Our Environment (Class 10): Notes और MCQ Practice

आसान भाषा में:

हमारा Environment biotic (living) और abiotic (non-living) components का balance है। Ecosystem में Food Chain के ज़रिए energy हमेशा एक ही दिशा (unidirectional) में flow करती है। हमारी activities, जैसे CFCs का इस्तेमाल और non-biodegradable waste, ozone layer और प्रकृति को नुकसान पहुँचा रही हैं।

Important Points & Definitions:

• Ecosystem: Biotic (plants, animals) और Abiotic (air, water, soil) components का interaction.
• 10% Law: एक trophic level से अगले level तक सिर्फ 10% energy transfer होती है, बाकी 90% life processes और heat में lose हो जाती है।
• Trophic Levels: Producers (Plants) → Primary Consumers (Herbivores) → Secondary Consumers (Carnivores) → Tertiary Consumers.
• Biological Magnification: Food chain में higher trophic levels पर toxic chemicals (जैसे pesticides) का concentration लगातार बढ़ना। Maximum concentration top level (humans) में होती है।
• Ozone Layer (O₃): Stratosphere में हानिकारक UV rays को रोकती है। UV radiation से skin cancer और cataracts हो सकते हैं।
• Formation: O₂ + UV → O + O, फिर O + O₂ → O₃
• Depletion: CFCs (Chlorofluorocarbons) की वजह से। (Montreal Protocol 1987 ने CFC production freeze किया)।
• Biodegradable vs Non-biodegradable: जो bacteria/fungi द्वारा decompose हो जाए वो Biodegradable (फल, कागज़); जो decompose न हो वो Non-biodegradable (plastic, glass)।

💡 2 Memory Tricks:

1. 10% Energy Rule: "ऊपर चढ़ो, एक ज़ीरो छोड़ो!" (10,000 J → 1,000 J → 100 J → 10 J).
2. Ozone Umbrella: O₂ + O = O₃ (दोस्त ऑक्सीजन + अकेला एटम = ओज़ोन की छतरी)।

⚠️ Common Board Exam Mistakes:

1. Energy Flow: Energy flow को cyclic मत लिखना; यह हमेशा Unidirectional (एक ही दिशा में) होता है।
2. Biological Magnification: गलती से producer level पर pesticide concentration highest मत लिखना; यह हमेशा top consumer/highest trophic level पर maximum होती है।

Chapter 15: Our Environment

1. Chapter in Short

This chapter explains how living organisms interact with each other and their physical surroundings to form an ecosystem. It explores how energy flows from the sun through various living beings via food chains and food webs, why harmful chemicals accumulate in our bodies (biological magnification), how human activities damage the protective ozone layer, and the challenges associated with waste disposal.

2. Key Concepts Explained Simply

A. Ecosystem and its Components

An ecosystem is a self-sustaining system where living organisms interact among themselves and with the non-living physical environment.

• Biotic Components (Living things): Plants, animals, bacteria, fungi.
• Abiotic Components (Non-living things): Air, water, soil, sunlight, temperature, rainfall.

Organisms in an ecosystem are categorized into:

1. Producers (Autotrophs): Green plants and blue-green algae that make food using solar energy by photosynthesis.
2. Consumers (Heterotrophs): Organisms that consume food produced by autotrophs (Herbivores, Carnivores, Omnivores, Parasites).
3. Decomposers: Microorganisms (bacteria and fungi) that break down dead remains and organic waste into simple inorganic substances, returning nutrients to the soil.

B. Food Chains and Food Webs

• Food Chain: A straight, sequential feeding relationship where one organism eats another to transfer energy.
• Example (Forest): Grass (Producer) → Deer (Primary Consumer) → Tiger (Secondary Consumer)
• Example (Aquatic): Phytoplankton → Zooplankton → Small Fish → Big Fish
• Food Web: In nature, animals do not eat just one type of food. Several food chains interlink to form a branching network called a food web.

C. Energy Flow and the 10% Law

• Sunlight capture: Green plants in a terrestrial ecosystem capture only about 1% of the sunlight falling on their leaves and convert it into food energy.
• Unidirectional Flow: Energy flows strictly in one direction (Sun → Producers → Herbivores → Carnivores). It never goes backwards.
• The 10% Law: During the transfer of energy from one trophic level to the next, on average only 10% of the energy is stored in the new biomass and made available to the next trophic level. The remaining 90% is lost as heat to the environment or used up for life processes (respiration, digestion, movement).
• Limit on Trophic Levels: Because so little energy reaches the top, food chains rarely have more than 3 to 4 steps.

D. Biological Magnification (Biomagnification)

• When farmers spray non-biodegradable pesticides (like DDT) on crops, these chemicals enter the soil and water bodies.
• They are taken up by plants and aquatic organisms.
• Since these chemicals are not broken down or excreted, their concentration increases progressively at each higher trophic level.
• As human beings occupy the top trophic level in many food chains, the maximum concentration of these harmful chemicals accumulates in human bodies.

E. Ozone Layer and Its Depletion

• What is Ozone? Ozone is a molecule containing three oxygen atoms (O³). While toxic at ground level, high up in the stratosphere it forms a protective shield that blocks harmful ultraviolet (UV) radiation from the sun.
• Formation:
• High-energy UV rays split molecular oxygen (O²) into free oxygen atoms:
• O² + UV radiation → O + O
• A free oxygen atom combines with molecular oxygen to form ozone:
• O + O² → O³
• Depletion: Synthetic chemicals such as Chlorofluorocarbons (CFCs), used in refrigerators and fire extinguishers, release chlorine that destroys ozone molecules, creating an "ozone hole".
• Action taken: In 1987, the United Nations Environment Programme (UNEP) succeeded in forging the Montreal Protocol, freezing CFC production at 1986 levels.

F. Managing Garbage

• Biodegradable Waste: Substances broken down into harmless materials by biological processes (action of bacteria/fungi). Examples: Vegetable peels, paper, cotton cloth.
• Non-Biodegradable Waste: Substances that cannot be broken down by saprophytic microorganisms and persist for a long time. Examples: Plastics, glass, synthetic pesticides.

3. Important Definitions, Formulas, Facts, and Dates

• Trophic Level: Each step or level of a food chain where energy transfer takes place.
• 10% Energy Transfer Formula:
• Energy available to next level = Energy at current level × 10 ÷ 100
• Sunlight Conversion Fact: Terrestrial green plants convert only 1% of solar energy hitting their leaves into food energy.
• Ozone: Triatomic molecule (O³); protects against skin cancer, cataract, and damage to crops caused by UV rays.
• Montreal Protocol: Signed in 1987 under UNEP to freeze and phase out CFC production globally.
• Decomposers: Clean up the environment and replenish soil nutrients naturally.

4. Solved Examples & Important Board-Style Questions

Question 1 (Numerical on 10% Law)

If 20,000 J of solar energy falls on green plants in a terrestrial ecosystem, calculate the amount of energy transferred to a snake in the following food chain:

Plants → Mice → Snakes → Hawks

Answer:

1. Energy trapped by Plants:

Plants trap only 1% of the solar energy falling on them.

• Energy in Plants = 20,000 J × 1 ÷ 100 = 200 J

1. Energy available to Mice (Primary Consumers):

Applying the 10% Law:

• Energy in Mice = 200 J × 10 ÷ 100 = 20 J

1. Energy available to Snakes (Secondary Consumers):

• Energy in Snakes = 20 J × 10 ÷ 100 = 2 J

Final Answer: The snake receives 2 J of energy.

Question 2

Why is the flow of energy in an ecosystem always unidirectional?

Answer:

1. The energy captured by autotrophs (producers) from sunlight cannot revert back to the sun.
2. The energy that passes to herbivores cannot flow back to autotrophs, and energy moving to carnivores cannot go back to herbivores.
3. As energy moves through trophic levels, a major portion is lost to the surroundings as heat and cannot be reused. Therefore, energy flow is strictly one-directional.

Question 3

What is biological magnification? Will the level of this magnification be different at different levels of the ecosystem?

Answer:

• Definition: Biological magnification is the progressive accumulation of non-biodegradable toxic substances at each successive trophic level in a food chain.
• Difference at levels: Yes, it is different. It is lowest at the producer level (first trophic level) and increases at each step. It is highest at the top carnivore level because these toxic substances cannot be digested, metabolized, or excreted.

Question 4

What is the role of decomposers in an ecosystem? What would happen if they completely disappear?

Answer:

• Role: Decomposers (bacteria and fungi) break down complex organic matter from dead plants and animals into simpler inorganic substances that return to the soil and air.
• If they disappear:

1. Dead bodies of plants and animals would pile up, creating foul odors and unhygienic conditions.
2. The recycling of essential nutrients (carbon, nitrogen, etc.) would stop, depriving plants of nutrients and eventually halting all life.

5. Common Mistakes and Quick Revision Points

Common Mistakes to Avoid:

• Mistake 1: Applying the 10% law to sunlight falling on leaves.
• Correction: Plants capture only 1% of sunlight. The 10% rule applies only when energy passes from one living organism to the next (trophic level to trophic level).
• Mistake 2: Confusing ozone depletion with global warming.
• Correction: Ozone depletion is caused mainly by CFCs and lets in harmful UV rays. Global warming is caused by greenhouse gases (like CO²) trapping heat.
• Mistake 3: Thinking non-biodegradable substances never change.
• Correction: They can break down under heat and physical pressure, but not by biological action of microorganisms.

Quick Revision Points:

• Sun → Producers (1% energy trapped).
• Trophic level to next trophic level = 10% energy transferred.
• Non-biodegradable chemicals increase up the food chain (Biomagnification).
• Highest concentration of chemicals is always in the top-most consumer.
• Ozone (O³) in the stratosphere blocks UV radiation; destroyed by CFCs.
• UNEP Montreal Protocol (1987) banned CFC manufacture.