3B Mass Transport Flashcards
What kind of protein is haemoglobin?
- globular
What is haemoglobin?
- an oxygen-carrying pigment found in vast quantities in red blood cells
Describe the structure of red blood cells
- biconcave discs for high SA:V ratio
- no nucleus
- more space for haemoglobin for more oxygen transport
Describe the quaternary structure of haemoglobin
- made up of 4 polypeptide chains (globin proteins)
- made of 2 alpha globins and 2 beta globins
- each globin has a prosthetic haem group
How are the 4 globin subunits held together and arranged in haemoglobin?
- held together by disulphide bonds
- arranged with hydrophobic R groups facing inwards which preserves the 3D spherical shape
Why does the hydrophilic R groups facing outwards in haemoglobin benefit the molecule?
- it maintains solubility
Why is the arrangement of the R groups within haemoglobin important for its function?
- if changes occur to amino acid sequence, the function of the protein can change
- eg. in sickle cell anaemia, valine (non-polar) replaces glutamic acid (polar) which affects solubility of haemoglobin (lessens it)
Describe the importance of the prosthetic haem groups in haemoglobin
- prosthetic haem group contains an iron (II) ion (Fe2+) which is able to reversibly combine with an oxygen molecule
- this forms oxyhaemoglobin
- the presence if this causes blood to appear bright red in colour
How many oxygen molecules can each haemoglobin molecule carry?
- 4
- each haem group can carry one molecule
Are all haemoglobin molecules the same?
- the haem group is the same for all types of haemoglobin
- the globin chains can differ lots from different species of haemoglobins
Describe the function of haemoglobin
- responsible for binding oxygen in the lung and transporting oxygen to the tissue to be used in aerobic metabolic pathways (respiration)
How does haemoglobin help with transport of oxygen?
- oxygen isn’t very soluble in water
- haemoglobin is soluble in water
- oxygen can be carried more efficiently around the body when bound to haemoglobin
What does the presence of the haem group enable?
- enables small molecules like oxygen to be bound more easily because as each oxygen binds the quaternary structure is altered
- this is due to changes in the teriary structure
- this causes haemoglobin to have a higher affinity for subsequent oxygen molecules
Describe cooperative binding of haemoglobin
- binding of first oxygen molecule results in a conformational change in the structure of the haemoglobin molecule
- this makes it easier for each successive oxygen molecule to bind
What does the existence of the iron (II) ion in the prosthetic haem group allow?
- allows oxygen to reversibly bind to form oxyhaemoglobin
Which oxygen is hardest to dissociate from the haemoglobin?
- the last one
Describe what partial pressure is
- the pressure of the gas if the gas were in the same volume and temperature by itself
- it can change with altitude
Does altitude affect % composition of a mixture of gases?
no
What does the oxygen dissociation curve describe?
- the relationship between the partial pressure of oxygen and the % saturation of haemoglobin with oxygen
Why can haemoglobin pick up lots of oxygen in the lungs?
- low CO2 in lungs so haemoglobin can pick up more oxygen
- also a high partial pressure of oxygen in the lungs
Why is oxygen dropped off by haemoglobin in respiring tissues?
- the partial pressure of oxygen is low
- the oxygen diffuses out into the body cells down a conc grad
Why can a small change in partial pressure of oxygen have a very large effect on the % saturation of haemoglobin with oxygen?
- because haemoglobin has such a high affinity for oxygen
How does the partial pressure of oxygen in different areas of the body help with transport of oxygen?
- it ensures oxygen is picked up from where there is lots of it and dropped off to where there is less of it
How does pH alter haemoglobin?
- CO2 makes blood more acidic
- pH alters the hydrogen bonds in haemoglobin
What does the Bohr shift explain and how?
- explains how the ability of haemoglobin to bind to and release oxygen changes
- when partial pressure of CO2 is high (eg. in respiring tissues) haemoglobin’s affinity for oxygen is reduced
- this is because CO2 lowers the pH of the blood by forming carbonic acid and causes the release of oxygen
- CO2 in the lungs is comparatively lower so haemoglobin’s affinity for oxygen is increased
- causes easier binding
How does more CO2 affect the position of the oxygen dissociation curve?
- more CO2 shifts the dissociation curve to the right
What can have a major impact on the evolution of haemoglobin within a species?
- environmental factors
Describe the effects of altitude on haemoglobin
- the pp of oxygen is lower at higher altitudes
- species living at high altitudes have haemoglobin that is adapted to these conditions
- eg. llamas have haemoglobin that binds much more readily with oxygen
- this is beneficial as it allows them to obtain a sufficient level of oxygen saturation in their blood when the pp of oxygen is low
Describe the deer mouse’s haemoglobin
- they populate much of the US at high and low altitudes
- this species inhabits the widest range of altitudes of any north american mammal and it has a large degree of genetic variation for haemoglobin
Describe the lugworm and how its oxygen dissociation curve compares to that of a deer mouse
- lugworms live in low oxygen conditions
- luworm/high altitude deer mouse curve is to the right of the low altitude deer mouse’s curve and reaches 100% saturation quicker
Describe the adaptations of foetal haemoglobin
- more efficient at absorbing oxygen at lower concs
- vital as it allows for a baby to obtain oxygen from its mother’s blood (via placenta)
- oxygen conc in mother’s blood is lower than oxygen conc in the lungs
- after birth, the baby produces adult haemoglobin as it is more suited for uptake of oxygen from the air
Describe myoglobin and its adaptations
- ‘muscle haemoglobin’
- higher affinity for oxygen than foetal and adult haemoglobin
- myoglobin can take oxygen from adult haemoglobin
- used for storing oxygen in muscles
Compare the oxygen dissociation curves of myoglobin, foetal haemoglobin and adult haemoglobin
- myoglobin is furthest left
- foetal haemoglobin is in the middle
- adult haemoglobin is furthest right
What tends to be the case in larger more complex organisms in terms of their important exchange sites?
- they tend to be far away from other cells within the organism
Why is diffusion a non-viable method for transport of substances in larger organisms?
- the distance is too far and the process would be inefficient
- diffusion wouldn’t be fast enough for metabolic requirements of cells
- diffusion is only involved at exchange sites right at the start and end of the process
What is mass transport?
- the bulk movement of gases or liquids in one direction
- usually via a system of vessels and tubes
Describe generally the mammal circulatory system as a mass transport system
- one-way flow of blood carries nutrients and gases to all the cells of the body
What do mass transport systems help to do?
- help to bring substances quickly from one exchange site to another
- they also help maintain diffusion gradients at exchange sites and between cells and their fluid surroundings
- they ensure effective cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range
Describe blood circulation within mammals (big and small)
- small animals with large SA:V can rely on diffusion to exchange oxygen, CO2 and nutrients
- larger animals have a smaller SA:V so diffusion alone is insufficient for exchange of materials
What do all organisms need to do?
Exchange materials with their environments
What are circulatory systems generally?
- systems which carry around fluids containing materials needed by the organism as well as waste that needs removing
Describe a closed circulatory system
- blood is pumped around the body and is always contained within a network of blood vessels
- possessed by all vertebrates and many invertebrates
Describe an open circulatory system
- blood isn’t contained within blood vessels but is pumped directly into body cavities
- possessed by arthropods and molluscs
Which type of circulatory system do humans possess?
- double closed circulatory system
Describe the pulmonary circulatory system
- right side of the heart
- pumps deoxygenated blood to lungs for gas exchange
Describe the systematic circulatory system
- left side of the heart
- pumps oxygenated blood efficiently around the body
- pumps at high pressure
State the pathway of circulation starting at the right atrium
right atrium
tricuspid valve
right ventricle
pulmonary artery
lungs
pulmonary vein
left atrium
bicuspid valve
left ventricle
aorta
body
(renal artery, kidneys, renal vein)
vena cava
right atrium
etc.
Describe the function of the heart
- hollow muscular organ located in the chest cavity which pumps blood
- cardiac muscle tissue is specialised for repeated involuntary contraction without rest
Describe the function of the arteries
- blood vessels that carry blood away from the heart
- walls contain lots of muscle and elastic tissue
- lumen is narrow to maintain high blood pressure
- arteries range from 0.4-2.5cm in diameter
Describe the function of arterioles
- small arteries which branch from larger arteries and connect to capillaries
- around 30um in diameter
Describe the function of the capillaries
- tiny blood vessels which connect arterioles and venules
- their size means they pass directly past cells and tissues and perform gas exchange and exchange of substances
Describe the function of the venules
- small veins which join capillaries to larger veins
Describe the function of the veins
- blood vessels which carry blood back towards the heart
- the walls of veins are thin in comparison to arteries having less muscle and elastic tissue but a wider lumen
- valves help maintain blood flow back towards the heart
Describe the pulmonary artery
- carries deoxygenated blood away from the heart towards the lungs
Describe the pulmonary vein
- carries oxygenated blood towards the heart away from the lungs
Describe the coronary arteries
- supply the heart with oxygenated blood
Describe the aorta
- carries oxygenated blood out of the heart and to the rest of the body
Describe the vena cava
- carries deoxygenated blood towards the heart
Describe the renal artery
- supplies the kidneys with oxygenated blood
Describe the renal vein
- carries deoxygenated blood away from the kidneys to the heart
What separates the left and right side of the heart?
- the septum
Describe valves in the cardiac cycle
- prevent backflow of blood
- open when pressure behind them is greater than the pressure in front
- closed when pressure is greater in front of them
Compare semilunar valves and atrioventricular valves
- semilunar separate ventricles and arteries
- atrioventricular separate atrium and ventricles
What is important that happens in regards to the coronary arteries?
- important that they stay free of plaques
- plaques can lead to angina or heart attacks
Describe the heart walls
- ventricular walls are thicker than the atria walls
- atria wall contractions don’t generate much pressure (only enough to force the blood into the ventricles)
Compare the walls of the left and right ventricles
- left wall is thicker than the right
- blood leaving the left ventricle needs to travel further so needs to be at a higher pressure
Describe systole
- contraction of the heart
- contraction pushes blood out of heart
- atrioventricular valves are closed
- semilunar valves are open
Describe diastole
- relaxation of the heart
- atrioventricular valves are open
- semilunar valves are closed
Describe the demands needed for the arteries
- must be able to withstand high pressures generated by the heart
- must be able to maintain these pressures when the heart is relaxed
Describe the structure of the arteries
- wall is thick with layers of collagen, smooth muscle and elastic fibres
- elastic fibres allow the artery wall to expand around blood surging through at high pressure
- elastic fibres recoil when the heart relaxes (works with small lumen to maintain high pressure)
Describe the function of the veins
- receive blood that has passed through capillary networks
- blood is at low pressure and must be returned to the heart
Describe the structure of the veins
- wall is relatively thin with thinner layers of collagen, elastic fibres and smooth muscle
- lumen is much bigger than artery’s
- contain valves that prevent backflow of blood which helps return blood to the heart
Describe the arterioles
- what the large arteries split into that then branch into capillaries
Describe how arteriole structure relates to function
- walls are similar too artery walls but have more smooth muscle and less elastic fibres because they don’t have to withstand as high a pressure
- they have the ability to contract due to smooth muscle which regulates the flow of blood to a tissue
- can contract and temporarily cut off blood flow to certain organs
- eg. during exercise, blood flow to intestines may be reduced
Describe the structure of the capillaries
- very small lumen which forces slower travel so diffusion can occur
- capillaries branch between cells for a shirt diffusion distance
- wall is made from a single layer of endothelial cells which gives short diffusion distance and allows small pores to form so blood plasma can leak out and form tissue fluid
Describe the general process of how tissue fluid forms
- when blood is at the arteriole end of a capillary, the hydrostatic pressure is great enough to push molecules out of the capillary
- proteins remain in blood as they are too large to fit through gaps
- increased protein content lowers water potential
- the overall movement of water is out of the capillary
- at the venule end, less fluid is pushed out as the hydrostatic pressure is less than osmotic pressure
- overall movement of water is into capillary
What can hypertension cause in terms of tissue fluid?
- oedema
- if blood pressure is high then the pressure at the arteriole end is even greater so more fluid is forced out
- this fluid accumulates around tissues
- this is called oedema
What is tissue fluid and where is it located?
- it is blood plasma without the plasma proteins
- it is located between/around cells
Describe the movement of lymph
- some tissue fluid reenters the capillaries while some enters the lymph capillaries
- larger molecules enter the lymphatic system as lymph (made by cells, not plasma proteins)
- the liquid moves along the larger vessels of this system by compression caused by body movement (backflow prevented by valves)
- plasma proteins escaped from blood are returned to blood via the lymph capillaries
- if plasma proteins aren’t removed from tissue fluid then the water pot is lower so water can’t be reabsorbed
What is chd?
- any condition that interferes with the coronary arteries which supply blood to the heart muscle
State some main risk factors of chd
- genetic factors
- age and sex (older men at most risk)
- high blood pressure (can cause thicker artery walls, smaller lumen and enlarged ventricles or atheromas (fatty deposits) can develop)
- smoking (nicotine and tobacco can damage lungs and heart)
- high conc of low-density lipoproteins in the blood (cause atheromas)
What does the xylem transport?
- dissolved mineral ions
- water
What does the phloem transport?
- dissolved organic compounds
Compare the uptake of water and minerals
- water is passive via osmosis
- minerals can be active or passive via active transport and diffusion respectively
What 2 routes are there for transport of water and dissolved solutes within a plant?
- apoplast pathway
- symplast pathway
Describe the apoplast pathway
- most water travels this way when transpiration rates are high
- series of spaces running through cell walls, dead cells and hollow tubes of the xylem
- water moves via diffusion
- faster than symplast pathway
When must substances switch from the apoplast to the symplast?
- when they reach the Casparian strip
- it is a thick waterproof waxy band of suberin within the endodermis cells’ cell wall
State the order of a flow diagram for the apoplast
- soil water with dissolved mineral ions
- root hair cell wall
- cortex cell wall
- endodermis cell wall
- casparian strip
(switch to symplast) - endodermis cell membrane
- endodermis cytoplasm
- endodermis cell membrane
- endodermis cell wall
- xylem vessel
Describe the symplast pathway
- smaller amount of substance travels this way
- consists of cytoplasm and plasmodesmata of cells
- water moves by osmosis into the cell, possibly into the vacuole and between cells through the plasmodesmata
- movement of water is slower than apoplast
State the order of the flow diagram for symplast
- soil water and mineral ions
- root hair cell wall
- root hair cell membrane
- root hair cell cytoplasm
- plasmodesmata
- cortex cytoplasm
- plasmodesmata
- endodermis cytoplasm
- endodermic cell membrane
- endodermis cell wall
- xylem vessel
Describe transpiration
- the loss of water vapour from a plant to its environment via diffusion
- this water is replaced by water taken in at the roots and transported to the plant via the xylem
Which 2 properties of water allow it to move up the xylem during transpiration#/#
- cohesion: water molecules sticking to each other via hydrogen bonds
- adhesion: water molecules sticking to xylem walls
State some advantages of transpiration
- cools the plant via evaporative cooling
- transpiration stream is helpful in the uptake of mineral ions
- the turgor pressure of the cells provides support to the leaves and the stem of non-woody plants
Explain the effect on transpiration when air movement is high
more
good airflow removes water vapour from the air surrounding the leaf which maintains a conc grad so water loss is increased
Explain the effect on transpiration when humidity is high
less
humidity is a measure of moisture in the air so when air is saturated with water vapour, the conc grad is weaker so less water is lost
Explain the effect on transpiration when light intesnity is high
more
guard cells are responsive to light so when it is high they are turgid and stomata are open so water is lost
Explain the effect on transpiration when temp is high
more
at higher temps particles have more kinetic energy so transpiration occurs at a faster rate
Describe the adaptations of phloem for mass flow
- the intracellular space and walls of the sieve cells are adapted for the mass transport of sugars and amino acids
- very few organelles, small amount of cytoplasm and a large vacuole in intercellular space
- phloem sap can flow easily by moving through the open corridor that has low resistance
- sieve cells have thick cell walls to help withstand the pressure exerted by the mass flow of sugars
What does phloem sap consist of?
- sugars (mainly sucrose)
- water
- other dissolved substances eg. amino acids, hormones
What could the source of assimilates be in a plant?
- green leaves and green stem
- storage organs eg. tubers and tap roots
- food stores in seeds which are germinating
What could the sink of assimilates be in a plant?
- meristems
- roots that are growing and/or actively absorbing mineral ions
- any part of the plant where the assimilates are being stored eg. fruits
Why are carbs usually transported as sucrose in plants?
- allows for efficient energy transfer and increased energy storage (disaccharide so contains more energy)
- it’s less reactive than glucose as it’s a non-reducing sugar
Describe the first stage of the mass flow theory: loading of assimilates into the sieve tube elements
- sucrose diffuses down a conc grad by facilitated diffusion into the companion cells
- modified companion cells (transfer cells) pump H+ ions out of their cytoplasm so that they diffuse back in through a co-transporter with sucrose
- sucrose then moves into the sieve tube cells via diffusion through the plasmodesmata
Describe the second stage of the mass flow theory: mass flow of sucrose through the sieve tube elements
- this mechanism permits some plants to build sucrose conc up to 3x the conc of it in mesophyll
- high conc of sucrose descreases water potential in the phloem and water enters via osmosis
- results in high hydrostatic pressure
- sucrose is used or converted to starch for stoareg at respiring tissues/sinks
- these cells then have low sucrose conc so it is actively transported there which lowers their water potential
- water moves into these cells so hydrostatic pressure decreases in sieve tubes and creates mass flow to these low pressure areas
Describe the third stage of the mass flow theory: unloading of assimilates
- occurs at the sinks
- sucrose is actively transported by companion cells out of the sieve tubes and into the sink cells
- to maintain the conc grad, sucrose us converted into other storage molecules eg. starch
State evidence supporting the mass flow theory
- when phloem are punctured, phloem sap oozes out which indicates it is at high pressure
- phloem sap taken from near a source has high sucrose conc more than at sink which shows water potential would result in osmosis
- when a plant virus is applied to well-lit leaves, the virus can be seen moving through phloem to the roots which demonstrates bulk flow in one direction
- when virus is applied in the dark it isn’t transported which suggests photosynthesis needs to occur for translocation to occur
State some evidence against the mass flow theory
- amino acids travel slower than sucrose but they should travel at equal speeds as they are both in phloem
- different substances in the same sieve tube travel in different directions
- it is suggested some sieve tubes translocate at different times
What do tracer and ringing experiments involve?
- the removal of a ring of surface tissues from the stem of the plant while leaving the stem core intact
