Which answer explains why Na+ ions enter the cell when voltage-gated Na+ channels are opened in neurons?

Which of the following statements about action potentials is correct?

The parathyroid gland secrete a hormone as a response to low ______ levels.

What is the function of the valves in the heart and veins?

Which statement best explains why cattle able to survive on a diet consisting almost entirely of plant material?

Not all poikilotherms are ectotherms.

You are doing a lab experiment on osmosis and are using sugar and water. In osmosis, water moves from an area of high sugar (solute) concentration to an area with lower sugar (solute) concentration. 

Which of the following types of cell-to-cell signaling describes tumor cells that influence surrounding cells by secreting growth factors?

The digestive system processes food, extracts nutrients, and eliminates the residue.  

Homeostasis refers to the property of maintaining particular physiological variables such as body temperature and solute concentrations absolutely constant with no variation.