The phase of the bacterial growth curve during which microbial growth slows and the rate of multiplication equals the rate of cell death is the

A. Deletion: A deletion mutation removes one or more nucleotides from the DNA sequence. While deletions can lead to frameshifts and potentially premature stop codons, the key feature in this scenario is the introduction of a stop signal, not the removal of nucleotides per se.

B. Nonsense: A nonsense mutation changes a codon that encodes an amino acid into a stop codon. In this example, “THE CAT ATE THE BIG RAT” is truncated to “THE CAT ATE (stop),” indicating translation terminates prematurely. This type of mutation produces a truncated, usually nonfunctional protein.

C. Silent: A silent mutation changes a nucleotide without altering the amino acid sequence. It does not produce a stop codon or truncate the protein, so it would not result in “THE CAT ATE (stop).”

D. Missense: A missense mutation changes a codon so that a different amino acid is incorporated. While it alters the protein sequence, it does not introduce a stop codon, so it cannot account for the premature termination seen here.

E. Insertion: An insertion adds one or more nucleotides into the sequence. Like deletions, insertions can cause frameshifts that might eventually produce a stop codon, but the defining characteristic in this example is the direct conversion of a codon to a stop codon, making this a nonsense mutation rather than a generic insertion.

A. Energy: Active transport requires energy, typically in the form of adenosine triphosphate (ATP), to move molecules across a cell membrane against their concentration gradient. This energy input allows cells to concentrate nutrients, ions, or other substances even when the extracellular concentration is lower than inside the cell.

B. No membrane proteins: Active transport depends on membrane proteins, such as pumps or transporters, to carry specific molecules across the lipid bilayer. Without these proteins, the cell cannot selectively move substances against their gradient.

C. No concentration gradient: Active transport can move substances against a concentration gradient, but a concentration gradient does not have to be absent. In fact, moving substances against an existing gradient is precisely why energy is required.