2.7.9Inquiry Process
Circulatory Systems — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 81 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Open and Closed Systems
Open system
- 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
- Closed system In vertebrates, blood stays inside vessels, so it can be directed to particular organs and kept at higher pressure.
Insect gas exchange
- 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
- Advantage of closed A closed system transports oxygen and nutrients faster and allows flow to be controlled,
- which supports larger, more active animals.
| Feature | Open | Closed |
|---|---|---|
| Blood in vessels | No, in cavity | Yes |
| Pressure | Low | Higher |
| Example | Insects | Mammals, 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
- Pulmonary circuit The right side of the heart sends deoxygenated blood to the lungs and oxygenated blood returns to the left side.
Systemic circuit
- 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
- 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
- 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