Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.7.9Inquiry Process

Circulatory Systems — IB Biology HL Revision Notes & Topical Questions

5 min read 4 parts Lesson 81 of 160

📚 IB Biology HL Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read

Part 1 of 4Open and Closed Systems

2.7.9 Circulatory Systems
Open system
  • In insects, blood (haemolymph) is pumped by a tubular heart into a body cavity and bathes the tissues directly before returning to the heart.
Closed system
  • In vertebrates, blood stays inside vessels, so it can be directed to particular organs and kept at higher pressure.
Insect gas exchange
  • Insects deliver oxygen through a network of tracheae, so their circulatory fluid does not need to carry respiratory gases.
Advantage of closed
  • A closed system transports oxygen and nutrients faster and allows flow to be controlled,
    • which supports larger, more active animals.
FeatureOpenClosed
Blood in vesselsNo, in cavityYes
PressureLowHigher
ExampleInsectsMammals, fish

Part 2 of 4Single Circulation in Fish

1
The two-chambered heart pumps deoxygenated blood to the gills.
2
In the gill capillaries blood picks up oxygen and loses carbon dioxide.
3
Blood leaves the gills and flows to the body organs without returning to the heart.
4
Passing through two capillary networks in a row means that blood pressure falls, so flow to the body is relatively slow.
5
Blood returns to the heart and the cycle repeats, so blood passes through the heart once per complete circuit.

Part 3 of 4Double Circulation in Mammals

Pulmonary circuit
  • The right side of the heart sends deoxygenated blood to the lungs and oxygenated blood returns to the left side.
Systemic circuit
  • The left side pumps oxygenated blood at high pressure to all other organs and then it returns to the right atrium.
Pressure boost
  • Returning blood to the heart after the lungs restores pressure before it is sent to the body, so tissues receive blood quickly.
Separation
  • Oxygenated and deoxygenated blood do not mix in a healthy mammalian heart, so oxygen delivery is efficient.

Part 4 of 4Exam Checklist & Tips

2.7.9 – Key Points for the Exam

  • Closed circulation A system in which blood remains inside vessels.
  • Open circulation A system in which fluid leaves vessels and bathes tissues directly.
  • Double circulation A system in which blood passes through the heart twice in each complete circuit of the body.
  • Haemolymph The circulating fluid of insects, combining blood and tissue fluid.

Common Mistakes

  • Saying that insects have blood that carries oxygen in vessels; their tracheae deliver oxygen directly.
  • Claiming fish have a double circulation; their blood passes through the heart once per circuit.
  • Thinking that double circulation means two hearts; there is one heart with two pumps.
  • Mixing up the pulmonary circuit (lungs) with the systemic circuit (body).

Last updated:

\n