The mesoderm gives rise to muscles, bones, the circulatory system, the gonads, and the kidneys. Think of the mesoderm as the means by which your body gets around on a daily basis: muscles and bones, heart to pump blood, and kidneys to excrete waste.

The respiratory system arises from the endoderm.

The retina of the eye originates as an outpouching of the diencephalon. The diencephalon is one of the five secondary vesicles in the early development of the neural tube, which is derived from the ectodermal germ layer.

The ectoderm gives rise to the epidermis, central nervous system, inner ear, and the lens of the eye.

Somites are small regions of specialized mesoderm, which give rise to the skeletal muscles and bones of the body.

The circulatory system arises from the mesoderm. Other mesoderm structures include the muscles, bones, gonads, and kidneys.

The ectoderm gives rise to the epidermis, nervous system, and lens of the eye. The neural crest originates from ectoderm cells.

The endoderm gives rise to several internal organs, including the liver and pancreas, as well as the linings of the digestive and respiratory tracts.

The neural tube is a structure derived from the ectoderm that is found in chordates. The neural tube is formed by the closing of the neural folds, and runs along the dorsal-ventral axis of the developing embryo. Cells within the neural tube give rise to the neural crest. Additionally, the mature neural tube continues to develop into the central nervous system.

The circulatory system is part of the mesoderm germ layer, and includes development of the heart. We know that three answer choices must also be part of the mesoderm, while one is not (the correct answer). The mesoderm is responsible for generating muscle, blood, and bone tissue, kidneys and gonads, as well as the heart.

This leaves us with lungs, the correct answer, which develop from the endoderm layer.

The bladder develops from the endoderm. The heart, kidney, skeletal muscle, and bone develop from the mesoderm.

The failure of the lens to form in the absence of the optic cup indicates that the optic cup is necessary for lens development, and may in fact induce it.

This fact says nothing in regards to the timing of neurulation, nor the timing of eye development. Finally, cell differentiation is a gradual process, not all-or-nothing, and the statement is irrelevant to the development of the optic cup and lens.

Anti-Mullerian hormone is present only in male fetuses. It is responsible for the degeneration of the Mullerian ducts, which form the oviducts, uterus, and upper vagina in females.

Osteoporosis is a disease that causes a decrease in bone mass and density and can be induced by malnutrition or calcium deficiency. Even if the disease appears unfamiliar, the prefix "osteo-" indicates a relationship to bone, which is closely linked to calcium levels int he body.

Calcium is also an important ion involved in neural action potentials; it is responsible for triggering the release of neurotransmitters into the synaptic cleft. A calcium deficiency may cause improper action potentials that result in spasms.

The axon hillock is located near the boundary of the cell body and the beginning of the axon. This region is where the totality of incoming nervous signals onto a single cell are summed, and only if this sum meets the threshold does the axon fire an action potential itself.