The embryonic stage extends from 16 days through the end of week 8.

A. Penetrate the vagina: The acrosome does not play a role in penetrating the vagina. Its function is specifically related to the sperm's ability to penetrate the ovum, making this option incorrect.

B. Dissolve the stickiness of the semen: While enzymes do play a role in semen liquefaction, this is not the function of the acrosome. The acrosome is primarily involved in the process of fertilization, not semen modification.

C. Dissolve the mucosa of the uterus: The acrosome is not involved in dissolving the mucosa of the uterus. Its function is related to penetrating the barriers surrounding the ovum.

D. Penetrate barriers surrounding the ovum: The acrosome contains enzymes that break down the outer layers of the ovum (such as the zona pellucida), allowing the sperm to penetrate and fertilize the egg. This is the correct answer.

A. Aerobic respiration; anaerobic fermentation: Aerobic respiration primarily occurs in the mitochondrion, and anaerobic fermentation occurs in the cytoplasm. Therefore, this is incorrect.

B. Glycolysis; the citric acid (Krebs) cycle: Glycolysis occurs in the cytoplasm, breaking down glucose into pyruvate. The citric acid (Krebs) cycle takes place in the mitochondrion, where it further processes pyruvate for energy production.

C. The citric acid (Krebs) cycle; mitochondrial electron-transport: Both the citric acid cycle and the mitochondrial electron transport chain occur in the mitochondrion.

D. Anaerobic fermentation; glycolysis: Glycolysis occurs in the cytoplasm and is the first step in both aerobic and anaerobic pathways, but anaerobic fermentation also occurs in the cytoplasm, so this option is not accurate in distinguishing between processes happening in different locations.