NCERT Class 10 Science Chapter 15: Our Environment YouTube Lecture Handouts

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NCERT Class 10 Science Chapter 15: Our Environment

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Brain Teasers!

  • 10% energy transfer – chemical energy

  • How much energy is absorbed from sun?

  • Why are cloth bags good over plastic bags?

  • Trophic level, biotic, abiotic

  • We do not clean ponds or lakes, but an aquarium needs to be cleaned. Why?

  • Harmful practices in agricultural land?

  • Cloth bags are:

    1. capable of carrying more things

    2. made of biodegradable material

    3. do not pollute our environment

    4. can be reused

An aquarium is an artificial and incomplete ecosystem in contrast to a pond/lake which are natural, self-sustaining and complete ecosystems.

Harmful practices in agricultural area;

(a) Excessive use of fertilizers changes the chemistry of soil and kills useful microbes.

(b) Excessive use of non-biodegradable chemical pesticides leads to biological magnification.

(c) Extensive cropping causes loss of soil fertility.

(d) Excess use of ground water for agriculture lowers the water table.

(e) Damage to natural ecosystem/habitat.

Ecosystem & Components

  • Ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals

  • Living organisms grow, reproduce and interact and are affected by abiotic components

  • These are natural ecosystems while gardens and crop-fields are humanmade (artificial) ecosystems

  • Aquarium - water, oxygen and food, space, plants – now is self-sustaining (not put animal that would eat others)

Grouping Organisms

  • Producer, Consumer and Decomposer

  • Which organisms can make organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun in the presence of chlorophyll – green plants do photosynthesis

  • The organisms which consume the food produced, either directly from producers or indirectly by feeding on other consumers are the consumers. Consumers can be classed variously as herbivores, carnivores, omnivores and parasites

  • The microorganisms, comprising bacteria and fungi, break-down the dead remains and waste products of organisms. These microorganisms are the decomposers as they break-down the complex organic substances into simple inorganic substances that go into the soil

Food Chain & Food Web

  • Each step or level of the food chain forms a trophic level. The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers. The herbivores or the primary consumers come at the second, small carnivores or the secondary consumers at the third and larger carnivores or the tertiary consumers form the fourth trophic level.

  • Autotrophs capture the energy present in sunlight and convert it into chemical energy

  • When one form of energy is changed to another, some energy is lost to the environment in forms which cannot be used again

  • The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight and convert it into food energy.

  • When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers.

  • 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers

  • Generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers.

  • The length and complexity of food chains vary greatly

  • Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web

Energy Flow

  • Unidirectional - The energy that is captured by the autotrophs does not revert back to the solar input and the energy which passes to the herbivores does not come back to autotrophs

  • The energy available at each trophic level gets diminished progressively due to loss of energy at each level

  • One of the reasons is the use of several pesticides and other chemicals to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants. As these chemicals are not degradable, these get accumulated progressively at each trophic level – known as biological magnification (food grains have pesticide residue and is not removed even by washing)

Ozone Layer

  • Ozone (O3) is a molecule formed by three atoms of oxygen. While O2, which we normally refer to as oxygen, is essential for all aerobic forms of life. Ozone, is a deadly poison. However, at the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun

  • UV rays can lead to skin cancer

  • Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some moleculer oxygen (O2) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone

  • The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. In 1987, UNEP succeeded in forging an agreement to freeze CFC production at 1986 levels. It is now mandatory for all the manufacturing companies to make CFC-free refrigerators throughout the world

Managing Garbage

  • Enzymes are specific in their action, specific enzymes are needed for the break-down of a particular substance

  • That is why we will not get any energy if we try to eat coal! Because of this, many human-made materials like plastics will not be broken down by the action of bacteria or other saprophytes.

  • These materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time.

  • Substances that are broken down by biological processes are said to be biodegradable

  • Substances that are not broken down in this manner are said to be non-biodegradable. These substances may be inert and simply persist in the environment for a long time or may harm the various members of the eco-system

  • Disposable cups in train - Kulhads

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