How Nature Works in Harmony Class 8 Notes Science Chapter 12

Students can rely on these Class 8 Science Notes Chapter 12 How Nature Works in Harmony Class 8 Notes for complete exam preparation.

Class 8 Science Chapter 12 How Nature Works in Harmony Notes

Class 8 Science Curiosity Chapter 12 Notes

Class 8 Science Chapter 12 Notes – How Nature Works in Harmony Notes Class 8

→ Habitat The natural home or environment where a plant, animal, or organism lives.

→ Population A group of individuals of the same species living in the same area at the same time.

→ Community All the different populations living and interacting in the same habitat.

→ Ecosystem A system formed by the interaction of living (biotic) and non-living (abiotic) components in an environment.

→ Consumer Organisms that eat other organisms to get energy.

→ Decomposer Organisms like fungi and bacteria that break down dead plants and animals.

→ Food chain A linear sequence showing how energy is transferred from one organism to another.

→ Food web A complex network of interconnected food chains in an ecosystem.

→ Trophic level The position an organism occupies in a food chain (e.g., producer, consumer)
Monoculture The agricultural practice of growing only one type of crop in a large area over a long period of time.

→ Name the term that describe the natural environment where a living organism lives, grows and carries out all its life processes.

→ What are the physical and chemical components that directly influence the survival of organisms?

→ Give an example of interactions between two abiotic components.

→ Why does a rodent stay active during the day in a forest?

→ Name the term which is used to a refers to a group of individuals of the same species living in a particular area at the same time.

→ Why would dragonflies avoid flying near water bodies with many fish?

→ Identify the type of population interaction in which two species compete for the same limited resources.

→ Honeybees collect nectar for food while pollinating flowers. Identify the type of interaction.

→ Name the scientist who proved that a healthy prey population is essential for predator survival, ensuring ecological balance.

→ Write the term for a self-sustaining unit where energy flows and materials cycle continuously.

→ A pond has fish, algae, insects and water. What type of ecosystem is this?

→ Give two examples of terrestrial and aquatic ecosystem.

→ Why do human-made ecosystems require constant human intervention?

→ Imagine an aquarium. Identify at least 3 living and 3 non – living things that make it an ecosystem.

→ What do you mean by the term Autotrophs in an ecosystem?

→ Classify the following organisms into producers, herbivores, carnivores and omnivores.
Grass, Tiger, Human, Cow, Lion, Algae, Crow

→ What is the primary function of producers in an ecosystem?

→ Which organisms occupy the second trophic level in most food chains?

→ How does decomposition help maintain soil fertility?

→ How are ecosystems economically important to humans?

→ What happens to oxygen levels in a water body when it becomes polluted?

→ Name the species of frog whose legs a were a used to export from India in the 1980s.

→ What role do mangrove ecosystem play is coastal areas?

→ Which type of farming practice can reduce the harmful effects of synthetic fertiliser?

Habitat

A habitat is the natural environment where a living organism lives, grow and carries out all their life processes.

It provides essential conditions that an organism needs to survive such as food, water, shelter, air and suitable climate. Habitats can be large like oceans, forests and deserts or small like a pond, a tree or even the bark of a tree.

A wildlife corridor is a natural or man – made path that connects two or more separate wildlife habitats. These corridors allow animals to move freely and safely from one area to another jn search of food, water, mates or shelter, especially when their habitat is broken up by roads, forms or buildings.

Components of a Habitat

The survival, growth and reproduction of an organism are influenced by specific components present in its habitat. These components are classified into two broad categories, which are as follows

1. Abiotic Components (Non-Living Things)

• These are the physical and chemical components that directly influence the survival of organisms.
• They determine the physical conditions of the habitat and influence the types of organisms that can exist here.
• Example of abiotic components are soil, water, air, humidity, temperature etc.

2. Biotic Components (Living Things)

• These includes all living organisms in the habitat and their interactions.
• Biotic components interact in various ways, including predation, competition, symbiosis and other ecological relationships.
• Example of biotic componetns are producer (plants, algae), consumers (lion, deer, human, cow), and decomposers (fungi, bacteria).

Interaction of Biotic and Abiotic Components

• The interaction between biotic (living) and abiotic (non-living) components is essential for the survival of all organisms. For example, in plants, abiotic factors such as sunlight, carbon dioxide, water and soil nutrients are necessary for photosynthesis, which helps them produce food and oxygen.
• This oxygen is used by animals for respiration which shows close interaction between living and non-living components to stay alive and function properly.
• These interaction of biotic and abiotic components in a habitat can be better understood by considering different criterias.
  1. Interaction between biotic and abiotic components These may influence the life processes such as nutrition, respiration, and reproduction in biotic components.
  2. Interaction between two abiotic components
     These may influence the physical characteristics of habitat.
  3. Interaction among the biotic component These
     interactions may influence the availability of resources needed for life processes like nutrition, respiration, etc.

The examples of the following interaction are given below

Criterion 1: Interactions between biotic and abiotic components	Criterion 2: Interaction between two abiotic components	Criterion 3: Interaction among the biotic components
Earthworms live in moist soil.	The day temperature is high due to the bright sunlight.	A frog eats insects.
Many microbes are present in the pond.	Water is evaporating fast due to the sunlight.	A water snake eats fish.
A fish lays eggs in water.	Air current is blowing slowly on the water surface creating gentle waves.	Frogs and fish may compete for small insects larvae.
	The soil near the pond is moist.	A fish lays eggs in water near vegetation to protect them from other fish or frogs.

Harmonious Nature of a Habitat

• Each habitat has its own unique set of biotic and abiotic (physical) components. Even though many different organisms may share the same habitat they often use the available resources in different ways and at different times, allowing them to live in harmony. This can understood with the help of examples of following habitats.

1. Forest Habitat

• A forest habitat may be warm during the day and cool at night. In such a forest, a rodent may be active during the daytime, using the sunlight to warm its body.
• In the same forest, a snake may come out only at night, avoiding the heat. Although both animals live in the same habitat. They experience different conditions and have different routines.

2. Pond Habitat

• A pond provides food, oxygen, shelter and space essential for an organism for survival.
• Animals like frogs, fish, turtles, snakes, dragonflies, mosquitos, snails, and ducks, meet their biotic needs from small plants other organisms and abiotic needs like oxygen, from water.
• All these living beings interact with each other and with their surroundings.

Populations and Communities

• A population refers to a group of individuals of the same species living in a particular area at the same time. These individuals interact with each other, compete for resources and reproduce, e.g., a herd of deer in a forest and a school of fish in a pond.
• A community consists of all the different populations (different species) living and interacting in the same habitat.
• Unlike a population, which includes only one species, a community includes multiple species that depend on each other for survival.
• The biotic components of a habitat, such as plants, animals, and microorganisms together form the community.
  For example, A pond community includes fish, frogs, water plants, insects and algae.
• A forest community includes trees, birds, deer, snakes, and insects coexisting in the same area.

Relationship between Population and Community

• Population is the part of a community. Different population in a community interact in various ways, such as organisms competing for the same resources.
• The balance of a community depend on the survival of different populations. If one population declines it affects others.
• The following example shows the connection between a population and its community
  • In a pond, fish feed on dragonflies, which in turn prey on bees.
  • If there is an increase in the fish population, it can lead to a decrease in dragonfly numbers. This, in turn, allows more pollinators like bees to survive and thrive.
  • These pollinators play an important role in plant reproduction by transferring pollen from one flower to another, which increases seed production.
  • However, if fish disappear, dragonfly numbers may increase, reducing the population of pollinatiors and ultimately affecting plant reproduction resulting in low seed production.
• This example shows how populations interact within community, influencing each other’s survival.

• A flower has green leafy sepals, brightly coloured petals and reproductive parts.
• The carpel (female part) contains ovules, while the stamen (male part) releases pollen grains.
• When insects, birds, bats or wind carry pollen from the stamen to the carpel of the same or a different flower, it leads to pollination.
• This process is essential for the formation of fruits and seeds.

Population Interactions

In nature, no organism exists in isolation. Different species constantly interact with each other. These population interactions influence survival, reproduction and the overall balance of nature.

Types of Population Interactions
These interaction can be beneficial, harmful or neutral as described below

1. Competition

• In this interaction two species compete for the same limited resources, e.g. food, space, and mates.
• It helps control population size and keeps the ecosystem balanced.
• It prevents overpopulation of the species and ensures a diverse ecosystem where multiple species coexist.
• e.g., tigers and leopards compete for prey in the same habitat.

2. Mutualism

• In this interaction, both species derive benefits.
• It is essential for pollination, nutrient cycling and ecosystem stability.
• e.g., honeybees collect nectar for food while pollinating flowers. It helps plant to reproduce.

3. Commensalism

• One species benefits without harming or helping the other species.
• e.g. orchids grow on tree branches for sunlight but do not harm the host tree.

4. Parasitism
• In this interaction, one organism benefits at the expense of the host (other organisms), e.g., ticks feed on dog’s blood, weakening the host.

Asir Jawahar Thomas Johnsingh (A.J.T. Johnsingh) was a renowned Indian wildlife biologist. He was pioneer in modern wildlife tracking system. During his work in Bandipur National park, Karnataka, he showed predators like tigers and leopards rely on prey such as deer and wild bear. He proved that a healthy prey population is essential for predator survival, ensuring ecological balance.

Ecosystem

• An ecosystem is a system where biotic components (plants, animals, and microorganisms) interact with each other and with the abiotic components (air, water, soil, sunlight, arid temperature) in their environment.
• It is a self – sustaining unit where energy flows and materials cycle continuously.
• Organisms in an ecosystem interact with abiotic components for food, shelter and protection.
• A forest, a pond, a grassland, a large banyan tree, mango or pilkhan tree, or even a small tree can be considered an ecosystem.

Types of Ecosystem

Ecosystems are classified based on their location and origin.
These are as follows

1. Terrestrial Ecosystem

• It is a type of ecosystem that is found on land. They are well – balanced and support a wide range of organisms.
• Tigers, deer, snakes, zebras, pine tress, cactus, camels etc, are found in these ecosystems.
• e.g., mountain, forest, grassland, desert ecosystem.

2. Aquatic Ecosystem

• These are found in water bodies. Found in lakes, ponds, sea, coral reefs etc.
• Different animals and plants are found such as dolphins, lotus, ducks, frogs, corals, algae etc.
• e.g., pond ecosystem, river ecosystem, and lake ecosystem.

3. Human-made (Artificial) Ecosystem

• These are ecosystem developed by humans for specific uses like decoration, farming, etc.
• Humans control the conditions in these ecosystems.
• These ecosystem can help reduce pollution, support biodiversity and provide recreational spaces for people.
• These system help maintain ecological balance and increase the population of certain animals and plants.
• e.g., crop field, aquarium, garden, botanical garden, fish farm etc.

• The ecological hierarchy shows how life is organised from simple to complex levels. It starts with an individual organism, followed by a population of the same species. Different populations form a community, and together with their physical environments, they make up an ecosystem.

Overlap of Different Terrestrial and Aquatic Ecosystems

• Overlapping means when two different ecosystems meet and share features of both.
For example, a small river (aquatic ecosystem) along with mountains, forest, grassland, and farmland shows the overlap of different terrestrial and aquatic ecosystems.

Structure of an Ecosystem

The structure of an ecosystem can be split into two main components, namely

1. Biotic components
2. Abiotic components

1. Biotic Components
It refers to all living components in an ecosystem. Based on nutrition, biotic components can be categorised into following terms
(a) Producers or Autotrophs (auto = self + troph = food)

• They produce food through process of photosynthesis.
• Producers use sunlight, carbon dioxide and water to produce food and oxygen.
• They provide energy directly or indirectly to all other living organisms, e.g., plants, algae and phytoplankton.

(b) Consumers or Heterotrophs (hetro = other + troph = food)
These organisms that cannot produce their own food and depend on producers or other animals for energy.
These are further divided into several types based on their food habits

1. Herbivores : Organisms that eat only plants, e.g., cow, deer, hare, grasshopper etc.
2. Carnivores : These organisms eat other animals, e.g., leopard, tiger, hawk.
3. Omnivores : These organisms eat both plants and animals, e.g., crows, foxes, mice, humans etc.

(c) Decomposers They thrive on the dead and decaying plant and animals, e.g., fungi and bacteria.

2. Abiotic Components
These are the non-living components of an ecosystem. It includes air, water, soil, minerals, etc.

Functions of an Ecosystem

• An ecosystem performs several important natural functions that help maintain balance in the environment.
• These functions involve the flow of energy through food chain and food web, and cycling of nutrients through decomposition of waste materials.
• These are discussed as follows

Food Chain and Trophic Level

• The interaction between living (biotic) components of an ecosystem, especially based on who eats whom can be shown through a food chain.
• A food chain is a simple, straight – line sequence. It represents how energy and nutrients pass from one organism to another.
• It begins with producers and moves through different levels of consumers. Food chain shows how each organism depends on the next for food.

Example of Simple Food Chain

• Each organisms in a food chain has a specific position called trophic level (troph = food).
• Each step in the food chain is a trophic level. It can be described as below table

Trophic level	Organism	Role
1st trophic level	Grass, trees, algae	Producer
2nd trophic level	Grasshopper, hares, deer	Herbivores
3rd trophic level	Frogs, crow	Small carnivores
4th trophic level	Tigers, vultures	Large carnivores

• An ecological pyramid depicts how energy and biomass decrease from lower to higher trophic levels.
• A diagram illustrating different trophic levels is shown below

Food web

• In nature, most organisms eat more than one type of food. They may be eaten by more than one predator. Therefore why food chains do not exist in isolation. They form a complex web of connections, known as a food web.
• A food web is a network of interconnected food chains in an ecosystem.
• It shows how different plants and animals are linked through various feeding relationships.

• Unlike a food chain, which follows just one path, a food web shows multiple path through which energy and nutrients flow.

Decomposition

• It is the natural process by which complex substances in dead plants and animals are broken down into simpler substances.
• The process of decomposition is carried out by certain organisms known as decomposers or saprotrophs (sapro = rotten + trophs = food).
• Microorganisms such as bacteria and fungi are the main decomposers. They feed on dead and decaying matter and convert it into simpler nutrients. These nutrients are then released back into the soil, making it fertile and helping new plants to grow.
• In addition to microorganisms, tiny insects like beetles and flies also help in the decomposition.
• For example, animal droppings such as elephant dung attract these insects, which feed on it and break it down further.
• Due to decomposers, nutrients are reused again and again, making them a vital part of nutrient cycling in nature.

Benefits of an Ecosystem

• Ecosystems are not just homes for plants and animals. They also provide many important benefits to humans and the environment.
• These benefits help maintain life on Earth and support our daily needs. Some of them are as follows
  1. It gives us a variety of foods such as fruits, vegetables, grains, fish, fibres, timber and medicines. They also store and supply freshwater.
  2. They help in controlling temperature, rainfall and humidity.
  3. It also offer aesthetic and recreational value.
• Every year, many migratory bird species visit India to escape cold winters and find food. Migratory birds, Demoiselle crane visit the water body of Khichan village in Jodhpur district during the winter months.
• These birds are important is many ways, some of them are as follows
• They maintain ecosystem balance by pollinating plants and spreading seeds.
• Control pests by eating insects (natural pest control).
• Help farmers by reducing crop – damaging insects.

Threats of Ecosystem

• Ecosystem is a gift of nature that provides us with everything we need. However, human activities are putting great pressure on the ecosystem.
• The excessive use of natural resources like water, fossil fuels and forests is leading to their depletion.
• Many animals are losing their homes due to deforestation and illegal hunting.
• These actions are disturbing the natural balance and creating serious environmental problems.
• Some of these actions are discussed below

(i) Impact of Water Pollution

• When water bodies become polluted, many aquatic plants begin to die, with fewer plants, oxygen levels drop and fewer nutrients are available for other organisms.
• As plants die, fish lose their food and shelter. This leads to decrease in their population. It disrupts the food chain, affecting predators like birds and larger aquatic animals.
• As a result, insects will increase in number. These insects may migrate to nearby farmlands, damaging crops.
• Farmers are then forced to used more pesticides, which can further harm the environment.

(ii) Impact of Overexploitation

• In the 1980, India was a major exporter of frog legs, especially of the Indian bullfrog (Hoplobatrachus tigerinus).
• The large – scale harvesting of frogs led to a sharp decline in their population.
• Frogs play an important role in controlling insect populations, as they feed on pest.
• With fewer frogs in the fields, the number of agricultural pests increased. As a result, farmers began using more synthetic pesticides to protect their crops.
• This overuse of chemicals harmed the soil, water quality, overall environmental healh and human health.
• To prevent further damage to the ecosystem, the Government of India banned the commercial export of frogs.

(iii) Impact of Human Activities on Mangrove Ecosystem

• The Sundarbans is the largest mangrove forest in the world. It is located at the meeting point of the Ganga and Brahmaputra rivers. It spreads across India and Bangladesh.
• This unique region is home to a wide variety of plants and animals, including several endangered species.
• The dense mangrove trees act as a natural barrier, protecting coastal areas by slowing down strong winds, cyclones and tidal floods.
• Because of its importance, the United Nations Educational, Scientific and Cultural Organisation (UNESCO) declared the Sundarbans a world heritage site in 1987.
• However, despite their importance, the Sundarbans are facing serious threats due to overuse of forest resources, illegal hunting, farming, cutting down of trees and polluted water from sewage and industrial waste.
• If not protected, the loss of this ecosystem could lead to severe ecological imbalance.

They are special regions set aside by the government to conserve wildlife, forests and natural habitats.

These areas are protected by law to ensure that plants, animals and many rare plants can thrive without human disturbance.

There are different types of protected areas such as national parks, wildlife sanctuaries, biosphere reserves and community conserved areas.

Famous examples include Jim Corbett National Park (Uttarakhand), Manas National Park (Assam), Nilgiri Biosphere Reserve (Western Ghats), Chilika Lake (Odisha), Eaglenest Wildlife Sanctuary (Arunachal Pradesh), Hemis National Park (Leh), Keibul Lamjao National Park (Manipur), Pirotan Island Marine National Park (Gujarat). Protected areas play a big role in saving nature for future generations.

(iv) Impact of Unsustainable Farming

• With rising population, India faced a major food shortages from 1950 to 1965 due to low crop production.
• To solve this crisis, the use of tractors, modern machinery, synthetic fertilisers and chemical pesticides was introduced in the mid 20th century.
• This led to a sharp rise in food production. This period is known as the Green Revolution.
• However, these farming methods are now considered unsustainable because of the overuse of synthetic chemicals, excessive extraction of ground water and growing only one type of crop (monoculture).
• Monoculture can reduce crop diversity and affect pollinators.

(v) Impact of Synthetic Fertilisers

• The excessive use of synthetic fertilisers can reduce the natural fertility of soil.
• It decreases the number of beneficial microorganisms and lower the amount of organic matter (humus). Humus is important for binding soil particles together.
• Without enough humus, the soil becomes loose and more likely to be eroded by wind or water.
• Overuse of chemicals also affects the balance of nature by reducing the number of natural predators like insects and birds. It leads to an increase in crop damaging pests.
• Heavy irrigation and repeated ploughing can also disturb soil organism like earthworm and snails; which maintain ecological balance.
• Some pests may develop resistance to pesticides, making them difficult to control.

Sustainable Farming

• It is a method of agriculture that focuses on growing food in a way that protects the environment.
• It maintains soil fertility and ensures the well-being of future generation.
• Some farmers are turning to organic and natural farming methods. These approaches are
  • Reduce synthetic fertilisers and chemicals.
  • Using compost, natural pest control and crop rotation.
  • The ancient text Yrikshayurveda emphasises on soil health and nourishment. The text strongly advocates for the continuous nourishment of the soil through organic manure like Kunapa Jala (a liquid fertiliser). It is made from animal and plant waste by the process of fermentation, the process of fermentation breaks complex substances into simpler ones) and other composted materials.