference between Biome and Biosphere

Biome	Biosphere
1. Unit of ecological organisation.	Highest ranking
2. Delimited by climate.	Comprises the whole living zone of the earth.
3. Usually of two types : terrestrial and aquatic.	Comprises lithosphere, hydrosphere and atmosphere.

Question 11. 
Study the graph given below and answer the questions that follows: 

(i) The curve ‘b’ is described by the following equation:
\(\frac{d N}{d t}=r N\left\{\frac{K-N}{K}\right\}\)
What does 'K' stand for in this equation? Mention its significance.
(ii) Which one of the two curves is considered a more realistic one for most of the animal populations?
(iii) Which curve would depict the population of a species of deer if there are no predators in the habitat? Why is it so?
Answer:
(i) 'K stands for ‘carrying factor’. The carrying capacity signifies the limit of habitat, i.e., limited resources in a given habitat to support growth upto a certain level beyond which no further growth can take place.

(ii) The curve ‘b’ is considered a more realistic one for most of the animal populations. It is so, because in the curve ‘b’, the sources of food and space are limited and it supports the growth curve of animal populations.

(iii) The curve ‘b’ would depict the population of a species of deer, if there are no predators in the habitat. In the
absence of predators, prey population will increase. Thus, the competition will increase due to the limited food and'shelter resources within the prey population. 

Question 12. 
Study the population growth curve given below and answer the questions that follow :

(a) Identify 'A' and 'B' shown in the graph.
Answer:
(a) A-Exponential growth.
B-Logistic growth.
When there are unlimited resources available the population grows exponentially and if the resources are limited then the population growth will be in limit and this growth is called logistic growth.

Question 13. 
Study the age pyramids ‘A’, ‘B’ and ‘C' of the human population given below and answer the questions that follow:

(a) Identify pyramids ‘B’ and ‘C’.
(b) Write the basic on which the above pyramids are plotted.    
Answer:
(a) B-Stable population.
C-Declining population.
(b) Age distribution of human male and female.

Long Answer Type Questions

Question 1. 
What are biomes? Name the major biomes in India. Give a detail explanation of any one of them.
Answer:
The term environment is referred to as the immediate surrounding area of an organism. It is the sum total of all the external factors either biotic and abiotic. Different organisms are adopted to their environment differently not only for their sxyvival but also for reproduction. But have you ever wonder that how the environment differs from place to place on the planet Earth? 

Tropical lain Forests in India :
In India tropical rain forests are found in Andamans, Western Ghats and North-Eastern Himalayas. The two most common tree species in tropical rain forests are Dipterocarpus and Hopea. A number of plants like Caryota, Livistonia, Calamus rotang, Pinanga and Bamboos (Bambusa, Dendrocolamus and Melocamna) occur at places, It is the most productive biomes and the standing crop biomass is also the highest amongst all terrestrial biomes in India.

Tropical Deciduous Forests :
Location : These forests are found in the outer tropics having moderate, seasonal rainfall. These occur in southern tropics as well as Northern tropics in Brazil, West Indies, Africa, Australia and Indo-China.

Physical Conditions : These forests are of warm areas having annual seasonal rainfall 100-200 cm. Trees are of short to medium size. These depends on the availability of moisture. The shorter trees are 10-20 metres high and the medium stature trees may be 20-30 m tall. Trees form 1-2 layers. Underneath them occur shrub and herbs on the ground. Epiphytes and vines occur but more abundant during rains, plants shed their leaves during summer. So that the forests appear leafless during this period. Due to this litter is abundantly found in soil. During rains forests become lush green with dense faliage, thick herbaceaus layer over the ground and numerous climbers and twiners can be seen.

Flora : The most common trees are Sal, Teak, Tendu and Khair. Other include Sandal, Red sandal, Bauhnia, Emblica, Shisoo, Casia, Alhizzia, Toona, Plum tree, Butea etc.

Fauna : They include Tiger, Elephant, Monkey, Bear, Deer, Pig, Ant eater. Birds, Lizards, Snakes etc.

In India tropical deciduous forests are found in North and South plains as well as low hilly areas. In North-west, these forests pass into tropical thorn forests. Rainfall mostly occurs during monsoon, hence these forests in India are also called Monsoon forests.

Question 2. 
Give a detail accound about Fauna and Flora of Tundra and Taiga biomes.
Answer:
Tundra :
Location : Tundra biome places in far north between the arctic ocean and polar ice caps in the north and the coniferous forests to the south. It ranges across Asia, Europe and North America above 60°N latitude. It presents only in the arctic region, hence, called Arctic Tundra.

Physical Conditions : Tundra is characterised by severer winter with a short duration of 60 days. Mean temperature varies between -35°C to 13°C. Annual rainfall is less than 25 cm. The ground remains permanently frozen and only top soil up to a depth of only a few centimetres thaws in summer. The permanent frozen duper layer is called permafrost. 

Flora or Vegetation : Tundra is considered as the Arctic desert and remains frozen for most of the time. This lacs trees completely. Vegetations are Sedges, Lichens, Thrushes, Mosses, Flowerin herbs and grasses. Plants are generally small with stunted growth.

Fauna and Animals : They include common mammals, Reindeer, Musk Ox, Arctic Fox, Caribou, Tundra vole, Arctic Hare, Polar Bear, Lemming, Arctic Ground Squirrel, Walrus and Seel. A large number of birds visit Tundra during summer. These include, Arctic Loon, Red-throated loon, Crane, Goose, Arctic Term and Snowy Owl.

Taiga (Temperate Coniferous Forests) :
Location : These forests are situated in cold temperate regions of Asia, Europe and North America and South of Tundra. They also located in parts of New Zealand and Australia.

Physical Condition : Annual rainfall is 50 cm in di’ier regions and up to 170 cm in water parts. Lakes, Marshes and bogs are abundant, especially in the wetter areas. Soil is acidic and poorly drained. Winter temperature goes down to -20°C but the average winter temperature is about 6°C where as summer temperature reaches up to 20°C average. Summer is pleasant, but winter is chilly. Precipitation occur both as rain and snow growing season is far 100-150 days.

Flora or Vegetation : Vegetation is predominantly evergreen and coniferous. In these plants, photosynthesis continues even below -20°C. Main vegetations are Pine, Deodar, Larch, Spruce, Fir, Juniper and Yew as conifers. Birch, maple, Aspen and populus as broad leaves plants. Shrubs, herbs, ferns, mosses and lichens are abundant. Epiphytic plants are very common. Sphagnum and cotton grass occur in marshes and bogs. 

Fauna or Animals : They include, insects, amphibians (Frog, tree frog), reptiles (Lizards and Snakes), birds (Grouse, Jay), mammals (Musk Rat, Pine Mouse, Beaver, Squirrel, Porcupine, Rabbit, Hare, Fox, Lynx, Puma, Weasel, Elk, Wolf, Bear etc.). Some of them undergo hibernation during winter, some migrate to warmer places. However, Reindeer and Caribou of Tundra pass the winter in this biome.

Question 3. 
What are Savana? Describe its physical conditions, Flora and Fauna.
Answer:
Location : These are found in warm climate plains of East, Central and South Africa, North Australia, South America and India.

Physical Condition : Savannas are warm climate plains with coarse grasses, scattered shrubs and trees, seasonal rain occurs in wet and periods and frequent fire. Woody species attain a height of 1-8 m. Savannas are natural as well as anthropogenic. Indian savannas are largely anthropogenic being derived from tropical forests and maintained by grazing as well as fire. Soil moisture determines composition and productivity of savannas.

Flora : Commo trees and shrubs of Indian savannas and Zizyphus, Acacia, Prosopis, Butea and Capons, common grasses are Imperata, Schima, Dicanthelium, Saccharum and Cencrus.

Fauna : Animals include Antelope, Girraffe, Zebra, Gazella, Wild goat, Rhino, Elephant, Lion, Kangaroos (in Australia) Tiger, Wolf etc.

Question 4. 
Name major abiotic factors. Describe the effects of temperature on plants and animals.
Answer:
Effect of Temperature on Animals :
1. Morphological Changes : Temperature affects a number of morphological characters such as :

• Birds and mammals of cold regions are large sized than those of warmer regions (Bergmen’s rule).
• Tail, snout, ears and legs of mammals are relatively shorter in colder regions than in the warmer regions (Allen’s rule).
• Fishes found in water of low temperature tend to have more vertebrae than those of warmer waters (Jorden’s rule). 
• Mammals, birds and insects of tropical region are darker in colour and heavily pigmented than those of arctic region (Gloger’s rule).

2. Metabolism : Enzymes control metabolic activities, they have a specific temperature optimum. At high temperature, enzymes are degenerated and of low temperature they tend to coagulate. Therefore, temperature affects the metabolic activities of animals.

3. Reproduction : Maturation of gonads in a large number of animals is governed by temperature. In fly calliphora sericate, the number of eggs laid per female, increases with increase in temperature up to 32.5°C (after which the number decreases). An increase in temperature from 22°C to 32°C increases the egg laying about 20-30 times in grasshopper. In human being the reproductive capacity is relatively lower whose live in colder regions than that of warmer regions.

4. Growth and Development : Growth rate increases with increase in temperature up to optimum level beyond which it decline or stops because of dwindling of metabolic activities. Similarly, incubation period of eggs decreases with rising temperature.

5. Sex Ratio : In Daphnia, only females are produced parthenogepetically, at normal temperature. But at high temperature both males and females are produced equally.

6. Effect of Distribution : Temperature affects the distribution of animals. For examples :

• Ice fish lives only in cold waters. Tuna fish occurs only in tropical sea. Snow leopard found in mountain area but are not found in kerala forests.
• Corals occur in sea water where temperature is above 21S°C.
• Intertidal barnacle, does not occur in areas with 0°C temperature, whereas Balnus balenoides occurs at a temperature below 7.2°C.

Effect of Temperature on Plants :
1. Metabolism : Both photosynthesis and respiration are affected by increase or decrease of temperature beyond optimum. Both these processes are enzyme based and.enzymes become denatured above 42°C and their activities are slowed down below 20°C.

2. Growth : Both low and high temperature retarded the growth and development of plants. Low temperature may cause desiccation, Chilling injury and Freezing injury.

3. Vernalization : In many plants species seeds require low temperature exposure before germination. This is called vernalization.
 
4. Reproduction : In plants, germination of seeds and flowering are temperature retarted. For example, Apple tree require a temperature below 7°C for a peirod of 800 hrs before flowering.

5. Absorption of Water and Minerals : Active absorption of water and minerals increases with increase in the atmospheric temperature because of low temperature, the nutrients remain bound with soil particles and need more energy for absorption.

Question 5. 
What do you understand by adaptations? Write plant and animal adaptation to aquatic environment.
Answer:
Adaptations are the useful changes that occur in structure, behaviour and development of organisms that enable them to survive and reproduce. Adaptations allows organisms to live successfully in different types of habitats. They may be genotypic or phenotypic.

Plant Adaptation of Aquatic Environment :
Plants which grow in water or water rich substratum are called hydrophytes. They are of five types :
1. Free-floating : These plants are not rooted in the soil but float freely on the surface of water. Larger free-floating hydrophytes have aerenchyma which provides buoyancy. Roots are poorly developed or absent. Examples : Trapa, Lemna, Walfia, Pistia etc.    

2. Floating Leaves, Rooted Hydrophytes : They are anchored at the bottom by roots and their leaves float on the water. To prevent wetting, the upper surface of leaves possess waxy coating, cuticle and stomata. Examples : Nymphaea, Eichornia, Nelumbo, Marsilea etc. 

3. Submerged Floating Hydrophytes : These plants occur jnside water and are free floating. They are rootless and not anchored to the muddy bottom. Examples : Utricularia, Caratophillum etc.

4. Submerged Rooted Hydrophytes : These plants are rooted in mud and remains completely submerged in water. Their leaves are ribbon shaped or greatly dissected to withstand water current. They have a soft and spongy stem with long internodes. Examples :    Potamogeton,
Valliomaria etc.

5. Rooted Emergent Hydrophytes : These plants grow in shallow water. They are anchored to the soil by roots and shoots emerge wholly or partially above the surface of water. Hence, they are called amphibious plants. Examples : Typha, Sagittaria, Rannuncuius, Lymnophilla heterophylla etc.

Characteristics of Hydrophytes

1. In these plants submerged parts are covered with mucilage for protection.
2. Roots are poorly developed, may be absent, or serve for balancing. Root hairs are absent. Instead of root caps, root pockets occur (pistia).
3. Stems are generally weak, slender and with long internodes.
4. Leaves are different types submerged leaves are thin, small, linear or finely dissected. Floating leaves are large with stomata and waxy coating on the upper surface. Both submerged and floating plants -show heterophylly.
5. Special air staring organs occur in floating plants.
6. Mechanical tissues are not present. Xylem is poorly developed or absent.

Strategies of Adaptation in Animals :
Adaptations of Animals to Water Scarcity 
Animals which inhabit in arid and dry conditions develop adaptations to manage water scarcity and reduce water loss to a minimum. For example :
1. Camel has a number of adaptations to adjust itself to arid conditions of deserts :

• When water is available, camel can drink up to 80 litres of water.
• It can remain without water for several days and can loose up to 25% body weight by losing water from its tissues (mainly adipose tissue present in its hump). 
• Camel does not sweat up to a body temperature of 50°C.
• Its urine is concentrated and faces are almost dry.
• Its eyes are covered by heavy eyelashes.
• It has fleshy pad in its legs for easily walking on hot sand.
• No stril size is reduced, nasal counter current system reduces loss of moisture during exhalation.

2. Spiny Lizard (Moloch horridus) of Australia has hygroscopic glands in its skin which absorb water from the environment.

3. Kangaroo rat (Dipodomys) found in North American deserts soldom drinks water. It feeds on dry seeds and vegetation. It meets 90% water requirement from metabolic water and 10% from food. It prevetns water loss by living in burrows during the dry.

Question 6. 
(i) List the different attributes that a population has and not an individual organism.
(ii) What is population density? Explain any three different ways the population density can be measured, with the help of an example each.
Answer:
(i) A given population has some unique attributes while an individual organism of this population does not show these attributes like :

(ii) Population Size or Density : It reflects the number of individuals of a species per unit area or volume at any given point of time. Generally it is the most appropriate measure but in some case it is either meaningless or difficult to determine. For example, in a given area there are 200 carrot grass (parthenium hysterophorus) plants but there is only a single banyan tree having a large canopy, here the population density of Banyan tree is very low as compare to that of carrot grass underestimating the role of banyan tree in this given community. So, here it is better to having an alternative way like percent cover or biomass consideration than that of population size.

Population Density = 

Birth Rate or Natality : It is defined as the number of births per 1000 individuals of a population per year.
For example : There are 20 lotus plants last year and through reproduction 8 new plants are added, so the birth rate is = \(\frac{8}{20}\) = 400 births on offspring per 1,000 lotus plant per year.

Death Rate : It is defined as the number of deaths per 1000 individuals of a population per year.
For example: In a given population of 40 fruitflies 4 individuals have died during a specific time interval. (May be a week, month etc.)
Death Rate =\( \frac{4}{40}\) x 1000 = 100 individual per thousand fruitfly per week

Sex Ratio: It is defined as the number of females and males per 1000 individuals of a population in a given time. An individual is either male or a female but in general population has a sex reatio. e.g., 60% of the population are females and 40% individuals are male.

Age Pyramid : A population at any given time is composed of individual of different ages. If the percent individuals of a given age or age group is plotted for the population, the resulting structure is called age pyramid. The different age groups are pre-reproductive and post reproductive.

The shape of any given pyramid reflects the growth pattern of the population showing whether it is expanding (Triangular shaped), stable (bell-shaped) or declining (Urn-shaped).