Mass Transport Flashcards
1
Q
Haemoglobin structure
A
- the haemoglobins are a group of chemically similar molecules found in many different organisms
- a large globular protein
- a quaternary structure
- made up of four polypeptide chains
- each chain has a haem group, which contains an iron ion (this gives it the red colour)
- one oxygen molecule binds to each iron ion, and therefore one molecules of haemoglobin can transport four oxygen molecules
2
Q
Function of haemoglobin
A
- ROLE - to transport oxygen from the gas exchange surface (the alveoli) in the lungs to the rest of the respiring cells (e.g. muscles) of the body.
- PROCESS - as red blood cells travel through the capillaries in the lungs, oxygen then diffuses across the alveolar epithelium and in turn the capillary endothelium into the red blood cells. The oxygen is “loaded” onto the haemoglobin in the red blood cells.
3
Q
Loading (function in haemoglobin)
A
- the process by which haemoglobin binds with oxygen
- also referred to as associating
- once the red blood cells reach the respiring cells, the oxygen is “unloaded” (or disassociates) from the haemoglobin
4
Q
Reversible reaction and O2 - function of haemoglobin
A
- four O2 molecules can bind to each haemoglobin molecule in this reversible reaction
- one haemoglobin molecule can transfer up to four oxygen molecules, or eight oxygen atoms
- 4O2 + Hb -reversible reaction sign- HbO8 (oxyhaemoglobin)
5
Q
Partial pressure - haemoglobin
A
- the pressure of a single type of gas in a mixture of gases
- in the context of haemoglobin, we refer to the partial pressure/pO2 of oxygen
- measured in kilopascals (kPa)
- proportional to concentration (the great the conc. of oxygen, the higher the partial pressure of oxygen)
6
Q
Haemoglobin’s affinity for oxygen
A
- affinity for oxygen means tendency to combined with oxygen
- we say haemoglobin has a high affinity for oxygen
7
Q
Oxyhaemoglobin dissociation curve
A
LOOK AT BOOKLET
8
Q
The cooperative nature of oxygen binding
A
- oxygens affinity to haemoglobin changed in different pO2
- low pO2 = low affinity for oxygen - because the structure of an empty haemoglobin molecule makes it hard for the first O2 molecule to bind
- however, once the haemoglobin has loaded, the tertiary structure changes, and as its pO2 increases so does its affinity for oxygen as new binding sites are uncovered.
9
Q
The cooperative nature of oxygen binding - effect on oxyhaemoglobin curve
A
- results in the S shape
- the curve is initially shallow as the structure of the empty haemoglobin makes binding difficult for the first O2 molecule. Therefore, there is little increase in saturation of pO2
- however, once the first O2 molecule has loaded, the tertiary structure of the haemoglobin changes, which makes it easier for the second oxygen molecule to bind, and when that binds, it makes it easier for the third. Therefore, the curve becomes steep in the middle as oxygen loads quickly.
- the third O2 molecule further changes this tertiary structure, which makes it easier for the final oxygen molecule to bind. However, because the haemoglobin is now nearly full, it makes it less likely for the fourth and final O2 molecule to associate, so the curve plateaus below 100%.
10
Q
What is the Bohr effect?
A
The fact that the affinity of haemoglobin for oxygen is affected by the partial pressure of oxygen and carbon dioxide.
11
Q
THE BOHR EFFECT - carbonic acid
A
- CO2 reacts with water (which there is a lot of in the plasma and cytoplasm) to form carbonic acid.
- the formation of carbonic acid lowers the pH of the plasma, which makes it more acidic.
- H+ ions are released by the carbonic acid, which changes the tertiary structure of haemoglobin
- this results in it having a lower affinity for oxygen and so it releases oxygen more readily to the cells.
- this is advantageous because the cells are respiring so require more oxygen.
12
Q
Effect of carbonic acid simplified
A
- in respiring tissue, there is more carbon dioxide produce which causes the haemoglobin to have a lower affinity for oxygen
- this means there is an increased rate of oxygen unloading at the respiring tissues where oxygen is needed.
13
Q
Effect of increased CO2 partial pressure on oxyhaemoglobin curve
A
- the curve shifts to the right because for any given partial pressure to oxygen, haemoglobin is less saturated with oxygen because it has unloaded it more easily
- this is the Bohr effect
14
Q
Haemoglobins in different species
A
- haemoglobins are a group of chemically similar molecules found in many different organisms
- different species of haemoglobins have slightly different amino acid sequences/primary structures
- these difference can affect the affinity of haemoglobin to oxygen
15
Q
Animals and different haemoglobins - low pO2 environment
A
- some animals like llamas are adapted to low pO2 environments, so their haemoglobin has a higher affinity for oxygen.
- for these animals, the oxyhaemoglobin curve shifts left.
16
Q
Animals and different haemoglobins - small animals
A
- smaller animals like mice need haemoglobin with a lower affinity for oxygen
- they have a large SA:V
- therefore, they lose body heat quickly
- they need to be replaced (to maintain a good body temperature) by heat released from respiration
- therefore these animals have a high respiratory or metabolic rate and their cells require a lot of oxygen
- this means their haemoglobin needs to have a low affinity for oxygen so it can be readily unloaded at respiring tissues to support a high rate of respiration
- for these, the oxyhaemoglobin curve shifts to the right
17
Q
Animals and different haemoglobins - birds
A
- many birds also need haemoglobin with a lower affinity for oxygen
- this is because they are very active animals and the flapping of their wings requires a lot of ATP from respiration for muscle contraction
- therefore, their haemoglobin needs a lower affinity for oxygen so that it unloads more readily at respiring tissues for a high rate of respiration
- like with smaller animals, their oxyhaemoglobin curve shifts to the right
18
Q
What is mass flow?
A
- multicellular organisms have a low SA:V ratio, so they need a specialised transport system
- therefore they need a specialised system to transport raw materials (e.g. oxygen, nutrients, glucose, amino acids, etc)
- these substances are transported over long distances by mass flow.
- in mass flow, these substances are transported in a fluid (usually water, dissolves solutes and suspended objects/things that aren’t dissolved)
- this fluid moves in a particular direction due to a force
- mass flow requires a source of energy to pump the fluid but is much faster than diffusion - the circulatory system in animals is an example of this
19
Q
What does closed circuit mean?
A
- in humans, blood circulated in a closed circuit
- this means all the blood is contained within the heart and blood vessels
20
Q
What is the double circulatory system?
A
- blood passes though the heart twice per complete circuit
- there are two circuits: the pulmonary circuit (through the lungs) and the systemic circuit (rest of the body)
21
Q
What vessels enter and leave the kidney?
A
- the renal arteries enter
- the renal veins leave
22
Q
Heart structure
A
REVIEW A PICTURE
The right side of the heart
- receives deoxygenated blood through the vena cava from the body
- the blood enters the right atrium via the vena cava
- it then goes past the atrioventricular valve and into the right ventricle
- the right ventricles had thinner walls than the less because less pressure is required to pump the blood to the nearby lungs
The left side of the heart
- receives oxygenated blood from the lungs and pumps it to the body
- blood enters the left atrium from the pulmonary vein
- then this blood moves through the atrioventricular valve into the left ventricle
- the left ventricles has thicker walls than the right to produces more pressure to pump the blood further distances as it needs to be pumped across the whole body
23
Q
Heart structure - ventricles vs atria
A
- ventricles have much thicker walls than the atria as they have to generate more pressure to pump blood longer distances
- the atria only need to move the blood to the adjacent chamber
24
Q
Function of valves
A
- ensure blood flow is unidirectional (only travels in one direction)
- ensure there is no backflow
- a higher pressure on one side of the valve causes it to open, and then the higher pressure on the other side causes it to close
25
Atrioventricular valves
- located between the atria and ventricles
26
Semilunar valves
- located between the ventricle and artery
- right ventricle and pulmonary artery
- left ventricle and aorta
27
Coronary arteries
- the heart muscle is supplied by its own blood vessels called coronary arteries
- these supply the heart tissues with everything necessary to respire so oxygen, glucose, etc.
- these coronary arteries branch of the aorta shortly after it leaves the heart
- they can be seen on the external surface of the heart
28
What is the cardiac cycle?
- the sequence of events in the heart during which the atria and ventricles contract and relax to pump blood and keep it circulating around the body
- one cardiac cycle = the end of one heart beat to the end of the next
- average cardiac cycle in humans takes about 0.8 seconds
- this results in an average heart rate of 75 bpm
29
The Cardiac Cycle - Diastole
- when the muscles in the walls in the atria and ventricles are relaxed, we call it diastole
30
The Cardiac Cycle - Atrial Systole
- when the atria contract simultaneously
31
The Cardiac Cycle - Ventricular Systole
- when the ventricles contract simultaneously from the base upwards
32
The Cardiac Cycle - THE PROCESS
1. **Diastole**: Initially, the muscles in the walls of the atria and ventricles are relaxed (diastole), which causes a reduction in pressure. This creates a pressure gradient, as the pressure in the vena cava and pulmonary veins is higher than that in the atria, so blood starts to go down the gradient and fill the atria. The pressure in the atria increases, and when it is higher than that in the ventricles, the atrioventricular valves open.
2. **Atrial Systole**: Next, the atria contract simultaneously (atrial systole). This reduces the volume of the atria and increases the pressure so blood is pushed into the ventricles.
3. **Ventricular Systole**: Then, the ventricles contract simultaneously (ventricular systole) from the base upwards. This decreases the volume and increases the pressure in the ventricles.
4. When the pressure in the ventricles is higher than that in the atria, the atrioventricular valves close to prevent backflow, and the tendons attached to these valves prevent them from turning inside out.
5. The atria are relaxed when the ventricles contract. As the ventricles continue to contract, the pressure rises further, which forces open the semilunar valves, as the pressure of the ventricles exceeds the pressure of the pulmonary artery and aorta.
6. Blood is pushed into the aorta and pulmonary artery and to the body and lungs respectively.
7. Finally, the walls of the ventricles relax, and we are back to diastole. When the pressure in the ventricles falls below the pressure in the aorta and pulmonary artery, the semilunar valves close. Blood returns to the atria via the major veins, and the process starts again.
33
Cardiac output equation
cardiac output = stroke volume x heart rate
34
What are the types of blood vessels?
Arteries, veins, capillaries, venules and arterioles.
35
What root does blood flow in (when looking at vessels)?
Ventricles (deoxygenated), artery (deoxygenated), arteriole (deoxygenated), capillary (both), venule (oxygenated), vein (oxygenated), atria (oxygenated)
36
Arteries function and structure
- carry blood away from the heart to the rest of the body
- they all carry oxygenated blood except the pulmonary arteries which carry deoxygenated blood away from the heart to be oxygenated
- **Thick muscle walls** - arteries have thick muscle walls containing elastic tissue
- these walls allow them to carry blood at high pressures, maintain that pressure, and withstand the pressure surges that occur with each time the ventricle contract
- **Elastic tissue** - the elastic tissue in their walls allows the arteries to stretch and recoil in order to even out the blood flow
- **Endothelium** - the inside is lined with a smooth endothelium to reduce friction, and this endothelium is folded up, which allows the artery to stretch
- narrow lumen
37
Arterioles function and structure
- arteries divide into smaller vessels, which are these arterioles
- **Muscular wall** - relatively thick for their size
- **Muscle fibres** - the fibres in the walls can contract or relax to restrict (contract) or allow (relax) full blood flow to the capillaries.
- in vasodilation and vasoconstriction, the arterioles control blood flow to the capillaries rather than the capillaries themselves constricting or relaxing
38
Capillaries structure and function
- capillaries the smallest blood vessels
- the site of exchange of substance being transported in the blood to and from the cells
- they are adapted for efficient exchange
- **surface area** - there are a very large number of capillaries which increases the surface area to increase rate of diffusion and exchanged
- **Short diffusion pathway** - capillaries are found near cells which decreases the diffusion distance. The capillary endothelium is **one cell thick** for a short diffusion pathway.
- **Role in formation of tissue fluid** - there are small gaps between endothelial cells which have a role in the formation of tissue fluid. Tissue fluid plays an important role in the exchange of substance between the blood in the capillaries and the body cells.
39
Venules function
- capillaries rejoin into venules
- these rejoin into increasingly larger veins
40
Veins structure and function
- veins carry blood back to the heart
- they always carry deoxygenated with the exception of the pulmonary veins
- veins have a wider lumen than arteries
- they have very little elastic or muscle tissue + thinner walls, as the blood is a lower pressure
- blood flows through the veins with the help of the contractions of adjacent skeletal muscles
- as the muscles contact, this squeezes the blood along the vein.
- valves prevent the blood from flowing backwards
41
Blood flow through blood vessels
- the smallest blood vessels
- the site of exchange of substances in the blood being transported to and from cells
- adapted for efficient exchange
42
COMPONENTS OF BLOOD - red blood cells
- biconcave shaped
- no nucleus - more room for haemoglobin
- packed with haemoglobin to transported oxygen around the body
43
COMPONENTS OF BLOOD - white blood cells
- many different types
- involved in immunity
44
COMPONENTS OF BLOOD- platelets
- fragments of cells involved in clotting
45
COMPONENTS OF BLOOD - plasma
- straw coloured liquid
- blood cells and platelets are suspended in it
- transports dissolved molecules like ions, glucose, amino acids, hormones and other blood proteins.
- play an important role in the formation of tissue fluid
46
What is tissue fluid?
- sometimes called interstitial fluid
- the fluid that surrounds all cells in the body
- virtually the same composition as blood plasma, but lacks plasma proteins
47
What does tissue fluid contain?
- water
- dissolved ions (Na+, K+, C-)
- dissolved monomers (amino acids, glucose)
- dissolved gases (O2, CO2)
- some hormones
- some white blood cells
48
THE PROCESS - formation of tissue fluid
1. **Ultrafiltration** - the blood enters the arteriole end of the capillaries. The hydrostatic pressure in the capillaries is higher than that of the tissue fluid. This difference of hydrostatic pressure means, the overall outward pressure (caused by the gradient) forces the fluid out through the gaps between the endothelial cells (fenestrations) of the capillaries. However, blood cells and plasma proteins remain in the capillary because they are too large to leave.
2. **Exchange of substance** - small dissolved substances such as oxygen and glucose move with the fluid, which means they can easily move into body cells. Waste substance like carbon dioxide and urea also move out of the body cells and into the tissue fluid.
3. **Reabsorption** - as described in stage one, fluid leaves the capillaries. This causes the hydrostatic pressure to be reduced so that at the venule end it is equal to the tissue fluid pressure. Due to fluid loss as well as an increasing concentration of plasma proteins (which can’t leave the capillary), the water potential at the venule end of the capillary is lower than that of the tissue fluid. Some water re-enters the capillary from the tissue fluid by osmosis due to this gradient.
4. **Lymphatic system** - not all of the water that left the capillary is reabsorbed. About 95% is, while the remaining 5% is drained into the lymphatic system and re-enters the blood at the superior vena cava (returns to heart to be oxidised).
49
What is the lymphatic system?
A network of tissues and organs that transport lymph, a fluid containing infection-fighting white blood cells, throughout the body to help get rid of toxins, waste and other unwanted materials.
50
Explain lymph vessels
- the lymphatic system contains lymph vessels
- they are blind ended (dead ended) tubes
- contain valves to keep fluid moving in the right direction
51
Explain lymph
- the fluid that moves through lymph vessels
- eventually empties back into the blood in large veins that run close to the collarbone
52
What is CVD?
- cardiovascular disease
- refers to a range of different problems that can develop in the blood vessels and the heat
- generally affects arteries
53
Cause vs correlation
- a correlation occurs when a change in a one of two variables is reflected by the change in the other over variable
- however a cause can only be shown by experimental evidence, which clearly shows how the change in one variable **leads** directly to the change in the other.
54
Describe positive correlation
As one variable increases, so does the other.
55
Describe negative correlation
As one variable increases, the other decreases.
56
What does it mean to be directly proportional?
A change in one variable is accompanied by a constant multiplier change in the other variable.
57
What is a risk factor?
A factor that increases the probability of getting a particular disease.
58
CVD - formation of atheroma
- CVD often starts with the formation of atheroma (fibrous fatty plaque)
- This builds up in the artery wall, gradually blocking the lumen
- This restricts blood flow to the tissue supplied by that artery.
59
CVD - thrombosis
- Blood clots may also form, which is known as thrombosis.
- Blood clots often form in arteries that have been damaged by the build up of atheromas (fibrous fatty plaque)
- Blood clots can block arteries at that point or can move through the blood vessels until they get lodged in a smaller artery, which causes a blockage at that location.
- like the atheroma, a clot restricts blood flow to the tissues supplied by that artery.
60
CVD - coronary artery blockages
- If coronary arteries become blocked by atheromas or blood clots, this can lead to the heart muscle itself not receiving enough blood.
- That means not enough oxygen or glucose for respiration, and the heart muscle may die.
- This is a heart attack or a myocardial infraction.
61
CVD - aneurysms
- Also a type of CVD.
- Aneurysms specifically affect arteries
- When a weakened artery wall allows an artery to swell or even balloon outwards.
- It is possible for aneurysms to burst, causing internal bleeding.
62
CVD - Risk factors
Lifestyle factors - high blood cholesterol, cigarette smoking, high blood pressure.
Uncontrollable factors - genetics, age, sex.
63
What does the xylem transport?
- water
- dissolved mineral ions
- transports these upwards to all other parts of the plant through the stem and leaves
64
Xylem structure
- narrow, hollow tubes
- these are made up of dead cells - therefore there is little resistance to water movement
- strong impermeable walls strengthened by a substance called lignin - this stops the xylem from collapsing under tension
65
COHESION-TENSION THEORY - H bonds
A weak bond between electropositive hydrogen and other electronegative atoms like oxygen
66
COHESION-TENSION THEORY - cohesion
A force resulting from attraction between molecules of the **same** substance. For example, water molecules stick to each other by cohesion, and therefore they are cohesive.
67
COHESIVE-TENSION THEORY - adhesion
A force resulting from attraction between molecules of **different** substances. Water molecules for example adhere to the sides of the xylem.
68
COHESION-TENSION THEORY - transpiration
The evaporation of water from a plant’s surface, especially the leaves. Water molecules evaporate from the mesophyll cell walls and accumulate in the air spaces, then diffuse out of the open stomata so down the concentration gradient.
69
Describe the process of cohesion-tension theory of water transport in the xylem
1. Water evaporates from the surface of a mesophyll cell into the leaf air space and diffuses out of open stomata.
2. As water leaves the mesophyll cell, its water potential decreases. Water moves into the cell from an adjacent cell. This happens across the leaf, through adjacent leaf cells and down a water potential gradient by osmosis. This pulls water into the leaf from the xylem.
3. Because water molecules are cohesive, when some are pulled into the mesophyll cell from the xylem, others follow, which creates tension (in other words, negative pressure). This ‘pull’ is transmitted down the xylem and the whole column of water in the xylem moves upwards.
4. Water enters the xylem at the bottom of the stem, from cells in the roots.
5. Water moves into the root cells from the soil by osmosis.
70
What evidence is there for the cohesion-tension theory?
- Tree trunk experiments show that the diameter of a branch or tree trunk will decrease when transpiration is occurring at a high rate.
- This is because the transpiration pull creates a tension, which reduces the diameter of the trunk.
- It has also been observed that if the xylem vessels are broke , the tree no longer draws up water, which suggests that water moves upwards in the xylem.
- And also, when a xylem vessel is broke, water does not leave out, suggesting there is a pull or force drawing the water up.
71
FACTORS AFFECTING TRANSPIRATION - air temperature
- increase in air temperature increases the rate of transpiration
- this is because particles move faster (as they gain kinetic energy) so evaporation and diffusion of water is faster
72
FACTORS AFFECTING TRANSPIRATION - air movement
- windy conditions increase rate of transpiration
- air movement causes the water molecules that have diffused out of the stomata to be blow away from the leaves
- this results in a steeper water potential gradient between the air spaces and the outside of the leaf - results in faster rate of diffusion and transpiration.
73
FACTORS AFFECTING TRANSPIRATION - humidity
**Humidity** - the concentration of water vapour in the air.
- low humidity increases the rate of transpiration
- at low humidities, there is a steeper water potential gradient of water molecules between the leaf and atmosphere, resulting in a faster rate of diffusion and transpiration.
74
FACTORS AFFECTING TRANSPIRATION - light
- light is needed to photosynthesise.
- when the light intensity is high, plants will open their stomata to gain CO2 for photosynthesis at a maximum rate, so more water is lost.
- this will increase the rate of transpiration as more stomata are open.
75
How do we normally measure the rate of transpiration?
With a potometer.
76
Explain the process of using a potometer
1. A shoot with roots cut off is sealed in one end of the potometer with a bung, where a continuous column of water runs through the shoot to a thin capillary tube to a beaker of water.
2. An air bubble is then introduced into the end of the capillary tube.
3. As water is lost from the leaves by transpiration, it is replaced by the water in the capillary tube. Therefore, we can see the movement of the air bubble and use that to measure the rate of transpiration by measuring with a ruler how far the bubble has moved.
4. Finally, water from the reservoir is used to move the bubble back to the starting position.
WHEN SETTING UP…
- important that there are no unwanted bubbles in the apparatus. To do this, the apparatus should be set up under the water and the joints should be sealed with grease.
- the leaves should be dried and the plant should be left to acclimatise
77
What is the equation for rate of water uptake?
Rate of water uptake (mm3 s-1) = cross sectional area of capillary tube (mm2 ) x distance bubble moves (mm s-1)
78
What is the process of transport (of organic substances like sugars) by the phloem called?
Translocation
79
Describe the structure of the phloem
- made up of living, phloem cells (also known as phloem sieve elements)
- phloem sieve elements are called this because the walls of the cells (called sieve plates) have pores in them
- phloem sieve tube elements are made of cellulose
- sieve elements have few organelles and only a thin layer of cytoplasm close to their walls
80
Companion cells - what and why.
- sieve tube elements cannot keep themselves alive, so have to be aided by companion cells
- companion cells respire on the sieve elements behalf, and therefore, they have many mitochondria to do so
- they play an important role in transporting sucrose into the phloem for translocation
81
What are the sources?
- where sugars (sucrose) and solutes are made
- e.g. leaves (palisade mesophyll)
82
What are sinks?
- the parts of the plant that need solutes (the part of the plant which uses the sugars)
- e.g. the roots
- low concentration of solute, as it is being used (for respiration) or stored (converted to starch)
83
TRANSLOCATION - explain source to sink
Phloem tissues transport solutes with sugars like sucrose made by the **sources** (e.g. the leaves) to the **sinks**, which are parts of the plant which need those solutes to use them (e.g. the roots).
84
What three substances does the phloem transport?
- sucrose
- amino acids
- growth factors (e.g. hormones)
85
TRANSLOCATION - mass flow hypothesis
1. Solutes (sucrose) are actively transported (using ATP) from the sources cells to the companion cells and then sieve tubes. The solutes are ‘actively loaded’ into the phloem.
2. As solutes (sucrose) are loaded into the phloem, the solute/sucrose concentration increases and the water potential inside the phloem consequently decreases. This creates a water potential gradient, so water enters the sieve tubes by osmosis from the xylem.
3. This entry of water creates a high hydrostatic pressure at the source end of the sieve tubes.
4. At the sink end of the sieve tubes, solutes are removed to be stored or used up. As the solutes leave, the concentration of solutes inside the sieve tube decreases and the water potential therefore increase.
5. Water now leaves the sieve tube by osmosis. This loss of water creates a lower pressure at the sink end of the sieve tube, resulting in a pressure gradient between the two sites.
6. Now, water and solutes move down the pressure gradient - pushed from the area of higher pressure at the source to the area of lower pressure at the sink.
