3.2 (7) - Mass Transport Flashcards
Haemoglobin Transport of oxygen by haemoglobin Circulatory system of a mammal The structure of the heart The cardiac cycle Blood vessels and their functions Transport of water in the xylem Transport of organic molecules in the phloem Investigating transport in plants
What is haemoglobin?
Haemoglobins are proteins with a quaternary structure that makes it efficient for unloading oxygen under one set of conditions, and unloading it under another.
Describe the levels of haemoglobin’s structure.
- Primary - sequence of amino acids in the 4 polypeptide chains
- Secondary - the 4 polypeptide chains are coiled into an ɑ-helix
- Tertiary - the polypeptide chains are folded into a precise shape
- Quaternary - all 4 polypeptides are linked together. Each polypeptide is associated with a haem group, which contains a ferrous (Fe+2) ion. Each Fe+2 ion can combine with a single O2, to make a total of 4 O2 molecules that can be carried by a single haemoglobin molecule in humans
What does ‘loading’ and ‘unloading’ mean? Where do they happen in humans?
- Loading - Hb binds with O2 (lungs)
- Unloading - Hb releases its O2 (tissues)
What is the function of haemoglobin?
Transporting O2
What must haemoglobin do to make O2 (un)loading more efficient?
To be efficient at (un)loading O2, Hb must:
- readily associate with O2 at the surface where gas exchange takes place - readily dissociated from O2 at those tissues requiring it
Why does Hb readily associate with O2 at the surface where gas exchange takes place and dissociated from O2 at those tissues requiring it?
These happen because Hb’s affinity for O2 changes under different conditions. It changes its shape in the presence of certain substances (eg. CO2).
In the presence of CO2, the new shape of the Hb molecule binds more loosely to O2, so the Hb releases its oxygen.
Define ‘partial pressure’.
A measure of O2 concentration. The greater the concentration of dissolved O2 in cells, the higher the partial pressure.
Why do different haemoglobins have different O2 affinities?
- Each species has a Hb with a slightly different amino acid sequence.
- Therefore, the Hb of a species has a slightly different tertiary and quaternary structure with different binding properties, so different Hbs have different affinities for oxygen.
What is an erythrocyte?
Red blood cell
How are RBCs adapted for their function?
- Biconcave shape maximises SA for gas exchange
- Small and flexible to pass through narrow capillaries
- No nucleus - more room to carry respiratory gases
- Packed with Hb
What allows lung tissue to have a high pO2?
Ventilation
When the pO2 is high, more oxygen is able to associate with Hb molecules to be transported.
What does an oxygen dissociation curve show the relationship between?
The relationship between Hb’s oxygen saturation and the partial pressure of O2.
What happens to haemoglobin after the first O2 molecule associates?
Its conformation changes, meaning that it’s easier for a second and third O2 molecule to associate with the Hb
Why does an oxygen dissociation curve plateau below 100% O2 saturation?
It is difficult for a 4th O2 molecule to associate with Hb, due to the reduced probability of an O2 molecule hitting the final binding site.
Why does foetal Hb need to get O2 from maternal to foetal blood?
It needs O2 from maternal blood because foetal Hb has a higher affinity for oxygen because a foetus needs more O2 to survive, meaning that it needs as much O2 as possible
- By the time the blood reaches the placenta, it has a lower pO2.
- Foetal Hb has a higher O2 affinity so that the Hb can bind to oxygen at the lower pO2
- It needs this oxygen to survive in the womb
Why are foetal Hb oxygen dissociation curves to the left of adult curves?
Foetal Hb’s stronger affinity means that they become saturated at a lower pO2.
In what 3 ways in CO2 transported through the circulatory system?
- Dissolved in blood plasma (5%)
- Associated with Hb to form carbaminohaemoglobin (10%)
- Transported as hydrogen carbonate ions (85%)
What happens to oxygen where the pO2 is low?
The oxygen dissociates from oxyhaemoglobin
Where is pO2 low?
In respiring tissues
What happens more often in respiring tissues?
In respiring tissues,:
- More CO2 is produced
- More carbonic acid is formed
- More H+ ions are dissociated
- More competition for Hb
- More oxygen is dissociated
What is the Bohr Effect?
- In a CO2-rich environment (respiring tissue), more O2 dissociates from oxyhaemoglobin
- O2 dissociation curve shifts to the right (because a higher pO2 is required to saturate Hb due to H+ competition)
How is CO2 transported through the circulatory system as hydrogen carbonate ions?
- CO2 dissolves in water to form carbonic acid
- Acid releases H+ protons (acid dissociation)
- HCO3 ions diffuse out of the RBC
- CL- diffuses into the cell to balance the charge out (chloride shift)
What does having a closed, double circulatory system mean?
CLOSED - The blood travels through vessels, instead of freely moving
DOUBLE - The heart has chambers that separate bloodstreams of different oxygen saturations
What type of blood does the right side of the heart receive? Where does it come from? Where is it going?
The right side receives deoxygenated blood from the body and pumps it to the lungs
What type of blood does the left side of the heart receive? Where does it come from? Where is it going?
The left side receives oxygenated blood from the lungs and pumps it to the body
What is an advantage of having separate bloodstreams?
- It makes circulation more efficient
- Allows pressure to be maintained around the body
What are the 4 chambers of the heart called?
- Right atrium
- Right ventricle
- Left ventricle
- Left atrium
What are the ____ veins and arteries of the heart?
Veins
- Pulmonary veins
- Superior and inferior vena cava
Arteries
- Pulmonary artery
- Aorta
What are the 4 valves of the heart?
- Tricuspid valve
- Pulmonary valve
- Aortic valve
- Mitral valve
Where is the tricuspid valve located?
Between the right atrium and ventricle
Where is the pulmonary valve located?
Between the right ventricle and pulmonary artery
Where is the aortic valve located?
Between the left ventricle and aorta
Where is the mitral valve located?
Between the left ventricle and left atrium
Which 2 valves are the atrioventricular valves?
Tricuspid and mitral valve
Which 2 valves are the semi-lunar valves?
Pulmonary and aortic valve
What is the difference between tricuspid and bicuspid valves?
Tricuspid valves have 3 cusps and bicuspid valves have 2 cusps
Which heart valve is the only bicuspid valve?
Mitral valve
What is the muscular wall that separates the ventricles called?
Septum
Why is the muscular wall of the left ventricle much thicker than the others?
The left ventricle has a thicker wall because it needs to contract with more force to get blood all around the body
What is the function of the atrioventricular valves?
Prevent the backflow of blood into the atria
What is the function of the semi-lunar valves?
Stop the blood returning to the heart (ventricles)
The heart is myogenic - what does this mean?
It can contract and relax without signals from nerves
What is atrial systole?
When the atria contract simultaneously
What is atrial diastole?
When the atria relax simultaneously
What is ventricular systole?
When the ventricles contract simultaneously
What is ventricular diastole?
When the ventricles relax simultaneously
What is diastole?
Where the atria and ventricles are both relaxed
What happens during atrial contraction (1st stage of cardiac cycle)?
The atria contract, forcing blood into the ventricles
What happens during isovolumetric contraction (2nd stage of cardiac cycle)?
- Atrioventricular valves close (lub sound)
- While the semi-lunar valves are closed, the ventricles contract
What happens during ventricular ejection (3rd stage of cardiac cycle)?
- Semi-lunar valves open
- Ventricles contract and blood is pumped into the aorta and pulmonary artery
What happens during isovolumetric relaxation (4th stage of cardiac cycle)?
- Semi-lunar valves close (dup sound)
- The heart relaxes and blood is sent to the lungs and around the body
What happens during atrial filling (5th stage of cardiac cycle)?
The atria fill with blood whilst the atrioventricular valves are closed
What happens during ventricular filling (6th stage of cardiac cycle)?
The ventricles fill with blood
Describe the structure of capillaries
- Very narrow lumen
- Walls = many layers of cells thick
- No elastic layer
- No muscular layer
- No valves
Describe the structure of arteries
- Narrow lumen
- Many layers of cells thick
- Thick elastic layer
- Thick muscular layer
- No valves
Describe the structure of veins
- Wide lumen
- Walls = many layers of cells thick
- Thin elastic layer
- Thin muscular layer
- Has valves
What are arterioles?
- Arterioles are the smaller vessels that arteries divide into
- They branch into capillaries
- Blood comes from the heart
What are venules?
- Small blood vessels that join into veins
- They branch from capillaries
- Blood is sent to the heart
What is tissue fluid?
- Tissue fluid is fluid which surrounds and bathes tissues
- Contains water, glucose, amino and fatty acids, ions and oxygen
What is hydrostatic pressure?
The pressure that causes fluid to be forced out of something (eg. tissue fluid being forced out of capillaries)
What is osmotic pressure?
The pressure under which water is forced from somewhere of a high concentration into an area of low concentration
How is tissue fluid formed in the capillaries?
- Arteriole end of capillary bed
- High blood pressure in arteriole end because blood is pumped from the heart
- High BP results in high hydrostatic pressure which forces water with small solutes out of the capillary, causing ultrafiltration
- Tissue fluid surrounds tissue cells
How is tissue fluid re-absorbed in the capillaries?
- At the venule end of the capillary bed
- Because the liquid in the capillaries has a low water potential and hydrostatic pressure (compared to the tissue fluid), the tissue fluid moves back into the capillaries by osmosis, down the concentration gradient
What is ultrafiltration?
When water, glucose, amino and fatty acids, ions and oxygen are forced out of the blood in a capillary due to high hydrostatic pressure
Why is the hydrostatic pressure at the venule end of the capillaries lower than at the arteriole end?
So much liquid has been forced out of the capillary so there is not much left to force out, meaning that the HS pressure is lower
Why does the liquid in the blood have a very negative water potential at the venule end of the capillaries, compared to the tissue fluid?
Large molecules remain in the blood and lots of water is forced out, causing its solute concentration to be higher and its water potential to be more negative
How is excess tissue fluid eventually absorbed into the bloodstream?
- Excess tissue fluid is absorbed into lymphatic veins (by osmosis) that surround the capillaries and tissues
- Once the tissue fluid is in the lymphatic veins, it is called ‘lymph’
- Lymphatic veins drain the lymph into lymphatic ducts, which empty the lymph into 2 subclavian veins (under the collarbones)
- The subclavian veins join to form the superior vena cava, so the lymph can be pumped through the heart
Because lymph isn’t moved by the pumping of the heart, how is it moved?
Lymph moves via:
- Hydrostatic pressure
- Contraction of body muscles that squeeze the lymph vessels
What is an atheroma?
Build-up of fatty deposits
How does coronary heart disease (CDH) develop?
- The (usually smooth) lining of the arterial endothelium can become damaged by excess pressure
- Macrophages and lipids clump together at the site of the damage, forming fatty streaks below the endothelium
- Over time, the streaks and clump grow and connective tissue builds up to form a fibrous plaque (atheroma)
- Atheroma partially blocks the lumen → restricts blood flow → blood pressure increases, which can aggravate the existing atheroma and can cause others to develop
What is an aneurysm?
A balloon-like swelling from an artery
How does an aneurysm form?
- Atheroma damages the artery
- High blood pressure may push a membrane through the elastic coating of the artery → creates a balloon-like structure (aneurysm)
- The aneurysm may burst, causing a haemorrhage
What is thrombosis?
Blood clot in a blood vessel
How does thrombosis occur?
- An atheroma can burst through the arterial endothelium into the lumen
- This creates a rough surface of the endothelium
- Platelets and fibrin attempt to repair the damage → causes a blood clot to form
- The blood clot may eventually block the artery or break off into pieces (pieces could cause blockages in narrower vessels)
- Debris from the clot may cause additional clots to form elsewhere
From left to right, what are the components of a horizontal cross section of a root?
Root hair → epidermis → cortex → endodermis → vascular tissue (xylem and phloem)
From the outside to the inside, what are the components of a vertical cross section of a root?
Root hair → epidermis → cortex → endodermis → casparian strip → pericycle → phloem → xylem
What are xylem vessels like?
- Narrow tubes made of dead cells (so that they don’t absorb the water)
- Strong walls made of lignin which stop the xylem from collapsing
Describe the process of transpiration
- There is a WP gradient from the air spaces in the leaf through the stomata and to the air
- Mesophyll cells in leaf lose water through evaporation
- The cells now have a lower WP so water enters by osmosis from the surrounding cells
- WP gradient is established, which pulls water up the xylem
What is a hydrogen bond?
A weak chemical bond between electropositive hydrogen and other electronegative atoms (eg. oxygen)
What is cohesion? Give an example
- A force resulting from attraction between molecules of the same substances
- Water molecules “stick” together by cohesion
What is adhesion? Give an example
- A force resulting from attraction between molecules of different substances
- Water molecules “stick” to the sides of the xylem
Explain the cohesion-tension mechanism
- Water evaporates from the leaf cell walls and diffuses out of the stomata (transpiration)
- This creates a tension (pulling) on the water in the xylem
- The cohesion of water (due to hydrogen bonding) transmits the pulling force all the way down to the roots (transpiration pull)
- Adhesion of the water to the xylem vessel also aids in resisting gravity
What are 3 pieces of evidence that support the cohesion-tension mechanism theory?
- The change in the diameter of a tree trunk during the day due to transpiration (more transpiration during the day means more tension → xylem shrinks)
- If a xylem vessel is broken and air enters, the tree can’t draw up water due to the broken column, so cohesion can’t occur
- When you break a xylem vessel, water doesn’t leak out but air is drawn in due to the tension
How do you use a potometer to measure transpiration rate?
1) Shoots with roots cut off are sealed in one end of the potometer with a bung
2) A continuous stream of water runs from the shoot through a thin capillary tube to a beaker of water
3) One air bubble is left in the far end of the capillary tube
4) Water is lost from the leaves by transpiration and replaced by water in the capillary tube
5) The faster/further the bubble travels, the fast the rate of transpiration
6) This is measured against a ruler in mm
7) Water from the reservoir is used to move the bubble back to the starting position
Describe phloem vessels
- Phloem cells (sieve tube elements):
- are alive but have few organelles
- have ends that form structures called ‘sieve plates’, through which cytoplasm can pass
- Sieve tube elements can’t keep themselves alive, so they have to be aided by companion cells which respire on their behalf
How are organic substances transported through the phloem?
- Phloem tissues transport solutes made in sources to parts of the plant that need them (sink cells)
- This is called translocation
- There is always a high concentration of solute in the source cells and a low concentration in the sink cells
What substances do phloem transport?
- Sucrose (solute carbohydrates)
- Hormones
Describe the process of translocation
1) Solutes are actively transported (by co-transport) from source cells → companion cells → sieve tubes
2) This lowers the water potential, so water also moves by osmosis into the sieve tubes
3) This creates a high pressure in the sieve tubes near source cells
4) Since solutes are used up or stored in sink cells, the opposite happens near the sink cells
5) This results in a pressure gradient between the two sites
6) Water and solute move down the pressure gradient
What are 4 pieces of evidence that support mass flow (movement of organic substances)?
- Ring bark experiments - bulge above ringed area.
- Radioactive tracing using carbon 14 to track movement of sugars
- Pressure of sap pouring out through damaged phloem. E.g. aphid mouthparts.
- Metabolic inhibitors stop ATP availability so prevent the active transport required to power the process.
