CBSE Class 8 Science Chapter 12 How Nature Works In Harmony MCQs Set 02

Answer: (B) Bananas and sugarcane

Explanation:
The chapter explicitly states that when vegetation is scarce in their natural habitat, elephants wander into nearby farms or plantations in search of food like bananas and sugarcane.

Answer: (B) Biotic components

Explanation:
Living organisms like fish, frogs, and birds are classified as biotic components, while water, soil, and sunlight are abiotic components. The chapter makes this distinction clear when explaining habitat composition.

Answer: (B) Population size at a specific location and time

Explanation:
A population is defined as a group of the same type of organism in a habitat at a given time. The activity teaches students to measure population by counting individuals of the same species within a defined space.

Answer: (B) By eating dragonfly larvae, which reduced dragonfly numbers, allowing more pollinators to survive

Explanation:
• Fish eat dragonfly larvae, reducing dragonfly populations in ponds with fish
• Fewer dragonflies mean fewer insects are eaten by dragonflies
• More bees, flies, and butterflies survive to pollinate flowers
• Increased pollination leads to more seeds in nearby plants

Answer: (B) Decomposition; they are decomposers that recycle nutrients

Explanation:
Fungi like mushrooms break down complex substances in dead plants into simpler ones through decomposition. They are classified as decomposers or saprotrophs and play the crucial role of returning nutrients to the soil.

Answer: (B) Ecosystems can adjust to changes through interactions among organisms while maintaining stability

Explanation:
A dynamic balance means ecosystems can shift and adjust while still remaining stable, rather than being frozen in one state. The chapter emphasizes that this balance can be disrupted by natural or human-made changes, showing ecosystems are flexible but vulnerable systems.

Answer: (B) Frog population declined → insect pests increased → farmers used more pesticides

Explanation:
Reduced frog populations meant fewer insects were eaten, causing pest numbers to rise. Farmers responded by using more synthetic pesticides, which harmed the environment and human health, leading to the government ban on frog leg exports.

Answer: (B) They make their own food through photosynthesis and are classified as autotrophs

Explanation:
Producers, or autotrophs, have the defining ability to manufacture their own food using sunlight, carbon dioxide, and water. All other organisms depend either directly or indirectly on this food-making process for their survival.

Answer: (B) Omnivores consume both plants and animals, while herbivores eat only plants

Explanation:
The chapter defines herbivores as organisms eating only plants, carnivores as eating only animals, and omnivores as eating both plants and animals. Crows, foxes, and mice are explicitly listed as examples of omnivores that consume mixed diets.

Answer: (B) It demonstrates that organisms may be eaten by multiple predators and consume multiple prey species

Explanation:
A food web shows how different food chains interconnect because organisms typically have multiple feeding relationships. In contrast, a simple food chain shows only one linear path, but real ecosystems involve complex overlapping relationships among many species.

Answer: (B) It demonstrates how a living organism depends on a non-living environmental condition for survival

Explanation:
Earthworms (biotic) require moist soil (abiotic) to survive. This exemplifies how living organisms depend on non-living physical factors in their environment for their life processes.

Answer: (B) The orchid benefits from physical support while the tree is unaffected

Explanation:
This relationship is commensalism—one organism benefits while the other is neither helped nor harmed. The orchid gains physical support from the tree branch, but the tree branch is unaffected by the orchid's presence.

Answer: (C) Creating wildlife corridors for elephant movement

Explanation:
Wildlife corridors are presented as a conservation solution created by humans to protect animals, not as a threat. The chapter lists cutting trees, illegal hunting, overuse of resources, and pollution as the actual threats damaging the Sundarbans.

Answer: (B) Tractors, machines, and synthetic fertilizers; their overuse causes soil degradation and environmental damage

Explanation:
The Green Revolution introduced tractors, machines, and synthetic pesticides that boosted production but are now viewed as unsustainable due to overuse of synthetic chemicals, excessive groundwater extraction, soil degradation, and reliance on monoculture practices.

Answer: (B) Planting only one crop eliminates the diverse flowering plants that many pollinators depend on for nutrition

Explanation:
Monoculture means growing the same crop repeatedly, which eliminates the variety of flowering plants pollinators need. Without diverse flora, pollinators cannot find sufficient food sources, reducing their populations and ultimately affecting crop pollination and food production.

Answer: (C) They conserve wildlife, their habitats, and endangered species while helping protect entire ecosystems

Explanation:
Protected areas are defined as land or water set aside to conserve wildlife and their habitats. Examples like Jim Corbett National Park and Manas National Park help protect entire habitats including endangered animals, birds, and rare plants for future generations.

Answer: (B) Bananas and sugarcane

Explanation:
The chapter explicitly states that when vegetation is scarce and waterholes dry up in their natural habitat, elephants may wander into nearby farms or plantations in search of food like bananas and sugarcane.

Answer: (B) Food, oxygen, shelter, and space to grow

Explanation:
The chapter explains that a pond provides food, oxygen, shelter, and space to grow—conditions essential for survival of organisms, using fish as an example of organisms obtaining both biotic needs like food and abiotic needs like oxygen from their habitat.

Answer: (B) Producers make their own food while consumers depend on other organisms for nutrition

Explanation:
Plants are producers because they make their own food through photosynthesis; consumers or heterotrophs cannot produce their own food and depend on other organisms for survival.

Answer: (B) Fish eat dragonfly larvae → fewer dragonflies → more bees and butterflies → more seed production

Explanation:
• Fish eat dragonfly larvae, so ponds with fish had fewer dragonflies
• Dragonflies usually eat flies, bees, and butterflies, so with fewer dragonflies, more bees, flies, and butterflies were found
• These insects help pollinate flowers, which helps plants produce seeds
• Therefore, flowers near ponds with fish may produce more seeds than those near ponds without fish.

Answer: (B) Matter cycles repeatedly through biotic and abiotic components

Explanation:
Decomposition demonstrates how nothing is wasted in nature—everything is reused. Fungi and bacteria transform complex substances in dead organisms into simpler forms that return nutrients to soil, which plants then use. This cycling of matter between living and non-living components is fundamental to ecosystem function.

Answer: (B) Multiple stressors prevent organisms from using alternative resources or migration corridors

Explanation:
The chapter explains that elephants are adapted to forest life, but sudden changes make it hard for them to survive. Multiple interconnected changes—both habitat loss and rainfall shifts—simultaneously reduce food availability, water sources, and space, leaving organisms with fewer options for survival or relocation.

Answer: (B) It controls population size and prevents one species from multiplying excessively

Explanation:
Without competition controlling population sizes, one species could multiply too much, causing an imbalance in the ecosystem. Competition naturally limits population growth and maintains relatively stable proportions among species.

Answer: (A) Frog decline → reduced insect populations → increased use of pesticides → environmental harm

Explanation:
The chapter clearly states: large-scale harvesting led to decline in frog populations; since frogs eat insects, their reduced numbers resulted in a rise in agricultural pests; this forced farmers to use more synthetic pesticides, which harmed the environment, soil, water quality, and human health.

Answer: (B) Non-living components can interact with each other independently of biotic components

Explanation:
This classification demonstrates that ecosystems are not just about living things eating each other. Physical processes like evaporation directly shape habitat conditions. These abiotic-abiotic interactions influence which organisms can survive in a given location, showing the layered complexity of ecosystem functioning.