Our Environment

A leaf falls beside a snack wrapper. Both have left someone’s use, but will they follow the same journey? A frog disappears from a garden. Does only the frog change, or do its food and predators change too? Environmental science begins by following connections rather than treating each object as isolated.

This note follows Class 10 Science, NCERT Chapter 13: Our Environment, with the 2026–27 CBSE scope checked. Explore ecosystems, feeding relationships, energy transfer, biological magnification, ozone depletion and waste. The optional Follow the connections workshop lets you trace a small food web, compare energy routes and redesign a waste decision.

Introduction

An organism’s environment includes the living things and physical conditions around it. A plant’s growth depends on light, water, temperature and nutrients, but also on herbivores, competitors and microorganisms. Humans belong within these relationships: food, breathable air, water and many livelihoods depend on ecological processes.

Three questions will carry you through this chapter: What is connected? What is transferred? What happens when the connection changes? The answer may involve energy, matter or a harmful substance. Those are different quantities, so the same arrow diagram cannot explain all of them without a key.

Ecosystems: what are their components?

An ecosystem consists of interacting organisms in an area together with its non-living surroundings. A pond includes algae, aquatic plants, fish, insects and microorganisms, along with water, dissolved substances, light and temperature. Listing the fish alone describes only part of the system.

• Biotic components are living organisms: producers, consumers and decomposers, including humans.
• Abiotic components are non-living factors such as light, temperature, air, water and mineral nutrients. Soil contains both non-living material and living organisms; its microbes do not become abiotic merely because they live underground.

A change can travel across this distinction. Shade changes an abiotic condition, which can change plant growth, which can affect the food available to herbivores. Organisms also alter their surroundings: roots affect soil structure, while decomposition returns substances that plants can use. Nutrients cycle between organisms and their physical surroundings; usable energy flows through the system and is eventually dispersed as heat. Ecosystems change over time; “balance” does not mean that every population remains constant.

Three feeding roles

Producers make organic food from inorganic materials. In the ecosystems studied here, green plants, algae and some bacteria use light energy in photosynthesis. Producers transform energy; they do not create it. Mineral nutrients are essential materials, but soil is not the source of a green plant’s food energy.

Consumers obtain organic food from other organisms. Herbivores eat plant material; carnivores eat animals; omnivores eat both. A consumer’s position depends on what it eats in the particular chain, not simply on its size or name.

Decomposers, especially many bacteria and fungi, break down dead organic matter and wastes. Their activity helps return nutrients to the environment. Earthworms and woodlice ingest fragments of dead material and help decomposition; vultures consume carcasses. These detritivores and scavengers assist the process, but calling all of them microbial decomposers hides how they feed.

Would adding more fish make a pond ecosystem more complete?

Not necessarily. More consumers also need food and oxygen and produce wastes. Ask whether producers, microorganisms and physical conditions can support them. An ecosystem is a set of relationships, not a collection that improves whenever more organisms are added.

Types of ecosystems

Forests, lakes and grasslands are examples of natural ecosystems. Gardens, crop fields and aquariums are examples created or managed by people. Human-made does not mean that ecological processes stop: plants still photosynthesise, organisms respire, and wastes must be processed.

NCERT’s aquarium activity invites us to think about food, oxygen, plants and cleaning. Use it as a design problem: draw the needed inputs and outputs before introducing any organisms. Adding a few plants does not guarantee a permanently self-sustaining aquarium. Its size, light, organisms, feeding and maintenance matter. A drawing or observation of an existing responsibly maintained aquarium is enough for this investigation.

Land-based and aquatic describe another distinction. A human-managed aquarium is aquatic; a garden is terrestrial. These labels answer different questions, so they should not be presented as mutually exclusive alternatives on one list.

Food chain and food web

A food chain shows a sequence of feeding relationships. In the conventional energy-flow direction, an arrow points from food to the organism eating it. Read “grass → grasshopper” as “energy in grass becomes available to a grasshopper that eats it”, not “grass attacks a grasshopper”.

One simplified chain is grass → grasshopper → frog → snake. An aquatic example is phytoplankton → zooplankton → small fish → larger fish, for organisms with those feeding relationships. The examples represent particular diets; they do not claim that every snake eats frogs or every fish occupies the same level.

Trophic levels describe positions

1. First trophic level: producers, such as grass.
2. Second: primary consumers eating producers, such as the grasshopper.
3. Third: secondary consumers eating primary consumers, such as the frog in this chain.
4. Fourth: tertiary consumers, such as the snake eating that frog.

People may act as primary consumers when eating plants and occupy higher positions when eating animals. An omnivore can participate at different levels in a food web. Humans are not automatically at the top of every food chain.

A food web joins multiple chains. In our fictional garden model, plants feed grasshoppers and mice; grasshoppers feed frogs; frogs and mice feed snakes. If frogs are removed, the mouse route to snakes remains. That does not prove snakes will be unaffected: food quantity, habitat and other interactions are not supplied by the diagram. A web shows possible relationships, not a guaranteed population forecast.

Dead material and waste from many levels enter decomposition pathways. A leaf → woodlouse → bird pathway begins with detritus, or dead organic material. Decomposers do not wait at a final level reached only after the largest predator dies; they act on material from across the system.

A bird eats seeds today and insects tomorrow. Did its “fixed level” change?

There was no single fixed level for the bird across all feeding relationships. Eating seeds puts it directly after a producer. Eating an insect that fed on a plant adds another transfer. State the diet and chain before assigning the trophic level.

Pyramid of trophic levels

Photosynthesis introduces usable chemical energy into the food relationships considered here. At each subsequent transfer, only part becomes biomass available to the next consumer. Organisms use energy in living processes, releasing heat through respiration. Some material is uneaten or leaves as waste and enters other pathways. Energy is conserved, but dispersed heat is not recycled by decomposers into a fresh supply of sunlight.

Use the 10% model carefully

NCERT uses about 10% as an average transfer approximation. For a school model, multiply the energy at one trophic level by 0.1 to estimate the next. It is not an exact efficiency measured for every species, meal or ecosystem.

Suppose producers supply 1,000 kJ in a specified area and period. With the model’s same boundaries and 10% transfer at each step:

• Primary consumers: 1,000 × 0.1 = 100 kJ.
• Secondary consumers: 100 × 0.1 = 10 kJ.
• Tertiary consumers: 10 × 0.1 = 1 kJ.

These values explain why long chains have progressively less energy available to support further transfers. They do not impose a universal maximum of four trophic levels. Do not read them as numbers of animals, and do not assume that all of the remaining 90% becomes heat immediately: uneaten material and wastes also carry energy into detrital pathways.

NCERT separately mentions plants capturing about 1% of the sunlight falling on their leaves. That describes the sunlight-to-producer step, whereas the 10% approximation describes transfer between trophic levels. If a question already gives energy stored by producers, do not multiply by 1% again.

Energy, biomass and numbers are different pyramids

An energy pyramid compares energy flow through trophic levels over a stated area and time; the energy available decreases upwards. A pyramid of numbers counts organisms, while a biomass pyramid compares the mass of living material at a particular time. Those latter two can have different shapes. For example, one tree can support many plant-eating insects. This optional distinction prevents a misleading inference from the drawing: fewer energy units do not necessarily mean fewer individual organisms in every case.

A secondary consumer has 20 kJ in the 10% model. How much was available at the producer level?

Work backwards through two transfers: 20 ÷ 0.1 = 200 kJ at the primary-consumer level; 200 ÷ 0.1 = 2,000 kJ at the producer level. The result follows the supplied model, not an exact measurement of nature.

Biological magnification

A food web can transfer pollutants as well as food. Certain persistent chemicals enter soil or water, are taken up by organisms, and pass to consumers. When uptake exceeds breakdown or elimination, a substance can accumulate within an organism. Eating many contaminated prey can contribute to higher concentrations at higher trophic levels.

• Bioaccumulation: build-up within an organism over time.
• Biomagnification, or biological magnification: increasing concentration across successive feeding levels.

The chemical’s properties matter. Not every pesticide, metal or non-biodegradable object magnifies in every chain. A plastic bottle persists, but its persistence alone does not establish a particular biomagnification pattern. Concentration means an amount per unit of tissue or other material; it is different from the total amount in a larger organism.

The US Geological Survey’s mercury account gives a documented example: methylmercury can magnify through aquatic food webs. Its occurrence depends on chemical transformations, feeding relationships and environmental conditions. This is why a clean-looking water body is not proof that its food web contains no contaminants.

Energy decreases up a chain. Must pollutant concentration decrease too?

No. Usable energy is transferred and dissipated through living processes. A persistent substance can be retained and concentrated as predators consume contaminated prey. They are different quantities with different pathways; the 10% energy model is not a rule for contaminant concentration.

How do our activities affect the environment?

Changing land use, releasing pollutants, removing organisms and producing waste can alter ecological relationships. The effects may spread beyond the place of release: water moves material downstream, air carries gases, and organisms carry substances through feeding.

This chapter examines ozone depletion and waste in detail. For each problem, separate the source, the process causing harm and the action that interrupts it. A neat pile of mixed waste still needs appropriate treatment. Likewise, moving an ozone-depleting gas from one place to another does not prevent its eventual release.

The ozone layer and how it is being depleted

Ozone, O₃, contains three oxygen atoms per molecule. The oxygen gas involved in aerobic respiration is O₂. In the stratosphere, ozone absorbs harmful ultraviolet radiation from the Sun and helps protect organisms. At ground level, elevated ozone is an air pollutant that can harm breathing and vegetation. The molecule is the same; its location changes its environmental role.

In a simplified account of stratospheric formation, ultraviolet radiation splits an oxygen molecule into atoms: O₂ → O + O. An oxygen atom can then combine with an oxygen molecule: O + O₂ → O₃. The second reaction is simplified here; in the atmosphere another molecule carries away excess energy. Ozone is continually formed and destroyed, so protection depends on the balance of these processes.

What changes that balance?

CFCs, or chlorofluorocarbons, were used in applications including refrigeration, foam manufacture and aerosol propellants. These stable compounds can reach the stratosphere, where intense ultraviolet light breaks them down and releases chlorine. Chlorine participates in reactions that destroy ozone and can be regenerated, allowing repeated destruction. Bromine-containing substances such as halons used in fire suppression also contribute.

This mechanism is explained by the US Environmental Protection Agency’s ozone science account. It is more useful than an undifferentiated list blaming every gas or every modern appliance. The ozone “hole” describes severe seasonal depletion, especially over Antarctica; it is not a puncture through which all air escapes.

Could producing ozone at street level repair the protective layer?

No. Ground-level ozone is harmful air pollution, not a safe replacement for the stratospheric layer. Its formation and effects must be considered at the relevant location. The EPA’s comparison distinguishes the two roles.

A global response: Montreal and Kigali

The Montreal Protocol, agreed in 1987 and in force from 1989, controls production and consumption of ozone-depleting substances through agreed phase-out measures. Its development shows how scientific evidence, industrial alternatives, monitoring and international cooperation can work together. It was not simply a promise by one country to clean its own air.

The 2016 Kigali Amendment addresses HFCs, widely used as replacements for some ozone-depleting substances. HFCs do not deplete ozone in the same way as CFCs, but many are powerful greenhouse gases. Their phase-down tackles climate warming. Ozone depletion and climate change interact, yet they are not the same problem.

Garbage management

“Away” is a destination, not disappearance. Waste may be collected, sorted, transported, processed, recycled, treated or finally disposed of. A useful plan follows the material through those stages and asks what happens to the remaining residues.

Biodegradable does not mean harmless anywhere

Biodegradable substances can be broken down through biological processes. Food scraps and untreated plant material are familiar examples. Non-biodegradable substances, in this chapter’s sense, are not readily broken down biologically under ordinary environmental conditions; many conventional plastics, glass and metals persist.

Microorganisms and their enzymes cannot process every material in the same way. Temperature, moisture, oxygen, material composition and time affect decomposition. Breaking a plastic item into smaller fragments is not the same as fully breaking it down biologically.

Biodegradable waste can still create problems if badly managed. Large amounts of decomposing organic matter in water can consume dissolved oxygen. Food waste decomposing under oxygen-poor landfill conditions can generate methane. Decomposition is a process with environmental consequences, not an automatic certificate of harmlessness.

A fork says “plant-based” and “compostable”. Can it go straight into garden soil?

The claims do not establish that route. Plant-based describes feedstock; compostability depends on conditions. Some products require industrial facilities and are unsuitable for a home pile. Check the exact label and whether the receiving facility accepts the item. The EPA’s plastics guidance explains these distinctions. None of the labels permits littering.

Choose a route that fits the material

• Prevent and reuse: avoid unnecessary material, plan food quantities, repair suitable items and use durable products repeatedly. Preventing waste avoids some collection and processing as well.
• Segregate: keep suitable food/plant waste separate from dry recyclables and materials requiring special handling. Follow the actual local collection rules; bin colours and accepted materials are not universal.
• Compost: managed aerobic decomposition turns suitable organic material into a soil amendment. Microorganisms need moisture and oxygen as well as appropriate ingredients.
• Vermicompost: earthworms and microorganisms process suitable organic material together. Worms are living organisms with particular conditions, not machines that consume every kind of refuse.
• Recycle: recover material through an available collection and processing system. A technically recyclable object is not necessarily accepted locally, and recycling still uses resources.
• Treat remaining wastes appropriately: engineered landfills manage residues, liquids and gases; controlled incineration requires suitable equipment and emissions management. These differ from open dumping or burning. Batteries, electronics and hazardous wastes need appropriate dedicated routes.

Anaerobic digestion is another managed process for suitable organic feedstocks: microorganisms work without oxygen and produce biogas and digestate. It differs from aerobic composting. Not every type of sewage or mixed rubbish can simply be put into a small digester and assumed safe or useful.

The EPA’s composting guide explains why food scraps, dry leaves, air and moisture play different roles. Its biological principles travel across countries; its local collection arrangements should not be assumed to describe your municipality.

Redesign a cup, then test your argument

NCERT asks us to compare disposable plastic, clay and paper cups. A material name alone cannot settle the choice. Consider how much material and energy manufacture needs, whether a cup has coatings, how often it can be reused safely, and the available collection or treatment route. A reusable cup also needs washing. State what you know and what you would need to measure before claiming one option is always best.

Why it still matters

The ozone story offers a useful evidence investigation. The 2022 scientific assessment reports progress in upper-stratospheric ozone and Antarctic recovery, alongside considerable year-to-year variability. Assuming continued compliance and the assessment’s baseline greenhouse-gas scenario, its projections put return to 1980 total-column values around 2040 for the near-global average between 60°N and 60°S, 2045 for the Arctic and 2066 for Antarctica. These are conditional projections for different regions, not a single date when a global hole closes permanently.

Try the global comparison: why do long-lived ozone-depleting gases require cooperation across borders, while a discarded lunch container also requires a working local collection route? Both need action at the source and evidence about what happens afterwards. The relevant institutions and time scales differ.

For a local investigation, record the clean items left after one ordinary snack or classroom activity. Use labels, drawings or already known quantities; do not handle mixed rubbish, sharps or electronic waste. Classify what could be prevented, reused, composted or recycled through a verified local route. Mark uncertain items as uncertain. Redesign the activity to reduce one category, then compare like with like on another day.

Finish with the Follow the connections workshop. Removing a food-web link, adding a trophic transfer and changing a waste destination create different consequences. Explain the mechanism before choosing the solution. For the surrounding course, continue through the Class 10 Science notes.

Sources

• NCERT Science, Chapter 13: Our Environment, Reprint 2026–27 — full chapter, figures, activities and exercises reviewed.
• CBSE Class X Science 2026–27 — assessed Unit V scope, checked through the official curriculum index.
• OpenStax Biology 2e: energy flow and ecological pyramids — optional distinction between energy, biomass and numbers.
• EPA: Municipal Solid Waste Landfills and controlled waste combustion — treatment safeguards and remaining residues.
• EPA: Anaerobic Digestion — controlled processing and its outputs.
• USGS: Mercury — chemical form, accumulation and food-web transfer.
• EPA: Basic Ozone Layer Science and Ground-level Ozone Basics — location, protective role and depletion mechanism.
• UNEP Ozone Secretariat: Montreal Protocol and 2022 assessment executive summary — international response and qualified recovery evidence.
• EPA: Composting at Home, Composting and plastic recycling and composting questions — decomposition conditions and appropriate material routes.

Source review: 7 September 2026. The questions and fictional models are original learning activities, not past examination questions. The chemistry detail, pyramid comparison and global evidence investigation support understanding; they do not add an unverified board or assessment claim.

Key takeaways

• Environmental science studies connections between objects and their surroundings, rather than treating each object as isolated.
• An organism's environment includes both living and non-living components that interact and affect each other.
• Ecosystems consist of biotic and abiotic components, and changes can travel across this distinction.
• Producers, consumers, and decomposers play different roles in ecosystems, with producers making organic food from inorganic materials.
• Ecosystems are dynamic and change over time, with no guarantee of constant population sizes or balance.

Test yourself

What is the main focus of environmental science?

Environmental science focuses on studying connections between objects and their surroundings, rather than treating each object as isolated.

What are the two main components of an ecosystem?

An ecosystem consists of biotic (living) and abiotic (non-living) components.

What is the role of producers in an ecosystem?

Producers make organic food from inorganic materials through photosynthesis.

Can adding more organisms to an ecosystem always make it more complete?

No, adding more organisms can also increase the need for food, oxygen, and waste processing, and may not always make the ecosystem more complete.

What is an example of a human-made ecosystem?

A garden, crop field, or aquarium are examples of human-made ecosystems, where ecological processes still occur but are managed by people.

Frequently asked questions

What is the difference between biotic and abiotic components in an ecosystem?

Biotic components are living organisms like producers, consumers, and decomposers, while abiotic components are non-living factors such as light, temperature, air, water, and mineral nutrients. Both interact and influence each other within the ecosystem.

Why are decomposers essential in an ecosystem even though they are not directly consumed by other organisms?

Decomposers break down dead organic matter and wastes, returning nutrients to the environment. This process supports plant growth and maintains the flow of matter within the ecosystem, ensuring its long-term sustainability.

How does energy move through an ecosystem, and why is it not recycled like nutrients?

Energy flows through an ecosystem as organisms consume one another, starting with producers converting sunlight into organic food. Energy is not recycled because it is eventually dispersed as heat at each trophic level, unlike nutrients which cycle continuously.

What happens when a connection in an ecosystem changes, such as the removal of a predator?

A change in one part of the ecosystem can ripple through the system. For example, removing a predator may increase herbivore populations, which could then overconsume producers, altering plant growth and affecting the entire food web.