Ch. 15 Our Environment

Q. What are the components of Ecosystem?

A. The components of the ecosystem are:

・Abiotic- These are nonliving components of the ecosystem. Eg. Air, water, light, temperature etc.

・Biotic- These are living components of an ecosystem. It includes following organisms: 

i) Autotrophs (producers i.e. trap sunlight) 

ii) Heterotrophs ( consumers like saprophytic, parasitic, holozoic)

Q. What are the functions of the ecosystem?

A. Energy flow via the food chain

Recycling of nutrients (Bio-Geo-Chemical Cycle)  eg. O₂ cycle, CO₂ cycle, Nitrogen Cycle

Q. What is food chain?

A. The food chain is a cycle that depicts who is eaten by whom.

Eg. Plant →Deer→Lion

Q. What is Trophic Level?

A. Each level in the food chain is Trophic level. 

Q. Give food chain in the aquatic ecosystem.

A. Phytoplanktons →  Zooplanktons→Small Fish →Big Fish→Kingfishers

      (Producer)           (Primary Consumer)                 (Secondary)               (Top Level Carnivores)

Q. Explain the characteristics of energy flow in the food chain?

A. The flow of energy is unidirectional

The energy level goes on decreasing as it moves from one trophic level to the next as per the 10% law.

Q. Bring out the significance of food chain.

A. It tells about the flow of energy, and matter in an ecosystem.

It also gives us information about organisms taking part at various biotic levels.

It can also help in tracing the flow of toxic substances in an ecosystem.

Q. What is food web?

A. Food web is a network of interconnecting food chains.

Q. Describe a food chain in:

i) A Forest

A. Plants→Deer→Tiger

ii) A Grassland

A. Grass→Grasshopper→Frog→Snake→Eagle

Q. How is energy in a trophic level utilized by an organism?

A. Interaction among various components of the environment involves the flow of energy from one component of the system to another. The autotrophs capture the energy present in sunlight and convert it into chemical energy. this energy supports all the activities of the living world. From autotrophs, this energy goes to the heterotrophs and decomposes.

The green plants capture about 1% of the energy of sunlight that falls on their leaves and converts it into food energy. When green plants are eaten, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction.

Q. Why are the number of trophic levels in a food chain restricted to 3 or 4?

A. Since so little energy is available for the next level of consumers, food chains generally consist of only 3 or 4 steps. The loss of energy at each step is so great that very little usable energy remains after 4 trophic levels.

Q. "The energy flow is unidirectional in a food chain". Justify.

A. The flow of energy is unidirectional. The energy that is captured by autotrophs does not revert back to the solar input and the energy which passes to herbivores does not come back to autotrophs.  As it moves progressively through the various trophic levels, it is no longer available to the previous level.

Q. What is Biomagnification?

A. Some harmful chemicals enter our bodies through the food chain. These chemicals contaminate the water as they get washed down into the soil. From the soil, these are absorbed by the plants along with water and minerals. This is one of the ways in which they enter the food chain. As these chemicals are not biodegradable, these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals gets accumulated in our bodies. This phenomenon is known as biomagnification.

Q. What is 10% Law?

A. According to 10% Law, only 10% of the energy entering a particular trophic level of organisms available for transfer to the next higher trophic level i.e. the energy available at each successive trophic level is 10% of the previous level.