3.4 Mass Transport Flashcards
1
Q
Describe the structure of haemoglobin
A
- Globular
- Water soluble
- Consists of four polypeptide chains, each carrying a haem group (quaternary structure)
2
Q
Describe the role of haemoglobin
A
- Present in red blood cells
- Oxygen molecules bind to the haem groups and are carried around the body to where they are needed in respiring tissues
3
Q
Name three factors affecting oxygen-haemoglobin binding
A
- Partial pressure of oxygen
- Partial pressure of carbon dioxide
- Saturation of haemoglobin with oxygen
4
Q
How does partial pressure of oxygen affect oxygen haemoglobin binding?
A
- As partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases
- So oxygen binds tightly to haemoglobin
- When partial pressure is low, oxygen is released for haemoglobin
5
Q
How does partial pressure of carbon dioxide affect oxygen-haemoglobin binding?
A
- As partial pressure of carbon dioxide increases, the conditions become acidic, causing haemoglobin to change shape
- The affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin
- Known as Bohr effect
6
Q
How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?
A
- It is hard for the first oxygen molecule to bind
- Once it does, it changes shape to make it easier for the second and third molecules to bind, known as positive cooperativity
- It is then slightly harder for the fourth oxygen molecule to bind because there is a low chance of finding a binding site
7
Q
Explain why oxygen binds to haemoglobin in the lungs
A
- Partial pressure of oxygen is high
- Low concentration of carbon dioxide in the lungs, so affinity is high
- Positive cooperativity (after the first oxygen molecule binds, binding of subsequent molecules is easier)
8
Q
Explain why oxygen is released from haemoglobin in respiring tissues
A
- Partial pressure of oxygen is low
- High concentration of carbon dioxide in respiring tissues, so affinity decreases
9
Q
What do oxyhaemoglobin dissociation curves show?
A
- Saturation of haemoglobin with oxygen (%), plotted against partial pressure of oxygen (kPa)
- Curves further to the left show the haemoglobin has higher affinity for oxygen
10
Q
How does carbon dioxide affect the position of an oxyhaemoglobin dissociation curve?
A
Curve shifts to the right because haemoglobin’s affinity for oxygen has decreased
11
Q
Name three common features a mammalian circulatory system
A
- Suitable medium for transport, water-based to allow substances to dissolve
- Means of moving the medium and maintaining pressure throughout the body, such as the heart
- Means of controlling flow so it remains unidirectional, such as valves
12
Q
Relate the structure of the chambers to their function
A
- Atria - thin walled and elastic, so they can stretch when filled with blood
- Ventricles - thick, muscular walls pump blood under high pressure. The left ventricle is thicker than the right because it has to pump blood all around the body
13
Q
Relate the structure of the vessels to their function
A
- Arteries have thick walls to handle pressure without tearing, and are muscular and elastic to control blood flow
- Veins have thin walls due to lower pressure, therefore requiring valves to ensure blood doesn’t flow backwards. Have less muscular and elastic tissue as they don’t have to control blood flow
14
Q
Why are there two pumps (left and right) needed instead of one?
A
- To maintain blood pressure around the whole body
- When blood passes through the narrow capillaries of the lungs, the pressure drops sharply and therefore would not be flowing strongly enough to continue around the whole body
- Therefore, it is returned to the heart to increase the pressure
15
Q
Describe what happens during cardiac diastole
A
- The heart is relaxed
- Blood enters the atria, increasing the pressure and pushing open the atrioventricular valves
- This allows blood to flow into the ventricles
- Pressure in the heart is lower than in the arteries, so semi-lunar valves remain closed
16
Q
Describe what happens during atrial systole
A
The atria contract, pushing any remaining blood into the ventricles
17
Q
Describe what happens during ventricular systole
A
- The ventricles contract
- The pressure increases, closing the atrioventricular valves to prevent backflow and opening the semi-lunar valves
- Blood flows into the arteries
18
Q
Name the nodes involves in heart contraction and where they are situated
A
- Sinoatrial node (SAN) = wall of right atrium
- Atrioventricular node (AVN) = in between the two atria
19
Q
What does myogenic mean?
A
The heart’s contraction is initiated within the muscle itself, rather than by nerve impulses
20
Q
Explain how the heart contracts
A
- SAN initiates and spread impulse across the atria so they contract
- AVN receives, delays and then conveys the impulse down the bundle of His
- Impulse travels into the Purkinje fibres which branch across the ventricles, so they contract from the base up
21
Q
Why does the impulse need to be delayed?
A
If the impulse spread straight from the atria into the ventricles, there would not be enough time for all blood to pass through and for the valves to close
22
Q
How are the structure of capillaries suited to their function?
A
- Walls are only one cell thick - short diffusion pathway
- Very narrow, so can permeate tissues and red blood cells can lie flat against the wall, effectively delivering oxygen to tissues
- Numerous and highly branched, providing a large surface area
23
Q
What is tissue fluid?
A
- A water substance containing glucose, amino acids, oxygen and other nutrients
- It supplies these to the cells, while also removing any waste material
24
Q
How is tissue fluid formed?
A
- As blood is pumped through increasingly small vessels, this creates a hydrostatic pressure which forces fluid out of the capillaries
- It bathes the cells, and then returns to the capillaries when the hydrostatic pressure is low enough
25
How is water transported in plants?
Through xylem vessels; long continuous columns that also provide structural support to the stem
26
Explain cohesion tension theory
- Water molecules form hydrogen bonds with each other, causing them to 'stick' together (cohesion)
- The surface tension of the water also creates this sticking effect
- Therefore, as water is lost through transpiration, more can be drawn up the stem
27
What are the three components of phloem vessels?
- Sieve tube elements = form a tube to transport sucrose in the dissolved form of sap
- Companion cells = involved in ATP production for active loading of sucrose into sieve tubes
- Plasmodesmata = gaps between cell walls where the cytoplasm links, allowing substances to flow
28
Name the process whereby organic materials are transported around the plant
Translocation
29
How does sucrose in the leaf move to the phloem?
- Sucrose enters companion cells of the phloem vessels by active loading, which uses ATP and a diffusion gradient of hydrogen ions
- Sucrose then diffuses from companion cells into the sieve tube elements through the plasmodesmata
30
How do phloem vessels transport sucrose around the plant?
- As sucrose moves into the tube elements, water potential inside the phloem is reduced
- This causes water to enter via osmosis from the xylem and increases hydrostatic pressure
- Water moves along the sieve tube towards areas of lower hydrostatic pressure
- Sucrose diffuses into the surrounding cells where needed
31
Give evidence for the mass flow hypothesis of translocation
- Sap is released when a stem is cut, therefore there must be pressure in the phloem
- There is a higher concentration in the leaves than the roots
- Increasing sucrose levels in the leaves results in increased sucroses in the phloem
32
Give evidence against the mass flow hypothesis of translocation
- The structure of sieve tubes seems to hinder mass flow
- Not all solutes move at the same speed, as they would in mass flow
- Sucrose is delivered at the same rate throughout the plant, rather than to areas with the lowest sucrose concentration first
33
How can ringing experiments be used to investigate transport in plants?
- The bark and phloem of a tree are removed in a ring, leaving behind the xylem
- Eventually, the tissues above the missing rings swells due to the accumulation of sucrose as the tissue below begins to die
- Therefore, sucrose must be transported in the phloem
34
How can tracing experiments be used to investigate transport in plants?
- Plants are grown the the presence of radioactive CO2, which will be incorporated into the plant's sugars
- Using autoradiography, we can see that the areas exposed to radiation correspond to where the phloem is
