Class 10 Science Notes Chapter 13 — Our Environment#

Ecosystem#

  • Ecosystem — all the living organisms in an area, together with the non-living parts of their environment, interacting with each other.
    • Biotic components: plants, animals, microorganisms.
    • Abiotic components: temperature, rainfall, wind, soil, minerals.
  • Natural ecosystems: forests, ponds, lakes. Human-made (artificial) ecosystems: gardens, crop fields, an aquarium.
Component Role Examples
Producers Make food from sunlight by photosynthesis (autotrophs) Green plants, blue-green algae
Consumers Eat producers or other consumers Herbivores, carnivores, omnivores, parasites
Decomposers Break down dead remains and waste into simple substances, returning nutrients to the soil Bacteria and fungi

Without decomposers, dead matter would pile up and nutrients would never return to the soil.

Food chains and food webs#

  • Food chain — a series of organisms, each eating the one before it. Example: grass → deer → lion; grass → grasshopper → frog → snake → eagle.

    GrassProducerGrasshopperHerbivoreFrogCarnivoreSnakeCarnivoreEagleTop carnivore
    A food chain. The arrows show the direction in which food (energy) moves.

  • Trophic level — each step of a food chain.

Trophic level Organisms
1st Producers
2nd Primary consumers (herbivores)
3rd Secondary consumers (small carnivores)
4th Tertiary consumers (large carnivores)
  • Food web — many food chains linked together. It is more common in nature than a single chain, since most organisms eat more than one kind of food.

Flow of energy#

  • Green plants capture only about 1% of the sunlight falling on their leaves.
  • 10% law: on average only 10% of the food eaten at one level becomes body mass and is available to the next level. The rest is lost mostly as heat, or used in digestion and work.
  • So food chains usually have only 3 or 4 trophic levels, and producers are the most numerous.
  • Energy flow is one-way (unidirectional). Energy that passes to a higher level never returns to the lower level, and the energy available decreases at each level.
Producers1000 JHerbivores100 JCarnivores10 JTop carnivores1 J10% passesto the next level90% lostmostly as heat
The 10% law: energy available falls at each trophic level, so food chains have only 3 or 4 levels.

Biological magnification#

  • Pesticides and other chemicals reach the soil and water, are absorbed by plants and aquatic organisms, and so enter the food chain.
  • These chemicals are not degradable, so they build up at each trophic level.
  • Biological magnification — the increase in concentration of harmful chemicals at higher trophic levels. Humans, at the top of food chains, get the highest concentration.
  • Pesticide residues are found in grains, vegetables, fruits and meat, and cannot always be washed off.

Ozone layer#

  • Ozone (O₃) is a molecule of three oxygen atoms. At ground level it is a deadly poison, but in the upper atmosphere it shields the earth from the sun’s UV radiation, which causes skin cancer.
  • Ozone is formed when UV radiation splits oxygen molecules: $$\text{O}_2 \xrightarrow{\text{UV}} \text{O} + \text{O}$$ $$\text{O} + \text{O}_2 \rightarrow \text{O}_3$$
  • Ozone levels began to drop sharply in the 1980s, mainly because of CFCs (chlorofluorocarbons), used as refrigerants and in fire extinguishers.
  • In 1987, UNEP (United Nations Environment Programme) got an agreement to freeze CFC production at 1986 levels. Refrigerators must now be CFC-free.

Managing garbage#

Biodegradable Non-biodegradable
Broken down by bacteria and other decomposers Not broken down by biological processes
Kitchen waste, paper, cotton, wood, leather Plastics, glass, metal cans, some chemicals (DDT)
Does not stay long; forms manure Stays in the environment and harms ecosystems
  • Ways to manage waste: reduce, reuse, recycle; composting of biodegradable waste; segregating waste; landfills; recycling plastic, paper and metal.
  • Changes in packaging create more waste. Disposable plastic cups on trains replaced kulhads (clay cups); kulhads were stopped because making them in large numbers would waste fertile topsoil. Disposable paper cups are a better option, since they are biodegradable.

Common mistakes#

  • Saying 10% of energy is lost at each level. 10% is passed on; about 90% is lost.
  • Saying producers have the most chemicals in biological magnification. The top consumers have the most.
  • Saying ozone is useful everywhere. At ground level it is poisonous.
  • Saying energy flow is cyclic. It is one-way; nutrients are recycled, energy is not.

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