CBSE Class 8 Science Chapter 12 How Nature Works In Harmony MCQs Set 03

Answer: (B) These crops provide concentrated nutrition and energy that matches what elephants would normally obtain from forest plants

Explanation:
Elephants seek out bananas and sugarcane when their natural food sources disappear because these cultivated crops offer similar nutritional value to the diverse vegetation they normally consume in forests. The chapter indicates that habitat loss due to vegetation scarcity drives them to farm crops as a substitute food source.

Answer: (B) Producers

Explanation:
Organisms that manufacture their own food through photosynthesis are called producers or autotrophs. The chapter explains that plants like trees and grass perform this function, distinguishing them from organisms that must obtain food from other sources.

Answer: (B) Insects like bees and butterflies that pollinated flowers

Explanation:
Fish in Pond A ate dragonfly larvae, reducing dragonfly numbers. With fewer dragonflies to eat them, bees, butterflies, and other pollinating insects increased in number, leading to greater pollination and seed production in nearby plants. This demonstrates an indirect ecological relationship.

Answer: (B) Fish and bacteria; water and sunlight

Explanation:
Biotic components are living organisms—including fish and bacteria—while abiotic components are non-living physical factors such as water and sunlight. The chapter defines these as the two fundamental categories needed to understand any habitat.

Answer: (B) Abiotic components are influenced and modified by biotic components

Explanation:
By explaining that plants both depend on abiotic components (soil, water, sunlight) and simultaneously modify them (releasing oxygen, preventing erosion, retaining moisture), the chapter demonstrates that the relationship between biotic and abiotic components is bidirectional.

Answer: (B) Energy is lost at each step in the food chain, requiring more producer biomass to support fewer consumers at higher levels

Explanation:
• Energy decreases as it moves through food chains
• Producers convert solar energy into food; herbivores consume plants but only retain part of that energy
• Carnivores eat herbivores and retain only a fraction of their energy
• Therefore, many more plants are needed to support fewer herbivores, which in turn support even fewer carnivores

Answer: (B) Reduced frog numbers → increased insects → increased pesticide use → environmental damage

Explanation:
With fewer frogs eating insects, insect populations rose, damaging crops and forcing farmers to use synthetic pesticides. This led to soil and water quality degradation, affecting human and environmental health. The government banned frog exports to prevent further ecological damage.

Answer: (C) A frog eats insects

Explanation:
A frog eating insects represents an interaction between biotic components (the frog and insects) and directly influences nutrition, which is a fundamental life process. While the other options involve interactions, they either represent abiotic-abiotic interactions or biotic-biotic interactions rather than the specified criterion.

Answer: (C) Ecological regulation and protection service

Explanation:
The chapter lists multiple benefits ecosystems provide to humans: food, fibres, timber, medicines, aesthetic value, and importantly, physical protection and climate regulation. The Sundarbans' role in reducing storm damage represents ecological regulation—a natural service that protects human settlements.

Answer: (B) Niche differentiation allows multiple species to coexist without direct conflict

Explanation:
By using the same habitat at different times, these organisms occupy different ecological niches, allowing them to coexist without directly competing for the same resources. The chapter explicitly states this is how organisms achieve harmony in the same habitat.

Answer: (C) Parasitism, because one organism benefits while the other is harmed

Explanation:
In parasitic relationships, one organism (the tick) benefits by obtaining food while the other organism (the dog) is harmed by skin irritation and nutrient loss. The chapter explicitly uses this example to define parasitism.

Answer: (B) It reduces pollinator populations permanently, affecting long-term food production sustainability

Explanation:
Monoculture reduces the plant diversity that supports diverse pollinator populations. When pollinators decline, food crop production depends increasingly on synthetic inputs. The chapter suggests this creates a cycle of unsustainability because these insects are crucial for ongoing food production.

Answer: (C) Decomposition by bacteria and fungi

Explanation:
Decomposers like bacteria and fungi break down dead organic matter and waste into simpler substances that return essential nutrients to soil, which plants then reabsorb. This recycling process exemplifies nature's efficiency in reusing resources rather than wasting them.

Answer: (B) They allow entire habitats and endangered species to survive and maintain ecosystem balance

Explanation:
Protected areas preserve entire ecosystems with their biotic and abiotic components intact, allowing natural processes and relationships to function without destructive human interference. The chapter emphasizes that these spaces protect endangered species and habitats for future generations.

Answer: (B) Overuse decreases friendly microorganisms and organic matter (humus), making soil prone to erosion and less fertile

Explanation:
• Synthetic fertilizers reduce populations of beneficial soil microorganisms
• They lower humus (organic matter) content that binds soil particles
• Without adequate humus, soil becomes compacted and prone to erosion
• This degradation reduces long-term soil fertility despite short-term yield increases

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 searching for food like bananas and sugarcane.

Answer: (C) Fish reduced dragonfly populations, allowing more pollinating insects to survive

Explanation:
• Fish eat dragonfly larvae, reducing dragonfly numbers in the pond
• Dragonflies normally eat flies, bees, and butterflies
• With fewer dragonflies, more pollinating insects survived and flourished
• These insects pollinated nearby flowers, increasing seed production

Answer: (B) A population consists of one type of organism in a habitat, while a community includes different populations of various organisms

Explanation:
The chapter defines a population as a group of the same type of organisms living together in a habitat at a given time, while a community comprises different populations sharing the same habitat, with various plants, animals, and microorganisms interacting together.

Answer: (C) Interactions between two abiotic components

Explanation:
Water and sunlight are both non-living, abiotic components of a habitat. Their interaction—where sunlight causes water to evaporate—demonstrates how two abiotic elements influence each other and affect the physical characteristics of an ecosystem.

Answer: (C) Honeybees pollinating flowers while obtaining nectar

Explanation:
Mutualism requires both organisms to gain benefits from the interaction. Honeybees receive nectar for food while flowers are pollinated, enabling reproduction—a clear case where both organisms benefit. The orchid example is commensalism (one benefits, other unaffected), and the tick and snake examples are parasitism or predation.

Answer: (B) The cycling and recycling of nutrients back into the environment

Explanation:
Decomposers break down complex substances in dead plants and animals into simpler ones, returning important nutrients to the soil. This process illustrates that in nature nothing is wasted—everything is reused, demonstrating the principle of nutrient cycling.

Answer: (A) Fewer frogs → fewer insects eaten → pest population increases → farmers use more pesticides → environmental harm

Explanation:
The chapter explains that large-scale harvesting of bullfrogs led to a 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, and water quality, ultimately affecting human health, leading to the export ban.

Answer: (B) Different species can reduce direct competition by using the same habitat in different ways

Explanation:
Even though a snake and rodent live in the same forest habitat, they face different physical conditions because they are active at different times. This demonstrates how organisms coexist in harmony by utilizing the same space in different ways, reducing direct competition for the same resources at the same time.

Answer: (D) Excessive rainfall and flooding in coastal areas

Explanation:
The chapter specifically identifies mangrove tree cutting, illegal hunting, overuse of resources, and pollution as serious threats to the Sundarbans. Excessive rainfall and flooding are natural phenomena, not listed as human-caused threats in the text. In fact, the mangroves are valued for their ability to slow strong winds and waves during storms.

Answer: (B) Overuse of synthetic fertilizers decreases friendly soil microorganisms and lowers organic matter content, making soil prone to erosion

Explanation:
The chapter explains that overuse of synthetic fertilizers reduces soil fertility by decreasing friendly microorganisms and lowering humus content. Humus helps bind soil particles, and without it, soil becomes prone to erosion. This directly compromises the long-term productivity of agricultural land.