3.4 - Mass transport

Question 1

What are the haemoglobins?

Answer 1

Group of chemically similar molecules found in many different organism
Protein with a quaternary structure

Question 2

What is the role of haemoglobin and red blood cells in oxygen transport?

Answer 2

To bind to oxygen and carry molecules

Question 3

Describe the loading, transport and unloading of oxygen by haemoglobin relative to the oxyhaemoglobin dissociation curve

Answer 3

Left - haemoglobin has a higher affinity for oxygen, so associates with oxygen molecules easily, forming oxyhaemoglobin
Right - (Bohr effect) haemoglobin has a lower affinity for oxygen, so dissociates from oxygen molecules more readily

Question 4

Describe the cooperative nature of oxygen binding to haemoglobin

Answer 4

Haemoglobin molecule undergoes conformational change to tertiary structure after binding of first oxygen, breaking hydrogen bonds, so it becomes easier for the subsequent molecules to bind
Creates another binding site

Question 5

Describe the effect of carbon dioxide concentration on the dissociation of oxyhaemoglobin

Answer 5

Bohr effect
Decreases pH
Oxygen dissociates from haemoglobin more readily as has a lower affinity for oxygen

Question 6

Does haemoglobin differ between animals?

Answer 6

Yes, they are adapted to their environment with different types which different transport properties

Question 7

Draw a labelled diagram of the structure of the heart (including valves) and blood vessels and highlight the flow of blood

Question 8

Name the blood vessel which supplies oxygen and glucose to the heart muscle

Answer 8

Coronary artery

Question 9

Describe precautions to take during/after a dissection

Answer 9

Carry sharp instruments pointed away from body
Disinfect instruments and surfaces
Disinfect hands
Dispose of organ in separate bag
Use a sharp scalpel
Wear gloves
Cover any cuts

Question 10

Explain how an artery can reduce blood flow into capillaries

Answer 10

Muscle contracts
Narrows lumen

Question 11

Explain how an atrioventricular valve maintains a unidirectional flow of blood

Answer 11

Pressure in atrium is higher than in ventricle so valve opens
Pressure in ventricle is higher than in atrium so valve shuts

Question 12

Describe the structure and function of arteries

Answer 12

Elastic fibres allow the walls to stretch following ventricular systole, artery maintains high pressure
Smooth endothelial lining which reduces friction of blood flow
Narrow lumen and thick muscular walls to maintain the high pressure so blood can be pushed far distances around the body
Thick smooth muscle layer to exert a high pressure during contraction

Question 13

Describe the structure and function of arterioles

Answer 13

Same as artery but:
Smaller, thinner muscle wall and elastic layer

Question 14

Describe the structure and function of veins

Answer 14

Wider lumen than arteries for blood to flow at lower pressures
Thin muscle wall and elastic tissue
Valves to prevent backflow of blood

Question 15

Describe the structure of capillaries and the importance of capillary beds as exchange surfaces

Answer 15

One cell thick and narrow lumen for short diffusion distance
Highly branched capillary network for large surface area

Question 16

Describe how tissue fluid forms and how it is returned to the circulatory system

Answer 16

Contraction of ventricle produces high hydrostatic pressure
This forces water out of capillaries
Returned: proteins remain
Creates water potential gradient
Water moves into blood by osmosis
Returns by lymphatic system

Question 17

How does the aorta maintain rate of blood flow?

Answer 17

Elastic recoil of wall

Question 18

Outline the cohesion-tension theory of water transport in the xylem

Answer 18

Water evaporates from stomata in leaves via transpiration
Lowers water potential of mesophyll cells
Water pulled up xylem creating tension
Water molecules cohere together by hydrogen bonds
Forming continuous water column
Adhesion of water molecules to walls of xylem

Question 19

Describe the mass flow hypothesis for translocation in the phloem

Answer 19

Sucrose actively transported into phloem at source
By companion cells
Lowers water potential of sieve tube and water enters phloem by osmosis
Increase in pressure causes mass movement towards sink
Sugars used in root for respiration for storage

Question 20

Describe the ringing experiment

Answer 20

Removal of ring of surface tissues from the stem of the plant while leaving the stem core intact
Removes phloem by xylem remains intact

Question 21

Describe the tracer experiment

Answer 21

Radioactive substance added that is readily absorbed by leaves and used in photosynthesis to produce sucrose (usually 14CO2)
Sucrose formed will be radioactive so its subsequent movement around the plant via translocation can be traced