CBSE Guess > Papers > Question Papers > Class X > 2008 >Science > Science Theory

Q. 20. Explain the terms analogous and homologous organs with one example of each.

Ans.

• Analogous organs : Those organs which have different basic structure but have similar appearance and perform similar functions are called analogous organs.
  e.g. → the wings of an insect and bird have different structures but perform the same function of flying.
• Homologous organs : Those organs which have the same basic structure but different functions are called homologous organs.
  e.g. → the forelimbs of man, a lizard, a frog, a bird and a bat seem to be built from the same basic design of bones but they perform different functions. The forelimbs of a human are used for grasping, the forelimbs of a lizard are used for running, the forelimbs of a bird and a bat are used for flying.

Ans. (a) Ozone is formed high up in the atmosphere by the action of ultraviolet radiation on oxygen gas. The high energy ultraviolet radiation coming from the sun splits oxygen gas into free oxygen atoms.

The free oxygen thus produced reacts with an oxygen molecule to form an ozone molecule.

O₂ + O = O₃

Ozone

(b) The depletion of Ozone layer is due to the use of chemicals called chloro fluoro carbons (CFC).

Q. 21. Study the following diagram :

Name the parts labelled ‘A’ and ‘B’ and state one function of each.

Ans. A → Stomatal pore Function :
• Massive amounts of gaseous exchange takes place in the leaves through these pores for the purpose of photosynthesis.
B → Guard Cell
• The opening and closing of the stomatal pore is a function of the guard cells.

Science 2008 Question Papers Class X
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