<span>Certainly. Every organism has a variety of different characteristics. One person writing a key might choose to use different characteristics than another person would use.
For example: Here's a key for separating fish, snake, frog and mouse
1.
A. Has scales on its skin ... 2
B. Has no scales on its skin ... 3
2.
A. Breathes with gills - fish
B. Breathes with lungs - snake
3.
A. Has hair or fur - mouse
B. Has no hair or fur - frog
Here's a different key for the same four animals:
1.
A. Has four legs ... 2
B. Does not have 4 legs ... 3
2.
A. is warm-blooded - mouse
B. is cold-blooded - frog
3.
A. has fins - fish
B. has no fins - snake</span>
Cells that have no mitochondria are unable to convert oxygen into energy, found in the form of adenosine triphosphate (ATP). All multicellular eukaryotic organisms, including plants and animals, have mitochondria in some cells, but prokaryotes and some single-cell eukaryotes do not have mitochondria.
Natural selection<span> is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations.</span>
It has not. Evolution is not a process that can happen to individual organisms; it's change that happens to a species over many generations.
