（单词翻译:单击）
Planktonic1 - a form of life style in which an organisms floats freely in a fluid without significant attachment2 or association with other living forms.
Plaque3 is a film of bacteria in a matrix of salivary4 and bacterial5 polymers. It can be called a biofilm as it has a complex population of organisms which when mature, reach an ecological6 balance with one another.
Plasma7 - the fluid part of blood, containing proteins and salts, from which the blood cells have been removed. see alsoserum.
Plasmid- a circular piece of DNA8 found in the cell cy lasm of bacteria which is able to reproduce itself independently of it host. Plasmids may transmit a resistance to antibiotics9 from one bacteria to another. They are of great importance in techniques using for recombinant DNA.
Platelet- derived10 growth factor - a cytokine found especially in platelets. It stimulates11 cell proliferation and encourages wound healing.
Platelets - are small colourless discs of cy lasm found in blood. When platelets come into contact with a damaged vessels12 surface they change in several important ways. They begin to swell13, their shape becomes irregular with protruding14 processes, they become sticky and they release an enzyme15 which causes the formation of thromboxane, one of the precursors16 of thrombin. Thromboxane also activates17 nearby platelets, thus starting a positive feedback which rapidly increases the mass of sticky platelets which form a platelet plug. This process accounts for daily damage to capillary18 walls. Damage on a larger scale requires other mechanism19 for haemostasis. Platelets also release serotonin which acts as a powerful vasoconstrictor
