Biology Chapter 14 Ecosystem

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The gradual and predictable change in the species composition of a given area is called ecological
succession.

(b) Differences between production and decomposition

(c) Differences between Upright pyramid and Inverted pyramid

(d) Differences between food chain and food web

(e) Differences between litter and detritus

(f) Differences between primary productivity and secondary productivity

Fig. A Pyramid of numbers 

(ii) Pyramid of biomass

Fig.B Pyramid of biomass.

(iii) Pyramid of energy

Fig. An ideal pyramid of energy.

Pyramid of biomass in an aquatic ecosystem is always inverted.
(iii) The biomass of  primary producer (PP) that is the phytoplanktons is smaller than biomass of zooplanktons. The latter constitute primary consumer (PC). The biomass of carnivores i.e. fish, a secondary consumer (SC) is more than the biomass of primary consumer. Thus the pyramid of biomass of aquatic ecosystem is inverted.

Pyramid of Biomass

Biotic and physiographic factors operating simultaneously are the causes of ecological succession.

Biotic factors- direct succession and
Physiographic factors include climate and other physical factors such as erosion of hills, filling up of lakes and streams.

An ecosystem comprises two main components :
(i) Biotic components including plants, animals and microorganisms : and
(ii) Abiotic components that mainly includes non-living factors like  water, minerals, temperature and light. 

Food web. In nature the food chains are not strictly linear, but are interrelated and interconnected with one another.  A network of food chains in a community are referred to as a food web. 

 
Fig. Food web 

Biomass. Biomass is biological material derived from living, or recently living organisms. It is the mass of living organisms. The biomass of a species is expressed in terms of fresh or dry weight. 

Standing State- The amount of nutrients, such as, carbon, nitrogen, phosphorus, calcium, etc. present in the soil at any given time, is referred to as the standing state. 

1. The natural reservoir of phosphorus is rock in the form of phosphates.

2. Minute quantities of phosphates get dissolved in the soil solution during weathering of rocks.

3. Phosphates enter the plants through their roots and then the food chain.

4. The organic wastes and dead organisms are decomposed by phosphate-solubilising bacteria, which release phosphorus back in the soil.

5. The atmospheric input of phosphorus through rainfall or gaseous exchange of phosphorus between organisms and environment, is negligible.

Phosphorus Cycle

An ecosystem comprises two main components :
(i) biotic including plants, animals and microorganisms : and
(ii) abiotic mainly includes non-living components like water, light, temperature, and soil. .

It is expressed in terms of gm^-2yr^-1 or kcal m^-2 yr^-1. Primary productivity depends upon a number of environmental factors like :

(a) Availability of nutrients which varies in different types of ecosystem.

(b) Photosynthetic capacity of plants.

(c) The plant species inhabiting a particular area.

(d) Environmental factors.

Decomposition involves the following processes :

1. Fragmentation - is the breaking down of the detritus into smaller particles . It increases the surface area of detritus for the action of microbes. 
2. Leaching is the downward movement of water soluble inorganic nutrients into the soil horizon and their precipitation as unavailable salts. 
3.Catabolism involves break down of detritus in the presence of extracellular enzymes released by the decomposers.
Usually the processes fragmentation , leaching and catabolism are carried out simultaneously on the detritus.
4.Humification  involves transformation of simplified detritus into fully decomposed, dark coloured and amorphous humus. Humus acts as a reservoir of nutrients.
5. Mineralisation is the further breakdown of the humus by microbes to relase inorganic nutrients.

Energy flows is the flow of energy through ecosystems in one direction, typically from the Sun, through photosynthetic organisms including green plants and algae, to herbivores to carnivores and decomposers.

 A generalised energy flow model of ecosystem—Boxes represent biotic components and the arrows show the pathways of energy transfer 
The plants fix energy from the sun by the process of photosynthesis. Only 2-10 percent of solar energy is captured by green plants (producers) during photosynthesis to be converted into food. The rate at which the biomass is produced by plants during photosynthesis is termed as ‘gross primary productivity’.
When these green plants are consumed by herbivores, only 10% of the stored energy from producers is transferred to herbivores while the remaining 90 % of this energy is used by plants for various processes such as respiration, growth, and reproduction and is lost as heat. Similarly, only 10% of the energy of herbivores is transferred to carnivores.The decomposers degrade the organic material and release energy as heat. 

1. The reservoir pool for a sedimentary cycle is Earth's crust or rocks.

2. The earth's crust or rocks act as a  reservoir, to meet the deficit which occurs due to imbalances in the rate of influx and efflux.

3. Environmental factors like temperature, soil nature and moisture can regulate the rate of release of nutrients.

4. Their speed is slower than gaseous cycle and hence take more time to complete.

5. They are generally imperfect in nature as bulk of nutrient remains immobile and is trapped in the  earth’s crust.

Carbon cycle is the simplest of all nutrient cycles. Its salient features are :

1. The reservoirs of carbon are : air( as Carbon dioxide), Water ( as dissolved carbon), earth's crust and ocean ( as bicarbonates) and  fossil fuels. 

2. Carbon dioxide is used by green plants for the process of photosynthesis and oxygen is released as a by-product. The fixed carbon enters the food chain and passed to herbivores, carnivores, decomposers. About 4 x 10¹³ kg of carbon is fixed in biosphere through photosynthesis annually.

2. CO₂ production and return to atmosphere.

(a) Carbon dioxide is released into the atmosphere by respiration of producers and consumers.

(b) It is also released by decomposition of organic wastes and dead bodies by decomposers by the action of bacteria and fungi of decay.

(c) Burning of wood and fossil fuels also produces C0₂.

(d) Volcanic eruptions and hot springs also release C0₂ into the atmosphere.

(e) Weathering of carbonate-containing rocks by the action of acids also add C0₂ to the atmosphere.

Nitrogen cycle
 
Fig. Nitrogen Cycle in Nature.

The structural component of an ecosystem may be classified under two main types :

(i) Biotic components

(ii) Abiotic components

Biotic components comprise the  living organisms present in an ecosystem. These include plants, animals and micro-organisms (bacteria and fungi). The biotic components of an ecosystem has been classified into three groups :(i) Producers (Green plants)
(ii) Macroconsumers (Usually animals
(iii) Microconsumers or decomposers (organisms like bacteria and fungi).

Abiotic components consist of the non living components like light, temperature, water, oxygen, carbon, nitrogen and minerals.  Various important abiotic factors have been classified as follows :

(i) Climatic factors. These include light, temperature, precipitation, atmospheric humidity and wind.

(ii) Topographic factors. These include altitude, surface slope and exposure, etc.

(iii) Edaphic factors. These include soil and substratum.

For Examples

The following services are provided by forests ecosystem. 

1. Purification of air.

2. Mitigation of droughts and floods.

3. Cycling of nutrients

4. Providing habitat and shelter to a number of wild life.

5. Act as storehouse of carbon

6. Influence the hydrological cycle.

7. Maintain biodiversity.

Typical food chain

 A typical food chain with Energy flow and Cycling of materials.

Examples of food chains
(i) Grass → Goat → Man
(ii) Algae → Zooplankton → Fish → Man
(iii) Algae → Insects → Frog → Snake → Peacock. 

The specific place in the food chain that is occupied by the organism based on the source of their nutrition or food is known as their trophic level.

Succession on bare rock

 Stages of ecological succession on bare rocks.
The lichens are the pioneer species and invade the bare rocks. They secrete acids which dissolve the rocks, help in their weathering and formation of soil. Mosses grow in with the lichens to form a mat over the substratum. 
Bryophytes or annual grasses succeed the lichens. They are able to hold small amount of soil.
Bigger trees appear in the later stages and are succeeded by other species untill a climax community forms an equilibrium with the environment. It leasds to the formation of forest ecosystem.

Stratification is the vertical distribution of different species occupying different levels. Stratification in the forest is represented by

i) Trees occupying the top layer

ii) Shrubs occupy the second layer. 

iii) Herbs and grasses the bottom most layers.

Predators play an important role in:

1. Maintaining the prey population and regulating intra-species competition. For example, if tigers are removed from a forest, spotted deer will multiply rapidly.

2. Indicating ecological disturbances. Usually, predators are small in number and highly sensitive to ecological changes, owing to their excessive adaptation. For example, Gharials (freshwater predators) start dying rapidly as soon as a river starts getting polluted, thus indicating a disturbance in the ecosystem.  

Primary productivity is the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. Primary productivity varies in different types of ecosystem because it depends on:

 a) The plant species inhabiting the area.

b) The variety of environmental factors.

c) The photosynthetic capacity of plants.

d) The availability of nutrients.

The relation between the gross and net primary productivity can be shown as:

(a) Gross primary productivity is the rate of production of organic matter during photosynthesis.

(b)Net primary productivity is the available biomass for the consumption to heterotrophs (herbivores or decomposers).

Gross primary productivity minus the respiratory losses is the net primary productivity

NPP = GPP-R, where,

NPP = Net primary productivity

GPP = Gross primary productivity

R = Respiration

Productivity is the rate of biomass production.

Gross productivity is the rate of production of biomass by green plants per unit time per unit area. It is the total amount of productivity.
Net primary productivity is the difference between the gross primary productivity and the loss due to respiration.                                                                        
Secondary productivity is the rate of formation of organic matter by the consumers.

The various advantages of keeping the ecosystems healthy are as follows:

1. Healthy ecosystem is the base for a wide range of economic, environmental and aesthetic goods and services.

2. The products of ecosystem processes are named as ecosystem services, as they are of great help to the organisms living within an ecosystem.

3. Healthy forest ecosystem purifies air and water.

4. It also mitigates droughts and floods and maintains the cycle nutrients.

5. Healthy ecosystem generates fertile soil, prevents soil erosion and provides wildlife habitat.

6. Maintenance of biodiversity is also an important aspect of healthy ecosystem.

7. It also provides aesthetic, cultural and spiritual values.

Phytophagous insects feed on plants.

Key process involved in carbon cycle is photosynthesis and respiration.

Carbon cycling occurs through atmosphere, ocean and through living and dead organisms.

1. Carbon is fixed during photosynthesis by the plants.

2. A large amount of carbon is returned to the atmosphere as CO₂ by the respiratory activities of organisms.

3. Decomposers also contribute substantially to the CO₂ by acting on waste materials and dead organic matters.

4. Some of the fixed carbon is lost to the sediments and removed from the circulation.

5. Burning of fossil fuels forest fire and combustion of organic matter volcanic activity also release CO₂ in the atmosphere.

(a) Pioneer species is the species of organism that invades the bare area. Lichens usually are the pioneer species on a bare rock. They secrete acids which dissolve rocks, thereby leading to weathering of rocks and soil formation. This paves the way for small plants like bryophytes which are able to take hold in the small amount of soil. They are succeeded by bigger plants, several more stages, and ultimately by a stable climax forest community which remains stable as long as the environment remains unchanged.

(b) Algal bloom is the excessive growth of the free-floating (planktonic ) in the water bodies , due to the presence of large amount of nutrients in the water. Water bodies in the industrial area have excess of nutrients which in turn promotes algal bloom. The algal bloom imparts a distinct colour to the water bodies and also robs the water of dissolved oxygen that is vital to aquatic organisms. They cause deterioration of the water quality and also produce toxins which are harmful to other organisms. The other pollutants flowing into the lake further decrease the oxygen levels in the water and poison the lake. Thus algal bloom can literally choke the lake to death.

(a) The amount of biomass produced per unit area over a time period by plants during photosynthesis is defined as the primary productivity. It is expressed as weight or energy. Productivity can be mainly divided into gross primary productivity (GPP) and net primary productivity (NPP). GPP is the rate of production of organic matter during photosynthesis.

Primary productivity is directly proportional to the amount of carbon dioxide, sunlight and water. It is inversely proportional to respiratory losses. NPP = GPP - Respiratory losses (R)

(b) Decomposition is an oxygen consuming process thus it is directly proportional to the concentration of the oxygen in the environment. It is controlled by the chemical composition of detritus and climatic conditions. The decomposition rate decreases when the detritus is rich in lignin and chitin while it is quicker if the detritus contains nitrogen and water-soluble substances such as sugars.

Biomagnification is the increase in the concentration of a toxin at successive trophic levels. The toxin gets accumulated because a toxic substance cannot be metabolised or excreted, and is thus passed on to the next higher trophic level. For example, DDT (dichlorodiphenyltrichloroethane) and other heavy metals such as mercury and cadmium are the toxins that cause biomagnification. In the aquatic ecosystem the concentration of DDT increases at successive trophic levels;  it is present in low amount in water and reaches a high concentration in fish-eating birds through biomagnification. Very high concentrations of DDT

disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking,eventually causing the decline in bird populations.

Flowchart of biomagnification of DDT

The pyramid of energy represents the total amount of energy consumed by each trophic level in a given food chain. An energy pyramid is always upright because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.

The pyramid of biomass is a graphical representation of the total amount of living matter present at each trophic level of an ecosystem. The pyramid of biomass can be both upright and inverted.

Inverted pyramid of biomass - The pyramid of biomass is inverted in a pond ecosystem as the biomass of fishes exceeds the biomass of zooplankton (upon which they feed).

The age pyramid reflects an expanding growth status of human population as the number of individuals in the post reproductive stage is lower than the Reproductive and the pre-reproductive stage.

Function of a reservoir in a nutrient cycle is to meet the deficit which occurs due to imbalance in the rate of influx & efflux. 

(a) Ecological pyramid is defined as a graphic presentation of the ecological functions like the number of individuals in the various trophic levels, the amount of biomass or the transfer of energy at different trophic levels. This give an apparently simple and fundamental basis for comparing: different ecosystems, seasonal variation within a particular ecosystem, change in an ecosystem. The size of the portion of the diagram associated with each trophic level illustrates the amount of energy, biomass, or number of individuals found in each trophic level.

There are three types of pyramids:

1. Pyramid of numbers- which represents the numbers of organisms at each trophic level.

2. Pyramid of biomass- which represents the weight (usually dry weight) or biomass of organisms at each trophic level.

3. Pyramid of energy - which monitor the energy content of the organisms at each trophic level.

For example - the pyramid of biomass in grassland ecosystem- The producers occupy the base which denotes that the biomass of producer is the highest. The herbivores like rabbits, rats etc. occupy the second trophic level followed by primary carnivores like snakes and lizards. The secondary carnivores occupy the last trophic level and have the lowest biomass.

(b) Upright pyramids - The base of most pyramid (pyramids of number, energy and biomass), representing the producers or the first trophic level is broad and it narrows down at the apex. These pyramids are called upright pyramids. It means producers are more in number and in biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than that at a higher level.

Inverted pyramids - are those in which the base is narrow and the apex is broad. It denotes that the number or biomass at the first trophic level or producer level is lower as compared to the higher trophics like herbivores or carnivores. These are inverted pyramids. For example- large number of insects feeding on a big tree gives an inverted pyramid of number. The pyramid of biomass in sea is also generally inverted because the biomass of fishes far exceeds that of phytoplankton.

(a) The pond ecosystem is fairly a self-sustainable unit.
A pond is a shallow water body in which all the above mentioned four basic components of an ecosystem are well exhibited.
The abiotic component is the water with all the dissolved inorganic and
organic substances and the rich soil deposit at the bottom of the pond.
The solar input, the cycle of temperature, day-length and other climatic
conditions regulate the rate of function of the entire pond.
The autotrophic components include the phytoplankton, some algae and the floating,
submerged and marginal plants found at the edges.
The consumers are represented by the zooplankton, the free swimming and bottom dwelling forms.
The decomposers are the fungi, bacteria and flagellates especially
abundant in the bottom of the pond.
This system performs all the functions of any ecosystem and of the biosphere as a whole, i.e., conversion of inorganic into organic material with the help of the radiant energy of the sun by the autotrophs;
consumption of the autotrophs by heterotrophs;
decomposition and mineralisation of the dead matter to release them back
for reuse by the autotrophs.
(b) In the pond ecosystem the Grazing Food Chain is the major food chain for the energy flow. 

In a food chain one trophic level is occupied by more than one species. On the  basis of sources of their nutrition, organisms occupy a specific position in the food chain called their trophic level. For example, in a grassland ecosystem, rabbits and insects occupy the same trophic level, while both are different species. Therefore one trophic contains more than one species and is a functional level of different species rather than only one. Thus the trophic level cannot be represented by a species. 

The given pyramid is an inverted pyramid. 
Inverted pyramid of biomass in a lake- Phytoplankton ----> Zooplankton-----> Fishes.
Inverted pyramid of number - Tree----> Insects-----> Birds.

Ecosystem services are the products of ecosystem processes. Forests are the major source of ecosystem services and are
prerequisite for environmental, aesthetic goods and indirect economic values in the following ways:
1. Environmental Values
(i) Carbon-fixation Huge amount of CO2 in the atmosphere is removed naturally and fixed by plants into organic
molecules and energy through photosynthesis. All the other trophic levels, i.e. consumers depend upon this
energy produced by them.
(ii) Release of oxygen by the producers as a byproduct in the process of photosynthesis, improves the air quality
and supports life on earth.
(iii) Soil Soil formation and soil protection are the major ecosystem services accounting for nearly 50% of their total
worth. Plant cover protects the soil from drastic changes in temperature. There is little wind or water erosion as
soil particles are not exposed to them. The soil remains spongy and fertile. There are not landslides and no floods.
(iv) Nutrient cycling There is no depletion of nutrients, but the same are repeatedly circulated.
2. Economic Value
(i) Ecosystem services provide certain economical important products also. These include timber, paper, rubber,
wax, medicines, cosmetics, resins, etc.
(ii) Ecosystem also provides other benefits such as aid in pollination. Bees and other insects of natural ecosystem visit
nearby farmlands to pollinate crops.
3. Other aesthetic values Natural ecosystems are a source of spiritual, cultural and aesthetic values.

It will not be able to remove particulate matter present in the exhaust of thermal power plants & hence cannot control pollution.

Tropic level: Organisms occupy a place in the natural surroundings or in a community according to their feeding relationship with other organisms. Based on the source of their nutrition or food, organisms occupy a specific place in the food chain and this is known as a trophic level.

Each trophic level has a certain mass of living material at a particular time and this is called as Standing crop. It is measured as the mass of living organisms (biomass) or the number in a unit area.

First trophic level is formed by producers. This is the basic unit. These organisms can live without feeding on any another level.
The only thing that these organisms need to survive is sunlight and water which they can turn into energy themselves. All other trophic levels depend on this level of energy.

GFC is Grazing Food Chain: It is depicted as below :
Producers → Primary consumers → Secondary consumers

DFC is Detritus Food Chain : It begins with the dead organic matter. It is made up of decomposers which are heterotrophic organisms like fungi, bacteria etc.

GFC is the major conduct for energy flow. DFC may be connected with GFC at some levels: Some of the organisms of DFC are prey to the GFC animals.

$$\begin{gathered} \mathrm{Producers} \stackrel{\downarrow \mathrm{Decomposers}}{\to } \mathrm{Primary} \mathrm{consumers} \\ \mathrm{Primary} \mathrm{consumers} \stackrel{\downarrow \mathrm{Decomposers}}{\to }\mathrm{Secondary} \mathrm{consumers} \end{gathered}$$

These natural interconnection of food chains forms food web.

C.

all living organisms which influence other organisms

Biotic factors include all the living organisms which influence the other organisms.

D.

Lichens

Lichens help secrete acids to dissolve rock helps in weathering of rocks and hence help in the formation of soil. 

A.

AG Tansley

The term ecosystem was coined by AG Tansley. 

C.

consumer

Secondary productivity is the rate of formation of new organic matter by consumers. primary productivity depends on the producers inhabiting a particular area. Decomposers break down complex organic matter. Into inorganic substance like carbon dioxide water and nutrients. Parasitic species food on the body of other organisms.

C.

rock

The natural reservoir of phosphorous is rock, which contains phosphorus in the form of phosphates. Sea water, animal bones and fossils are reservoirs of carbon.

A.

methane, hydrogen sulphide and carbon dioxide

Biogas is a mixture of gases (mainly methane) produced by the microbial activity and which may be used as fuel. During biogas production, the bacteria called methanogens digest the activated sludge and produce a mixture of gases such as methane, hydrogen sulphide, carbon dioxide and hydrogen.

A.

Fragmentation - Carried out by organisms such as earthworm

Fragmentation is one of the steps during decomposition, in which detritus is converted into small fragments. Humification leads to a dark coloured amorphous substance called humus that is highly resistent to microbial action and undergoes decomposition at an extremely slow rate. 
Catabolism is the set of metabolic pathways that breaks down metabolic pathways that break down molecules into smaller units to release energy. Leaching refers to the loss of water-soluble plant nutrients from the soil due to rain and irrigation

A.

Petromyzon (lamprey) is an ectoparasite on fishes, which belongs to Cyclostomata. lchthyophis is a limbless amphibian. Limulus (king crab) is a living fossil, which belongs to Arthropoda. Admasia having polyp body form is a coelenterate.

A.

The biogeochemical cycles are of two types i.e., gaseous cycles, in which the reservoir for the nutrient elements is in the atmosphere (air) or hydrosphere(water). The four most abundant elements in the living systems, i.e. hydrogen, carbon, oxygen and nitrogen have predominantly gaseous cycles.
In sedimentary cycles, the reservoir for the nutrient elements is in sediments of the earth. Elements, such as phosphorus, sulphur, potassium and calcium have sedimentary cycles. 

C.

Genome, chromosome, gene, nucleotide

The correct order of organisation of genetic material from largest to smallest is as follows:
Genome, chromosome, gene, nucleotide.
Genome: It is the total genetic material of an individual.
Chromosome: It is a packed and organised structure containing most of the DNA of a living organism.
Gene: It is a segment of DNA that encodes for a protein. 
Nucleotide: It is one of the structural components or building blocks of DNA and RNA.

A.

the gradual and predictable change in species composition occurs in a given area.

The gradual and fairly predictable change in the species composition of a given area is called ecological succession. During succession some species colonise an area and their populations become more numerous, whereas populations of other species decline and even disappear.

D.

detritivores

Most animals that live in deep oceanic waters and called benthos are scavengers or detritivores. These organisms include crustaceans, polychaetes and some microorganisms.

A.

senescent leaves

Deficiency of both nitrogen (N) potassium (K) visible in senescent (older) leaves i.e., due to the deficiency symptoms of N  chlorosis while, the deficiency of cause the inhibition of protein synthesis and scorching of older leaves.

B.

Phosphorus cycle

Phosphorus cycle is a sedimentary biogeochemical cycle. It describes the lithosphere, hydrosphere and biosphere and the main reservoir pool is lithosphere. Atmosphere does not play any significant role in the movement of phosphorus because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth. The production of phosphine gas occurs only in specialized, local conditions. 

C.

cobra

A.

Level PC is insects and level SC is small insectivorous birds

The given figure shows spindle-shaped pyramid of number in single tree ecosystem. Here a single large sized tree provides food to a large number of herbivores which support a few carnivores and the later are eaten by small number of top carnivores. So, here PP is used for producer, ie., single tree, PC is Primary consumers, i.e., large number of insects, SC is secondary consumers, i.e., small insectivorous bird and TC is Top consumers which may be eagles or falcon, etc.

D.

Stratification

Vertical distribution of different species occupying different levels is called stratification. It represent the structural unit of an ecosystem. For example, trees occupy top vertical strata and herbs and grasses occupy the bottom layers.

B.

forest

Pyramid of number represents the number of individuals per unit area at various trophic levels. It is always upright in grassland, pond and lake ecosystems. But in forest or single tree ecosystem, it is spindle-shaped and if parastic food chain is considered, then it will be an inverted pyramid. 

B.

secondary productivity

The amount of energy accumulated in green plants through the process of photosynthesis is known as primary productivity. It may gross PP (i.e., the total organic matter synthesised) or Net PP (i.e., the weight of organic matter stored). The rate of resynthesis of organic matter by the consumers is known as secondary productivity.

C.

B.

Phylum - Arthropoda is the largest phylum of the animal kingdom with the largest group, i.e, insects. The second largest population of phylum - Mollusca. The third one is occupied by crustaceans. All other animals combinedly indicate the D portion of the pie chart.

A.

0.02 J

According to 10% law of energy flow by Raynold Lindman. The total amount of energy that can be transferred to the next trophic level is the 10% hence, the peacock will receive 0.02 J of energy as a top consumer. Energy received by other organisms are 
Plant --> 20 J
Mice -->  20 x 10 % = 2J
Snake--> 2 x 10 %  = 0.2 J.

A.

Producers utilize the radiant energy of sun which is transformed to chemical form during photosynthesis. Thus, green plants occupy the first trophic level. The herbivores constitue the secondary trophic level and the carnivores the third trophic level. Deer is herbivores, rabbit and rat are also herbivores but frog eats the grasshoppers.

B.

stratification

Stratification is the vertical distribution of different species occupying different levels in a biotic community. It is formation of vertical layers where vegetation is dense, i.e. - 5-7 strata (layer) in tropical rain forests with emergent tall trees, canopy trees, shrub layer below tree layer, bottom layer of herbs and grass at ground level.
 Zonation is the horizontal categorisation of biomass into zones based on their distribution or arrangement in habitat as determined by environmental factors, e.g. altitude, latitude, temperature, biotic factors, etc.

B.

degraded forest

Secondary succession takes place on degraded forest. It is the process of regrowth of an ecosystem which undergoes a destructive event such as fire, avalanche, agricultural clearing, deforestation or disease. The rate of succession and establishment of communities is faster as compared to growth in primary succession. 

D.

standing crop

The total dried biomass of living organisms present at a trophic level at a particular time is known as standing crop.
Standing state is the amount of inorganic nutrients present at any time in the soil or water of ecosystem. The gross primary productivity is the total organic matter synthesised by producers during photosynthesis per unit time and area while net primary productivity is weight of organic matter stored by producers in unit area/volume per unit time.

B.

gross primary productivity 

The rate of production of organic matter (chemical energy) as biomass that primary producers (via photosynthesis) created in a  given duration of time is called Gross Primary Productivity (GPP).
Net primary production is the rate at which all plants (producers) in an ecosystem produces net useful chemical energy, it is equal to difference between the rate at which plants in an ecosystem produce useful chemical energy (GPP) and the rate at which they use some of that energy during respiration. 
NPP = GPP - respiration (by plants)
Secondary productivity is the generation of biomass or organic matter by heterotrophic (consumers) in a system.
Net productivity is the amount of energy trapped in organic matter during a specific interval at a given trophic levels less than that lost by the respiration of the organisms at that level.

A.

It occurs on a deforested site

Secondary succession or subsere is ecological succession that takes place in a recently denuded area which still contains a lot of organic debris, remains and propagules of previously living organisms. It is a more common and caused by baring of an area due to forest fires, deforestation, excessive overgrazing, landslides, earthquakes, repeated floods, etc. Only 50 to 100 years are required for establishment of a grassland over a recently denuded area. Formation of forest requires 100 to 200 years.

B.

It is inverted in shape

Pyramid of energy is graphic representation of energy per unit area sequence-wise in various rising trophic levels with producers at the base and top carnivores at the apex. Pyramid of energy is upright in all the cases. It is also more accurate than other types of ecological pyramids. 

B.

less than 50%

PAR ( photosynthetically active radiation) designates the spectral range of solar radiation from 400 to 700 nm that photosynthetic organisms are able to use in the process of photosynthesis. Of the total incident solar radiation, the proportion of PAR is less than 50%.

A.

Sparrow

Sparrow feeds upon grains hence, is called primary consumer or herbivore and belong to second trophic level (T₂). it also feeds upon insects in the same ecosystem at the same time, hence, called secondary consumer or primary carnivores and now belongs to third trophic level (T₃)

A.

medium water conditions

Hydrarch succession takes place in water areas and the successional series progress from hydric to the mesic conditions. As against the xerarch succession takes place in dry areas and series progress from xeric to mesic conditions. Hence, both hydrarch and xerarch succession lead to medium water conditions (mesic)-neither too dry (xeric) nor too wet (hydric).

B.

fragmentation

The breakdown of detritus (dead remains of plants and animals) into smaller particles by detrivores like earth worm is called fragmentation. it is the first step in the process of decomposition.