Mass Transport

Question 1

Describe the quaternary structure of haemoglobin.

Answer 1

Four polypeptide chains linked together by hydrogen bonds to form a spherical molecule, each polypeptide chain is associated with a haem group which aids in the co-operative binding of oxygen by serving as the binding sites for oxygen.

Question 2

How many oxygen molecules can haemoglobin molecule carry?

Answer 2

Four O2 molecules where each O2 molecule binds to a haem group (Fe2+).

Question 3

Describe the primary structure of haemoglobin, and what does this determine?

Answer 3

4 sequences of amino acids, which determines the proteins function and properties.

Question 4

Describe the secondary structure of haemoglobin, and what does this contribute to?

Answer 4

Amino acid sequence coiled into a helix or pleat held together by hydrogen bonds, which contributes to the overall shape of the protein.

Question 5

Describe the tertiary structure of haemoglobin, and how the formation aids in its function.

Answer 5

Each helix or pleat is folded into a specific shape (held together by hydrogen bonds, ionic bonds and disulphide bridges) which is crucial for its function in oxygen transport.

Question 6

Describe how O2 concentration, CO2 concentration and affinity of oxygen would be affected in:
- gas exchange surfaces
- respiring tissues

Answer 6

• Gas exchange surfaces - high O2 concentration, low CO2 concentration, high oxygen affinity.
• Respiring tissues - low O2 concentration, high CO2 concentration, low oxygen affinity.

Question 7

What is the process called when haemoglobin binds with oxygen, and where does it occur?

Answer 7

Loading/Associating, occurs in the lungs.

Question 8

What is the process called when haemoglobin releases its oxygen and where does it occur?

Answer 8

Unloading/Dis-associating, occurs in the tissues where oxygen is needed.

Question 9

Define Affinity.
Describe the difference between high affinity and low affinity haemoglobin.

Answer 9

Affinity - the strength by which two or more molecule interact or bind.

High affinity haemoglobin is adapted for efficient oxygen uptake (releasing it less easily), while low affinity haemoglobin is adapted for efficient oxygen release (up taking it less easily).

Question 10

What factors about haemoglobin may make it have a different affinity for oxygen?

Answer 10

• different shape of haemoglobin.
• different sequence of amino acids.

Question 11

What is the primary role of haemoglobin?
How can it do this efficiently in different circumstances (e.g: gas exchange surfaces vs respiring tissues)

Answer 11

To transport oxygen.

Efficient transport requires:
- the haemoglobin to readily associate with oxygen at gas exchange surfaces which allows for efficient uptake in the lungs.
- the haemoglobin to readily disassociate with oxygen at respiring tissues which allows for efficient release/delivery of oxygen in the cells that need it.

Question 12

Define haemoglobin.

Answer 12

• A group of chemically similar molecules found in a wide variety of organisms.
• Protein molecules with a quaternary structure that has evolved to make it efficient at carrying O2.

Question 13

What is PO2?

Answer 13

The partial pressure of oxygen (e.g: the ‘concentration of oxygen’)

Question 14

Describe how the curve shifting can affect the oxygen affinity in haemoglobin on an oxygen dissociation curve.

Answer 14

• A curve shifting further to the left of the graph means a greater affinity for oxygen.
• A curve shifting further to the right of the graph means a lower affinity for oxygen.

Question 15

Describe the Bohr effect (give the equation)
Explain the effect of it.

Answer 15

How carbon dioxide concentration affects an oxygen dissociation curve.
CO2 + H20 <==> H+ + HC03-

-Higher carbon dioxide concentration would decrease haemoglobin affinity for oxygen.
-Lower carbon dioxide concentration would increase haemoglobin affinity for oxygen.

Question 16

How does the Bohr effect explain the behaviour of haemoglobin:
- in the lungs?
- in the muscles?

Answer 16

• Low CO2 concentration as it’s been excreted therefore higher affinity for oxygen as oxygen being loaded.
• High CO2 concentration as it’s being produced in the muscles therefore lower affinity for oxygen as oxygen being unloaded due to higher demand. (haemoglobin changes shape to reduce affinity)

Question 17

Why does haemoglobin have a higher affinity got oxygen at lower CO2 concentrations? (explain why shape changes)

Answer 17

Higher CO2 concentration, therefore lower pH, so tertiary structure in haemoglobin changes, so binding site releases oxygen more easily.

Question 18

Explain the uneven absorption of oxygen into haemoglobin when exposed to different partial pressures of oxygen.

Answer 18

• At very low concentrations of oxygen, the 4 chains in the haemoglobin are very closely united, making it difficult to load the first oxygen molecule.
• Once the first is loaded, the oxygen causes the chains to load the next oxygen molecule(s) more easily due to positive cooperativity.

Question 19

Why does the oxygen dissociation curve level off at the end?

Answer 19

Not all of the haemoglobin can become fully loaded with oxygen.

Question 20

Define the double circulatory system.
What are the two ‘stages’?

Answer 20

Blood passes through the heart twice before being pumped to the tissues of the body.
- Pulmonary - including the heart and lungs
- Systemic - including the heart and the rest of the body.

Question 21

Describe the basic structure of blood vessels and how they aid the structure.

Answer 21

• Tough outer layer - resist pressure changes.
• Muscle layer - contracts and relaxes to control the flow of blood.
• Elastic layer - stretch and recoil to maintain blood pressure.
• Endothelium - smooth, prevents friction and thin to aid diffusion.
• Lumen - where the blood flows through. (inside ‘space’ of blood vessel.)

Question 22

Describe the differences between veins, arteries and capillaries.

Answer 22

Arteries - Thick muscular layer, thick elastic layer, small lumen and thick overall wall. (Everything else same as veins)
Veins - Thin muscular layer, thin Elastic layer, large lumen, thin overall wall, and contains valves. (Everything else same as arteries)
Capillaries - Absence of elastic/muscular/outer layer and very thin overall wall with large lumen.

Question 23

Describe how the adaptations of the veins aid the function.

Answer 23

• Thin muscular layer - veins carry blood away from tissues, so their constriction and dilation don’t need to control flow of blood to tissues.
• Thin elastic layer - lower blood pressure won’t cause risk of veins bursting, and blood pressure too low to create recoil action.
• Thin wall overall - no need for thick walls as no risk of bursting from high pressure, and allows them to flatten easily to aid blood flow.
• Valves - prevents back flow of blood due to low pressure.

Question 24

Describe how the adaptations of arteries aid the function.

Answer 24

• Thick muscular layer - smaller arteries can be constricted and dilated to control volume of blood passing through them.
• Thick elastic layer - stretches at each heart beat then springs back to maintain a high blood pressure.
• Thick wall overall - prevents vessels bursting under high blood pressure.

Question 25

Describe the adaptations of capillaries and how they aid their function(s).

Answer 25

• Absence of elastic/muscular/outer layer - allows their walls to be extremely thin to have a short diffusion pathway for materials (O2).
• Numerous + branched - helps provide large surface area for exchange.
• Narrow diameter - Allows them to permeate tissues so no cell is far from a capillary and for a short diffusion path.
• Narrow lumen - red blood cells are squeezed flat against capillary side to help reduce diffusion distance.
• Spaces between endothelial cells - allows escape for white blood cells to deal with infections within tissues.

Question 26

Describe the formation and return of tissue fluid.

Answer 26

• Due to high hydrostatic pressure in the arteriole end of the capillaries (from the heart beating), small molecules (e.g: amino acids, glucose, oxygen) and water molecules are forced out of the capillaries into the surrounding tissues (ultrafiltration). This is tissue fluid. The larger molecules (e.g:plasma proteins) which were too large to move out of the capillaries remain in them.
• As you move to the venule end of the capillaries, the water potential in the capillaries decreases. This is because water molecules are constantly leaving the capillaries, however the large molecules are remaining, so water potential decreases.
• Decreased water potential in the venule end of the capillaries means water molecules can diffuse back into the capillaries by osmosis down it’s water potential gradient, returning the tissue fluid to the capillaries.
• Other tissue fluid that is not returned this way can return to the circulatory system via the lymphatic system.

Question 27

What is tissue fluid and where is it formed?

Answer 27

• It is a watery liquid that contains glucose, amino acids, fatty acids, ions in solution and oxygen.
• It supplies all these essential substances to the tissues, and receives carbon dioxide and other water materials in return.
• It is formed outside of the arteriole end of the capillaries, in the immediate environment of cells.

Question 28

What is the cardiac cycle?
What are the three main stages of the cardiac cycle?
How do you calculate cardiac output?

Answer 28

The Cardiac cycle - The sequence of events that make up one heart beat
3 Stages - Atria and Ventricular diastole, Atrial systole, Ventricular systole.
Cardiac output = heart rate x stroke volume

Question 29

Describe how Aortic pressure varies during the cardiac cycle.

Answer 29

• Rises when ventricles contract as blood is forced into the aorta.
• Gradually falls due to elasticity of its walls which creates recoil action.
• Recoil produces temporary ride in pressure at start of relaxation phase.

Question 30

Describe how Ventricular pressure varies during the cardiac cycle.

Answer 30

• Low at first but gradually increases as ventricles fill with blood as atria contract.
• Left atrioventricular valve closes and pressure rises dramatically as thick, muscular walls of ventricle contract.
• As pressure rises above the aortas, blood is forced into the aorta past the semi-lunar valves.
• Pressure falls as ventricles empty and walls relax.

Question 31

Describe how ventricular volume is affected during the cardiac cycle.

Answer 31

• Rises as atria contract and ventricles fill with blood, then drops suddenly as blood is forced into aorta when semi-lunar valves open.
• Volume increases again when ventricles fill with blood.

Question 32

Describe how atrial pressure varies during the cardiac cycle.

Answer 32

• Is always relatively low as thin walls of atrium cannot create much force.
• Highest when they are contract in, but drops when left atria-ventricular valve closes and it’s walls relax.
• The atria then fill with blood, leading to gradual pressure build up until slight drop when left atria-ventricular valve opens and some blood moves into the ventricle.

Question 33

Define cardiac output.
What is Stroke volume?

Answer 33

Cardiac output - Volume of blood pumped by one ventricle of the heart in one minute.
Stroke volume - Volume of blood pumped out at each beat.

Question 34

Describe the Cohesion-Tension theory which allows for the transport of water in a plant (through the xylem).

Answer 34

1- Water evaporates from mesothelioma cells in the leaves, causing a continual decrease in water potential.
2- This allows water from the soil to diffuse into the root hair cells by osmosis and travel to the xylem vessel.
3- Water is drawn up the xylem vessel in a transpiration stream due to its cohesive forces, in a continuous column.
4- The water then reaches the mesophyll cells.

Question 35

Why is the transpiration stream in the movement if water through a plant important?

Answer 35

• It carries water required for photosynthesis to the palisade cells in the leaves.
• The turf or pressure helps keep cells rigid.
• Water is necessary for hydrolysis.
• Water carries essential mineral ions/salts in solution.
• Evaporation from the leaves has a cooling effect.

Question 36

Describe the difference between cohesive forces and adhesive forces in water molecules.

Answer 36

• Cohesive forces - The tendency of water molecules to ‘stick’ together by hydrogen bonds.
• Adhesive forces - The tendency of water molecules to ‘stick’ to the walls of its container (e.g: the xylem)

Question 37

Name and describe the 3 main pathways of transport for water up the xylem.

Answer 37

• Root pressure - water ‘pushing’ up the xylem, caused by the mineral ions that are actively transported into xylem vessels in the root by endodermal cells, making the xylem water potential more negative.
• Capillarity - water ‘crawls’ up the xylem, adhesive forces of water molecules means they stick to the walls of the xylem vessel.
• Cohesion tension - water pulled up the xylem as water evaporates from the mesophyll cells.

Question 38

Describe the process of translocation in the phloem. (The mass-flow theory).

Answer 38

• Sucrose found in the source cell due to photosynthesis (e.g: leaf) diffuses into the neighbouring companion cell, where it then actively transports into the phloem, which requires ATP energy due to the higher concentration of sucrose in the phloem.
• This active transport of sucrose lowers the water potential in the phloem, so water from a neighbouring xylem vessel diffuses into the phloem by osmosis, which then raises water potential but also hydrostatic pressure.
• The sucrose diffuses through the phloem due to the raised hydrostatic pressure, which then raises water potential int he lower parts of the phloem =, causing water to diffuse back into the xylem vessel by osmosis. This then lowers hydrostatic pressure.
• The sucrose then actively transports into the companion cell which neighbours a sink cell, before actively transporting into the sink cell where it is required (e.g: root hair cell)

Question 39

Describe the structure of the sieve-tube elements in phloem, and the companion cells which keep them alive.

Answer 39

• The sieve-tube elements are large pores which allow for the movement of substances through them, however they don’t;t contain the necessary organelles to survive alone.
• Companion cells have very thin cell walls, with dense cytoplasm. They have a centrally placed nucleus and lots of mitochondria and they connect to the sieve-tube elements with plasmodesmata.

Question 40

EVIDENCE FOR TRANSLOCATION