Mass Transport (Haemoglobin, Transpiration and Translocation) Flashcards
(58 cards)
1
Q
Describe the structure of a haemoglobin.
A
- water soluble
- globular protein
- has 4 polypeptide chains, each containing a haem group
- has a quarternary structure
2
Q
What is the structure of the 4 polyptide chains in the haemoglobin?
A
- two are beta pleated sheets
- two are alpha helixes
3
Q
How many molecules of oxygen can a haemoglobin carry?
A
4
4
Q
What is the reaction between haemoglobin and oxygen?
A
Hb + 4O2 ⇌ Hb(O2)4
Hb(O2)4 is oxyhaemoglobin
5
Q
What is the partial pressure of oxygen?
pO2
A
the measure of oxygen concentration
6
Q
Where in the body is pO2 is high?
A
the lungs
7
Q
Where in the body is pO2 is low?
A
the body tissues (muscles)
8
Q
What is pO2 measured in?
A
kPa or kilopasclas
9
Q
What is another word for pO2?
A
oxygen tension
10
Q
What does affinity mean?
A
a tendency to attract
11
Q
How does the levels of pO2 affect affinity?
A
- where there is a high pO2 (lungs) there is a high oxygen affinity (more oxygen uptake/binding)
- where there is a low pO2 (body tissues) there is a low oxygen affinity (more oxygen unloading/bonds breaking)
12
Q
What graphs shows how pO2 affects Hb saturation?
A
Oxygen Dissociation Curve
13
Q
What is the shape of a Oxygen Dissociation Curve?
A
S shape
14
Q
Explain the S shape of the Oxygen Dissociation Curve.
A
- beginning there is a low pO2 but not much change to Hb saturation (not a very steep curve)
- middle there is a small change in pO2 and a large change (steep curve)
- end there is a high pO2 but not much change to Hb saturation (not a very steep curve)
15
Q
Explain the S shape of the Oxygen Dissociation Curve.
using what is happening in the Haemoglobin
A
- beginning of the graph, first molecule of oxygen binds to an Hb, which distorts the shape and takes a long time
- middle of the graph, change of shape means that it’s easier for first and second oxygen to bind
- more difficult for fourth oxygen to bind so line flatterns
16
Q
Why is it more difficult for the fourth oxygen molecule to bind?
A
all the other oxygen-binding sites are are occupied so it’s less likely that it will find one
17
Q
How does the haemoglobin exchange oxygen with the lungs?
A
- when blood has a lower pO2 than the lungs
- this creates a concentration gradient for oxygen to move into the blood from the alveoli
- when the oxygen moves out of the alveoli it is uploaded onto the Hbs until 96% full to produce oxyhaemoglobin
this process is the forward reaction
18
Q
How does the haemoglobin exchange oxygen with body tissues (muscles)?
A
- cells are constantly respiring which means that there is a low pO2
- Hb will unload oxygen which will diffuse into the tissue for aerobic respiration
19
Q
Why does carbon dioxide cause oxygen to be unloaded at the tissue?
Explain The Bohr Effect
A
- when the cells respire they produce CO2 which creates a high pCO2
- carbon dioxide is slighly acidic which affects the H+ bonds that make up the haemoglobin’s tertiary structure, causing a conformational change
- this decreases Hb’s affinity for oxygen so more oxygen is given up readily (more dissociation)
20
Q
How does carbon affect the Oxygen Dissociation Curve?
A
- it makes the curve shift to the right
- this is because saturation decreases as more oxygen is released
21
Q
What does it mean if the Oxygen Dissociation Curve shifts to the left?
A
- there is a greater affinity for oxygen
- more oxygen is taken from the lungs (alveoli)
occurs for animals who live in an area with less oxygen (high up, underground ect)
22
Q
What does it mean if the Oxygen Dissociation Curve shifts to the right?
A
- there is a lower affinity for oxygen
- more oxygen is given out into the tissues (for examples the muscle tissue)
occurs for animals who are very active (like animals who fly or run a lot) because they need it for respiration
23
Q
Explain the difference between an adult and fetal haemoglobin.
A
fetal haemoglobin has a higher affinity for oxygen because by the time blood has reached the placenta (for the fetus to absorb) oxygen saturation has decreased
*this allows them to survive in an area of low pO2 *
*their S curve shifts to the left *
24
Q
What is transpiration?
A
- is movement of water from the roots through the xylem to the surface of plant (mainly in the leave cells stomata) where it evaporates
- the evaporation occurs because the cells are coated in a layer of water, which means it has a higher water potebntial than the atmosphere therefore it moves out into the atomsophere by osmosis
25
What theory explains how the water travels up the xylem?
the cohesion-tension theory
26
Explain the cohesion-tension theory.
* Water transpires off the surface of a plant
* This lowers the water potential of cells
* this creates tension as it causes water to be pulled up the xylem, in a single column through adhesion and cohesion of the water molecules
* Water from the xylem moves into the surrounding cells down the water potential gradient by osmosis
27
How is water able to travel up the xylem against gravity?
* capillary action (cohesion and adhesion) and root pressure
* cohesion is the hydrogen bonds between each water molecule that causes them to stick together
* adhesion is the hydrogen bonds bwteen the water molecules and the xylem walls that causes them to stick together
* root pressure is the pressure increase caused by the increase of water volume in the roots after osmosis which is then forced upwards into the xylem
28
Describe the xylem's structure.
* it has no end walls therefore it's a long continuous tube
* has no organelles
* thick walls made of lignin
* has pits in the walls
29
Why is the xylem having no end walls important?
it means that there is always a continuous water column
30
Why is the xylem having no organelles important?
it means nothing can obstruct the flow of water
31
Why is the xylem having thick walls made of lignin important?
* lignin is strong therefore if the walls and thick and have lignin in it, the xylem will be able to withstand tension
32
Why is the xylem having pits important?
it allows for lateral movement to get around blocked vessels
33
What evidence is there to support the cohesion-tension theory?
* If the stem is cut air, instead of water from roots, is pulled up xylem ∴ there is tension in xylem
* When you measure the diameter of a tree trunk, it is smaller when transpiration is at its max, this supports cohesion as it shows the negative tension in the xylem created by cohesion (capillary action)
34
What is translocation?
the movement of assimilates in the phloem
35
What are assimilates?
products of photosynthesis (for example sugars)
36
Describe the process of translocation.
* companion cells actively transport sucrose (from the leaves/source) into the seive tube element
* this causes the water potential of the sieve tube element to decrease, allowing water from the xylem to move in via osmosis
* this increases hydrostatic pressure causing water and sucrose to then move down to the sink (the roots)
* sucrose is then actively transports into the sink and is turned into glucose (for resporation) or stored as starch
37
What experiments are there to support the mass flow theory?
* the ringing experiment
* traser experiment
38
Describe and explain the ringing experiment.
* a ring of bark is removed from the tree (in order to remove phloem)
* this causes the area to swell on the source side
* the swolen area has a higher amount of sugar than the area below it
* the area below dies
* this shows that transpiration occurs in the phloem as the swolen area can't transport sugar to the area below it because there is no phloem
39
Describe and explain the tracer experiment.
* leaf is supplied with radiactive tracers (radiactive carbon)
* the radiactive carbon is used to make assimilates
* they were then tracked as translocated using autoradioaugraphy
* this showed that substances are transported through the phloem
40
Describe the structure of the phloem.
* has companion cells
* has no organelles
41
Explain how phloems having no organlles are important.
* it maximises the amount of substances that can be transported as organelles aren't taking up space
* it also prevents organelles from obstructing transport
42
Explain how phloems having companion cells are important.
the companion cells have a lot of mitochondria therefore it can supply a lot of ATP for active transport of assimilates
42
What are the arguments against the mass flow hypothesis?
* the purpose of sieve plates are ambiguous as they look like they would obstruct flow
* not all substances travel at the same speed which they should according to the theory
43
How do you set up a potometer?
1. Cut the shoot underwater at a slant
2. Assemble potometer with capillary tube
end submerged in a beaker of water
3. Insert shoot underwater
4. Ensure apparatus is watertight / airtight
5. Dry leaves and allow time for shoot to
acclimatise
6. Shut tap to reservoir
7. Form an air bubble
8. quickly remove end of capillary tube from water
44
Why should the shoot be cut and put in the potometer under water?
to prevent air from entering the xylem
45
Why should you dry the leaves before?
because any moisture on the leaves can affect the rate of transpiration
46
How do you reset the air bubble?
open the tap
47
How do you find the rate of transpiration using a potometer?
* record the initial position of the bubble
* record the distance over a certain amount of time (minute)
* use the distance and the area of the capillaries cross section to find the volume
* use distance-speed-time to find the rate
48
What issues are there with using a potometer?
* the rate of water uptake and the rate of transcription may not be the same
* the rate of water uptake in the shoot may not be represenantive of uptake in a whole plant
49
Why may the rate of water uptake different to the rate of transpiration?
* plants use water in photosynthesis and make it in respiration
* water is used in to support
50
51
Why may the rate of water uptake in the shoot may not be represenative of water uptake in a plant?
* shoots don't have roots like plants do
* xylem cells are narrow
52
What factors increases the rate of transpiration?
* high light intensity
* high temperature
* high wind intensity
53
What factor decreases the rate of transpiration?
high humidity
54
Why does high light intensity increase the rate of transcription?
when it's light the stomata opens to let CO2 in for photosynthesis
this means water is able to leave through transpiration)
55
Why does high temperatures increase the rate of transcription?
* heat gives the water molecules more kinetic energy
* this means they can evaporate faster (transpire faster)
56
Why does high wind intensity increase the rate of transpiration?
* wind blows the water away from the stomata
* this decreases the water potential of the area surrounding the stomata which steepens the water potential gradient
* this allows water to evaporate faster (transpire faster)
57
Why does high humidity decrease the rate of transpiration?
* it increases the water potential of the air around the stomata
* this therefore makes the waterr potential gradient less steep and causes water to evaporate slower (transpire slower)
