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ScienceCh-13 15 min comprehensive revision
NCERT Class 10 Science — Chapter 14

Our Environment

Ecosystem structure (biotic and abiotic components), food chains and food webs, Lindeman's 10% law of energy transfer, biological magnification (biomagnification of pesticides), ozone layer depletion (CFC mechanisms, UNEP 1987 Montreal Protocol), and solid waste management.

Quick Key Takeaways:
Ecosystem Components: Biotic (Producers/Autotrophs, Consumers/Heterotrophs: Herbivores, Carnivores, Omnivores, Decomposers: Fungi/Bacteria) and Abiotic (Sunlight, Temperature, Water, Soil, Minerals).
Lindeman's 10% Law of Energy Flow: Only 10% of energy entering a trophic level is transferred to the next higher level; 90% is lost as metabolic heat, respiration, and excretion. Energy flow is strictly unidirectional.
Biological Magnification (Biomagnification): The progressive increase in concentration of non-biodegradable toxic substances (like DDT, heavy metals) at successive trophic levels, reaching maximum concentration in top carnivores / humans.
Ozone Layer Depletion: Ozone (O3\text{O}_3) in stratosphere shields biosphere from lethal UV radiation (which causes skin cancer, cataracts, immune damage). Depleted by Chlorofluorocarbons (CFCs): O2→UVO+O,O+O2⟶O3\text{O}_2 \xrightarrow{\text{UV}} \text{O} + \text{O}, \quad \text{O} + \text{O}_2 \longrightarrow \text{O}_3
Waste Management: Biodegradable waste (broken down by decomposer enzymes: food scraps, paper) vs Non-Biodegradable waste (plastics, glass, synthetic pesticides).
Jump to Concept:1. 1. Ecosystem Architecture, Food Chains & 10% Energy Transfer Law2. 2. Biomagnification, Ozone Layer Depletion & Waste Management3. 3. High-Yield Solved Board Examination Questions (3-Mark & 5-Mark)4. 4. Practical Laboratory & Competency-Based Case Drill: Kulhad Eco-Friendly Clay Cups vs Disposable Plastic Cups in Indian Railways5. 5. CBSE Examiner Marking Scheme, Scientific Notation & Deduction Traps
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1. Ecosystem Architecture, Food Chains & 10% Energy Transfer Law

Fundamental Principles

Core scientific laws, chemical equations, anatomical structures, and visual model for Our Environment.

• Trophic Levels & Energy Flow Dynamics
•
Trophic Levels: Producers (T1T_1, Green Plants) ⟶\longrightarrow Primary Consumers (T2T_2, Herbivores) ⟶\longrightarrow Secondary Consumers (T3T_3, Small Carnivores) ⟶\longrightarrow Tertiary Consumers (T4T_4, Top Carnivores).
•
Why Food Chains Rarely Exceed 4–5 Trophic Levels: According to the 10% Law, so little usable energy remains after 4–5 transfers that it cannot support a viable population at higher trophic levels.
•
Lindeman's 10% Law Calculation Example:
- Solar energy available to plants: 1,000,000 J1,000,000\text{ J}
- Captured by Producers (1%1\% of solar energy): 10,000 J\mathbf{10,000\text{ J}}
- Transferred to Herbivores (10%10\% of 10,000 J10,000\text{ J}): 1,000 J\mathbf{1,000\text{ J}}
- Transferred to Carnivores (10%10\% of 1,000 J1,000\text{ J}): 100 J\mathbf{100\text{ J}}
- Transferred to Top Carnivore (10%10\% of 100 J100\text{ J}): 10 J\mathbf{10\text{ J}}
📊 Environment: Trophic Energy Pyramid & BiomagnificationVisual Model
Top Carnivores (10 J)Small Carnivores (100 J)Herbivores / Insects (1,000 J)Producers / Green Plants (10,000 J)10% ENERGY LAWOnly 10% energy istransferred to next level.90% lost as heat / life.BIOMAGNIFICATIONToxic chemicals max at top.

Visual schematic mapping the 10% ecological energy pyramid, progressive pesticide biomagnification, and stratospheric ozone depletion.

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2. Biomagnification, Ozone Layer Depletion & Waste Management

Mechanisms & Experiments

Step-by-step chemical reaction mechanisms, experimental activities, and physiological pathways for Our Environment.

• Biomagnification & Stratospheric Ozone Chemistry
•
Biological Magnification Mechanism:
- Non-biodegradable pesticides (e.g. DDT) washed into water bodies are absorbed by phytoplankton (0.04 ppm0.04\text{ ppm}).
- Small fish consume large quantities of plankton (0.5 ppm0.5\text{ ppm}).
- Large fish eat multiple small fish (2.0 ppm2.0\text{ ppm}).
- Fish-eating birds/Humans consume large fish (25.0 ppm25.0\text{ ppm} - 600-fold bioaccumulation).
- Reason: Non-biodegradable chemicals cannot be metabolized or excreted by organisms.
•
Ozone (O3\text{O}_3) Formation & Catalytic Destruction by CFCs:
1. UV split: O2→UVO+O\text{O}_2 \xrightarrow{\text{UV}} \text{O} + \text{O}
2. Formation: O+O2⟶O3\text{O} + \text{O}_2 \longrightarrow \text{O}_3
3. CFC Breakdown: CF2Cl2→UVCF2Cl+Cl∙\text{CF}_2\text{Cl}_2 \xrightarrow{\text{UV}} \text{CF}_2\text{Cl} + \text{Cl}^\bullet
4. Catalytic cycle: Cl∙+O3⟶ClO∙+O2\text{Cl}^\bullet + \text{O}_3 \longrightarrow \text{ClO}^\bullet + \text{O}_2; a single chlorine radical can destroy over 100,000100,000 ozone molecules.
- UNEP Montreal Protocol (1987): International treaty freezing and phasing out CFC production globally.
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3. High-Yield Solved Board Examination Questions (3-Mark & 5-Mark)

Solved Board Questions

Standard CBSE board exam questions with complete scientific justifications and marking scheme step protocols.

• 3-Mark Standard Board Question: If 20,000 J of solar energy falls on the leaves of green plants in a forest ecosystem, calculate the amount of energy available to: (a) Green plants, (b) Deer, (c) Tiger. Draw the food chain.
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Food Chain: Sunlight⟶Green Plants (Producers)⟶Deer (Primary Consumer)⟶Tiger (Secondary Consumer)\text{Sunlight} \longrightarrow \text{Green Plants (Producers)} \longrightarrow \text{Deer (Primary Consumer)} \longrightarrow \text{Tiger (Secondary Consumer)}.
•
(a) Energy Available to Green Plants:
Terrestrial green plants capture only about 1% of solar energy falling on their leaves:
Eplants=1% of 20,000 J=1100×20,000=200 JoulesE_{\text{plants}} = 1\% \text{ of } 20,000\text{ J} = \frac{1}{100} \times 20,000 = \mathbf{200\text{ Joules}}
•
(b) Energy Available to Deer (Herbivore):
By Lindeman's 10% Law:
Edeer=10% of 200 J=10100×200=20 JoulesE_{\text{deer}} = 10\% \text{ of } 200\text{ J} = \frac{10}{100} \times 200 = \mathbf{20\text{ Joules}}
•
(c) Energy Available to Tiger (Carnivore):
Etiger=10% of 20 J=10100×20=2 JoulesE_{\text{tiger}} = 10\% \text{ of } 20\text{ J} = \frac{10}{100} \times 20 = \mathbf{2\text{ Joules}}
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Final Boxed Summary: Plants=200 J,Deer=20 J,Tiger=2 J\mathbf{\text{Plants} = 200\text{ J}, \quad \text{Deer} = 20\text{ J}, \quad \text{Tiger} = 2\text{ J}}
• 5-Mark Comprehensive Question / Numerical: (a) What is Biological Magnification? Will the levels of this magnification be different at different levels of the ecosystem?
(b) What is Ozone and how does it affect any ecosystem? Explain why ozone is deadly poison at ground level but a protective shield in the stratosphere.
•
Part (a) Biological Magnification Analysis:
- Biological magnification is the progressive accumulation and concentration increase of non-biodegradable toxic substances at successive trophic levels in a food chain.
- Yes, the concentration levels differ dramatically across trophic levels: it is lowest in primary producers (plants) and increases progressively at each step, reaching the maximum concentration at the highest trophic level (top carnivores/humans).
•
Part (b) Ozone (O3\text{O}_3) Dual Role:
1. In the Stratosphere (Beneficial Shield):
- Ozone absorbs harmful, high-energy Ultraviolet (UV-B, UV-C) radiation from the sun.
- Prevents lethal biological damage, such as skin cancers, cataracts, genetic mutations, and phytoplankton destruction in marine ecosystems.
2. At Ground Level / Troposphere (Deadly Pollutant):
- Ozone is a toxic, highly reactive oxidant gas.
- When inhaled at ground level, it causes severe respiratory damage, lung irritation, asthma exacerbation, and damages plant chlorophyll tissues.
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4. Practical Laboratory & Competency-Based Case Drill: Kulhad Eco-Friendly Clay Cups vs Disposable Plastic Cups in Indian Railways

Practical & Case Drill

Experimental observation analysis, chemical gas tests, and assertion-reason drills.

• Laboratory Activity Context: Kulhad Eco-Friendly Clay Cups vs Disposable Plastic Cups in Indian Railways
In an attempt to reduce non-biodegradable plastic waste, Indian Railways introduced disposable earthen clay cups ('Kulhads') to replace plastic cups, before considering disposable paper cups.
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Q1: Why are plastic cups ecologically harmful? →\rightarrow Plastic is non-biodegradable; it persists in the environment for hundreds of years, clogging drainage systems and releasing toxic dioxins if incinerated.
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Q2: Why was large-scale use of Kulhads discontinued? →\rightarrow Manufacturing millions of clay kulhads on a mass commercial scale resulted in the loss of fertile topsoil, causing land degradation.
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Q3: Why are modern disposable paper cups preferred? →\rightarrow Paper is made from renewable pulp, is fully biodegradable, and does not deplete fertile topsoil or produce persistent non-biodegradable landfill waste.
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5. CBSE Examiner Marking Scheme, Scientific Notation & Deduction Traps

Important Solved Board Questions

Examiner step-marking allocations, mandatory scientific terminology, and common error avoidance.

• Step-by-Step Marking Rubric & Key Terminology
•
1 Mark: Calculating 1% solar capture for plants and 10% transfer for consumers.
•
1 Mark: Defining biological magnification and identifying top trophic level accumulation.
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2 Marks: Writing chemical reactions for ozone formation and CFC catalytic destruction.
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1 Mark: Differentiating biodegradable vs non-biodegradable waste mechanisms.
• Common Error Deduction Traps
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Trap 1: Applying 10% law from Sun to plants (plants capture only 1% of solar energy; 10% law applies between trophic levels).
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Trap 2: Claiming that humans have lowest concentration of pesticides (biomagnification ensures humans have the highest concentration).
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Trap 3: Confusing global warming (CO2\text{CO}_2, greenhouse effect) with ozone depletion (CFCs, UV radiation shield).
Authentic Board Question (3 Marks)Topic: Our Environment Biological Mechanisms & Physiological Pathways
Describe the anatomical structures, physiological pathways, and biological significance associated with Our Environment.

Official CBSE Step-by-Step Marking Breakdown:

Step 1: Biological Terminology & Organ/Enzyme Identification: Accurately name the specific biological structures, enzymes (pepsin, trypsin, lipase), hormones, or genetic alleles involved.
1 Mark
Step 2: Step-by-Step Mechanism / Pathway Flow: Describe the sequential biological pathway (circulation, filtration, reflex arc, reproduction mode, or Punnett square cross).
1 Mark
Step 3: Biological Function & Homeostatic Significance: Explain why this process is essential for organism survival, energy production, variation, or ecological balance.
1 Mark
Model Student Answer (Target: Full 3/3 Marks):
For full marks in CBSE Biology on Our Environment:

1. Structural Identification: Name the specific organs, cell types, or biochemical catalysts responsible for the process.
2. Physiological Process: Outline the step-by-step sequential pathway using directional flow arrows.
3. Functional Outcome: Conclude with the physiological necessity (e.g., ATP synthesis, waste removal, species survival).
Examiner Mark Deduction Traps:
•Use standard NCERT biological terminology rather than everyday descriptive language.
•In genetics questions, always show the complete parent phenotype →\to genotype →\to gametes →\to F1/F2F_1/F_2 Punnett square.

High-Frequency Conceptual Doubts & FAQs

Curated answers to the most common questions asked by Class 10 students.
In an ecosystem, only about 10% of the energy entering a trophic level is transferred and made available to the next higher trophic level as biomass. The remaining 90% is lost as metabolic heat during respiration, digestion, movement, and excretion. Because energy diminishes rapidly, food chains rarely exceed 4 to 5 trophic levels.

Related YouTube Videos & Masterclasses

5 Verified Class 10 Videos

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Our Environment | our environment class 10 | our environment class 10 one shot

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