Question

$a.$ Where does all this energy come from for our daily life activities such as absorption, transport, movement, reproduction or even breathing?
$b.$ Where do plants and microorganisms get their energy from?

Answer 1

Aerobic respiration:
The breakdown of organic substances in the presence of oxygen, to produce energy molecules is called aerobic respiration. The substrates used for respiration include various nutrients like proteins, fats and carbohydrates. Thus the energy for all the metabolic activities within the human body comes from aerobic respiration.

Energy in Plants:
In plants the glucose produced during photosynthesis is used as a substrate during respiration to obtain energy.

Energy in microorganisms:
Microorganisms obtain energy by either aerobic or anaerobic respiration depending on their habitat, availability of oxygen.