21 Explain two possible reasons why a person who looks well could still be a source of infecting
microorganisms. (130-140 words)

Due to strong immune system and dormant state.

Explanation:

If a person who looks well could still be a source of infecting  microorganisms because the microorganisms present in its body not affected him due to powerful immune system but it can cause infection in the body of those person who have weak immune system. The other reason is that microorganisms are present in dormant state due to unavailability of good growing condition but when they got good conditions they became active and causes infection.

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

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