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.

The sodium-potassium pump moves three sodium ions out of the cell for every two potassium ions it moves in. ATP is used to accomplish this because the direction of movement for both ions is against their concentration gradients.

By removing three sodium ions for the entry of every two potassium ions, the pump creates an electrical imbalance: three positive charges exit the cell, but only two enter. There is a net movement of positive charge out of the cell, leading to the electrochemical gradient. The ion imbalance leads to the negative resting potential of the cell.

The question states that the sodium-potassium pump requires ATP, indicating that the pumping action uses energy and is classified as active transport. Recall that active transport involves movement of molecules against their electrochemical gradient. This means that the sodium and potassium ions are moved against their gradients. Since they are moving against their gradients, sodium and potassium ions must move from a region of low concentration to a region of high concentration.

The question states that sodium ions are moving from the inside to the outside of the cell; therefore, there must be a higher concentration of sodium ions outside the cell than inside the cell.

A dendrite carries electrical signals into the cell body of a neuron. This dendrite, however, is typically not myelinated like the axon. There are also frequently many dendrites, while a single axon is the typical rule. Different types of neural cells can carry different arrangements of dendrites depending on their function.