CBSE Class 10 · Science · board exam 2027
Chapter 13: Our Environment — notes
The chapter’s 8 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. Biodegradable and non-biodegradable substances
First, think about this.
- • Vegetable peels: break down in the soil
- • Plastic bag: stays as it is
- • Enzymes are specific in their action
- • No enzyme of bacteria acts on plastics
- • Biodegradable: broken down by biological processes
- • Non-biodegradable: not broken down by biological processes
- • | | Biodegradable | Non-biodegradable |
- • | Examples | peels, grass, wood, paper | plastics, DDT |
- • | Broken down by | bacteria, saprophytes | only heat, pressure |
- • | Effect | no long-term harm | persist; may harm organisms |
2. The ecosystem and its components
Look at the figure.
- • Ecosystem = biotic components + abiotic components
- • | Natural | Human-made (artificial) |
- • | forest, pond, lake | garden, crop-field, aquarium |
- • Producers: green plants, blue-green algae (make their own food)
- • Consumers: herbivores, carnivores, omnivores, parasites
- • Decomposers: bacteria, fungi
- • complex organic substances → simple inorganic substances → soil → plants
3. Food chains and trophic levels
Look at the figure.
- • Food chain: a series of organisms feeding on one another
- • Grass → Deer → Lion
- • | Trophic level | Organism | Role |
- • | 1 | Grass | producer |
- • | 2 | Deer | primary consumer |
- • | 3 | Lion | secondary consumer |
- • consumer number + 1 = trophic level
- • large carnivores (tertiary consumers) = 4th trophic level
4. Flow of energy and the ten percent law
Look at this figure, and read it from the bottom.
- • Green plants capture about 1% of the sunlight falling on their leaves
- • Ten percent law: on average 10% passes from one trophic level to the next
- • The rest: heat, digestion, work, growth, reproduction
- • Producers: 10000 J
- • 10/100 × 10000 = 1000
- • Primary consumers: 1000 J
- • 10/100 × 1000 = 100
- • Secondary consumers: 100 J
- • Food chains: generally 3 or 4 steps
- • Greatest number of individuals: producers
- • The flow of energy is unidirectional
- • producers' energy → not back to the Sun
- • herbivores' energy → not back to the producers
5. Food webs
Look at the figure.
- • Food web: a network of interconnected food chains
- • Grass → Grasshopper → Frog → Snake → Eagle
- • Grass → Mouse → Eagle (shorter: more energy)
6. Biological magnification
Farmers use pesticides and other chemicals to protect crops from diseases and pests.
- • pesticides → soil, water → plants, aquatic animals → food chain
- • Biological magnification: progressive accumulation of harmful chemicals at each trophic level
- • Maximum: in human beings (top level)
- • Example: DDT
7. The ozone layer and its depletion
A molecule of oxygen has two atoms, O₂. A molecule of ozone has three, O₃. O₂ is essential for all aerobic forms of life, but ozone itself is a deadly poison.
- • Oxygen: O₂ (two atoms)
- • Ozone: O₃ (three atoms), a deadly poison
- • Ozone layer: shields the earth from the Sun's ultraviolet (UV) radiation
- • UV radiation → skin cancer in human beings
- • Word equation: oxygen molecule → oxygen atoms
- • O₂ → O (unbalanced)
- • | Atom | Left side | Right side |
- • | O | 2 | 1 → 2 after writing 2O |
- • with UV radiation: O₂(g) → 2O(g)
- • | Atom | Left side | Right side |
- • | O | 1 + 2 = 3 | 3 |
- • combination reaction: O(g) + O₂(g) → O₃(g)
- • Ozone depletion: linked to CFCs (chlorofluorocarbons)
- • used as refrigerants, in fire extinguishers
- • 1987: UNEP agreement: freeze CFC production at 1986 levels
8. Managing the garbage we produce
Visit any town or tourist spot.
- • Why waste has increased:
- • 1. changes in lifestyle
- • 2. more disposable things
- • 3. changes in packaging
- • plastic glasses (returned) → disposable cups → kulhads → paper cups
- • kulhads on a large scale: loss of fertile top-soil
Summary
Waste is biodegradable or non-biodegradable. An ecosystem has biotic and abiotic components, and organisms are producers, consumers and decomposers. Each step of a food chain is a trophic level, and chains join up into food webs. Energy flows one way, and only about ten percent passes on at each step. Harmful chemicals build up the most in human beings, by biological magnification. The ozone layer shields us from UV radiation, and C F Cs deplete it. You did very well today. You next time!
AskMedha · Medha Ma’am — CBSE Class 10 Science, Chapter 13. Written from the textbook, checked twice.
Questions parents and students ask
- How do I get the "Our Environment" notes as a PDF?
- Press "Save as PDF" — the phone’s print sheet opens; choose "Save as PDF" there. The PDF holds the notes only.
- Where are these notes written from?
- From the chapter’s own textbook text, part by part, in the book’s own terms; a second, independent model then checked every part against the book. The full lesson, a check question for each part and the practice are in the AskMedha app.
The same preparation, with Medha Ma’am — on your phone
Every question of every chapter with its model answer, practice questions in the board’s own shapes, 60 minutes of class a day, written answers marked, a test every Sunday and a WhatsApp report to parents.
Medha Ma’am is an AI teacher, not a live tutor. Every answer is checked twice; a person takes responsibility.