BIOLOGY 5 Marks Questions

An ecological pyramid is a graphical representation of various ecological parameters such as the number of individuals present at each trophic level, the amount of energy, or the biomass present at each trophic level. Ecological pyramids represent producers at the base, while the apex represents the top level consumers present in the ecosystem. There are three types of pyramids:

1. Pyramid of numbers
2. Pyramid of energy
3. Pyramid of biomass

Pyramid of numbers: It is a graphical representation of the number of individuals present at each trophic level in a food chain of an ecosystem. The pyramid of numbers can be upright or inverted depending on the number of producers. For example, in a grassland ecosystem, the pyramid of numbers is upright. In this type of a food chain, the number of producers (plants) is followed by the number of herbivores (mice), which in turn is followed by the number of secondary consumers (snakes) and tertiary carnivores (eagles). Hence, the number of individuals at the producer level will be the maximum, while the number of individuals present at top carnivores will be on the other hand, in a parasitic food chain, the pyramid of numbers is inverted. In this type of a food chain, a single tree (producer) provides food to several fruit eating birds, which in turn support several insect species.
Pyramid of energy: An energy pyramid is a graphical model of energy flow in a community. The different levels represent different groups of organisms that might compose a food chain. From the bottom-up, they are as follows: Producers bring energy from nonliving sources into the community.
Pyramid of biomass: A pyramid of biomass is a graphical representation of the total amount of living matter present at each trophic level of an ecosystem. It can be upright or inverted. It is upright in grasslands and forest ecosystems as the amount of biomass present at the producer level is higher than at the top carnivore level. The pyramid of biomass is inverted in a pond ecosystem as the biomass of fishes far exceeds the biomass of zooplankton (upon which they feed).east.

Decomposition is the breakdown of dead or waste organic matter by micro-organisms. Decomposition is both physical and chemical in nature. Process involved in decomposition are - fragmentation, catabolism & leaching.

• Fragmentation- The process primarily due to the action of detritus feeding invertebrate (detritivores) causes it to break into smaller particles. The detritus gets pulverized when passing through the digestive tracts of animals. Due to fragmentation, the surface area of detritus particles is greatly increased.
• Catabolism- Enzyme degradation of detritus into simpler organic substances by bacteria and fungi.
• Leaching- The process by which nutrients, chemicals or contaminants are dissolved & carried away by water, or are moved into a lower layer of soil.

Various inorganic and organic substances are obtained by decomposition. Inorganic substances are obtained in the process of mineralization while organic substances are obtained in humiflcation. A dark coloured amorphous substance called humus is formed by decomposition. Humus is highly resistant to microbial action & undergoes extremely slow decomposition. It serves as a reservoir of nutrients.

Energy enters an ecosystem from the Sun. Solar radiations pass through the atmosphere and are absorbed by the Earth's surface. These radiations help plants in carrying out the process of photosynthesis. Also, they help maintain the Earth's temperature for the survival of living organisms. Some solar radiations are reflected by the Earth's surface. 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. The remaining 90% of this energy is used by plants for various processes such as respiration, growth, and reproduction. Similarly, only 10% of the energy of herbivores is transferred to carnivores. This is known as ten percent law of energy flow.

The components of an ecosystem can be divided into two categories: biotic and abiotic.

1. Biotic components:

1. Producers- Green plants which can synthesize their own food.
2. Consumers- They do not synthesize their food. They may be,

• Primary consumer/ herbivores - consuming plants as food.
• Secondary and tertiary consumers or carnivores- They feed on either herbivores or carnivores.

3. Decomposers- These organisms breakdown the dead bodies or waste products of plants and animals into simpler inorganic compounds.

2. Abiotic components:

1. Climatic components.

• Light
• Temperature
• Wind
• Atmospheric gases
• Rain
• Atmospheric humidity

2. Soil factors

• Organic materials
• Minerals
• Soil, water
• Soil air

3. Topographic factors

• Altitude
• Direction and steepness slope

1. Graphical representation of the relationship among the organisms at different trophic level.

Pyramid of Energy	Pyramid of Bio Mass	Pyramid of Numbers
Shows transfer of Energy from one tropic level to other	Shows transfer of amount of food/ biomass from one tropic level to other	Pyramid of Numbers shows numbers of organism at each tropic level.
Always upright	Mostly upright but can be inverted	Mostly upright can be inverted.

2. It does not accomodate the food web/does not take into account the same species belonging to two or more tropic levels , Saprophytes are not given any place.

1. Productivity - conversion of inorganic substances into organic material with the help of radiant energy/sunlight by the autotrophs/producers. (phytoplankton, algae, floating, submerged plants)

Decomposition - decomposers (fungi, bacteria, flagellates) breakdown dead decayed organic matter into simpler compounds.

Energy Flow - Unidirectional movement of energy towards higher trophic levels (producer to consumer ) and its dissipation and loss as heat to the environment

Nutrient cycle - Mineralisation of dead matter to release them back for reuse of autotrophs.

2. Grazing food chain/detritus food chain.

Purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, provide wild life- habita, maintain biodiversity, pollinate crops, provide storage site for carbon, provide aesthetic cultural and spiritual value recreation, climate regulation.

1. Purify air/purify water.
2. Mitigates drought/mitigates flood.
3. Cycle nutrients.
4. Generate fertile soil.
5. Provide wildlife habitat.
6. Maintain biodiversity.
7. Pollinate crop.
8. Provide storage site for carbon.
9. Provide aesthetic value/provide cultural value/provide spiritual value.
10. Provide stable food chain.
11. Provide economically useful forest produces.

Age pyramids show age distribution of males and females in a combined diagram.
The shape of the pyramid reflects the growth status of the population whether it is growing or stable or declining.
Pyramids also indicate the ratio of pre-reproductive, reproductive and post-reproductive individuals in a population.
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Planning of health/education/transport/infrastructure/finance/food/employment can depend on the age-pyramid analysis of a population.

1. Lichens on a bare rock, acids to dissolve rock, soil formation-bryophyte to hold the soil, retention of water-grass, scrubs and trees.

1. Primary productivity: amount of biomass/organic matter produced per unit area over a time period by the plant during photosynthesis.

Factors: availability of nutrients/quality of light available/availability of water/temperature of the given place/type of plant species of the area/photosynthetic capacity of the plants.

2. Oxygen increases rate of decomposition.

Chemical: decomposition is slowwhen chitin and lignin are present.

Fragmentation: Breakdown of detritus into smaller particles.
Leaching: Water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
Catabolism: Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.
Humification: It leads to the accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
Mineralization: The humus is further degraded by some microbes and release inorganic substances by this process.

Phosphorus a major constituent of biological membrane/ nucleic acids/ cellular energy transfer system, Many animals need it for making shells/ bones and teeth, the natural reservoirs of phosphorous is rock, which contains phosphorous in the form of phosphate reserves, on weathering minute amount of phosphate dissolve in soil solution, and absorbed by roots, Herbivores, obtain these elements from plants waste products and dead organism, decomposed by phosphate-solubilising bacteria, releasing phosphorus. Marks can also be awarded for the steps given in the proper sequence, with other details,

1. Succession that occurs in wetter areas and the successional series progress from hydric to the mesic condition is called the hydrarch succession.
2. The species that invade a bare area are called the pioneer species while the climax community is established over the process of succession and it is in near equilibrium with the environment. The pioneer species of hydrarch succession are phytoplankton and the climax community is the xerophytic forest. The pioneer species of xerarch succession are lichens and the climax community is the mesophytic forest.
3. In secondary succession the species that invade depend on the condition of the soil, availability of water, the environment and the seeds and propagules already present. Since the soil is in existence already, the rate of secondary succession is faster than the primary succession, in which the soil is gradually produced.

This entire sequence of communities that successively change in a given area are called sere (s). All the biotic and abiotic factors play crucial role in this transition process and thus enable a community to reach the climax. If biotic and abiotic factors are not supportive enough for climax then the community may remain in a particular seral stage without reaching the climax. Presence of sparse vegetation at table top mountain can be one example of a community in seral stage. The community at the table top mountain may be in a stage in which only ferns and mosses may be present. In due course of time, it would pave way for higher plants.

1. Food chain is the sequence of populations or organisms of an ecosystem through which food and the energy contained in it passes to each member and ultimately reaches last member of a sequence. It is a feeding chain of organisms in an ecosystem.
2. Grass is the producer which captures the solar energy and feeds the energy into food chain through photosynthesis. Goat is the primary consumer while man is secondary consumer.
3. There are mainly two types of food chain-

1. Grazing Food Chain (GFC) - Begins with producers.
2. Detritus Food Chain (DFC) - Begins with dead organic matter and decomposers.
3. Jeremy is keen and vigilant towards his studies practical applications.

S.No.	Column I	S.No.	Column II
(A)	Pyramid of energy	(iv)	Alwayes upright
(B)	Pyramid of biomass	(iii)	Upright/ inverted
(C)	Climax community	(ii)	Mesic forest
(D)	Hydrarch succession	(i)	Phytoplantons

In any ecosystem, the number of trophic levels can go up to a maximum of five and in that case the food chain will look like following:
Producer → Primary Consumer → Secondary Consumer → Tertiary consumer → Quaternary Consumer.
In a food chain, only 10% of the total amount of energy is passed on to the next trophic level from the previous trophic level. So, there is a decrease in the amount of energy available at the successive trophic levels. As we move higher up in the food chain the amount of energy diminishes to a level at which it cannot sustain any trophic level, thereby limiting the number of trophic levels.

1. Earthworms are known as detritivores as they breakdown detritus (dead remains of plants and animals) into smaller particles. Earthworms are often called farmer's friend.
2. Fragmentation is the first step in the process of decomposition. It is the process by which detritivores (e.g, earthworm) breakdown detritus in smaller particles.
3. The steps involved in decomposition are fragmentation, leaching, catabolism, humification and mineralisation.
4. Arun is very alert, curious and had scientific attitude.

The second law of thermodynamics says that the entropy of an isolated system never decreases; such a system will spontaneously proceed towards thermodynamic equilibrium. The configuration with maximum entropy is in thermodynamic equilibrium.An ecosystem needs a constant supply of energy to synthesize the molecules they require. In an ecosystem, the energy flows is always unidirectional because as per the law of thermodynamics; reverse flow of energy would put the system in non-equilibrium.
We have seen that energy from the sun is trapped by producers and producers function as conduit to supply energy to the next trophic levels. Energy never flows from a higher trophic level to a lower trophic level because it cannot be in tune with the law of thermodynamics.

Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). Net primary productivity is the available biomass for the consumption to heterotrophs (herbivores and decomposers).

• Nature tends to increase the gross primary productivity so that it can utilise much of the solar energy and convert it into food.
• Man tends to increase the net primary productivity so that sufficient food is provided to the growing human population.

• A young forest can be assumed as a community which is yet to reach climax. This means the density of trees is less in this forest. Less number of trees means a lower primary productivity.
• A natural old forest can be assumed as a community which has reached its climax. Most of the plants must be big tress with thick foliage. This will result in a higher level of primary productivity.
• A shallow polluted lake may not have much of producers. Pollution must have taken its toll on the ecosystem in this pond. Thus, this pond may be having very low primary productivity.
• An alpine meadow is full of grasses with little or no tree. Less number of trees means low primary productivity.
• In the context of above discussions, it can be said that the natural old forest has the highest level of primary productivity.

1. He occupies three trophic levels in three different food chains.
2.  

1. Plants (vegetables) Pragyan.
2. Plants Insects Hen Egg Pragyan.
3. Plants → Hen Egg Pragyan.

3. Food chain-

1. gives him maximum energy. This is because plants are autotrophs, i.e. they produce food through the process of photosynthesis and according to 10% law only 10% energy is passed on to next trophic level

4. Pragyan is a sincere child, who possesses scientific attitude towards his daily life.

1.	A community plus its physical environment.	d.	Ecosystem
2.	Study of the interactions of organisms with each other and with the physical environment.	a.	Ecology
3.	All populations that are found in a particular area.	c.	Community
4.	All members of the same species that inhabit a particular area.	b.	Population

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:

1. Carbon-fixation Huge amount of co, 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.
2. Release of oxygen by the producers as a byproduct in the process of photosynthesis, improves the air quality and supports life on earth.
3. 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.
4. Nutrient cycling There is no depletion of nutrients, but the same are repeatedly circulated.

2. Economic Value:

1. Ecosystem services provide certain economical important products also. These include timber, paper, rubber, wax, medicines, cosmetics, resins, etc.
2. 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:

1. Natural ecosystems are a source of spiritual, cultural and aesthetic values.

1. Productivity: Conversion of inorganic into organic material with the help of solar energy by the autotrophs.
2. Energy flow: Unidirectional movement of energy towards higher trophic level (and its dissipation and loss as heat to the environment).
3. Decomposition: Fragmentation, leaching, catabolism, humification, mineralization by bacteria, fungi and flagellates (abundant at the bottom of lake).
4. Nutrient cycling: Decomposition of dead matter to release the nutrients back to be re-used by the autotrophs.

Food chain in aquatic ecosystem (lake):
Phytoplanktons → Zooplanktons → Small fish → Big fish (Any other appropriate example).

Ecomposition It is the process of breaking down of complex organic matter into inorganic substances like water, carbon dioxide and nutrients by decomposers. Detritus is the raw material for decomposition. It includes dead remains of plants (leaves, bark and flowers) and animals including faecal matter.Different steps involved in the process of decomposition are:

1. Fragmentation: It is process of breakdown of detritus into smaller particles by detritivores (e.g. earthworm).
2. Leaching: It is the process by which water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
3. Catabolism: It is the process of degradation of detritus into simple organic material by the action of bacterial and fungal enzymes and then their further conversion into simpler inorganic compounds.

3. Humification: It is a process that leads to accumulation of a dark coloured amorphous and colloidal substance called humus, which is highly resistant to microbial action and undergoes decomposition at a very slow rate. Being colloidal in nature, it serves as a reservoir of nutrients.
4. Mineralisation: It is process of degradation of humus by microbial action and release of inorganic nutrients

1. Pyramid of biomass can be both upright and inverted. This can be understood from the examples given below:

1. The pyramid of biomass in a pond ecosystem is inverted. Because, the sum total of the weight of phytoplankton (producer) is far less than a few fishes feeding on them, at higher trophic levels.

2. Pyramid of biomass in a forest ecosystem is upright because producers are more in biomass than primary consumers. Primary consumers are more than secondary consumers and secondary consumers are more than tertiary consumers (top). Pyramid of energy is never inverted, (i.e. it 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. Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time.

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2. Pyramid of energy: It represents total energy of the organisms in each trophic level. Pyramid of energy is always upright, i.e. it can never be inverted, because when energy is transferred from a particular trophic level to the next trophic level some energy is always lost as heat at each step.

Some important points about ecological pyramids are given below:

1. A trophic level represents a functional level, not a species as such.
2. A given species may occupy more than one trophic level in the same ecosystem at the same time, e.g. a sparrow is primary consumer, when it eats seeds, fruits, peas, etc., and a secondary consumer when it eats insects and worms.
3. In most ecosystems, all the pyramids of number, biomass, energy are upright, i.e. producers are more in number and biomass than the herbivores and herbivores are more in number and biomass than carnivores.
4. Energy at lower trophic level is always more than higher rrophic level. However, there are few exceptions to this generalisation also.
5. Pyramid of biomass in sea is generally invented because the biomass of fishes far exceeds that of phytoplankton.

1. Refer to Fig. 14.5 in the text.
2. The nutrients are cycled such that they are brought back to soil from where producers can taken them.

1. The four component in an ecosystem functions as unit as follows:

1. Productivity: This is represented by the autotrophic phytoplanktons same algae and the floating and marginal plants found at the edges.
2. Energy flow: Represented by water in the pond with all the dissolved organic and inorganic substances, the solar energy and other climate conditions that regulate the rate of function of the pond. The consumers are represented by the 200 planktons and bottom dwelling forms.
3. Decompositions: The decomposers are the fungi bacteria and flagellates abundant at the bottom of the pond.
4. Nutrient cycling: The pond ecosystem converts inorganic material into organic material using solar energy by the autotrophs. The autotrophs are eaten up by hetrotrophs, decomposition and mineralisation of dead matter for resuse by autotrophy is done by decomposers.

2. Grazing food chain exists in a pond.

1. Structure of a pyramid of number is given below:

2. Differences between pyramid of number and biomass in a tree ecosystem are:

S. No.	Pyramid of biomass in a tree ecosystem	Pyramid of number in a tree ecosystem
1.	The biomass ol the single tree is much more than the biomass of insects.	The base is much smaller with a single tree compared to the thousands of insects.
2.	The pyramid looks upright with these two levels.	The pyramid looks inverted with these two levels.
3.	The biomass of birds is much more than those of insects.	The number of birds feeding on the insects is less than that of insects.

Ecological Succession:

1. The sequential, gradual and predictable changes in the species composition in an area are called succession or ecological succession.
2. The entire sequence of communities that successively changes in a given area are called sere(s).
3. The individual transitional communities are termed as seral stages or seral communities.
4. The community that is in near equilibrium with the environment is called a climax community.
5. The species that invade a bare area are called pioneer species.

The changes that occur in successive seral stages to reach a climax community are:

1. Changes in the diversity of species of organisms.
2. Increase in the total biomass.
3. Increase in the number of species and organisms.

Ecological succession is of two types:

1. Primary succession: It begins in areas where no living organisms ever existed.

Therefore, the establishment of a biotic community is very slow, e.g., newly cooled lava, bare rock, newly created pond or reservoir.

2. Secondary succession: It begins in areas where natural biotic communities have been destroyed, e.g., abandoned farm lands, buried or cut forests. Since soil is available, it is a faster process.

An ecological pyramid is the graphic representation of the number, food/ energy relationship or biomass of the different trophic levels of a food chain at a given time.

1. In general the pyramids of number, of biomass and of energy are upright.
2. It is because the producers are more in number and biomass than the herbivores and the herbivores are more in number and biomass than the carnivores.
3. The pyramid of energy in any ecosystem is always upright because energy at the producer level is the highest and decreases at successive higher trophic levels; when energy flows from one trophic level to the next, higher trophic level, some amount of energy is lost as heat and only 10% of the energy is transferred.

The four components of an ecosystem function as a unit in a pond in the following manner:

1. Productivity: The producers include phytoplanktons, some algae and the floating, submerged and marginal plants, they carry out photosynthesis and produce organic food and release oxygen.
2. Decomposition: The decomposers are the fungi bacteria and some flagellates, which are abundant at the bottom of the pond.
3. Energy flow: There is unidirectional flow of energy as follows.

Producers → Zooplanktons → free swimming organisms (fish) → bottom dewellers.

4. Nutrient cycling: The organic matter produced by autotrophs is consumed by consumers and the decomposers carry out humification and mineralisation of the dead organic matter for reuse by plants. Grazing food chain operates in a pond.

Biogeochemical cycle: The movement of nutrients through various elements of ecosystem is called nutrient cycling or biogeochemical cycle. Nutrient cycling ensures that nutrients are never lost form the ecosystem. They keep on getting replenished in the reservoirs in ecosystem,
Role of reservoir: Whenever there is an imbalance between efflux and influx of a particular nutrient, there can be deficit of that nutrient. The reservoir counters this deficit by supplying the required nutrient.
Phosphorus cycle: The reservoir of phosphorus is located in the earth’s crust. Phosphorus cycle is one of the examples of sedimentary cycle. Rocks are the natural reservoirs of phosphorus. Phosphorus is present in rocks in the form of phosphates. During weathering of rocks, minute quantities of phosphates get dissolved in soil solution.
Phosphates in soil solution are absorbed by roots of plants. The primary and secondary consumers get phosphates from plants.
When dead organisms are decomposed by phosphates-solubilising bacteria, phosphorus is released back to the environment.

The relation between producers and consumers in an ecosystem can be graphically represented in the form of a pyramid called ecological pyramid.

• Structure: The base always represents the producers or the first trophic level and the apex represents top level consumer or the last trophic level.
• Ecological pyramids are of three types:

1. Pyramid of number: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of number called pyramid of number.

2. Pyramid of biomass: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of biomass called pyramid of biomass.

It can be:

1. Upright, e.g., in case of grassland ecosystem;
2. Inverted, e.g., in case of pond ecosystem.

3. Pyramid of energy: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid, in terms of flow of energy called pyramid of energy. It is always upright because energy is always lost as heat at each step.

1.  

• The change is orderly and sequential; it is also parallel with the changes in the physical environmental The gradual and fairly predicatable change in the species composition of a region, is called ecological succession.
• During succession, some species colonisc an area and their populations become more numerous, whereas populations of some other species decline or even disappear.
• In the successive stages, there is a change in the diversity of species of organisms, increase in the number of species and organisms and an increase in the biomass.

2.  

• Climax community refers to the community that gets established finally in succession and is in equilibrium with the environment.
• Sere refers to the entire sequence of communities that successively change in a given area.

3. Differences:

S.No.	Primary Succession	Secondary Succession
(i)	The ecological succession that takes place in a region, where no life existed before, is called primary succession.	The ecological succession that occurs in a region where natural biotic communities existed before, but got wiped out completely, is called secondary succession.
(ii)	It is a slow process, as suitable substratum/ soil has to be formed e.g. sucession on a bare rock or a newly formewd pond.	It is comparatively faster as the soil or sediment is already present. e.g. succession on a fire.devaStated forest or land that has been floaded.

An ecological pyramid is a graphic representation of an ecological parameter like number of individuals present in various trophic levels of a food chain with producers forming the base and top carnivores forming the tip.There are three types of ecological pyramids:

1. Pyramid of numbers.
2. Pyramid of biomass.
3. Pyramid of energy.

Limitations:

1. It assumes that food chains are simple. Simple food chains do not occur in nature. Instead food webs are present.
2. A simple species may operate at two or more trophic levels. Ecological pyramids have no method of accommodating such cases.

1. Carbon dioxide.
2. Burning of fossil fuels-petrol/ diesel, in the vehicle produces carbon dioxide.
3. Carbon dioxide is a green house gas and absorbs the infrared radiation emitted by the earth; this results in an increased mean temperature of the atmosphere, also called global warming.
4. Melting of ice caps.
5. Measures to reduce global warming include:

• Reducing the use of fossil fuels to reduce emission of greenhouse gases.
• Reducing deforestation and planting more trees.

The three ecological pyramids that are usually studied are:

1. Pyramid of number.
2. Pyramid of biortiass.
3. Pyramid of energy.

• Any calculations of energy content, biomass, or numbers has to include all organisms at that trophic level. No generalisations we make will be true if we take only a few individuals at any trophic level into account. Also a given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.
• In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and 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 at a higher level.

1.  

1. The biogeochemical cycle shown is carbon cycle.
2. Volcanic activity and mining or microbial decomposition of organic matter

2. Due to large scale deforestation, the flow of carbon in the environment will be discribed because plants ale the major consumers. which utitlise carbon during photosynthesis. This would lead to accumulation of carbon in the atmosphere.
3. Increase in level of carbon in the atmosphere will result in greenhouse effect. This will lead to heating of earth's surface and finally to global warming. The rise in temperature results in odd climatic changes called EI Nino effects, which are harmful for the environmen

1. The cellular components, where phosphorus is abundant include:

• Biological membranes.
• Nucleic acids.
• Energy transfer systems (like ATP and GTP).

2. The natural reservoir of phosphorus is rock.
3. Phosphorus cycle:

• The rocks contain phosphorus in the form of phosphates.
• During weathering of rocks, some amount of phosphates dissolve in the soil solution and plants absorb them.
• Herbivores and other carnivores obtain it directly or indirectly, plants.
• The phosphate-solubilising bacteria release phosphorus back to the soil, when they decompose the dead and decaying organic matter.

Refer to Fig. 14.5 in the text,

1. The gradual and fairly predictable change in the species composition of a given area = 1. During succession some species colonise an area and their populations become more numerous, where as population of other species decline and even disappear = 1 + 1 = 2.
2.  

	Primary Succession	Secondary Succession
1.	It occurs in an area which has been bare from the beginning.	It occurs in an area which has been denuded recently.
2.	Soil is absent at the time of beginning of primary succession.	Soil is present in the area where secondary succession begins.
3.	Takes a long time for completion.	Takes less time for completion.

1. Difference:

S.No.	Hydrarch Succession	Xerarch Succession
(i)	The ecological successsion that starts in water bodies and prodeeds to mesic conditioins is callled hydrarch succession.	The ecological succession that starts with bare rocks/ xeric condition is called xerarch succession.
(ii)	Phytoplanktons form the pioneer community.	Lichens form the pioneer community.

Similarities:

• They both lead towards mesic conditions.
• The structure and composition undergoes an orderly and sequential change.

2. Role of organisms:

• The roots of plants absorb the minute quantities of phosphates found dissolved in the soil solution.
• The consumers obtain this element either directly (herbivores) or indirectly (carnivores) from plants.
• The organic wastes from the living organisms and the dead organisms are decomposed and the phosphate solubilising bacteria release phosphorus.

Xerarch succession:

1. In the primary xerarch succession, lichens are the pioneer species; they secrete acids to dissolve the rock, facilitating weathering and soil formation.
2. With formation of soil, small plants like bryophytes occupy the area.
3. They are succeeded by bigger plants over a long period of time. After several more seral stages, a stable climax forest community is formed.
4. The climax community remains stable as long as the environment remains unchanged.
5. The xeric habitat is changed into a mesic habitat.

The ratio of gross production and community respiration is called P/ R ratio of a community. This can be 1, less than 1 or more than 1.The P/ R ratio in a pioneer community can be less than or more than 1.
On the other hand, the P/ R ratio of a climax community is 1.
In case of pioneer community, two situations can be present.

1. When gross productivity is more and there are very few consumers then level of respiratory loss would be less. This will result in a P/ R ratio more than 1.
2. When rate of decomposition is more because of large population of decomposers, then gross productivity will be less than respiratory losses. In this case, the P/ R ratio is less than 1.

In case of climax community, P/ R ratio is equal to one. This happens because of stability in the community.
The following graph shows the P/ R ratio at different stages of community succession.
Primary community is shown at the origin, while climax community is shown at extreme right.

Pyramid of numbers: This pyramid shows the number of individuals at different trophic levels. Producers are kept at the bottom of the pyramid; followed by primary consumers, secondary consumers and so on. In most of the cases, the shape of the pyramid bottom heavy. In some cases, this pyramid can be inverted in shape.
Pyramid of biomass: This pyramid shows the biomass (in terms of dry weight) at different trophic levels. Producers are kept at the bottom of the pyramid; followed by primary consumers, secondary consumers and so on. In most of the cases, the shape of the pyramid bottom heavy. In some cases, this pyramid can be inverted in shape.

S.No.	Column I	S.No.	Column II
(A)	Standing crop	(v)	Mass of living matter in a trophic level at a given time
(B)	Standing state	(i)	The amount of mineral nutrients in the soil at a given time
(C)	Climax community	(iv)	In near equilibrium with the environment
(D)	Primary producers	(vi)	Phytoplanktons
(E)	Phosporus cycle	(ii)	Sedementary cycle
(F)	Secondary producers	(iii)	Herbivores and carnivores