CBSE Class 8 Science Chapter 12: How Nature Works in Harmony — Assertion & Reason
CBSE Class 8 Science Assertion & Reason
Expert crafted · Instant PDF download · 2026-27
The following Assertion and Reason questions are based on Chapter 12: How Nature Works in Harmony from the NCERT Class 8 Science textbook Curiosity. Each question has four options — read both the Assertion (A) and Reason (R) carefully before selecting your answer.
How to attempt Assertion & Reason questions:
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is NOT the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is NOT the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Assertion & Reason Questions
1
Assertion (A): A pond habitat consists only of biotic components like fish and frogs.
Reason (R): Water, soil, and sunlight are abiotic components that are essential for the survival of living organisms in a habitat.
Reason (R): Water, soil, and sunlight are abiotic components that are essential for the survival of living organisms in a habitat.
Answer: (d)
A is false, but R is true. A habitat consists of both biotic components (living beings) and abiotic components (non-living things like water and soil) interacting together.
2
Assertion (A): All the different fish, frogs, and insects living together in a pond form a single population.
Reason (R): A population is a group of the same type of organisms living in a habitat at a given time.
Reason (R): A population is a group of the same type of organisms living in a habitat at a given time.
Answer: (d)
A is false, but R is true. A population refers only to a group of the SAME type of organisms. Different populations living together (fish, frogs, insects) make up a community.
3
Assertion (A): Green plants are called producers or autotrophs.
Reason (R): Plants make their own food through the process of photosynthesis using sunlight, carbon dioxide, and water.
Reason (R): Plants make their own food through the process of photosynthesis using sunlight, carbon dioxide, and water.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Because plants have the ability to synthesise their own food via photosynthesis, they serve as the producers in an ecosystem.
4
Assertion (A): Herbivores, carnivores, and omnivores are all classified as heterotrophs.
Reason (R): Heterotrophs cannot produce their own food and depend on other organisms for nutrition.
Reason (R): Heterotrophs cannot produce their own food and depend on other organisms for nutrition.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Since these animals must consume plants or other animals for energy, they fall under the category of heterotrophs (consumers).
5
Assertion (A): In a food chain, herbivores like deer and hares are placed at the first trophic level.
Reason (R): Producers, such as green plants, always occupy the first trophic level in a food chain.
Reason (R): Producers, such as green plants, always occupy the first trophic level in a food chain.
Answer: (d)
A is false, but R is true. Producers are at the first trophic level because they create the food. Herbivores occupy the second trophic level as they consume the producers.
6
Assertion (A): In a natural ecosystem, food chains are usually interlinked to form a complex network called a food web.
Reason (R): An organism in an ecosystem can be eaten by two or more different types of organisms.
Reason (R): An organism in an ecosystem can be eaten by two or more different types of organisms.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Feeding relationships are rarely simple straight lines. Because predators have varied diets and prey have multiple predators, food chains interconnect into food webs.
7
Assertion (A): Mushrooms growing on dead trees act as decomposers in an ecosystem.
Reason (R): Decomposers break down complex substances in dead plants and animals into simpler ones, recycling nutrients back into the soil.
Reason (R): Decomposers break down complex substances in dead plants and animals into simpler ones, recycling nutrients back into the soil.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Fungi like mushrooms (saprotrophs) play a vital role in cleaning the environment and replenishing soil nutrients by decomposing dead organic matter.
8
Assertion (A): The relationship between honeybees and flowers is an example of mutualism.
Reason (R): In mutualism, one organism benefits while the other is harmed.
Reason (R): In mutualism, one organism benefits while the other is harmed.
Answer: (c)
A is true, but R is false. Honeybees and flowers show mutualism because BOTH organisms benefit (the bee gets nectar, and the flower gets pollinated). When one is harmed, it is called parasitism.
9
Assertion (A): Ticks living on the body of a dog is an example of a parasitic interaction.
Reason (R): The tick benefits by feeding on the dog's blood, while the dog is harmed and gets skin irritation.
Reason (R): The tick benefits by feeding on the dog's blood, while the dog is harmed and gets skin irritation.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Parasitism is precisely defined by one organism (the parasite) gaining at the expense of the other (the host).
10
Assertion (A): Orchids growing on the branches of trees is an example of commensalism.
Reason (R): In commensalism, both organisms benefit equally from the relationship.
Reason (R): In commensalism, both organisms benefit equally from the relationship.
Answer: (c)
A is true, but R is false. It is commensalism, but the reason is incorrect. In commensalism, one organism benefits (the orchid gets physical support and sunlight) while the other (the tree) is completely unaffected.
11
Assertion (A): Farmlands and agricultural fields are examples of natural terrestrial ecosystems.
Reason (R): Farmlands are human-made ecosystems that need human care and management to grow crops.
Reason (R): Farmlands are human-made ecosystems that need human care and management to grow crops.
Answer: (d)
A is false, but R is true. Farmlands are not natural; they are artificial or human-made ecosystems designed to meet human agricultural needs.
12
Assertion (A): Competition among organisms for food and space helps keep an ecosystem balanced.
Reason (R): Without competition, a single species could multiply excessively and disrupt the balance of the ecosystem.
Reason (R): Without competition, a single species could multiply excessively and disrupt the balance of the ecosystem.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Competition acts as a natural control mechanism for population sizes, ensuring that resources are not entirely depleted by one species.
13
Assertion (A): Large-scale hunting of frogs can lead to an increase in the use of synthetic pesticides by farmers.
Reason (R): Frogs eat insects, so a decline in frog populations causes an increase in agricultural pests, forcing farmers to use pesticides.
Reason (R): Frogs eat insects, so a decline in frog populations causes an increase in agricultural pests, forcing farmers to use pesticides.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. This is an example of how one change in a food web (removing a predator) has cascading effects on the ecosystem and human activities.
14
Assertion (A): The Sundarbans mangrove forest protects nearby areas by slowing down strong winds and waves during storms.
Reason (R): The Sundarbans are a completely safe ecosystem free from any human-made threats or pollution.
Reason (R): The Sundarbans are a completely safe ecosystem free from any human-made threats or pollution.
Answer: (c)
A is true, but R is false. While the Sundarbans do act as a protective barrier against natural disasters, they are currently under severe threat from human activities like illegal logging, pollution, and over-harvesting.
15
Assertion (A): Repeatedly growing the same crop on the same land (monoculture) is the best practice for maintaining long-term soil health.
Reason (R): Monoculture reduces crop diversity and can negatively affect pollinators essential for food production.
Reason (R): Monoculture reduces crop diversity and can negatively affect pollinators essential for food production.
Answer: (d)
A is false, but R is true. Growing the same crop repeatedly is an unsustainable farming practice that depletes specific soil nutrients and reduces crucial biodiversity.
❓ Frequently Asked Questions
What is covered in CBSE Class 8 Science Chapter 12 How Nature Works in Harmony?
This chapter covers all key topics from How Nature Works in Harmony as per CBSE 2026-27 syllabus.
Is this Assertion & Reason useful for CBSE board exams?
Yes, designed for CBSE Class 8 board exam preparation covering the complete syllabus.
Are these CBSE Class 8 Science Assertion & Reason updated for 2026-27?
Yes, all content at eBookPublisher is updated as per the latest 2026-27 CBSE syllabus.
How many chapters are in CBSE Class 8 Science?
All chapters of CBSE Class 8 Science are covered at eBookPublisher with free Assertion & Reason for each chapter.
Can I study How Nature Works in Harmony online for free?
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