Mass Transport
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in which organisms is a mass transport system needed and why?
• larger organisms that have a small SA:V • since their diffusion distance is too large so they cannot exchange substances over their surfaces • they must have a specialised exchange surface for gas exchange and digestion as well as a transport system around the body (circulation)
why is a mass transport system not needed in small organisms?
• singled celled organisms have a large SA:V and therefore a short diffusion distance from their outer surfaces to their tissues. • they can diffuse substances through their outer surfaces
name some advantages of a double circulatory system in mammals
• blood can be pumped at a higher pressure • therefore nutrients are transported at a faster rate • more efficient delivery of oxygen and glucose • so metabolic rate, rate of respiration and other reactions can be higher
what are the names of the blood vessels entering and leaving the heart, lungs and kidneys?
• heart = coronary • lungs = pulmonary • kidneys = renal
give the structural features and purpose of the artery
purpose = transport blood (at high pressure) away from the heart to arterioles structural features = - thick wall made up of a thick muscle layer and thick elastic layer - no valves (except in arteries leaving heart (aorta and pulmonary))
how does each feature of the artery allow it to carry out its purpose?
• thick muscle and elastic walls allow it to withstand high pressure and prevent bursting • contraction of the thick muscle allows constriction of the lumen in order to control the volume of blood • maintain high BP as the elastic can stretch then recoil as well as smooth blood flow • no valves are needed since such high pressure the blood is forced away from the heart
give the purpose and structural features of an arteriole
purpose = control blood flow from arteries to capillaries structural features = thick muscle and thick elastic layers
how do the features of an arteriole help it to carry out its purpose?
• contraction of the muscle constricts the lumen of the arteriole, restricting blood flow into capillaries • elastic isn’t needed as much due to the blood being pumped at a lower pressure
give the purpose and structural features of a capillary
purpose = allow exchange of materials e.g O2 and CO2 between blood and cells of the body structural features = - walls made of only endothelial cells - numerous and many branches - narrow diameter - narrow lumen - some gaps between endothelial cells
how do the structural features of a capillary help it carry out its purpose?
• thin layer so substances have a short distance to diffuse over • many branches creates a large surface area for exchange • no cell is too far away from a capillary therefore a short diffusion distance • the narrow diameter means red blood cells have to squeeze through making both a short diffusion distance and a long time for diffusion
give the purpose and structural features of veins
purpose = transports blood back to the heart structural features = - thin muscle layer - thin elastic layer - overall thickness of wall is small - valves
how do the structural features of veins help it to carry out its purpose?
• veins have no need to constrict as blood is carried away from tissues so no need for thick muscles and elastic • blood pressure so no thick elastic needed to stretch and recoil • the valves prevent backflow of blood