Crossing over is a process that happens between homologous chromosomes in order to increase genetic diversity. During crossing over, part of one chromosome is exchanged with another. The result is a hybrid chromosome with a unique pattern of genetic material.
B. an atom
Atoms are the basic units of matter and the defining structure of elements.
A tropism.
A plant movement to a light stimulus is a phototropism.
A plant movement to water stimuli is a hydrotropism.
etc. etc. :)
