The process of passing genetic material from one generation to the next depends completely on how cells grow and divide. To reproduce, a simple organism such as bacteria or yeast simply copies its DNA (through a process called replication) and splits in two. But organisms that reproduce sexually go through a complicated dance that includes mixing and matching strands of DNA (a process called recombination) and then reducing the amount of DNA in special sex cells to arrive at completely new genetic combinations for their offspring.
There are two basic kinds of organisms — ones with a nucleus and those without a nucleus (a compartment filled with DNA surrounded by a membrane called a nuclear envelope):
<span>Prokaryotes: Organisms whose cells lack a nucleus and therefore have DNA floating loosely in the liquid center of the cell. Prokaryotes divide, and thus reproduce, by simple mitosis.</span><span>Eukaryotes: Organisms that have a well-defined nucleus to house and protect the DNA. Eukaryotes divide by meiosis for sexual reproduction.</span>
An isolated colony on a selective medium is not considered a pure culture because inhibited organisms might be masked by the colonies. This statement is true.
On the basis of their constitution or usage, culture media can be classified into various groups; these include defined, complex, selective, as well as enrichment medium.
A selective medium consists of dyes or noxious substances/chemicals which inhibit the growth of specific microorganisms but promote the growth of other microbes.
A pure culture is a laboratory culture which contains a single species of microorganism. It is free from other microorganisms.
Since selective media affects the growth of distinct organisms differently, therefore, an isolated colony formed in such type of medium is not considered a pure culture.
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