This MCQ module is based on: Ecosystems, Food Chains and Food Webs
TOPIC 48 OF 50
Ecosystems, Food Chains and Food Webs
🎓 Class 10
Science
CBSE
Theory
Ch 13 — Our Environment
⏱ ~18 min
🌐 Language: [gtranslate]
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Introduction — A Web of Living & Non-Living
Open a kitchen window on a winter morning — a crow caws on the neem tree, ants file along the wall, sunlight warms the floor, moisture from last night still clings to leaves. Each of these — the crow, the tree, the ants, sunlight, water — is part of the same environment. Chapter 13 examines how these parts are linked, how energy flows among them, and how human activities (from DDT spraying to plastic dumping) can damage these links.
13.1 Ecosystem — Its Components
A garden, a pond, a forest and even a small aquarium are all ecosystems. Every ecosystem has two sets of components that cannot be separated in practice:
Two components of an ecosystem:
Biotic: all the living things — plants, animals, bacteria, fungi.
Abiotic: the non-living physical factors — sunlight, temperature, rainfall, soil, air, water, minerals.
Biotic: all the living things — plants, animals, bacteria, fungi.
Abiotic: the non-living physical factors — sunlight, temperature, rainfall, soil, air, water, minerals.
13.1.1 Types of Ecosystems
- Natural ecosystems — formed and maintained by nature itself. Examples: forest, pond, lake, ocean, grassland, desert.
- Artificial (man-made) ecosystems — created and maintained by humans. Examples: crop field, garden, aquarium, dam.
13.1.2 Biotic Components — Three Roles
(a) Producers — green plants, and a few bacteria, that make their own food from CO2 and water using sunlight (photosynthesis). They enter energy from the Sun into the living world.
(b) Consumers — animals that cannot make their own food and depend on producers or on other consumers.
(c) Decomposers — fungi and bacteria that break down dead plants and animals, returning simple substances to the soil and air.
(b) Consumers — animals that cannot make their own food and depend on producers or on other consumers.
(c) Decomposers — fungi and bacteria that break down dead plants and animals, returning simple substances to the soil and air.
Kinds of Consumers
| Type | Food | Examples |
|---|---|---|
| Herbivores | Plants only | Cow, deer, goat, grasshopper |
| Carnivores | Animals only | Tiger, lion, frog, snake |
| Omnivores | Both plants & animals | Human, crow, bear |
| Parasites | Live on/in another organism | Lice, Cuscuta, tapeworm |
Why decomposers matter: Without fungi and bacteria the world would be buried in dead leaves and bodies within a few years. Decomposers recycle carbon, nitrogen and minerals — keeping the abiotic store of nutrients from running out.
13.2 Food Chains & Food Webs
A food chain shows the linear path along which food (and therefore energy) moves from one organism to another. A simple land chain:
In nature, organisms rarely eat only one kind of food. A grasshopper is eaten by a frog, a bird and a lizard; the same grass may be eaten by a goat, a rabbit or a grasshopper. Many food chains intersect and form a network called a food web.
13.2.1 Trophic Levels
Each step of a food chain is a trophic level. Producers form the first (T1), herbivores the second (T2), primary carnivores the third (T3), and so on.
13.2.2 Flow of Energy — The 10% Law
Green plants capture only about 1% of the Sun's energy falling on their leaves. From one trophic level to the next, a large part of that stored energy is used for the organism's own life processes (respiration, movement, body heat) and is lost to the environment. Only a small share is locked away in body mass that can be eaten by the next level.
Lindemann's 10 % Law (1942): On average only 10 % of the energy present at one trophic level is passed on to the next; the remaining 90 % is lost, mostly as heat during respiration. This is why food chains rarely have more than four or five steps — by then hardly any usable energy is left.
13.2.3 Unidirectional Flow of Energy
Energy flow is one-way — from the Sun to producers, then on to consumers. It never returns from a carnivore back to a plant. Matter, on the other hand, moves in cycles (carbon cycle, nitrogen cycle, water cycle) because decomposers return it to the soil.
13.3 Biological Magnification (Biomagnification)
Modern agriculture uses pesticides like DDT to kill insect pests. These chemicals do not easily break down; they stick to the fat of plants and animals. At each higher trophic level the toxin builds up because predators eat many prey, each already carrying the poison.
Biological magnification: the progressive increase in the concentration of harmful, non-biodegradable chemicals at successive higher trophic levels of a food chain.
Humans sit at the top of many food chains — cereals, milk, fish — so we end up with the highest concentration of such pesticides in our bodies. This is a direct reason for preferring organic farming and bio-pesticides.
Activity 13.1 — Build Your Own Food Web
L4 AnalyseYou need: paper, pen, and this list — grass, paddy plant, grasshopper, rat, sparrow, frog, snake, hawk, decomposer bacteria.
- Place the producers at the bottom of a sheet.
- Draw arrows from each organism to the one that eats it.
- Now remove all frogs from the picture. Strike out every arrow that begins or ends at a frog.
Predict: Which populations will rise and which will fall once the frogs vanish?
With frogs gone, grasshoppers and other insects will rise because their main predator is missing; the snake population will fall because snakes had one less kind of prey; the extra insects will eat more grass, so grass cover may decrease. This is how the removal of one species disturbs many others — a real-life lesson on why food webs matter.
Competency-Based Questions
A farmer in Punjab sprays DDT on her wheat crop to control grasshoppers. The wheat is eaten by rats, which are eaten by snakes, which are eaten by hawks. Over five years the hawk population falls sharply and chicks are found dead in nests.
Q1. Identify the producer and the top consumer in this food chain. L1 Remember
Producer = wheat plant; top consumer = hawk.
Q2. (MCQ) The highest concentration of DDT will be found in the L2 Understand
(d) Hawk — it is at the top of the food chain, so DDT is biomagnified to the highest level in its body.
Q3. If the wheat plant traps 10 000 J of solar energy, how much energy will finally reach the hawk according to the 10 % law? L3 Apply
Wheat 10 000 J → Rat 1 000 J → Snake 100 J → Hawk 10 J. Only 0.1 % of the original solar energy finally reaches the hawk.
Q4. (Short answer) Why is the food chain normally limited to 4–5 trophic levels? L2 Understand
Because only 10 % of the energy moves to the next level, by the 5th step there is too little energy left to support a new population. The ecosystem cannot economically feed a sixth level.
Q5. (Analyse) The farmer switches to biological control (releasing ladybird beetles to eat aphids) instead of DDT. Give two environmental benefits. L4 Analyse
(i) No biomagnification — ladybirds are living agents, they don't accumulate in top predators. (ii) Non-target species are safe — bees, frogs and birds are not poisoned. (iii) Soil & ground water stay free of chemical residues. (Any two.)
Assertion–Reason Questions
Options: (A) Both A & R true, R correctly explains A. (B) Both A & R true, R does NOT explain A. (C) A true, R false. (D) A false, R true.
Assertion (A): Flow of energy in an ecosystem is unidirectional.
Reason (R): Energy lost as heat at each trophic level cannot be reused by the producers.
(A) — Both true; R correctly explains A. Once heat is dissipated, plants cannot capture it again for photosynthesis, so energy moves only one way.
Assertion (A): Human beings usually carry the highest body load of DDT among animals.
Reason (R): Humans are omnivores and sit at the top of several food chains.
(A) — Both true; R correctly explains A. Because we eat producers as well as primary and secondary consumers, DDT biomagnifies into our bodies.
Assertion (A): Decomposers are not essential for an ecosystem.
Reason (R): Decomposers return simple nutrients to the soil.
(D) — A is false (decomposers are indispensable) but R is true.
Frequently Asked Questions — Ecosystems, Food Chains & Food Webs
What is ecosystems, food chains & food webs in Class 10 Science (CBSE board)?
Ecosystems, Food Chains & Food Webs is a key topic in NCERT Class 10 Science Chapter 13 — Our Environment. It explains structure of ecosystems, producers, consumers, decomposers, food chains, food webs and flow of energy. Core ideas covered include ecosystem, biotic component, abiotic component, producer. Mastering this subtopic is essential for scoring well in the CBSE Class 10 Science board exam because board papers repeatedly test these concepts through MCQs, short answers and long-answer questions. This part gives a complete, exam-ready explanation with activities, diagrams and competency-based practice aligned to NCERT.
Why is ecosystem important in NCERT Class 10 Science?
Ecosystem is important in NCERT Class 10 Science because it forms the foundation for understanding ecosystems, food chains & food webs in Chapter 13 — Our Environment. Without a clear idea of ecosystem, students cannot answer higher-order CBSE board questions involving biotic component, abiotic component, producer. Board papers regularly include 2-mark and 3-mark questions on this concept, and competency-based questions often link ecosystem to real-life situations. Building clarity here pays off directly in board marks.
How is ecosystems, food chains & food webs tested in the Class 10 Science CBSE board exam?
The CBSE Class 10 Science board exam tests ecosystems, food chains & food webs through a mix of 1-mark MCQs, 2-mark short answers, 3-mark explanations with examples, 5-mark descriptive questions (often with diagrams or balanced equations) and 4-mark competency-based questions. Expect direct questions on ecosystem, biotic component, abiotic component and application-based questions drawn from NCERT activities. Students who follow NCERT thoroughly and practice this chapter's questions consistently score in the 90%+ range.
What are the key terms to remember for ecosystems, food chains & food webs in Class 10 Science?
The key terms to remember for ecosystems, food chains & food webs in NCERT Class 10 Science Chapter 13 are: ecosystem, biotic component, abiotic component, producer, consumer, decomposer. Each of these concepts carries exam weightage and regularly appears in the CBSE board paper. Write clear one-line definitions of every term in your revision notes and revisit them before the exam. Linking these terms visually through a flowchart or concept map makes recall easier during the Class 10 Science board exam.
Is Ecosystems, Food Chains & Food Webs included in the Class 10 Science syllabus for 2025–26 CBSE board exam?
Yes, Ecosystems, Food Chains & Food Webs is a part of the NCERT Class 10 Science syllabus (2025–26) prescribed by CBSE. It falls under Chapter 13 — Our Environment — and is examined in the annual board paper. The current syllabus retains the full treatment of ecosystem, biotic component, abiotic component as per the NCERT textbook. Because CBSE bases every board question on NCERT, studying this part thoroughly ensures complete syllabus coverage and guarantees marks from this chapter.
How should I prepare ecosystems, food chains & food webs for the CBSE Class 10 Science board exam?
Prepare ecosystems, food chains & food webs for the CBSE Class 10 Science board exam in three steps. First, read this NCERT part carefully, highlighting definitions and diagrams of ecosystem, biotic component, abiotic component. Second, solve every in-text question and end-of-chapter exercise — CBSE questions often come directly from NCERT. Third, practice competency-based and assertion-reason questions to sharpen reasoning. Write answers in the exam-style format (point-wise with diagrams) and time yourself. This method delivers confidence and full marks in the board exam.
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