Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

1.2.1Unit 1: Lifestyle, Transport, Genes and Health

The Need for a Circulatory System — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 4 parts Lesson 13 of 29 Unit quiz

📚 IAL Edexcel Linear 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 4Why Diffusion Is Not Enough

Small organisms exchange substances directly, but large ones cannot meet their needs this way.

Surface area to volume
  • Surface area to volume As an organism grows, its volume increases faster than its surface area, so its surface area to volume ratio falls.
Diffusion distance
  • Diffusion distance In a large body the distance from the surface to the inner cells is far too great for diffusion alone to supply them in time.
High metabolic rate
  • High metabolic rate Active animals such as mammals use oxygen and glucose rapidly, so supply by diffusion alone would not meet demand.
Single-celled organisms
  • Single-celled organisms These have a high ratio and short distances, so simple diffusion across the cell surface is enough.

Part 2 of 4Features of Mass Transport Systems

Features of Mass Transport Systems
Fluid medium
  • Fluid medium Blood carries dissolved and suspended substances such as oxygen, nutrients, hormones and wastes around the body.
Pump
  • Pump The heart creates the pressure that moves blood quickly around the system, so transport is by mass flow, not by diffusion.
Vessels
  • Vessels A closed network of tubes keeps blood flowing in the right direction and allows the flow to be directed to tissues that need it.
Gradients
  • Gradients Constant flow removes products from exchange surfaces, which maintains steep concentration gradients for diffusion.

Part 3 of 4The Double Circulation

1
Deoxygenated blood from the body enters the right atrium, passes to the right ventricle, and is pumped to the lungs in the pulmonary artery.
2
In the lungs the blood picks up oxygen and loses carbon dioxide, and returns to the left atrium in the pulmonary vein.
3
Oxygenated blood passes to the left ventricle, which pumps it at high pressure into the aorta and around the body.
4
The blood returns to the right side of the heart in the vena cava, completing one circuit of the body.
5
Blood passes through the heart twice in every full circuit, which is why the system is described as a double circulation.
CircuitFromTo
PulmonaryRight ventricleLungs and back to left atrium
SystemicLeft ventricleBody and back to right atrium

Part 4 of 4Exam Checklist & Tips

1.2.1 – Key Points for the Exam

  • Mass transport Bulk movement of substances in a fluid over long distances, usually driven by pressure.
  • Closed circulation A system in which blood stays within vessels all the time.
  • Double circulation A system in which blood passes through the heart twice in each circuit.
  • Surface area to volume ratio The surface area of an organism divided by its volume.

Common Mistakes

  • Stating that large organisms have a larger surface area to volume ratio;
    • the ratio becomes smaller as size increases.
  • Saying that all arteries carry oxygenated blood; the pulmonary artery carries deoxygenated blood.
  • Describing a double circulation as two hearts; it is one heart with two pumps and two circuits.
  • Forgetting that the circulation also removes waste, as well as delivering oxygen and nutrients.

Last updated:

\n