This is false. There are elements that have three letters, however they don't occur as often as those with one or two letter formulas.
Ingestion is the process of obtaining food that requires specialized mouthparts
The theory would be endosymbiont theory. It was developed on the idea that some eukaryotic organelles come from prokaryotic organisms. It is also known as symbiogenesis. This theory says that these organelles were first from prokaryotic cells that is living inside a host cell.
Gametes have a single copy of an allele for each gene while zygotes have two copies for each gene.
