Our Environment – Concept Booster | Class 10 Science CBSE

Q: You rarely see a food chain with 6 or 7 animals in it. Why? Because of the 10% Law, energy drops massively at every single step. If plants have $10,000 \text{ J}$ of energy, Herbivores get $1,000 \text{ J}$. Carnivores get $100 \text{ J}$. Top Carnivores get $10 \text{ J}$. If there were a 5th trophic level, it would only get $1 \text{ J}$—which is simply not enough energy to survive or sustain a population. The massive loss of energy as heat limits the number of trophic levels in any ecosystem to 3 or 4.

Apply the 10% Law at each step: 1. Grass (Producer): $20,000 \text{ J}$ (Given) 2. Grasshopper (Primary Consumer): $10\%$ of $20,000 = 2,000 \text{ J}$ 3. Frog (Secondary Consumer): $10\%$ of $2,000 = 200 \text{ J}$ 4. Snake (Tertiary Consumer): $10\%$ of $200 = 20 \text{ J}$

Q: Ozone ($\mathrm{O_3}$) is a highly reactive, toxic gas. If you breathe it in at ground level, it damages your lungs. Yet, without it in the stratosphere, terrestrial life would burn. High-energy UV radiation from the Sun splits normal Oxygen ($\mathrm{O_2}$) into free oxygen atoms ($\mathrm{O}$). These free atoms immediately combine with intact $\mathrm{O_2}$ molecules to form Ozone ($\mathrm{O_3}$). When UV light hits the Ozone, it absorbs the radiation and breaks back into $\mathrm{O_2}$ and $\mathrm{O}$. This continuous cycle absorbs the dangerous UV rays before they reach the Earth’s surface, preventing skin cancer and cataracts.

Justification: The ozone layer shields the Earth from the Sun’s harmful Ultraviolet (UV) radiation. Damage to this layer allows UV rays to reach the surface, which can cause skin cancer, cataracts in human eyes, and destroy crops and marine phytoplankton. Steps to limit damage: 1. Completely phase out the use of Chlorofluorocarbons (CFCs) in refrigerators, ACs, and aerosol sprays. 2. Replace them with safe alternatives like Hydrofluorocarbons (HFCs) that do not degrade ozone.

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Home Concept Boosters CBSE CBSE Class 10 Science Our Environment

Table of Contents

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How to Use This Page

Read each concept carefully, then check the common mistake and exam tip before moving to the next. This page completely covers Our Environment for CBSE Class 10 Science, exploring the delicate balance of energy and matter that sustains life on Earth.

Key Concepts

Class 10 · Science · Biology / Ecology

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Ecology & Environment

The interactions between living beings and their physical world

Class 10 · Ch 15

Ecosystem Definition

A self-sustaining system where living organisms (Biotic components like plants, animals, microbes) interact with each other and their non-living physical environment (Abiotic components like soil, air, water, temperature). Can be natural (forest, pond) or artificial (crop field, aquarium).

Producers, Consumers, and Decomposers Categories

Producers: Organisms that make their own food using sunlight (Autotrophs).
Consumers: Organisms that depend on others for food (Herbivores, Carnivores, Omnivores, Parasites).
Decomposers: Microorganisms (bacteria, fungi) that break down dead organic matter, recycling nutrients back into the soil.

Food Chain & Trophic Levels Sequence

A linear sequence of organisms through which nutrients and energy pass as one eats another. Each step or level of the food chain forms a Trophic Level.

$$\text{Producer} \rightarrow \text{Primary Consumer} \rightarrow \text{Secondary Consumer} \rightarrow \text{Tertiary Consumer}$$

Food Web Concept

In nature, food chains are rarely isolated linear sequences. Because most organisms consume—and are consumed by—more than one species, they form a complex, interconnected network of food chains called a Food Web.

The 10% Law of Energy Flow Rule

Formulated by Raymond Lindeman. Only about 10% of the organic energy present in one trophic level is passed on to the next higher level. The remaining 90% is lost as heat, used for life processes, or goes to decomposers.

$$10,000 \text{ J (Plants)} \rightarrow 1,000 \text{ J (Deer)} \rightarrow 100 \text{ J (Lion)}$$

Unidirectional Flow of Energy Concept

Energy enters the ecosystem from the Sun, is captured by producers, and flows up the trophic levels. It is continuously lost as heat and never returns to the Sun or cycles back down the food chain. (Unlike nutrients/matter, which do cycle).

Biological Magnification Phenomenon

The progressive increase in the concentration of harmful, non-biodegradable chemicals (like DDT pesticides) at each successive trophic level. Top predators (including humans) accumulate the highest, most toxic doses.

Ozone Layer & Its Depletion Chemistry

Ozone ($\mathrm{O_3}$) is a deadly poison at ground level, but in the stratosphere, it acts as a shield absorbing harmful UV radiation from the Sun. Synthetic chemicals like Chlorofluorocarbons (CFCs) (used in old refrigerants) destroy ozone molecules, causing the “Ozone Hole”.

$$\mathrm{O_2 \xrightarrow{UV} O + O} \quad \text{then} \quad \mathrm{O_2 + O \rightarrow O_3}$$

Biodegradable Waste Category

Substances that can be broken down into simpler, harmless substances in nature in due course of time by the action of biological decomposers (bacteria/fungi). E.g., paper, food waste, cotton.

Non-biodegradable Waste Category

Substances that cannot be broken down by biological processes. They persist in the environment for a long time or harm the various members of the ecosystem. E.g., plastics, synthetic fibers, heavy metals, glass.

Concept Deep Dive

Why Are Food Chains So Short?

The limit of the 10% Law

Core Ecological Principle

You rarely see a food chain with 6 or 7 animals in it. Why?

Because of the 10% Law, energy drops massively at every single step.
If plants have $10,000 \text{ J}$ of energy, Herbivores get $1,000 \text{ J}$. Carnivores get $100 \text{ J}$. Top Carnivores get $10 \text{ J}$.
If there were a 5th trophic level, it would only get $1 \text{ J}$—which is simply not enough energy to survive or sustain a population. The massive loss of energy as heat limits the number of trophic levels in any ecosystem to 3 or 4.

The Paradox of Ozone

A deadly protector

Environmental Chemistry

Ozone ($\mathrm{O_3}$) is a highly reactive, toxic gas. If you breathe it in at ground level, it damages your lungs.

Yet, without it in the stratosphere, terrestrial life would burn. High-energy UV radiation from the Sun splits normal Oxygen ($\mathrm{O_2}$) into free oxygen atoms ($\mathrm{O}$). These free atoms immediately combine with intact $\mathrm{O_2}$ molecules to form Ozone ($\mathrm{O_3}$). When UV light hits the Ozone, it absorbs the radiation and breaks back into $\mathrm{O_2}$ and $\mathrm{O}$. This continuous cycle absorbs the dangerous UV rays before they reach the Earth’s surface, preventing skin cancer and cataracts.

Compare & Contrast

✗ Natural Ecosystems

Develop naturally without human interference.
Highly diverse (many different species).
Complex food webs make them very stable and self-regulating.
Examples: Forests, Oceans, Lakes, Deserts.

✓ Artificial Ecosystems

Created and maintained by humans.
Low diversity (often single-species focus, like crops).
Simple food chains; highly fragile and require constant maintenance (fertilizers, cleaning).
Examples: Aquariums, Botanical Gardens, Crop fields.

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Remember

Energy flow is Unidirectional, but nutrient/matter flow (like Carbon, Nitrogen, Water) is Cyclic. Nutrients return to the soil via decomposers to be used by plants again!

Common Mistakes to Avoid

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Mistake 1

The “Sunlight to Plant” 10% Trap: Examiners often trick students by giving the energy of the Sunlight falling on the leaves (e.g., $1,000,000 \text{ J}$). Students immediately apply the 10% law. WRONG! Plants only capture 1% of sunlight. So the plant gets $10,000 \text{ J}$. Then you apply the 10% law for the rest of the animals.

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Mistake 2

Confusing Global Warming with Ozone Depletion: These are entirely different issues!
– Ozone Depletion: Caused by CFCs destroying the $\mathrm{O_3}$ layer, letting in UV light.
– Global Warming: Caused by excess greenhouse gases (like $\mathrm{CO_2}$, Methane) trapping infrared heat inside the atmosphere. Don’t use them interchangeably.

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Mistake 3

Misunderstanding Biomagnification: Students often think the chemical concentration decreases up the food chain like energy does. It’s the exact opposite! Because the toxic chemical isn’t excreted or broken down, a predator has to eat many contaminated prey items, causing the toxin concentration to multiply at each higher level.

Exam Tips

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Tip 1

Structuring “Food Web” Answers: If asked to define a food web, always state that it provides alternative pathways for food availability. If one species goes extinct, the predator can eat something else, which is why food webs provide stability to an ecosystem.

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Tip 2

The UNEP Agreement: Memorize the Montreal Protocol (1987). It was the historic agreement by the United Nations Environment Programme (UNEP) to freeze CFC production at 1986 levels to save the ozone layer. Examiners love asking about this specific event.

Expected Exam Questions

Board Pattern Questions

Class 10 · Science · CBSE Exam

Class 10 · Ecology

In a food chain consisting of: Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake $\rightarrow$ Eagle. If $20,000 \text{ J}$ of energy is available at the producer level, calculate the amount of energy available to the Snake. [2 marks]

Answer $20 \text{ J}$ 📝

Explanation

Apply the 10% Law at each step:
1. Grass (Producer): $20,000 \text{ J}$ (Given)
2. Grasshopper (Primary Consumer): $10\%$ of $20,000 = 2,000 \text{ J}$
3. Frog (Secondary Consumer): $10\%$ of $2,000 = 200 \text{ J}$
4. Snake (Tertiary Consumer): $10\%$ of $200 = 20 \text{ J}$

“Damage to the ozone layer is a cause for concern.” Justify this statement. Suggest any two steps to limit this damage. [3 marks]

Answer It allows harmful UV rays to reach Earth. Stop CFC use. 📝

Explanation

Justification: The ozone layer shields the Earth from the Sun’s harmful Ultraviolet (UV) radiation. Damage to this layer allows UV rays to reach the surface, which can cause skin cancer, cataracts in human eyes, and destroy crops and marine phytoplankton.
Steps to limit damage:
1. Completely phase out the use of Chlorofluorocarbons (CFCs) in refrigerators, ACs, and aerosol sprays.
2. Replace them with safe alternatives like Hydrofluorocarbons (HFCs) that do not degrade ozone.

Why is a lake considered a natural ecosystem, while a crop field is considered an artificial ecosystem? Why are crop fields generally less stable? [3 marks]

Answer Lakes are self-sustaining. Crop fields are human-maintained and lack diversity. 📝

Explanation

A lake is a natural ecosystem because it operates and sustains itself in nature without human intervention; its biotic and abiotic components are naturally balanced.
A crop field is artificial because it is created and intensely maintained by humans (plowing, watering, fertilizing).
Less Stable: Crop fields usually consist of a single type of plant (monoculture). They lack biodiversity and complex food webs. If a specific pest attacks or a disease breaks out, the entire ecosystem can collapse, unlike a natural forest which has natural checks and balances.

Concept Map

Our Environment connects to →

Ecosystem Dynamics

Life Processes (Respiration vs Photosynthesis balance)

Chemistry (Ozone creation and CFC reactions)

Sustainability (Waste management)

Our Environment – Concept Booster | Class 10 Science CBSE

Key Concepts

Ecology & Environment