Organisms And Population - Class 12 Medical Biology - Extra Questions

The interspecies interaction in which both the organisms co-exist and support each other is called as mutualism.
For example, the bacteria present inside the digestive system of cattle provide cellulase enzyme for digestion of cellulose and in return, the cattle provide bacteria with shelter.

Orchid growing on a mango tree shows Commensalism. Here one of the species is benefited other is unaffected.

Clown fish living near the mouth of Sea Anemone shows the interaction named as Commensalism as this protect them from the predator.

The biotic component of an ecosystem interacts with each other as they are interdependent. Mutualism is the interaction between the living organism where each individual benefits from the activity of the other. It occurs between two different species. Similar interactions within a species are known as co-operation. A well-known example of mutualism is the relationship between ungulates (such as Bovines) and bacteria within their intestines. The ungulates benefit from the cellulase produced by the bacteria, which facilitates digestion; the bacteria benefit from having a stable supply of nutrients in the host environment.
Mutualism plays a key part in ecology. For example, mutualistic interactions are vital for terrestrial ecosystem function as more than 48% of land plants rely on mycorrhizal relationships with fungi to provide them with inorganic compounds and trace elements. In addition, mutualism is thought to have driven the evolution of much of the biological diversity we see, such as flower forms (important for pollination mutualisms) and co-evolution between groups of species.

We should conserve forest as they are hot spots of biodiversity. If we will not conserve it will lead to ecological imbalance in nature. Forests maintain biological diversity prevent erosion of soil and flood apart from influencing rainfall.

No. Along with advantageous variations, a number of indifferent variations remain in the populations. Only the disadvantageous variations which are either lethal or extremely harmful are eliminated. All other variations persist in the population. Many of them function as preadaptations. 

(A) $$\rightarrow$$ q, (B) $$\rightarrow$$ r, (C) $$\rightarrow$$ s, (D) $$\rightarrow$$ p.

Rats and snakes escape the desert's intense heat by hiding themselves deep into the burrows in the sand during the daytime. They come out during the night when it is cool outside.

Explanation:

Brood parasitism is a condition in which some species of birds thrive by leaving their eggs in the care of other birds due to similarities in physical features.
For example, a cuckoo leaves its eggs in the crow's nest. This cuckoo egg hatches and matures for some period of time in the crow's nest and then flies away.

Clownfish and sea anemone show a type of interaction known as commensalism, In this interaction, one species is benefited while the other is neither harmed nor benefited. Sea anemone has stinging tentacles that provide protection to clownfish from predators. The anemone does not appear to derive any benefit from the clown fish.

The interaction between a whale and the barnacles growing on its back is commensalism.

The relationship between the fig tree and wasp shows mutualism, the wasp lays its eggs and also pollinates the fig's inflorescence. On the other hand, the fig not only provides shelter (fruit) for oviposition to wasp but also allows its larva to feed on seeds. 

The relation between a mango tree and an orchid is commensalism. 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. 

Orchids are epiphytes. These are the autotrophic plants that lack mechanical tissues and grow on the surface of some other supporting plants. Orchid growing on mango tree derive support from the tree but do not derive nutrition from it. It represents commensalism wherein orchid plant is getting support from its association with mango tree while the later is not affected.

Mutualism is the way two organisms of different species exist in a relationship in which each individual benefits from the activity of the other.
The two examples of the organisms involved that are commercially exploited in agriculture are as follows:
(i) In order to replenish the lost nutrients (especially nitrogen) in the soil, farmers grow leguminous crops containing Rhizobium in its roots.
(ii) Farmers use Mycorrhiza commercially in agriculture as it improves the soil quality and reduces soil erosion by improving plant rooting capacity. 

The interaction is parasitism where Cuscuta is the parasite which infests the shoe flower bush and derives nutrition from it. 

Biological control of pest management exploits predation. Predation is the ecological interaction between predators and preys where predators drives energy from preys. By this control method predator keeps the population size of pest and insects under control. 

Parasitism is an association of organisms where one organism is benefitted at the expense of other. Whereas, the association of organisms wherein one organism is benefitted while other remains unaffected is called as Commensalism. Mutualism is the association of organisms wherein both are benefitted. There is no negative effect of association on another organism. Thus, the correct answer is D.  

Population density is a criteria used as a measurement of the population in a particular region or per unit volume. This criterion helps in the recording of the number of deaths and births in that region. The birth and death rate affects the population density. 

The relationship between two organisms where one organism is benefited but the other one is neutral i .e it is neither benefited nor harmed is called as commensalism.

Agricultural water pollution	Shipping water pollution
Includes sediments, fertilizers and farm animal wastes which enter into the water bodies from agricultural land.	Includes both human sewage and other wastes, the most important of which has been oil.

Competition	Mutualism
Interaction between the organisms or species in which the fitness of one overpowers the presence of another.	Biological interaction between the two organisms belonging to different species where both of them derive benefit.

Natality	Mortality
Natality means the birth rate of a population.	Mortality means the death rate of a population.
Natality increases the growth rate of the population.	Mortality decreases the growth rate of the population.

A population is a unit of biotic community made up of permanent group of an interbreeding individual of a species found in a space or geographical area at a particular time. 

Ecological competition is the struggle between two organisms for the same resources within an environment. Resources are components of the environment that are required for survival and reproduction such as food, water, shelter, light, territory, and substrate. Members of the same species may also compete for mates. 

Fig tree and wasp share a mutual relationship. A wasp pollinating fig flower is an example of obligate mutualism. It is a type of mutualism in which the species involved are in close proximity and interdependent with one another in a way that one cannot survive without the other. The wasp lays its eggs and also pollinates the fig's inflorescence. On the other hand, the fig not only provides shelter (fruit) for oviposition to wasp but also allows its larva to feed on seeds. 

Mortality is defined as the state of the individual being dead. The mortality rate is the death rate of a population which is calculated on the basis of the deaths in the particular region.

a) The competitive exclusion principle is also referred to as Gause's law states that two species in the same ecosystem but different niche competing for the same resource cannot coexist at constant population values if the other factors remain constant in the ecology. 

Lifespan is the oldest age to which a species is known to survive.
Life expectancy is the average age that a newborn infant can expect to attain in any given society. 

The four basic processes which result in the fluctuation in the density of the population of a given habitat are natality, mortality, immigration and emigration. Natality is the birth rate and the mortality is defined as the death rate. Immigration is the movement of people inside a particular region. Immigration is the movement of people out of a particular region. 

Some species of insects and frogs avoid from being detected easily by the predators by camouflage technique in which they get blended with their surrounding.

Immigration is an arrival of new species from another population in search of better conditions to survive. Thus the population increases in case of immigration. Carrying capacity of a population determines the health of the growing population.

Some of the abiotic factors are-

The relationship between two organisms where one organism is benefited but the other one is neutral i .e it is neither benefited nor harmed is called as commensalism. The sucker fish lives in close association with the shark. The shark preys upon the fishes and the bits which are remained are eaten by the sucker fish. 

The density of population in a given habitat increase or decrease due to different reasons. The factors responsible fro the increase in the population of a given area are:

The J-shaped of growth curve for the population growth in a species indicates the exponential form of growth. There is rapid increase in the growth rate due to the favorable factors. 

Answer:

Forest has various layers of plants. The five layers of the forest include, canopy, understory, shrub layer, herb layer, and forest floor. The herb layer consists of ferns, grasses and wildflowers. It is the thickest layer in the forest. It is the home for various forest animals that live on the ground such as insects, mice, snakes etc. It is the layer just above the forest floor.

Population density is a measurement of population per unit area. It is frequently applied to living organisms, specially to humans.  

A population has certain attributes that an individual organism does not possess. Followings are some important attributes of a population:

NATALITY	MORTALITY
1) The birth rate in a given population is called Natality. 2) Birth rate refers to the total number of live births per 1000 in a given population during a given time period or a year.	1) The death rate in a given population is called Mortality. 2) Death rate refers to the measure of number of deaths or the number of deaths per 1,000 individuals per year.

Most of the rural population which forms the bulk of our society are still illiterate, ignorant and superstitious. They also do not know the functioning of the human reproductive system. Among the people from lower strata of society, children are regarded as a gift of God and a sign of prosperity. Therefore they make no effort to avoid pregnancy. Due to the high infant mortality rate in our country, people from the economically weaker section think it safer to produce more children so that at least some may survive. Poor standards of living and poverty provide no recreation other than sex. Hence, the population keeps on rising and so does poverty. As the population increases the quality of life goes down.

The two advantages of a small family are:

(i) The financial costs of maintaining a household are lower.

(ii) Each child receives more parental attention and educational advantages, which generally raises his\her self-esteem

Interaction between them is mutualism, as both are equally benefitted. The female wasp uses the ovary not only as a site for oviposition but uses the developing seed within the fruit for nourishing its larvae. In return, the wasp pollinates the fig inflorescence, while searching for suitable egg-laying site.

A lichen is an organism that results from a mutualistic relationship between a fungus and an algae. The other organism is usually a cyanobacterium or green alga. The fungus grows around the bacterial or algal cells. The fungus benefits from the constant supply of food produced by the photosynthesizer. The photosynthesizer benefits from the water and nutrients absorbed by the fungus.

roots associated with fungi are called mycorrhizal roots. These are found in certain plants like Pinus. In these plants, fungi performs the absorption of water and salts, phosphorous solubilization, promotes disease resistance.

(a) Predation: In predation, one organism kills and consumes another. Predation provides energy to prolong the life and promote the reproduction of the organism that does the killing, the predator, to the detriment of the organism being consumed, the prey.

Mutualism Lichens, Rhizobium (nitrogen-fixing-bacterium),  Proto-cooperation Association of hermit crab and sea anemone.

Brood parasitism is a method of parasitism in which the organism lays its eggs in the nest of other birds and let that other bird to incubate them. Example : The cuckoo bird lays its eggs in the nest of crow and during the period of evolution, eggs of cuckoo bird has began to resemble with the eggs of crow.

Parasitism is an interaction between two species in which one (known as parasite) obtains its food in ready-made form from the other living organism (said to be host). Whereas, predation is a kind of direct food relationship between two species of animals in which one, called predator, captures and feeds on the other, the prey. In contrast to a parasite which derives nourishment from its host without killing, a predator is free-living which catches and kills another species for food.

The population interactions are as follows -

During the course of evolution, the eggs of koel have evolved to resemble the host’s (crow) egg in size and colour to reduce the chances of the host bird detecting the koel’s eggs and ejecting them out of the nest.

The clown fish and the sea anemone pair up for their struggle for life , the clown fish depends on sea anemone for protection from the predators where as the sea anemone depend on clown fish for food . In this relationship both are benefited .This type of relationship is called mutualism or symbiotic relationship .

Both predation and scavenging are a kind of direct food related interspecific interactions. But in predation, one organism called predator, captures and feeds on the other, the prey. The predator is a free-living organism which catches and kills another species for food. However, in scavenging, one organism, called scavenger, eats the dead bodies of other animals which have died naturally or are killed by some other animals.

Carrying capacity is the maximum number of individuals which the environment can support or sustain.

There are two basic population growth curves-(i) S-shaped (ii) J-shaped 

Biotic potential refers to the inherent power of a population to increase in numbers when all. environmental conditions are favourable, whereas carrying capacity refers to the maximum population size that a given environment can support for an indefinite period or on a sustainable basis.

The biotic potential refers to .the inherent power of a population to increase in numbers when all environmental conditions are favourable.

In the absence of light the plants remain etiolated. Shade produces elongated internodes and thinner and broader leaves. It increases the succulence of many vegetables. Strong light, in the contrary, helps in the production of more mechanical tissue and thicker leaves. Palisade parenchyma becomes multilayered under strong light but remains single layered under moderate initensities of light (e.g., Peach). The effect of light has also been observed by Cunningham in flat fish Solea. The fish habitually rests on left side. It develops pigmentation and eyes on right side, the side exposed to sun. If left side is exposed to sunlight in the young fish, both eyes and pigmentation develop on that side.

S = CA^Z 

Commensalism is the type of interaction where,of the two organisms, one is benefited while the other is nither benefited nor harmed

Aphids and other posts are kept under check by beetles and other insects, the latter by birds and so on.

r is the intrinsic rate of natural increase in the given equation.

The number of deaths per year for each one thousand individuals in a population.

The benefit to the female wasp derived from the mutualism with fig plants is that fig plant offers food for the developing wasp larvae in the form of seeds.

Movement of cattle in the field stirs up the vegetation so insects come out . Now they can be easily seen by egrets and can be caught up so, they are seen along with grazing cattle. Cattle is unaffected so, the interaction is Commensalism.

Here N is population density, t is time and K is carrying capacity .

Type of interaction involved is Mutualism. Wasp pollinates the fig inflorescence and fig offers some of it's developing seeds.

An ecosystem has two types of components, biotic and abiotic.
Biotic Components. They are living organisms found in an ecosystem. Biotic components are of five types - producers, consumers, detrivores, decomposers and parasites.
(i) Producers. They are autotrophs which synthesize organic food from inorganic nutrients with the help of solar energy. The process is called photosynthesis. Solar energy is changed into chemical energy of food.
(ii) Consumers. They are animals which feed on other oranisms. Herbivores feed on plants. Carnivores prey upon other animals. Depending upon trophic level they are called primary carnivores (second order consumers), secondary carnivores (third order consumers) and top carnivores which are not preyed upon by others.
(iii) Detrivores. They feed on detritus causing its fragmentation and pulverisation, e.g., Earthworm, Vulture.
(iv) Decomposers. They are saprophytes which pour digestive enzymes over the organic matter for its solubilisation. It results in humification and mineralisation of organic matter.
(v) Parasites. They belong to different groups which obtain food from other living organisms called hosts.
Abiotic Components. They include climate, edaphic and topographic factors.
1. Temperature. There are four temperature zones - tropical, subtropical, temperate and arctic or alpine. Different types of organisms occur in different zones.
2. Light. Photosynthesis depends upon the availability of light which is maximum in tropical areas and decreases progressively towards poles. Plants growing under shade of large trees show less photosynthetic activity. In the form of photoperiods, light influences a number of activities including flowering, leaf fall, migration and breeding in many animals.
3. Wind. It influences transpiration, pollination, dissemination, tree growth and flight animals.
4. Humidity. It Influences luxuriance of biota.
5. Precipitation. Amount and periodicity of rainfall control forest type of the area. Water availability and humidity also depend upon rainfall.
6. Water. Depending upon its availability, plants are xerophytes, mesophytes, hydrophytes and hygrophytes.
7. Background. Most animals have colour, pattern and texture similar to background.
8. Topography. Topography or surface behaviour of earth influences other abiotic factors.
9. Gases. $$CO$$, concentration determines the rale of photosynthesis and warmth of the atmosphere. Oxygen concentration is supra optimum for $$C_3$$ plants and optimum for $$C$$, plants.
10. Soil. It determines vegetation growth and pattern.
11. $$pH$$. Tree growth is favoured by slightly acidic $$pH$$. Earthworms do not occur in acidic soils. Euglena and other flagellates are abundant.
12. Mineral Elements. Both excess and deficiency of minerals are harmful to biota. Optimum mineral elements are required for optimum growth.

Commensalism	Ammensalism
It is a positive interaction i.e. one or two species are benefited.	It is a negative interaction i.e. either one or both the species are harmed.
One species is benefited called Commensal other is unaffected.	One species isharmed called Ammensal other is unaffected.
Example: Woody climbers take support of trees. Jackals follow lion or tiger for food.	Example: Tagetes secrete chemicals toxic to soil nematodes. Smoother crops do not allow the weeds to grow nearby.

Type of interaction involved is Mutualism. The fungus helps the plant to absorb essential nutrients from the soil and plant provide energy rich carbohydrates to fungi.

The interaction due to which smaller barnacles were excluded because of the dominance of Balanus in the coast of Scotland is competition.

A symbiotic relationship is a type of relationship which describes close interaction between two or more species, it is of three different types mutualism, commensalism, protocooperation. Both the partners are equally benefited, neither is harmed in mutualism, one partner is benefited without harming the other in commensalism & both partners are benefited without establishing physical contact in protocooperation.

The plants found in the boreal forest are:

Multicellular organisms like humans reproduce sexually. In the cycle of reproduction when a human dies, his whole body gets wasted, flesh, blood, bones etc get decayed, none of these go to the next generation. Therefore we say a person died.

Most of the single cell organism divide into two new single-cell organisms. In this cycle of reproduction, there is no dead body, each and every part is converted into new organisms.

An example of a unicellular organism is an amoeba.

The interaction between organisms of different species in which both the organisms benefit from each other.  It is interspecific.

Commensalism is defined as the association of two organisms in which one of them extracts benefit and the other individual is unaffected.

A) Mutualism - It is a relationship between two or more individuals of different species in which all the organisms are mutually benefitted by one another.

An organism that lives in or on an organism of another species (its host) and benefits by deriving nutrients at the other's expense is called Parasite, Eg: Human parasites like certain protozoa and worms infect humans and cause parasitic diseases. Human parasites are divided into endoparasites, which cause infection inside the body, and ectoparasites, which cause infection superficially within the skin.

When resources are unlimited, populations exhibit exponential growth, resulting in a J-shaped curve. When resources are limited, populations exhibit logistic growth. In logistic growth, population expansion decreases as resources become scarce.

The relationship between organisms from which one organism is negatively affected and the other organism is unaffected is termed as Amensalism.

Biodiversity maintained by apex predation. Predators may increase the biodiversity of communities by preventing a single species from becoming dominant. Such predators are known as keystone species and may have a profound influence on the balance of organisms in a particular ecosystem. e.g. lion, zebra, bear, fish, fox and rabbit.

• The streamlined body of birds helps them to fly continuously for a particular time by reducing the air resistance.
• The air cavities in their bones serves to make their skeleton light so that birds can fly high.

As we know the death rate is equal to two ratios of the number of individuals that to the total number of individual.

Lichen is a symbiotic relationship of algae/cyanobacteria/chlorophyceae living among filaments of a fungus, forming a lichen. The algae benefit their fungal partner by producing carbon compounds via photosynthesis and the fungal partner, in turn, provides for the protection and also gather nutrients and moisture from the environment.

Commensalism: This is the interaction in which one species benefits and the other is neither harmed nor benefitted. An orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale benefit while neither the mango tree nor the whale derives any apparent benefit.
Mutualism: This interaction confers benefits on both the interacting species. Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria. Similarly, the mycorrhizae are associations between fungi and the roots of higher plants. The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the fungi with energy-yielding carbohydrates.

The per capita (per person) growth rate of a population remains the same in exponential growth regardless of population size, making the population grow quicker and quicker as it grows bigger.A J-shaped curve generates exponential growth

• Commensalism is an association between two organisms in which one benefits and the other derives neither benefit nor harm. For example, Orchids and forest tree.
• An orchid growing on the branch of a forest tree is an epiphyte. Epiphytes are plants growing on other plants which, however, do not derive nutrition from them. Therefore, the relationship between a forest 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, allows the orchids to receive more sunlight for photosynthesis, receive nutrients from the air, while the mango tree remains unaffected.
• Hence Commensalism is the term used to describe a population intersection between an orchid growing on a forest tree.

Population in a metro city tend to decline if natality rate (the number of births) and Immigration rate (the number of individuals of the same species that have come into the habitat from elsewhere) declines and mortality rate (the number of deaths) and emigration (the number of individuals of the population who left the habitat and gone elsewhere) increase.

Features in deer that helps it to detect the presence of predator are-
i. Long ears that help it to recognise the movement of predators.
ii. Its eyes are on the side of its head that help it to see in all directions. 
iii. Due to its thin legs. it is able to run away faster from the predator. 

A biome is a very large ecosystem that comprise of a wide variety of vegetation and animal life. The identification of biomes is done on the basis of the vegetation cover constituting them. Biomes are classified into terrestrial biomes, freshwater biomes and marine biomes. Steppe grasslands in Central Asia and Pampas in South America are examples of biomes.

Population in a metro city tend to increase if natality rate (number of births) and Immigration rate (number of individuals of the same species that have come into the habitat from elsewhere) increases.

Parasitism is a type interaction in which one of the partners is benefited because it resides outside or inside the body of the host and gets free accommodation and food while the host is affected due to loss of nutrients. Ectoparasites and endoparasites devoid the host of its nutrition. Some of the parasites are known to cause diseases like Ascaris/roundworm which is an endoparasite of intestine causes ascariasis. Another example is of Wuchereria which causes elephantiasis or filariasis. It is an endoparasite which lives in lymphatic vessels of lower limbs. Lice or ticks which are found in humans and dogs respectively are examples of ectoparasites. They absorb the nutrients from their host. 

When resources are unlimited, growth rate of the population is exponential. This gives a J- shaped curve on graph.

Following are the positive interactions between species: 
(a) Mutualism: Thin is a relationship between two organisms in which both the organisms are benefited. Lichen is an example of mutualism. Lichen is an association of fungi and algae. The fungal part attaches to the substratum and gets water and minerals for the algal part. The algal part carries out photosynthesis and provides food to the fungal part. 
(b) Commensalism: This is a relationship between two organisms in which one organism is benefited, while another organism is neither at gain nor at loss. Egrets keep on sitting on the back of herbivore animals: like buffalo, cow, etc. when the cattle forage for grass, the insects under the grass fly away haphazardly. This gives a chance to the egrets to feed on insects. 
Without the help of cattle, it will be difficult for egrets to find insects, however, the cattle is neither benefited nor harmed.

(a) Migratory animal - Siberian crane (Migrates to India during summer)
(b) Camouflaged animal -Chameleon (protects itself from predators by camouflaging with the surrounding) 
(c) Predator animal - Lion (predator of herbivores like  
(d)Biological control agent -  Dragonfly (predators of mosquitoes and other small flying insects)
(e) Phytophagous animal - Honey bee (feeds on nectar and pollen from flowers)
(f) Chemical detenteagent - Capsaicin produced by chilli pepper ( prevents its consumption by mammals including humans)

The interaction between two species is called interspecific interaction. 

Termite and Trichonympha show mutualism; a relationship in which both the organisms are benefited from each other. Trichonympha breaks down cellulose in the wood and thus help the termite in digestion of wood. Trichonympha also feeds on fragments of wood. 

 Relationship between two organisms in which one organism is benefitted and there is neutral effect on another organism; is called commensalism. Many commensals live In the alimentary canal of humans to get shelter and food but they have neither positive nor negative impact on humans. 

Egrets ride on the back of cattle. When cattle forage for grass, insects fly away abruptly. This gives the Egrets a chance to feed on those insects. In this relationship, cattle get no benefit from Egrets. 

Answer:

Predation: A predator is any consumer that kills and eats another living organism in order to obtain energy. The organism being eaten is called prey. Examples are Lions, Wolves, and Eagles.

A biome is a climatically and geographically contiguous area with similar climatic conditions. Both organic and inorganic components are similar in a particular type of biome. However, regional and local variation exist within each biome. To understand this. let us consider following examples. 
Coniferous forest is a type of biome which mainly contains trees which bear cones with seeds inside. In all the coniferous forests around the world, coniferous trees are the main plant species. But regional variations exist in coniferous forests. The coniferous forests of North America are dominated by black spruce. On the other hand, the coniferous forests of north east Europe are dominated by Norway spruce. Forests of Siberia are dominated by pine. This shows regional variations in a particular type of biome.

Population Density:

• Population density is a measurement of the population of organisms in per unit area or unit volume. Population density is a numerical expression.
• For Example, 100 trees per acre or 200 fishes per km or 50 billion diatoms  per $$m^3$$.

Parasitism: There is a type of symbiotic relationship between organisms of different species is called parasitism where one organism, the parasite, benefits at the expense of the other, the host. Examples of Parasitism are tapeworms, flukes, the Plasmodium species, and mosquitoes.

The population is individuals of the same species that occupy a specific area. A species can have one or more than one population. The community is the group of populations of different species living together in a habitat.

To find carrying capacity on a graph, we need to locate the point on the graph where the population line is horizontal. Alternatively, the carrying capacity may be explicitly marked with a dotted horizontal line or a horizontal line of a different color. Typically, the graph is going to have a population on the y-axis and some measurement of time (in months, years, etc) on the x-axis. Once, the population has reached a steady state, it will show zero growth, which will result in a slope of zero, i.e., a horizontal line. 

(A) $$\rightarrow$$ s (B) $$\rightarrow$$ r (C) $$\rightarrow$$ q (D) $$\rightarrow$$ p

Terms involved in nitrogen cycle are
1. Nitrogen fixation : Plants cannot use free nitrogen present in the air. This nitrogen molecule is converted into nitrates and nitrites which can be taken up and used to make the required molceule. This is called nitrogen fixation which can be done by the bacterias that live in the root nodules of leguminors  plants. By physical process during lightning, the high temperatures and pressures is created in the air which convert nitrogen into oxides of nitrogen and dissolve in water and come down along with rain. This is also called nitrification.
2. Ammonification. The nitrogen compounds formed are taken by plants to form proteins which are further  converted into ammonia.
3. Denitrification. The nitrates and nitrites of nitrogen are acted upon by other group of microbes e.g. Pseudomonas bacteria,which convert these compounds into free nitrogen gas.
Nitrogen cycle:
1. Free nitrogen from atmosphere is converted into nitrates by bacterias or by lightning.
2. Nitrates mix with soil, is absorbed by the plants to make proteins.
3. The proteins in plants and animals are converted into amino acids and ammonia.
 4. Ammonia is converted into nitrates nitrates and then these nitrates and nitrites present in soil is acted up on by other group of bacterias called denitrifying bacteria. The process is called denitrification, nitrates are converted into free nitrogen and is released back to the atmosphere.

There are two models which describes the pattern of growth in a particular population. They are as follows-
1. Exponential growth model: Here, the population increase over time as a result of the number of individuals available to reproduce without regard to resource  limits. The Population size increases at an exponential rate over time, continuing upward.

Host–parasite co-evolution is a special case of co-evolution. it is defined as the reciprocal adaptive genetic change of two antagonists (e.g. different species or genes) through reciprocal selective pressures. Hosts and parasites exert reciprocal selective pressures on each other, which may lead to rapid reciprocal adaptation. In the particular case of host–parasite coevolution the antagonists are different species of host and parasite.

Gause's Competitive Exclusion Principle states that two species that compete for the exact same resources cannot stably coexist.
One of the two competitors will always have a slight advantage over the other that leads to extinction of the second competitor in the long run. As a consequence, competing related species often evolve distinguishing characteristics in areas where they co-exist.

Characteristics which are exhibited by population and not individual:

1. Population density / size - Number of individuals of a species per unit area or volume.
   
2. Population dynamics - Population growth change during time and depends on food availability, predation, pressure, weather and also depend on natality, mortality, immigration and emigration. 
   

(a) Three ways of measuring population density of a habitat are:

1. Percent cover for trees with larger canopy
   
2. Number of fishes caught per trap
   
3. Pugmarks or fecal pellets or tiger census
   

The egrets are present very close to the grazing cattle. This is a type of interaction called as commensalism. This is a type of interaction in which one of the partners is benefitted while the other partner is unharmed or remain neutral. The egrets feed on the small insects which are present in the grass. The cattle while grazing cause the insects to come out of the grass and the egrets can feed on these insects. 

Brood parasitism is a method whereby the organisms lay their eggs in the nest of the other birds. The other birds help in incubating the eggs and take care of the eggs. This kind of parasitism occurs in birds.
For example, the cuckoo bird lays its eggs in the nest of the crow. During the period of evolution, eggs of cuckoo bird have begun to resemble similar to the eggs of crow. This creates a misconception that the eggs are of the crow and it takes care of those eggs. 

(a) Birth rate or natality is the number of live births per 1000 people of population per year
(b) Death rate or Mortality is the number of deaths per 1000 people per year.
(c) Population density is the number of individuals per square kilometre at any given time.
(d) Exhaustible resources are those resources which are present in limited quantity and can be completely used up by human activities are called exhaustible resources.
(e) Growth rate of the population is the difference between the birth rate and the death rate. As long as the birth rate exceeds the death rate, the population grows. If the birth rate is lower than the death rate, the population declines.

Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. Predators are an important part of a healthy ecosystem. Predators cull vulnerable prey, such as the old, injured, sick, or very young, leaving more food for the survival and prosperity of healthy prey animals. Also, by controlling the size of prey populations, predators help slow down the spread of disease. Predators will catch healthy prey when they can, but catching sick or injured animals helps in natural selection and the establishment of healthier prey populations as the fittest animals are left to survive and reproduce.

• Symbiosis is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasitic. 
• Symbiosis is also classified by physical attachment; symbiosis in which the organisms have bodily union is called conjunctive symbiosis, and symbiosis in which they are not in union is called disjunctive symbiosis.
•  Mutualism or interspecies reciprocal altruism is a long-term relationship between individuals of different species where both individuals benefit. 
• Mutualistic relationships may be either obligate for both species, obligate for one but facultative for the other, or facultative for both.
  
• Commensalism describes a relationship between two living organisms where one benefits and the other is not significantly harmed or helped.
  

The population density will increase if the number of births plus the number of immigrants (B + I) is more than the number of deaths plus the number of emigrants (D + E), otherwise it will decrease.

• Interspecific competition is competition between individuals of different species. It occurs when organisms of different species have similar feeding habits. They belong to the same trophic level.
  
• Intraspecific competition is competition between individuals of same species. It is more acute as the requirements are same and can reduce the size of the population.
  

Prairies of the United States represent "grasslands".

• The life span of an organism is the period from birth to the natural death of the individual. 
  
• The life span of :

(i) Crocodile is 60 years

b) Population density is the number of individuals of a species per unit area or volume.

• The different ways by which the population density of different species can be measured are:-
• 1) Natality- is the number of births during a given period in the population.

2) Mortality- is the number of deaths in the population during a given period.

3) Immigration- is the number of individuals that have come into the habitat from elsewhere during the time period.
4) Emigration- is the number of individuals of the population who left the habitat and moved elsewhere during a given time period.

(a) Mycorrhizae is a symbiotic association between fungi and plant. It is a type of mutualism where both plant and fungi get benefitted.

S-shaped growth curve (sigmoid growth curve) A growth pattern in which an organism's population density rises slowly originally in a fresh setting, in a favorable acceleration stage ; then rises quickly approaching an exponential growth rate as in the J-shaped curve ; but then decreases in a negative acceleration stage until the population stabilizes at zero growth rate.

Ectoparasite: Parasites which live  attached to the external body surface of  the  host are called ectoparasites, e.g. Leech and Ticks.
Endoparasites: Parasites which live  attached to the internal body surfaces of the host are called endoparasites, e.g. roundworms and hookworms. 

Species A	Species B	Type of interaction	Example
-	+	Predation	Rabbit and lion
+	+	Mutualism	Lichen
+	0	Commensalism	Egrets and cattle

(a)Bacteria -  Number /unit volume 
(b) Banyan tree - Number/ square kilometer(Area) 
(c) Deer - Number/ square kilometer (Area) 
(d) Fish -Number /unit volume

Answer-

Lianas are structural parasites on other trees, while taking support from other trees, lianas usually strangulate the other tree. They also compete for sunlight and water and in the process and harm the host tree.