What is an ecosystem and what are its components?

An ecosystem is a self-sustaining unit of nature in which living organisms (biotic components) interact with each other and with the non-living physical environment (abiotic components). Biotic components include producers (green plants that make food through photosynthesis), consumers (animals that eat plants or other animals), and decomposers (bacteria and fungi that break down dead organic matter and return nutrients to the soil). Abiotic components include sunlight, temperature, water, soil, air, and minerals. All these components interact through energy flow and nutrient cycling. Examples of ecosystems include forests, ponds, oceans, deserts, and grasslands. The biosphere is the sum of all ecosystems on Earth. A healthy ecosystem maintains a balance between all its components through various feedback mechanisms, making it resilient to disturbances.

What is a food chain and how is energy transferred through it?

A food chain is a linear sequence showing how energy and nutrients are transferred from one organism to another through feeding relationships. It always begins with a producer (green plant), followed by herbivores (primary consumers), then carnivores (secondary and tertiary consumers). For example: Grass → Grasshopper → Frog → Snake → Eagle. Energy flows in one direction along the food chain. However, not all energy is transferred — only about 10% of the energy at one trophic level is available to the next level, while 90% is lost as heat (10% law). This is why food chains rarely have more than four to five links — too much energy is lost to sustain higher levels. A food web is a complex network of interconnected food chains in an ecosystem, providing alternative pathways for energy flow and making the ecosystem more stable.

What is biological magnification and how does it affect food chains?

Biological magnification (also called bioaccumulation or biomagnification) is the process by which the concentration of certain harmful substances increases progressively at each successive trophic level in a food chain. This happens with non-biodegradable chemicals like pesticides (DDT), mercury, and some industrial pollutants. These substances cannot be broken down or excreted by organisms, so they accumulate in fatty tissues. At the producer level, the concentration may be very low. At each higher level, consumers must eat large amounts of lower-level organisms, concentrating the chemicals in their bodies. Top predators (including humans) accumulate the highest concentrations. For example, DDT used in paddy fields reaches extremely high levels in fish-eating birds, causing reproductive failure by thinning eggshells. In humans, it can cause hormonal disruption and cancer. This is why even small amounts of pesticides in the environment can have devastating effects on apex predators.

What is ozone layer depletion and what are its causes and effects?

The ozone layer is a thin region of the upper atmosphere (stratosphere, about 15–35 km above Earth) that contains a high concentration of ozone (O₃). It acts as a protective shield by absorbing harmful ultraviolet (UV) radiation from the sun before it reaches Earth's surface. Depletion of the ozone layer is caused mainly by Chlorofluorocarbons (CFCs) — chemicals used in refrigerants, air conditioners, aerosol sprays, and foam packaging. CFCs release chlorine atoms that react with and destroy ozone molecules in a chain reaction. The resulting thinning, especially the hole over Antarctica, allows more UV radiation to reach Earth. Effects include increased skin cancer, cataracts, immune system suppression in humans, damage to phytoplankton (affecting food chains), and harm to crops. The Montreal Protocol (1987) is an international agreement to phase out CFC production.

NCERT Solutions for Class 10 Science Chapter 13 Our Environment

Q: What is the difference between biodegradable and non-biodegradable waste?

Biodegradable waste consists of materials that can be broken down naturally by microorganisms like bacteria and fungi into simpler, harmless substances. Examples include food scraps, leaves, paper, cotton, wood, and animal dung. These wastes decompose relatively quickly and return nutrients to the environment, making them environmentally friendly. Non-biodegradable waste consists of materials that cannot be broken down by natural processes, or take hundreds to thousands of years to decompose. Examples include plastic bags, polythene, glass, DDT, metal cans, and synthetic fibres. These materials accumulate in the environment, pollute soil and water, harm animals (who may ingest or become entangled in plastic), and disrupt ecosystems. Biological magnification occurs when non-biodegradable chemicals like DDT concentrate progressively at higher trophic levels in a food chain.

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NCERT Solutions for Class 10 Science Chapter 13 – Our Environment

Class 10 Science Chapter 13, "Our Environment," is where Biology meets real-world responsibility. It's not just about learning how ecosystems work — it's about understanding why they're under threat and what that means for every living being on Earth, including us. The chapter walks students through the structure of ecosystems, the flow of energy through food chains and food webs, the crucial difference between biodegradable and non-biodegradable waste, and the alarming reality of ozone layer depletion. One of the most eye-opening concepts here is biological magnification — the process by which harmful chemicals like DDT become more concentrated as they move up the food chain, ending up in highest concentrations in top predators, including humans.

This chapter also connects directly to environmental concerns that students see in the news daily: plastic pollution, greenhouse gases, and the damage done to the protective ozone shield above us. The NCERT Solutions for Class 10 Science at Myclass24 present these answers in a student-friendly manner that makes ecological concepts easy to understand, retain, and reproduce in board exams.

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Chapter 13 Our Environment – Core Concepts, Facts & NCERT Q&A Guide

Chapter 13 is relatively concise compared to Electricity or Magnetic Effects, but it punches above its weight in CBSE board exams — especially since environmental topics are increasingly featured in value-based questions and long-answer questions. Here's a comprehensive topic-wise breakdown to help you master the chapter.

Components of an Ecosystem

Component	Type	Examples	Role in Ecosystem
Plants, Algae	Producers (Autotrophs)	Grass, phytoplankton	Fix solar energy via photosynthesis
Herbivores	Primary Consumers	Grasshopper, rabbit, deer	Feed directly on producers
Carnivores (small)	Secondary Consumers	Frog, small fish	Feed on primary consumers
Carnivores (large)	Tertiary Consumers	Eagle, shark, lion	Top of food chain
Bacteria, Fungi	Decomposers	Rhizopus, Aspergillus	Break down dead matter; recycle nutrients

Energy Flow in a Food Chain – The 10% Law

Trophic Level	Organism	Energy Available
Level 1 (Producers)	Plants	10,000 J (assumed base)
Level 2 (Primary Consumers)	Deer / Insects	1,000 J (10% of L1)
Level 3 (Secondary Consumers)	Frogs / Small birds	100 J (10% of L2)
Level 4 (Tertiary Consumers)	Eagle / Hawk	10 J (10% of L3)

The 10% Law (Lindeman's Law) states that only 10% of the energy stored at one trophic level is transferred to the next. The remaining 90% is lost as heat during metabolic processes. This is why food chains rarely have more than four or five links — there simply isn't enough energy left for another level.

Important Fact: Biological magnification (biomagnification) explains why pesticide concentration is lowest in plants and highest in top predators. In water bodies affected by DDT runoff, fish-eating birds may accumulate concentrations thousands of times higher than what's present in the water itself.

Biodegradable vs Non-Biodegradable Waste

Waste Type	Examples	Broken Down By	Environmental Impact
Biodegradable	Food scraps, paper, cotton, wood	Microorganisms (bacteria, fungi)	Low impact; returns nutrients to soil
Non-biodegradable	Plastic, DDT, synthetic fibres, glass	Cannot be broken down naturally	Accumulates; causes pollution & biomagnification

Ozone Layer – Protection, Depletion & Facts

Aspect	Details
Location	Stratosphere, approximately 15–35 km above Earth's surface
Chemical formula	O₃ (three oxygen atoms)
Function	Absorbs harmful UV radiation (UV-B and UV-C) from the Sun
Main depleting agents	CFCs (Chlorofluorocarbons) from refrigerants, aerosol sprays
Damage caused by UV	Skin cancer, cataracts, damage to marine ecosystems
International action	Montreal Protocol (1987) – global ban on CFC production

NCERT Exercise – Chapter 13 Question Focus

Question	Topic Tested	Type
Q1	What is an ecosystem?	1-mark definition
Q2	Producers in an ecosystem	Conceptual short answer
Q4	Why are food chains limited to 3–4 steps?	Application – 10% Law
Q5	Biodegradable vs Non-biodegradable with examples	3-mark comparison
Q6	Ozone layer – importance and threats	5-mark long answer
Q8	Biological magnification of pesticides	Application/concept

Chapter 13 also encourages students to reflect on everyday choices — from refusing single-use plastic to understanding why household waste segregation matters. These aren't abstract ideas; they connect directly to the scientific principles taught in this chapter. The NCERT solutions on Myclass24 present all exercise answers in clear, point-wise format so students can write structured responses in board exams and score full marks on every question.