Ecosystems, Food Chains, and Environmental Management
How Nature Recycles Everything — And How We Must Help Protect It
Our Environment contributes 6–8 marks in CBSE Boards. Food chains, food webs, and the 10% energy flow rule are standard 2-mark questions. Biodegradable vs non-biodegradable waste, ozone depletion, and waste management are guaranteed topics. NTSE includes ecosystem component identification and energy flow MCQs.
10% rule is a guaranteed easy mark — if grass has 10,000 J, grasshoppers get 1,000 J, frogs get 100 J. Biological magnification: pesticides (DDT) accumulate at each trophic level, highest in top predators. Ozone depletion: CFCs release Cl radicals that break O₃ into O₂. These three concepts cover 90% of this chapter's exam questions. Time investment: 1–2 days.
When energy flows from one trophic level to another:
Hence,
\[ Efficiency = \frac{Energy\ transferred}{Energy\ received} \times 100 \approx 10\% \]
A farmer uses excessive pesticides in his field ecosystem.
Question: How will it affect the ecosystem?
Answer: Excessive pesticide use kills beneficial organisms and disrupts food chains. It leads to biomagnification, reduces biodiversity, and disturbs ecological balance.
Organisms that synthesize their own food using sunlight, carbon dioxide, and water through photosynthesis.
Photosynthesis Equation:
\[ \small 6CO_2 + 6H_2O \xrightarrow[\text{chlorophyll}]{\text{sunlight}} C_6H_{12}O_6 + 6O_2 \]
Examples: Green plants, algae, cyanobacteria
Organisms that depend on producers or other organisms for food.
Microorganisms that decompose dead organic matter into simpler inorganic substances.
Function: Nutrient recycling and soil enrichment
Examples: Bacteria, fungi
Energy flows from producers to consumers and finally to decomposers:
\[ Sun \rightarrow Producers \rightarrow Consumers \rightarrow Decomposers \]
This flow is unidirectional and follows the 10% law.
A forest ecosystem loses its decomposers due to pollution.
Question: What will happen to the ecosystem?
Answer: Dead organic matter will accumulate, nutrients will not be recycled, soil fertility will decrease, and producers will not survive. This will ultimately collapse the ecosystem.
Climatic factors are atmospheric conditions that directly influence biological processes and species distribution.
Edaphic factors refer to soil properties that determine which plants can grow and how well they thrive.
Chemical factors are essential substances required for metabolic processes in living organisms.
Topographic factors relate to physical landscape features that influence microclimate and species distribution.
The growth of organisms is controlled not by the total resources available, but by the scarcest resource (limiting factor).
Example: Low rainfall limits plant growth even if sunlight is abundant.
A region receives very low rainfall and has high temperature.
Question: What type of ecosystem will form and why?
Answer: A desert ecosystem will form because low water availability and high temperature act as limiting factors, restricting vegetation and supporting drought-resistant organisms only.
Balanced Equation:
\[ 6CO_2 + 6H_2O \xrightarrow[\text{chlorophyll}]{\text{sunlight}} C_6H_{12}O_6 + 6O_2 \]
Photoautotrophs use sunlight as their energy source and carbon dioxide as their carbon source through photosynthesis.
They contain chlorophyll and produce carbohydrates using the equation:
6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂
Chemoautotrophs use chemical energy from inorganic compounds (instead of sunlight) and carbon dioxide as their carbon source.
They oxidize chemicals like ammonia, hydrogen sulfide, or iron through chemosynthesis.
If producers capture 1000 J of solar energy:
\[ Energy_\text{{primary consumers}} = 100 \, J \]
(Based on 10% law of energy transfer)
A water body loses its phytoplankton due to pollution.
Question: Predict the effect on the ecosystem.
Answer: Loss of phytoplankton reduces primary productivity, disrupts food chains, decreases oxygen levels, and may lead to collapse of aquatic life.
Primary consumers (herbivores) feed directly on producers (plants) and represent the second trophic level in food chains.
Secondary consumers feed on primary consumers and occupy the third trophic level. They are typically small carnivores or omnivores.
Tertiary consumers are apex predators that feed on secondary consumers and rarely have natural predators themselves.
Omnivores can feed on both producers (plants) and consumers (animals) at multiple trophic levels.
Parasites live on or inside host organisms, deriving nutrients while often harming the host.
Consumers follow the 10% Law of energy transfer:
\[ Energy_{next\ trophic\ level} = 0.1 \times Energy_{previous\ level} \]
Example: If producers contain 1000 J energy, primary consumers receive 100 J, secondary consumers receive 10 J, and so on.
Energy Flow Rule: Only ~10% energy transfers to next level (90% lost as heat). As we move up trophic levels, available energy decreases (100% → 10% → 1% → 0.1%) while organism size and dominance increase.
A sudden decrease in herbivore population is observed in a forest.
Question: What will be its effect on producers and carnivores?
Answer: Producers will increase due to less grazing, while carnivores will decline due to lack of food. This disrupts the balance of the ecosystem.
Micro-decomposers (bacteria & fungi) are microscopic organisms that secrete extracellular enzymes to chemically break down complex organic matter into simple soluble compounds.
Detritivores (macro-decomposers) physically fragment and ingest dead organic matter (detritus), aiding initial breakdown and increasing surface area for microbial action.
A region loses its microbial decomposers due to chemical pollution.
Question: Predict long-term ecological consequences.
Answer: Nutrient cycling will stop, soil fertility will decline, dead matter will accumulate, and producers will eventually die, leading to ecosystem collapse.
\[ \mathrm{Grass \rightarrow Grasshopper \rightarrow Frog \rightarrow Snake \rightarrow Eagle} \]
Here, grass is the producer, grasshopper is the primary consumer, frog is the secondary consumer, snake is the tertiary consumer, and eagle is the top predator.
\[ \mathrm{Energy_{next\ level} = 0.1 \times Energy_{previous\ level}} \]
Only about 10% of energy is transferred to the next trophic level, while the rest is lost as heat.
| Food Chain | Food Web |
|---|---|
| Linear sequence | Complex network |
| Single pathway | Multiple pathways |
| Less stable | More stable |
| Rare in nature | Common in nature |
A pesticide enters a food chain starting from plants.
Question: What will happen at higher trophic levels?
Answer: The pesticide concentration will increase at higher trophic levels due to biomagnification, affecting top predators the most.
100% Energy Available - Autotrophs that convert solar energy into chemical energy through photosynthesis.
~10% Energy Transfer - Herbivores that consume producers and convert plant biomass into animal tissue.
~1% Energy Transfer - Carnivores/omnivores that prey on primary consumers.
~0.1% Energy Transfer - Apex predators with no natural enemies that control populations below them.
\[ Energy_{n+1} = 0.1 \times Energy_n \]
Only about 10% of energy is passed to the next trophic level, while the rest is lost as heat.
\[ Grass \rightarrow Deer \rightarrow Tiger \]
A food chain shows five trophic levels.
Question: Is this possible? Explain.
Answer: It is rare because energy decreases drastically at each level. Generally, only 3–4 trophic levels are sustainable due to energy limitations.
\[ \mathrm{Water \rightarrow Phytoplankton \rightarrow Small\ Fish \rightarrow Big\ Fish \rightarrow Human} \]
If water contains a small amount of DDT, phytoplankton absorb it. Small fish eat many phytoplankton, increasing toxin levels. Big fish accumulate even more, and humans consuming fish receive the highest concentration.
Fish in a polluted river show high mercury levels.
Question: Predict its impact on humans consuming these fish.
Answer: Humans consuming contaminated fish will accumulate mercury, leading to severe health issues like nervous system damage and poisoning.
Sources: Burning fossil fuels (coal, petrol), industrial emissions, vehicle exhaust releasing CO₂, SO₂, NOₓ, particulate matter (PM2.5).
Sources: Domestic sewage, industrial effluents, agricultural runoff (pesticides, fertilizers), plastic waste, oil spills.
Types: Overexploitation of renewable (forests, fisheries) and non-renewable (minerals, fossil fuels) resources beyond regeneration capacity.
Thinning of stratospheric ozone layer that protects Earth from harmful UV radiation.
Trapping of Earth's heat by atmospheric gases creating natural temperature balance.
\[\small\ce{CO₂ + CH₄ + N₂O + H₂O vapor absorb infrared → Heat retention → Global temperature regulation}\]
Non-biodegradable municipal waste including plastics, metals, glass, and electronic waste (e-waste) that accumulates in landfills and environment.
Persistent synthetic polymers that don't decompose naturally, entering food chains through fragmentation.
Hazardous chemical, industrial, biomedical, and nuclear waste containing heavy metals, persistent organic pollutants.
Removal of forest cover for agriculture, timber, urbanization destroys natural habitats.
Unsustainable harvesting of wild species beyond reproductive capacity.
Non-native species outcompete local organisms, disrupting established food webs.
A city shows increased pollution due to rapid industrialization.
Question: Predict long-term environmental effects.
Answer: Increased pollution will degrade air and water quality, harm health, reduce biodiversity, and contribute to climate change.
Segregating waste at source makes recycling super easy, cuts pollution, and helps fight climate change. Use color-coded bins: green for biodegradable, blue for non-biodegradable!
These processes turn everyday waste into treasures, reducing pollution and saving energy. Try making compost at home!
\[ \mathrm{Proper\ Waste\ Management \Rightarrow Reduced\ Pollution + Resource\ Conservation} \]
A city mixes all types of waste before disposal.
Question: What problems may arise?
Answer: Mixed waste becomes difficult to recycle, increases pollution, spreads diseases, and overloads landfills.
Master ecosystems, food chains, ozone depletion & waste management with concept-first learning, step-by-step solving, and interactive modules.
Everything from Ecosystem basics to Ozone Depletion — organized by concept.
All living organisms in an ecosystem — producers (plants), consumers (animals), and decomposers (bacteria, fungi). Each plays a distinct energy role.
All non-living factors — sunlight, temperature, wind, soil, water, minerals. These determine which organisms can survive where.
Organisms that synthesise food from sunlight via photosynthesis. Form the base of every food chain. Examples: green plants, algae, phytoplankton.
Cannot make their own food. Herbivores eat plants (primary), carnivores eat animals (secondary, tertiary). Omnivores eat both.
Break down dead organic matter into simple inorganic substances, returning nutrients to the soil. Examples: bacteria, fungi. Often called saprotrophs.
Inorganic matter is cycled continuously between living organisms and the environment (e.g., nitrogen cycle, carbon cycle). Decomposers are essential to this process.
Only 10% of energy from one trophic level passes to the next. 90% is lost as heat, respiration, and metabolic activity. This is why food chains rarely exceed 4–5 levels.
Multiple interconnected food chains in an ecosystem. More realistic than a single food chain. Provides stability — if one organism disappears, others can compensate.
T1: Producers | T2: Herbivores | T3: Primary Carnivores | T4: Secondary Carnivores. Energy decreases at each step.
All energy in a food chain ultimately comes from the Sun. Producers capture solar energy via photosynthesis. Consumers harvest it secondhand.
| Trophic Level | Organism Type | Energy Available (J) | Example |
|---|---|---|---|
| T1 | Producer | 10,000 | Grass, Algae |
| T2 | Herbivore | 1,000 | Deer, Grasshopper |
| T3 | Carnivore I | 100 | Fox, Frog |
| T4 | Carnivore II | 10 | Hawk, Snake |
Shows the number of organisms at each level. Usually upright (more producers than consumers). Exception: a tree ecosystem has inverted pyramid — one tree supports many insects.
Shows the total dry weight of organisms at each level. Upright in most terrestrial ecosystems. Can be inverted in aquatic systems (phytoplankton reproduced rapidly).
Shows the total energy content at each trophic level. Always upright and never inverted. Most accurate representation — follows the 10% law strictly.
Non-biodegradable chemicals are not excreted. They accumulate in fat tissues. As predators eat many prey, the chemical concentrates — a large fish eats thousands of small fish, each carrying traces.
DDT concentration: Water → Phytoplankton → Zooplankton → Small fish → Large fish → Birds. Birds at top suffer thin eggshells, reproductive failure.
Humans are at the top of many food chains, so chemicals accumulate most in us. This causes hormonal disruption, cancer, and neurological damage.
Broken down by natural decomposers into harmless substances. Examples: food scraps, paper, cotton, wood, agricultural residue.
Cannot be broken down by natural processes. Persists in the environment for centuries. Examples: plastic, DDT, synthetic fibres, metals, glass.
Industrial effluents, sewage, agricultural runoff (fertilisers, pesticides) contaminate water bodies, causing eutrophication and death of aquatic life.
Burning of fossil fuels, industrial emissions, CFCs deplete the ozone layer and cause acid rain, smog, and greenhouse effect.
| Property | Biodegradable | Non-Biodegradable |
|---|---|---|
| Decomposed by | Bacteria, Fungi | Cannot be decomposed |
| Time to decompose | Days to months | Decades to centuries |
| Environmental effect | Minimal (returns nutrients) | Severe (pollutes soil, water) |
| Example | Vegetable peels, manure | Plastic, DDT, glass |
| Biomagnification | No | Yes (if toxic) |
A molecule of 3 oxygen atoms (O₃). Present in the stratosphere (15–35 km altitude). Formed when UV light splits O₂ molecules, which then combine with another O₂.
Absorbs harmful UV-B and UV-C radiation from the sun. Without it, UV radiation causes skin cancer, cataracts, immune suppression, and DNA damage in all life forms.
Chlorofluorocarbons (CFCs) from refrigerators, ACs, aerosols reach the stratosphere. Each Cl atom from CFC can destroy 100,000 ozone molecules.
Discovered over Antarctica in 1985. A region where ozone concentration drops significantly during spring. Growing due to continued CFC use.
Every quantitative formula and relationship in Chapter 13 — ready for quick reference.
Where T₁ = Producer level, T₂ = Herbivore level, etc. Only 10% of energy is transferred; 90% is lost as heat, respiration, locomotion.
Net effect: O₃ is destroyed and Cl acts as a catalyst (not consumed), so one Cl atom can destroy up to 100,000 O₃ molecules.
Chemical concentration multiplies by roughly 10× at each trophic level (inverse of energy transfer — energy goes down, chemical concentration goes up).
| Quantity | Value / Relationship | Context |
|---|---|---|
| Energy transfer efficiency | 10% | Between each trophic level |
| Energy loss per level | 90% | Lost as heat + metabolism |
| Max food chain length | 4–5 levels | Due to 10% rule limiting energy |
| Ozone height in stratosphere | 15–35 km | Above Earth's surface |
| CFC destructive power | 1 Cl → 100,000 O₃ | Catalytic destruction |
| Ozone formula | O₃ | Triatomic oxygen molecule |
Original concept-building questions with full solutions — organized by topic.
Memory shortcuts, mnemonics, and exam strategies for Chapter 13.
10% Rule Trick: "Add a zero at the beginning when going DOWN (from T1 to T2), remove a zero when going UP." If T2 has 500 J → T1 has 5,000 J. If T1 has 8,000 J → T2 has 800 J.
Mnemonic — Ecosystem Components: "B-ABC" → Biotic = Autotrophs (producers), B-Heterotrophs (consumers), C-Decomposers. Abiotic = Everything else.
Pyramid Trick — "Energy is ALWAYS Up": The Pyramid of Energy is ALWAYS upright (biggest at base = most energy). Remember: Energy = Erect Always. For others, exceptions exist.
CFC Trick: CFCs → Chlorine → Catches ozone (destroys it). Chlorine is the agent, CFCs are the source, stratosphere is the location. Three C's to remember!
Biomagnification vs Energy — Opposites: Energy goes DOWN as you go up the food chain. Chemical concentration goes UP as you go up the food chain. They are always inversely related.
Food Chain Start: Every food chain MUST start with a producer (green plant). If a question gives you an animal as the start — it's a trap! Check again — you may be joining a chain mid-way.
Biodegradable Trick: If it comes FROM nature (wood, paper, cotton, food), it IS biodegradable. If it was MADE by humans chemically (plastic, nylon, DDT), it's NON-biodegradable. Works 90% of the time!
Ozone Location: Ozone is in the STRATOsphere. Remember: Strato = Shield. The shield is in the stratosphere. NOT the troposphere (where we live and breathe).
Exam Tip — "Justify" Questions: When asked to justify why food chains are short, always mention TWO reasons: (1) 10% law reduces energy rapidly, and (2) higher organisms need more energy to sustain themselves.
Montreal Protocol Year: Remember 1987 = Montreal Protocol. Trick: "1-9-8-7 = saving heaven from seven CFC sins." Montreal sounds like Mountain — mountains are cold like refrigerators (which use CFCs)!
Errors students frequently make in exams — and how to avoid them.
Mistake: Thinking decomposers are consumers.
Correction: Decomposers are a separate category. They break down dead organic matter externally using enzymes and absorb nutrients. They do not eat or ingest food. They could replace consumers in diagrams but are never listed as T2/T3.
Mistake: "10% of energy is lost at each level."
Correction: Exactly the opposite! 10% is TRANSFERRED and 90% is LOST. Students often confuse which is lost and which is passed on.
Mistake: Pyramid of Biomass is always upright.
Correction: It can be inverted in aquatic ecosystems where phytoplankton (small biomass) supports large zooplankton biomass due to rapid reproduction. Only Pyramid of Energy is ALWAYS upright.
Mistake: Ozone is in the troposphere (the air we breathe).
Correction: The protective ozone is in the stratosphere (15–35 km). Ground-level ozone (troposphere) is actually a pollutant and harmful to breathe.
Mistake: Biological magnification happens for all pollutants.
Correction: Only non-biodegradable toxic chemicals undergo biomagnification (e.g., DDT, mercury). Biodegradable substances are broken down, so they don't accumulate.
Mistake: Energy flows in a cycle through ecosystems.
Correction: Energy flows in one direction only (sun → producers → consumers → lost as heat). It does NOT cycle back. Matter (nutrients) cycles, energy doesn't.
Mistake: DDT is a medicine or fertiliser.
Correction: DDT (Dichlorodiphenyltrichloroethane) is a synthetic pesticide — used to kill insects (especially mosquitoes). It is non-biodegradable and highly prone to biomagnification.
Mistake: A food web is just many food chains side by side.
Correction: A food web shows interconnected food chains where organisms can feed at multiple levels. It's more realistic and provides ecosystem stability — something parallel chains alone don't offer.
Mistake: Removing a species from a food web just removes that one link.
Correction: Removing one species causes a cascade effect. Prey of the removed predator may overpopulate; food sources of the removed organism may decrease due to less predation pressure. This ripples through the web.
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