Notes Chapter 12 Science Curiosity Class 8 CBSE Board

How Nature Works in Harmony

1. Introduction

In many Indian states like Odisha, Jharkhand, West Bengal, Assam, and Chhattisgarh, elephants enter farms due to loss of forests and water.

This happens because of:

1. Cutting trees

2. Less rainfall

3. Drying waterholes

Elephants look for food like bananas and sugarcane.

Elephant corridors are created to help animals move safely between forests.

2. What is a Habitat?

A habitat is a place where an organism lives.

It has:

1. Biotic (living) components – animals, plants, microbes

2. Abiotic (non-living) components – air, water, soil, temperature

3. Components of a Habitat

Example 1: Pond

• Biotic: fish, frogs, turtles, ducks, insects, plants like algae
• Abiotic: water, soil, sunlight, oxygen

Example 2: Forest

• Biotic: birds, trees, snakes, insects
• Abiotic: soil, air, temperature, sunlight

4. Population and Community

Population: A group of same kind of organisms (e.g., many frogs).

Community: Different populations living together (e.g., frogs, fish, insects, plants in a pond).

5. Types of Organisms

Producers: Make their own food (plants).

Consumers: Eat other organisms.

• Herbivores: Eat only plants (deer, hare).
• Carnivores: Eat only animals (fox, tiger).
• Omnivores: Eat plants and animals (crow, human).

Decomposers: Break down dead matter (fungi, bacteria).

6. Food Chain and Food Web

Food Chain: Simple line of who eats whom.

• Example: Grass → Grasshopper → Frog → Snake → Eagle

Food Web: Many food chains linked together.

Trophic levels: Position in the food chain:

1. Producer
2. Primary consumer
3. Secondary consumer
4. Tertiary consumer

 7. Interactions in Nature

Biotic ↔ Abiotic interactions: e.g., fish need oxygen from water.

Biotic ↔ Biotic interactions: e.g., frog eats insects.

Abiotic ↔ Abiotic interactions: e.g., sunlight heats water.

8. Types of Relationships in Nature

1. Mutualism: Both benefit (bee and flower)

2. Commensalism: One benefits, other not affected (orchid on tree)

3. Parasitism: One benefits, other is harmed (tick on dog)

 9. Decomposition in Nature

Decomposers (like fungi, bacteria, flies) break down dead plants and animals.

This returns nutrients to the soil.

Example: Mushrooms on dead trees.

10. Chain Reactions in Ecosystems

One change leads to another:

• Polluted pond → plants die → less oxygen → fish die → insects increase → more pesticide use → environmental damage.

 11. Human Activities and Nature

• Overharvesting (e.g., frog legs) caused pest problems in farms.
• Pollution, deforestation, and pesticides disturb the balance in nature.

 12. Importance of Ecosystem Balance

Ecosystems stay balanced through:

• Feeding
• Competition (for food, water, light, space)

If one species grows too much, it creates imbalance.

13. Benefits of Ecosystems to Humans

• Forests provide air, food, medicine, water.
• Aquatic ecosystems give food and water.
• Example: Sundarbans mangrove forest protects from floods, but is under threat due to cutting trees and pollution.

14. Natural and Human-made Ecosystems

Natural ecosystems: forests, rivers, ponds.

Human-made ecosystems: farms, fish ponds, parks.

• Need human care and planning.

15. Farming and Sustainability

Green Revolution increased food using machines, fertilizers, and pesticides.

Now, it causes:

• Soil damage
• Pest resistance
• Loss of biodiversity

Sustainable farming uses natural methods to protect soil and health.