We can learn many things about yoga from a cell.
The cell is the building block for all life. Each cell is made up of a membrane, cytoplasm and a nucleus. Through the membrane each cell gets its nutrients and releases its waste. The membrane is permeable but it must be in balance; otherwise toxicity or starvation will result. If a cell’s membrane is too permeable it loses integrity which will cause it to explode from pressures within or implode from pressures without.
Yoga is 90% waste removal. ~TKV Desikachar
Prana refers to what nourishes a living thing. It is also understood to mean the action of bringing nourishment in (ex. breathing).
Apana refers to waste that is being eliminated and the act of elimination.
Yoga is akin to Tao in that there exists a way that is in flow.
We practice getting rid of all that is unnecessary and blocks our natural flow. We practice this in stance (how we move and are still), in heart, in thought, and deed.
Kaminoff, Leslie, and Amy Matthews. Yoga Anatomy. Champaign: Human Kinetics, 2012. Print.