3 Marks Question

Question 13 Marks

What is food chain? Discuss the various types of food chains.

Answer

In ecosystem, food energy is transferred from producers to organisms each feeding on the proceeding organism and providing raw materials and energy for the other organisms. Such chain is called food chain. Food chain consists of herbivores, carnivores and decomposers. There are three types of food chains in nature :
(1) Predator or grazing food chain : This type of food chain directly based on solar energy which starts from green plants and moves through carnivores and ends at supreme (top) carnivore. Therefore, it begins with smaller organisms and ends at bigger organisms. e.g. Food chain in grassland.
(2) Parasitic food chain : This chain begins from bigger organisms (herbivorous animals) and ends at smaller organisms (parasite) i.e. it moves from host to parasite. Bigger herbivorous organisms are called host. Example :

(3) Detritus or Saprophytic food chain : This type of food chain begins with dead decaying organic matter and goes through the detritivores present in soil and ends at the organisms that feed on detritivores. Example :
Dead and decay $\rightarrow$ Earthworm $\rightarrow$ Frog $\rightarrow$ Snake $\rightarrow$ Organic matter.

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Question 23 Marks

Explain the pyramid of energy in ecosystem. ###What is meant by ecological pyramid? Describe an ideal pyramid of energy with diagram.

Answer

Ecological Pyramid : Ecological pyramids were at first drawn by Charles Elton in 1927. All the trophic levels are arranged in sequence wise one after another in a food chain in each ecosystem. Considering the first trophic level as base and followed by successive trophic levels, are represented in a diagram, then a pyramid is formed, called ecological pyramid. Pyramid of energy : It is a graphic representation of amount of energy trapped per unit time and area in different trophic levels of a food chain.
The pyramid of energy clearly represent the nature of ecosystems as a whole. The energy in the form of food that gets transferred from producers to consumers or from one trophic level to another. It is certain that amount of energy that reaches the next trophic level is lesser than it was present in the earlier trophic level. Therefore, the amount of energy decreases with each higher trophic level.
This is why of the total stored energy at each trophic level only 10% energy is transferred to next trophic level as biomass. Therefore, maximum energy is available at producer level and decreases gradually to primary to secondary to tertiary to top consumers. When the graphical representation is drawn, such pyramids of energy are always formed upright possessing the producer at base and top consumer at the apex of pyramid.

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Question 33 Marks

Name the types of ecosystem.

Answer

There are two types of ecosystem : (1) Natural ecosystem (2) Artificial ecosystem
(1) Natural ecosystem : These are the ecosystems found naturally on the earth. These are of following types :
(i) Terrestrial : Ecosystem existing on land, i.e. forest, grass land, desert ecosystems.
(ii) Aquatic : This ecosystem is of two types :
(a) Fresh water ecosystem : It includes— (i) Lotic e.g. waterfall, river, spring etc. (ii) Lentic e.g. lake, pond, swamp etc.
(b) Marine water ecosystem : e.g. ocean, sea, Estuary, salt lakes etc.
(2) Artificial Ecosystem : These ecosystems are created and maintained by human beings e.g. agriculture garden, orchard tree plantation, aquarium.

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Question 43 Marks

Explain the ecological efficiency.

Answer

In each ecosystem, organisms obtain their food and convert the food into biomass for providing energy to next trophic level.
Ecological efficiencies are the percentage ratios between energy flow at different trophic levels of a food chain.
The unit of measurement of energy is Kcal/m2 /year. At the producer level, photosynthetic efficiency and net production efficiency are important. The efficiency with which a producer uses, incident solar radiation is measured by photosynthetic efficiency.
Photosynthetic efficiency $($ Producer level $)=$$\frac{\text { Gross Primary Productivity }}{\text { Incident Total Solar Radiation }}\times 100$
$\begin{array}{l}\text { Net production efficiency }= \frac{\text { Net Primary Productivity }}{\text { Gross Primary Productivity }} \times 100\end{array}$
Assimilatory efficiency (trophic levels) $=$ $\frac{\text { Net Primary Productivity }}{\text { Food Energy Ingested }} \times 100$

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