2.57 Describe the composition of the blood: red blood cells, white blood cells, platelets and plasma

• 55% of the blood is plasma
• More red blood cells than white blood cells
• Platelets

Platelets are fragments of dead cells.

White blood cells can be lymphocytes or phagocytes.

I don't know if this is technically needed in this specification point, but I'll include it anyway because...well...it's good to know. :)

\/

Phagocytes are the white blood cells that swallow up the pathogen (which can be a bacterium, virus or protoctist). As can be seen below in figure 1, the cytoplasm forms little 'feelers' called pseudopodia. These surround the pathogen and form a vacuole. Then, digestive enzymes are released into the vacuole which digest and kill the pathogen.

Lymphocytes release antibodies which are complimentary to the antigens on the surface of a pathogen - that is how they (pathogens) are identified. Lymphocytes can cause the pathogens to stick together, leave a clearer chemical trail (so the phagocytes can follow them more easily) or explode.

Erythrocytes, aka red blood cells, have a bioconcave shape, no nucleus and have lots of haemoglobin. This allows them to carry oxygen around the body.

Plasma is used to transport stuff (see next posts(s))

Figure 1