Diatoms have cell walls composed of
a. silicon dioxide
b. carbon dioxide
c. chitin

A. Silicon dioxide

Diatoms are unicellular algae that are found in the freshwater, brackish and marine water. These organisms exhibit cell wall that are made up of silica that is hydrated silicon dioxide. This type of cell wall is called as frustule. The cell wall is divided into two valves called as thecae.

•there must be variation for the particular trait within a population.

•the variation must be inheritable (that is, it must be capable of being passed on from the parents to their offspring).

•individuals with one version of the trait must produce more offspring than those with a different version of the trait.good

explanation:

not only is it colder, it also becomes darker, less salty, and more dense.