Mass Transport Flashcards
Describe the structure of haemoglobin
A globular protein with a quaternary structure:
-4 coiled polypeptide chains
-4 heam groups
What to heam groups contain, and why are they known as a ‘prosthetic group’?
-Contains an iron ion that combines with oxygen molecules
-Prosthetic as they are not actually made out of amino acids, although a globular protein.
What is the role of haemoglobin?
Binds to O2 and transports it
What is ‘affinity’?
Ability of haemoglobin to bind or attract to O2
What is saturation?
When haemoglobin is holding the maximum amount of O2 it can bind to.
What is loading/association?
The binding of oxygen to haemoglobin
What is unloading/dissociation?
When oxygen detaches, or unbinds, from heamoglobin
Haemoglobin + Oxygen =?
Oxyhaemoglobin
What is the shape of an ‘Oxyheamoglobin dissociation curve’ and why?
S/sigmoid curve
Due to cooperative binding of O2 to the haem groups, e.g 1st one is the hardest, knock on effect, 4th is the easiest
How many oxygen molecules can heamoglobin hold?
4
What does the ‘oxyheamoglobin dissociation curve’ show?
-O2 is loaded in regions with a high partial pressure of O2 (e.g alveoli)
-O2 is unloaded in regions of low partial pressure of O2 (e.g respiring tissues)
What is ‘cooperative binding’?
When haemoglobin changes shape when the 1st O2 binds, which then makes it easier for further O2 molecules to bind.
-Always hardest for the first O2 to bind
What is the ‘Bohr Effect’?
When a high conc of CO2 causes the oxyhaemoglobin curve to shift right.
The affinity for O2 decreases because the acidic CO2 changes the shape of haemoglobin slightly.
What happens to the curve when there is a low pressure of CO2 in the alveoli? (Bohr shift)
Curve shifts left, increased affinity, loads more O2.
What happen when there is a high partial pressure of CO2 at respiring tissues? (Bohr shift)
Curve shifts right, decreased affinity, unloads more O2.
Summarise the effect of increasing and decreasing partial pressure of CO2 on O2 loading
Increase CO2= decrease O2 load
Decrease CO2= increase O2 load
-Increasing temp has a similar effect
How does the haemoglobin in different mammals differ?
-Have different types, which have different affinities for O2, an adaptation to their environment
Variations in:
-Polypeptide chain structure
-Number of polypeptide chains
-Number of haem groups
When does haemoglobin release O2?
In tissues where O2 conc is low
What is the function of the cardiac cycle?
Sequence of events which propels blood through the heart and blood vessels.
Describe Diastole (1)
-Atria and ventricular muscles are relaxed
-So blood will enter the atria via the vena cava and pulmonary vein
-Blood flowing into the atria increases the pressure within the atria.
Describe Atrial Systole (2)
-Atria muscular walls contract, increasing the pressure further (as vol decreases)
-This causes the atrioventricular valves to open and blood flows into the ventricles.
-Ventricular muscular walls are relaxed
Describe Ventricular Systole (3)
-After a short delay, the ventricle walls contract, increasing the pressure beyond that of the atria.
-Causes atrioventricular valves to close and semi-lunar valves to open.
-Blood id pushed out of the ventricles into the arteries (pulmonary + aorta).
Define Cardiac Output
The volume of blood which leaves one ventricle in one minute
What is the equation to find cardiac output?
Heart rate x stroke volume
What is heart rate?
Beats of the heart per minute (min-1)
Average: 60-80
What is stroke volume?
Volume of blood that leaves the heart in each beat (dm3)
Where are the semi-lunar valves?
In the aorta and pulmonary artery (top ones)
Where are the atrioventricular valves?
Between the atria and ventricles
bicuspid- left
tricuspid- right
When do valves open and close?
Open- pressure is higher behind the valve
Closed- pressure is higher in front of the valve
-Prevents backflow
Describe the structure and function of arteries
Carry blood away from the heart.
-Thick walls to withstand high blood pressures
-Elastic tissue for stretch and recoil
-Smooth muscle to vary blood flow
-Small lumen
Describe the structure and function of arterioles
Branch off of arteries, to feed into blood capillaries
-Thinner
-Less muscular walls
Describe the structure and function of capillaries
Site of metabolic exchange
-Smallest blood vessel
-One cell thick for fast exchange
Describe the structure and function of veins
Carry blood from body to heart
-Wide lumen to maximise vol of blood
-Thin walls as there is low pressure
-Contain valves to prevent backflow
Outline the structures of blood vessels from the inner most layer to outer
-Membrane
-Tunica intima
-Tunica media
-Tunica externa
What are venules?
Larger than capillaries, smaller than veins
Connect the two
What is tissue fluid?
Fluid containing water, glucose, amino acids, fatty acids, ions, and oxygen which bathes tissues
How is tissue fluid formed?
-Capillaries have small gaps in walls so liquid and small molecules can be forced out
-As blood enters capillaries from arterioles, the smaller diameter results in a higher hydrostatic pressure, smaller substances are forced out (tissue fluid)
This is ultrafiltration.
What is is forced out in tissue fluid?
-Water
-Dissolved minerals and ions
-Glucose
-Small proteins and amino acids
-Fatty acids
-Oxygen
What remains in the capillary during ultrafiltration?
-Red blood cells
-Platelets
-Large proteins
How is tissue fluid reabsorbed?
-Large molecules in capillaries create lowered water potential
-Towards venule end of capillary the hydrostatic pressure is lowered due to loss of liquid, so water potential is low
-Water re-enters the capillaries by osmosis
Explain what lymph is and why we have it
-Not all tissue fluid is reabsorbed back to the capillary, as eventually an equilibrium is met.
-The rest of the fluid is absorbed into the lymphatic system and will drain back into the bloodstream near the heart.
What is transpiration?
The loss of water vapour from the stomata by evaporation
What factors effect transpiration and how?
Light intensity: positive effect, stomata open
Temperature: positive effect, more kinetic energy
Humidity: negative effect, reduces water potential gradient
Wind: positive effect, blows away humid air
What does the cohesion-tension theory explain?
How water moves up the roots against gravity
What 3 factors make up the cohesion-tension theory?
Cohesion
Capillary (adhesion)
Root pressure
Explain the cohesion part of the cohesion-tension theory
-Water is dipolar which enables hydrogen bonds to form different molecules
-Creates cohesion, they stick together and water travels up xylem in a continuous water column
Explain the capillary part of the cohesion-tension theory
-Adhesion of water is when water sticks to other molecules, sticks to xylem walls
-The narrower the xylem the bigger the impact of the capillary
Explain the root pressure part of cohesion-tension theory
-As water moves into roots via osmosis it increases the vol of liquid inside the root, so pressure increases.
-This pressure forces water upwards
Describe the process of transpiration
- Water vapour evaporates out of stomata on leaves. Loss in water vol creates lower pressure.
- When water is lost by transpiration more water is pulled up the xylem to replace it
- Due to hydrogen bonds between water molecules, they are cohesive, creates a column of water.
- Water molecules adhere to walls of xylem, helps pull water upwards.
- As column of water is pulled up the xylem it creates tension, pulling the xylem to be narrower
What are the two components of the phloem tissue?
Sieve tube elements
Companion cells
Characteristics of sieve tube elements?
-Living
-No nucleus
-Few organelles
Role of companion cells?
Provides ATP required for active transport of organic substances
What is the mass-flow hypothesis?
-Sucrose (made) lowers the water potential of the source cell, so water enters by osmosis, increases hydrostatic pressure
-Respiring cells (sink) is using up sucrose and therefore it has a more positive water potential, water leaves by osmosis, decreases hydrostatic pressure
-As the source cell has higher hydrostatic pressure, solution is forced towards the sink cell via the phloem.
Describe translocation 1
- Photosynthesis occuring in the chloroplasts creates organic substances (source cell).
- Sucrose is actively transported into sieve tube elements using the companion cell * (ATP)
*Transports H+ to surrounding tissues creating a diffusion gradient, H+ diffuses back to companion cells and brings sucrose in with it using co-transport
Describe translocation 2
- Increase of sucrose in the sieve tube element lowers the water potential.
- Water moves into sieve tube elements from surrounding xylem vessels via osmosis.
- The increase in water vol increases hydrostatic pressure causing the liquid to be forced towards the sink.
Describe translocation 3
- Sucrose used in respiration at the sink or stored as insoluble starch
- More sucrose is actively transported into sink cell, causing water potential to decrease
- This results in osmosis of water from sieve to sink
- Removal of water decreases vol in sieve tube element so hydrostatic pressure decreases.
What are ringing experiments?
Investigates if phloem is responsible for mass flow.
-Bark and phloem of a tree is removed
-Overtime the tissues above the missing ring swell with sucrose and tissue below dies
What are tracer experiments?
-Plants are grown in an environment that contains radioactivity labelled CO2. They are incorporated into the sugar produced in photosynthesis.
-Movement of these sugars can now be traced through the plant using autoradiography.
