21.1–21.3: The circulatory system is the chief route of distribution in animals.

The circulatory system transports gases, nutrients, waste products, immune system cells, and hormones. It also helps animals maintain homeostasis.

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Question 21.18

The heartbeat in a vertebrate:

  • a) is initiated by modified muscle tissue, the sinoatrial (SA) node, that contracts without nerve stimulation.
  • b) is triggered by rhythmic stimulation from the cardiac nerve.
  • c) begins at the bottom of the ventricles and moves upward through the heart.
  • d) cannot be recorded by an EKG, but the neurons that control it can be.
  • e) is initiated by the atrioventricular (AV) node.

Question 21.19

Both red blood cells and white blood cells are derived from cells in the:

  • a) heart.
  • b) liver.
  • c) spleen.
  • d) lungs.
  • e) bone marrow.

Question 21.20

In a person at rest, most of his or her blood is likely to be in the:

  • a) heart.
  • b) capillaries.
  • c) veins.
  • d) arteries.
  • e) interstitial fluid.

Question 21.21

Which of the following components of human blood is a cell fragment?

  • a) spiracle
  • b) red blood cell
  • c) white blood cell
  • d) plasma
  • e) platelet

Question 21.22

How are the blood-circulation system and the lymphatic system related to each other?

  • a) Blood carries nutrients to cells. The lymphatic system removes waste from cells.
  • b) Blood carries nutrients and oxygen to cells and removes their waste. The lymphatic system removes bacteria and debris from the blood.
  • c) Blood carries nutrients and oxygen to cells and removes their waste. The lymphatic system takes the cellular waste to the kidneys.
  • d) Blood carries oxygen to the cells. The lymphatic system removes carbon dioxide from the blood and carries it to the lungs.
  • e) Blood carries carbon dioxide from tissues to the lungs. The lymphatic system carries oxygen from the lungs to the body tissues.