NCERT Exemplar · Class 10 Science Our Environment

Energy enters as sunlight and is passed on one trophic level at a time.Producers trap only about $\displaystyle 1$% of incident sunlight. At each transfer most of the energy received is used in respiration and lost as heat; only a small share reaches the next level: \[E_{n+1} \approx 10\%\times E_n \qquad (E_n = \text{energy at trophic level } n) \] Radiated heat cannot be recaptured: organisms gain energy only by feeding or photosynthesis, never from dissipated heat. A level therefore cannot pass energy back to the one before it, and the flow runs only forward. Answer: Sun → producers → herbivores → carnivores; it is unidirectional because energy is lost as heat at every transfer and cannot be returned to the earlier level.

Decomposers are micro-organisms — mainly bacteria and fungi — that break down the dead remains of plants and animals, along with organic waste, into simple inorganic substances: \[\text{dead organic matter} \xrightarrow{\text{decomposers}} \text{simple inorganic substances} \to \text{soil (nutrients for producers)} \] This is how nutrients locked in dead bodies are returned for producers to use again. Without decomposers this pathway breaks: dead plant and animal matter and waste would keep piling up uncleared, essential nutrients would stay trapped instead of re-entering the soil, and producers would be starved of raw material — disrupting the nutrient cycle the whole ecosystem depends on. Answer: Decomposers (bacteria, fungi) break down dead organic matter into reusable inorganic nutrients; without them, waste would accumulate and nutrient recycling to producers would stop.

Answer: Cloth bags over plastic, composting biodegradable waste, walking/cycling/public transport, and saving electricity with LED bulbs and switching off unused appliances.

A food chain is a single straight-line sequence in which each organism feeds on just the one before it; a food web is many food chains interconnected into a branching network, so most organisms have more than one food source.In a food chain, removing one species breaks the whole chain; in a food web the same species still has alternative feeding links, so the community is more stable against the loss of any one organism. Answer: ($\displaystyle 1$) Food chain = single linear sequence of feeding steps; food web = many interconnected chains. ($\displaystyle 2$) A food-chain organism has one food source/predator; a food-web organism has several, making the web more resistant to the loss of a species.

Daily household waste: biodegradable kitchen waste, paper, plastic wrappers, glass/metal containers, and occasional e-waste or batteries. Disposal — segregate biodegradable from non-biodegradable at source first; mixing the two undoes everything that follows. Compost the biodegradable share into manure; send paper, plastic, glass and metal for recycling. Cut plastic use with reusable bags/containers, and take batteries or e-waste only to a proper collection point, never the regular bin. Answer: Kitchen waste, paper, plastic, glass/metal, occasional e-waste; segregate at source, compost the biodegradable part, recycle the rest, and route hazardous waste to a collection point.

A fertiliser plant's waste is gaseous (ammonia, \(\displaystyle \mathrm{NO_x}\), \(\displaystyle \mathrm{SO_x}\)), liquid (acidic or alkaline effluent with unused nutrients) and solid (gypsum, sludge), each needing its own treatment.Acidic effluent is neutralised with lime before discharge: \[\mathrm{H_2SO_4 + Ca(OH)_2 \to CaSO_4 + 2H_2O} \] Gases pass through scrubbers that trap ammonia and the oxides before the stack. Never release effluent until it has been neutralised and checked against pollution-board limits. Recoverable by-products such as gypsum are sold on, not dumped. Answer: Scrub gaseous emissions, neutralise acidic or alkaline effluent (e.g. with lime) in an effluent treatment plant, recover saleable by-products like gypsum, and release treated effluent only after checking it against pollution-board limits.

By-products are gases (ammonia, \(\displaystyle \mathrm{NO_x}\), \(\displaystyle \mathrm{SO_2}\)), liquid effluent carrying unused nitrates and phosphates, and solid gypsum and sludge. Oxides of sulfur and nitrogen dissolve in atmospheric moisture to form acids: \[\mathrm{SO_2 + H_2O \to H_2SO_3} \] \[\mathrm{4NO_2 + O_2 + 2H_2O \to 4HNO_3} \] The acid rain damages plants and buildings and acidifies soil and water bodies. Nutrient effluent reaching a river or lake causes eutrophication: \[\text{nitrates, phosphates}\uparrow \Rightarrow \text{algal bloom} \Rightarrow \text{decay} \Rightarrow \text{dissolved } \mathrm{O_2}\downarrow \Rightarrow \text{fish die} \] Answer: Gaseous \(\displaystyle \mathrm{NO_x}\) and \(\displaystyle \mathrm{SO_2}\), nutrient-rich effluent and solid gypsum/sludge; the oxides cause acid rain, and nitrate–phosphate effluent causes eutrophication that starves water of oxygen and kills aquatic life.

Fertiliser and pesticide residues washed off fields into rivers/ponds over-feed algae (eutrophication) and poison aquatic organisms directly. Pesticides are non-biodegradable, so they do not break down but pass up the food chain, becoming more concentrated at each step: \[\text{trophic level}\uparrow \;\Rightarrow\; \text{pesticide concentration in the body}\uparrow \quad (\text{biological magnification}) \] reaching harmful levels in top consumers. Continuous use of chemical fertilisers and monocropping exhausts soil nutrients and kills beneficial soil micro-organisms; over-irrigation waterlogs and salinises the land. Clearing natural vegetation for farmland increases soil erosion and reduces biodiversity. Answer: Fertiliser/pesticide runoff causes eutrophication and direct toxicity; non-biodegradable pesticides biomagnify up the food chain; overuse of fertilisers and monocropping degrade soil fertility; over-irrigation causes waterlogging/salinity; and clearing land for farming raises erosion and lowers biodiversity.