If the skin is cut, the wound must be closed to prevent blood loss and the entry of pathogenMicroorganism that causes disease.. The formation of a scab does just that.
Blood contains tiny fragments of cells called platelets. These platelets are involved in blood clotting and scab forming.
Forming a scab
When skin is wounded, platelets are able to:
release chemicals that cause soluble proteins to form a mesh of insolubleUnable to dissolve in a particular solvent. For example, sand is insoluble in water. fibres across the wound
stick together to form clumps that get stuck in the mesh
Red blood cells also get stuck in the mesh, forming a clot. This develops into a scab, which protects the wound as it heals.
A scab is formed when platelets get stuck in fibrin mesh
Plasma
blood plasmaThe liquid part of the blood containing useful things like glucose, amino acids, minerals, vitamins (nutrients) and hormones, as well as waste materials such as urea. is a straw–coloured liquid that makes up just over half the volume of blood. The plasma has many functions:
transports carbon dioxide from respiring cells to the lungs
transports digested food from the small intestine to respiring cells
transports urea from the liver to the kidneys for excretion
distributes heat all around the body
transports hormones from the glands where they are made to the target organs