Class 8 Science NCERT Notes – Chapter 12: How Nature Works in Harmony (PDF, MindMap, Q&A, Quizzes)

Study Notes: How Nature Works in Harmony

1. The Interconnectedness of Nature: The Elephant Corridor

The natural world is a complex web of interconnected elements. A clear example of this is the phenomenon of human-elephant conflict in Indian states like Odisha, Jharkhand, West Bengal, Assam, and Chhattisgarh. The shrinking and drying of forests, caused by factors like deforestation for roads and buildings and changes in rainfall and temperature, lead to a scarcity of vegetation and water. This forces elephants, adapted to forest life, to wander into human farms and villages in search of food like bananas and sugarcane, resulting in crop damage and potential harm to humans and domestic animals. To mitigate this, wildlife ecologists have established “elephant corridors”—marked pathways that connect forest habitats, allowing elephants and other wildlife safe passage between larger forest areas without conflicting with human settlements.

2. Core Components of an Environment

Habitat

A habitat is the specific place where an organism lives. It provides the essential conditions for survival, including food, oxygen, shelter, and space. A habitat can be as large as a forest or as small as the bark of a tree.

Biotic and Abiotic Components

Every habitat is composed of two types of components:

• Biotic Components: These are all the living or once-living organisms within a habitat. This includes plants, animals, fungi, and microorganisms.
• Abiotic Components: These are the non-living physical and chemical parts of a habitat that affect living organisms. This includes air, sunlight, water, temperature, and soil.

For example, in a pond habitat, the biotic components include fish, frogs, turtles, snails, ducks, algae, and lotus plants. The abiotic components include the water, oxygen dissolved in it, and sunlight.

3. Levels of Ecological Organization

Organisms in nature are organized into several hierarchical levels:

• Population: A group of organisms of the same kind (species) living together in the same habitat at a given time. For instance, all the fish of a particular species in a pond constitute a population.
• Community: All the different populations of plants, animals, and microorganisms that live and interact in the same habitat. A community represents the sum of all biotic components in an area.
• Ecosystem: An ecosystem is formed by the interaction of a community (all biotic components) with its abiotic components (air, water, soil, sunlight). Ecosystems can be large or small and are categorized into two main types:
  • Aquatic Ecosystems: Water-based environments like ponds, rivers, and lakes.
  • Terrestrial Ecosystems: Land-based environments like forests, farms, grasslands, or even a single large tree.
  • Human-Made Ecosystems: Artificial ecosystems like fish ponds, farms, and parks, which require human care and management.

4. Interactions Within Ecosystems

Ecosystems are defined by the constant interactions among their components. These interactions are vital for the survival of organisms and the stability of the habitat.

• Between Biotic and Abiotic Components: Living organisms depend on non-living things. For example, plants require sunlight, carbon dioxide, and water for photosynthesis; animals need air for respiration; and earthworms live in moist soil. Conversely, biotic components also influence abiotic ones; plant roots hold soil to prevent erosion, and photosynthesis releases oxygen into the atmosphere.
• Among Biotic Components: Organisms interact with each other for processes like nutrition, reproduction, and protection. These relationships can be for feeding (predator-prey) or for other purposes.
• The Pond Study Example: A study demonstrated how the presence of fish in a pond could indirectly affect plants on the nearby land. Ponds with fish had fewer dragonflies (as fish eat dragonfly larvae). With fewer dragonflies, populations of pollinators like bees and butterflies increased. This increase in pollinators led to greater seed production in the flowering plants around the pond, illustrating a complex chain of direct and indirect effects.

5. Feeding Relationships and Energy Flow

Roles in the Ecosystem

Organisms are classified based on how they obtain food:

• Producers (Autotrophs): Organisms, primarily green plants, that produce their own food through photosynthesis.
• Consumers (Heterotrophs): Organisms that cannot produce their own food and must consume other organisms. They are categorized as:
  • Herbivores: Eat only plants (e.g., deer, hare, rabbit).
  • Carnivores: Eat only other animals (e.g., leopard, snake, frog).
  • Omnivores: Eat both plants and animals (e.g., foxes, mice, crows).
• Decomposers (Saprotrophs): Microorganisms like fungi and bacteria that break down dead organic matter (dead plants, animals, waste). This process, called decomposition, is crucial for recycling nutrients back into the soil, making them available for producers.

Food Chains and Food Webs

• Food Chain: A simple, linear sequence showing the flow of energy in an ecosystem, illustrating “who eats whom.” For example: Grass → Grasshopper → Frog → Snake → Eagle.
• Trophic Level: The specific position an organism occupies in a food chain. Producers are at the first level, herbivores at the second, and carnivores at subsequent levels.
• Food Web: A complex network of many interconnected food chains within an ecosystem. It provides a more realistic representation of feeding relationships, as most organisms are eaten by more than one type of predator.

6. Maintaining Balance in Ecosystems

A healthy ecosystem remains in a state of dynamic balance, where interactions keep populations and resources stable.

Types of Interactions

Besides feeding, other interactions help maintain this balance:

• Competition: Occurs when organisms require the same limited resources (food, water, space). Competition helps control population sizes.
• Mutualism: A relationship where both organisms benefit (e.g., bees get nectar from flowers, and flowers get pollinated).
• Commensalism: One organism benefits while the other is unaffected (e.g., orchids growing on a tree branch get support without harming the tree).
• Parasitism: One organism (the parasite) benefits, while the other (the host) is harmed (e.g., ticks feeding on a dog’s blood).

Disruptions to the Balance

Ecosystem balance can be disrupted by natural events or human activities.

• The Indian Bullfrog Case: In the 1980s, large-scale harvesting of Indian bullfrogs for export led to a decline in their population. Since frogs eat insects, this resulted in a rise in agricultural pests, forcing farmers to use more pesticides, which in turn harmed the environment and human health. This illustrates how removing one species can have cascading negative effects.

7. Humans and Ecosystems

Benefits and Threats

Humans are deeply connected to and benefit from ecosystems, which provide essential services like fresh air, clean water, food, timber, medicines, and climate regulation. However, human activities pose significant threats:

• The Sundarbans Case Study: The Sundarbans, the world’s largest mangrove forest, is a UNESCO World Heritage Site that protects coastal areas from storms, absorbs carbon dioxide, and hosts immense biodiversity. It is threatened by mangrove cutting for fuelwood, illegal hunting, and pollution from industrial and sewage waste.
• General Threats: Across India, ecosystems face threats from deforestation, overuse of resources, pollution, the spread of invasive species, and unsustainable land use.

Conservation Efforts

Protected areas like national parks (e.g., Jim Corbett), wildlife sanctuaries, and biosphere reserves are established to conserve wildlife and their entire habitats for future generations.

Agriculture and Sustainability

Farming is a human-made ecosystem. The Green Revolution in the mid-20th century increased food production through tractors, synthetic fertilizers, and pesticides. However, these methods are now considered unsustainable due to:

• Soil Degradation: Overuse of chemicals can reduce soil fertility, kill beneficial microorganisms, and lower humus content, making soil prone to erosion.
• Pest Resistance: Some pests can develop resistance to pesticides.
• Loss of Biodiversity: Monoculture (growing only one type of crop) reduces crop diversity and can harm vital pollinators. Sustainable alternatives like organic and natural farming aim to reduce chemical use and work in harmony with natural ecosystems.

Short Answer Quiz

Instructions: Answer the following questions in 2-3 sentences.

1. Differentiate between the biotic and abiotic components of a habitat.
2. What is an ecosystem, and what are its two main types?
3. Explain the key difference between a food chain and a food web.
4. What is the primary role of decomposers in an ecosystem?
5. Why have wildlife ecologists established elephant corridors in India?
6. Describe the impact of India’s large-scale harvesting of the Indian bullfrog in the 1980s.
7. What are two negative environmental consequences of the farming methods associated with the Green Revolution?
8. Define mutualism and provide an example.
9. What are trophic levels, and which type of organism occupies the first level?
10. How do the Sundarbans mangrove forests benefit both the environment and human populations?

Answer Key

1. Biotic components are all the living organisms in a habitat, such as plants, animals, and microbes. Abiotic components are the non-living physical parts of the environment, including air, water, soil, sunlight, and temperature.
2. An ecosystem is the interaction between a community of living organisms (biotic components) and their non-living environment (abiotic components). The two main types are aquatic ecosystems (e.g., ponds, rivers) and terrestrial ecosystems (e.g., forests, grasslands).
3. A food chain is a simple, linear path showing how energy is transferred from one organism to another, illustrating ‘who eats whom’. A food web is more complex, consisting of multiple interconnected food chains that show how organisms can have several different predators and prey.
4. Decomposers, like fungi and bacteria, break down dead organic matter, such as dead plants and animals. This process, called decomposition, recycles essential nutrients back into the soil, making them available for plants to use.
5. Elephant corridors were established to connect fragmented forest habitats. They provide safe passage for elephants and other wildlife, allowing them to travel between large forest areas without entering human settlements, which helps reduce human-wildlife conflict.
6. The harvesting of Indian bullfrogs led to a decline in their population. Since frogs are natural predators of insects, this caused an increase in agricultural pests, forcing farmers to rely more heavily on synthetic pesticides, which damaged the environment.
7. Two negative consequences are soil degradation from the overuse of synthetic fertilizers, which reduces fertility and beneficial microbes, and the development of pesticide resistance in pests. Additionally, these practices led to excessive groundwater extraction and reduced crop diversity through monoculture.
8. Mutualism is a type of interaction where both organisms involved benefit from the relationship. An example is the relationship between honeybees and flowers, where bees get nectar for food, and in the process, they pollinate the flowers.
9. Trophic levels are the specific positions that different organisms occupy in a food chain. Producers, such as green plants that make their own food, are at the first and lowest trophic level.
10. The Sundarbans slow down strong winds and waves during storms, protecting coastal communities from floods. Environmentally, the mangrove trees absorb large amounts of carbon dioxide from the atmosphere and release oxygen, helping regulate the climate.

Essay Questions

1. Using the research study on ponds with and without fish, explain how the removal or addition of a single biotic component can create a cascading series of direct and indirect effects throughout an ecosystem.
2. Discuss how human activities can disrupt the balance of natural ecosystems. Use the case studies of the Sundarbans mangrove forests and the export of Indian bullfrog legs to support your argument.
3. Compare and contrast natural ecosystems (like forests) with human-made ecosystems (like farms). Address their components, the level of human management required, and their long-term sustainability.
4. Describe the organizational hierarchy of life within an environment, starting from an individual organism and progressing to an ecosystem. Clearly define population and community in your explanation.
5. Evaluate the legacy of the Green Revolution in India. Discuss its initial benefits and the subsequent unsustainable practices that have led to environmental and soil health issues.

Glossary

Term	Definition
Abiotic Components	The non-living parts of a habitat, such as air, water, soil, sunlight, and temperature.
Aquatic Ecosystem	An ecosystem based in a body of water, such as a pond, river, or lake.
Autotrophs	Also known as producers; organisms that can produce their own food, typically through photosynthesis (e.g., plants).
Biotic Components	The living or once-living organisms in a habitat, including plants, animals, and microorganisms.
Carnivores	Consumers that eat only other animals.
Commensalism	An interaction where one organism benefits and the other is not significantly affected.
Community	All the different populations of organisms (plants, animals, microbes) living and interacting in the same habitat.
Competition	An interaction where organisms vie for the same limited resources like food, water, or space.
Consumers	Also known as heterotrophs; organisms that cannot produce their own food and depend on other organisms for nutrition.
Decomposers	Also known as saprotrophs; microorganisms like bacteria and fungi that break down dead organic matter.
Decomposition	The process by which complex substances in dead plants and animals are broken down into simpler ones, returning nutrients to the environment.
Ecosystem	A system formed by the interaction of biotic components (the community) and abiotic components in a specific area.
Food Chain	A simple, linear sequence that shows the flow of energy in an ecosystem by illustrating ‘who eats whom’.
Food Web	A network of interconnected food chains in an ecosystem, showing more complex feeding relationships.
Habitat	The natural home or environment of an animal, plant, or other organism, which provides the conditions needed for survival.
Herbivores	Consumers that eat only plants and plant products.
Heterotrophs	Also known as consumers; organisms that cannot make their own food.
Monoculture	The agricultural practice of growing the same crop repeatedly on the same land.
Mutualism	An interaction between two organisms where both benefit from the relationship.
Omnivores	Consumers that eat both plants and animals.
Parasitism	An interaction where one organism (the parasite) benefits at the expense of the other (the host), which is harmed.
Pollination	The process of transferring pollen from the male part (stamen) to the female part (carpel) of a flower, essential for fruit and seed formation.
Population	A group of organisms of the same kind living together in a habitat at a particular time.
Producers	Also known as autotrophs; organisms at the first trophic level that make their own food.
Protected Areas	Parts of land or water set aside to conserve wildlife and their habitats, such as national parks and wildlife sanctuaries.
Saprotrophs	Also known as decomposers; organisms that feed on dead and decaying organic matter.
Terrestrial Ecosystem	A land-based ecosystem, such as a forest, grassland, or farm.
Trophic Level	The specific position an organism occupies in a food chain.