Gas Exchange- Insect, Fish, Mammals

Circulation
Insect adaptations
· Insects have an open circulatory system (s) in which blood bathes the tissues directly and does not remain in vessels for an entire circuit (f)
· A dorsal heart (s) pumps the haemolymph (f)
diagram
· Blood flows (f) from posterior to anterior through a tubular heart (s) and anterior to posterior in the body cavity
· Blood returns to the heart via valves called ostia (s)– these allow blood into the heart in one direction (f)
· Insect “blood” or haemolymph is 90% water, but contains proteins, amino acids, diglycerides, phosphates, trehalose and cells eg., phagocytes(s) – it perform the functions of transporting nutrients, wastes, hormones and heat (f)
· Haemolymph does not contain a respiratory pigment because O2 transport is not a function of the the haemolymph – this is done by the trachea (m)
Fish adaptations
· fish have a single closed circulatory system (s) in which blood remains in vessels for an entire circuit and passes through the heart just once per circuit (f)
· fish have a four sectioned heart (s) which pressurizes the blood (f)

· the sinus venosus (s) receives blood from the body (f); the sinus venosus (s) initiates and controls the heart beat– it is the site of the pacemaker (f)
· from the SV blood flows to the atrium (s) – the atrium’s function is to fill the ventricle (f)
· the ventricle has massively thick muscular walls (s) – its function is to contract strongly, this pressurizes the blood so that it is able to complete a journey through the gills and tissues (f)
· the final part is the bulbus arteriosum, an enlarged muscular portion of the ventral aorta (s) - its function is to further pressurize the blood (f)
· the ventricle and bulbus (s) send the blood under high pressure (~ 11 kPa) to the gills (f)
· there are backflow valves between each chamber of the heart (s)– these function to prevent blood flowing back into the previous chamber (f)
· deoxygenated blood is transported...