The Living World
Biology is the science of life forms and living processes.
All living organisms — present, past and future, are linked to one another by the sharing of common genetic material, but to varying degrees.
What is Living?
When we try to define 'living', we look for distinctive characteristics exhibited by living organisms. We can list these as Growth, Reproduction, Metabolism, Cellular Organization, and Consciousness.
What is Biology?
It is the "Story of Life on Earth" and the "Story of Evolution of Living Organisms on Earth".
Characteristics of Living Beings
Differentiating between Absolute and General Properties.
1. Growth
Increase in mass and number. Non-living objects like mountains also grow (by accumulation), so it is not a defining property.
2. Reproduction
Production of progeny. Some organisms (mules, sterile worker bees) cannot reproduce, so it is not a defining property of all life.
3. Metabolism
Sum total of all chemical reactions. No non-living object exhibits metabolism. It is an absolute defining feature.
4. Consciousness
Ability to sense surroundings and respond to stimuli. This is the most technically complicated and defining feature of life.
Key Exam Point
Cellular Organization is also a defining property because all living organisms are made of cells.