At the end of the second week of development (day 14), what is the composition of the embryonic disk

Explanation:

The floor of the amniotic cavity is formed by the embryonic disc, which is composed of a layer of prismatic cells and the embryonic ectoderm. ... In humans, the formation of the embryonic disc occurs after implantation and prior to embryonic folding (between about day 14 to day 21 post-fertilization).

The embryonic disc forms the floor of the amniotic cavity. It is composed of a layer of cells – the embryonic ectoderm, derived from the inner cell mass and lying in apposition with the endoderm.

The correct answer would be oxygen.

Cellular respiration is the process of producing energy in the form of ATP by oxidation of the food (particularly carbohydrate or glucose).

Oxygen is one of the most important component required for complete oxidation of the glucose.

It is the final acceptor of the electron in the electron transport chain. It gets reduced to water.

Glucose + oxygen → carbon dioxide + water + ATP (approx 38).

Animals living on land gets their oxygen from the air they breathe in and animals living in the water extract dissolved oxygen from the surrounding water.

Fishes have specialized structures called gills which help them in extracting maximum amount of dissolved oxygen from the water.