Chapter -15 Notes Our Environment 




•Everything that surrounds us is environment. It includes both living(biotic) and non-living (abiotic)Components.

•Interaction between these biotic and abiotic components forms an ecosystem.

•In an ecosystem living components depends on each other for their food which give rise to food chains and food webs in nature.

•Human activities lead to environment problems such as depletion of ozone layer and production of huge amount of garbage.

All the interacting organisms in an area together with the non-living constituents of the environment from an ecosystem.Eg forest , pond etc.

Types of ecosystem:It Is of two types:

(a)Natural ecosystem:The ecosystem which exist in nature on its own.Eg forest, lake, Ocean.

(b)Artifical ecosystem:Man -made ecosystem are called artificial ecosystem.Eg , crop field, aquarium, garden.










(a)Abiotic Components:All the non-living components such as air, land ,  water, light, temperature etc.Form the components.


(b)Biotic Components:All the living components such as plants, animals, bacteria , fungi, etc from the biotic components.

On the basis of nutrient biotic components are further divided into:


Producers:All green plants and blue-green algae can produce their own Food using abiotic components(photosynthesis), hence called producers.

Consumers:Include All animals which depend on producers directly or indirectly for their food.

Consumers are further divided into:
(1)Herbivors:Plant eaters eg ; goat , deer.
(2)Carnivors:Flash eaters e.g , tiger , Crocodile.
(3)Omnivores:Eats both plants and animals e.g human.
(4)Parasites:live on the body of host and take food from it Eg; lice, cascuta.

Decomposers:Include organisms which decompose the dead plants and animals e.g bacteria , fungi.These help in the replenishment of natural resources.

•Food chain is a series of organisms in which one organism eats another organism as food for e.g

















Grass→Deer→Lion

•In a food chain various steps where transfer of energy take place is called a trophic level.

Flow of energy between trophic levels

•Flow of energy in a food chain is uni directional.

•Green plants capture 1℅ of sunlight and convert it into food energy.

•10 percent law:Only 10℅ of energy is transferred to the next tropic level.The remaining 90℅ energy is used in life processes(digestion, growth, reproduction etc) by present trophic level.










•Due to this gradually decrease in energy , food chain, contain 3-4 tropic levels.










Biological Magnification:The concentration of harmful chemicals increase with every next trophic level in a food chain .This is called biological magnification.

•Maximum concentration of such chemicals get accumulated in human bodies as human occupy the top level in any food chain.

Food web:In nature large number of food chain are interconnected forming a food web.





















Environmental Problems:changes in the environment affect us and our activities change the environment around us .Human activities lead to pollution, deforestation etc.


Ozone layer

•Ozone layer is a protective blanket around the earth which absorbs most of the harmful UV(ultraviolet)rediations of the sunlight,this protecting living beings from many health hazards such .skin cancer, cataract, destruction of plants etc.

•Ozone (O³)layer is present at higher levels of atmosphere (I.e, stratosphere)It is a deadly poison at ground level.


Formation of ozone molecule

(i)The high energy UV radiations break down the O² molecules into free oxygen (o) atoms.

    

(ii)These oxygen atoms then combine with oxygen (O²) molecule to form the ozone molecule.




Ozone layer
Ozone layer is a protective blanket around the earth which absorbs most of the harmful UV(ultraviolet) radiations of the sunlight,this protecting the earth.

Depletion of ozone layer

•The decrease in the thickness of ozone layer over Antarctica was first observed in 1985 and was termed as ozone hole.

•This decrease was linked to excessive use of synthetic chemicals like chlorofluorocarbons(CFCs) which are used in refrigerators, Acs, Fire-extinguishers, aerosols spray etc.

•United Nations environment Programme (UNEP) succeeded in forging an agreement to stop CFC production at 1986 levels(KYOTOPROTOCOL)by all countries.

Garbage disposal
Improvements in lifestyle have resulted in accumulation of large amounts of waste materials.

Garbage contains Following type of materials:

(a)Biodegradable waste:Substances which can be decomposed by the action of micro-organisms are called biodegradable wastes.Eg:Vegetable tells, cotton, jute, dung, paper etc.


(b)Non-Biodegradable waste:Substances which cannot be decomposed by the action of micro-organism are called non-biodegradable wastes.Eg;plastic,polythene's, metals , synthetic fibres,radiation waste, pesticides etc.

Micro-organisms release enzymes which decompose the materials but these enzymes are specific in their action that's why enzymes cannot decompose all the materials.


Some methods of waste disposal

(a)Biogas plant:Biodegrable waste can be used in biogas plant to produce biogas and manure.

(b)sewage treatment plant:The drain waste can be cleaned in sewage treatment plant before adding it to rivers.

(c)land Fillings:The wastes are buried in low lying areas and are Compacted by rolling with bulldozers.

(d)Composting:Organic wastes are filled in a compost pit and covered with a layer of soil , after about three months garbage changes to manure.

(e)Recycling:Non-biodegradable waste are recycled to make new items.

(f)Reuse:It is a conventional technique to use an item again eg; newspaper for making envelops.


Chapter 15 - Our Environment

NCERT Solutions


Question 1: What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

Answer: Trophic levels are the various levels in a food chain at which energy is transferred through different organisms. Each trophic level represents a step in the flow of energy and nutrients within an ecosystem. For example:

Example of a Food Chain: Grass → Grasshopper → Frog → Snake → Hawk

  • Trophic Level 1 (Producers): Grass (Plants)
  • Trophic Level 2 (Primary Consumers): Grasshopper (Herbivores)
  • Trophic Level 3 (Secondary Consumers): Frog (Carnivores)
  • Trophic Level 4 (Tertiary Consumers): Snake
  • Trophic Level 5 (Top Predators): Hawk


Question 2: What is the role of decomposers in the ecosystem?

Answer: Decomposers, like bacteria and fungi, play a critical role in the ecosystem by breaking down dead plants and animals, as well as organic waste materials. They recycle nutrients back into the soil, making them available for producers like plants. This process helps maintain the nutrient cycle and contributes to soil fertility.


Question 3: Why are some substances biodegradable and some non-biodegradable?

Answer: Substances are biodegradable if they can be broken down by natural processes, mainly by microorganisms, into simpler, non-toxic forms. For instance, food waste, paper, and cotton can decompose and are therefore biodegradable.

Substances are non-biodegradable if they cannot be broken down by natural processes and persist in the environment for long periods. Plastics, metals, and certain synthetic chemicals are examples of non-biodegradable substances. Their chemical structures are resistant to decomposition by microbes.


Question 4: Give any two ways in which biodegradable substances would affect the environment.

Answer:

  1. Nutrient Recycling: Biodegradable substances break down and release essential nutrients back into the soil, which are used by plants to grow, thus supporting the ecosystem’s productivity.
  2. Soil Fertility: The decomposition of biodegradable waste adds organic matter to the soil, enhancing its fertility and helping plants thrive.


Question 5: Give any two ways in which non-biodegradable substances would affect the environment.

Answer:

  1. Pollution: Non-biodegradable substances, like plastics, can accumulate and lead to soil and water pollution, harming wildlife and ecosystems.
  2. Disruption of Food Chains: Non-biodegradable substances can be ingested by animals, leading to bioaccumulation and biomagnification, which harms organisms higher up the food chain, including humans.


Question 6: Define ecosystem.

Answer: An ecosystem is a community of living organisms (plants, animals, and microbes) interacting with each other and with their non-living (abiotic) environment (like air, water, and minerals). An ecosystem can be as large as a forest or as small as a pond. It is self-sustaining, with energy flowing from the sun to producers and then through consumers, with decomposers recycling nutrients.


Question 7: What is the impact of human activities on the environment?

Answer: Human activities, like deforestation, pollution, overuse of natural resources, and industrialisation, negatively impact the environment by:

  1. Pollution: Air, water, and soil pollution from waste, chemicals, and plastics harm biodiversity and human health.
  2. Climate Change: Excessive greenhouse gas emissions from factories, vehicles, and deforestation contribute to global warming, affecting ecosystems globally.
  3. Loss of Biodiversity: Habitat destruction and pollution lead to the loss of plant and animal species, disrupting ecosystems.
  4. Depletion of Natural Resources: Overexploitation of resources such as fossil fuels and freshwater threatens the sustainability of ecosystems.


Question 8: What are food chains and food webs?

Answer:

  • Food Chain: A food chain is a linear sequence that shows how energy and nutrients flow from one organism to another in an ecosystem. For example:

    • Grass → Rabbit → Fox → Eagle

  • Food Web: A food web is a complex network of interconnected food chains in an ecosystem, showing how various organisms are interdependent. It represents the multiple paths through which energy and nutrients move within an ecosystem.


Question 9: Why is it important to manage our waste?

Answer: Managing waste is important to reduce pollution, conserve resources, and protect ecosystems. Proper waste management, like recycling, composting, and reducing plastic use, helps prevent soil, water, and air contamination and reduces the burden on landfills, ultimately preserving the environment for future generations.


Question 10: Suggest some measures for the management of non-biodegradable waste.

Answer:

  1. Recycling and Reusing: Encourage recycling and reuse of materials like plastics, glass, and metals to reduce waste accumulation.
  2. Banning Single-Use Plastics: Reduce single-use plastic items, which are major contributors to non-biodegradable waste.
  3. Promoting Eco-Friendly Materials: Use biodegradable and eco-friendly alternatives for packaging and everyday items.
  4. Waste Segregation: Separate biodegradable and non-biodegradable waste at the source to make recycling more efficient.