🩸 The Internal Environment of the Body
Blood & Immunity — A Chemistry Perspective
Grade 8 Biology | Understanding What Blood Is Made Of and How It Carries Oxygen
Part 1: What Is Blood Plasma Made Of?
The Liquid Part of Blood
If you let a tube of blood sit still (or spin it in a centrifuge), it separates into layers. The top layer — a light amber (straw-colored) liquid — is blood plasma. It makes up about 55% of your total blood volume. The remaining 45% consists of red blood cells, white blood cells, and platelets.
Key Definition: Blood plasma is the liquid matrix of blood in which cells and cell fragments are suspended. It is roughly 90–92% water, but the remaining 8–10% contains dissolved substances that are absolutely critical for life.
Interactive visualization — available in the full lesson
The Dissolved Solutes in Plasma
Even though water dominates, the dissolved solutes are what make plasma so important. Let's break them down:
🧬 Proteins (~7%)
The three major plasma proteins are:
- Albumins (~60% of plasma proteins): Maintain osmotic pressure — they keep water from leaking out of blood vessels into surrounding tissues.
- Globulins: The second most abundant type. Alpha and beta globulins transport lipids (fats), metal ions, and fat-soluble vitamins. Gamma globulins are antibodies used in immunity.
- Fibrinogen: Essential for blood clotting. When you get a cut, fibrinogen is converted to fibrin threads that form a mesh to stop bleeding.