TNPSC Science Notes: 7th Standard - Biology - Eco System

TNPSC 7th Standard - General Science Notes 

TNPSC Notes for Group 4 Exam 2016

An Eco System

· A community of living organisms with the physical environment of a definite geographical region form an eco system. Eco-systems may be natural or artificial.

· Elephants live in forests. Forest is an ecosystem. Forests are the natural habitats of elephants. People have been cutting down trees and reducing forest cover for cultivation and other purposes.

· The elephants lose their habitations in the reduced forest area. So they are forced to come out of their forest homes (ecosystems) and move in the areas where people live.

Natural Eco-systems

· A pond, a grassland, a forest, a lake, a desert etc. are examples of natural eco-systems.

Artificial Eco-systems.

· An aquarium, a park, a paddy field, etc. are examples of artificial eco-systems.
Components of Eco-system

· An eco-system consists of two main components. They are biotic (living) and abiotic (non-living) components.

Biotic Components

· Plants, Animals Biotic Components of the Eco System.
Biotic Components The living components are broadly classified into three categories.

1. Producers:

· They are green plants that prepare their own food by the process of photosynthesis.

2. Consumers:

· We know that animals eat plants and they in turn are eaten by other animals. Hence the food produced by green plants is directly or indirectly consumed by all kind of animals, which are called consumers. eg. Goat.

3. Decomposers:

· They are organisms which feed upon dead matter to get energy and give back the nutrients to the soil. eg. bacteria and fungi.

Abiotic Components

· Siol, Air, Water, Sunlight are the Abiotic Components of the Eco System.

· Abiotic Components These include the soil, water, air and climatic factors such as temperature, sunlight, humidity etc.

Food Chain

· The sun is the ultimate source of energy to all living things. Green plants capture solar energy and convert carbon-dioxide and water into food by photosynthesis.

· This food energy is transferred to the primary consumer when they eat plants.

· Then the primary consumer is eaten by the secondary consumer which in turn is eaten by a tertiary consumer.

· So, in a given ecosystem, there is a process of organisms eating some others or being eaten by some other organisms.

· The path of energy transfer from one organism to another in a single direction is called a food chain.

· In a food chain, each group of organisms occupies a particular position. The position of organisms in a food chain is called trophic level.

· Plants are producers and form the first trophic level. The second trophic level comprises of plant eaters the herbivores. Carnivores which eat the herbivores form the third trophic level.

· The fourth trophic levelis occupied by the large carnivores.

· If one link in a food chain is broken it would result in the extinction of a species.

Food Web

· In a given ecosystem, a single food chain may not exist separately. An animal can eat more than one kind of food. For eg. an eagle can eat a rabbit, a mouse or a snake and a snake can feed on a mouse or a frog. So, many food chains get interlinked. A network of interlinked food chains is called a food web.

Flow of Energy

· The sun is the ultimate source of energy for all living things. At first, the solar energy flows from the sun to the surface of the earth. Green plants trap the solar energy and convert it into chemical energy (food).

· The amount of energy decreases from one trophic level to another. The flow of energy is always in one direction only.


· An ecosystem may be small or big. When small ecosystems are put together, they form a vast geographical area which supports a wide variety of flora and fauna. At the same time such a vast area has a different type of climate. Such a vast geographical area is called biome.

The different Biomes

· We can view our earth as various biomes based on their climate and also the latitude and longitude on which they are present. Based on the types of flora and fauna, the biomes are classified into many types.

Types of Forests

1) Tropical Rain Forest:

· They are found in South America, Africa and Indo Malaysia region near the equator. The weather is warm (20oC-25oC). Rainfall is plentiful, 190 cm per year.

· In India, they are found in Andaman and Nicobar Islands, Western ghats, Assam and West Bengal.

2) Savannah:

· They are found South Africa, Western Australia, North West India and Eastern Pakistan. They love a dry weather alternating with wet weather.

· The rainfall is about 25cm per year. Frequent fires occur during the dry season. In India, grassy plains are found in the Nilgiris, Khasi hills and Naga hills.

3) Deserts:

· They are found Africa, Arizona in America and Mexican desert in Mexico. The days are hot and nights are cold. The annual rainfall is less than 25 cm. In India, it is found in Rajasthan (The Thar Desert).

4) Temperate Grassland:

· It is found in North and South America and parts of Europe. The annual rainfall is 25cm to 100 cm. They have two very severe dry seasons. They have windy hot summers and cold winters. In India, It is found in Uttar Pradesh.

5) Deciduous Forests:

· They are found in North America, Eastern Asia and Europe. They receive 75 to 100 cm of rainfall. The climate is moderate with mild winters. In India, it is found in Punjab, Tamil Nadu, Uttar Pradesh, Bihar, Odisha and Madhya Pradesh.

6) Taiga:

· It is found Canada, Europe and Russia. They are also called Boreal Forests. The climate is of a short cool summer and a long winter with abundant snowfall. The annual rainfall is 20cm to 60 cm. Most of it is covered with snow and ice. It is found in Himachal Pradesh, Punjab and Kashmir in India.

7) Tundra:

· It is found south of the ice covered poles in the Northern hemisphere. Though it receives 25 cm of rainfall, it has permanently frozen soil.

· The climate is extremely cold and windy. The temperature is less than 10oC. In India, it is found in the Himalayas.

Importance of Forests

1. Forests are the sources for the formation of rivers.
2. They increase the rainfall.
3. They prevent soil erosion and floods.
4. They become habitats to animals.
5. They maintain the oxygen and carbon dioxide balance in nature. Forests are considered as God’s first temples. They play an important role in our day-to-day life.

“Vanamahotsav” Festival

· Vanamahotsav is an annual Indian tree planting festival celebrated in the month of July. It is to create an enthusiasm in the minds of people to conserve forests.

Different Flora and Fauna

· Biomes have a variety of plants and animals. The flora and fauna found in one biome is completely different from that in the other biome due to the different climatic conditions. 

· India is one of the 12 mega biodiversity centres in the world with immense flora and fauna.

· The kind of flora and fauna found in different biomes are given below:

Important Questions and Answers

1. Pick out the correct answer:
a) Forest is an area with high density of __________ (trees / grass)
· Answer: trees
b) _______ is an example of a natural ecosystem. (Paddy field / Desert)
· Answer: Paddy field
c) The third trophic level in a food chain comprises of _________________ (herbivore / carnivore)
· Answer: Carnivore)
d) A network of interlinked food chain is called a __________________(food web / food cycle)
· Answer: Food Web
e) The festival of “Vanamahotsav” is celebrated in the month of _________. (June / July)
· Answer: July

2. Rearrange the following words to form a food chain.

(a) snake, mouse, paddy, eagle, grasshopper.
_______> ___________> __________> ________> ___________

Answer:  Paddy, mouse, snake, eagle, grasshopper

(b) man, big fish, phytoplankton, small fish, insects.
----------> -----------------> -------------> -------------> ----------
Answer: Phytoplankton, insects, small fish, big fish, man

Characteristic feature Types of Forest

a. Savannah: Frequent forest fire
b. Tundra: Windy weather
c. Taiga: Snow and ice
d. Desert: Hot days and cold nights
e. Grassland: Ice covered frozen soil
f. Rain forest: Plentiful rainfall

8 List of animals with the biome where they are found.

a) Cheetah - Savannah
b) Snake - Tropical Rain Forest
c) Camel - Desert
d) Antelope - Grassland
e) Black bear - Deciduous forest
f) Grey wolf - Taiga
g) Penguin - Tundra

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