CONTENTS 1.0 Introduction 2.0 Objectives 3.0 Main Content
3.1 Energy Flow in Ecosystem
3.2 Components of Energy Flow in the Ecosystem 3.3 Energy Transformation
4.0 Conclusion 5.0 Summary
6.0 Tutor-Marked Assignment 7.0 References/Further Reading
1.0 INTRODUCTION
Energy may be defined as the capacity to do work. All living organisms may be regarded as working machines which require continuous supply of energy in order to keep working, and to stay alive. Energy can neither be created nor destroyed (the law of conservation of energy). Energy can be transferred from one form to another as we will see in this unit.
2.0 OBJECTIVES
By the end of this unit, you will be able to:
list the process of energy flow in ecosystem
explain the two aspects with respect to energy flow in the ecosystem
discuss energy transformation in ecosystem.
3.0 MAIN CONTENT
3.1 Energy Flow in Ecosystem
Energy and carbon enter the ecosystems through photosynthesis and are incorporated into living tissue, transferred to other organisms that feed on the living and dead plant matter, and eventually released through respiration.
The carbon and energy incorporated into plant tissues (net primary production), is either consumed by animals while the plant is alive, or it remains uneaten when the plant tissue dies and becomes detritus. In terrestrial ecosystems, roughly 90% of the net primary production ends
up being broken down by decomposers. The remainder is either consumed by animals while still alive and enters the plant-based trophic system, or it is consumed after it has died, and enters the detritus-based trophic system.
In aquatic systems, the proportion of plant biomass that gets consumed by herbivores is much higher. In trophic systems photosynthetic organisms are the primary producers. The organisms that consume their tissues are called primary consumers or secondary producers—herbivores.
Organisms which feed on microbes (bacteria and fungi) are termed microbivores. Animals that feed on primary consumers—carnivores—are secondary consumers. Each of these constitutes a trophic level.
The sequence of consumption—from plant to herbivore, to carnivore—
forms a food chain. Real systems are much more complex than this—
organisms will generally feed on more than one form of food, and may feed at more than one trophic level. Carnivores may capture some prey which is part of a plant-based trophic system and others that are part of a detritus-based trophic system (a bird that feeds both on herbivorous grasshoppers and earthworms, which consume detritus). Real systems, with all these complexities, form food webs rather than food chains (see Figure 5.1).
Fig.5.1: Energy Flows and Material Cycles.
Source: Sharma, 2009.
3.2 Components of Energy Flow in the Ecosystem
There are two components with respect to energy flow in ecosystem.
These include:
(i) Unidirectional or one way flow of energy in the ecosystem i.e., from producers through herbivores to carnivores. The energy cannot be transferred in the reverse direction i.e. the energy that is captured by the autotrophs does not revert back to solar input; or
the energy which passes to the herbivores does not pass back to the autotrophs.
(ii) The amount of energy flow decreases with successive trophic levels. Producers capture only a small fraction of solar energy (1–
15% of total radiation) and the bulk of unutilised energy is dissipated mostly as heat. Part of energy captured in gross production of producers or Gross Primary Production (GPP) is used for maintenance of their standing crop (respiration and for providing food to herbivores (herbivory). The unutilised Net Primary Production (NPP) is ultimately converted to detritus, which serves as energy source to decomposers.
3.3 Energy Transformation
The transformations of energy in an ecosystem begin with the input of energy from the sun. Energy from the sun is captured by the process of photosynthesis. Carbon dioxide is combined with hydrogen (derived from the splitting of water molecules) to produce carbohydrates (the shorthand notation is "CHO"). Energy is stored in the high energy bonds of adenosine triphosphate, or ATP.
The prophet Isaiah said "all flesh is grass", earning him the title of first ecologist, because virtually all energy available to organisms originates in plants. Because it is the first step in the production of energy for living things, it is called primary production. Herbivores obtain their energy by consuming plants or plant products, carnivores eat herbivores, and detritivores consume the droppings and carcasses of us all.
4.0 CONCLUSION
In this unit, we have examined the principle of energy flow in an ecosystem. Also, two aspects with respect to energy flow in the ecosystem were discussed. The transformation of energy in an ecosystem was also examined.
5.0 SUMMARY
In this unit, students have learnt that:
Energy may be defined as the capacity to do work;
Flow of energy in an ecosystem takes place through the food chain and it is this energy flow which keeps the ecosystem going;
There are two aspects with respect to energy flow in ecosystem that energy flow is unidirectional or one-way flow unlike the nutrients which move in a cyclic manner and the amount of energy flow decreases with successive trophic levels; and
The transformation of energy is an ecosystem begins first with the input of energy from the sun.
Primary production is the first step in the production of energy for living things from plants.
6.0 TUTOR-MARKED ASSIGNMENT
Give an account of energy flow in an ecosystem.
Explain the two components of energy flow in the ecosystem.
7.0 REFERENCES/FURTHER READING
Chapin, F.S., Matson, P.A., & Harold, M. (2002). Principles of Terrestrial Ecosystem Ecology. New York: Springer
Sharma, J.P. (2009). Basics of Environmental Studies. New Delhi:
University Science Press
Srivastava, S. (2013). Environment and Ecology. New Delhi: S.K. Kataria and Sons.
Taylor, D. J. (et al.). (2002). Biological Science. (3rd ed.). United Kingdom: Cambridge University Press.
Wessells, N.K. & Hopson, J.L. (1988). Biology. New York: Random House.
http://www.environmentalpollution.in/environment/scope-and-components-of-environmental- studies/198