Home › Free notes › Class 8 Science › How Nature Works in Harmony

How Nature Works in Harmony – Class 8 Science notes, important questions and MCQs

NCERT Class 8 Science, chapter 12. Notes, key terms, important questions with answers and MCQs.

Chapter overview

In nature, living things depend on each other and on their surroundings. Food chains, food webs and relationships like pollination keep ecosystems balanced.

Interdependence

Producers (plants) → herbivores → carnivores; decomposers recycle nutrients.
Food webs are many connected food chains; removing one species affects others.
Relationships: pollination by insects, seed dispersal by birds, lichens (alga + fungus living together).

Balance and conservation

Forests regulate rainfall, soil and climate; deforestation causes floods, soil erosion and loss of habitat.
Protected areas: national parks, wildlife sanctuaries and biosphere reserves.
Endangered species need protection (e.g. tiger, Olive Ridley turtle).

Key terms

Ecosystem: living things and their non-living surroundings working together
Food web: network of interlinked food chains
Biosphere reserve: large protected area for conserving biodiversity and supporting local people

Formulas

Sun → producers → consumers → decomposers

Important questions with answers

What are decomposers? Give two examples.2 marks

Organisms that break down dead plants and animals into simple substances, returning nutrients to the soil. Examples: bacteria and fungi (also earthworms help).

Explain how a food web is different from a food chain.3 marks

A food chain is a single path of who eats whom. A food web is many food chains connected together, because most animals eat more than one kind of food; it shows the real feeding links in an ecosystem.

What is an ecosystem? Describe its components and explain how humans disturb the balance, with three ways to protect it.5 marks

An ecosystem is a community of living things interacting with each other and with non-living surroundings (air, water, soil, sunlight). Components: producers (plants), consumers (herbivores, carnivores, omnivores), decomposers, and abiotic factors. Humans disturb it by cutting forests, polluting air and water, overhunting and bringing in harmful species, which breaks food chains. Protection: plant native trees and save forests; reduce waste and pollution; protect wildlife through biosphere reserves, sanctuaries and national parks.

Quick revision

Every species has a role.
Decomposers return nutrients to soil.
Deforestation disturbs balance.

Exam tips

Explain any "what happens if…" question by following the food web both ways.
Similipal (Odisha) is a biosphere reserve and tiger reserve.

Practice MCQs

Plants in a food chain are
1. consumers
2. producers
3. decomposers
4. predators
Show answer
Answer: (b) producers. They make food.
Lichen is an association of
1. insect and flower
2. bacteria and virus
3. two plants
4. alga and fungus
Show answer
Answer: (d) alga and fungus. Mutual benefit.
If all frogs in a pond disappear, insects will most likely
1. increase
2. decrease
3. stay the same
4. become plants
Show answer
Answer: (a) increase. Fewer predators.
Which helps in pollination?
1. earthworm
2. mushroom
3. honeybee
4. fish
Show answer
Answer: (c) honeybee. Bees carry pollen.
In the food chain grass → grasshopper → frog → snake, the frog is a
1. producer
2. secondary consumer
3. primary consumer
4. decomposer
Show answer
Answer: (b) secondary consumer. Eats a herbivore.
Cutting forests on hills most directly causes
1. more oxygen
2. soil erosion and floods
3. colder winters only
4. more wildlife
Show answer
Answer: (b) soil erosion and floods. Roots stop holding soil.
A biosphere reserve is meant for
1. hunting
2. only tourism
3. conserving biodiversity along with local people's needs
4. mining
Show answer
Answer: (c) conserving biodiversity along with local people's needs. Conservation with sustainable use.
If all frogs are removed from a field, the number of grasshoppers will most likely
1. decrease
2. become zero
3. stay the same
4. increase
Show answer
Answer: (d) increase. Fewer predators.

All chapters of Class 8 Science

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.