Our Environment — NCERT Solutions, AI Tutor & Practice

Understand: An ecosystem is a self-sustaining unit in which living organisms interact with one another and with their non-living surroundings, exchanging materials and energy.

Analyze — the two components:

• Biotic components (living): producers, consumers and decomposers. Examples: plants, deer, tigers, bacteria, fungi.
• Abiotic components (non-living, physical factors): Examples: air, water, soil, temperature, sunlight, minerals.

Conclude: Both components are interdependent — abiotic factors support life while biotic organisms modify the physical environment. A pond, a forest, or an aquarium are all examples of ecosystems (natural or artificial).

Producers (autotrophs): Organisms that prepare their own food from simple inorganic substances using sunlight (photosynthesis). Example: green plants, algae.

Consumers (heterotrophs): Organisms that depend directly or indirectly on producers for food.

• Herbivores (eat plants) — deer
• Carnivores (eat animals) — lion
• Omnivores (eat both) — human

Decomposers: Micro-organisms that break down dead remains of plants and animals into simpler substances, returning nutrients to the soil. Example: bacteria and fungi.

Conclude: These three groups together keep the nutrients cycling in an ecosystem.

Understand: A food chain is a series of organisms through which food energy passes from one level (trophic level) to the next as one organism eats another.

Analyze — a grassland food chain:

$\text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog} \rightarrow \text{Snake}$

• Grass — Producer (1st trophic level)
• Grasshopper — Primary consumer / herbivore (2nd level)
• Frog — Secondary consumer (3rd level)
• Snake — Tertiary consumer (4th level)

Conclude: Energy flows unidirectionally from producers to top consumers, decreasing at each step.

Statement (10% Law – given by Lindeman): Only about 10% of the energy present at one trophic level is transferred and stored as living tissue at the next trophic level. The remaining 90% is lost, mainly as heat during respiration and in life processes.

Explanation with numbers: If green plants capture $1000\text{ J}$ of energy:

• Herbivores get $\approx 100\text{ J}$ ($10\%$ of $1000$)
• Small carnivores get $\approx 10\text{ J}$
• Top carnivores get $\approx 1\text{ J}$

Conclude: Because energy shrinks so rapidly, food chains are usually limited to only 3 or 4 trophic levels — there is too little energy left to support more.

Understand: Energy enters the ecosystem from the Sun, is captured by producers, and passes to consumers along the food chain.

Analyze:

• At each level, a large part of energy is used up in life processes and released as heat.
• This heat energy cannot be recaptured by plants (they can only use sunlight, not heat).
• Energy therefore always moves in one direction: Sun → Producers → Consumers → lost as heat.

Conclude: Since energy is never returned to an earlier level and is continuously lost, its flow is unidirectional and non-cyclic. (In contrast, nutrients like carbon and nitrogen are recycled.)

Trophic levels: The different feeding steps in a food chain are called trophic levels. Producers form the first level, herbivores the second, and so on.

Pyramid of numbers: A graphic showing the number of organisms at each trophic level, with producers at the base.

Why usually upright:

• Producers (grass) are very large in number.
• Herbivores feeding on them are fewer.
• Carnivores are still fewer.

$\text{Grass (thousands)} > \text{Grasshoppers (hundreds)} > \text{Frogs (tens)} > \text{Snakes (few)}$

Conclude: Since numbers decrease at each higher level (because energy available decreases), the pyramid is broad at the base and narrow at the top — an upright pyramid.

Understand: Biological magnification (biomagnification) is the progressive increase in the concentration of harmful, non-biodegradable chemicals (like pesticides, DDT) in the bodies of organisms at each successive trophic level of a food chain.

Analyze:

• These chemicals are absorbed but cannot be broken down or excreted.
• As a bigger organism eats many smaller contaminated ones, the chemical accumulates in its body.
• Therefore concentration is lowest in producers and highest in top consumers.

$\text{Water} < \text{Plankton} < \text{Small fish} < \text{Large fish} < \text{Humans}$

Conclude: Since humans occupy the top of many food chains, they receive the maximum concentration of such toxins, which can cause serious health effects.

| Feature | Biodegradable | Non-biodegradable | |---|---|---| | Definition | Broken down by decomposers/micro-organisms | Cannot be broken down by decomposers | | Examples | Vegetable peels, paper, cow dung | Plastic, DDT, glass, metals | | Persistence | Decompose quickly | Remain for a very long time |

Harmful effect of non-biodegradable wastes:

• They cause environmental pollution and accumulate in soil and water.
• They undergo biological magnification, harming animals and humans.

Conclude: Reducing non-biodegradable waste is essential for a clean environment.

Understand: Ozone ($O_3$) is a molecule of three oxygen atoms present in the upper part of the atmosphere (stratosphere), forming the ozone layer.

Protective role:

• It absorbs harmful ultraviolet (UV) radiation from the Sun.
• UV rays can cause skin cancer, cataracts and damage to crops and organisms; the ozone layer acts as a shield.

Formation: Higher-energy UV splits oxygen molecules: $O_2 \xrightarrow{UV} O + O$ $O + O_2 \rightarrow O_3$

Damage: Chemicals called chlorofluorocarbons (CFCs) — used in refrigerators, air-conditioners and aerosol sprays — rise up and break down ozone, forming an ozone hole.

Conclude: To protect the layer, the Montreal Protocol (1987) froze CFC production; using CFC-free products helps save the ozone shield.

Why waste management is necessary:

• Accumulated waste causes soil, water and air pollution.
• It spreads diseases and gives off foul smell.
• Non-biodegradable waste stays for years and enters food chains (biomagnification).

Ways to reduce waste generation (the 3 R's):

1. Reduce — use fewer resources (e.g., save electricity, avoid excess packaging).
2. Reuse — use items again instead of throwing them (e.g., reuse containers, cloth bags).
3. Recycle — convert used paper, plastic, glass, metal into new products.

Additional measures: Segregate biodegradable and non-biodegradable waste; compost kitchen waste.

Conclude: Proper waste management keeps the environment clean and conserves natural resources.

Given: Energy in grass (producer) $= 10000\text{ J}$. Apply the 10% law.

Step 1 — Energy to deer (herbivore): $= \frac{10}{100} \times 10000 = 1000\text{ J}$

Step 2 — Energy to lion (carnivore): $= \frac{10}{100} \times 1000 = 100\text{ J}$

Conclude: The deer receives $1000\text{ J}$ and the lion receives only $100\text{ J}$ — showing how sharply energy decreases up the food chain.

Understand: Decomposers break down dead plants and animals and waste matter into simpler inorganic substances.

Analyze — if decomposers disappear:

• Dead bodies and organic waste would pile up and not decay.
• Essential nutrients (nitrogen, carbon, minerals) would remain locked in dead matter and not return to the soil.
• Nutrient cycling would stop, so producers would not get raw materials.
• Plants would eventually die, and the whole food chain and ecosystem would collapse.

Conclude: Decomposers are vital cleaners and recyclers; without them the ecosystem cannot function.