What plasma is (spec 2.60)
The straw-coloured liquid part of blood, mostly water.
Blood is not just one substance — it is made of cells floating in a liquid. That liquid is called plasma.
- Plasma is the straw-coloured (pale yellow) liquid part of blood.
- It is mostly water (about 90% water).
- The blood cells — red blood cells, white blood cells and platelets — are carried floating in the plasma.
The water in plasma is very useful for transport. Many important substances dissolve in this water, and once dissolved they can be carried around the body as the blood flows.
Exam tip. Two phrases score reliably for describing plasma: "straw-coloured liquid" and "mostly water". A common one-mark question is simply "What is plasma?" — those two ideas answer it.
- Plasma = the straw-coloured liquid part of blood.
- Plasma is mostly water (~90%).
- Dissolved substances are carried around the body in plasma.
See the full worked example for role of plasma in transportation →