Cells are fluid filled balloons having an outer membrane. Their fluid spaces contain organelles, enzymes and chemicals. Cells are the smallest entity within a living cell. It is the structural and functional part of all living organisms because this small unit itself contains the identity of the whole organism. So we can say all living like dog, cat, human, horse, insects have multiple cells having multiple specific functions. These cells perform all the biological and metabolically processes which are required for the proper functioning of organisms. 

• They maintain their structure by maintaining the turgor pressure inside the cell. 
• They process their own food, process it into energy and eliminate waste as well. 
• They reproduce continuously by cell division, so that the organism won’t die. For example in humans the life span of RBCs (red blood cells) is of 120 days, so this means after 120 days we should die, but this doesn’t happen because cells keep on dividing simultaneously and maintain their number in our body.