CBSE Guess > Papers > Question Papers > Class X > 2009 > Science > Science
Q. 23. Name the major component of biogas. List two main advantages of using biogas over fossil fuels. 2
Ans. The major constituent of biogas is methane.
Advantages of biogas over fossil fuels:
(i) Biogas burns without smoke and hence does not cause air pollution.
(ii) Biogas burns completely without leaving behind any residue. So, it is
a clean fuel.
Q. 24. How is ozone formed in the upper atmosphere? Why is the damage of ozone layer a cause of concern to us? State a cause of this damage. 2
Ans. Ozone is formed high up in the atmosphere by the action of ultraviolet
radiation on oxygen gas by the following process:
Step 1. The high energy UV radiation running from the sun splits oxygen
gas into free oxygen atoms
Step 2. The free oxygen atoms thus produced are very reactive. One oxygen atom reacts with an oxygen molecule to form an ozone molecule.
This layer of ozone prevents the entry of harmful UV radiation to the earth’s surface, hence the damage to ozone layer is a cause of great concern to the mankind.
Chlorofluorocarbons (CFCs), which are used in refrigerants, deodrandts and in fire extinguishers, are one of the major causes of depletion of ozone layer.
Q. 25. Distinguish between acquired and inherited traits giving one example of each. Why are traits acquired during the lifetime of an individual not inherited?
Ans .
| Acquired traits | Inherited traits |
| 1) A trait (or characteristic) of n organism which is ‘not inherited’ but develops in response to the environment is called an aquired trait. | 1) A trait (or characteristic) of an organism which is caused by a change in its genes (or DNA) is called an inherited trait. |
| (2) The acquired traits of an organism can not be passed on to its future generations. e.g. ‘low weight’ of beetle, ‘cut tail’ of a mouse. | 2) The inherited traits of an organism are passed on to its future generations. e.g. red colour of beetles, fur coat of guinea pigs. |
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