Class 8 Science Chapter 12 How Nature Works in Harmony (New Course)

Key Concept: Mutualism

a) Honeybees and flowers
[Solution Description] In mutualism, both organisms benefit from the interaction. An example is the relationship between honeybees and flowers. The bee gets nectar for food, while the flower gets pollinated, which helps it reproduce.

Key Concept: Environmental impact, conservation efforts

c) They protect biodiversity by preserving habitats
[Solution Description] Conservation efforts such as establishing national parks and sanctuaries help mitigate the adverse effects of deforestation and habitat loss by preserving large tracts of natural habitats that serve as refuges for diverse flora and fauna. These protected areas restrict activities like logging, mining, and hunting, which are primary causes of habitat destruction. By maintaining ecological balance and protecting biodiversity, these efforts ensure the survival of numerous species and maintain essential ecosystem services such as water regulation and carbon storage. National parks and sanctuaries also promote environmental awareness and eco-tourism, further supporting conservation initiatives.

Key Concept: Identifying Organism Populations

b) Group of 25 frogs
[Solution Description] A population is defined as a group of organisms of the same species living together at a particular place and time. In this case, the frogs form a distinct population within the pond ecosystem with a count of 25 individuals.

Key Concept: Impact of synthetic fertilizers on soil health

b) Reduction in soil fertility
[Solution Description] Synthetic fertilizers, when overused, can reduce the population of friendly microorganisms in the soil and lower organic matter content, known as humus. The decline in humus makes the soil more prone to erosion because it loses its ability to bind soil particles together effectively.

Key Concept: Competition and Resource Use

d) They occupy different feeding niches within the habitat
[Solution Description] The two bird species would compete for the insect resource. This competition helps regulate each species’ population size. If one species becomes too numerous, it will feel more pressure from limited resources leading to a natural check on its growth. Additionally, they may adapt by feeding at different times or in slightly different niches to reduce direct competition.

Key Concept: Cascading Effects of Pollution

b) Less oxygen in the water
[Solution Description] When many plants in a pond die because of pollution, this leads to less oxygen being produced in the water. The plants in the pond are responsible for photosynthesis, which releases oxygen into the water. Without them, the oxygen levels decrease significantly.

Key Concept: Understanding feeding habits of different organisms

d) Grasshopper
[Solution Description]
A primary consumer in an ecosystem is an organism that feeds on producers. Producers are typically plants or autotrophs that produce their own food via photosynthesis. The primary consumers feed directly on these plants and are herbivores. In the context of a grassland ecosystem, grasshoppers are known to feed on grasses, making them primary consumers.

Key Concept: Ecosystem benefits and resource management

Correct Answer option c) Degraded environments force urban migration, altering social structures
[Solution Description] Unsustainable exploitation of natural resources can diminish ecosystem services, thereby eroding the foundational support systems necessary for human survival and well-being. This overuse may lead to resource scarcity, reduced air and water quality, and a decline in recreational spaces, ultimately resulting in societal instability and diminished quality of life as humans struggle to compensate for lost ecological functions.

Key Concept: Interaction between organisms in different habitats

c) They enter human villages for food
[Solution Description]
Elephants, when faced with scarcity of vegetation and waterholes drying up in their natural habitat, tend to move into nearby farms or plantations in search of food like bananas and sugarcane. This behavior shows adaptation as they wander into human-inhabited areas primarily for survival, demonstrating how animals might adjust when their natural environment becomes unsupportive.

Key Concept: Pesticide Use

b) Reduces beneficial microorganisms
[Solution Description] Excessive use of pesticides can harm beneficial microorganisms in the soil. These microorganisms are crucial for maintaining soil fertility and structure. Their decline leads to reduced organic matter (humus), making soil more prone to erosion.

Key Concept: Ecosystem Benefits

b) Fresh air and medicines
[Solution Description] Forest ecosystems provide several benefits including fresh air, fertile soil, food, fibers, timber, and medicines. These resources are crucial for human survival and well-being.

Key Concept: Role of Organisms in Ecosystem

d) Decomposers like bacteria and fungi
[Solution Description] Decomposers, such as bacteria and fungi, are primarily responsible for breaking down dead organic materials in an ecosystem. By converting complex compounds into simpler substances, they play a pivotal role in nutrient cycling and ecosystem functioning.

Key Concept: Natural vs. Synthetic Inputs, Soil Health

b) Organic builds structure; synthetic erodes microbes
[Solution Description]
Synthetic fertilizers provide immediate nutrients but can lead to soil degradation over time by disrupting soil microbial communities and decreasing humus levels. This absence of organic matter makes soils prone to erosion and reduces their ability to retain water and nutrients, leading to declining fertility. On the other hand, organic inputs like Kunapa Jala improve soil health by enhancing microbial activity, increasing humus content, improving soil structure, and, consequently, sustaining long-term fertility.

Key Concept: Habitats and Their Components

c) Algae
[Solution Description]
In a pond ecosystem, biotic components refer to living organisms present. Examples include fish, frogs, turtles, dragonflies, etc. Among the given options, algae are living organisms that play an active role in the ecosystem.

Key Concept: Ecosystem Interactions, Food Webs, and Impact of Biotic Components

c) Herbivore populations controlling the plant were suppressed, increasing plant survival.
[Solution Description] When the top predator is removed from the ecosystem, the population of its prey typically increases due to reduced predation pressure. If these prey species are herbivorous or have a diet that includes the intermediate consumers like small mammals or insects that feed on plants, their increased numbers can lead to a decrease in the population of the organisms that control the plant population either by direct consumption or by other ecological interactions such as competition. This could result in less grazing on the plant species, leading to an increase in its population. Thus, the dynamics of food webs and trophic cascades demonstrate how interconnected biotic components affect each other’s populations.

Key Concept: Pollination Process

c) Pollinators assist in spreading pollen, aiding fertilization and seed production.
[Solution Description] Pollinators such as bees, flies, and butterflies transfer pollen from one flower to another, facilitating fertilization. This process results in the formation of seeds. Increased pollinator activity due to fewer predators like dragonflies enhances this process, resulting in higher seed production.

Key Concept: Function of Fungi in Nutrient Recycling

b) Decompose organic matter like cellulose into simpler materials
[Solution Description]
Fungi act as decomposers by breaking down tough organic matter such as cellulose and lignin, which many other organisms cannot decompose. By secreting enzymes that digest this material externally, fungi help convert it into simpler molecules that can be absorbed by plants and other organisms. This action releases essential nutrients into the soil, thus supporting plant growth and contributing to nutrient cycling in ecosystems.

Key Concept: Examples of Habitats

a) Soil
[Solution Description]
In a forest habitat, there are various components that include both biotic and abiotic elements. The abiotic components in a forest include air, sunlight, water, temperature, and soil. Therefore, one example of a forest habitat component is soil.

Key Concept: Trophic Levels, Energy Flow, Ecosystem Disruption

b) Decrease in secondary consumers
[Solution Description] In a forest ecosystem, primary consumers are herbivores that feed on producers (plants). If their population decreases significantly, the immediate effect will be an increase in the plant population due to reduced grazing pressure. This could lead to changes in the availability of resources for higher trophic levels. Secondary consumers, which rely on primary consumers for food, may experience a decrease in their population due to the lack of food sources. Thus, a reduction in primary consumers can indirectly affect secondary consumers by decreasing their available energy. Therefore, the most likely immediate effect would be a decrease in the population of secondary consumers.

Key Concept: Role of organisms in ecosystem, Pollination mechanisms

a) They enable pollination of nocturnally blooming plants
[Solution Description] Bats typically pollinate nocturnal flowers that open at night and are often large and pale-colored to stand out in low light. Their role is crucial as they cover larger distances than most insects and can provide pollination services when other pollinators like birds and insects are inactive during the night.

Key Concept: Interaction between two abiotic components

a) Sunlight causes water evaporation
[Solution Description] The evaporation of water due to sunlight represents an interaction between two abiotic components: water and solar energy. This interaction affects the habitat by influencing humidity levels, temperature regulation, and water availability, all crucial factors for sustaining various life forms within the ecosystem.

Key Concept: Community, Trophic Levels, Food Webs

b) Decrease in small fish population due to lack of primary producers
[Solution Description] Algae serve as primary producers in aquatic ecosystems, converting sunlight into energy through photosynthesis. A drastic reduction in algae means there will be less energy available to support the primary consumers, such as small fish that feed on algae. Consequently, the small fish population will likely decline due to insufficient food supply. This decline will have a cascading effect leading to a possible reduction in the large fish population that preys on small fish.

Key Concept: Ecosystem Interactions

c) Overpopulation of prey species
[Solution Description]
The removal of a top predator such as a tiger from a food web can lead to an increase in the population of its prey species because there is less predation pressure. This imbalance can cause overgrazing or depletion of vegetation, leading to negative effects on other species that depend on those plants. Additionally, it may result in competition among prey species, further disrupting the ecosystem balance.

Key Concept: Interactions within an ecosystem

b) A bee pollinating a flower
[Solution Description] Mutualism is a type of symbiotic relationship where both organisms involved benefit from each other. An example of mutualism is the relationship between bees and flowering plants. Bees collect nectar from flowers for food, and in the process, they help in pollinating the plants, allowing them to reproduce.

Key Concept: Chain Reaction in Ecosystems

b) Decrease in oxygen production
[Solution Description]
In a pond ecosystem, plants play a crucial role by producing oxygen through photosynthesis. When the plant population decreases due to pollution, less oxygen is produced. This reduction in oxygen levels can adversely affect aquatic life that depends on this oxygen for survival.

Key Concept: Biotic interactions – competition

b) Competition
[Solution Description]
In an ecosystem, competition is a type of interaction where different organisms vie for the same resources such as food, shelter, or mates. When two species of birds compete for limited nesting sites, it exemplifies interspecific competition because they are of different species yet require similar resources. This competition ensures that no single species dominates the resource availability, thus maintaining ecological balance.

Key Concept: Nutritional interactions among biotic components

b) Predator-prey relationship
[Solution Description]
Frogs and insects have a predator-prey relationship, where frogs feed on insects. This interaction is part of the food chain within an ecosystem, influencing nutrient cycles and energy flow. Frogs help regulate insect populations, while gaining nutrition necessary for their survival and reproduction from this food source. This exemplifies nutritional dependency among biotic components.

Key Concept: Role of Decomposers in Nutrient Recycling

a) They convert complex organic matter into simpler inorganic substances that can be absorbed by plants.
[Solution Description] Decomposers, such as fungi and bacteria, break down complex organic materials from dead plants and animals into simpler substances. These simpler substances are nutrients which are released back into the soil. Plants absorb these nutrients for growth, thus completing the cycle of nutrient recycling.

Key Concept: Living and Non-living Components in Habitats

d) Aquatic Plants, Sunlight, Water, Rocks
[Solution Description] To evaluate this question, one must understand the typical biotic (living) and abiotic (non-living) factors present in a pond habitat. Common living organisms in a pond include fish, algae, insects, and aquatic plants, while non-living components are water, rocks, sunlight, and soil.

Key Concept: Commensalism

a) A suckerfish attaching to a shark and gaining transportation
[Solution Description]
Commensalism occurs when one organism benefits, and the other is unaffected. As per the syllabus, an example is orchids growing on trees; the orchid gains nutrition and support without affecting the tree.

Key Concept: Interaction of Biotic and Abiotic Components

c) By holding soil in place with their roots
[Solution Description] Plants play a crucial role in maintaining soil structure through their root systems. The roots help bind the soil particles together, preventing erosion by water or wind. Additionally, dead plant materials contribute organic matter to the soil, which enhances its fertility and structure. This interaction exemplifies how biotic components (plants) influence abiotic components (soil).

Key Concept: Understanding Community vs. Population

c) A community comprises multiple populations coexisting
[Solution Description] A community consists of various populations that inhabit a common environment and interact with each other. In contrast, a population is a group of individuals of the same species inhabiting a specific area. Hence, while a community includes diverse species, a population is limited to one species.

Key Concept: Natural Pest Control, Ecosystem Services

a) They prey on pests; Aid in seed dispersal
[Solution Description] Migratory birds, such as the Demoiselle Crane, play a significant role in controlling pest populations. By feeding on insects and small pests in agricultural areas, they naturally reduce pest numbers without the need for chemical pesticides. Additionally, migratory birds contribute to seed dispersal, which fosters plant diversity and resilience within ecosystems. Their movement across large areas aids in distributing seeds and thus maintaining healthy plant communities.

Key Concept: Food Chain: Simple sequence of who eats whom

c) The snake population may decline
[Solution Description]
Frogs are part of the diet for snakes in a typical grassland ecosystem. A decrease in the frog population would lead to a reduced food source for snakes, potentially causing a decline in the snake population due to lack of available prey.

Key Concept: Sustainable Farming Practices, Impact on Human Health

c) Lower risk of chronic diseases in humans
[Solution Description] Adopting sustainable farming practices that minimize synthetic pesticide use benefits both human health and the environment. Reducing pesticide application decreases exposure to harmful chemicals, lowering risks of health issues such as cancers and neurological disorders. Environmentally, it promotes biodiversity among crops and wildlife, maintains soil health, and prevents water contamination from chemical runoff.

Key Concept: Ecosystem Services: Clean air

b) They provide clean air
[Solution Description] Forest ecosystems play a crucial role in providing clean air, which is essential for human survival and well-being. Trees and plants in forests absorb carbon dioxide and release oxygen through the process of photosynthesis, thus purifying the air.