Short essay on the concept of Energy Flow in Ecosystem

Living organisms are highly organised. In order to survive and maintain its internal order, organisms need constant supply of energy. Organisms need energy when they make new cells, this condition is called growth.

Respiration releases energy where relatively large molecules, such as glucose, are broken down to smaller less ordered molecules i.e. carbon dioxide and water. Organisms need to have nutrients (for example, glucose) from where they can obtain their energy through respiration.

Primary production in the world is mostly due to photosynthesis, which the autotrophs do when they turn carbon dioxide and water into larger structural molecules. With this process, the plants grow in size.

Gross Primary Productivity – (G.P.P.)

GPP is a measure of the total amount of dry matter prepared by plants in photosynthesis. All organisms, including autotrophs respire. During respiration some of the matter from the gross primary productivity is utilised and lost. After this loss, whatever remains is Net Primary Productivity (NPP). Hence, XPP = GPP – Rcspriration.

Different Plant communities have different net primary productivity. In a terrestrial community, GPP is approximately 2.7 times of XPP while the same is 1.5 times in occans.

Capture of Light by Plants

Green Plants have the capacity to combinc carbon dioxide and water to produce sugar using the energy of sunlight. The process is callcd Photosynthesis. It is the main spring of all life and it represents the basic productive capability of any ecosystem. Ecologically, the most important aspect of this process photosynthesis requires (1) plants containing chlorophyll (2) light (3) carbon dioxide (4) water (5) some oxidant ions such as Fe or Mg and finally (6) phosphorus in the form of phosphates. Green plants are not just the producers of glucose and carbohydrates; they also synthesize highly ordered molecules like lipids, proteins and vitamins, all of which are fundamental chemical constituents of protoplasm.

Even in the most productive communities, plants trap only about 1-3% of the energy which they receive in sunlight.

Efficiency of photosynthesis = Total energy fixed in photosynthesis

Total energy falling on the field

Generally speaking, the efficiency of phtotosynthesis which is also called “ecologic efficiency” averages less than 1%. In large bodies of water such as ocean, the ecologic efficiency is as low as 0.18%. F”ood Chain and Food Webs

The transfer of energy from plants through a series of other organism constitutes food chains. The term trophic level refers to the parts of a food chain in which a group of organism secures food in the same “general way.

Thus all animals which obtain their energy by directly eating grass, such as grasshoppers and cattle are part of the same trophic level. An assemblage of trophic levels within an ecosystem is known as “trophic structure”. An ecosystem may have 3 to 6 trophic levels through which energy and organic materials pass. A very common example of a short parctical food chain would be grass – cow – man. Another example of food chain is grass – grasshopper – bird – snake – eagle.

In aquatic ecosystcm, algal phytoplanktons occupy the same trophic level as the grass while the animals like crustaceans, insects and herbivorous fishes occupy the same trophic level as the cattle.

Trophic structures tend to be simple in the polar region as they become more complex on progressing through the temperate regions to the tropics. The conccpt of food
chain, although simple to understand, practically remains very complicated. This is because the organism is eating a variety of other organism that may be at different trophic levels.

This net – like trophic interrelationship is called a “food web”. For example, a bird may feed on fruits / seeds and also fishes or insects depending on supply position. In fact, food chain is only of acadcmic interest, but the rule of nature is food web. Food web provides ecologic strength and security in complcx trophic structures usually seen in stable ecosystems worldover.