CBSE Notes Class 10 Science Chapter 13 - Our Environment

The term "environment" is frequently mentioned in media and public discourse. Our elders often remark on how the environment has changed compared to the past, while discussions about working in a healthy environment or global environmental issues at summits remind us of its importance. This article explores how the different elements of the environment interact and how human activities affect this delicate balance.

1.0Ecosystems and Their Components

• Ecosystem is the basic unit of ecology and the biotic and abiotic components present in it influence each other. 
• Both the components are essential for the sustenance of life. 
• Ecosystem term was given by Arthur Tansley Ecosystem is a self-sustained unit of living things (plants, animals and decomposers) and their nonliving environment (soil, air and water). 
• Biotic components : The biotic components include all kinds of living organisms with which the organism interacts (all animals, plants, microorganisms). 
• Abiotic components : The abiotic components are the physical factors such as climatic factors (e.g., Air, Water, Temperature, Humidity, Light, Wind, Precipitation etc.).

Biotic (living) components

• The biotic community of an ecosystem includes 3 types of organisms 
• Producers : Those organisms which can prepare their own food from simple inorganic substances like carbon dioxide and water by using sunlight in the presence of chlorophyll. e.g., Green plants and certain blue green algae. 
• Consumers : Those organisms which consume food or eat food prepared by producers are called consumers. The consumers depend on producers for food, directly or indirectly. All the animals are consumers.
• Consumers can be further divided into three groups 
• Herbivores - Those animals which eat only plants are called herbivores. e.g., Buffalo, goat, sheep, horse, deer, camel, grasshopper, etc. Since herbivores obtain their food directly from plants or producers therefore herbivores are primary consumers. 
• Carnivores - Those animals which eat only other animals as food are called carnivores or those animals which eat the meat or flesh of other animals are called carnivores. e.g., Lion, tiger, frog, vulture, kingfisher, etc. 
• Omnivores - Those animals which eat both plants and animals, are called omnivores or those animals which eat plant food as well as the meat or flesh of other animals. e.g., Man, dog, crow, sparrow, bear and ant, etc.
• Decomposers -  The micro-organisms which break down the complex organic compounds present in dead organisms like dead plants and animals and their products like feces, urine into simpler substances are called decomposers. e.g., Bacteria and fungi.

2.0Food Chains and Food Webs

• It is a series of organisms, each feeding on the one below it. It is structured into different levels called trophic levels. 
• At the base are the autotrophs or producers that convert solar energy into chemical energy, which supports life on Earth. 
• Herbivores form the second trophic level, small carnivores at the third, and larger carnivores at the fourth level.
• As energy flows through these trophic levels, some energy is lost as heat or through processes like digestion and reproduction. 
• On average, only about 10% of energy from one level is passed on to the next, explaining why food chains rarely extend beyond three or four levels. 
• The complexity of food chains varies, and multiple organisms interact in a food web, creating a more intricate flow of energy than a simple linear chain.

3.0Energy Flow and its Unidirectional Nature

• The energy flow through an ecosystem is unidirectional, meaning it moves from producers to consumers and decomposers, never returning to the previous level. 
• Once autotrophs capture energy from sunlight, it is progressively passed on but diminishes at each trophic level. 
• As a result, energy becomes less available as it moves up the food chain.
• In addition to energy loss, harmful chemicals can also travel up the food chain in a process known as biological magnification. 
• Chemicals used in agriculture, such as pesticides, can be absorbed by plants and eventually consumed by animals and humans. 
• Since these chemicals are non-biodegradable, they accumulate in increasing concentrations at each trophic level, posing serious health risks to those at the top, including humans.

Ten Percent law 

• It was put forth by Lindeman (1942). It is also termed as the second law of thermodynamics or law of entropy. 
• According to this law, transfer of energy from one trophic level to another trophic level is never 100 percent. 
• It is so because most of the energy gets lost as heat in the environment during each transfer. On an average, about 10% of energy is actually available to the next trophic level.

4.0Human Impact on the Environment

• Humans are an integral part of the environment, and our activities significantly impact it. 
• Environmental degradation due to pollution, deforestation, and industrial waste has been well-documented. 

Ozone Layer Depletion

• This is a protective shield in the upper atmosphere, and is critical in blocking the Sun's harmful ultraviolet (UV) radiation. 
• UV radiation can cause severe health issues, including skin cancer. 
• The ozone layer is formed when UV radiation reacts with oxygen molecules (O2), breaking them apart into individual oxygen atoms. These atoms combine with other oxygen molecules to form ozone (O3).
• However, human-made chemicals, especially chlorofluorocarbons (CFCs), have caused significant depletion of the ozone layer. 
• CFCs, used in refrigeration and fire extinguishers, release chlorine atoms when they reach the upper atmosphere. They react with ozone and break it down. 
• Recognizing the threat posed by CFCs, the international community agreed to limit their production under the Montreal Protocol in 1987. Since then, efforts have been made to phase out CFCs and manufacture CFC-free products to protect the ozone layer.

Waste Disposal and Its Challenges

• Waste disposal is another major environmental challenge. We produce vast amounts of waste daily, including non-biodegradable materials like plastics. 
• While bacteria and fungi break down biodegradable materials into simpler substances that nature can reuse, non-biodegradable materials persist in the environment for a long time, often harming ecosystems.
• For instance, plastic waste accumulates in landfills and water bodies, posing risks to wildlife. 
• Animals may ingest plastics, mistaking them for food, which can lead to injury or death. 
• Moreover, non-biodegradable materials can release toxic substances over time, polluting soil and water sources.