Ecosystem Question Answers: NCERT Class 12 Biology

In the aquatic ecosystem (food chain in the pond) food chain, large fishes or frogs are the secondary carnivores.

When the succession initiated with the establishment of pioneer communities in the dry land and on the bare rock is known as xerarch succession and their successional stages are called as xerosere. During the succession, early successional species referred to as pioneer species which are usually characterized by commomly high growth rates, smaller size, and high degree of dispersal and contains high rates of per capita population growth too. On the other hand, late successional species commonly have lesser rates of dispersal and colonization, slower growth rate, they are larger and long- lived.

Among the bryophytes, mosses or lichens are the pioneer species because they are present firstly.  

An ecosystem does not have its own source of energy so they receive the energy from the sun (sunlight or solar radiations). Total incoming solar radiations trapped by the producers (green plants) and change this energy into the chemical energy in the synthesis of food. When the green plants are eaten by the herbivores with the efficiency of energy capture 1% of sunlight, a lot of energy amount is lost as heat or consumed in the metabolic reactions for their growth and the rest is used for the development or reproduction.

Autotrophs are those organisms which prepare their own food. They make organic food from the inorganic matter by their own by the photosynthesis. On the other hand, heterotrophs are those organisms which cannot make their own food and they are dependent on other organism for the food consumption i.e., they feeds on autotrophs.

The edible mushroom is a heterotroph because it cannot make their own food and depends on the other organisms as it does not contain chlorophyll. Mushrooms are saprophytes and contain saprophytic type of nutrition also known as absorptive nutrition, which absorbs the fluid in the form of food through their body surface (food is broken down outside the body and then absorbed).

Oceans are the largest and most diversified type of ecosystem. It occupies nearly 70- 73% of the earth’s surface. Ocean is categorized in the marine ecosystem and contains high salt content. The chief salts are found: chlorides, sulphates, bicarbonates and bromides of sodium, magnesium, calcium and potassium.

Ocean environment is generally classified into many zones on the basis of light penetration (euphotic, disphotic and aphotic zones), on the basis of distance from shore and water depth (littoral or intertidal, neritic or oceanic zone); in the open water (pelagic zone) or bottom (benthic zones). Oceans are least productive because they do not receive enough sunlight that is necessary for the primary productivity. There is insufficient sunlight decreases with the increasing depth. There is deficiency of nitrogen in the ocean that is important for the plants.

Diagram:

Note*: the epipelagic zone is also known as sunlight zone in the ocean environment and is 200m from the surface; is the region where the photosynthesis occurs and thus contains the large biodiversity.

Productivity is the rate of accumulation of energy containing organic matter per unit area per unit time and secondary production involves the repackaging of energy that is previously captured by the producers. In the simple way, secondary productivity is the rate of production of new biomass by the consumers, i.e. the rate at which consumers convert organic material into the new biomass of consumers for its consumption which is the resultant of primary productivity from the producers or the green plants.

The Earth is a closed system with respect to matter and all matter on the Earth cycles. Nutrient cycling (or element cycling) is the movement of elements through both the biotic and abiotic components of the Earth. It is the transport and transformations of elements within and among ecosystems. It involves the incorporation of elements by living organisms and their subsequent release back into the environment through the decomposition. It binds biotic and abiotic parts of ecosystem. The movement of elements through atmosphere, hydrosphere, lithosphere and biosphere is normally termed as Biogeochemical Cycles (bio- living organisms and non- living things and geo means- rocks, air and water etc.).

The ecological succession is broadly classified into two categories and xerarch succession is one of them. Succession initiated with the pioneer communities in dry land and on the rock is termed as xerarch succession. This succession takes place on minimal moisture conditions; it can be Lithosere (on rocky habitat), Pasmmosere (on sandy habitat) or Halosere (on salty soil or in saline water) and eventually these are the examples of xerarch succession.

Self- sustainability and self- sufficiency are the overlapping states of being in which the person or the system or organization needs little or no help from the external sources or from others. It entails the self being enough to fulfill their needs and can maintain itself or we can say independent efforts. 

1. Desert Ecosystem: this biome is driest of all the biomes and covers one fifth of the Earth’s surface. Its surface receives more than twice the solar radiations that are received by the humid regions and lose almost in twice amount of heat at night.
2. As the soil are coarse textured, shallow, rocky or gravely with good drainage and contains no subsurface water. The vegetation bears the characters of xerophytes and are modified in the specific way to conserve water. Examples of flora: succulent plants like cacti, Euphorbia found in hot and dry deserts.  

They all are detritivores or saprophytes which shows detritus food chain. This food chain starts with dead organic material which is eaten by decomposers or detrivores and small carnivores that feeds on these detrivores and then they are eaten by further more organisms and food energy passes from one trophic level to the next one.

For example:

                                   Detritus                              Earthworm                            Sparrow                              Falcon

Ecological pyramid is defined by Charles Elton in 1927, as the graphical representation of the numbers or biomass and accumulated energy at each trophic level in the food chain. The relationship between numbers, biomass and energy flow in biotic community can be represented graphically by ecological pyramids. The base of the each pyramid represents the producers level or first trophic level while the apex represents the next trophic levels like tertiary or high level consumers and other consumer trophic levels in between them.

Ecological succession is the universal process of natural changes in the community structure on the ecological time scale. These communities are dynamic and undergoes continuous change in structure and function; important characteristic is that there structure constantly changes in response to the changing environmental conditions and these changes are directional and sequential. Under the natural conditions or human induced disturbances like volcanism, glaciation, fire, floods, deforestation etc. are the specific or unique stage in the process of succession that would revert back to an earlier stage. 

Stratification in ecology is defined as the vertical layering of a habitat or the arrangements of vegetation in layers. It classifies the layers or strata of vegetation according to their different heights in which plants grow. The vertical stratification of vegetation in the forest is determined by the life forms of the plants, their size, branches or leaves which are influenced by the vertical gradient of light. The following layers are generally represented as in this sequence: forest floor (roots and mosses layers), herbs, shrubs, understory and canopy layers. The given name of layers in question, they are arranged as follows:

Grass (forest floor), Amaranths, shrubby plants and then last will be Teak (tree).

An omnivore that occurs in both grazing food chain and the decomposers food chain is sparrow or crow that feeds on plant food and as well as on decay or dead organisms or we can say organic matter. Omnivores are not highly prevalent and they usually feeds on the species in adjacent trophic levels.

Pitcher plants are known as the carnivorous plants which modified their leaves for the pitfall trapping which is a prey trapping mechanism for the insects and the animals. These plants lure insects and other animals into their cup like cavity or pitchers with the attractive scent. These plants are chlorophyllus and they evolved a mechanism to direct use the energy of sunlight for the preparation of organic food from inorganic matter from their own. They take carbon dioxide and water from the environment and convert them into the glucose and oxygen with the help of sunlight which is absorbed by the chlorophyll and this process is known as Photosynthesis. 

Omnivores remain present in an ecosystem and reproduce as well. Omnivory allows both the trophic level, i.e. producer and primary consumer to flourish. As their presence in the ecosystem will lead to its stability as when there is decrease in plants than they will shift their feeding on the animals and vice versa. Human beings and birds are the two organisms that can occupy more than one trophic level because they feeds on plant food and as well as on decay or dead organisms or we can say organic matter. When they feeds on plants they are said to be herbivores or primary consumers and when they eat on meat or dead organic matter, they are then said to be secondary or tertiary consumers.

In the North East region of the India, during the process of Jhum cultivation, Forests are cleaned up by burning and left for regrowth of the plants after a year of cultivation. In the ecological terms, we explain the regrowth of forest as the secondary succession. Secondary succession is the type of ecological succession where regeneration of communities follows disturbances that has destroyed a community. Sites of this secondary succession may be generated by fire, timber harvest, windstorm, hurricane, flooding, insect outbreak etc. it takes more than hundred years for building a climax community as there is already the presence of organic number occurs.

Ecological succession is the change in the community structure and functions over the period of time. It involves in energy partitioning, species and community structure processes over the time. Ecological succession leads to gradual changes in the flora and the fauna communities in an area following disturbance or the creation of the new substrate. Primary succession is the establishment and development of biotic communities on newly exposed or formed geological substrates. Site of this succession may be generated by volcanic deposition, lava flows, retreating glaciers, landslides, sand dunes, river beds, alluvial sediments etc. On the other hand, Secondary succession is where regeneration of communities follows disturbances that has destroyed a community. Sites of this secondary succession may be generated by fire, timber harvest, windstorm, hurricane, flooding, insect outbreak etc.

Climax stage is achieved quickly in secondary succession as compared to primary succession because there is already some organic number or substratum is present, so it’s easy to build a new community and it takes more than hundred years to build a climax community. In the primary succession, it takes more than thousands of years to build a new climax community as there is no organic number present in soil at beginning. In this process starts from the bare area, i.e. rocks.     

(a) Plants are called as Autotrophs because they fix carbon dioxide.

(b) In an ecosystem dominated by trees, the pyramid (of numbers) is of Inverted type.

(c) In aquatic ecosystems, the limiting factor for productivity is Light.

(d) Common detritivores in our ecosystem are Earthworms.

(e) A major reservoir of carbon on Earth is Oceans.

Decomposition is the process that involves the breakdown of complex organic matter or biomass from the body of dead plants and animals with the help of decomposers into inorganic raw materials such as carbon dioxide, water, and other nutrients. The various processes involved in decomposition are as follows:

(1) Fragmentation: It is the first step in the process of decomposition. It involves the breakdown of detritus into smaller pieces by the action of detritivores such as earthworms.

(2) Leaching: It is a process where the water soluble nutrients go down into the soil layers and get locked as unavailable salts.

(3) Catabolism: It is a process in which bacteria and fungi degrade detritus through various enzymes into smaller pieces.

(4) Humification: The next step is humification which leads to the formation of a dark-coloured colloidal substance called humus, which acts as reservoir of nutrients for plants.

(5) Mineralization: The humus is further degraded by the action of microbes, which finally leads to the release of inorganic nutrients into the soil. This process of releasing inorganic nutrients from the humus is known as mineralization.

Decomposition produces a dark coloured, nutrient-rich substance called humus. Humus finally degrades and releases inorganic raw materials such as CO2, water, and other nutrient in the soil.

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.

Sedimentary cycles have their reservoirs in the Earth’s crust or rocks. Nutrient elements are found in the sediments of the Earth. Elements such as sulphur, phosphorus, potassium, and calcium have sedimentary cycles.

Sedimentary cycles are very slow. They take a long time to complete their circulation and are considered as less perfect cycles. This is because during recycling, nutrient elements may get locked in the reservoir pool, thereby taking a very long time to come out and continue circulation. Thus, it usually goes out of circulation for a long time.

The carbon cycle is an important gaseous cycle which has its reservoir pool in the atmosphere. All living organisms contain carbon as a major body constituent. Carbon is a fundamental element found in all living forms. All biomolecules such as carbohydrates, lipids, and proteins required for life processes are made of carbon. Carbon is incorporated into living forms through a fundamental process called ‘photosynthesis’. Photosynthesis uses sunlight and atmospheric carbon dioxide to produce a carbon compound called ‘glucose’. This glucose molecule is utilized by other living organisms. Thus, atmospheric carbon is incorporated in living forms. Now, it is necessary to recycle this absorbed carbon dioxide back into the atmosphere to complete the cycle. There are various processes by which carbon is recycled back into the atmosphere in the form of carbon dioxide gas. The process of respiration breaks down glucose molecules to produce carbon dioxide gas. The process of decomposition also releases carbon dioxide from dead bodies of plants and animals into the atmosphere. Combustion of fuels, industrialization, deforestation, volcanic eruptions, and forest fires act as other major sources of carbon dioxide.

(d) Decomposers

Decomposers include micro-organisms such as bacteria and fungi. They form the largest population in a food chain and obtain nutrients by breaking down the remains of dead plants and animals.

(b) Zooplankton

Zooplankton are primary consumers in aquatic food chains that feed upon phytoplankton. Therefore, they are present at the second trophic level in a lake.

(a) Herbivores

(b) 50%

Out of total incident solar radiation, about fifty percent of it forms photosynthetically active radiation or PAR.

 (a) Grazing food chain and detritus food chain

(b) Production and decomposition

(c) Upright and inverted pyramid

(d) Food chain and Food web

(e) Litter and detritus

(f) Primary and secondary productivity

An ecosystem is defined as an interacting unit that includes both the biological community as well as the non-living components of an area. The living and the non-living components of an ecosystem interact amongst themselves and function as a unit, which gets evident during the processes of nutrient cycling, energy flow, decomposition, and productivity. There are many ecosystems such as ponds, forests, grasslands, etc.

The two components of an ecosystem are:

(a) Biotic component: It is the living component of an ecosystem that includes biotic factors such as producers, consumers, decomposers, etc. Producers include plants and algae. They contain chlorophyll pigment, which helps them carry out the process of photosynthesis in the presence of light. Thus, they are also called converters or transducers. Consumers or heterotrophs are organisms that are directly (primary consumers) or indirectly (secondary and tertiary consumers) dependent on producers for their food.

Decomposers include micro-organisms such as bacteria and fungi. They form the largest population in a food chain and obtain nutrients by breaking down the remains of dead plants and animals.

(b) Abiotic component: They are the non-living component of an ecosystem such as light, temperature, water, soil, air, inorganic nutrients, etc.

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:

(a) Pyramid of numbers

(b) Pyramid of energy

(c) 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 least.

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 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).

It is defined as the amount of organic matter or biomass produced by producers per unit area over a period of time.

Primary productivity of an ecosystem depends on the variety of environmental factors such as light, temperature, water, precipitation, etc. It also depends on the availability of nutrients and the availability of plants to carry out photosynthesis.