There could be a lot of reasons. To help break down food for the plants, kill off bad and harmful things that might damage the plant.
That would be C. Uracil.
In RNA we’ve got Uracil instead of Thymine.(which is in DNA)
The mouth is the beginning of the digestive tract; and, in fact, digestive starts here when taking the first bite of food
Nonsense mutations make stop codons. If the mutation is towards the beginning of a gene, then the protein that gets created will be cut short and not function properly. But if it was towards the end, there is still a chance that the protein will still be able to work.
