CBSE Class 8 > Class 8 Notes > Science Curiosity - New NCERT > Cheat Sheet: How Nature Works In Harmony
Cheat Sheet: How Nature Works In Harmony
1. How Nature Works in Harmony
1.1 Interconnectedness
- All parts of nature are interconnected.
- Small changes in one part affect other parts.
- Water, sunlight, plants, animals, and humans form linked relationships.
1.2 Habitats and Components
| Term | Definition |
|---|---|
| Habitat | The place where an organism lives and which provides conditions for its survival. |
| Biotic components | All living things in a habitat (plants, animals, microbes). |
| Abiotic components | Non-living elements of a habitat (air, water, sunlight, soil, temperature, stones). |
| Diversity in habitats | Different habitats host different kinds of living beings adapted to local conditions. |
2. Organisms, Populations and Communities
2.1 Population and Community
| Term | Definition |
|---|---|
| Population | Group of the same kind of organisms living together in a specific area at a given time. |
| Community | All different populations of organisms living and interacting in the same habitat. |
2.2 Measuring Population
- Mark a fixed area (e.g., 1 m × 1 m).
- Count the number of individuals of each kind in that area.
- Record the count as the population for that area and time.
3. Ecosystem and Interactions
3.1 Ecosystem: definition and types
| Term | Definition |
|---|---|
| Ecosystem | All living and non-living things in an area together with their interactions. |
- Aquatic ecosystems: ponds, rivers, lakes.
- Terrestrial ecosystems: forests, grasslands, farmlands.
- Ecosystems can overlap (e.g., a river through a forest).
3.2 Types of interactions
| Interaction | Definition |
|---|---|
| Biotic-abiotic interactions | Relationships between living organisms and non-living environmental factors. |
| Abiotic-abiotic interactions | Interactions among non-living elements that affect habitat conditions. |
| Biotic-biotic interactions | Relationships among living organisms within a community. |
| Mutualism | Both organisms benefit. |
| Commensalism | One benefits; the other is unaffected. |
| Parasitism | One benefits; the other is harmed. |
3.3 Pollination
| Term | Definition |
|---|---|
| Flower structure | Flowers have sepals, petals, stamens (male), and carpels (female). |
| Pollination | Transfer of pollen grains from a stamen to a carpel of the same or another flower. |
| Pollination agents | Wind, water, insects, bats, and birds carry pollen. |
| Pollination importance | Essential for the formation of fruits and seeds. |
4. Feeding Relationships: Producers, Consumers, Decomposers
4.1 Producers and Consumers
| Term | Definition |
|---|---|
| Producers (Autotrophs) | Organisms that make their own food (usually plants via photosynthesis). |
| Consumers (Heterotrophs) | Organisms that obtain energy by eating other organisms. |
| Herbivores | Consumers that eat only plants (examples in source: deer, horse). |
| Carnivores | Consumers that eat only animals (examples in source: vulture, shikra). |
| Omnivores | Consumers that eat both plants and animals (examples in source: fox, mouse). |
| Decomposers | Organisms that break down dead matter and recycle nutrients (mushrooms, bacteria). |
4.2 Food chains, food webs and trophic levels
- Food chain: a sequence showing who eats whom.
- Example chain 1: Grass → Hare → Tiger.
- Example chain 2: Grass → Grasshopper → Frog → Snake → Eagle.
| Term | Definition |
|---|---|
| Trophic levels | Positions of organisms in a food chain indicating energy transfer. |
| First trophic level | Producers (plants such as grass, millet). |
| Second trophic level | Herbivores (organisms that eat plants, e.g., hare, mouse). |
| Third trophic level | Small carnivores that eat herbivores (e.g., frogs). |
| Fourth trophic level and above | Large carnivores or top predators (e.g., eagle, hawk, fox). |
- Ecological pyramid: numbers of organisms at each trophic level form a pyramid with producers at the base.
- Food web: overlapping food chains where organisms may be eaten by multiple predators.
5. Decomposers, Migration and Waste
5.1 Decomposers and decomposition
| Term | Definition |
|---|---|
| Decomposers | Organisms that break down dead plants, animals, and waste into simpler substances. |
| Examples of decomposers | Mushrooms (fungi), bacteria, beetles, flies. |
| How decomposition works | Decomposers feed on dead material and convert complex substances into simpler forms. |
| Nutrient recycling | Decomposition returns nutrients to the soil for plant use. |
| Ecological balance | Decomposers prevent buildup of dead material and waste. |
| Saprotrophs | Alternate name for decomposers (saprotroph = "rotten" + "food"). |
5.2 Migratory birds
| Term | Definition / Note |
|---|---|
| Migratory birds | Birds that travel long distances between habitats and countries to avoid harsh climates or find food. |
| Example | Demoiselle Cranes visit Khichan village in Rajasthan every winter. |
- Roles of migratory birds: enhance beauty, act as pollinators and seed dispersers, and provide pest control.
6. Human Impacts, Threats and Conservation
6.1 Cascading effects and human interventions
- Plant death in ponds reduces oxygen; fish decline; insect numbers rise; insects harm nearby crops; farmers increase pesticide use.
- Overfishing removes many fish; predator removal can alter populations of other organisms and reduce pollination.
- Frog-leg export case: in the 1980s India exported many Indian bullfrogs; frog populations fell; insect pests rose; pesticide use increased; government banned frog-leg exports to restore balance.
6.2 Threats to ecosystems
- Deforestation.
- Pollution (industrial waste, untreated sewage).
- Unsustainable land use and overuse of natural resources.
- Illegal hunting.
- Spread of invasive species.
6.3 Conservation and protected areas
| Term | Definition |
|---|---|
| Protected areas | Parts of land or water set aside to conserve wildlife and their habitats. |
| Benefits of protected areas | They protect habitats including endangered animals, birds, and rare plants. |
- Famous examples: Jim Corbett National Park; Manas National Park; Nilgiri Biosphere Reserve; Chilika Lake; Eaglenest Wildlife Sanctuary; Hemis National Park; Keibul Lamjao National Park; Pirotan Island Marine National Park.
- Community action and sustainable practices help conserve resources and avoid pollution.
6.4 Human-made (artificial) ecosystems and farming
- Human-made ecosystems: farms, fish ponds, parks; require continuous human care.
- Green Revolution (mid-20th century, between 1950 and 1965) used tractors, machines, synthetic fertilizers, and pesticides to increase food production.
- Harms of intensive methods: overuse of chemicals, excessive groundwater extraction, monoculture, soil degradation, loss of soil fertility, reduced humus, soil erosion, disturbance of soil organisms, pest resistance to pesticides, reduced pollinators.
- Some farmers explore organic and natural methods to reduce synthetic inputs and protect ecosystems.
6.5 Scientific heritage and traditional practices
| Term | Definition / Note |
|---|---|
| Vrikshayurveda | Ancient text emphasizing soil health and nourishment. |
| Kunapa Jala | Liquid fertilizer made by fermenting animal and plant waste for continuous soil nourishment. |
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