NCERT Class 7 Science Chapter 17: Forests Our Lifeline YouTube Lecture Handouts

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NCERT Class 7 Science Chapter 17: Forests: Our Lifeline (NSO/NSTSE)

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Brain Teasers

  • What is Canopy?

  • Do all forest have same climate conditions?

  • Nothing goes waste in forest – Why?

  • Why are forests destroyed?

  • Humus by decomposers

  • Dead animals become food for vulture

  • Broken branches as fuel by people


Forest visit

Forest Visit

Forest visit

  • Factory by clearing forest area, increasing population – job creation

  • Forest as green lung and water purifying system

  • Peaceful environment with animals – bison, boar

  • Not recommended to go deep in forest areas

Do Not Cut a Tree

Preserve trees

Preserve Trees

Preserve trees

Forest As Habitat - Some Forest animal




Some Forest Plants

Wood and tree products

Wood and Tree Products

Wood and tree products

  • sal, teak, semal, sheesham, neem, palash, fig, khair, amla, bamboo, kachnar

  • Creepers and climbers with sun barely visible

Wood products

Wood Products

Wood products

  • Plywood, fuel wood, boxes, paper, matchsticks, and furniture

  • The forest floor provides favorable conditions for them to germinate and develop into seedlings

  • Different forests vary – have different species.

Forest Products

Forest products

Forest Products

Forest products

Catechu, honey, gum

Some Crown Shapes




  • Tall trees look like roof over the plants in forests

  • Herbs are lowest layer

  • Due to different climatic conditions there are variations in the types of trees and other plants

Forest Floors

Forest floors

Forest Floors

Forest floors

  • Spiders, squirrels, ants and various other small animals on the bark of the trees, plant leaves and on decaying leaves on the forest floor

  • The forest floor seemed dark coloured (converted to humus) and was covered with a layer of dead and decaying leaves, fruits, seeds, twigs and small herbs. The decaying matter was moist and warm.

  • Mushrooms over decaying leaves

Interrelationship of Plant, Soil and Decomposers in a Forest

Tree and sun

Tree and Sun

Tree and sun

  • In the forest, there is interaction between soil, water, air and living organisms.

  • Food chain - Grass insects frog snake eagle. Many food chains can be found in the forest. All food chains are linked

  • Disturbance in one food chain affects the another

  • The micro-organisms which convert the dead plants and animals to humus are known as decomposers

Balance of Oxygen and Carbon Dioxide

Respiration and combustion

Respiration and Combustion

Respiration and combustion

  • Photosynthesis

  • Forests are lungs

  • Trees take in water from their roots and release water vapour into the air through evaporation

  • Forest – source of food, shelter, water and medicine

  • Droppings of animals; footprints of animals

Deer in a Forest

Deer from forest

Deer from Forest

Deer from forest

  • The animals also disperse the seeds of certain plants and help the forest to grow and regenerate. The decaying animal dung also provides nutrients to the seedlings to grow.

  • Forest gives opportunity for herbivores

A Sapling on a Wall

Plant in wall

Plant in Wall

Plant in wall

Forest is a ‘dynamic living entity’ — full of life and vitality (decomposers help to grow and regenerate)

Rainwater Drips from Trees and Seeps into Ground

  • The closed canopy and many layers of vegetation slow down the speed of raindrops

  • The root system helps water to seep down in the ground

  • Covered ground with decaying material acts like a sponge

  • Forest acts as a natural absorber of rainwater and allows it to seep. It helps maintain the water table throughout the year. Forests not only help in controlling floods but also help maintain the flow of water in the streams so that we get a steady supply of water

  • Roots bind with soil but in their absence soil is washed

  • Forest lead to good rain, less noise pollution

Trouble - High CO2, No Shelter for Animals, Floods Will Occur, Deforestation

  • Forests are the lifeline for the forest-dwelling communities.

  • Forests influence climate, water cycle and air quality.

  • Indiscriminate felling of trees, cutting of forests, overgrazing, urbanization, industrialization

  • Forests:

  • Provide us with oxygen.

  • Protect soil and provide habitat to a large number of animals.

  • Prevent erosion

  • Maintain ground water level

  • Bring good rainfall in neighboring areas.

  • Source of medicinal plants, timber and many other useful products.

  • We must preserve our forests.

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