Our Environment

1. Ecosystems

An ecosystem is a complex system which consists of all the living organisms and the non-living constituents of an area.

These may include:

• Biotic components, comprising living organisms
• Abiotic components, including physical factors like
  • temperature
  • rainfall
  • wind
  • soil

1.1 Examples of Ecosystems

Take a pond for example. A variety of animals and plants (biotic components) can be found in and around a pond. These living beings are dependent on each other as well as the surrounding water, air and soil (abiotic components). Therefore the area in and around a pond forms an ecosystem.

Other examples of ecosystems include:

• Forests
• Grasslands
• Lakes
• Large animals (including human beings)

1.2 Producers, Consumers and Decomposers

According to the manner in which they obtain sustenance from the environment, organisms can be classified into Producers, Consumers and Decomposers.

Producers

Producers are the living organisms that create organic “food” (like starch and sugars) from inorganic materials, like sunlight.
All green plants and certain bacteria fall into this category.

Consumers

Consumers either consume food produced by Producers or they eat other Consumers.
All animals are Consumers.
Consumers are classified into three categories:

• Herbivores: eat Producers (e.g. cows, sheep)
• Carnivores: eat Consumers (e.g. lions, tigers, cats)
• Omnivores: eat both Consumers and Producers (e.g. human beings, dogs)

Decomposers

Decomposers eat and break down waste products and remains of dead organisms. These broken down components go to the soil and are used up by plants.
Most fungi and bacteria fall into this category.

1.3 Food Chains and Webs

In simple terms, a food chain is just a large chain showing who eats whom.

1.3.1 Trophic levels

Each step or level of a food chain forms a trophic level.

• 1st trophic level: Producers or autotrophs (mostly plants)
• 2nd trophic level: Primary Consumers or herbivores (cows, sheep)
• 3rd trophic level: Secondary Consumers or small carnivores (insects and fish and small carnivorous mammals)
• 4th trophic level: Tertiary Consumers or large carnivores (lions, tigers, sharks)

1.3.2 Some important points to remember

• There are usually a higher number of organisms on lower trophic levels.
• Flow of energy in a food chain is unidirectional, e.g. the energy passed to a cow does not go back to the plant.

1.3.3 Biological Magnification

• Some harmful chamicals make their way through the food chain. For example, pesticides and other chemical wash down into the soil, get absorbed by the plants, and finally make their way into the human body.
• These chemicals are non-biodegradable and therefore get progressively concentrated as they make they way up the food chain.
• Since humans are on the top of any food chain, we receive the maximum concentration of these chemicals.
• This phenomenon is called Biological Magnification.

2. Human activities and their effect on the environment

2.1 Ozone layer depletion

2.1.1 Ozone

• Ozone (O₃) is a triatomic molecule of oxygen.
• It is the deadly and poisonous counterpart of oxygen. (Pro life tip: Don’t breathe in too much ozone)
• Although it is poisonous and deadly, ozone performs the essential function of shielding Earth’s surface from UV radiation, which is highly damaging to organisms and causes skin cancer in humans.

Formation of Ozone

High-energy UV radiation splits apart oxygen atoms into two… $$\ce{O2 ->[UV] O + O}$$ … which combine with molecular oxygen to form ozone. $$\ce{O + O2 -> O3} (Ozone)$$

2.1.2 Ozone depletion

• In the 1980s, atmospheric ozone began to drop sharply.
• This was linked to the production of synthetic chemicals like chlorofluorocarbons (CFCs).
• CFCs were used in fire extinguishers and as refrigerants.
• In 1987, the UNEP (United Nations Environment Programme) successfully forged an agreement to freeze CFC prduction at 1986 levels.
• It is now mandatory to make CFC-free refrigerators throughout the world.

Glossary

autotroph: an organism that can produce its own food using inorganic substances like sunlight and carbon dioxide.