Question

Circle the odd one out. Give reasons for your choice.

respiration, photosynthesis, combustion, decay of dead plants and animals.

Answer 1

The decay of dead plants and animals is the odd one out.

Reasons - The process of decomposition does not involve any gases and is carried out by microorganisms.

The process of respiration, combustion, and photosynthesis either release or absorb oxygen gas.

• Combustion - The process of reaction of oxygen with a substance(fuel) which results in the release of heat and light is called combustion.
• Respiration - The process by which organisms get energy by the conversion of glucose in the presence of oxygen into carbon dioxide and water vapour.

$\mathrm{Glucose}\left(\mathrm{s}\right)+\mathrm{Oxygen}\left(\mathrm{g}\right)\to \mathrm{Carbon}\mathrm{dioxide}\left(\mathrm{g}\right)+\mathrm{Water}\mathrm{vapour}\left(\mathrm{g}\right)+\mathrm{Energy}$

• Photosynthesis- The process by which plants use carbon dioxide and water in presence of sunlight to form sugar(carbohydrate) and oxygen.

$\mathrm{Carbon}\mathrm{dioxide}\left(\mathrm{g}\right)+\mathrm{Water}\left(\mathrm{l}\right)\stackrel{\mathrm{sunlight}}{\to }\mathrm{Glucose}\left(\mathrm{s}\right)+\mathrm{Oxygen}\left(\mathrm{g}\right)$