Food is a vital necessity for all the humans and animals to live.
It is also true that we all of us strive everyday to achieve our food.
But why food is necessary? and why do we feel hunger?
We feel the hunger because it is a bodies call to replenish or restore the reserve food. The food inside the body as is used for supply of energy. So what we ate previously gives us energy now and what we eat now gives us energy in the next requirement of the body.
But body has a very alert mechanism to use the food resources very scarcely. This helps us survive in times of lack of food.
When we eat food, it releases into the blood the reserve supply of glucose from the liver. This glucose is carried by blood to provide instant energy to the body. But in case we don’t have food, it releases very scarcely and hence we feel weak and lethargic.
It is well described in biochemistry,
1. Food breaks down to glucose, amino acids and fats.
2. The Glucose molecules breaks down to produce ATP
This ATP (Adenosine triphosphate is the end energy molecule).
There are many intermediary steps in between glucose and ATP formation but they are outlined shortly at the bottom.
We will concentrate on basics of how this energy is formed only here.
Glucose is a carbohydrate (CH2O), which means it has carbon (C), hydrogen (H) and Oxygen (O) in the structure. This structure is formed in the plants due to photosynthesis.
This photosynthesis is a process happening in the green leaves under the influence of sunlight. The energy from sunlight is captured to form carbohydrate by use of carbon-dioxide (CO2) and water (H2O).
So in other words we can say that the energy from sun is captured in carbohydrate form. When we eat these carbohydrates in the form of sugar, starch (potato) etc, this energy is released into the body cells. The glucose molecule is broken down in cell to smaller forms. These are then converted by mitochondria (one of the cell organelles) into energy (ATP). During this conversion, the carbohydrate molecules is broken down back into carbon-dioxide (CO2) and water (H2O).
So we breath out the above released CO2 by lungs and water is excreted by urine.
On the contrary, the plants breath in CO2 by leaves and absorb water by roots to form these carbohydrates.
Thus energy from sunlight is taken by plants and given to us. In this process CO2 and H2O are involved as principle intermediates.
Let’s see the procedure in detail:
a) Food we eat consists of carbohydrate, proteins, fats etc. This gets digested in the gut to glucose, amino-acids and fatty acids respectively.
b) Glucose is stored in liver as glycogen while amino acids help in building protein and fatty acids get stored.
c) In case of need, glycogen in liver breaks down to glucose and is released into blood.
d) This glucose in the blood is absorbed into every tissue and the cells by the help of Insulin.
e) Inside the cell, glucose breaks down into two molecules of acetyl-CoA.
f) These Acetyl-coA molecules enter into mitochondria and undergo a process called KREB’s cycle.
g) There each acetyl-coA produces 2 more molecules of ATP by breaking down to water (H2O) & carbon dioxide (CO2).
h) This ATP acts as energy and fuels all the body movements, processes and also biochemical reactions reactions.
Thus food is converted to energy in our body by breakdown of glucose from food. This happens in presence of oxygen inside the mitochondria. So mitochondria are call power houses of our body cells.
So for production of energy we require oxygen from lungs besides food. Oxygen is needed on immediate basis and continuously while glucose is produced even from the reserve supply.
Also See: How Energy is used in the body.
Interestingly, in case of starvation, fatty acids stored convert to acetyl-coA to produce energy and aminoacids also breakdown to produce actyl-CoA to produce energy. Hence a starving person looks lean and loses his weight as the reserve substances are consumed out to produce energy.