CLASS 8 SCIENCE · CHAPTER 12 · STUDY NOTES
How Nature Works in Harmony
Understand how nature works in harmony through short explanations, labelled models and original practice. Read one topic, explain it in your own words, then check.
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A habitat includes living and non-living conditions
Find both the organism and what it needs around it.Picture from the NCERT book
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- Habitat
- The place where an organism lives, with the conditions it needs.
- Biotic component
- A living component, such as a plant, animal or microbe.
- Abiotic component
- A non-living environmental component, such as water, sunlight, air or temperature.
A pond provides aquatic organisms with water, dissolved gases, food and shelter. A forest provides different conditions, and even tree bark can be a small habitat.
Organisms sharing a habitat may use different spaces, foods or times of day. A habitat is not just a background picture; its conditions affect survival.
Take a moment. What do you think?
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Question
In a pond, classify a frog and the water: which is biotic and which abiotic?
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One organism, one population, one community
Specify the species, place and time when describing a population.Include more at each level
- Population
- Individuals of the same species in a stated area at a stated time.
- Community
- The different populations living and interacting in an area.
- Ecosystem
- Living communities and their non-living environment interacting as a system.
All frogs of one species in a pond at a particular time form a population. The frogs, fish, plants and microbes together belong to its community. Add their interactions with water, light and other conditions to describe the ecosystem.
A population is not simply “all animals.” A community includes different species but the water itself is not a member of the living community.
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Question
Does “all fish in a lake” always describe one population?
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A fish can affect flowers without eating them
Trace each link rather than guessing a direct connection.Name what each connection changes
- Indirect effect
- An effect on one organism through changes in other organisms or conditions.
In the book’s pond example, fish eat dragonfly larvae. Fewer adult dragonflies can mean less predation on pollinating insects; more pollinator visits can help nearby plants set seed.
This is a possible causal chain supported by the described study, not a guarantee that adding fish improves every pond. Other species, nutrients and physical conditions also matter.
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Question
How could fewer dragonfly larvae eventually influence nearby flower seed production?
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Food arrows point from food to the eater
Follow where food and its energy go.Food travels towards the consumer
- Producer
- An organism that makes its own food, such as a photosynthetic green plant.
- Consumer
- An organism that obtains food from other organisms.
- Trophic level
- A feeding position within a particular food chain.
A simple chain can be grass → grasshopper → frog. The grasshopper eats grass, and the frog eats the grasshopper. Herbivores eat plant material; carnivores eat animals; omnivores eat both.
Real organisms often have several food sources and predators, connecting chains into a food web. Counting individuals at each level can give a pyramid of numbers in some examples, but not every ecosystem has the same count pattern.
Let’s look a little closer.
Go deeper: A web is more realistic than one chain
A frog may eat several insects, and more than one predator may eat frogs. These overlapping chains form a food web. Removing one species can affect many links, but predicting exact numbers requires evidence about the actual ecosystem.
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Question
In grass → grasshopper → frog, why does the arrow start at grass and point to the grasshopper?
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Decomposers return nutrients; energy is not recycled
Keep the nutrient loop separate from the flow of energy.Trace a nutrient loop
- Decomposition
- Breaking down dead organic material and wastes into simpler substances.
- Decomposer
- An organism, such as a bacterium or fungus, that carries out decomposition.
Decomposers help return nutrients to soil and water so producers can use them again. Detritus-feeding animals also break material into smaller pieces and assist the process.
Nutrients cycle, but energy flows through organisms and is eventually dissipated as heat. “Everything is reused” is not a claim that energy returns unchanged to a plant.
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Question
If dead leaves were never decomposed, how would that affect the soil nutrient cycle?
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Ask who benefits and who is harmed
Different interactions have different outcomes.A mutual benefit has two different jobs
- Mutualism
- An interaction in which both participants benefit.
- Commensalism
- An interaction benefiting one participant without a significant effect on the other in the example.
- Parasitism
- An interaction in which one organism benefits while its host is harmed.
- Competition
- An interaction in which organisms use the same limited resource.
| Interaction | Participant 1 | Participant 2 |
|---|---|---|
| Mutualism | Benefits | Benefits |
| Commensalism | Benefits | No significant effect in the example |
| Parasitism | Parasite benefits | Host harmed |
| Competition | Access can be reduced | Access can be reduced |
A bee can gain nectar while helping a flower receive pollen: both benefit. An orchid growing on a tree can gain support without taking the tree’s food. A blood-feeding tick benefits while harming its dog host.
Competition can occur within one species or between species. It is not always a fight, and no single interaction guarantees that every population will remain constant.
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Question
Two seedlings draw water from the same drying soil. Must they physically fight to compete?
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Ecosystems change, and damage can spread
Explain a mechanism without claiming every change has one fixed result.A connection changes access
- Habitat fragmentation
- Breaking a habitat into smaller separated areas.
- Wildlife corridor
- A connection that helps animals move between habitat areas.
When forest routes are cut off, animals may enter farms while searching for food or water. Corridors can help reconnect habitat. Pollution can also affect aquatic plants, oxygen availability and feeding relationships.
Mangroves provide habitat and can reduce some coastal wave impacts, but they do not guarantee safety from every storm or tsunami. Protecting habitats and following disaster warnings are complementary actions.
Go deeper: Protection includes places and people
The Sundarbans span India and Bangladesh and include mangrove habitats important to biodiversity and livelihoods. National parks, sanctuaries and community conservation protect habitats in different ways. Management must account for local needs and evidence about species, pollution and land use.
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Question
Why can a road between two forest areas create a problem even if trees remain on both sides?
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A farm is an ecosystem people manage
Protect productivity as well as soil, water and other life.Manage several resources together
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- Sustainable farming
- Managing farming to meet present needs while protecting the resources and ecosystems needed in the future.
- Monoculture
- Growing one type of crop over an area or repeatedly in a farming system.
Fertiliser, irrigation, machinery and pest control can increase production. Overuse or poorly managed use can also pollute water, damage soil and reduce helpful organisms. “Natural” does not automatically mean harmless, and every farm needs suitable management.
Crop diversity, appropriate nutrient use, water conservation, composting and protecting natural pest predators can help. Farmers and specialists should choose methods for the crop, soil and local conditions.
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Question
Why might killing all insects in a crop field make pest control harder later?
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Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 10, 16, 17, 20.