NCERT Exemplar Solutions Class 10 Science Chapter 13

The one-line filter: who is in charge? The fastest way to spot an artificial ecosystem is to ask whether a human is steering it.

Concept used. Ecosystems are graded by how much they self-regulate. Natural ecosystems have many species and many food links, so they recover from small shocks on their own. Artificial ecosystems are kept simple on purpose (often one main crop) and need constant outside input of water, fertiliser and pest control to stay that way.

1. Sort the four options into two groups. Self-running: pond, lake, forest. Human-run: crop field. Only one option sits in the human-run group, so it is the answer.
2. Cross-check with the species count. A forest has hundreds of interacting species; a wheat field is basically one plant species plus a few pests. Low diversity is a fingerprint of an artificial system.
3. Sanity check. A pond left alone for years still has fish, plants and microbes. A crop field left alone for one season is taken over by wild plants, proving it was being held in place by people.

Option (b): a crop field is artificial because humans set it up and maintain it.

Restating the choice (a): carnivores fill the third rung of every standard food chain.

Concept used. A food chain is read like a staircase of who eats whom. The label on each step never changes: the maker of food is first, the plant-eater is second, and the meat-eater that hunts the plant-eater is third.

1. Write a real chain. Grass (T1) → grasshopper (T2) → frog (T3). The frog eats the grasshopper, so the frog is a carnivore at level three.
2. Rule out the distractors. Producers are always T1, so (d) is wrong. Herbivores are always T2, so (b) is wrong. Decomposers (c) have no numbered position in the chain.
3. Generalise. Whatever the example (snake, frog, small bird), the animal at the third level always feeds on a herbivore, which by definition makes it a carnivore.

Option (a): the third trophic level is occupied by carnivores.

Confirming (c): an ecosystem is biotic + abiotic, always together.

Concept used. The very idea of an ecosystem is interaction. Plants need sunlight, water and minerals (abiotic) to grow; those abiotic factors are in turn changed by the plants and animals. Study either half alone and you no longer have an ecosystem, just a list of organisms or a list of physical factors.

1. Picture a pond. Fish, plants and microbes are biotic; the water, dissolved oxygen, sunlight and mud are abiotic. Remove the water and the fish die, so the two halves are locked together.
2. Eliminate partial answers. Options (a) and (b) each describe only one half, which is why they fail. Option (d) wrongly suggests the parts come and go.
3. Generalise. This is true for every ecosystem, from a drop of pond water to a whole forest: living and non-living parts coexist at all times.

Option (c): living organisms together with non-living factors make an ecosystem.

Locking the answer (d): 5000 kJ at the grass level.

Concept used. Energy flows one way and shrinks ten-fold at each rise in trophic level. To trace backward to the producer, reverse the ten-fold drop: each step down multiplies the energy by ten.

1. Tag the level asked for. The fourth trophic level in Grass → Grasshopper → Frog → Snake → Hawk is the Snake, given as 5 kJ.
2. Build a table going down. Snake (T4) =5 kJ; Frog (T3) =510=50 kJ; Grasshopper (T2) =5010=500 kJ; Grass (T1) =50010=5000 kJ.
3. Match with the formula. Three steps down means 5 × 10³ = 5000 kJ, which agrees with the table.

Option (d): the producer (grass) holds 5000 kJ.

Settling on (c): the term is biomagnification.

Concept used. Two properties drive this effect. First, the chemical is non-biodegradable, so it is never broken down. Second, a predator eats many prey, so it takes in all the chemical stored in all of them at once. Together these make the dose climb at every level.

1. Trace the build-up. If each small fish carries a little DDT and a big fish eats hundreds of small fish, the big fish now holds all that DDT. The bird that eats the big fish gets even more.
2. Separate the look-alike words. Eutrophication harms water bodies through excess nutrients, not pesticides up a food chain; that rules out (a). "Pollution" and "accumulation" are too vague to be the exact term.
3. Why humans should care. Humans often eat at the top of food chains (large fish, meat), so they can receive the highest concentration of such chemicals.

Option (c): increasing pesticide load up the chain is biomagnification.

Confirming (a): CFCs are the chief ozone-depleting chemicals.

Concept used. Ozone is constantly made and broken in the upper atmosphere in a natural balance. CFCs tip this balance because the chlorine they release acts as a catalyst: it breaks ozone yet is not used up itself, so it keeps attacking ozone over and over.

1. Source of the problem. CFCs were widely used as coolants and aerosol propellants. Being stable, they drift up to the ozone layer intact.
2. The damage step. High up, ultraviolet light splits CFCs and frees chlorine. The chlorine then converts O₃ back to ordinary oxygen, removing the protective shield.
3. Why the other options fail. Carbon monoxide, methane and pesticides cause real harm elsewhere, but they are not the catalysts that thin the ozone layer. The 1987 Montreal Protocol banned CFCs precisely for this reason.

Option (a): chlorofluorocarbons mainly deplete ozone.

Backing option (b): the food-makers are producers.

Concept used. The chapter splits organisms by how they get food. Autotrophs ("self-feeders") make their own using sunlight; heterotrophs ("other-feeders") must eat ready-made food. The description in the question is the textbook definition of an autotroph.

1. Decode the keywords. "Carbohydrates" = food made; "inorganic compounds" = CO₂ and water as raw materials; "radiant energy" = sunlight. All three point to photosynthesis.
2. Name the group. Only green plants and some algae do this, and in food-chain language they are called producers.
3. Place them in the chain. Because they make the first food, producers always start the chain and feed every consumer above them.

Option (b): producers make carbohydrates using sunlight.

Confirming (c): food energy travels as chemical energy.

Concept used. Energy changes form as it enters and moves through a food chain. It comes in as light, is converted by photosynthesis into chemical energy, and is then handed up the chain in that chemical form. At every transfer about 90% leaks away as heat.

1. Trace the form change. Sunlight (light) → stored in glucose (chemical) → eaten by herbivore (chemical) → eaten by carnivore (chemical).
2. Spot what 10% refers to. The 10% rule is about the food energy that one level can pass to the next, which is the chemical energy in the body of the prey.
3. Reject heat (a). Heat is the lost 90%, not the transferred 10%, so it cannot be the answer.

Option (c): chemical energy is what passes between trophic levels.

Choosing (a): multiple feeding links make a food web.

Concept used. In nature, very few animals eat only one kind of food. A frog may eat insects and worms; a hawk may eat snakes, mice and small birds. These overlapping diets join separate chains into one big network, the food web.

1. Anchor on the keyword. "Several types of organisms at a lower level" means the consumer has many food options, which is the defining feature of a web.
2. Eliminate near-misses. An ecological pyramid (b) shows numbers or energy as bars, not feeding links. An ecosystem (c) is the whole biotic + abiotic unit, too broad. A food chain (d) is a single line, too narrow.
3. Why webs matter. Because many links exist, a food web is more stable: if one prey disappears, predators can switch to another, keeping the system going.

Option (a): feeding on several organisms forms a food web.

Settling on (a): energy flow is strictly one-way.

Concept used. The one-way nature follows from the laws of energy. Each transfer wastes most of the energy as heat, and heat spreads out into the environment where no organism can gather it back to feed a lower level. So energy can only go forward, never back.

1. Direction of travel. Sun to producer to consumer is the only path; there is no route from carnivore back to producer.
2. Reason it cannot loop. The big heat loss at every step leaves too little usable energy, and that heat cannot be re-collected, so a return flow is impossible.
3. Reject the other options. Bidirectional and multidirectional flow would need energy to climb back down, which the heat loss forbids.

Option (a): the flow of energy is unidirectional.

Confirming (c): the harmful pair is (i) and (iii).

Concept used. UV rays act mainly on tissues that face the Sun or that control body defence. The skin takes the direct hit, and the immune cells in the skin are weakened, so both skin cancer and immune suppression follow naturally.

1. Keep the true effects. Skin cancer (iii) comes from UV damaging the DNA of skin cells; immune-system damage (i) comes from UV harming defence cells. Both are listed UV hazards.
2. Drop the wrong effects. Lungs (ii) are harmed by breathing pollutants, not by UV light, which does not reach deep internal organs. Peptic ulcers (iv) are a digestive problem unrelated to sunlight.
3. Pick the matching option. Only option (c) pairs the two true effects, (i) and (iii).

Option (c): excessive UV causes immune damage and skin cancer.

Confirming (d): only groups (ii) and (iv) qualify.

Concept used. The deciding test is whether microbes can digest each item. Natural, once-living materials (wood, paper, leather, grass) rot away; man-made polymers and stable synthetics (plastic, PVC, bakelite, DDT, detergents) do not.

1. Mark each item. Wood, paper, leather, grass = rots (biodegradable). Polythene, PVC, plastic, bakelite, DDT, detergent = does not rot (non-biodegradable).
2. Apply the "only" rule group by group. (i) all biodegradable, reject; (iii) has grass, reject; (ii) all non-biodegradable, keep; (iv) all non-biodegradable, keep.
3. Select the option. Both surviving groups are (ii) and (iv), which is option (d).

Option (d): (ii) and (iv) contain only non-biodegradable items.

Locking in (a): energy loss caps the chain length.

Concept used. Every organism needs a minimum amount of energy to live and reproduce. Because energy falls ten-fold per level, there comes a point where the remaining energy is below this minimum, and no new level can form.

1. Show the drop with numbers. Start with 1000 units: level 2 gets 100, level 3 gets 10, level 4 gets 1. By level 5 there is almost nothing left.
2. Connect to chain length. Since each higher level has far less energy, only a few levels (3 to 4) can be supported.
3. Dismiss other options. Food supply (b), polluted air (c) and water (d) may affect populations, but the universal reason chains are short is the rapid loss of energy.

Option (a): the decrease in energy at higher trophic levels limits the number of levels.

Confirming (b) as the incorrect one: plants do not feed on organic compounds.

Concept used. Producers are autotrophs: they take simple inorganic inputs and assemble them into complex organic food. Saying they "get food from organic compounds" reverses this; that would make them consumers, not producers.

1. Verify the true statements. (a) producers include green plants and blue-green algae, correct. (c) producers use inorganic raw materials, correct. (d) photosynthesis turns light into chemical energy, correct.
2. Expose the false one. (b) claims plants take food from organic compounds. In reality they create organic food from inorganic carbon dioxide and water.
3. Confirm the choice. Since the three others are correct, the single incorrect statement is (b).

Option (b): the incorrect statement is that green plants get food from organic compounds.

Confirming (c): groups (ii) and (iii) fail the food-chain test.

Concept used. A food chain needs a producer base and a logical predator-prey order. Mixing organisms from different habitats, or listing two top predators with no link between them, breaks the chain.

1. Check group (ii). Plankton and fish are aquatic, but a grasshopper is a terrestrial insect; the members do not share one chain, so it is invalid.
2. Check group (iii). Wolf, snake and tiger are all flesh-eaters and grass is a producer, but they cannot be lined up as eater-and-eaten (no herbivore links grass to these carnivores), so it is invalid.
3. Confirm the valid ones. Group (i): Grass → rabbit → wolf (lion fits as a separate predator). Group (iv): Grass → grasshopper → frog → snake → eagle. Both work, so the answer is (ii) and (iii).

Option (c): (ii) and (iii) are not constituents of a food chain.

Backing option (a): about 1% of sunlight is used in photosynthesis.

Concept used. Photosynthesis can only use certain colours of visible light, and even those are not fully absorbed. Most sunlight either bounces off leaves or turns into heat, leaving roughly 1% for food-making.

1. Account for the losses. A large share of sunlight is reflected or is of a wavelength the plant cannot use; much of the rest warms the leaf. Only a thin slice drives photosynthesis.
2. Fix the value. The standard NCERT figure for this captured slice is about 1%.
3. Reject the larger options. 5%, 8% and 10% overstate the plant's efficiency, so they are wrong.

Option (a): roughly 1% of solar radiation is absorbed for photosynthesis.

Confirming (c): the base level T1 has the most energy.

Concept used. An energy pyramid is drawn upright and never inverted, because energy strictly decreases upward. The producers at the base trap the original solar energy, and every level above keeps only one-tenth of what is below.

1. Identify the base. T1 is the lowest, widest band; in the figure it is the producer level.
2. Apply the rule. Going up: T1 to T2 keeps 10%, T2 to T3 keeps 10% again, and so on. Each rise loses energy, so the highest amount is at T1.
3. Reject the top levels. T2, T3 and T4 each hold less than the level below, so none of them can have the maximum.

Option (c): T1 (the producer base) has the maximum energy.

Confirming (d): fewer tigers, more grass.

Concept used. A food chain is a chain of dependence. Each species both eats the one below and feeds the one above. Pull out the middle link (deer) and the effects spread up and down at once.

1. Look upward. The tiger ate only the deer here. No deer means no food, so tiger numbers decline.
2. Look downward. The deer kept the grass in check by grazing. Without the deer, nothing grazes the grass, so it spreads and increases.
3. Reject impossible options. A tiger cannot suddenly eat grass (c) because it is a carnivore, and its numbers cannot rise (a) when its food is gone.

Option (d): removing the deer lowers tiger numbers and raises grass.

Backing option (b): decomposers break organic into inorganic.

Concept used. The direction of change is the key. Producers build inorganic into organic; decomposers do the reverse, breaking organic back into inorganic. The two together keep nutrients cycling endlessly.

1. Set the direction. Decomposition means breaking down, so complex organic matter becomes simple inorganic substances.
2. Spot the reversed options. Option (c) describes producers (inorganic to organic), the opposite of decomposers. Option (d) wrongly says they do not break down organic matter.
3. Confirm (b). Only (b) states the correct organic to inorganic conversion.

Option (b): decomposers convert organic material to inorganic forms.

Confirming (c): primary consumer to secondary consumer.

Concept used. The consumer ranks are set by what each animal eats. Eat a plant and you are a primary consumer; eat a primary consumer and you are a secondary consumer. Energy moves up this rank, from prey to predator.

1. Rank the grasshopper. It feeds on grass (a producer), so it is a primary consumer.
2. Rank the frog. It feeds on the grasshopper (a primary consumer), so it is a secondary consumer.
3. Set the flow. Eating transfers energy from the eaten to the eater, so from primary consumer (grasshopper) to secondary consumer (frog), which is option (c).

Option (c): the transfer is from primary consumer to secondary consumer.

Confirming (d): plastic plates are non-biodegradable.

Concept used. Waste is judged mainly by whether nature can recycle it. Biodegradable waste rots and returns to the soil; non-biodegradable waste does not, so it builds up and pollutes for generations. Plastic falls firmly in the second group.

1. Classify plastic. It is a synthetic polymer that microbes cannot digest, so it is non-biodegradable.
2. Trace the harm. Discarded plates litter land and water, block drains, and can choke or poison animals that swallow pieces.
3. Reject weaker reasons. Light weight (a) is not a drawback. While some plastics can be toxic (b), the central problem named in the chapter is that they do not break down (d).

Option (d): avoid plastic plates because they are non-biodegradable.

The bigger picture. Poor disposal does not just look bad; it quietly damages every part of the environment.

Concept used. Nature can recycle waste only if biodegradable matter is exposed to decomposers and non-biodegradable matter is kept out of soil and water. Improper disposal defeats both, so pollution spreads and lingers.

1. Air. Rotting waste releases foul, sometimes toxic gases, and burning waste adds smoke and harmful fumes.
2. Water and soil. Liquids seeping from dumps (leachate) poison groundwater and make soil unfit for crops.
3. Living things. Disease-carrying pests breed in waste, and plastics injure animals; chemicals can move up food chains to reach humans.

Carelessly dumped waste pollutes air, water and soil, breeds disease, harms wildlife, and persists for years, which is why it is a curse to the environment.

Reading the pond chain. Each arrow means "is eaten by", so energy flows from left to right.

Concept used. A pond is a self-contained aquatic ecosystem. Its producers are floating microscopic plants, and the consumers above them get larger at each step while their numbers get smaller.

1. Base level. Phytoplankton (and aquatic plants) trap sunlight and make food, so they are the producers.
2. Rising levels. Small animals such as zooplankton and insect larvae graze the phytoplankton; fish then eat these small animals.
3. Top level. Fish-eating birds, such as kingfishers, feed on the fish, completing the chain.

A typical pond food chain is phytoplankton → zooplankton/larvae → fish → bird.

Why the swap helps. Choosing cloth over plastic removes a long-lasting pollutant from daily shopping.

Concept used. The harm from plastic comes from its single-use, non-biodegradable nature. A reusable, biodegradable alternative breaks that cycle of waste.

1. Durability. Cloth bags are tough and hold more weight without tearing, so fewer bags are needed.
2. Reusability. They can be washed and used over and over for years, so very little waste is produced.
3. Eco-friendliness. Being made of natural fibre, they rot down naturally at end of life and do not choke drains, soils or animals.

Cloth bags are stronger, reusable, biodegradable and non-polluting, making them clearly better than plastic bags.

The human hand. A crop field exists only because people make it and keep it going.

Concept used. Ecosystems are called natural when they self-organise and artificial when human action sets and maintains their biotic and abiotic parts. A crop field is shaped at every stage by farmers.

1. Biotic control. Farmers select a single main crop and remove other plants (weeds), so the living community is human-chosen.
2. Abiotic control. Irrigation supplies water and fertilisers supply nutrients, so even the physical conditions are managed.
3. Conclusion. Since people steer both halves of the ecosystem, the crop field is artificial, unlike a self-running forest or pond.

A crop field is artificial because its plants and physical conditions are deliberately set up and maintained by humans.

One test, two groups. The single dividing question is: can microbes digest it?

Concept used. Decomposers can attack natural, once-living materials but cannot break stable man-made polymers. This splits all waste into two clear groups with very different fates.

1. Biodegradable group. Once-living or natural matter such as wood, paper, leftover food and cow dung is digested by microbes and returns to the soil.
2. Non-biodegradable group. Synthetic or very stable materials such as plastic, DDT, polythene and glass resist microbes and persist for decades or longer.
3. Why it matters. Knowing the group decides the disposal method: compost the first, recycle or carefully manage the second.

Biodegradable substances (wood, paper) decompose via microbes; non-biodegradable substances (plastic, DDT) do not and persist as pollution.

Matching word to meaning. Each clue contains a giveaway that points to one exact term.

Concept used. The chapter's core vocabulary covers the whole unit (environment), its energy steps (trophic levels), its non-living factors (abiotic), and its food-dependent organisms (consumers).

1. (a) Whole surroundings. "Physical and biological world where we live" is the environment or biosphere.
2. (b) Energy step. "Each level where energy is transferred" is a trophic level.
3. (c) and (d). Pure physical factors are abiotic factors; food-dependent organisms are consumers (heterotrophs).

(a) Environment/biosphere; (b) Trophic level; (c) Abiotic factors; (d) Consumers.

The clean-up crew. Decomposers do the unglamorous but vital job of breaking down what dies.

Concept used. Nutrients are limited. If they stayed locked in dead bodies, the soil would soon run out. Decomposers unlock those nutrients so the cycle can repeat.

1. Break down. Bacteria and fungi digest dead leaves, bodies and droppings, turning complex organic matter into simple inorganic substances.
2. Return nutrients. Substances like nitrates and phosphates go back into the soil and air.
3. Support producers. Plants reabsorb these nutrients to grow, so decomposers indirectly feed the entire food chain.

Decomposers recycle nutrients by breaking down dead matter and returning simple substances to the soil, sustaining plant growth and a clean environment.

Spotting the odd pair. Three pairs are textbook-correct; one gives only part of the truth.

Concept used. An ecosystem is by definition biotic plus abiotic. Any definition that mentions only living components misses the soil, water and climate that are equally part of it.

1. Confirm the correct pairs. (a) biomagnification rising up a chain, (c) aquarium as a man-made ecosystem, and (d) parasites feeding on living hosts are all accurate.
2. Identify the error. (b) defines an ecosystem as only the biotic components, which is incomplete.
3. Write the correction. An ecosystem = biotic components + abiotic components of the environment, interacting together.

(b) is mismatched; corrected: an ecosystem consists of both biotic and abiotic components of the environment.

Complete versus incomplete. The difference comes down to whether the system can recycle its own waste.

Concept used. A self-sustaining ecosystem has every functional group: producers, consumers and decomposers, in working balance. An aquarium copies only part of this, so it cannot fully recycle waste.

1. Natural water body. A pond or lake holds a large, balanced community including many decomposers that continuously break down dead matter and waste.
2. Aquarium. It is a tiny, controlled tank with limited organisms and few decomposers, so uneaten food and droppings accumulate.
3. Result. Because the aquarium cannot clean itself, we must change its water and remove waste; the pond manages this on its own.

Ponds and lakes self-clean because they are complete natural ecosystems with decomposers; an aquarium is incomplete and lacks them, so it needs manual cleaning.

Why the arrow never turns back. The one-way nature of energy flow is a direct result of constant heat loss.

Concept used. Energy obeys strict physical rules: it changes form (light to chemical to heat) but at each living step most of it becomes heat that spreads into the environment, where it is useless to organisms.

1. Entry and capture. Sunlight is the only major input; producers fix it as chemical energy, setting the base at, say, 100% of the captured amount.
2. Stepwise loss. Herbivores receive only about 10% of the producers' energy; carnivores receive about 10% of that, so only about 1% remains two steps up.
3. No return path. The 90% lost at each step leaves as scattered heat that cannot be gathered again, so energy cannot climb back down. This loss also limits chains to a few levels.

Energy flows one way from Sun to producers to consumers; the heavy heat loss at each transfer cannot be reversed or recaptured, making the flow unidirectional.

Imagine a world without them. Removing decomposers would break the nutrient cycle that every ecosystem depends on.

Concept used. Nutrients are finite and must be reused. Decomposers are the only group that unlocks nutrients from dead matter, so without them the supply to producers dries up.

1. Their normal job. Bacteria and fungi convert dead leaves, bodies and droppings into simple substances such as nitrates and minerals.
2. Immediate effect of absence. Dead organisms and waste would not rot; they would accumulate everywhere, fouling the environment.
3. Long-term effect. The nutrients stuck in undecayed matter would not return to the soil, so plants would starve of minerals, growth would crash, and consumers depending on plants would die out.

Decomposers recycle nutrients by breaking down dead matter; their absence would cause waste to pile up, halt nutrient recycling, and lead to the breakdown of the whole ecosystem.

Everyday choices that add up. Small, repeated actions are the most effective form of environmental care.

Concept used. The core ideas are reduce, reuse and recycle, plus conserving natural resources. Each suggested habit applies one of these.

1. Sort and compost. Separating waste lets biodegradable matter be composted and the rest be recycled, cutting landfill.
2. Cut plastic. Choosing cloth, jute or paper bags reduces non-biodegradable waste at the source.
3. Save resources. Harvesting rainwater conserves water, and switching off unused lights and fans (or using CFL/LED) saves electricity and reduces pollution from power generation.

Eco-friendly habits include segregating and composting waste, replacing plastic bags with cloth/paper, harvesting rainwater, and saving electricity.

Line versus network. The cleanest way to remember the difference is single thread (chain) against woven net (web).

Concept used. Real ecosystems are webs because almost no animal eats only one food. A food chain is a simplified slice we pull out of the web to study one path.

1. Structure. A chain is one line: A → B → C. A web joins many such lines wherever organisms share food, forming a net.
2. Feeding choice. In a chain a predator has a single food; in a web it has several, so it can switch if one runs short.
3. Stability. This choice makes webs more stable: the loss of one prey species rarely collapses the whole web, whereas it can break a single chain.

A food chain is a single feeding line with one food per consumer; a food web is many interlinked chains where consumers have several food options, making it more stable.

A simple home plan. Sort first, then treat each type the right way.

Concept used. The reduce-reuse-recycle approach works best when waste is separated at source, because mixed waste is hard to compost or recycle.

1. Identify the waste. Wet waste: kitchen scraps, vegetable and fruit peels. Dry waste: newspaper, envelopes, bags, plastic packaging.
2. Treat the wet waste. Compost or vermicompost it in a pit; peels placed near plants also decompose and enrich the soil.
3. Treat the dry waste. Reuse what you can, then hand paper and plastic to recyclers; never burn plastic, as it releases toxic fumes.

Generate kitchen scraps, peels, paper and plastic daily; segregate them, compost the biodegradable part, and reuse or recycle the non-biodegradable part.

Clean it before it leaves. The guiding rule is to treat all waste at the factory, not to let it pollute and clean up later.

Concept used. Pollution from a fertiliser plant comes through two routes, the chimney and the drain, so the control measures must target both.

1. Air route. Install scrubbers, filters and electrostatic precipitators in chimneys to remove harmful gases and dust before emission.
2. Water route. Send liquid effluent to an effluent treatment plant that neutralises and removes harmful chemicals before the water is released.
3. Reduce and reuse. Recover useful chemicals from the waste where possible and reuse treated water within the plant to cut total discharge.

Treat gaseous waste with scrubbers/filters and treat liquid effluent in a treatment plant before discharge, and recover or reuse waste where possible.

From chimney to acid rain. The harmful gases released here travel far and return to the ground as acid rain.

Concept used. Both sulphur dioxide and nitrogen oxides are acidic gases. In the atmosphere they react with water vapour to form sulphuric and nitric acids, which fall as acid rain.

1. Identify the by-products. Manufacturing fertilisers releases SO₂ and oxides of nitrogen as the main gaseous by-products.
2. Air pollution. These gases directly pollute the air, irritating lungs and harming plants near the factory.
3. Acid rain damage. On dissolving in rain they form acids that lower soil and water pH, damage leaves and crops, and corrode buildings and statues.

Fertiliser industries release SO₂ and oxides of nitrogen, which pollute the air and form acid rain that harms plants, soil, water bodies and buildings.

The cost of intensive farming. The same practices that boost crop output can quietly degrade the environment if pushed too far.

Concept used. Soil, water and biodiversity are limited resources. Overusing chemicals and water, and clearing land, draws down these resources faster than they can recover.

1. Chemical harm. Excess fertilisers change soil pH and kill helpful microbes; persistent pesticides accumulate up food chains and reach humans.
2. Resource loss. Repeated cropping strips soil of nutrients and lowers fertility, while heavy irrigation lowers the groundwater table.
3. Habitat loss. Expanding farmland clears forests and grasslands, destroying natural habitats and reducing wildlife.

Intensive agriculture harms the environment by altering soil chemistry, killing soil microbes, causing pesticide biomagnification, reducing soil fertility, depleting groundwater, and destroying natural habitats.