FOOD CHAINS AND WEBS
We are an integral part of the environment. Changes in the environment affect us and our activities change the environment around us. We have already seen in Class IX how our activities pollute the environment. In this chapter, we shall be looking at two of the environmental problems in detail, that is, depletion of the ozone layer and waste disposal.
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. 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—
O2 \(\xrightarrow{UV}\) O + O
O + O2 \(\to\) O3
(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, the United Nations Environment Programme (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.
Activity 15.4:
* Find out from the library, internet or newspaper reports, which chemicals are responsible for the depletion of the ozone layer.
* Find out if the regulations put in place to control the emission of these chemicals have succeeded in reducing the damage to the ozone layer. Has the size of the hole in the ozone layer changed in recent years?
Questions:
What is ozone and how does it affect any ecosystem?
Source: This topic is taken from NCERT TEXTBOOK
MANAGING THE GARBAGE WE PRODUCE
In our daily activities, we generate a lot of material that are thrown away. What are some of these waste materials? What happens after we throw them away? Let us perform an activity to find answers to these questions.
Activity 15.5:
* Collect waste material from your homes. This could include all the waste generated during a day, like a kitchen waste (spoilt food, vegetable peels, used tea leaves, milk packets and empty cartons), waste paper, empty medicine bottles/strips/bubble packs, old and torn clothes and broken footwear.
* Bury this material in a pit in the school garden or if there is no space available, you can collect the material in an old bucket/ flower pot and cover with at least 15 cm of soil.
* Keep this material moist and observe at 15-day intervals.
* What are the materials that remain unchanged over long periods of time?
* What are the materials which change their form and structure over time?
* Of these materials that are changed, which ones change the fastest?
We have seen in the chapter on ‘Life Processes’ that the food we eat is digested by various enzymes in our body. Have you ever wondered why the same enzyme does not break-down everything we eat? 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. How many of the substances you buried were 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.
Activity 15.6:
* Use the library or internet to find out more about biodegradable and non-biodegradable substances.
* How long are various non-biodegradable substances expected to last in our environment?
* These days, new types of plastics which are said to be biodegradable are available. Find out more about such materials and whether they do or do not harm the environment
Visit any town or city, and we are sure to find heaps of garbage all over the place. Visit any place of tourist interest and we are sure to find the place littered with empty food wrappers. In the earlier classes, we have talked about the problem of dealing with the garbage that we generate. Let us now look at the problem a bit more deeply.
Activity 15.7:
* Find out what happens to the waste generated at home. Is there a system in place to collect this waste?
* Find out how the local body (panchayat, municipal corporation, resident welfare association) deals with the waste. Are there mechanisms in place to treat the biodegradable and non- biodegradable wastes separately?
* Calculate how much waste is generated at home in a day.
* How much of this waste is biodegradable?
* Calculate how much waste is generated in the classroom in a day.
* How much of this waste is biodegradable?
* Suggest ways of dealing with this waste.
Activity 15.8:
* Find out how the sewage in your locality is treated. Are there mechanisms in place to ensure that local water bodies are not polluted by untreated sewage?
* Find out how the local industries in your locality treat their wastes. Are there mechanisms in place to ensure that the soil and water are not polluted by this waste?
Improvements in our lifestyle 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. What do you think will be the impact of these on our environment?
Disposable cups in trains
If you ask your parents, they will probably remember a time when tea in trains was served in plastic glasses which had to be returned to the vendor. The introduction of disposable cups was hailed as a step forward for reasons of hygiene. No one at that time perhaps thought about the impact caused by the disposal of millions of these cups on a daily basis. Some time back, kulhads, that is, disposable cups made of clay, were suggested as an alternative. But a little thought showed that making these kulhads on a large scale would result in the loss of the fertile top-soil. Now disposable paper-cups are being used. What do you think are the advantages of disposable paper-cups over disposable plastic cups?
Activity 15.9:
* Search the internet or library to find out what hazardous materials have to be dealt with while disposing of electronic items. How would these materials affect the environment?
* Find out how plastics are recycled. Does the recycling process have any impact on the environment?
Questions:
1. Why are some substances biodegradable and some non-biodegradable?
2. Give any two ways in which biodegradable substances would affect the environment.
3. Give any two ways in which non-biodegradable substances would affect the environment.
4. How can you help in reducing the problem of waste disposal? Give any two methods.
Source: This topic is taken from NCERT TEXTBOOK