Ch 13Our Environment

Chapter 13: Our Environment

1. Ecosystem and its Components

An ecosystem is a self-contained unit of nature where all living organisms (plants, animals, microorganisms) interact among themselves and with the non-living physical factors of the environment. Examples of natural ecosystems are forests, ponds and lakes; examples of artificial (man-made) ecosystems are gardens, crop fields and aquariums.

An ecosystem has two components:

• Biotic components — all living organisms (producers, consumers, decomposers).
• Abiotic components — non-living physical factors such as air, water, soil, temperature, light and humidity.

2. Biotic Components in Detail

• Producers (autotrophs): green plants and blue-green algae that make their own food from inorganic substances using sunlight through photosynthesis. They trap solar energy and form the base of every food chain.
• Consumers (heterotrophs): organisms that depend on producers directly or indirectly for food.
  • Herbivores (primary consumers) — eat plants, e.g. deer, goat, grasshopper.
  • Carnivores (secondary/tertiary consumers) — eat other animals, e.g. lion, frog, snake.
  • Omnivores — eat both plants and animals, e.g. humans, crow.
  • Parasites — live on/in a host, e.g. lice, Cuscuta.
• Decomposers: microorganisms such as bacteria and fungi that break down dead remains and waste products of organisms into simple inorganic substances. They replenish soil nutrients and are called nature's cleaners / scavengers.

3. Food Chains and Food Webs

A food chain is a series of organisms feeding on one another, showing the flow of food energy from one organism to the next. Each step or level of the food chain is called a trophic level.

A food web is a network of many interconnected food chains, since one organism may be eaten by several others and may itself feed on several kinds of food.

4. Flow of Energy — the 10% Law

The flow of energy in an ecosystem is unidirectional (one-way). Green plants capture only about 1% of the sunlight falling on their leaves and convert it into food energy.

According to the Ten Per Cent Law (given by Lindeman), only about 10% of the energy entering a trophic level is passed on to the next trophic level; the remaining 90% is lost as heat, used in life processes (respiration, movement) or remains undigested.

Biological magnification (biomagnification): Harmful chemicals such as pesticides enter food chains. Since these chemicals are not degradable, their concentration increases at each successive trophic level. As humans occupy the top of most food chains, the maximum concentration of such chemicals accumulates in our bodies.

5. Biodegradable and Non-biodegradable Substances

Both types of waste affect the environment: biodegradable waste can produce foul smell and disease-carrying organisms if it accumulates, while non-biodegradable waste chokes drains, harms wildlife and enters food chains.

6. The Ozone Layer

Ozone (O₃) is a molecule made of three oxygen atoms. High up in the atmosphere (stratosphere), ozone forms a protective layer that absorbs harmful ultraviolet (UV) radiation coming from the Sun. UV rays can cause skin cancer, cataract and damage to crops.

Ozone is formed when high-energy UV radiation splits O₂ molecules into free oxygen atoms, which then combine with O₂:

Depletion of ozone: Man-made chemicals called chlorofluorocarbons (CFCs), used in refrigerators and fire extinguishers, break down ozone and cause a decrease in the ozone layer (the "ozone hole"). In 1987, the UNEP succeeded in getting many countries to sign an agreement (the Montreal Protocol) to freeze and reduce CFC production.

7. Managing the Garbage We Produce

The huge amount of waste we generate must be disposed of properly. Common methods include:

• Recycling of paper, glass, metals and plastics.
• Preparing compost from biodegradable kitchen and garden waste.
• Sewage treatment before releasing water into rivers.
• Segregation of waste into biodegradable and non-biodegradable before disposal.