• Energy source: Sun → captured by producers (green plants) via photosynthesis → passed to consumers → finally to decomposers; heat is lost at every step; energy flow is one-way (does not return to Sun).
• Trophic levels: Producers (1st), Herbivores—primary consumers (2nd), Carnivores—secondary (3rd), Tertiary/Apex (4th/5th). Biomass & energy decrease upwards.
• Food chain: Linear sequence of “who eats whom”. Food web: Interconnected food chains making a natural network; more stable than single chains.
• Energy pyramid: Shows energy drop at each level (e.g., Aquatic: Phytoplankton → Zooplankton → Fish → Humans). Typically ~10% energy is transferred to next level.
• Decomposers: Release nutrients back to soil/water/air; without them, dead biomass & locked energy/nutrients would accumulate.
• Cycles: Matter (C, O, N, etc.) moves in cycles (bio-geo-chemical cycles) among atmosphere, hydrosphere, lithosphere & biosphere.
• Carbon cycle: CO\(_2\) → plants (photosynthesis) → consumers → decomposers → back to CO\(_2\); also from combustion, volcanoes; balanced by photosynthesis/respiration.
• Oxygen cycle: Produced in photosynthesis; consumed in respiration, combustion, rusting, decomposition; present as O\(_2\), H\(_2\)O, CO\(_2\), etc.
• Nitrogen cycle: N\(_2\) (inert) → fixed by lightning/industry/bacteria → NH\(_3\) → NO\(_2^-\)/NO\(_3^-\) (nitrification) → plants/food → ammonification → denitrification → N\(_2\) back.
• Balance & human impact: Deforestation, pollution, overfishing disrupt webs & cycles; conservation maintains ecosystem equilibrium.

1) What is the primary source of energy for ecosystems?

The Sun; producers capture solar energy as chemical energy in food.

2) Define producers.

Autotrophs (plants/algae) that make food via photosynthesis.

3) Who are primary consumers?

Herbivores that eat producers (e.g., deer, grasshopper).

4) Who are apex consumers?

Top carnivores (e.g., tiger) with no natural predators.

5) Define food chain.

A linear sequence of energy transfer: who eats whom.

6) Define food web.

Network of interconnected food chains in an ecosystem.

7) What is a trophic level?

Step/level of an organism in a food chain based on its food source.

8) What does an energy pyramid represent?

Decreasing energy content at successive trophic levels.

9) Are decomposers producers or consumers?

Neither; they break down dead matter and recycle nutrients.

10) Do nutrients flow one-way?

No, nutrients cycle repeatedly (biogeochemical cycles).

11) Does energy cycle?

No; energy flows one-way with heat loss at each step.

12) Name one gaseous cycle.

Carbon/Oxygen/Nitrogen cycle.

13) Name one sedimentary cycle.

Phosphorus/Calcium/Iron cycle.

14) What converts CO\(_2\) to biomass?

Photosynthesis in plants/algae.

15) What returns CO\(_2\) to air?

Respiration, decomposition, combustion, volcanoes.

16) What is nitrogen fixation?

Conversion of N\(_2\) gas into usable compounds (NH\(_3\), NO\(_3^-\)).

17) What is nitrification?

Bacterial conversion of NH\(_3\) → NO\(_2^-\) → NO\(_3^-\).

18) What is denitrification?

Bacterial conversion of nitrates to N\(_2\) gas.

19) Give one role of decomposers.

Release nutrients back to soil/water for plant uptake.

20) Why are tertiary consumers fewer?

Energy & biomass decrease up the pyramid; less energy supports fewer top predators.

1) Why is a food web more stable than a single food chain?

Multiple alternate pathways of energy reduce collapse risk if one link fails.

2) State the typical energy transfer efficiency.

Roughly \(\approx 10\%\) to the next trophic level (rest lost as heat/activities).

3) Example of an omnivore in natural ecosystems.

Bear / Humans (eat plants and animals).

4) Who forms the 1st trophic level?

Producers (green plants/algae).

5) What connects energy flow and nutrient cycling?

Food chains/webs transport both energy and matter through levels.

6) Why is energy flow called ‘one-way’?

Heat is lost at each transfer; energy doesn’t recycle back to Sun.

7) One abiotic process adding CO\(_2\) to air.

Combustion of fossil fuels.

8) One biotic process removing CO\(_2\) from air.

Photosynthesis.

9) One use of oxygen in nature other than respiration.

Combustion / rusting / decomposition.

10) What is ammonification?

Decomposition releasing NH\(_3\) from organic matter.

11) Name any nitrogen-fixing agents.

Rhizobium/Azotobacter/lightning/industrial Haber process.

12) State two reservoirs in cycles.

Atmosphere, oceans, soil/rocks.

13) Write a simple aquatic chain.

Phytoplankton → Zooplankton → Fish → Human.

14) Why are decomposers vital?

They recycle nutrients; prevent accumulation of dead matter.

15) What is meant by gaseous cycle being “speedier”?

Gases disperse quickly in air; faster turnover than rock-bound nutrients.

16) One human action that disturbs cycles.

Deforestation / excessive fertilizer use / pollution.

17) What is a top predator in Indian forests?

Tiger.

18) On which level is frog usually placed?

Secondary consumer (feeds on insects).

19) Do plants also respire?

Yes, plants respire continuously (day & night).

20) Write the photosynthesis summary.

\(\text{CO}_2 + \text{H}_2\text{O} \xrightarrow{\text{light, chlorophyll}} \text{Glucose} + \text{O}_2\).

1) Describe the relationship between producers and primary consumers.

Producers convert solar energy into food; herbivores eat this biomass and obtain energy & matter for growth and reproduction.

2) Why is energy lost at each trophic transfer?

Due to metabolic heat, movement, growth & waste; only a fraction becomes biomass for the next level (≈10% rule).

3) Explain why apex consumers are few in number.

Cumulative losses of energy support fewer individuals at higher levels, limiting top-predator populations.

4) Differentiate food chain and food web with an example.

Chain is linear (Grass → Deer → Tiger); web is interconnected (deer also eaten by leopard; grasses eaten by many herbivores).

5) State the role of decomposers in energy and matter flow.

They return nutrients to abiotic pools and release some energy as heat, completing matter cycling.

6) Why is the energy pyramid always upright?

Energy diminishes at higher levels; cannot increase upwards due to thermodynamic losses.

7) List any two abiotic processes in the carbon cycle.

Combustion of fuels/wood, volcanic activity, CO\(_2\) dissolution in oceans.

8) How does respiration balance photosynthesis?

Respiration releases CO\(_2\) and uses O\(_2\), countering photosynthesis that consumes CO\(_2\) and releases O\(_2\).

9) Outline the steps of nitrogen fixation in nature.

Lightning/soil bacteria fix N\(_2\) to NH\(_3\); then nitrifying bacteria convert to NO\(_2^-\)/NO\(_3^-\) usable by plants.

10) What is denitrification and its ecological effect?

Conversion of nitrates to N\(_2\) gas by bacteria; returns nitrogen to atmosphere, closing the cycle.

11) Explain the term “sedimentary cycle” with one example.

Nutrients mainly stored in rocks/soil (e.g., phosphorus); generally slower turnover than gaseous cycles.

12) How does a balanced food web benefit stability?

Alternate prey/predator options prevent population crashes and maintain homeostasis.

13) Why are phytoplankton crucial in aquatic ecosystems?

They form the producer base supporting zooplankton, fish, and higher consumers; also major oxygen contributors.

14) Mention two human actions to restore cycle equilibrium.

Afforestation, reduced fossil-fuel use, controlled fertilizers, wetland conservation.

15) Distinguish energy flow vs nutrient flow.

Energy: unidirectional, dissipative; Nutrients: recycled between biotic and abiotic pools.

16) Write a terrestrial grazing chain.

Grass → Rabbit → Fox → Tiger.

17) Write a detritus chain snippet.

Leaf litter → Earthworms → Birds of prey.

18) Why is biodiversity important for energy flow?

More species = more pathways for energy transfer & resilience against disturbances.

19) How do microbes participate in oxygen cycle?

Most respire aerobically using O\(_2\); decomposers consume oxygen during breakdown.

20) Show the respiration equation.

\(\mathrm{C_6H_{12}O_6 + 6\,O_2 \rightarrow 6\,CO_2 + 6\,H_2O + \text{Energy}}\).

Cycle	Biotic processes	Abiotic processes
Carbon	Photosynthesis (CO\(_2\) → carbohydrates), respiration (releases CO\(_2\)), decomposition (releases CO\(_2\)), food transfer across trophic levels.	Combustion of fuels/wood, volcanic emissions, dissolution in oceans, sedimentation as carbonates/fossil formation.
Oxygen	Photosynthesis (O\(_2\) release), respiration (O\(_2\) use), decomposition (O\(_2\) use).	Combustion, rusting/corrosion, ozone formation/photolysis, mixing between atmosphere–hydrosphere–lithosphere.
Nitrogen	Biological fixation (Rhizobium, Azotobacter), ammonification, nitrification, assimilation by plants/food web, denitrification.	Atmospheric fixation by lightning, industrial fixation (Haber process), leaching/runoff, storage in soil & sediments.

a) Carnivores occupy the second trophic level in the food chain.

Correct: Carnivores are generally at the third or higher trophic levels; the second level is occupied by herbivores (primary consumers).

b) The flow of nutrients in an ecosystem is considered to be a ‘one way’ transport.

Correct: The flow of nutrients is cyclic (biogeochemical cycles). Energy flow is one-way, not nutrients.

c) Plants in an ecosystem are called primary consumers.

Correct: Plants are producers (autotrophs), not consumers.

a) Energy flow through an ecosystem is ‘one way’.

At each transfer, energy is lost as heat and cannot be reused by lower levels or return to the Sun; hence it is unidirectional.

b) Equilibrium is necessary in the various biogeochemical cycles.

Stable cycling keeps nutrient levels optimal for life; imbalance (e.g., excess CO\(_2\), eutrophication) harms organisms and ecosystem services.

c) Flow of nutrients through an ecosystem is cyclic.

Nutrients move between biotic and abiotic reservoirs repeatedly via processes like decomposition, assimilation, and weathering.

a) Carbon cycle

CO\(_2\) → plants (photosynthesis) → consumers → decomposers → CO\(_2\) back; plus combustion/volcanoes add CO\(_2\); oceans absorb/release CO\(_2\).

b) Nitrogen cycle

N\(_2\) fixation (lightning/bacteria/industry) → NH\(_3\) → NO\(_2^-\) → NO\(_3^-\) (nitrification) → plant uptake → food web → ammonification → denitrification → N\(_2\).

c) Oxygen cycle

Photosynthesis releases O\(_2\); respiration, combustion, rusting, decomposition consume O\(_2\); O\(_2\) interconverts among O\(_2\), H\(_2\)O, CO\(_2\), O\(_3\).

Afforestation & protecting green cover; efficient energy use, shift to clean energy; reduce/reuse/recycle; soil & water conservation; balanced fertilizer use; protect wetlands & biodiversity; proper waste management; awareness drives.

Multiple food chains intersect to form a food web. A species can occupy different positions in different chains (e.g., omnivores). Webs provide alternate routes for energy/matter transfer, enhancing ecosystem stability.

Types: Gaseous (C, O, N, water vapour) & Sedimentary (P, Ca, Fe). Importance: Replenish essential elements, maintain soil fertility, regulate climate/atmospheric composition, support continuous productivity.

a) What change occurs in energy from plants to apex consumers?

Energy decreases at each step due to metabolic heat loss; hence far less energy reaches apex consumers than is fixed by producers.

b) Differences between flow of matter and energy & why?

Energy flow is one-way (lost as heat; obeys thermodynamics). Matter (elements) is recycled via biogeochemical processes, so it flows cyclically.

Trophic level	Example	Indicative energy*
Producers (1st)	Phytoplankton	\(10{,}000\ \text{kcal}\)
Primary (2nd)	Zooplankton	\(1{,}000\ \text{kcal}\)
Secondary (3rd)	Small fishes	\(100\ \text{kcal}\)
Tertiary/Apex	Humans/Large fish-eaters	\(10\ \text{kcal}\)

*Illustrative to show ~10% transfer rule.