A dichotomous key is defined as a biological tool for identifying unknown organisms to a particular taxonomic level. It is constructed with many levels and series of couplets.
So, by observing the given dichotomous key, it is concluded that the correct answer is Option A- Organism X and Z have at least one observable trait in common in this dichotomous key.
Answer - Theory
Reasoning - Your best bet and term to describe the evolution by natural selection is theory as to still scientific theory/research is still ongoing and changes can be made in a different direction.
Answer: Codon
Explanation: A codon is a triplet of nucleotides in an mRNA that codes for specific amino acids. There are 64 possible codons. They are called the genetic codes. Three of these codons (UAA, UAG, UGA) do not code any known amino acid and are thus called termination codons. One of the codons (AUG) signals the beginning of translation and is thus called initiation codon.
Answer:
secrete a cytokine that triggers apoptosis
Explanation:
Cytotoxic T cells secrete granzymes and perforins when targeting cells. Additionally they secrete cytokines such as IFN-, TNF-α and TNF-β that act to activate macrophages and help kill infected cells.