Notes Chapter 12 Science Curiosity Class 8 CBSE Board

Notes For All Chapters – Science Curiosity Class 8

How Nature Works in Harmony

Elephant Corridor – Introduction

In states like Odisha, Jharkhand, West Bengal, Assam, and Chhattisgarh, elephants often enter farms and villages.

Reasons:

1. Loss of forest cover.
2. Drying of waterholes.
3. Scarcity of natural food.

• Elephants search for bananas, sugarcane, etc. in farms.
• This causes crop damage and may harm people or animals.
• Cutting trees for roads/buildings + changes in rainfall and temperature shrink forests.
• Wildlife corridors are created to allow safe movement of animals between forests.
• This shows how all elements of nature are connected.

12.1 How Do We Experience and Interpret Our Surroundings?

• Habitat → place where an organism lives (example: pond, forest, tree bark).
• Biotic components = living things (plants, animals, microbes).
• Abiotic components = non-living things (air, water, soil, sunlight, temperature).
• Fish in pond: get food, oxygen, shelter, space.
• Other pond organisms: frogs, turtles, snakes, dragonflies, mosquitoes, snails, ducks, algae, lotus.
• Example of coexistence: Snake active at night, rodent active during day → same habitat, different conditions.

12.2 Who All Live Together in Nature?

• Population → group of organisms of the same kind living in a habitat at a given time.
• Community → different populations living together in the same habitat (plants, animals, microbes).
• Example: Fish population in pond + frog population + plant population = community.

Pollination

• Flowers have sepals, petals, carpels (female), stamens (male).
• Pollen moves from stamen to carpel with help of wind, water, insects, bats, or birds.
• This is pollination → necessary for fruits and seeds.

12.3 Does Every Organism in a Community Matter?

• Study of ponds:
  • Pond A (with fish) → fewer dragonflies → more bees and butterflies → more pollination → more seeds.
  • Pond B (without fish) → more dragonflies → fewer bees and butterflies → fewer seeds.
• Conclusion: Fish indirectly help plants by controlling dragonflies.
• Biotic and abiotic components affect one another.

12.4 What Are the Different Types of Interactions?

• Biotic-abiotic interactions: Plants need sunlight, CO₂, water, soil.
• Abiotic-abiotic interactions: Sunlight increases temperature, water evaporates.
• Biotic-biotic interactions: Frog eats insects, fish eat larvae, organisms compete for resources.

Ecosystem

• Combination of living (biotic) and non-living (abiotic) components.
• Types:
  • Aquatic ecosystems: ponds, rivers, lakes.
  • Terrestrial ecosystems: forests, farms, grasslands.
• Ecosystems can be small or large.

12.5 Who Eats Whom? (Food Relationships)

1. Producers (plants) → make food by photosynthesis.

2. Consumers (animals):

• • Herbivores (eat plants) → deer, hare.
  • Carnivores (eat animals) → leopard.
  • Omnivores (eat plants + animals) → crow, fox, mouse.

3. Food Chain: Linear feeding relationship (e.g., Grass → Grasshopper → Frog → Snake → Eagle).

4. Trophic levels:

• Producers (plants).
• Herbivores.
• Small carnivores.
• Large carnivores.

5. Food Web: Many interlinked food chains in an ecosystem.

12.6 What Happens to Waste in Nature?

• Decomposition: Breaking down of dead plants/animals into simple nutrients.
• Decomposers (saprotrophs): fungi, bacteria, beetles, flies.
• Nutrients return to soil → used by plants.
• Nothing is wasted in nature.

Migratory Birds

• Travel long distances for food and climate.
• Help in pollination, seed dispersal, pest control.
• Example: Demoiselle Crane visits Khichan (Rajasthan) in winter.

12.7 How Does One Change Lead to Another?

Example of pond pollution:

• • Plants die → less oxygen → fish die → insects increase → insects damage crops → farmers use pesticides → more environmental problems.
• Example: Overharvesting frogs in 1980s → fewer frogs → more pests → more pesticides → environmental damage → frog leg exports banned.
• Conclusion: Small changes create chain reactions in ecosystems.

12.8 How Do Interactions Maintain Balance?

• Competition: Organisms compete for food, water, sunlight, space.
• Prevents overpopulation, maintains balance.

Types of relationships:

1. Mutualism → both benefit (bee & flower).
2. Commensalism → one benefits, other not affected (orchid on tree).
3. Parasitism → one benefits, other harmed (tick on dog).

12.9 What Are the Benefits of an Ecosystem?

1. Ecosystems provide:

• • Fresh air, fertile soil, food, timber, medicines.
  • Water, biodiversity, beauty, recreation.
• Example: Sundarbans
  • Largest mangrove forest, home to rare animals.
  • Protects against storms and absorbs CO₂.
  • Declared UNESCO World Heritage Site (1987).
  • Threats: cutting trees, hunting, pollution, overuse of resources.

2.Protected Areas

• National Parks, Wildlife Sanctuaries, Biosphere Reserves.
• Examples: Jim Corbett, Manas, Nilgiri, Chilika Lake, Keibul Lamjao, Hemis, Pirotan Island.

3. Human-made Ecosystems

• Farms, fish ponds, parks.
• Need human care.

4. Farming and Ecosystems

• Green Revolution increased food but used synthetic fertilizers/pesticides.
• Problems: soil degradation, pest resistance, loss of biodiversity.
• Sustainable farming → organic manure, natural pest control, crop diversity.
• Ancient Vrikshayurveda promoted soil nourishment with organic manure like Kunapa Jala.

Snapshots (Summary)

• Habitat → provides conditions for living.
• Biotic + Abiotic components → form an ecosystem.
• Ecosystems can be terrestrial (forests, deserts) or aquatic (ponds, oceans).

Organisms classified as:

• 1. Producers (plants).
  2. Consumers (herbivores, carnivores, omnivores).
  3. Decomposers (fungi, bacteria).
• Food chains and food webs show feeding relationships.
• Interactions include mutualism, commensalism, parasitism.
• Ecosystems provide air, water, food, medicine, and climate regulation.
• Human activities (pollution, deforestation, overuse) threaten balance.
• Conservation through parks, sanctuaries, and sustainable practices is vital.