Class 11 | Environmental Science | Question and Answers | NCERT | AHSEC
1. Define the term ecology?
Ecology is the study of the relationships between organisms and their environment, and the balances between these relationships as well. Literally ecology is the study of the earth as a household that include plants, animals and microorganisms.
2. What do you mean by ecosystem?
An ecosystem is the functional unit of nature in which all the living organisms interact with each other and also with their surrounding physical environment. It can be described as a geographical area where plants, animals and other organisms including weather and landscape interact together and form a bubble of life.
3. Classify the ecosystems.
The ecosystems can be classified into two broad categories –
i) Natural – These are ecosystems that occur freely in nature without human interaction. They are further sub-divided as – aquatic and terrestrial.
a) Aquatic – These ecosystems are the most common that covers 75 percent of the earth’s surface. They are again sub-divided as – freshwater and marine ecosystems.
Freshwater – These are the rare forms of ecosystems occurring in only 1.8 percent of the earth’s surface. Lakes, rivers, streams and springs comprise of such ecosystems. They support most of the fish species, amphibians, reptiles, insects, fungi, phytoplankton and bacteria. Freshwater ecosystem may be lotic (free flowing type like rivers) or lentic (still type like pond).
Marine – These are ecosystems with high levels of salts. They are sub-divided as shallow ocean, deep ocean water and deep ocean surfaces. These support coral reef, planktons and crustaceans.
b) Terrestrial – Terrestrial ecosystems are the landforms and they are categorized into large biomes. Examples are tropical rain forests, coniferous forests, deciduous forests, savannahs, deserts, and tundra.
ii) Artificial or man-made – These ecosystems are created by man by chance or by choice. For example – cropland ecosystem, fisheries, aquarium etc.
4. What are lotic and lentic ecosystems? Give examples.
A lotic ecosystem has flowing water. Examples are rivers, streams, springs, creeks, brooks, runs and channel. A lentic ecosystem has still water. Examples include ponds, lakes, reservoirs, ditches, seeps and ephemeral pools.
5. What are producers, consumers and decomposers?
The organisms which produce their own food are called producers or autotrophs. They are mainly the green plants that undergo photosynthesis and prepare food.
The organisms which cannot prepare their own food but depend on producers or other consumers for their food are called consumers or heterotrophs. For example, deer feeds on grass(producer) while a tiger feeds on deer(consumer).
Decomposers feed on all the dead remains of plants and animals. They break down the dead remains into their nutrient components so that plants can use them.
6. Write briefly on structure and functions of an ecosystem.
The structure of an ecosystem denotes the description of organisms and the physical features of an environment. Besides, it also provides information about the distribution of nutrients in a particular habitat including the range of climatic condition of the area.
From structural point of view, all ecosystems consist of these basic components –
i) Abiotic components – These are the non-living components of an ecosystem that include soil, water, oxygen etc. and physical factors like moisture, wind currents and solar radiation.
ii) Biotic components – The biotic components include all the living components of an ecosystem. These include plants, animals and microorganisms. They are further classified on the basis of nutrition as – producers, consumers and decomposers.
Functions of an ecosystem
- It regulates the essential ecological processes, support life systems and maintains stability.
- It cycles the nutrients between biotic and abiotic components.
- It helps in flowing of energy through various trophic levels.
- It maintains the balance among various trophic levels.
7. What are food chain and food web?
A food chain is a linear network of food links that starts from producer organisms and ends at apex predator species. Here, each organism depends on the other as a source of food. Food web, on the other hand, is the collection of all the food chains involved in an ecosystem. It depicts the complete food connections among species in a given habitat.
8. What is a trophic level?
A trophic level refers to the level or position of an organism in a food chain, food web or an ecological pyramid. Organisms are placed into various trophic level depending upon their feeding behaviour.
9. What do you mean by ecological pyramids? Name the different types of ecological pyramids.
The graphical representation of the relationships among various organisms in an ecosystem is called ecological pyramid. Each of the bars that forms the pyramid represents a trophic level. The order which is based on ‘who eats whom’ represent flow of energy.
Types of ecological pyramids
i) Pyramids of numbers – It represents the number of organisms in each trophic level of an ecosystem. Generally, they are larger at the bottom and become smaller as they go up. But there are exceptions too.
ii) Pyramids of biomass – This represents the total mass of organisms in each tropic level.
iii) Pyramids of productivity – The pyramids of productivity focus on the total amount of energy present at each trophic level and also on the loss of energy between trophic levels.
10. Mention the main characteristics of food chain and food web.
The main characteristics of food chain and food web are –
- It exist in a progressive straight line.
- In a food chain the flow of energy is unidirectional.
- A food chain consists of a minimum of two and a maximum of five trophic levels.
- They do not exist in straight lines .
- A number of interconnected food chains give rise to a food web.
- Complex food webs help in the existence of ecosystem.