Bacteria Morphology Questions and Answers

Answer: C

Correct answer: linking the sugar of the disaccharide-peptide unit to the growing peptidoglycan chain

The order of the last steps is: the subunit is carried across the membrane on bactoprenol, added to the growing glycan chain by transglycosylation, and only then cross-linked to a neighbouring strand by transpeptidation. So the next-to-last step is the attachment of the sugar, and cross-linking - the step penicillin blocks - is the last.

Answer: A

Correct answer: Streptococci

Streptococci divide repeatedly in one plane and remain attached, so the cells form chains. Dividing in one plane but separating after each division gives diplococci; dividing in several planes gives clusters.

Answer: C

Correct answer: peritrichous

Peritrichous means flagella distributed over the whole surface - the arrangement in E. coli and Salmonella. When they all turn counter-clockwise they gather into a single bundle that drives a straight run; when one reverses, the bundle flies apart and the cell tumbles.

Answer: A

Correct answer: the area between the inner and outer membranes of gram-negative bacteria

The periplasm is the compartment between the plasma membrane and the outer membrane, and it contains the thin peptidoglycan layer along with binding proteins, hydrolytic enzymes and the β-lactamases that destroy penicillin. Gram-positive cells have no outer membrane, so no true periplasm.

Answer: B

Correct answer: Gram-positive bacteria

Peptidoglycan is the major constituent of the gram-positive wall - half or more of its dry weight, in many layers. Gram-negative bacteria have only a thin single layer, most of their wall being outer membrane, and fungal walls are made of chitin and glucans, with no peptidoglycan at all.

Answer: D

Correct answer: spirilla

Spirilla are rigid helically curved rods, moved by polar flagella. Spirochaetes are the flexible helical forms, driven by internal axial filaments; cocci are spherical and bacilli straight rods.

Answer: B

Correct answer: Mycoplasma

Mycoplasma has no cell wall - its membrane is strengthened with sterols instead - so it is pleomorphic and naturally resistant to penicillin and every other drug that attacks wall synthesis. Treponema, Staphylococcus and Klebsiella all have walls.

Answer: D

Correct answer: None of the above

All three statements are correct: peptidoglycan is a polymer of NAG and NAM with short peptide chains; it is found in the prokaryotic cell wall; and the cross-linking makes it a single bag-shaped macromolecule (the sacculus) enclosing the whole cell. Since none of them is untrue, the answer is none of the above.

Answer: A

Correct answer: cocci

Cocci are spherical. Bacilli are rods, spirilla helical rods, and pleomorphic describes organisms such as Mycoplasma that have no fixed shape because they have no wall.

Answer: C

Correct answer: amphitrichous

Amphitrichous means flagella at both poles - one at each, or a tuft at each. Monotrichous is a single flagellum at one pole, lophotrichous a tuft at one pole, and peritrichous flagella all over.