6. LIFE PROCESSES
Organisms show many properties such as movement (growth-related or not). But the visible movement is not a defining characteristic of life because a plant may not grow visibly and some animals can breathe without visible movement.
Viruses do not show any molecular movement in them until they infect some cells.
Living organisms are well-organised structures having tissues, cells, cell organelles etc.
Due to the effects of the environment, living structures may be broken down and dead. So they must be repaired.
Since these structures are made up of molecules, they must always move molecules around.
Life processes are all the maintenance processes to prevent damage and break-down of the body of an organism. E.g. nutrition, respiration, excretion, growth etc.
For this, energy is needed from the outside. This energy source is called food.
Since life depends on carbon-based molecules, most of the food sources are carbon-based.
Foods are broken down or built up in the body. They are finally converted to a uniform source of energy (for molecular movements) & molecules for growth and development.
Oxidising-reducing reactions are some of the most common chemical means to break down molecules. For this, many organisms use oxygen.
In cells, various chemical reactions create useless and harmful by-products. These are removed from the body by a process called excretion.
In unicellular organisms, the entire surface is in contact with the environment. So, no specific organs are needed for food intake, gas exchange or removal of wastes.
In multicellular organisms, all cells are not in contact with the environment. So, simple diffusion will not meet the requirements of all the cells. That’s why they have specialised body parts to perform various functions.
A transportation system is needed to carry food & oxygen to all body parts and waste products from tissues to excretory system.