chapter 7 - mass transport Flashcards
what is translocation?
Translocation is the movement of sugars and assimilate (amino acids and sucrose) through the phloem in both directions.
What is transpiration?
Transpiration is the movement of water in a plant through the xylem vessels in only One Direction
What is the structure of mature xylem
mature xylem or made of dead cells called vessel elements. They do not have end walls or living contents therefore they are hollow. This allows unrestricted unrestricted flow of water through the vessel. At certain points in the xylem walls there are pits (bordered pits) these are undignified regions and allow movement of water between xylem vessels. Xylem vessels are stacked end to end
What is the function of lignin in the xylem
xylem cells are lined with a waterproof coat made of the polysaccharide ligament. Lignin provides the strength and support to the cell walls of the xylem and it prevents water from escaping the tube. The xylem can also withstand pressure changes due to the movement of water with the support of lignin.
what is the function of vessels being being hollow in the xylem.
It provides minimum resistance to the flow of water up the xylem vessel.
What is the function of bordered pits in this xylem
they allow the flow of water and mineral ions from one element to another linking water uptake in roots with transpiration in leaves.
how are xylem vessels formed
Immature xylem vessels are waterproofed When lignin is deposited on the inside of their cell walls. This process of lignification kills the cells and allows for maximum flow of water through the hollow tubes.
describe the cohesion tension theory for when water moves up the xylem of plants
water from the soil travels by osmosis into the root hair cells [large surface area] as there is more volume of water in the root there is now a high pressure in the root. This high pressure pushes water upwards from The xylem to the leaves where there is a negative pressure due to water being lost from evaporation (from exchange surfaces). hydrogen bonds between water molecules causes the column of water to not break [cohesion] water molecules are attracted to the walls of the xylem vessels (adhesion). As the column of water is pulled up the xylem it creates tension pulling in the xylem in to become narrower this increases capillary action.
What are the four factors affecting the rate of transpiration
temperature -As the temperature increases the rate of transpiration increases as more water is being evaporated.
humidity- a lower humidity increases transpiration rate. as spaces are normally saturated with water where is outside the leaf it is less humid the greater the difference in humidity the faster the water vapor will diffuse out of the leaf.
air movement-greater air movement will increase transpiration rate. increases evaporation.
light intensity-higher light intensity will increase transpiration rate. stomata open in light and close in dark.
What is a potometer
A potometer is a device used for measuring the rate of water uptake from a leafy plant shoot the main reason for water uptake is transpiration. By changing the the surrounding atmospheric conditions the effects of transpiration of wind, heat, humidity and light can be measured. Potometers are difficult to set up because air bubbles in the xylem of the plant or in the apparatus itself will prevent the device from working properly
Describe the symplastic pathway
The movement of water between the cytoplasm and the vacuoles through the plasma membrane ‘s. This process is slow or compared to the Apoplasic pathway.
Describe the apoplastic pathway
water and minerals are transported through the cell walls this is a faster process compared to the symplastic pathway.
what two structures is the phloem made out of
companion cells
sieve tube elements
Where is the xylem located and where is the flow am located in vascular bundles
The xylem is located on the inner side of the vascular bundle and the phloem is located on the outside of the vascular bundle
Describe the structure of phloem tissue
Sieve tube elements are lined up end to end to allow the flow of sap. Sieve tube elements have little cytoplasm and no nucleus to maximize space for sap. However the cell is still alive. Between the ends of sieve tubes are sieve plates.
Companion cells control transport in the sieve tube elements. Companion sells may contain mitochondria because the phloem requires active transport to move sap in translocation.
What is a source
A source is a region of the plant where sucrose is loaded into the phloem, this could be the leaf as this is where photosynthesis takes place, producing glucose / sucrose. However it could also be a storage or getting West starch is stored/hydrolyzed and sugars are released.
What is a sink
A region of the plant where sucrose is removed from the phloem. This could be the root tip or bud [growth points] storage organs or where sugar is used in respiration or converted into starch for storage.
how does the process work at the source
Sucrose is actively loaded into the sieve tube elements this requires a companion cell to transport H+ ions and sucrose into the STE. This lowers the water potential in the STE therefore water moves into the STE by osmosis from the xylem from a less negative to a more negative water potential. This generates a high hydrostatic pressure causing mass flow towards the sink cells.
describe the process at the sink
sucrose is unloaded and enters the sink cells. This lowers the water potential of the sink cells. Water followed by osmosis from the sieve tube down a water potential gradient. A lower hydrostatic pressure is produced
describe active loading at the source
H+ ions are pumped out from the companion cells to the surrounding leaf tissue creating a diffusion gradient of H+ using active transport. H+ ions diffuse back into the companion cells through co-transporter proteins bringing sucrose with them. High concentrations of sugar in companion cells cause sucrose to defuse into the STE.
Describe the radioactive tracer method for evidence of translocation
radioactive carbon 14 [C14] can be used to follow the path of organic substances in a plant. The plant is supplied with CO2 and is allowed to photosynthesize. The sucrose produced will contain radioactive carbon as the sucrose moves to other parts of the plant it can be detected using autoRadiography. The sample is exposed to photographic/x-ray film and any radioactive areas will produce a dark shadow on the film showing where sucrose has been transported to.
Describe the ringing experiment for evidence of translocation
Ringing a plant means to remove a ring of phloem tissue around the circumference of a plant [the xylem is left in tact] this will mean that sucrose cannot be transported past at this point. When phloem tube is cut the flow in sap oozes and this is simple evidence to suggest that the contents of the tube or under pressure. [This is usually studied in conjunction with a radioactive tracer]
Describe the structure of a hemoglobin molecule and how it is formed
primary structure-Sequence of amino acids in four polypeptide chains.
Secondary structure-in which each of these polypeptide chains is coiled into a helix.
tertiary structure-each polypeptide chain is folded into a precise shape for the ability to carry oxygen. Quaternary structure-for polypeptides are linked together to form an almost safari cool molecule each polypeptide [4] is associated with a haem group. which contains a FE2+ ion. each ion can combine with a single oxygen molecule. Making a total of four oxygen molecules that can be carried by a single hemoglobin molecule in humans.
Describe the process in which oxygen binds to hemoglobin
The process is called loading or association. in humans this takes place in the lungs.
When there is a high partial pressure of oxygen there is high affinity and oxygen associates
Describe the process of hemoglobin releasing oxygen
This process is called unloading or disassociating. In humans this takes place in the tissues or muscles.
When there is a low partial pressure of oxygen there is a lower affinity and oxygen disassociates
What does hemoglobin with a high affinity for oxygen mean
hemoglobin with a high affinity for oxygen takes up oxygen more easily but releases it less easily
When there is a high partial pressure of oxygen that is a higher Finity and oxygen associates
what does hemoglobin with a low affinity for oxygen mean
hemoglobin with a low affinity of oxygen means that it takes up oxygen less easily and releases it more easily
When there is a low partial pressure of oxygen that is a low affinity and oxygen disassociate
How many Beta chains and how many alpha chains are in a single molecule of hemoglobin
They are two Beta chains and two alpha chains in a single molecule of hemoglobin
What is formed when hemoglobin is combined with oxygen
Oxyhemoglobin
Form via a condensation reaction
What does partial pressure of oxygen mean
It is a measure of how much oxygen is available to hemoglobin
Describe the oxygen disassociation curve for adult hemoglobin
The code is an S shape due to the behavior of hemoglobin in different partial pressures
The first oxygen molecule combines with hemoglobin and slightly distorts it the joining of the first molecule is quite slow. After the first molecule has joined the quaternary structure of hemoglobin has changed making it easier for the second and third oxygen to join. this is shown by the curve becoming steeper. joining the fourth Oxygen molecule is more difficult as the majority of the binding sites are occupied so it is less likely that the oxygen molecule can reach an empty site.
This is called positive Cooperativity As the binding of the first molecule made the binding of the second easier
describe the oxygen disassociation curve with the effects of carbon dioxide
In the presence of carbon dioxide hemoglobin has a reduced affinity for oxygen. The greater the concentration of carbon dioxide the more readily the hemoglobin releases its oxygen [bohr affect] When red blood cells reach a capillarity in a muscle the tissue will have a low partial pressure of oxygen because the tissues have been using oxygen for respiration. Oxyhemoglobin will unload completely in the presence of carbon dioxide [from respiring muscles]. This releases oxygen more readily for respiration and the dissolved carbon dioxide is acidic on the low pH cause the hemoglobin to change shape.
Describe the three factors affecting hemoglobin saturation
Blood pH-lowering blood pH causes the presence of H+ ions from lactic acid or carbonic acid to reduce the affinity for hemoglobin so more oxygen is delivered to acidic sites which are aspiring more.
Blood temperature-and increased blood temperature reduces hemoglobin affinity hence more oxygen is delivered to warmed up tissue
Carbon dioxide concentration-the higher the carbon dioxide concentration in tissue the less affinity of hemoglobin for oxygen so the higher the rate of respiration the more oxygen is released.
Comparing fetal and maternal hemoglobin
Fetal hemoglobin has a much greater affinity for oxygen because it binds too oxygen from the mothers blood stream.
The fetal hemoglobin can combine with a much higher percent of oxygen it will combine until it is 60% saturated. This allows the fetus to obtain oxygen from the Mum’s blood at low partial pressures
Why do large organisms have a transport system
Large organisms have a transport system because diffusion is fast enough for transport over short distances however the efficient supply of materials over larger distances requires a mass transport system.
What happens to the surface area to volume ratio when an organism increases in mass [size]
The surface area to volume ratio decreases
Features of transport systems
- A suitable medium to carry materials [blood] this is usually a liquid because water dissolves in substances and can be moved around easily but it can also be a gas such as a breathed in and out of the Lungs.
- A closed system of tubular vessels that contain the transport medium and form a branching network to distribute it to all parts of the organism
- A mechanism for transporting medium within the vessels [pressure difference]
Features of a transport system in plants
- Mechanism to maintain the mass flow of movement in one direction [valves]
- A way of controlling the flow of the transport medium to suit the changing needs of the different parts of the organism
- Mechanism for the mass flow of water or gas is for example intercostal muscles and die from during breathing in mammles