Our Environment — Notes

An ecosystem consists of all the interacting organisms in an area together with the non-living constituents of the environment. Natural ecosystems: forests, ponds, lakes, grasslands. Artificial ecosystems: gardens, crop fields, aquariums.

Biotic components (living): plants, animals, micro-organisms. Abiotic components (non-living): temperature, rainfall, wind, soil, minerals, water, sunlight.

• Producers — green plants and certain bacteria that make food from simple inorganic substances using sunlight (photosynthesis).
• Consumers — depend on producers directly or indirectly: herbivores (cow), carnivores (tiger), omnivores (crow, humans), parasites (tapeworm, Cuscuta).
• Decomposers — bacteria and fungi that break down dead remains and wastes; they convert complex organic substances into simple inorganic ones that return to the soil and are used again by plants (replenishing the soil, recycling nutrients).

A food chain is a series of organisms each feeding on the one before it, e.g. grass → grasshopper → frog → snake → eagle. Each step is a trophic level: producers (1st), herbivores or primary consumers (2nd), carnivores or secondary consumers (3rd), large carnivores or tertiary consumers (4th). Arrows point from food to feeder — the direction of energy flow. Interconnected food chains form a food web, which makes an ecosystem more stable.

Energy flow:

• Green plants capture about 1% of the sunlight falling on their leaves.
• 10 percent law: only about 10% of the energy at one level is passed on to the next; the rest is used in life processes and lost, mostly as heat.
• So food chains usually have only 3 or 4 trophic levels, there are fewer organisms at higher levels, and energy flow is unidirectional — it never returns to the producers.
• Energy at level $n$ (from $E_1$ at the producers): $E_n = E_1 \times (0.1)^{n-1}$.

Biological magnification: non-biodegradable chemicals (some pesticides) are not broken down or excreted; they accumulate and their concentration increases at each trophic level. Humans, at the top of many food chains, can accumulate the most.

Ozone ($\ce{O3}$) is a molecule of three oxygen atoms. In the upper atmosphere it shields the Earth from the Sun’s harmful ultraviolet (UV) radiation; at ground level it is a deadly poison.

Formation: UV radiation splits oxygen molecules, $\ce{O2 ->[UV] O + O}$; the free atoms combine with oxygen molecules, $\ce{O + O2 -> O3}$.

Depletion: the amount of ozone began to fall sharply in the 1980s, mainly because of synthetic chlorofluorocarbons (CFCs) used as refrigerants and in fire extinguishers. A thinner layer lets more UV reach the Earth, which can cause skin cancer in human beings and harm other organisms.

Action: in 1987 the United Nations Environment Programme (UNEP) forged an agreement to freeze CFC production at 1986 levels; it is now compulsory to make CFC-free refrigerators.

Substances broken down by biological processes (bacteria, fungi and other saprophytes, using specific enzymes) are biodegradable; those not broken down are non-biodegradable. Non-biodegradable substances are inert, persist for a long time and can harm the various members of an ecosystem — plastics swallowed by animals, drains blocked by polythene, pesticides magnified in food chains.

What we can do:

• Segregate waste at source: wet (biodegradable) and dry (non-biodegradable) bins.
• Compost kitchen and garden waste.
• Reduce (cloth bags, avoid single-use plastic), reuse (glass jars, steel plates), recycle (paper, glass, metal, some plastics).
• Do not burn plastics or dump waste in water bodies.