Which of the following stimuli is most likely to increase secretion of antidiuretic hormone (ADH)?

Which of the following are the only vertebrates in which blood flows directly from respiratory organs to body tissues without first returning to the heart?  In other words, blood only passes through the heart once during each complete circuit. 

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?