Mass Transport

Question 1

in which organisms is a mass transport system needed and why?

Answer 1

• 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)

Question 2

why is a mass transport system not needed in small organisms?

Answer 2

• 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

Question 3

name some advantages of a double circulatory system in mammals

Answer 3

• 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

Question 4

what are the names of the blood vessels entering and leaving the heart, lungs and kidneys?

Answer 4

• heart = coronary
• lungs = pulmonary
• kidneys = renal

Question 5

give the structural features and purpose of the artery

Answer 5

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))

Question 6

how does each feature of the artery allow it to carry out its purpose?

Answer 6

1. thick muscle and elastic walls allow it to withstand high pressure and prevent bursting
2. contraction of the thick muscle allows constriction of the lumen in order to control the volume of blood
3. maintain high BP as the elastic can stretch then recoil as well as smooth blood flow
4. no valves are needed since such high pressure the blood is forced away from the heart

Question 7

give the purpose and structural features of an arteriole

Answer 7

purpose = control blood flow from arteries to capillaries
structural features = thick muscle and thick elastic layers

Question 8

how do the features of an arteriole help it to carry out its purpose?

Answer 8

• 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

Question 9

give the purpose and structural features of a capillary

Answer 9

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

Question 10

how do the structural features of a capillary help it carry out its purpose?

Answer 10

• 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

Question 11

give the purpose and structural features of veins

Answer 11

purpose = transports blood back to the heart
structural features =
- thin muscle layer
- thin elastic layer
- overall thickness of wall is small
- valves

Question 12

how do the structural features of veins help it to carry out its purpose?

Answer 12

• 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