Where do spindle fibers attach to guide and separate chromosomes?

kinetochore
Spindle fibers  are aggregates of micro-tubules that move chromosomes during cell division. They attach to the kinetochore, a structure on chromatids, that when it's pulled separated sister chromatids. The kinetochore is a specialized protein complex found in the centromere of the chromosome.

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.

The principle of independent assortment describee how different genes independently separate from one another when reproductive cells develop.