Quiz Class 7th Science 13-05-2026

Welcome To My School Study

Do You Know

1. Autotrophs and Green Plants

Correct Answer: Green Plants

Explanation

Autotrophs are living organisms that can prepare their own food. Green plants are called autotrophs because they make food with the help of sunlight, water, carbon dioxide, and chlorophyll. This process is known as photosynthesis.

Plants absorb water from the soil through roots and carbon dioxide from the air through tiny pores called stomata. In the presence of sunlight, leaves prepare food for the plant.

Because green plants produce their own food, they are known as producers in the food chain.

Step-by-Step Process of Photosynthesis

Step 1: Roots absorb water from the soil.

Step 2: Leaves take carbon dioxide from the air.

Step 3: Chlorophyll traps sunlight.

Step 4: Plants use sunlight energy to prepare food.

Step 5: Oxygen is released into the atmosphere.

Why Green Plants are Important

• They prepare food for themselves.
• They provide oxygen to living organisms.
• They are the starting point of food chains.
• They help maintain ecological balance.

Examples of Autotrophs

1. Grass
2. Mango tree

Both make their own food using sunlight.

Important Terms

Photosynthesis

The process by which green plants make food using sunlight.

Chlorophyll

The green pigment in leaves that absorbs sunlight.

Producer

An organism that prepares its own food.

Key Points

• Green plants are autotrophs.
• They make food by photosynthesis.
• Sunlight is necessary for food preparation.
• Plants release oxygen during photosynthesis.
• Green plants are called producers.

2. Forests Help in Maintaining Oxygen Supply

Correct Answer: Oxygen

Explanation

Forests are called the “lungs of the Earth” because they continuously supply oxygen into the atmosphere. Trees and green plants in forests perform photosynthesis and release oxygen.

Living organisms like humans and animals need oxygen for breathing. Forests help maintain the balance of oxygen and carbon dioxide in nature.

Without forests, oxygen levels would decrease and life would become difficult.

Step-by-Step Process

Step 1: Trees absorb carbon dioxide from the air.

Step 2: Plants use sunlight to make food.

Step 3: Oxygen is produced during photosynthesis.

Step 4: Oxygen is released into the atmosphere.

Step 5: Humans and animals use oxygen for respiration.

Importance of Oxygen

• Needed for breathing
• Supports life on Earth
• Helps in respiration
• Maintains atmospheric balance

How Forests Help the Environment

• Purify air
• Reduce pollution
• Maintain climate balance
• Increase rainfall

Examples

1. Amazon Rainforest
2. Sundarbans Forest

Both produce huge amounts of oxygen.

Important Terms

Respiration

The process by which living organisms use oxygen to release energy from food.

Atmosphere

The layer of gases surrounding Earth.

Key Points

• Forests release oxygen.
• Oxygen is essential for life.
• Trees absorb carbon dioxide.
• Forests help maintain gas balance.
• Forests reduce air pollution.

3. Forest Disappearance Increases Carbon Dioxide

Correct Answer: Carbon Dioxide

Explanation

Forests absorb carbon dioxide from the atmosphere. When forests disappear due to deforestation, fewer trees remain to absorb carbon dioxide.

As a result, the amount of carbon dioxide in the air increases. Increased carbon dioxide causes global warming and climate change.

Trees act like natural cleaners of the atmosphere.

Step-by-Step Understanding

Step 1: Trees absorb carbon dioxide.

Step 2: Trees use carbon dioxide during photosynthesis.

Step 3: Deforestation reduces the number of trees.

Step 4: Less carbon dioxide gets absorbed.

Step 5: Carbon dioxide level in air increases.

Effects of Increased Carbon Dioxide

• Global warming
• Rise in temperature
• Climate change
• Melting glaciers
• Irregular rainfall

What is Deforestation?

Deforestation means cutting down forests on a large scale.

Causes of Deforestation

• Urbanization
• Farming
• Road construction
• Industries
• Mining

Examples

1. Cutting forests for buildings
2. Clearing forests for agriculture

Important Terms

Global Warming

Increase in Earth’s average temperature due to greenhouse gases.

Greenhouse Gas

A gas that traps heat in the atmosphere.

Key Points

• Forests absorb carbon dioxide.
• Deforestation increases carbon dioxide.
• Increased carbon dioxide causes global warming.
• Trees help control climate.
• Forest conservation is important.

4. Forests as Natural Purifiers

Correct Answer: Both Air and Water

Explanation

Forests naturally clean both air and water. Trees absorb harmful gases and dust from the atmosphere, making the air cleaner.

Forests also help filter rainwater through soil. Roots hold soil particles together and prevent water pollution.

Thus, forests work as natural purifiers.

How Forests Purify Air

• Absorb carbon dioxide
• Release oxygen
• Trap dust particles
• Reduce harmful gases

How Forests Purify Water

• Filter rainwater through soil
• Prevent soil erosion
• Increase groundwater recharge
• Reduce water pollution

Step-by-Step Process

Step 1: Trees trap dust and pollutants.

Step 2: Leaves absorb harmful gases.

Step 3: Rainwater enters forest soil.

Step 4: Soil filters impurities naturally.

Step 5: Clean water reaches underground layers.

Importance of Forest Purification

• Cleaner environment
• Better health
• Safe drinking water
• Reduced pollution

Examples

1. Forests near rivers help clean water.
2. Trees along roads reduce air pollution.

Important Terms

Soil Erosion

Removal of top fertile soil by wind or water.

Groundwater

Water stored beneath Earth’s surface.

Key Points

• Forests clean air naturally.
• Forests help purify water.
• Trees reduce pollution.
• Forest roots prevent soil erosion.
• Forests support healthy ecosystems.

5. Decomposers Maintain Nutrient Supply

Correct Answer: Growing Plants

Explanation

Decomposers are organisms that break down dead plants and animals into simple substances. These simple substances mix with the soil and become nutrients for plants.

Decomposers play a very important role in nutrient recycling.

Without decomposers, dead matter would keep accumulating on Earth.

Examples of Decomposers

1. Bacteria
2. Fungi

These organisms help decompose dead material.

Step-by-Step Process

Step 1: Plants and animals die.

Step 2: Decomposers break down dead matter.

Step 3: Nutrients return to the soil.

Step 4: Plants absorb nutrients through roots.

Step 5: Plants grow healthy again.

Importance of Decomposers

• Clean the environment
• Recycle nutrients
• Improve soil fertility
• Support plant growth

Nutrient Cycle

Nutrients move continuously through:

• Soil
• Plants
• Animals
• Decomposers

This movement is called the nutrient cycle.

What Happens Without Decomposers?

• Dead bodies would pile up
• Soil fertility would decrease
• Plant growth would stop slowly
• Ecosystem balance would be disturbed

Examples from Nature

1. Fallen leaves becoming manure
2. Dead animals decomposing in soil

Important Terms

Nutrients

Substances needed for growth and survival.

Humus

Dark organic matter formed after decomposition.

Key Points

• Decomposers break down dead matter.
• Nutrients return to the soil.
• Plants use these nutrients for growth.
• Fungi and bacteria are decomposers.
• Decomposers help maintain ecosystem balance.

Additional NCERT Learning Points

Importance of Forests

Forests are important because they:

• Provide oxygen
• Maintain rainfall
• Prevent floods
• Protect wildlife
• Maintain climate balance

Forest Ecosystem

A forest ecosystem includes:

• Plants
• Animals
• Microorganisms
• Soil
• Water
• Air

All are connected with each other.

Food Chain in Forest

Example:

Grass → Deer → Tiger

Plants are producers, herbivores are primary consumers, and carnivores are higher consumers.

Conservation of Forests

We should:

• Plant more trees
• Reduce deforestation
• Save wildlife
• Use forest resources carefully

Quick Revision

1. Green plants are autotrophs.
2. Forests maintain oxygen supply.
3. Deforestation increases carbon dioxide.
4. Forests purify air and water.
5. Decomposers recycle nutrients for plants.

Final Important Learning Points

• Forests are essential for life on Earth.
• Green plants are producers of food and oxygen.
• Trees help maintain environmental balance.
• Decomposers recycle nutrients naturally.
• Protecting forests means protecting life.