It seems that bacteria and molds should grow well in jam. It’s extremely high in sugar, a substance cells use for energy, and contains enough other nutrients to support cell growth. Yet jam can be left unrefrigerated for a very long time without contamination by microorganisms. Why is this?

Question

a. The high sugar concentration causes bacteria and molds to shrink and die.

b. The high sugar concentration causes bacteria and mold cells to swell and rupture.

c. Bacteria and molds cannot grow on fruits.

d. Bacteria and molds cannot get into the jam because its high concentration of sugar makes it sticky.

Group of answer choices

b

a

d

c

Answer 1

The correct answer is:

a. The high sugar concentration causes bacteria and molds to shrink and die.

High sugar concentrations create a hypertonic environment, which can lead to osmotic pressure that causes microbial cells to lose water (plasmolysis), inhibiting their growth and survival. This is why jam can be preserved for a long time without refrigeration.