Thinking Process

On the basis of mode of nutrition organism can be classified as autotrophs and heterotrophs.

Answer

(c) Autotrophs (Chemoautotrophs and photoautotrophs) are those organisms which are able to synthesise their own food. e.g., plants while the organisms which derive their food, (from autotrophs or plants) are termed as heteroptrophs. Heterotrophs may be herbivores, carnivores and omnivores.

Saprotrophs are the organisms which obtain their nourishment from dead organic matter or remains of both plant and animals. They are also known as decomposer as they play an important role in recycling of minerals by decomposing dead organic matter.

Answer

(a) Five important steps occured during the process of decomposition are fragmentation eaching, catabolism humification and mineralisation. Humus and mineral (inorganic nutrients) are obtained by humification and mineralisaton.

Mineralisation is also responsible for release of inorganic substances, both minerals $\left(K^{+}, Mg^{++}, Ca^{++}\right.$ and $\left.NH_{4}^{+}\right)$and non-minerals like $H_{2} O$ and $CO_{2}$ from dead organic matter of plant’s and animal’s remains.

Answer

(c) Productivity is the rate of production of biomass or organic matter by any trophic level per unit area over a time period. It is expressed/measured in term of weight (e.g., $\mathrm{gm} / \mathrm{m}^{2} / \mathrm{yr}^{2}$ ) or energy (e.g., $\mathrm{kcal} / \mathrm{m}^{2} / \mathrm{yr}$ ).

Thinking Process

Biomass is the amount of living organic matter in an ecosystem while its pyramid show relationship between producer and consumer in an ecosystem.

Answer

(b) In case of aquatic ecosystem like pond ecosystem, marine ecosystem, pyramid of biomass is inverted because the biomass of fishes exceeds than that of phytoplanktons which make the small standing crop of aquatic ecosystems.

In aquatic ecosystem biomass of trophic level depends upon reproductive potential and longevity of its members.

Answer

(b) Agaricus belong to basidiomycetes fungi which is, heterotrophs (saptrotrophs) class. It is popularly called as mushroom. Whereas Spirogyra, is a green algae and an autotrophs, i.e., producer Nostoc and Volvox are blue-green algae (cyanobacteria) and are also a producer (autotroph).

Answer

(b) In terms of net primary productivity tropical rain forest is at the top followed by coral reef, easturies and desert and ocean. Thus option ‘b’ is correct while ’ $a$ ‘, ’ $c$ ’ and ’ $d$ ’ are wrong.

Thinking Process

Ecological pyramids are generally prepared on the basis of 3 ecological parameters, number of individuals, organic matter or biomass and amount of energy.

Answer

(c) Pyramid of number in ecosystems can be inverted or upright. In terrestrial ecosystem pyramids of number is upright. In case of successive decrease in members of trophic level like a big tree it is inverted whereas pyramid of energy is always upright.

Whereas pyramid of biomass may also be upright or inverted. In none of the case always inverted pyramid or neither any pyramid may be of obtained thus other options wrong.

Answer

(b) Sun is the ultimate source of energy in all ecosystems except deep hydrothermal ecosystem. Of the incident solar radiation (less than $50 \%$ is Photosynthetically Active Radcation (PAR)) and about $2-10 \%$ or $1-5 \%$ of solar incident energy is captured by the autotrophs and is converted to chemical energy by the process of photo synthesis.

Thinking Process

Tropical rain forest biome show well defined stratification, i.e., grouping of plants in well defind layer of trees according their heights. These layer of plant are called as strata or storeys. The biome may contain a minimum of five storeys, or vegetation or strata.

Answer

(a) The lowest strata/storey/forest floor of the tropical rain forest recieve little solar radiation and soil is rich in mineral and humus.

As the high temperature and moisture (humidity) are favourable for high microbial activity of decomposers to decompos the fallen leaves and dead organic matter, process of decomposition is fastest in this type of biome.

Answer

(d) In a predator or grazing food chain predation occurs at every steps. Like herbivore are eaten up by carnivore. If they die naturally, then the energy trapped in the body of herbivore (or any tropic level) is transferred to decomposers.

Only $10 \%$ of herbivore productivity is utilised for raising productivity of next tropic level (primary carnivores), while the rest $90 \%$ is eaten and used up, in process like respiration, maintenance of body heat and other activities.

Answer

(a) The gradual and predictable changes in the species composition of a given area is called ecological succession. These changes are orderly and sequential. The entire seqences of communities that successively change in a given area are termed as sere.

The other options as random or quick change are not the features of ecological succession. Also the ecological succession is influenced by physical environment thus all the other options are wrong.

Answer

(b) During ecological or biotic succession, climax community is stable, self perpetuating and is the final biotic community. It is developed at the end of succession and is in state of perfect hormony and equilibrium with physical environment.

Climax community has maximum diversity and niche specialisation, thus all the other options are not related to climax community and are wrong.

Answer

(d) Phosphorus, nitrogen and sulphur biogeochemical cycle does not have any losses due to the process of respiration. while cycles like carbon and oxygen are affected by the process of respiration.

Answer

(d) The sequences of communities of primary succession in hydrosere is phytoplankton (pioneer stage) $\rightarrow$ rooted submerged hydrophytes $\rightarrow$ floating hydrophyte (floating stage) $\rightarrow$ reed swamp $\rightarrow$ sedges $\rightarrow$ meadow and woodland (trees). The other options are wrong.

Thinking Process

Nutrient cycles are of two types, gaseous and sedimentry.

Answer

(b) There are two stores of nutrients reserve pool and cycling pool. The reservoir for gaseous type of nutrient and biogeochemical cycle (nitrogen and carbon cycle) exists in atmosphere while earth crust is the reservoir for sedimentry cycle. Whereas stratosphere ionosphere and lithosphere are the parts of atmosphere.

Answer

(c) Producer $\rightarrow \underset{\text { (Primary consumer) }}{\text { Ist Trophic level }} \rightarrow \underset{\text { (Secondary consumer) }}{| \text { Ind Trophic level }} \rightarrow \underset{\text { (Tertiary consumer) }}{\text { IIrr Throphic level }}$

Scavengers are the detrivores which feeds on the tissue of dead animals (e.g., vultures) and do not play role in carbon fixation. Producers fix the carbon dioxide which is passed through the different trophic level.

Answer

(c) In true desert biome rainfall is less than $100 \mathrm{~mm} /$ year, characterised by extremely hot days and cold nights. Evaporation from true desert alwaays exceeds 7-50 times the precipitation (rainfall). Desert ecosystem of biomes are more in Northerm hemisphere than Southern hemisphere.

Whereas Grassland ecosystem receives medium rain fall ranging from 25-75 cm/yr but evaporation rate is not higher than precipitation rate.

Shrubby forest receives rainfall $90-150 \mathrm{~cm} / \mathrm{yr}$.

Mangrove forests receive annual rainfall ranging from $100-150 \mathrm{~cm} / \mathrm{yr}$.

Thus, there options are wrong.

Thinking Process

On the basis of light availability, an aquatic habitat can be categorised into lettoral, limnetic profundal and benthic zone.

Answer

(d) The littoral zone is the zone at the edge of a lake or ocean or in aquatic habitat which is alternatively exposed to air, hence, light is also available and immersed in water.

This costal zone is rich producers from surface to bottom, with a large number of brown and red alga attached at the zone. Different zones is an equatic ecosystem.

Pelagic zone Any zone of water in a sea or lake that is neither close to bottom nor the shore is pelagic zone.

Benthic zone It is the bottom part of the water body (aphotic zone) light is not available here and it is dark. microorganisms and benthic organisms are found in this zone.

Lentic zone refers to standing or relatively still water in an equatie ecosystem.

Different zones in an equatic ecosystem

Thinking Process

Edaphic factor is type of abiotic factors, the other are termed as climatic factors.

Answer

(b) Edaphic factor refers to soil like soil texture, background, mineral, its topography and $\mathrm{pH}$ value etc.

Water, relative humidity and altitude another abiotic components of an ecosystem but affects the climatic conditions hence are climatic factors. The variations in these factors affects the ecosystem and these factors are also the deciding factor of the different types of ecosystem found on earth.

Answer

(d) A natural ecosystem maintain its biotic and abiotic factors naturally. The products of ecosystem processes are called the ecosystem services. A healthy ecosystem provides a wide range of economic, environmented and aesthetic goods and services. The various ecosystem services provided by a natural ecosystem includes

(i) Purify air and water

(ii) Migration of droughts and floods

(iii) Nutrient cycling

(iv) Generation of fertile soil

(v) Maintenance of biodiverstity

(vi) Provide storage site for carbon

(vii) Pollinate crops

(viii) Also provides aesthetic, cultural and spiritual valves

Thus, all the above options are correct.

Answer

In an aquatic ecosystem, food chain can be drawn as follows

Producer (Phytoplankton) $\rightarrow$ Primary consumer (Zooplankton) $\rightarrow$ Secondary consumer (small fish and water beetle) (Ist to carnivore) $\rightarrow$ Tertiary consumer (Ilnd carnivore like large fish, water birds like fowl and duck).

So, the large fish and water birds like ducks and water fowls which are the tertiary consumers in an aquatic ecosystem occupy a position of secondary carnivore.

Answer

The base tier of the ecological pyramids represent the producers or first trophic level in case of three ecological pyramids (i) Pyramid of number (ii) Pyramid of biomass (iii) Pyramid of energy

Answer

Natural disturbances like fire, flood or any other natural disaster and anthropogen activities can revert back to an earlier stage of succession.

Answer

Vertical stratification (dispersion) of species in a forest ecosystem is arranged as grass (floor of forest) $\rightarrow$ Amaranthus $\rightarrow$ Shrubby plants $\rightarrow$ Teak (tree).

Answer

Cockroaches and crow are two omnivore, that are present in both grazing or predator and detritus food chain.

Answer

Pitcher plant (Napenthes) is an insectivores plant, which is chlorophyllus and capable of trapping solar radiations for chemical energy for photosynthesis. It is infectivorous plant which are produced in the soil lacking nitrogen thus to make up their nitrogen deficiency they trap insects.

Answer

Human being (man) and birds (sparrow) can be frequently seen in more than one trophic level, in an ecosystem.

Answer

Forests that are cleared by burning and left for regrowth will show secondary succession. Since, soil is already present, the buried seeds oen to germinate. Due to wind dispersal and some other natural forces, new seeds will be brought into the area and new species will colonise the forest again.

Answer

The rate of ecological succession is quicker in secondary succession as compared to primary succession as the soil (substratum) is already available for further succession. While in primary succession, the succession starts from bare rocks. Which take time for first colonisation by plants as there is no nutrient holding mechanisms.

Answer

The species that invade a bare area are called pioneer species. In a xeric succession, the pioneer species are usually lichens then bryophytes which are succeeded by ferns and some other bigger plants.

Lichen produces lichen acid and carbonic acid which corrodes rock surface and release minerals required for growth. The corroded rock accumulate soil particle by wind and provides substrate for Bryophytes and ferms.

Answer

Solar radiation is the ultimate source of energy for the ecosystem except deep hydrothermal ecosystem.

Answer

Common edible mushroom (Agaricus) is achlorophyllous (does not possess chlorophyll) and is a heterotroph.

Answer

Oceans are least productive because

(i) There is insufficient radiation as sunlight decreases with the increasing depth of the ocean.

(ii) Oceans are nitrogen deficient which is an important nutrient for plants.

(iii) Conditions of high salinity which is not favourable for all plants.

(iv) there is no substratum to support plants.

Answer

The rate of assimilation of energy at herbivore level is called secondary productivity because the biomass available to the organisms of next trophic level (consumer) for further consumption is a resultant of the primary productivity which is formed by autotrophs (plants).

Answer

Nutrient cycles are called biogeochemical cycles because ions/molecules of a nutrient are transferred from the environment (rocks, air and water) to organisms (life) and then brought back to the environment in a cyclic pathway. The literal meaning of biogeochemical is bioliving organism and georocks, air and water.

Answer

Xerarch succession of ecological communities originates in extremely dry conditions such as sand deserts and rock deserts (as there is no water and the substratum does not absorb rain water).

Answer

Self sustainability is the maintenance of an ecosystem itself or naturally. i.e., A system that maintain itself by its own independent efforts is a self-sustainable ecosystem.

Answer

(i) It is a tropical deciduous forest ecosystem.

(ii) In India this type of forest ecosystem is characterised by Tectona, Dipterocarpus Jamun, Amla, Palas, mahua and Semul plants.

Answer

They all are designated as primary consumer in a detritus food chain and are termed as detritivores.

Answer

Energy flow in the ecosystem follows the 10 % energy flow law, proposed by Lindman. According to this law only $10 \%$ of the energy available at each trophic level, gets transferred to the next trophic level, the rest is lost in the environment as heat.

As we move to higher trophic levels, the energy available to organisms keeps on decreasing.Thus, the top carnivore gains the lesst energy in a food chain. Heat energy last during Respiration.

$10 \%$ energy flow low showing transfer of energy from one trophic level to others

Answer

The number of trophic level in an ecosystem are each limited and are not more than 4-5. because the amount of energy flow decreases with successive trophic level as only $10 \%$ of energy is transferred from one trophic level to the next successive level.

So rest of the energy is lost in the form of respiration and other vital activities to maintain life. If more trophic levels are present, the residual energy will be limited and decreases to such an extent that it cannot further support any trophic level by the flow of energy.

So, the food chain is generally limited to $3-4$ trophic levels only.

e.g., $\quad \underset{(30,000 {J})}{\operatorname{\text{Sun}}} \quad \xrightarrow{1 \% \text{asborbed}} \quad\underset{(300 {~J})}{\text { Plants }} \quad \xrightarrow{10 \% \text{transferred}} \quad\underset{(30 {~J})}{\text { Deer }} \quad \xrightarrow{10 \% \text {transferred}} \quad \underset{(3 {~J})}{\text { \text{Tiger} }}$

Answer

Aquarium is a man made ecosystem (artificial). If an ecosystem possess all physical and biological component, then it is said to be complete. Since aquarium has biotic (plants and fishes) and abiotic component (air, water) required for survival of fishes, so it is an complete ecosystem.

Answer

Tropics are characterised by high temperature and moisture and soil is rich in humus and minerals. As the decomposition rate is regulated by climatic factors, thus optinum temperature and humidity enhance the activity of decomposrs while the dead remain is also available in rich amount, which supports the faster rate of decomposition in the tropics.

Answer

Two human activities that interfere with carbon cycles are

(i) Rapid deforestation and

(ii) Massive burning of fossil fuel for energy and transport.

Answer

Flow of energy in an ecosystem is always unidirectional, i.e., energy flow in one way and is noncyclic, like

$$ \underset{\text { Ist Trophic level }}{\text { Plants }} \quad \longrightarrow \underset{\text { Ilnd Trophic level }}{\text { Herbivore }} \quad \longrightarrow \underset{\text { Ill rd Trophic level }}{\text { Carnivore }} \quad \longrightarrow \text { Top carnivore } $$

As the energy content is decreasing from Ist trophic level to next trophic level and so on, thus the energy cannot pass in reverse direction.

Answer

On the basis of nutrition, organisms are classified as autotrophs and heterotrophs. Autotrophs are further categorised into photoautotrophs and chemoautotrophs, while heterotrophs may be parasite pred or a saprophyte etc.

Microbes are saprotrophs and derive nourishment or energy from dead organic matter or remain of plants and animals and this digestion is extracellular.

Answer

Tiger represents an important part of the food web and helps in maintaining the ecological stability. As a carnivore, it keeps a check on the unlimited growth of herbivoresing the and also removes sick or old animlas from the population. It also acts as an indicator of the forest’s health.

Saving the tiger means we save the forest. Since, tiger (top carnivore of the food chain) cannot live in places where trees or herbivores, that it hunts, have vanished and in turn secure food and water for all.

Answer

In an ecosystem, flow (transfer) of energy is unidirectional. As energy trapped in Ist tropic level, only $10 \%$ of energy is transferred to next trophic level.

$\underset{\text{(Biomass 10 kg)}}{\text{Deer}} \xrightarrow{\text{Energy lost in process of respiration and other vital activitiees 90 \% i.e, 9 kg}}\underset{\text{ (1 kg)}}{\text{Lion}} $

Answer

Primary productivity is the rate at which primary producers (plants) capture and store solar radiation to form chemical energy. Primary production depends upon producer (green plant) which are variable in different ecosystem.

So, primary productivity varies from ecosystem to ecosystem.

Answer

Sometimes climax remains in a particular seral stage without reaching to the climax because during ecological succession any change in abiotic and biotic component may affect the particular seral stage, leading to preclimax stage before the climax is achieved.

This type of condition occurs presence of seeds and other propagules. This secondarily based area may be invaded by moss or exotic weeds thus exhibiting succession seriously and the climax community is never regenerated. in the case of natural calamities like-fire landslide, floods, change in soil texture.

Answer

An ecosystem comprises with biotic and a biotic component. A biotic component include light, air, water, temperature, humidity etc, while biotic factor comprises all living organism. Absence or limited availability of any component (either abiotic or biotic) makes an ecosystem incomplete like the profundal and benthic zone in an aquatic ecosystem.

Answer

Ecological pyramids are the graphical representation of ecological parameter. These are characterised by pyramid of number, pyramid of mass and pyramid of energy in an ecosystems. Assumption of a simple food chain is the major shortcoming of ecological pyramids.

If we do not accomode food web, a clear position of or trophic levels of an organisms cannot be given. Saprophytic organism are not given any place in the ecological pyramid, though they are the important component in an ecosystem.

Answer

Humification is the process of decomposition of soil that leads to accumulation of a dark-coloured amorphous substance called humus. Humus are highly resistant to microbial action and under goes dicomposition at a very slow rate.

Mineralisation is the process by which the humus is further degraded by microbes and inorganic nutrients or minerals are released back into the substratum.

Answer

(i) First trophic level (producers) - Plants

(ii) Second trophic level (primary consumers) - Herbivores

(iii) Third trophic level (secondary consumers) - Carnivores

(iv) Fourth trophic level (tertiary consumers) - Top carnivores

Answer

Decomposition of dead remain or matter of animal and plant is carried out by microorganisms like bacteria, fungi etc. The growth rate of these decomposers is affected by abiotic factors like temperature, humidity, $\mathrm{pH}$ of soil and light etc.

The soil pH affect the composition of acidophilic and basophilic microorganisms. In absence or presence of oxygen aerobic and anaerobic processes occurs.

In presence of oxygen, complete degradation of substance occureds while in absence of oxygen, there will be an incomplete degradation. Similarly, at high temperature microbes can not grow optimally but high or low temperature favours the growth of stress tolerant microorganisms.

Answer

(a) Farmer’s expression for his crop harvestation (a) he has harvested 10 quintal of wheat, (b); He has harvested 10 quintals of wheat in one acre of land (c), six, months after sowing mean one and the same thing. Because crop an artificial ecosystem can be prepared with inclusion of bitoic and abiotic component in a given area.

Here abiotic components like water, is given by the farmer, while climatic factor like light, humidity, air is supplied naturally. The living component is wheat plant, which are obtained on harvestation by farmer.

Answer

In term of ecsosystem dynamics, flow of energy takes place from one trophic level to the next trophic level and occured in unidirectional way. About $50 \%$ of solar energy incident over earth is present in Photosynthetic Active Radiation (PAR) and only 2-10 % of this PAR is utilised by green plants to form chemical energy (Gross Primary Productivity) (GPP).

Out of $90 \%$ of gross primary productivity is lost maximum during respiration and other vital activities. GPP utilised by plants in respiration minus respiration losses is the net primary productivity and is available to the organism of next trophic level (herbivore and decomposers) for consumption.

Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis.

So nature tend to increase gross primary productivity through supporting the large number of plant (producers) in an ecosystem.

Net primary productivity is the available biomass for the consumption to heterotrophs (human and animals) man tries to increase net primary productivity by cultivating food and other crops which the depend on to fullfil their needs.

Formula to genrate NPP is

$$ \mathrm{NPP} \rightleftharpoons \mathrm{GPP}-\mathrm{R} $$

Answer

Primary Productivity can be defind as the rate at which primary producers (Green plants) traps and store solar radiation in form of biomass. This is measured in term of weight $\left(\mathrm{g}^{-2}\right)$ and in term of energy ( $\mathrm{Kcal} \mathrm{m}^{-2}$ ) per year in given time.

So, primary productivity varies from ecosystem to ecosystem and the ecosystem which possess more producer will be more productive in term of primary productivity. So young forest grow quicker than older, mature forest and are more productive in terms of productivity. The shallow polluted lake and alpins meadow will be less productive because of less number of producers and high amount of dead matter.

Answer

Ecological Pyramids An ecological pyramid is a graphical representation of an ecological parameter as number of individual present in various trophic level of food chain.

Properties of ecological pyramid

(i) The trophic structure of an ecosystem is represented in the form of ecological pyramids.

(ii) The base of each pyramid represents the producers or the first trophic level, while the apex represents tertiary or top level consumer.

The three types of ecological pyramids are

(a) Pyramid of number shows relationship between producers and consumers in an ecosystem in terms of numbers. It may be inverted or upright pyramid.

Trophic Level $\quad \quad \quad \quad \quad \quad \quad$ Number of Individuals

Pyramid of numbers in a grassland ecosystem

(b) Pyramid of biomass shows relationship between producers and consumers in an ecosystem terms of biomass. It can be

(a) Upright, e.g., in case of grass land ecosystem.

(b) Inverted, e.g., in case of pond ecosystem.

Trophic Level

Dry Weight $\left(\mathrm{kg}-\mathrm{m}^{-2}\right)$

Inverted pyramid of biomass.

Small standing crop of phytoplankton supports large standing crop of zooplankton

(c)Pyramid of energy is the relationship between producers and consumers in an ecosystem in terms of flow of energy. It is always upright because energy is always lost as heat at each step.

An ideal pyramid of energy. Observe that primary producers convert only $1 \%$ of the energy of the sunlight available to them into Net Primery Productivity.

Answer

Ecological pyramids are graphical representations of the relationship between organisms of different trophic levles that can be expressed in terms of number, biomass or energy.

In most ecosystems, the pyramid of number is upright, i.e., producers are more in number than the herbivores and herbivores are more in number than the carnivores. But, the pyramid of number may be inverted as in a forest ecosystem, where the number of insects (primary consumers) are greater than the number of trees (producers).

The pyramid of biomass is upright, generally, as the biomass of producers is more than biomass of herbivores and that of herbivores is more than biomass of carnivores. But, it is inverted in ecosystems like sea ecosystem, where the biomass of fishes (primary consumers) exceeds than phytoplankton (producers)

Answer

Food Chain and Food Web A straight line sequence of ‘who eats whom’ or eating and being eaten in an ecosystem is called a food chain. A network of cross connecting food chains involving producers, consumers and decomposers are termed as a food web.

Lion, Tiger - Top carnivore (Top tropic level)

Spider, cockroach, lizard, wolf, snake, toad, fish, crane - Secondry Consumer (Illrd trophic level).

Crustaceans, grasshopper, deer, mouse, squirrel, rabbit, elephant, goat - Primary Consumer (Illnd trophic level).

Phytoplankton, algae, Hydrilla, maize plant, Nymphaea, Spirogyra - Producers (Ist trophic level).

Answer

According to second law of thermodynamics every activity involving energy transformation (According to first law - energy can be transferred and transformed) is accompanied by dissipation of energy as heat and only a part of it is used in building up tissues in an organisms.

This trapped energy as biomass is transferred to next trophic level. According to Lindman law only $10 \%$ of the stored energy is passed from one trophic level to successive trophic level.

Answer

(a) Removal of all producer reduce primary production in the ecosystem. Hence, no biomass will be available to the successive/higher trophic level or heterotrophic organisms.

(b) Elimination of all organisms of herbivore level results into an increase in primary productivity and biomass of producer and carnivorous animal will not survive due to inavailability of food herbivores.

(c) Removal of top carnivores also disturb the ecosystem as it will result in huge increase in number of herbivores which will finish plants (producers) creating desertification.

Answer

Aquarium and farm house, are artificial or man made ecosystem. In artificial ecosystem biotic and abiotic component are maintained artificially like cleaning, feeding and supply of oxygen to fishes in aquarium and irrigation in crop or farm house.

While abiotic and biotic component of natural ecosystem are maintained naturally like nutrient cycle, self sutainability, prevention of soil erosion, pollutant absorption and reduction of threat to global warming (ecological servicer), etc.

Answer

During ecological succession biodiversity increase or changes from pioneer to climax stages.

Following are the effects of ecological succession

(a) It leads to changes in vegetation that affects food and shelter for various types of animals.

(b) As succession proceeds, the numbers and types of plants, animals and decomposers also change.

(c) At any time during primary or secondary succession, natural or human induced disturbances (fire, deforestation, etc.) can convert a particular seral stage of succession to an earlier stage.

Also such disturbances can create new conditions that encourage some species and discourage or eliminate other species of producer, consumers and decomposers.

(d) Over the time, they are succeeded by bigger plants and, ultimately a stable climax forest community is attained.

(e) The climax community remains stable if the environment remains unchanged.

(f) With time, the xerophytic habitat may gets converted into a mesophytic one.

Answer

Biogeochemical Cycle

(i) The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling or biogeochemical cycles (Bio-living; geo-including air, water and rocks).

(ii) Nutrient cycles are of two types

(a) Gaseous

(b) Sedimentary

(iii) Atmosphere is the reservoir for gaseous type of nutrient cycle (e.g., nitrogen and carbon cycle).

(iv) Earth’s crust is the reservoir of sedimentary cycle (e.g., sulphur and phosphorus cycle).

(v) The function of the reservoir is to meet with the deficit, which occurs due to imbalance in the rate of influx and efflux.

(vi) Environmental factors, e.g., soil, moisture, $\mathrm{pH}$, temperature, etc., regulate the rate of release of nutrients into the atmosphere.

Phosphorus Cycle

Phosphorus cycle is an example of sedimentary nutrient cycle since, it moves from land and sedimented at the bottom of the seas, then back to land again.

The natural reservoir of phosphorus is earth’s crust. Rock contains phosphorus in the form of phosphates. By weathering and soil erosion, phosphates enter streams, rivers and then to oceans.

With great movements of the crustal plates, sea floor is uplifted and phosphates become exposed on the drained land surfaces. From here, weathering over long periods of time releases phosphates.

From rocks, minute amount of these phosphates dissolve in soil and are absorbed by the roots of the plants.

Herbivores and other animals obtain this element from plants when they consume plants as their food.

The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria thus releasing phosphorus.

A simplified model of phosiphorus cycling in a terrestrial ecosystem

Answer

Production/Respiration ratio $(P / R)$ ratio It shows the relationship between gross production and total community respiration where $P / R=1$ a steady state community result.

This result may be instantaneously daily one or over a longer period. If $P / R$ is persistantly greater or less than/then organic matter either accumulates or is depleted respectively.