Topic 3 Circulatory System: Circulation in Invertebrates

Question 1

• Responsible for circulating and transporting nutrients, oxygen, carbon dioxide, hormones, and red blood cells throughout the body

Answer 1

Circulatory System

Question 2

• Unicellular animal-like (due to movement) protists

- Rely on movement of gas via simple diffusion within cell

Answer 2

1. Protozoans

Question 3

• Body walls are 2 cells thick, so all cells are in direct contact with internal or external environment
  a. Example: hydra

Answer 3

2. Cnidarians

Question 4

• Includes most insects and mollusks
  a. Open circulatory systems: pump blood into internal cavity called hemocoel (has smaller cavities called sinuses), which bathes tissues in oxygen and nutrient containing fluid called hemolymph
  b. Hemolymph returns to heart through holes called ostia
  c. Mollusks: have open circulatory systems except for cephalopods: have closed due to large oxygen demands and have gill hearts
  d. Annelids: earthworms; have closed in which blood is confined to vessels

Answer 4

3. Arthropods

Question 5

• Away from heart: aorta -> arteries -> arterioles -> capillaries
• Back to heart: capillaries -> venules -> veins
• The dorsal vessel functions as the main heart or pump; aortic loops link the dorsal and ventral vessels together, which function in pumping blood

Answer 5

Path of Circulation in Closed System