CLASS 10 Science
CHAPTER 15
Our Environment (NCERT Notes)
Substances that are broken down by biological processes are said to be biodegradable. For example vegetable waste, manure etc.
Substances that are not broken down by biological processes are said to be non-biodegradable. For example 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.
ECO-SYSTEM — WHAT ARE ITS COMPONENTS?
All organisms such as plants, animals, microorganisms and human beings as well as the physical surroundings interact with each other and maintain a balance in nature. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.
An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals. Example of ecosystems are forests, ponds and lakes. These are natural ecosystems while gardens and an aquarium ,crop-fields are human- made (artificial) ecosystems.
Organisms can be grouped as producers, consumers and decomposers according to the manner in
which they obtain their sustenance from the environment.
All green plants and certain blue-green algae which can produce food by photosynthesis come under this category and are called the producers.
Organisms depend on the producers either directly or indirectly for their sustenance. These 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 and are used up once more by the plants.
Food Chains and Webs
A series of organisms feeding on one another. This series or organisms taking part at various biotic levels form a food chain.
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.
The interactions among various components of the environment involves flow of energy from one component of the system to another. The autotrophs capture the energy present in sunlight and
convert it into chemical energy. This energy supports all the activities of the living world. When one form of energy is changed to another, some energy is lost to the environment in forms which cannot be used again.
The flow of energy between various components of the environment: –
The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves 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.
Therefore, 10% can be taken as the average value for the amount of organic matter that is present at each step an reaches the next level of consumers.
Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.
There are 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.
The energy flow diagram states that:-
The flow of energy is 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. As it moves progressively through the various trophic levels it is no longer available to the previous level.
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 and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies. This phenomenon is known as biological magnification.
Ozone Layer and How it is Getting Depleted
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. 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. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.
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 molecular oxygen (O2) into free oxygen (O)atoms. These atoms then combine with the molecular oxygen to form ozone as shown—
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, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.
Managing the Garbage we Produce Improvements in our life-style have resulted in greater amounts of waste material generation. Changes in attitude also have a role to play, with more and more things we use becoming disposable. Changes in packaging have resulted in much of our waste becoming non-biodegradable.
( From NCERT Book )