Notes For All Chapters – General Science Class 8
1. Introduction to Ecosystems
- An ecosystem is a system where living (biotic) and non-living (abiotic) things interact with each other.
- It includes plants, animals, microorganisms, air, water, soil, and sunlight.
- Every ecosystem has a balance, and changes in one part affect the entire system.
2. Components of an Ecosystem
(A) Biotic (Living) Factors
- Producers (Plants) → Make their own food using sunlight (photosynthesis).
- Consumers (Animals) → Depend on plants or other animals for food.
- Decomposers (Bacteria, Fungi) → Break down dead plants and animals, recycling nutrients.
(B) Abiotic (Non-Living) Factors
- Sunlight → Helps plants grow and provides energy.
- Air → Provides oxygen for animals and carbon dioxide for plants.
- Water → Essential for all living beings.
- Soil → Provides nutrients for plants.
3. Types of Ecosystems
(A) Natural Ecosystems (Formed by nature)
Terrestrial (Land) Ecosystems
- Forest: Dense trees, animals like tigers, elephants, monkeys.
- Desert: Hot, sandy, dry; animals like camels and cacti.
- Grassland: Large open lands with grasses, animals like deer, lions.
Aquatic (Water) Ecosystems
- Pond: Small body of freshwater with fish, frogs, and plants.
- River: Flowing freshwater, home to fish, crocodiles, and aquatic plants.
- Ocean: Saltwater, large marine life like whales, sharks, and corals.
(B) Man-Made Ecosystems (Created by humans)
- Farms → Grown for food and agriculture.
- Gardens → Created for decoration and nature preservation.
- Dams → Provide water and electricity but change ecosystems.
4. Food Chain and Food Web
(A) Food Chain
- A food chain shows how energy flows in an ecosystem.
- Example: Grass → Grasshopper → Frog → Snake → Eagle
(B) Food Web
- A food web is a combination of many food chains in an ecosystem.
- It shows how different organisms depend on each other for food.
5. Biomes
A biome is a large ecosystem covering a vast area with similar climate and organisms.
Examples of Biomes:
- Tropical Rainforest → Heavy rainfall, evergreen trees.
- Savanna → Grassland with scattered trees.
- Desert → Dry, very little rain.
- Tundra → Very cold, little vegetation.
6. Human Impact on Ecosystems
(A) Deforestation
- Cutting down trees destroys ecosystems.
- Causes soil erosion, reduces oxygen, and affects rainfall.
(B) Pollution
- Air pollution: Factories and vehicles release harmful gases.
- Water pollution: Waste from industries and plastic harms aquatic life.
- Soil pollution: Chemicals and plastics make land infertile.
(C) Urbanization
- Forests and wetlands are destroyed for roads, buildings, and cities.
- Wildlife loses their natural habitat, leading to species extinction.
(D) Overpopulation
- More people = More use of natural resources.
- Leads to overfishing, excessive farming, and habitat destruction.
(E) Effect of Wars on Ecosystems
- Wars destroy forests, rivers, and animal habitats.
- Nuclear explosions damage land and air for many years.
7. Conservation of Ecosystems
(A) Reforestation
- Planting trees to replace lost forests.
(B) Wildlife Protection
- Setting up national parks and wildlife sanctuaries.
- Example: Rhinoceros were reintroduced in Dudhwa National Park.
(C) Pollution Control
- Reducing plastic use and switching to biodegradable materials.
- Recycling waste to prevent land and water pollution.
(D) Sustainable Development
- Using renewable energy sources like solar and wind power.
- Conserving water and reducing overuse of natural resources.
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