Get authentic, comprehensive, and scoring-oriented solutions for DAV Class 6 Science Chapter 1: Our Environment from the official DAV textbook The Living World. All questions from Something To Know (Sections A, B, C, D, E) are thoroughly answered following DAV Board marking schemes with structured comparison tables, bold keywords, step-by-step reasoning, and previous years’ examination questions (PYQs).
🌿 Chapter 1 Quick Revision & Key Concepts Summary:
- Environment: The physical and biological world where organisms live, comprising interacting biotic and abiotic components.
- Biotic Components: Living entities classified into Producers (Autotrophs), Consumers (Heterotrophs), and Decomposers (Microorganisms).
- Abiotic Components: Non-living physical factors including Air, Water, Soil, Light, and Temperature that shape organism adaptations.
- Mineral Cycle: Decomposers (bacteria and fungi) break down organic remains into basic minerals, returning them to soil for plant absorption.
- Atmospheric Balance: Photosynthesis consumes carbon dioxide and releases oxygen, while Respiration consumes oxygen and releases carbon dioxide.
- Waste Management: Segregating waste into Biodegradable (kitchen waste, paper) and Non-Biodegradable (plastic, aluminium foil) using the 3R principle.
Something To Know — A. Fill in the blanks
1. Plastic is non-biodegradable as it cannot be broken down into simpler substances in nature.
Exam Note: Non-biodegradable materials persist in the environment for centuries and should be minimized using the Reduce-Reuse-Recycle principle.
2. We must say ‘No’ to plastic and use paper or clothes bags.
Exam Note: Paper and cloth are biodegradable and compostable, preventing toxic clogging of municipal drain systems and soil contamination.
3. The flowers of the Ipomoea bloom with sunrise and close after sunset.
Exam Note: Also commonly known as morning glory, displaying photoperiodic sensitivity to sunlight.
4. Polar bears and penguins are among the animals found only in cold regions.
Exam Note: Adapted with thick subcutaneous blubber and dense fur/feathers for thermal insulation against freezing temperatures.
5. Respiration and photosynthesis processes help in balancing of carbon dioxide and oxygen in the atmosphere.
Exam Note: Plants absorb carbon dioxide in daylight for photosynthesis and release oxygen; all living beings consume oxygen in respiration.
B. Write True or False for the following statements
1. Herbivores can prepare their own food.
Answer: False
Correction / Scientific Reason: Herbivores are primary consumers that depend directly on green plants (producers) for nutrition. Only autotrophs (green plants) can synthesize their own food via photosynthesis.
2. Fungi and bacteria are organisms that can be easily seen by the human eye, by itself.
Answer: False
Correction / Scientific Reason: Bacteria and individual fungal spores are microscopic microorganisms that cannot be seen with naked eyes; they require a compound microscope for observation.
3. The sunflower faces the east in the morning.
Answer: True
Scientific Reason: Sunflowers exhibit heliotropism, dynamically orienting their blooms towards the rising sun in the east to maximize light absorption.
4. Camels do not have sweat glands.
Answer: True
Scientific Reason: Absence of functioning sweat glands helps camels conserve vital body water in arid desert environments by eliminating evaporative perspiration.
5. Soil is an important biotic component of our environment.
Answer: False
Correction / Scientific Reason: Soil is an abiotic (physical) component of the environment consisting of weathered rock minerals, air, and water, although it houses diverse biotic organisms.
C. Tick the correct option
1. Biotic environment includes—
(a) only the producers and the consumers
(b) only the consumers and decomposers
(c) only the decomposers and the producers
(d) producers, consumers as well as decomposers
Answer: (d) producers, consumers as well as decomposers
Explanation: The biotic environment encompasses every living entity in an ecosystem across all trophic levels, spanning primary producers, diverse consumer organisms, and recycling decomposers.
2. The group of organisms, which use light for making food, are called—
(a) autotrophs
(b) heterotrophs
(c) decomposers
(d) scavengers
Answer: (a) autotrophs
Explanation: Autotrophs (literally ‘self-feeders’) synthesize organic glucose from atmospheric carbon dioxide and soil water in the presence of sunlight and chlorophyll.
3. Decomposers include—
(a) bacteria only
(b) fungi only
(c) bacteria as well as fungi
(d) only the scavengers
Answer: (c) bacteria as well as fungi
Explanation: Both bacteria and saprophytic fungi secrete digestive enzymes to decompose dead plant and animal organic tissues into inorganic soil minerals.
4. Which of the following is not biodegradable?
(a) vegetables
(b) fruits
(c) earthworm
(d) aluminium foil
Answer: (d) aluminium foil
Explanation: Aluminium foil is an elemental metallic product that cannot be enzymatically degraded or decomposed by natural microorganisms.
5. Vermicomposting is done by—
(a) fungus
(b) bacteria
(c) worms
(d) aquatic animals
Answer: (c) worms
Explanation: Vermicomposting specifically utilizes specialized red earthworms (redworms) to convert organic kitchen waste into nutrient-rich humus compost.
6. An animal, that is not affected much by the heat of the desert, is the—
(a) rat
(b) camel
(c) cow
(d) lion
Answer: (b) camel
Explanation: Known as the ‘Ship of the Desert’, the camel possesses anatomical adaptations like water-conserving kidneys, absence of sweat glands, and high body temperature tolerance.
D. Answer the following questions in brief
1. Why should we segregate different types of wastes?
Answer: We must segregate waste into biodegradable and non-biodegradable categories at source because:
1. Biodegradable waste can be safely processed into nutrient-rich compost or vermicompost for agriculture.
2. Non-biodegradable waste (plastics, metals, glass) can be channelled into recycling facilities, preventing hazardous pollution of landfills, water bodies, and soil ecosystems.
2. Write the meaning of the term ‘vermicomposting’.
Answer: Vermicomposting is the biological process of converting moist organic kitchen waste, vegetable peels, and animal dung into nutrient-rich compost with the help of redworms (a specialized species of earthworms). It provides high-grade natural manure that enhances soil fertility.
3. Which component of air gets ‘used-up’ during the process of photosynthesis?
Answer: Carbon dioxide gas (CO2) present in the air gets ‘used-up’ by green plants during the process of photosynthesis to synthesize glucose food in the presence of sunlight and chlorophyll.
4. Suggest any five activities that can help to save the environment.
Answer: Five key practical activities to protect and save the environment are:
1. Say No to Single-Use Plastics: Replace plastic carry bags with reusable cloth or jute bags.
2. Waste Segregation & Composting: Convert biodegradable domestic kitchen waste into natural compost.
3. Afforestation: Actively plant native trees and preserve existing urban greenery.
4. Conserve Energy & Water: Turn off lights, fans, and water taps when not in active use; adopt rainwater harvesting.
5. Adopt Cleaner Transport: Walk or use bicycles for short commutes and use shared public transport to curtail air pollution.
5. How does nature maintain a balance, between the amounts of oxygen and carbon dioxide, in the atmosphere?
Answer: Nature maintains an equilibrium between oxygen and carbon dioxide through the complementary interdependence of two fundamental biological processes:
1. Respiration: All plants and animals consume oxygen from atmospheric air and release carbon dioxide.
2. Photosynthesis: Green plants absorb atmospheric carbon dioxide in daylight to manufacture food and release pure oxygen back into the air.
This continuous reciprocal cycle prevents atmospheric depletion of either vital gas.
E. Answer the following questions in detail
1. Distinguish between:
(a) Autotrophs and Heterotrophs
(b) Decomposers and Scavengers
| Feature / Parameter | Autotrophs (Producers) | Heterotrophs (Consumers) |
|---|---|---|
| 1. Definition & Meaning | Organisms that manufacture their own food from basic inorganic substances. (‘Auto’ = self, ‘troph’ = food). | Organisms that cannot make their own food and must depend on others. (‘Hetero’ = other, ‘troph’ = food). |
| 2. Mode of Nutrition | Synthesize organic food via photosynthesis using sunlight, water, and CO2. | Derive nutrition by consuming plants or other animals directly or indirectly. |
| 3. Presence of Chlorophyll | Contains green photosynthetic pigment (chlorophyll). | Completely lack chlorophyll. |
| 4. Key Examples | Green plants, green algae, photosynthetic cyanobacteria. | Cows, goats, deer, lions, humans, birds. |
| Feature / Parameter | Decomposers | Scavengers |
|---|---|---|
| 1. Nature of Organism | Microscopic organisms (microbes) such as bacteria and fungi. | Larger animals and birds that consume dead flesh. |
| 2. Feeding Mechanism | Secrete external digestive enzymes to break down decaying organic matter into minerals. | Directly eat and ingest dead animal carcasses and flesh. |
| 3. Role in Mineral Cycle | Crucial for recycling nutrients back into the soil for plant absorption. | Prevent environmental contamination by rapidly cleaning large carcasses. |
| 4. Key Examples | Soil bacteria, bread mould, mushrooms, saprophytic fungi. | Vultures, crows, jackals, hyenas, kites. |
2. State the difference between biodegradable and non-biodegradable materials. Give one example of each.
| Feature | Biodegradable Materials | Non-Biodegradable Materials |
|---|---|---|
| 1. Microbial Action | Substances that are broken down naturally into simpler inorganic forms by microorganisms (bacteria and fungi). | Substances that cannot be decomposed or broken down by microbial activity in nature. |
| 2. Environmental Impact | Eco-friendly; do not persist in nature; convert into natural manure/compost. | Persist for hundreds of years; cause soil, water, and air pollution; clog municipal drains. |
| 3. Source | Derived from living plant and animal matter. | Synthetic man-made chemical materials or processed metals. |
| 4. Authentic Examples | Fruit and vegetable peels, waste paper, cotton cloth, animal dung. | Plastic bags, aluminium foil, glass bottles, DDT, nylon fibres. |
3. How does decomposition of dead animals turn out to be useful?
Answer: Decomposition of dead animals is profoundly useful to the ecosystem in two primary ways:
1. Natural Soil Enrichment (Nutrient Recycling): When dead animals are acted upon by decomposers (bacteria and fungi), complex organic molecules break down into simpler inorganic minerals (nitrogen, phosphorus, potassium). These minerals mix thoroughly with topsoil and serve as vital nutrients for green plants to grow.
2. Environmental Cleansing: Without active decomposition, dead organic matter and animal carcasses would accumulate indefinitely across the planet, generating lethal disease pathogens and foul odours.
4. Why is Rain water harvesting a ‘ray of hope’ for overcoming the present ‘scarcity of water’ in cities?
Answer: Rainwater harvesting is considered a ray of hope for modern urban centres because:
1. Replenishes Depleted Groundwater: Rapid urban construction of concrete roads and buildings prevents rainwater from percolating into the soil. Harvesting structures divert rainwater underground to recharge fast-depleting aquifer water tables.
2. Direct Alternative Water Supply: Collected rainwater stored in clean underground cisterns satisfies secondary household requirements (flushing, gardening, washing vehicles, laundry), drastically mitigating water crises during harsh peak summer months.
3. Prevents Urban Flooding: Capturing run-off rainwater reduces overloading of storm drainage networks and curbs monsoon road waterlogging.
5. Why do buffaloes cool themselves in water during summer?
Answer: Buffaloes cool themselves in water bodies (ponds, streams, rivers) during summer due to distinct physiological characteristics:
1. Dark Skin Pigmentation: Buffaloes possess dark black skin which is a superior absorber of intense solar radiant heat, making them feel hotter very rapidly.
2. Absence of Efficient Sweat Glands: Unlike humans and cattle, buffaloes lack an adequate density of sweat glands. Consequently, they cannot cool their bodies through evaporative perspiration.
3. Thermoregulation by Wallowing: Submerging in cool water ponds (wallowing) provides immediate physical conductive heat dissipation, keeping their core body temperature within healthy limits.
6. Draw a diagram that shows the relationship between the biotic and the abiotic components of the environment.
Answer: Green plants (producers) absorb abiotic factors such as sunlight, carbon dioxide from air, and water with dissolved minerals from soil to synthesize food. Herbivores and carnivores (consumers) feed on plants and each other. When plants and animals die, decomposers (bacteria and fungi) decompose their bodies, releasing minerals back into the soil and carbon dioxide into the air, establishing a perpetual cycle.
Value-Based Questions (VBQ) & HOTS (Higher Order Thinking Skills)
💡 Value-Based Question (VBQ):
Question: Rohan observed that in his school cafeteria, all waste (food leftovers, aluminium foils, plastic wrappers, paper napkins) was being dumped into a single garbage bin. He spoke to the principal and arranged separate green and blue dustbins.
Values Displayed & Impact:
1. Environmental Consciousness & Responsibility: Rohan demonstrated active civic duty towards sustainable waste management.
2. Scientific Application: Placing green bins for biodegradable organic waste facilitates natural school vermicomposting, while blue bins for non-biodegradable recyclables prevents dumping in public landfills.
🧠 Higher Order Thinking Skill (HOTS):
Question: What would happen to life on Earth if all decomposers (bacteria and fungi) were completely eliminated by a chemical spray?
Answer: If decomposers ceased to exist:
1. Dead plant litter, fallen leaves, and animal carcasses would accumulate indefinitely without decaying.
2. The mineral recycling cycle would collapse because essential inorganic minerals locked in dead tissue would never return to the soil.
3. The soil would become completely exhausted of nutrients, leading to starvation and death of green plants, ultimately extinguishing all herbivorous and carnivorous life on Earth.
🎯 DAV Examination Corner: Authentic Board Exam Questions (PYQs 2022–23 & 2023–24)
Below are authentic questions directly retrieved from the DAV Public Schools Common Examination (Half-Yearly & Annual Board Papers) covering Chapter 1:
Q1. [DAV Half-Yearly Exam 2022–23 • 1 Mark VSA]
The worms which are required for vermi-composting are —
(i) Hookworms (ii) Redworms (iii) Pinworms (iv) All of the above
Model Answer: (ii) Redworms. Redworms feed voraciously on decomposing plant waste and excrete nutrient-dense organic vermicastings.
Q2. [DAV Half-Yearly Exam 2023–24 • 1 Mark VSA]
State one importance of decomposers in our environment.
Model Answer: Decomposers break down dead plant and animal matter, recycling essential nutrients and minerals back into the soil to sustain plant growth and keep the earth clean.
Q3. [DAV Half-Yearly Exam 2022–23 • 1 Mark Assertion-Reason]
ASSERTION (A): Animals, plants etc. are abiotic or physical components present in our environment.
REASON (R): These components are living in nature and play important roles in mineral cycle.
Codes: (a) Both A and R are true and R explains A (b) Both A and R true, R doesn’t explain A (c) A is true, R is false (d) A is false, but R is true.
Model Answer: (d) A is false, but R is true. Plants and animals are living, which means they are biotic components (making Assertion A false). They are living and play active roles in the mineral cycle (making Reason R true).
Q4. [DAV Half-Yearly Exam 2023–24 • 2 Marks SA-I]
We often see buffaloes cooling themselves in pond during summer. Give reason.
Model Answer: Buffaloes have dark black skin which readily absorbs heat from solar rays. Additionally, they do not possess sweat glands to dissipate body heat via perspiration. Therefore, wallowing in pond water provides immediate cooling and prevents heat stress.
Q5. [DAV Half-Yearly Exam 2023–24 • 3 Marks SA-II]
A balance is maintained between the amount of oxygen and carbon dioxide in the atmosphere. Express it through a schematic diagram / description.
Model Answer: The balance is maintained continuously through biological reciprocal cycles:
• Atmospheric Oxygen (O2): Used by animals and plants for respiration → produces Carbon Dioxide (CO2).
• Atmospheric Carbon Dioxide (CO2): Absorbed by green plants during daylight for photosynthesis → releases Oxygen (O2) back into the atmosphere.
This closed-loop interaction ensures the atmospheric proportions of O2 (21%) and CO2 (0.04%) remain stable.
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