Monday 21 November 2011

CBSE - Class 10 - Biology - Chapter 15 - Our Environment

Chapter: Our Environment

Q1: Define Ecology

Answer: Ecology is a scientific study of the interactions between organisms and the environment. Ecology integrates all areas of biological research and  informs environmental decision.

Q2: What is the scope of Ecology Research?

Answer: Ecology study can be broadly classified as:
           a. Organismal Ecology
           b. Population Ecology
           c. Community Ecology
           d. Ecosystem Ecology
           e. Landscape Ecology
           f. Global Ecology

In nutshell, Ecology study advocates protection of nature and the environment.

Q3: Define Ecosystem.

Answer: An environment comprises of all living (biotic) and non-living (abiotic) things that occur naturally on the Earth or any of its region. All these living organisms interact with each other and their growth, reproduction and other activities are affected by the abiotic components of ecosystem.

Q4: Is garden an example of Ecosystem?

Answer: Yes. In an garden, all biotic components (e.g. plants, trees, animals like rats, frogs, birds, insects etc.) interact with each other and with abiotic components (garden soil, water etc.) for their growth and reproduction and other activities. Thus garden forms an ecosystem.

Q5: Give examples of natural ecosystems.

Answer: Forests, ponds, lakes, sea, oceans, coral reefs, rivers etc.

Q6: Give examples of human made (artificial )ecosystems.

Answer: Gardens, Crop-fields etc.

Q7: Name different abiotic factors that affect the ecosystem.

Answer: Temperature, water, sunlight, salinity, rocks, soil, precipitation and wind.

Q8: What do you mean by biogeochemical cycle? Name examples of biogeochemical cycles exist in ecosystem.

Answer: A biogeochemical cycle is a pathway by which a chemical element or molecule moves through both biotic and abiotic compartments of Earth. These are critical to life and hence for the ecosystem sustenance. A few examples of the biogeochemical cycles are:
  • Nitrogen Cycle
  • Water Cycle
  • Carbon Cycle
  • Oxygen Cycle
  • Phosphorus Cycle
Q9: What do you mean by biosphere?

Answer: Biosphere is the area on the earth where life exists. It includes about 20 kilometers upwards in the atmosphere and 11 kilometer downwards. In the Biosphere different plants and animals are present. This diversity of life is an important characteristic of earth.

Q10: Define food chain.

Answer: The pathway of transfer of food from one trophic level to another is known as food chain.

Q11: What are trophic levels?

Answer: Trophic levels are the feeding levels in an ecosystem. The trophic levels of living beings represent their placement in a food chain. It also tells the order of consumption and energy transfer throughout the ecosystem (or environment).
In general 4 or 5 trophic levels exist in a food chain. These are:

Producers or Autotrophs:  Producers make up the first trophic levels that supports the other trophic levels. It consists mainly of green plants and certain types green algae and some types of bacteria. They convert solar energy (photosynthesis) into food consumable by other organisms.

Primary Consumers: These are the consumers which feed upon producers. In general these are herbivores. Examples are horse, cow, deer, insects, zoo planktons (shrimps, protists etc.) and birds.

Secondary Consumers: Secodnary or second level consumers eat primary consumers. In general these are omnivores and carnivores. On land, secondary consumers cover many small mammals and reptiles that eat insects, as well as large carnivores that eat rodents and grazing mammals. In aquatic ecosystems, secondary consumers are mainly small fish that eat plankton.

Tertiary Consumers: These are third level consumers which feed on secondary consumers.  E.g. snakes eating rodents, Lion, bear etc.

Quanternary Consumers: Fourth level consumers are defined in a few food chains. E.g. hawks eating owls or snakes.
All food chains end up with top predators, animals having little or no natural enemy.

Q12: Define Dertivores

Answer: Dertivores or Decomposers are the consumers that get energy from dead organic matter (detritus). Important groups of dertivores are prokaryotes and fungi. These organisms secrete enzymes to digest organic matter. They link the consumers and primary producers of an ecosystem.

Q13: Explain energy relationship with trophic levels.

Answer: The energy relationship within trophic levels can be represented in a form of the pyramid as shown in the figure. Following conclusions are arrived:
a. In a biosphere, energy transfer takes place only through food chains.

b. Each food chain can be considered as an energy chain.

c. The energy that is captured by the autotrophs does not revert back to the solar input and the energy which passes to the herbivores does not come back to autotrophs. As it moves progressively through the various trophic levels it is no longer available to the previous level.

d. Plants utilize only 50% of the total available energy for their life processes. But each of the trophic levels utilizes 90% of their available energy for their metabolic activities. Remaining 10% of the energy alone is transferred to the next trophic level. This is the reason long food chains are not commonly seen in nature.

Q14: Explicate the principle of the food web.

Answer: Each organism is generally eaten by two or more other kinds of organisms which in turn are
eaten by several other organisms. So instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web.

Q15: Define biological magnification.

Answer. It means the accumulation of poisonous materials in successive trophic levels in a food chain.  This happens when a toxin is ingested or eaten and moved up the food chain from one organism to another organism. As it moves up the food chain the toxin levels gets magnified or more concentrated. DDT is one example of a harmful substance that has contaminated food chains.

Q16: Explain Ozone depletion and its impact on our environment?
Ozone Depletion at Antartica

Answer: Life on the Earth is protected from the damaging Ultra-violet radiation by a layer of ozone molecules $(O_3)$ The amount of ozone began to drop sharply in 1980. This decrease has been linked to synthetic chemicals like chrolo-fluorocarbons (CFCs) which are used in refrigerants and in a fire extinguisher.

1. UV radiation causes a Chlorine atom to break away from CFC molecule.

2. The free chlorine atoms hits on ozone molecule and pulls away one oxygen atom from it.

3. A free oxygen atom hits the chlorine monoxide molecule which results another chlorine atom.
4. In this way, free chlorine will continue to deplete ozone in the stratosphere.  One Chlorine atom can destroy more than 100,000 ozone molecules before it is removed from the stratosphere.

Decrease ozone levels in stratosphere increase the intensity of UV radiation. Its consequences can be very harmful and may lead to an increase in skin cancers and cataracts among humans. UV radiation are also harmful to crops and other primary producers and may lead to unpredictable results.