Class 8, Science, Chapter-5, Lecture-1, Biosphere (Notes)
BIOSPHERE:
The life-supporting zone of the Earth where the atmosphere, hydrosphere and the lithosphere interact and make life possible is known as the biosphere.
ECOSYSTEM:
The structural and functional unit of biosphere, constituting all the living and non-living components which is capable of independent existence is called an ecosystem.
Examples: natural ecosystems : forests, deserts, mountains, lakes.
Man-made ecosystems : Gardens, Ponds, Crop fields
FOOD CHAIN:
A sequence of the living organisms in a community, through which food energy is transferred from one organism to another organism by consuming, is called a food chain. Examples of food chain.
BIOGEOCHEMICAL CYCLES:
A constant interaction in which continuous transfer of matter and energy between the biotic and abiotic components of the biosphere occur, which makes the biosphere a dynamic but stable system, is known as a biogeochemical cycle.
Examples: Water cycle, Nitrogen cycle, Carbon cycle, Oxygen-cycle
BIODIVERSITY:
The existence of various kinds of living organisms based on features and inter-relationship of organisms is termed as Biodiversity.
WILDLIFE:
The plants and animals which are found in their natural habitat and are not cultivated or domesticate are termed as wildlife.
DEFORESTATION:
The clearing of forests over a wide area due to cutting of trees by human beings or due to natural calamities (forest fire, droughts) is termed as deforestation.
CAUSES OF DEFORESTATION:
- Procuring land for cultivation
- Building houses and factories
- Obtaining wood for fuel
- Making furniture
- Making paper
CONSEQUENCES OF DEFORESTATION:
- Global warming due GREENHOUSE EFFECT caused by increase in CO2
- DROUGHTS due to decrease in Rainfall
- DESERTIFICATION due to reduced soil fertility caused by soil erosion
- Frequent FLOODS due to reduced infiltration rate of surface water
- Shortage of forest products
- Reduced BIODIVERSITY due to extinction of wild animals and plants
Soil erosion:
Removal of topmost layer of soil by wind, water or other activities is called soil erosion. Roots of plants prevent soil erosion by firmly holding the soil particles.
Green House Effect:
The rise in temperature of the environment due to absorption of infra-red radiations radiated by the earth by the gases present in the atmosphere is called greenhouse effect.
Deforestation causes Drought.
Justification:
Plants help in water cycle by putting ground water into the atmosphere by transpiration.
Plants also maintain temperature by reducing level of CO2 by using it for photosynthesis.
Both these factors help in formation of cloud and thus causes rain.
Deforestation will disturb the water cycle and may reduce rainfall, thus causing drought.
Deforestation causes Desertification.
Justification:
Roots of plants keep soil held together and prevent soil erosion.
Dead leaves of plants enrich the top layer of soil with nutrients and humous.
Deforestation leads to soil erosion which removes the fertile top layer and causes desertification.
Deforestation causes Floods.
Justification:
Deforestation reduces percolation of water from soil surface into the ground. So, runoff water goes to rivers.
Deforestation leads to soil erosion. The eroded soil is carried by runoff water and is deposited at river beds. This reduces water carrying capacity of rivers.
Global warming caused by deforestation leads to melting of glaciers. This increases flow of water into the rivers.
The combined effect of all the above three factors lead to frequent floods.