Organisms and Population Question Answers: NCERT Class 12 Biology

Diapause is a stage of suspended development to cope with unfavourable conditions. Many species of Zooplankton and insects exhibit diapause to tide over adverse climatic conditions during their development.

Hibernation or winter sleep is a resting stage where in animals escape winters (cold) by hiding themselves in their shelters. They escape the winter season by entering a state of inactivity by slowing their metabolism. The phenomenon of hibernation is exhibited by bats, squirrels, and other rodents.

(a) Hibernation and Aestivation

(b) Ectotherms and Endotherms

(a) Adaptations of desert plants and animals:

(i) Adaptations of desert plants:

Plants found in deserts are well adapted to cope with harsh desert conditions such as water scarcity and scorching heat. Plants have an extensive root system to tap underground water. They bear thick cuticles and sunken stomata on the surface of their leaves to reduce transpiration. In Opuntia, the leaves are entirely modified into spines and photosynthesis is carried out by green stems. Desert plants have special pathways to synthesize food, called CAM (C₄ pathway). It enables the stomata to remain closed during the day to reduce the loss of water through transpiration.

(ii) Adaptations of desert animals:

Animals found in deserts such as desert kangaroo rats, lizards, snakes, etc. are well adapted to their habitat. The kangaroo rat found in the deserts of Arizona never drinks water in its life. It has the ability to concentrate its urine to conserve water. Desert lizards and snakes bask in the sun during early morning and burrow themselves in the sand during afternoons to escape the heat of the day. These adaptations occur in desert animals to prevent the loss of water.

(b) Adaptations of plants to water scarcity

Plants found in deserts are well adapted to cope with water scarcity and scorching heat of the desert. Plants have an extensive root system to tap underground water. They bear thick cuticles and sunken stomata on the surface of their leaves to reduce transpiration. In Opuntia, the leaves are modified into spines and the process of photosynthesis is carried out by green stems. Desert plants have special pathways to synthesize food, called CAM (C₄ pathway). It enables their stomata to remain closed during the day to reduce water loss by transpiration.

(c) Behavioural adaptations in animals

Certain organisms are affected by temperature variations. These organisms undergo adaptations such as hibernation, aestivation, migration, etc. to escape environmental stress to suit their natural habitat. These adaptations in the behaviour of an organism are called behavioural adaptations. For example, ectothermal animals and certain endotherms exhibit behavioral adaptations. Ectotherms are cold blooded animals such as fish, amphibians, reptiles, etc. Their temperature varies with their surroundings. For example, the desert lizard basks in the sun during early hours when the temperature is quite low. However, as the temperature begins to rise, the lizard burrows itself inside the sand to escape the scorching sun. Similar burrowing strategies are exhibited by other desert animals. Certain endotherms (warm-blooded animals) such as birds and mammals escape cold and hot weather conditions by hibernating during winters and aestivating during summers. They hide themselves in shelters such as caves, burrows, etc. to protect against temperature variations.

(d) Importance of light to plants

Sunlight acts as the ultimate source of energy for plants. Plants are autotrophic organisms, which need light for carrying out the process of photosynthesis. Light also plays an important role in generating photoperiodic responses occurring in plants. Plants respond to changes in intensity of light during various seasons to meet their photoperiodic requirements for flowering. Light also plays an important role in aquatic habitats for vertical distribution of plants in the sea.

(e) Effects of temperature or water scarcity and the adaptations of animals.

Temperature is the most important ecological factor. Average temperature on the Earth varies from one place to another. These variations in temperature affect the distribution of animals on the Earth. Animals that can tolerate a wide range of temperature are called eurythermals. Those which can tolerate a narrow range of temperature are called stenothermal animals. Animals also undergo adaptations to suit their natural habitats. For example, animals found in colder areas have shorter ears and limbs that prevent the loss of heat from their body. Also, animals found in Polar regions have thick layers of fat below their skin and thick coats of fur to prevent the loss of heat.

Some organisms exhibit various behavioural changes to suit their natural habitat. These adaptations present in the behaviour of an organism to escape environmental stresses are called behavioural adaptations. For example, desert lizards are ectotherms. This means that they do not have a temperature regulatory mechanism to escape temperature variations. These lizards bask in the sun during early hours when the temperature is quite low. As the temperature begins to increase, the lizard burrows itself inside the sand to escape the scorching sun. Similar burrowing strategy is seen in other desert animals.

Water scarcity is another factor that forces animals to undergo certain adaptations to suit their natural habitat. Animals found in deserts such as desert kangaroo rats, lizards, snakes, etc. are well adapted to stay in their habitat. The kangaroo rat found in the deserts of Arizona never drinks water in its life. It has the ability to concentrate its urine to conserve water. Desert lizards and snakes bask in the sun during early morning and burrow in the sand as the temperature rises to escape the heat of the day. Such adaptations can be seen to prevent the loss of water.

All non- living components of an ecosystem form abiotic components. It includes factors such as temperature, water, light, and soil.

(a) Endothermic animal: Birds such as crows, sparrows, pigeons, cranes, etc. and mammals such as bears, cows, rats, rabbits, etc. are endothermic animals.

(b) Ectothermic animal: Fishes such as sharks, amphibians such as frogs, and reptiles such as tortoise, snakes, and lizards are ectothermic animals.

(c) Organism of benthic zone: Decomposing bacteria is an example of an organism found in the benthic zone of a water body.

Population:

A population can be defined as a group of individuals of the same species residing in a particular geographical area at a particular time and functioning as a unit. For example, all human beings living at a particular place at a particular time constitute the population of humans.

Community:

A community is defined as a group of individuals of different species, living within a certain geographical area. Such individuals can be similar or dissimilar, but cannot reproduce with the members of other species.

(a) Commensalism: Commensalism is an interaction between two species in which one species gets benefited while the other remains unaffected. An orchid growing on the branches of a mango tree and barnacles attached to the body of whales are examples of commensalisms.

(b) Parasitism: It is an interaction between two species in which one species (usually smaller) gets positively affected, while the other species (usually larger) is negatively affected. An example of this is liver fluke. Liver fluke is a parasite that lives inside the liver of the host body and derives nutrition from it. Hence, the parasite is benefited as it derives nutrition from the host, while the host is negatively affected as the parasite reduces the host fitness, making its body weak.

(c) Camouflage: It is a strategy adapted by prey species to escape their predators. Organisms are cryptically coloured so that they can easily mingle in their surroundings and escape their predators. Many species of frogs and insects camouflage in their surroundings and escape their predators.

(d) Mutualism: It is an interaction between two species in which both species involved are benefited. For example, lichens show a mutual symbiotic relationship between fungi and blue green algae, where both are equally benefited from each other.

(e) Interspecific competition: It is an interaction between individuals of different species where both species get negatively affected. For example, the competition between flamingoes and resident fishes in South American lakes for common food resources i.e., zooplankton.

The logistic population growth curve is commonly observed in yeast cells that are grown under laboratory conditions. It includes five phases: the lag phase, positive acceleration phase, exponential phase, negative acceleration phase, and stationary phase.

(a) Lag phase: Initially, the population of the yeast cell is very small. This is because of the limited resource present in the habitat.

(b) Positive acceleration phase: During this phase, the yeast cell adapts to the new environment and starts increasing its population. However, at the beginning of this phase, the growth of the cell is very limited.

(c) Exponential phase: During this phase, the population of the yeast cell increases suddenly due to rapid growth. The population grows exponentially due to the availability of sufficient food resources, constant environment, and the absence of any interspecific competition. As a result, the curve rises steeply upwards.

(d) Negative acceleration phase: During this phase, the environmental resistance increases and the growth rate of the population decreases. This occurs due to an increased competition among the yeast cells for food and shelter.

(e) Stationary phase: During this phase, the population becomes stable. The number of cells produced in a population equals the number of cells that die. Also, the population of the species is said to have reached nature’s carrying-capacity in its habitat. A Verhulst−pearl logistic curve is also known as an S-shaped growth curve.

(d) One organism is benefited, other is affected.

Parasitism is an interaction between two species in which one species (parasite) derives benefit while the other species (host) is harmed. For example, ticks and lice (parasites) present on the human body represent this interaction where in the parasites receive benefit (as they derive nourishment by feeding on the blood of humans). On the other hand, these parasites reduce host fitness and cause harm to the human body.

A population can be defined as a group of individuals of the same species, residing in a particular geographical area at a particular time and functioning as a unit. For example, all human beings living at a particular place at a particular time constitute the population of humans.

Three important characteristics of a population are:

(a) Birth rate (Natality): It is the ratio of live births in an area to the population of an area. It is expressed as the number of individuals added to the population with respect to the members of the population.

(b) Death rate (Mortality): It is the ratio of deaths in an area to the population of an area. It is expressed as the loss of individuals with respect to the members of the population.

(c) Age Distribution: It is the percentage of individuals of different ages in a given population. At any given time, a population is composed of individuals that are present in various age groups. The age distribution pattern is commonly represented through age pyramids.

If a marine fish is placed in a fresh water aquarium, then its chances of survival will diminish. This is because their bodies are adapted to high salt concentrations of the marine environment. In fresh water conditions, they are unable to regulate the water entering their body (through osmosis). Water enters their body due to the hypotonic environment outside. This results in the swelling up of the body, eventually leading to the death of the marine fish.

Phenotypic adaptation involves changes in the body of an organism in response to genetic mutation or certain environmental changes. These responsive adjustments occur in an organism in order to cope with environmental conditions present in their natural habitats. For example, desert plants have thick cuticles and sunken stomata on the surface of their leaves to prevent transpiration. Similarly, elephants have long ears that act as thermoregulators.

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 (which far exceed 100°C) 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.

A population can be defined as a group of individuals of the same species residing in a particular geographical area at a particular time and functioning as a unit. For example, all human beings living at a particular place at a particular time constitute the population of humans.

The main attributes or characteristics of a population residing in a given area are:-

(a) Birth rate (Natality): It is the ratio of live births in an area to the population of an area. It is expressed as the number of individuals added to the population with respect to the members of the population.

(b) Death rate (Mortality): It is the ratio of deaths in an area to the population of an area. It is expressed as the loss of individuals with respect to the members of the population.

(c) Sex ratio: It is the number of males or females per thousand individuals.

(d) Age Distribution: It is the percentage of individuals of different ages in a given population. At any given time, the population is composed of individuals that are present in various age groups. The age distribution pattern is commonly represented through age pyramids.

(e) Population density: It is defined as the number of individuals of a population present per unit area at a given time.

A population grows exponentially if sufficient amounts of food resources are available to the individual. Its exponential growth can be calculated by the following integral form of the exponential growth equation:

N_t = N_o e^rt

Where,

N_t= Population density after time t

N_O= Population density at time zero

r = Intrinsic rate of natural increase

e = Base of natural logarithms (2.71828)

From the above equation, we can calculate the intrinsic rate of increase (r) of a population.

Now, as per the question,

Present population density = x

Then,

Population density after two years = 2x

t = 3 years

Substituting these values in the formula, we get:

⇒ 2x = x e^3r

⇒ 2 = e^3r

Applying log on both sides:

⇒ log 2 = 3r log e

Hence, the intrinsic rate of increase for the above illustrated population is 0.2311.

Several plants have evolved various mechanisms both morphological and chemical to protect themselves against herbivory.

(1) Morphological defence mechanisms:

(a) Cactus leaves (Opuntia) are modified into sharp spines (thorns) to deter herbivores from feeding on them.

(b) Sharp thorns along with leaves are present in Acacia to deter herbivores.

(c) In some plants, the margins of their leaves are spiny or have sharp edges that prevent herbivores from feeding on them.

(2) Chemical defence mechanisms:

(a) All parts of Calotropis weeds contain toxic cardiac glycosides, which can prove to be fatal if ingested by herbivores.

(b) Chemical substances such as nicotine, caffeine, quinine, and opium are produced in plants as a part of self-defense.

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.

The basis of various biological control methods is on the concept of predation. Predation is a biological interaction between the predator and the prey, whereby the predator feeds on the prey. Hence, the predators regulate the population of preys in a habitat, thereby helping in the management of pest insects.

Figure 1 represents the interaction between the individuals of single population of the same species A and with their environment.

Figure 2 represents the interaction between individuals of three different species A, B and C that are living in a community.

Figure 3 represents the biome (distinct ecological community of plants and animals which lives together in a particular climate) having three different communities which are at different stages of development.

Soil salinity is defined as the salt content in the soil, which is caused by improper irrigation. The process of increasing salt concentration or content is known as salinization. This occurs due to improper irrigation method from a salt laden water table. When the salt concentration in soil is increased then it get accumulated due to evaporation.

Human activities like fertilizing crops is also responsible for salinity of soil. Fertilizer contains potassium, form salt- sylvite. Soil salinity degrades soil and vegetation too. Generally the soil pH occurs between 2.2- 9.7, above this soil will be degraded by this salt content.    

Yes, light factor affects the distribution of plants. Since, plants produce food through photosynthesis process which is possible only when sunlight is present as the source of energy. Light is an important factor that affects the distribution of plants. Examples:

1. Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesis optimally under very low light condition because they are constantly overshadowed by tall canopied trees.
2. Many plants are also dependent on the sunlight to meet their photoperiodic requirement for flowering. Animals too depends on light factor, for animals light is important in that way, they use the diurnal and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities.
3. Many plants in the shade will grow vertically to gain access to the light. These plants will appear to have smaller leafs and smaller than others of the same age found in conditions with better sunlight.

i. Mango etc.

Shelford’s law of tolerance defines that there are upper and lower limit of tolerance threshold values on the environment gradient beyond the species cannot survive. As the upper limit of tolerance of temperature factor is known is eurythermal organisms.

ii. Thermus aquaticus, bacteria etc.

Hot springs are also known as thermal spring which contains water with the higher temperature.

iii. Xenophyophores, amphipods etc.

Trench is an excavation which is very deeper and narrow when compared along with its length.

iv. Mites, snails, bugs, beetles etc.

Compost pit is defined as the degrading the biodegradable substances in a dig or a pit for the decay so that manure and fertile substances are produced for the soil.

v. Some Cuscuta species.

Parasitic plants are those which gets nutrition from the other plants. Those plants which gets nutrition are parasites and other by which plant they are getting nutrition are known as hosts.

vi. Eucalyptus etc.

Shelford’s law of tolerance defines that there are upper and lower limit of tolerance threshold values on the environment gradient beyond the species cannot survive. As the lower limit of tolerance of temperature factor is known as stenothermal organisms or species.

vii. Mites, worms, beetles, bugs etc.

Soil organisms are those which are found in soil.

viii. Bacteria, fungi, crustaceans etc.

Benthic organisms are those which are found in this benthic zone or bottom zone.

ix. There are some proteins that acts as antifreeze compounds like Antarctic Notothenioids.

Antifreeze compounds are those substances that lowers the freezing point which protects from getting ill from the effects of ice such as ethylene glycol etc.

x. Amphibians, reptiles etc.

Those organisms whose homeostasis is highly influenced by external environment factors like temperature, nutrients etc.

Two microorganisms that inhabits the human intestine are:

1. E. coli
2. Lactobacillus
3. Clostridium  

Tree line is the edge of the habitat where trees are capable of showing growth. Due to various environmental conditions such as too low temperature, high altitude or lack of moisture, trees are not found beyond this line and if they are found then they show stunted growth and forms low dense matted bushes.

‘Zero population growth rates’: When a population, the number of births become equal to the number of deaths, there will be no change in the growth of the population. This is termed as zero population growth. It shows stationary or Bell- shaped pyramid.

Diagram:

There are several characteristics that are used in the human population census:

1. Natality: This is also known as the birth rate of the individuals in the population. It is defined as the number of individuals produced per female per unit time (at specific interval of time). 
2. Mortality: This is also known as the death rate of the individuals in the population. It is defined as the number of individuals died during a given period. 
3. Age structure and age pyramid: Different age groups are present in the population. Then age structure is defined as the relative numbers of young and old individuals in a population which influences the behaviour of birth and death rate; so this relative proportion of individuals in each different age group is age structure. And, an age pyramid is a graphical representation which shows the number and the proportion of the individuals that belongs to various age classes in a population of an individual at the given time.
4. Dispersion: It is defined as the spatial or temporal distribution pattern of the individuals of a population within the boundaries of the population. It is divided into three major patters: Regular (even distribution), Random (unrelated or scattered distribution) and Clumped (aggregated or contagious distribution).

(a) Migratory animals: Migratory animals are those which moves from one place to another and later they get return to avoid the unfavourable climatic conditions. For example: Eels, which lives in the western world. They migrates from fresh water down into the open sea in the northern region for the reproduction. For the development, their young ones return to the original place up the stream.

(b) Camouflaged animal: Camouflaged animals are those which have the ability to blend themselves with the environment. So that they remain unnoticed for the protection or aggression from being captured by the predators. For example: Leaf insect is green in colour, so they resembles with the green leaf, therefore camouflaging themselves to avoid predators.

(c) Predator animal: Predatory animals are those which feeds on the prey (which is being caught). All the carnivores are the predatory animals. For example: Tiger, Lion which feeds on the deer etc.

(d) Biological control agent: Biological control agents are those which reduces the growth of pests or an unwanted organisms that affects the growth of plants, by using biological agents. For example: release of parasitic wasps to control aphids (sap sucking insects) etc.

(e) Phytophagous animal: Phytophagous are those animals which feeds on green plants and attacks on roots, stems etc. For example: all species of grasshopper are phytophagous.

(f) Chemical defense agent: Chemical defensive agents like venomous substances etc. are used by the prey for the reduction of predator attack.   

Predation is the negative interaction where the one living organism is eaten by the other organism through capturing, killing and eating. The one who feeds on the organism is known as predator and the other who is being eaten is known as prey. Mutualism is the positive interaction which is a symbiotic relationship between the members of two different species in which both the members get benefitted. Commensalism is the type of positive interaction and is a symbiotic relationship between the two species in which one species is benefitted and other neither benefits or nor is harmed. Climbers (lianas) takes tree’s support for exposing their canopy without doing harm to the tree itself.

1. Mutualism is the positive interaction which is a symbiotic relationship between the members of two different species in which both the members get benefitted. Figure A shows mutualism relationship because in this, the bee contains nectar from the flower and the flower is getting pollinated.
2. Figure D is showing predation association because this picture is showing that the lion is eating deer, in which lion is a top predator which gets benefitted and the other that is being eaten called host or prey get harmed.   
3. Two organisms are buffalo and the egret is sitting on one of them. Figure C shows commensalism association which is a type of positive interaction and is a symbiotic relationship between the two species in which one species is benefitted and other neither benefits or nor is harmed. When the buffalo eats grass then the egret feeds on these insects from the grass. So the egret gets benefit and buffalo is not getting benefitted or nor get harmed.
4.  

Population is defined as the group of individuals of the same species which lives together at the particular region. Population contains several characteristics or attributes that are functions of whole group not of an single individual:

1. Population density: When the size of population is defined by its fundamental properties is known as Density which is expressed as the number of individuals or biomass per unit area or volume. Population size is determined on the basis of density which is expressed as number of individuals per unit area (on land) or per unit volume (in aquatic system). Population size or density can be calculated by various methods: Complete counts/ Total counts, Incomplete counts, Indirect counts and Mark- recapture method (widely used method). Population size formula (mark- recapture method):

N = Total individuals marked in first sample x size of second sample                                                                                                                            Number of marked individuals recaptured in second sample

2. Natality: This is also known as the birth rate of the individuals in the population. It is defined as the number of individuals produced per female per unit time (at specific interval of time). 

3. Mortality: This is also known as the death rate of the individuals in the population. It is defined as the number of individuals died during a given period. 

4. Age structure and age pyramid: Different age groups are present in the population. Then age structure is defined as the relative numbers of young and old individuals in a population which influences the behaviour of birth and death rate; so this relative proportion of individuals in each different age group is age structure. And, an age pyramid is a graphical representation which shows the number and the proportion of the individuals that belongs to various age classes in a population of an individual at the given time. There are three types of age pyramid: Upright broad based pyramid, Bell shaped pyramid and Urn shaped pyramid.

Diagram:

5. Dispersion: It is defined as the spatial or temporal distribution pattern of the individuals of a population within the boundaries of the population. It is divided into three major patters: Regular (even distribution), Random (unrelated or scattered distribution) and Clumped (aggregated or contagious distribution).

Diagram:

Population is divided into three important age classes: Pre- reproductive, Reproductive and Post- reproductive. An age pyramid is a graphical representation which shows the number and the proportion of the individuals that belongs to various age classes in a population of an individual at the given time. There are three types of age pyramid: Upright broad based pyramid, Bell shaped pyramid and Urn shaped pyramid.

Figure A is the Upright broad base pyramid which represents the expanding population with the high birth rate. It shows high proportion of pre- reproductive age class individuals than the reproductive and post- reproductive age class; which gives pyramid shaped age structure.

Figure B is the Bell- shaped pyramid which represents the stable population which contains moderate proportion of young to old population. Pre- and reproductive age class becomes equal in size and the post- reproductive remains small in size which makes this pyramid bell shaped.

Figure C is the Urn- shaped structure pyramid which shows declining population. It contains low proportion of pre- reproductive age class individuals due to low natality in comparison to reproductive and post- reproductive age class.

Population is the changing entity and we can say this because of the change in number (increases or decreases) of individuals in the population with the time which is determined by the four factors: Birth, Death, Immigration and Emigration. It also represents the growth curves: Exponential and Sigmoid shape.

The Upper diagram that is showing in the question represents the Logistic growth or Sigmoid shaped curve. In this growth curve, resources are unlimited but they are slowed down by the limiting factors in the idealized situation (i.e. contains limited factors). When the population density increases each individual will contain their own few resources. And, their limit will be set by their environmental factor over the space. It is also be limited by the various factors like predation, competition, climatic conditions etc. The curve shows slow growth initially at the establishment state and then get more faster at exponential phase and then suddenly slows down due to various environmental resistance factors like completion, predation etc. and then finally stable or stationary phase comes where the population becomes stable (no increase occurs from this stage) and is represented by K (carrying capacity). The S- shaped curve is also known as Verhulst- Pearl Logistic curve, which is represented by the following equation:

Where, N is the population size

r is the intrinsic rate of increase;

• If r is positive then the population is increasing
• If r is positive then the population is decreasing
• If r is zero then the population does not change in size

dN/dt is the rate of change in population numbers over the time

K is the carrying capacity.

This equation can also be written as:

Firstly, after the lag phase, the population will grow in an exponential manner where the nutrients and space will be abundant.

When the food sources get depleted, the population density starts decreasing and ends in an asymptote phase, then the population density reaches the carrying capacity (K). Population shows logistic growth curve and S- shaped growth curve. The S- shaped curve is also known as Verhulst- Pearl Logistic curve, which is represented by the following equation:

Where, N is the population size

r is the intrinsic rate of increase;

• If r is positive then the population is increasing
• If r is positive then the population is decreasing
• If r is zero then the population does not change in size

dN/dt is the rate of change in population numbers over the time

K is the carrying capacity.

Diagram of S- shaped growth curve:

Population can also be affected by the interactions that occurs between the organisms in the ecosystem. There are various types of positive interaction that are as follows:

(+) sign represents the positive effect of the one species on another species and (0) shows no effect.

Mutualism is the positive interaction which is a symbiotic relationship between the members of two different species in which both the members get benefitted. For example: Lichens are the mutualistic association of the photoautotrophic algae and heterotrophic fungi. 

Commensalism is the type of positive interaction and is a symbiotic relationship between the two species in which one species is benefitted and other neither benefits or nor is harmed. For example: Climbers (lianas) takes tree’s support for exposing their canopy without doing harm to the tree itself.

Competition is a rivalry relationship (competition for the same thing) between two or more organisms. A competition between individuals of same species (intraspecific) is more acute than the competition between individuals of different species as all the members in a intraspecific competition that have some basic requirements such as food, water, light, space, mating and shelter.

But it is true only when the resources are limited. According to Gause’s principle, if the two competing species coexist in a stable or same environment then it leads to differentiation of their realized niches; and if there no differentiation then one competing species will be eliminated, i.e. one of the species is to be eliminated. But recent studies have revealed that species facing intraspecific competition may evolve mechanism to encourage co- existence rather than exclusion which can also be done by a method known as ‘resource partitioning’.

While living in and on the host species, the animals parasite contains or involved some adaptations like the loss of unnecessary sense organs, i.e. in leech and mites don’t contains wings; presence of adhesive organs or suckers to cling on the host, i.e. tapeworm and leeches; loss of digestive system and high reproductive capacity, i.e. tapeworm. 

Biome is a unique ecological community of plants and animals living together a particular climate, consists of wide variety of habitats. In this, climate is the main factor that determines the soil type which automatically defines the vegetation type. They both determines the variety of microorganisms and animals.

The other determining factors are the latitude and altitude, intensity and duration of winter and summer days, water mass and topography. The most common biome of the world does not show any boundary of any country and regional and local variations that exists in each biome. For example: Temperate grassland contains dominant vegetation and contains hot summer and cold winters and rainfall exceeds approximately 25 to 75cm; and tropical rainforests contains high temperature, high rainfall and greater biodiversity.