Here is a compilation of essays on ‘An Ecosystem’ for class 6, 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘An Ecosystem’ especially written for school and college students.
Essay on an Ecosystem
Essay Contents:
- Essay on the Meaning of Ecosystem
- Essay on the Concept of Ecosystem
- Essay on the Types of Ecosystem
- Essay on the Structure and Function of an Ecosystem
- Essay on the Ecological Balance and Awareness
- Essay on the Food Chains and Food Web
- Essay on the Ecological Characteristics of Major Ecosystems
- Essay on the Energy Flow in an Ecosystem
Essay # 1. Meaning of Ecosystem:
An ecosystem is simply an easy way to refer to all the life forms (plant and animal) in a cohesive, relatively independent area, and their relationship to one another. In a perfect world, an ecosystem is in balance. That is, the predator species keep the prey species’ population in check without completely destroying them, and plant life remains varied without one type predominating and crowding out the rest.
Ecosystems are rarely in balance, and this is often cause for alarm. For instance, pollution runoff from a factory can effect marine life in a lake, causing the fish population to plummet. This destabilizes the entire surrounding ecosystem, and birds and animals that prey on the fish either die off or migrate to areas with more food.
Attempting to counteract damage to an ecosystem requires a complete understanding of all the interrelationships between plants, animals and atmosphere in the system. Since such perfect understanding is rarely possible, unintended consequences are often the result.
In nature, no ecosystem can be said to be independent of neighboring ecosystems or indeed, the global ecosystem, since ecosystems are open and plants and animals can move between them. All ecosystems are effected by planet-wide trends that effect the atmosphere, such as pollution and global warming.
A key idea in ecology is that of the ecosystem. An ecosystem consists of all the organisms and creatures in a biotope, or particular environment type, that in turn is made up of biotic and abiotic (non-living) components. Related to the ecosystem is the notion of the biome, but this unit is defined by the makeup of its vegetation, such as tundra, desert, or savanna.
In every ecosystem there is a food chain, though it is more of a circle than a chain. At the bottom of the chain are the plants that (for the most part) are capable of photosynthesis. These are normally called autotrophs, because they generate their own energy from sunlight and by uptake of nutrients from soils. Creatures that feed on autotrophs are known as consumers.
Primary consumers are the herbivores that eat plants. Secondary consumers eat the animals that eat the plants. The final link is the decomposers. These are the organisms such as bacteria that process the organic matter produced by other life forms in the food chain. As a result of their activities, nutrients return to the soil for plants to take up, and the cycle continues.
In this sense, ecology studies flows of energy throughout systems. Everything, including ourselves, belongs to one or more systems. Humans have a unique capacity to intervene in those systems and alter their functioning.
Essay # 2. Concept of Ecosystem:
A biotic community lives in an environment, which provides material, energy requirement and other living conditions to it. “An ecological system in which the community and the non-living environment function together is called Ecosystem.”
The term Ecosystem was introduced by Sir Arthur Tansely (1935). An ecosystem is a group of biotic communities of species interacting with one another and with their non-living environment exchanging energy and matter. Now ecology is often defined as “the study of ecosystems”. In other words, an ecosystem can be defined i.e., as a structural and functional unit of biosphere or segment of nature consisting of community of living beings and the physical environment both interacting and exchanging materials between them.
In an ecosystem the biotic communities and abiotic environment influence each other. This relationship is called “holocenosis”.
An ecosystem is a natural grouping of nutrients, minerals, plants animals and their wastes linked together by flow of food, nutrients and energy from on part of the system to another part.
Thus, the ecosystem is the smallest units of biosphere that has all the characteristic to sustain life. Pond stream, seas, deserts, grasslands etc. are all examples of ecosystem.
Essay # 3. Types of Ecosystem:
An ecosystem may be natural (e.g., forest, grassland, lake etc.) or man made (e.g., on aquaria, crop field etc.) temporary (rain fed pond) or permanent (e.g., lake, forest etc.) or terrestrial (e.g., grassland, forest etc.). The aquatic ecosystem can be either fresh water (e.g., ponds, lakes, streams) or salt water (e.g., marine, estuaries type) Fig. 2.1.
1. Natural Ecosystem:
These systems operate by themselves under natural conditions without any major interference by man.
These are further divided into:
(i) Terrestrial ecosystem- which include forest, grassland and desert etc.
(ii) Aquatic ecosystem may be further distinguished as:
(a) Fresh Water:
As which may be lotic (running water as spring, stream or rivers) or lentic (standing water as lake, pond, pools, ditch, puddles, swamp etc.).
(b) Marine Water:
Such as ocean (deep bodies) or sea (shallow ones).
2. Artificial (Man-Made) Ecosystem:
These are maintained artificial by man where, by addition of energy and planned manipulations, natural balance is distributed regularly. For example, croplands like maize, wheat, rice fields etc. Where man tries to control the biotic community as well as the physio-chemical environment, are man engineered ecosystem.
Essay # 4. Structure and Function of an Ecosystem:
The structure of an ecosystem is characterised by the physical organisation of biotic and abiotic components.
The major structural features of ecosystem are:
1. Species Composition:
Each ecosystem has its own type of species composition. Different ecosystems have different species composition. A great variety of species is found in forest ecosystem, whereas a few species occurs in a desert ecosystem.
2. Stratification:
The organisms in each ecosystem form one or more layers or strata, each comprising the population kind of species. In some ecosystems, such as tropical rain forest, the crown of trees, bushes and ground vegetation form different strata and are occupied by different species. On the other hand, the desert ecosystem shows a low discontinuous herb layer consisting of fewer and extensive bare patches of soil.
3. Trophic Organisation:
Food relationship of producers and consumers is another way to depict ecosystem structure. Trophic (food) structure of ecosystem is based on the existence of several trophic levels in the ecosystem. The producers (autotrophs) form the first trophic level or T1, herbivores the second or T2 and carnivores constitute the third or T3.
There may be 2-3 levels of carnivores. The top carnivore belong to T4 or T5 trophic levels. Decomposers form ultimate or detritus trophic level (Fig. 2.2). Parasites feed upon the organisms of all trophic levels. Therefore, they do not have a fixed trophic level. Similarly there is no fixed trophic level for omnivorous organism like man.
In an ecosystem there can be only 4-5 successive trophic levels, because:
(i) All the food available at one trophic level is not eaten by the animals of the next trophic level. Some of the food energy is lost in this manner.
(ii) All the food eaten by an animals is not useful, thus a good deal of energy containing food is passed out as waste.
(iii) A large amount of energy is lost in respiration to derive organism’s metabolism, and thus, there is not much energy left to support higher trophic levels. Trophic structure may also be described in terms of the amount of living material present in different trophic levels. The amount of the living material perceive different trophic levels at a given time is called standing crop.
It is commonly expressed as the number or biomass of organisms per unit area. The biomass of a species may be expressed in terms of either fresh or dry weight. But, generally dry weight is preferred so that the variations in weight due to seasonal moisture differences in biomass can be avoided.
4. Nutrients:
In each ecosystem, the nutrients necessary for the growth of living organism are accumulated in the biomass and the abiotic components like soil. The amount of nutrients such as nitrogen phosphorus and calcium present in the soil at any given time is termed as standing state. Different ecosystems have different standing state of nutrients. The standing state of nutrients may vary at different time even in the same ecosystem.
Essay # 5. Ecological Balance and Awareness:
Especially for those who embrace philosophical ideas about a holistic universe, the notion of ecological balance is an important one. But not all ecologists view the situation in such holistic terms. If we bring in the idea of natural evolution, the idea of ecological balance becomes more complicated. It is true that an ecosystem (or other unit) can maintain a balanced state, sometimes for very long time spans, and that there are sometimes ‘self-correcting’ mechanisms.
In this sense, ecosystems may be resilient. They may adapt to a toxin, or climate change, or the arrival of a new species. But we also know that in the past, events have occurred that have caused irreversible damage to ecosystems. We know too that ecosystems are constantly changing. Some ecologists therefore dispute the idea that there is some ‘normal’ ecological equilibrium to which ecosystems and environments naturally return.
Ecological Awareness:
In the past, people had little or no concept of ecological wholes, evolutionary rhythms or the ripple effects that human activity can have on the natural world. Not only is awareness of ecological principles vital in a world threatened by ecological catastrophe resulting from global warning (sic), but such principles can be the basis for our behaviour. Ecology demands more harmonious relations between people and nature, and even between nations, who are sometimes able to bury their differences in the cause of a larger and greater good.
Essay # 6. Food Chains and Food Web:
Food chains, in ecology, are the sequence of transfers of matter and energy from organism to organism in the form of food. Food chains do not normally encompass more than five trophic levels because energy, in the form of heat, is lost at each step. Food chains combine into highly complex food webs because most organisms consume more than one type of animal or plant.
A food chain shows how each living thing gets its food. Some animals eat plants and some animals eat other animals. For example, a simple food chain links the trees & shrubs, the giraffes (that eat trees & shrubs), and the lions (that eat the giraffes). Each link in this chain is food for the next link. A food chain always starts with plant life and ends with an animal.
1. Plants are called producers because they are able to use light energy from the Sun to produce food (sugar) from carbon dioxide and water.
2. Animals cannot make their own food so they must eat plants and/or other animals. They are called consumers. There are three groups of consumers.
(a) Animals that eat ONLY PLANTS are called herbivores (or primary consumers).
(b) Animals that eat OTHER ANIMALS are called carnivores.
i. Carnivores that eat herbivores are called secondary consumers
ii. Carnivores that eat other carnivores are called tertiary consumers
3. Animals and people who eat BOTH animals and plants are called omnivores.
4. Then there are decomposers (bacteria and fungi) which feed on decaying matter.
These decomposers speed up the decaying process that releases mineral salts back into the food chain for absorption by plants as nutrients.
Do you know why there are more herbivores than carnivores?
In a food chain, energy is passed from one link to another. When a herbivore eats, only a fraction of the energy (that it gets from the plant food) becomes new body mass; the rest of the energy is lost as waste or used up by the herbivore to carry out its life processes (e.g., movement, digestion, reproduction).
Therefore, when the herbivore is eaten by a carnivore, it passes only a small amount of total energy (that it has received) to the carnivore. Of the energy transferred from the herbivore to the carnivore, some energy will be “wasted” or “used up” by the carnivore. The carnivore then has to eat many herbivores to get enough energy to grow.
Because of the large amount of energy that is lost at each link, the amount of energy that is transferred gets lesser and lesser.
1. The further along the food chain you go, the less food (and hence energy) remains available:
The above energy pyramid shows many trees and shrubs providing food and energy to giraffes. Note that as we go up, there are fewer giraffes than trees and shrubs and even fewer lions than giraffes, as we go further along a food chain, there are fewer and fewer consumers. In other words, a large mass of living things at the base is required to support a few at the top many herbivores are needed to support a few carnivores.
2. Most food chains have no more than four or five links:
There cannot be too many links in a single food chain because the animals at the end of the chain would not get enough food (and hence energy) to stay alive. Most animals are part of more than one food chain and eat more than one kind of food in order to meet their food and energy requirements. These interconnected food chains form a food web.
A change in the size of one population in a food chain will affect other populations.
This interdependence of the populations within a food chain helps to maintain the balance of plant and animal populations within a community. For example, when there are too many giraffes; there will be insufficient trees and shrubs for all of them to eat. Many giraffes will starve and die. Fewer giraffes means more time for the trees and shrubs to grow to maturity and multiply. Fewer giraffes also means less food is available for the lions to eat and some lions will starve to death. When there are fewer lions, the giraffe population will increase.
Grazing Food Chain:
This food chain starts from producers (living green plant base) and extends towards herbivores and then carnivores.
Some common examples of food chains (Fig. 2.6) are given below:
Most of the ecosystem (such as grassland, forest etc.) in nature follow grazing food chain. It is directly dependent on influx of solar energy.
Ecological Pyramids:
A rational study of a various trophic levels in ecosystem is termed as ‘ecological pyramid’. This study is based on various factors viz., number of individuals, biomass or energy in a particular trophic level. Generally producers form the base of pyramid due to large constituent. After that it decreases in size as go to the successive trophic level and become taper at top.
Ecological pyramids are of three types:
(i) Pyramid of Number.
(ii) Pyramid of Biomass.
(iii) Pyramid of Energy.
(i) Pyramid of Number:
This pyramid is based on the number of individuals per unit area at each trophic level. In this pyramid generally, number of individuals decreases successively and it show relationship between producers, herbivores and carnivores and it is known as upright pyramid. But, number of pyramid may be inverted and spindle shaped. Inverted pyramid show increasing number of individuals at successive levels and spindle shaped pyramid show both sides tapered (Fig. 2.7).
(ii) Pyramid of Biomass:
Total amount of living material in any organism is known as biomass. It is measured in terms of dry weight of organisms per unit area. In terrestrial ecosystem, there is gradual decrease in biomass at different trophic levels. But, in aquatic ecosystem, inverted biomass pyramid are also seen (Fig. 2.8).
(iii) Pyramid of Energy:
This pyramid always found in upright pattern because ~10% energy is lost at each successive trophic level. Producers have higher energy than herbivores and carnivores. Energy is represented in terms of calories (Fig. 2.9).
Ecological Food Webs:
Ecological food webs are based on the productivity of green plants (or photoautotrophs), which are the only organisms capable of utilizing diffuse solar radiation to synthesize simple organic compounds from carbon dioxide and water. The fixed energy of the simple organic compounds, plus inorganic nutrients, are then used by plants in more complex metabolic reactions to synthesize a vast diversity of biochemical. Plants utilize the fixed energy of their biochemical to achieve growth and reproduction.
On average, plant photosynthesis utilizes less than 1% of the solar radiation that is received at the surface of the earth. Higher efficiencies are impossible for a number of reasons, including the second law of thermodynamics, but also other constraining factors such as the availability of nutrients and moisture, appropriate temperatures for growth, and other environmental limitations.
Ecological pyramids are based on the productivity of organisms. Plants account for 90% of the total productivity of the food web, and herbivores account for most of the rest. Carnivores are responsible for less than 1 % of ecological productivity. Courtesy of Gale Research. However, even relatively fertile plant communities can only achieve conversion efficiencies of 10% or so, and only for relatively short periods of time.
The solar energy fixed by green plants in photosynthesis is, of course, the energetic basis of the productivity of all heterotrophic organisms that can only feed upon living or dead biomass, such as animals and microorganisms. Some of the biomass of plants is consumed as food by animals in the next trophic level, that of herbivores.
However, herbivores cannot convert all of the energy of the vegetation that they eat into their own biomass. Depending on the digestibility of the food being consumed, the efficiency of this process is about 1-20%. The rest of the fixed energy of the plant foods is not assimilated by herbivores, or is converted into heat.
Similarly, when carnivores eat other animals, only some of the fixed energy of the prey is converted into biomass of the predator. The rest is ultimately excreted, or is converted into heat, in accordance with the requirement for entropy to increase during any energy transformation.
Essay # 7. Ecological Characteristics of Major Ecosystems:
Different ecosystems like a pond, a lake, a river, a stream, a spring, an estuary, the sea, a forest, grassland, a desert, and a cropland are operating as self-sufficient interacting systems in the biosphere. The major ecosystems with their groups of climax plants and associated animals are called biomes. These ecosystem have a more of less similar fundamental plan of their gross structure and function. However, they differ in respect of their species composition and productivity rates.
The ecological characteristics of the major ecosystems are described below:
a. Forest Ecosystem:
Forests are natural plant communities with dominance of trees. In India, the forest occupies roughly 19% of the total land area.
The major forest biomes found in India are:
(i) Tropical rain forest,
(ii) Tropical deciduous forest,
(iii) Temperate brad leaf forest,
(iv) Temperate needle leaf or coniferous forest.
The different components of forest ecosystem are as follows:
1. Abiotic Components:
These include inorganic and organic substances present in the soil and atmosphere. The climate (temperature, light rainfall etc.) and soil (minerals) vary from forest to forest. In addition to minerals the occurrence of litter is characteristic feature of majority of forests.
2. Biotic Components:
(i) Producers:
These are mainly trees show much species diversity and greater degree of stratification especially in tropical rain and tropical deciduous forests. Besides trees, there are also present shrubs and ground vegetation. In these forests, the producers include the dominant tree species such as Dipterocarpus. Tectona grandis (Teak), Butea frondosa (Dhak) and shorea robusta (sal). In temperature broad leaf forests several species of Quercus (Oak), occur ad dominant species, where in temperature coniferous forests the dominant trees are Pinus, Cedrus (Deodar), Picea (Spruce) and Abies (Silver fir), etc.
(ii) Consumers:
Following types of consumers occur in the forest biomes:
(a) Primary Consumers:
These are the herbivores that include smaller animals feeding on tree leaves as ants, flies, beetles, leaf-hoppers, bugs, spiders, etc., and larger animals grazing on shoot and or fruits of producers as elephants, neelgai, deer, moles, squirrels, shrews flying foxes, mongooses etc.
(b) Secondary Consumers:
These are the carnivores like snakes, birds, lizards, fox, etc., feeding on the herbivores.
(c) Tertiary Consumers:
These are the top carnivores like lion, tiger, etc. that eat upon carnivores of secondary consumer’s level.
(iii) Decomposers:
These are wide variety of microorganisms including fungi (species of aspergillus, Polyporus, Alternaria, Fusarium, Trichoderma, etc.), bacteria (species of Bacillus, Pseudomonas, Clostridium etc.), and actionmycetes (species of Streptomyces). Rate of decomposition in tropical and subtropical forests is more rapid than in the temperate ones.
b. Grassland Ecosystem:
The grassland biomass occurs in the regions, where the climate is cool to cold during winters and hot in summers.
The different components of a grassland ecosystem are as follows:
1. Abiotic Components:
These include nutrients present in soil and the atmosphere. Thus the elements like C, H, O, N, P, S, etc., are supplied by carbon dioxide, water, nitrates, phosphates and sulphates present in air and soil of the area.
2. Biotic Components:
(i) Producers:
The grasslands are characterised by treeless herbaceous plant cover dominant by a wide variety of grass species. The main grasses are species of Dichanthium, Cynodon, Phragmites, cenchrus, Imparata and Saccharum, etc. Besides them a few herbs and shrubs also occur as producers.
(ii) Consumers:
The various types of consumers occurring in grassland are as follows:
(a) Primary Consumers:
The herbivores feeding on grasses the mainly such grazing animals as cows, buffaloes, deer, rabbit, mouse, etc. Besides them, there are also present some insect species as Leptocorisa, Dysdercus, Oxyrhachis, Cicindella, Cocinella, and some termites millipedes, etc., that feed on the leaves of grasses.
(b) Secondary Consumers:
Snakes, lizards, birds, jackals, fox, etc. are common secondary consumers which feed on herbivores.
(c) Tertiary Consumers:
These include hawks, which fed on secondary consumers.
(iii) Decomposers:
Several fungi (Mucor, Aspergillus, Penicillium, Ladosporium, Fusarisum etc), actinomycetes and bacteria decay the dead organic matter of different forms of higher life. They bring about minerals back to the soil, thus making them available to the producers.
c. Desert Ecosystem:
The desert biomes are characterised by extremely low rainfall (less than 25 cm). They occupy about 17% of the land. Due to scarcity of water and high temperature, the biota is poorly represented.
The various components of desert biomes are as follows:
1. Abiotic Components:
In desert ecosystem temperature is found to be very high and rainfall is very low. The nutrient cycling is poor is due to scanty biota.
2. Biotic Components:
(i) Producers:
These are shrubs, especially bushes, some grasses, and a few trees, the shrubs have widespread-branched root system with their leaves, branches and stems variously modified. Sometimes a few succulents like cacti are also present. Some lower plants like lichens and xerophytic mosses may also be present.
(ii) Consumers:
Insects, reptiles, nocturnal rodents, birds camels, etc. are the main consumers.
(iii) Decomposers:
These are very few, as due to poor vegetation the amount of dead organic matter is correspondingly less. These are some fungi and bacteria, most of them are thermophilic.
d. Aquatic Ecosystem:
There are many kinds of aquatic ecosystems ranging from small temporary puddles to large ocean. They differ widely with regard to abiotic factors and living organisms.
The important aquatic ecosystems are described below:
A. Pond or Lake Ecosystem:
A pond or lake is a good example of a self-sufficient and self-regulating ecosystem (Fig.2.3). Location size, depth and substratum of a pond or lake constitute the biology of the ecosystem.
The various components of the ecosystem are as follows:
1. Abiotic Components:
Temperature, light, water, and several inorganic and organic substances like, C, H, O, N, P, Ca, S and carbohydrates, proteins, and lipids make abiotic components. Some proportions of nutrients are in solution state but most of them are present stored in particulate matter as well as in living organisms. The amount of minerals present at any time in the physical environment of the pond is called standing state.
2. Biotic Components:
(i) Producers:
These include green photosynthetic organisms and are of two types:
Phytoplanktons and Macrophytes:
(a) Phytoplanktons:
These are minute floating or suspended lower plants belong to some algae are flagellates. Ulothrix, Spirogyra, Oedogonium, Chalamydomonas, Zygnema, Volvox, Pandorina, Cosmarium, Scenedesmus, Closterium, Anabaena, Pediastrum, Microcystis, diatoms etc. are common algal phytoplanktons.
(b) Macrophytes:
Ceratophyllum, Hydrilla, Utricularia, Vallisneria, Jussiaea, Nitella, Wolfia, Lemna, Spirodella, Pistia, Eichhornia, Azolla, Salvinia, Trapa, Typha, Marsilea, etc. are included in this category. This may be classified further into Submerged, Free floating and Amphibious plants.
(ii) Consumers:
(a) Primary Consumers:
These include zooplanktons and benthos forms. Zooplankton comprises ciliates, flagellates, other protozoans, small crustacean like Copepods and Daphnia, etc. These animals drift with water current and are found along with phytoplankton upon which they feed. Benthos or bottom forms comprise the bottom dwelling animals, e.g., annelids and molluscs, which feed on plants directly or on plant remains at the bottom.
(b) Secondary Consumers:
These are the carnivores, which feed on the herbivores, e.g., insects and fish.
(c) Tertiary Consumers:
These are some large fish as game fish that feed on the smaller fish.
(iii) Decomposers (or Microconsumers):
Several bacteria fungi, (Aspergillus, Cephadosporium, Phythiurn, etc.) and actinomycetes represents the group.
B. River or Stream Ecosystem:
The running water of a stream or a river is usually well oxygenated because it has a large surface area to absorb oxygen from the air.
The various components of river or stream ecosystem are as follows:
Abiotic Components:
The river or stream water has lesser mineral content and greater penetration of light. In the lower reaches water is usually muddy cutting down the light at the river bed.
Biotic Components:
(i) Producers:
In slow moving water of banks, phytoplanktons, attached algae, water grasses and other amphibious plants are the producers. In swift water floating populations of plankton are generally absent.
(ii) Consumers:
These include flatworms, leeches, water insects, snails, fishes, and crocodiles. Many birds and mammals also get their food from rivers and streams.
(iii) Decomposers:
Several bacteria and fungi represent this group.
C. Ocean or Marine Ecosystem:
Oceans cover more than two third of the earth’s surface. The marine environment is characterised by its high concentration of salts and mineral ions. The ocean represents a very large and stable ecosystem.
The main components of the ocean ecosystem are as follows:
1. Abiotic Components:
Marine environment as compared with fresh water, appears to be more stable in chemical composition due to being saline. The other physio-chemical factors such as dissolved oxygen, light and temperature are also different waves of various kinds and tides prevail there. Ocean also show distinct horizontal and vertical zones (Fig. 2.4).
2. Biotic Components:
Producers:
This category includes phytoplanktons and larger marine plants. The former group includes diatoms and dinoflagelates. The latter group includes sea weeds (algae) belonging to chlorophyceae, phaeophyceae and rhodophyceae and angiosperms. Ruppia. Zostera, Posidonia, Halophila, Enhalus, etc. are true marine angiosperm while various species of Rhizophora.
Essay # 8. Energy Flow in an Ecosystem:
In ecology, energy flow (calorific flow) refers to the flow of energy through a food chain. In an ecosystem, ecologists seek to quantify the relative importance of different component species and feeding relationships.
A general energy flow scenario follows:
i. Solar energy is fixed by the photoautotrophs, the so called primary producers, like green plants. They absorb most of the stored energy in the plant through digestion, and transform it into the form of energy they need, adenosine triphosphate, through respiration. A part of the energy received by the herbivore is converted to bodily heat (an effect of respiration), which is radiated away and lost from the system. Energy loss also occurs in the expulsion of egesta, which contains undigested energy compounds.
ii. Secondary Consumers then consume the primary consumers. Energy that had been used by the primary consumers for growth and storage is thus absorbed into the secondary consumers through the process of digestion. As with primary consumers, secondary consumers convert this energy into a more suitable form (ATP) during respiration. Again some energy is lost from the system, since energy which the primary consumers had used for respiration cannot be utilised by the secondary consumers.
iii. Tertiary consumers then consume the secondary consumers, and most of the energy is passed along, while some is again lost in the ways described above and below.
iv. A final link in the food chain is decomposers which break down the organic matter of the tertiary consumers (or whichever consumer is at the top of the chain) and release nutrients into the soil. Saprotrophic bacteria and fungi are decomposers, and play a pivotal role in the nitrogen and carbon cycles.
The energy is passed on from trophic level to trophic level and each time most (about 90%) of the energy is lost, with some being lost as heat into the environment (an effect of respiration) and some being lost as egesta. This means the top consumer of a food chain receives the least energy, as a lot of the food chain’s energy has been lost between trophic levels. This loss of energy at each level limits typical food chains to only 4-6 links.
Energy Capture and Use:
At the base of an ecosystem, primary producers are actively converting solar energy into stored chemical energy. Photosynthesis is the process of converting solar energy, water, and carbon dioxide into carbohydrates and oxygen. The process occurs in two steps; first light energy is absorbed by chlorophyll to split a molecule of water releasing hydrogen and oxygen. The second step uses the energy to convert carbon dioxide to carbohydrates.
The carbohydrate (QH12O6) can be converted into starch and stored by the plant. Carbohydrate can be combined with other sugar molecules to make cellulose, the basic structural material of a plant.
Oddly enough, of all the solar radiation striking a plant, only about 1 percent is used in photosynthesis. The rate of photosynthesis is dependent on several things, especially the amount of light received up to a point. As solar radiation increases the rate of photosynthesis increases.
For many plants there is an upper limit to the rate of photosynthesis. In some plants as incident solar radiation increases the rate of photosynthesis levels off, or may decrease. The increasing solar energy load causes the plant to be too hot and the need to cool the plant increases. As a result, transpiration takes over as the dominate plant process. Transpiration, the loss of water from plants, acts to cool the plant by releasing latent energy. Adequate supplies of water, carbon dioxide and the availability of nutrients in the soil affect photosynthesis.
Respiration:
While photosynthesis builds stored chemical energy in a plant, respiration is the process of “burning” stored chemical energy, basically through oxidation, for maintaining plant metabolism. During plant respiration, carbohydrates combine with oxygen and is reduced to carbon dioxide, water, and heat.
C6H12 O6 + 6O2 6CO2 + 6H2O + 2830 kJ
While photosynthesis operates only during day when sunshine is available, respiration goes on both night and day. Plant growth occurs so long as photosynthesis exceeds respiration.