The lowermost portion of the atmosphere where most weather occurs is called the:

The breakdown of food is accomplished by enzymes. a. physical b. chemical c. mechanical d. none of the above

Which kind of mutation has occurred when the codon for an amino acid is changed to a stop codon? a. a silent mutation b. a missense mutation c. a frameshift mutation d. a nonsense mutation

Which of the following is a feature of all cells? o a. all cells have a nucleus. o b. all cells have dna for at least part of their life cycle. het . o c. all cells are spheres. o d. all cells have a rigid cell wall.