Many antibiotics work by preventing the proper synthesis of the peptidoglycan cell wall. These antibiotics are most likely to be effective against what types of bacteria

Gram-positive bacteria.

Explanation:

Gram-positive bacteria are those bacteria that stain dark blue or violet by Gram staining. This is due to the structure of the cell envelope, since they possess a cell wall composed of a thick layer of peptidoglycan, which surrounds the previous one. The cell wall is attached to the cytoplasmic membrane by lipoteichoic acid molecules. The peptidoglycan layer confers high resistance to these bacteria and is responsible for retaining the stain during Gram staining. Unlike gram-positive bacteria, gram-negative bacteria have a second lipid membrane outside the cell wall and a single peptidoglycan layer.

An antibiotic is a chemical substance produced by a living being or synthetically derived, which kills or prevents the growth of certain classes of sensitive microorganisms, such as bacteria. An antibiotic could be bacteriostatic if it prevents the growth of bacteria or bactericidal if it destroys them.

Antibiotics usually attack cell walls, such as β-lactams that act on the peptide chains of the bacterial cell wall. That is, they act by inhibiting peptidoglycan synthesis. This is why gram-positive bacteria are susceptible to certain types of antibiotics because they possess a large amount of peptidoglycan.

it would be c. xylem.

colors do exist. the color of the sky is actually violet; humans percieve the color of the sky as blue.