Question

question 20 (1 point) saved a virulence factor is one which allows a microbe to invade and establish itself on the host. allows a host to evade infection. normal flora use against invading microorganisms. invading organisms use against normal flora. question 21 (1 point) saved discovered penicillin when he observed clearing around penicillium notatum on bacterial plates. alexander fleming robert koch gerhard domagk louis pasteur question 22 (1 point) saved the basic unit of dna structure is the nitrogenous base. purine. pyrimidine. nucleotide.

Explanation:

• Question 20: Virulence factors are traits of a microbe that help it invade and establish itself on a host (e.g., adhesins, toxins).
• Question 21: Alexander Fleming discovered penicillin in 1928 after observing the inhibitory effect of Penicillium notatum on bacteria.
• Question 22: DNA is a polymer made up of nucleotides. Each nucleotide consists of a nitrogen - containing base, a pentose sugar (deoxyribose in DNA), and a phosphate group.

Answer:

• Question 20: allows a microbe to invade and establish itself on the host.
• Question 21: Alexander Fleming
• Question 22: nucleotide.