CBSE Class 8 Science Chapter 12 How Nature Works In Harmony MCQs Set 01

Answer: (B) when vegetation becomes scarce and water sources dry up in their natural habitat

Explanation:
The chapter explicitly states that when vegetation is scarce and waterholes dry up in their natural habitat, elephants wander into nearby farms or plantations in search of food. This occurs due to habitat loss from deforestation and changes in rainfall and temperature patterns.

Answer: (C) plants, animals, and microorganisms

Explanation:
Biotic components are living organisms found in a habitat. Plants, animals, and microorganisms all fall into this category. The other options describe abiotic (non-living) components such as physical conditions and environmental factors.

Answer: (B) a population consists of one type of organism while a community contains different populations sharing the same habitat

Explanation:
The chapter defines a population as a group of the same type of organisms in a habitat, while a community comprises different populations sharing the same habitat. They are hierarchically ordered—a community is made up of multiple populations.

Answer: (B) fish decreased dragonfly populations, which led to more pollinators and increased seed production

Explanation:
• Fish eat dragonfly larvae, reducing dragonfly numbers
• Dragonflies eat insects like bees and butterflies
• With fewer dragonflies, more pollinators survived
• These insects pollinated flowers, leading to more seeds in plants near fish ponds

Answer: (B) decomposition

Explanation:
Decomposition is the process by which microorganisms like fungi and bacteria break down complex substances in dead plants and animals into simpler ones, returning important nutrients to the soil. This is distinct from other metabolic processes listed.

Answer: (B) because the balance can change over time due to natural or human-made changes while still remaining stable

Explanation:
The chapter states that ecosystem balance is dynamic, not fixed, and can be disrupted by natural or human-made changes. This means the balance adjusts and shifts based on conditions, rather than remaining completely unchanging.

Answer: (B) the decline in frog populations reduced the consumption of insects

Explanation:
Since frogs eat insects, when their populations declined due to large-scale harvesting for export, the reduced number of natural predators resulted in a rise in agricultural pests, forcing farmers to use more synthetic pesticides.

Answer: (C) grass → grasshopper → frog → snake

Explanation:
A food chain shows energy flow from producers to consumers in the correct order. Grass (producer) is eaten by grasshopper (primary consumer), which is eaten by frog (secondary consumer), which is eaten by snake (tertiary consumer).

Answer: (B) they break down dead matter and recycle nutrients back into the environment

Explanation:
Decomposers like bacteria and fungi break down complex substances in dead organisms into simpler ones, returning important nutrients to the soil. This recycling process is essential because plants absorb these nutrients from the soil for growth.

Answer: (B) in mutualism both organisms benefit while in parasitism one benefits and the other is harmed

Explanation:
The chapter defines mutualism as a relationship where both organisms benefit (example: honeybees and flowers), while parasitism is when one organism benefits and the other is harmed (example: ticks on dogs). These outcomes directly oppose each other.

Answer: (C) that different ecosystems interact with each other at any given point

Explanation:
Figure 12.6 and the accompanying text show how small rivers (aquatic ecosystems) exist alongside mountains, forests, and farmland (terrestrial ecosystems), illustrating that these systems interact with each other continuously rather than operating in isolation.

Answer: (B) it reduces biodiversity and affects pollinators crucial for food production

Explanation:
Growing the same crop repeatedly, known as monoculture, can reduce biodiversity and affect pollinators, which are crucial for food production. The chapter identifies this as a harmful consequence of unsustainable farming methods.

Answer: (B) due to mangrove trees being cut for fuelwood and farming, illegal hunting, overuse of resources, and pollution from industrial waste

Explanation:
The chapter lists multiple human activities threatening the Sundarbans: mangrove trees are cut for fuelwood and farming, illegal hunting occurs, forest resources are overused, and industrial pollution damages water and habitat. These threats persist despite UNESCO protection.

Answer: (B) it helps control population size and prevents one species from multiplying excessively

Explanation:
Competition for resources like food, water, and space helps control population size and keeps the ecosystem balanced. Without competition, one species could multiply too much and cause an imbalance in the ecosystem, as stated in the chapter.

Answer: (B) to allow safe movement of animals between large forest areas without conflict with human settlements

Explanation:
Wildlife ecologists identified and marked corridors to enable safe movement of animals like elephants between forest habitats, reducing conflicts with human settlements. This practical conservation measure recognizes that habitat fragmentation forces animals to seek food and water in populated areas.

Answer: (C) Because fewer dragonflies allow more bees and butterflies to flourish without being eaten

Explanation:
The chapter describes how fish eat dragonfly larvae, reducing the dragonfly population. Since dragonflies normally eat flies, bees, and butterflies, fewer dragonflies means these pollinating insects survive in greater numbers.

Answer: (B) They occupy the same physical space but face different environmental conditions at those times

Explanation:
The chapter notes that a snake active at night and a rodent active during the day both inhabit the same forest but experience different conditions, allowing them to coexist without direct competition by using resources at different times.

Answer: (B) • Frogs were exported in large numbers • Insect pest population rose • Farmers increased pesticide use • Environmental and soil quality suffered

Explanation:
The case study traces a clear cause-and-effect chain: large-scale frog export reduced frog populations, which ate insects, so pest numbers rose, forcing farmers to use more synthetic pesticides that harmed the environment and health.

Answer: (B) Living organisms can alter abiotic components, showing reciprocal dependence in ecosystems

Explanation:
The chapter explicitly states that just as biotic components depend on abiotic ones, abiotic components are influenced by biotic ones—plants release oxygen, hold soil, and retain moisture, demonstrating two-way interaction between living and non-living parts of ecosystems.

Answer: (B) Commensalism, because one organism benefits while the other is unaffected

Explanation:
The chapter defines commensalism as a relationship where one organism benefits while the other is not affected. Orchids on trees receive support (benefitting) while trees remain unaffected, making this a clear example of commensalism.

Answer: (C) Because their activities are essential for soil health and affect the survival of plants that feed entire food chains

Explanation:
The chapter describes how heavy irrigation and ploughing disturb these organisms, which are important for maintaining ecological balance. Since plants depend on healthy soil, and entire food chains depend on plants, the loss of soil organisms disrupts multiple ecosystem functions.

Answer: (B) Consumers require energy from multiple producer organisms, so more plants are needed to support fewer herbivores

Explanation:
Activity 12.7 demonstrates that when organisms are arranged by trophic levels, the pyramid shows highest numbers at the base (producers) and decreasing numbers at higher levels, because energy transfer up food chains requires more plants to sustain fewer herbivores.

Answer: (B) Sustainable practices aim to minimize interference with natural ecosystems and maintain soil health rather than maximizing production through chemical inputs

Explanation:
The chapter contrasts Green Revolution methods (tractors, machines, synthetic fertilizers, pesticides) with sustainable organic and natural farming that reduce synthetic inputs and support natural ecosystems, emphasizing minimal interference in ecological processes.

Answer: (B) Criterion 2: Interaction between two abiotic components

Explanation:
Water evaporation caused by sunlight involves only non-living things—water and sunlight—making it an interaction between two abiotic components, exactly as defined in Criterion 2 of Activity 12.4.

Answer: (B) Birds carry pollen, disperse seeds, control pests, and link habitats across vast distances, showing how distant ecosystems remain interconnected through mobile species

Explanation:
The 'Ever heard of' section describes how migratory birds enhance habitats, act as pollinators and seed dispersers, control pest populations, and physically link different regions, demonstrating that ecosystems are not isolated but interconnected through the movement and activities of living organisms.