Experts have designed these Class 8 Science Notes Chapter 12 How Nature Works in Harmony Class 8 Notes for effective learning.
Class 8 Science Chapter 12 How Nature Works in Harmony Notes
Class 8 How Nature Works in Harmony Notes
Class 8 Science Chapter 12 Notes – How Nature Works in Harmony Notes Class 8
→ Habitat: A habitat is a place where an organism lives and obtains all the necessary resources to survive, including food, water, shelter, and the optimal temperature. It could even be just the bark of a tree. The plants and animals interact with each other and adapt to survive in the surrounding conditions they live.
→ Components of a Habitat: Two types of components are:
- Biotic components: The living parts of an ecosystem, including plants, animals, fungi, bacteria, and all other organisms.
- Abiotic components: The non-living physical and chemical elements in the environment, such as sunlight, temperature, water, air, soil, and minerals.
→ Types of Habitat: Habitats can be of many types. Here are a few examples:
→ Pond Habitat: A freshwater ecosystem characterised by standing water and home to a variety of species such as such as frogs, freshwater turtles, snakes, dragonflies, mosquitoes, snails, and ducks, along with plants like algae, diatoms, duckweeds, lotus) and abiotic (water, mud, oxygen) factors.
→ Forest Habitat: A densely wooded ecosystem where trees are the main feature. Animals such as snakes, rodents, and birds live here. Forests provide shelter, food, and breeding grounds for a diverse range of wildlife.
→ Coexisting in Nature: Different species share a habitat with balanced interactions. For example, a rodent is active during day and a snake at nightboth live in the same forest but use it differently.
→ Population and Community: A group of individuals of the same species living in a specific area at a given time is known as population. All the different populations of living organisms (plants, animals, fungi, microorganisms) that live and interact in a specific area or habitat are known as a community.
→ Flower and Pollination: A flower is the reproductive part of a plant. It contains sepals, petals, and two reproductive parts-carpels and stamens. Petals attract pollinators, while sepals protect the bud. Stamens release pollen, which is carried by wind, water, insects, birds, or bats to the carpel. The transfer of pollen from the stamens to the carpels of the same and different flowers, leading to the formation of seed and fruit, is called pollination.
→ St. John’s wort: A flowering plant known for its bright yellow flowers. It is often studied for its medicinal properties and interactions with insects and pollinators.
→ Role of Different Organisms in a Community: The biotic components (fish, dragonflies, pollinators, plants) and abiotic components (temperature, water, nutrients) interact with and affect each other.
- Overfishing: The practice of catching too many fish from a body of water, faster than they can reproduce, leading to population decline and ecological imbalance.
- Reproduction: The biological process by which organisms produce offspring, ensuring the continuation of their species.
→ Types of Interactions Among Organisms and their Surroundings: Plants and animals need air, water, soil, and sunlight to grow. Living organisms (biotic community) depend on nonliving things (abiotic components) for their survival. Plants and animals also depend on each other for nutrition, respiration, and reproduction.
- Both types of interactions – among biotic components, and between biotic and abiotic components – are important for survival in any habitat.
- Abiotic components also depend on biotic components. For example, plants release oxygen during photosynthesis, roots hold soil in place and prevent erosion, and plants retain soil moisture and help cool the atmosphere.
→ Ecosystem and its Types: A community of living organisms (biotic factors) interacting with their non-living environment (abiotic factors) such as soil, air, and water is known as ecosystem.
→ There are two main types of ecosystems in nature.
- Aquatic ecosystems include ponds, rivers, and lakes.
- Terrestrial ecosystems include forests, farms or even large trees like banyan, mango, or pilkhan (white fig) tree.
→ Pilkhan: A large deciduous (white fig) tree (Ficus infectoria) native to parts of South Asia, often found in forests or rural areas, supporting various wildlife species.
→ Farmland: Land used for agricultural purposes, including growing crops and raising livestock. It is a human-made ecosystem with ecological importance.
→ Producers or Autotrophs: Organisms (like green plants, algae) that produce their food using sunlight through photosynthesis and form the base of the food chain.
→ Eating Habits of Different Organisms: Organisms that cannot produce their food and depend on other organisms for their food, are known as consumers, or heterotrophs. These are further classified as:
- Herbivores: Eat only plants and plant products, such as deer and hares.
- Carnivores: Eat only other animals, such as tigers, vultures, etc.
- Omnivores: Eat both plants and animals, such as foxes, mice, etc.
→ Linkage: The connections and relationships among living organisms and between organisms and their environment.
→ Food Chain: A food chain shows the relationships between organisms in an ecosystem.
→ Pyramid: A diagram that shows the number of organisms at each trophic level in a food chain. The base is wide (producers), and it narrows as we move up to herbivores, then carnivores, and finally top predators, showing how energy decreases at each level.
→ Trophic Level: The positions that different organisms occupy in a food chain are called trophic levels.
→ Food Web: A network of interconnected food chains showing “who eats whom” in an ecosystem is called food web. It depicts the complex feeding relationships among organisms, where one organism may be eaten by two or more type of organisms.
→ Decomposition is the natural process of breaking down dead plants, animals, and waste into simpler substances by decomposers (like fungi and bacteria). The organisms carrying out the process are called decomposers or saprotrophs.
→ Nature Recycles Waste: Decomposers play an important role in recycling nutrients that help break down waste and return nutrients to the soil.
→ Migratory birds travel long distances seasonally to escape extreme weather or find food and breeding grounds. For example, the migratory bird Demoiselle Crane visits the water body of Khichan village in Jodhpur district during the winter months.
→ Predators: Organisms that hunt, kill, and eat other animals (prey) for food. For example, foxes, eagles, and snakes. Predators help control prey populations and maintain ecosystem balance.
→ Impact of Human Activities on Nature:
- Farmers use pesticides to kill pests like insects and fungi that harm crops. However, overusing them pollutes the soil and water, harms wildlife, and affects human health.
- Human activities or natural changes cause environmental issues like climate change, deforestation, pollution, and the loss of biodiversity, which damage ecosystems.
- People cause ecological damage by polluting, overusing natural resources, or destroying habitats.
An ecosystem stays in balance when interactions among organisms and their environment keep populations and resources stable. This balance is dynamic, not fixed, and can be disrupted by natural or human-made changes.
→ Interactions in Ecosystems: The relationships among organisms and their environment, such as competition, mutualism, commensalism, and parasitism.
- Competition: Organisms compete for common resources like food, water, physical space, or sunlight to maintain the ecosystem balanced.
- Mutualism: This is an interaction where both organisms benefit. For example, honeybees get nectar from flowers, and in return, they help in pollination, aiding seed and fruit formation.
- Commensalism: Commensalism is a relationship where one organism benefits, while the other remains neither harmed nor helped, e.g., orchids growing on trees.
- Parasitism: When one organism benefits while the other is harmed. For example, ticks feeding on the body of dogs is a parasitic relationship.
These interactions are all part of the complex web of life in an ecosystem.
→ Notable Scientist: Asir Jawahar Thomas Johnsingh (A.J.T. Johnsingh) was a famous Indian wildlife biologist. He studied forest ecosystems by observing animals and using modern tracking methods. In Bandipur National Park, he showed that predators like tigers need enough prey to survive. He inspired many young people to protect wildlife and forests in India.
→ Benefits of an Ecosystem: Humans get benefits from the forest ecosystem, such as:
- Forests provide fresh air, fertile soil, food, fibres, timber, and medicines.
- Aquatic ecosystems provide water and food.
→ Example of a Threatened Ecosystem: The Sundarbans, world’s largest mangrove forest, lies at the confluence of the Ganges and Brahmaputra Rivers and was declared a UNESCO World Heritage Site in 1987. They protect us from storms and floods by reducing wind and wave impact, and their trees absorb carbon dioxide and release oxygen. However, deforestation, illegal hunting, overuse of resources, and pollution are damaging the habitat and disrupting the ecosystem’s natural balance.
→ Endangered: A species is called endangered when its population is very low and it is at risk of extinction. Example: Royal Bengal Tiger, Indian Vulture.
→ Invasive Species: Non-native species that are introduced to an area and spread rapidly, often harming native plants and animals by competing for resources.
→ Scrublands: Ecosystems with small shrubs and scattered trees, found in dry or semi-dry regions. They are often home to unique species adapted to such climates.
→ Wetlands: Lands that are covered with water, either permanently or seasonally. Examples include marshes and swamps. Wetlands are rich in biodiversity and help in water purification and flood control.
→ Protected Areas: These places help protect entire habitats, including endangered animals, birds, and many rare plants. These areas are parts of land or water set aside to conserve wildlife and their habitats. Protected areas play a big role in saving nature for future generations.
→Human-made Ecosystems: Artificial ecosystems, like fish ponds, farms, and parks, are well designed by humans to help reduce pollution, support biodiversity, and provide recreational spaces for people.
→ Green Revolution: A period (1950s-1965s) when new farming technologies like high-yield seeds, tractors, irrigation, and chemical fertilisers increased food production in India and other countries. These farming methods are now considered unsustainable due to overuse of synthetic chemicals, excessive groundwater extraction, and growing only one type of crop for commercial gain.
→ Synthetic fertilisers and pesticides have improved crop production and helped countries like India become food secure. However, their long-term overuse can harm the environment and soil health. Overusing synthetic fertilisers may reduce soil fertility by decreasing helpful microorganisms and humus in the soil, which can cause erosion. It also lowers the population of natural predators, leading to an increase in pests.
→ Humus is dark, organic matter in soil formed from the decomposed part of plants and animals. It improves soil fertility, holds water, and supports plant growth.
→ Monoculture: The practice of growing only one type of crop over large areas. Though it increases short-term yield, it reduces biodiversity and can lead to soil degradation and pest problems.
→ Sustainable Farming: Farming that protects the environment, uses natural resources wisely, and ensures long-term food production. It includes organic farming, crop rotation, and reduced chemical use.
→ Food Security: The condition in which all people have access to sufficient, safe, and nutritious food at all times to maintain a healthy and active life.
→ Protecting our ecosystems through efforts, such as conservation like national parks and sanctuaries, plays an important role.
→ Our Scientific Heritage: The ancient Indian text Vrikshayurveda emphasises the importance of soil health and nourishment. It promotes the use of organic manure like Kunapa Jala, a fermented liquid made from animal and plant waste, to enrich the soil naturally.