Blood looks like a homogenous red liquid when it gets spilled, but it actually has four main components, only one of which is a liquid.

This liquid is plasma, which makes up 55% of the volume of normal blood. It is actually a yellow fluid, not red at all. It is responsible for carrying dissolved substances in the body – carbon dioxide, glucose, amino acids, fatty acids and urea.

The blood also contains white blood cells, red blood cells and platelets. White blood cells are important in protecting the body from infection – they make antibodies and fight off bacteria and viruses. Red blood cells, which give the blood its colour, are specialised oxygen carriers. They contain the protein haemoglobin, which has a very strong affinity for oxygen in the lungs, but gives it up easily in the tissues, where cells need it for respiration. Platelets are important in blood clotting. They rupture and produce proteins that form a mesh to stop blood escaping through cuts in the skin.

  Blood actually has four main components, only one of which is a liquid.
This liquid is plasma, which makes up 55% of the volume of normal
blood. It is actually a yellow fluid, not red at all. It is responsible
for carrying dissolved substances in the body – carbon dioxide,
glucose, amino acids, fatty acids and urea.
The blood also contains white blood cells, red blood cells and
platelets. White blood cells are important in protecting the body from
infection – they make antibodies and fight off bacteria and viruses.
Red blood cells, which give the blood its colour, are specialised
oxygen carriers. They contain the protein haemoglobin, which has a very
strong affinity for oxygen in the lungs, but gives it up easily in the
tissues, where cells need it for respiration. Platelets are important
in blood clotting. They rupture and produce proteins that form a mesh
to stop blood escaping through cuts in the skin.