Biology Unit 2- Exchange & transport

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  • Created by: FireDwarf
  • Created on: 18-02-14 16:13
What affects the type of exchange surface and transport system?
The size and metabolic rate of the organisim will effect the rates of exchange and thus to actual surface.
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What is the SA: V ratio for exchange to be effective?
High SA: V ratio.
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What organisims have this? How does volume increase as organisim size increases? Compare with SA? Therefore?
small ones- Volume increases faster then SA. Therefore SA:V ratio becomes lower as organisim bigger, less effective exchange.
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What are the two features larger organisms have developed to combat this?
A flatterned shape, so no cell is far away from the surface OR/AND specilised exchange surfaces with a large SA.V ratio.
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What are the features of an exchange surface?
Large SA:V ratio, thin so diffusion pathway is short, partially permmable, control of envriomental medium & internal medium
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Diffusion is proportional too..?
SA x diff in conc/ Lengh of D pathway.
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How is gas exchanged in a typical single-celled organisim?
Via diffusion across their body surface, which is covered only in a partially permmable membrane.
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Why can insects not just engage in diffusion for gas exchange?
They have a waterproof coating and a small SA:V ratio to prevent water loss, which also reduces gas exchange and therefore reduces the efficiency .
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What do they have instead? (names)
Spiracles then Tracheae which divide into tracheoles.
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So how does the system work?
Gas enters and leaves the tracheae through spiriacles on the body surface. The gases diffuse down the tracheae (which are supported by rings), which then divide into smaller tubes (tracheaoles) which extend through all the tissues of the insect
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advantage of this?
Tissues recieve the o2 and lose the c02 directly.
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How do gases move out and in of the trachea system? (2 ways)
Diffusion gradient; O2 is used up in resperation so the concentration falls at the end of the tracheaoles. This creates a gradient which causes o2 to diffuse from atmosphere into the tracheae and tracheaoles and into the cells.
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Movement of the muscles in insects causes mass movements of air in and out of the tracheae.
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How do spiracles open and close? What is the bad point of spiracles?
Via a valve. They do however cause water loss, thus need to remain closed most of the time.
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Disadvantages of the system?
The diffusion pathway must be kept short, therefore insects are limited by their size.
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Why cant fish just carry out diffusion?
Because they have a waterproof coating and therefore a gas-tight coating. Also small SA:V ratio.
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Where are the gills located?
Within the body of the fish, behind the head.
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What are gills made up of?
Gill filaments & gill lamellae.
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How are the gill filmaments and gill lamellae organised?
Gill filaments stacked up in a pile, with gill lamellae at right angles to the filaments to increase the surface area.
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How does water travel through the fish? What is this opposite too? What is this called?
It travels through the mouth, forced over the gills, then exits through a an opening in each side of the body. Flow is opposite to the blood & this is called countercurrent flow.
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Why is the countercurrent flow good?
To maintain the most efficent diffusion gradient. Blood high in o2 meets water high in o2 conc. Therefore, diffusion of o2 occurs from water into blood. Blood low in o2 conc meets water which has most but not all o2 diffused out.
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What do we observe therefore?
almost constant rate of diffusion at the entire lengh of the gill lamellae. (80%)
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If they flowed in the same direction?
then we would see less diffusion occur, therefore less efficent (about 50%)
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What is diffrent about the plant compared to animal cells?
They engage in photosythesis & resperation.
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What happens during photosythesis?
Some C02 is used from resperation of cells but most from the atmposhere. Some o2 used for resperation but most of it is diffused out.
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When photosythesis cant take place?
O2 diffuses into leaf & co2 diffuses out (resperation)
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How is a plant adapted for gas exchange?
No living cell is farm from external air & diffusion takes place in the gas exchange so therefore faster.
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How are leaves adapted for exchange?
Thin, flat shape. Many pores called stomata to allow for exchange. Air spaces in the mesophyll tissue.
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Pores which occur mainly on the leaves, especially the underside. Each surrounded by guard cells, which can open and close the pore. Control rate of gas exchange and reduce water loss therefore.
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What is the lowest level of the plant cell called? and above?
Waxy cuticle and then Lower epidermis
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Order of layers & features after those two?
spongey mesophyll layer which contains air spaces. Then mesophyll pallisade which contains pallisade cells. Then upper epidermis, then waxy cuticle.
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Why do we have air spaces? Epidermis thin and transparent? Pallisades on top of leaf?
to increase the speed of gas exchange. To access sunlight and short diffusion pathway. Lots of chloroplasts and access to the light.
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Why can plants not absorb water across their general body surface? What is their special exchange surface called?
Waterproof coating which is there to prevent waterloss. Root hairs.
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What does a root contain?
The xylem, pholem, cortex, endodermis (which has the protoplast (cytoplasm) and a casparian strip), root hair
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How is water uptaken by root hairs?
Hairs surrounded by a soil solution with a high water potential (slightly less then zero). The root hair has sugars, amino acids and ions dissolved in them. Their WP is therefore lower then the soil solution. Water therefore moves in via osmosis.
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What are its adapatations to this role?
Root hairs provide a large SA as they are long extensions and occur in thousends on a branch of a root. Thin surface layer (cell membrane and celluose cell wall) so substances move across it easilly.
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How does the water continue across the root once absorbed via osmosis?
Apoplastic pathway and the symplastic pathway.
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What is the apoplastic pathway?
when water gets drawn into endodermal cells, the cohesive properties of water pull more water behind it. This creates a tension which draws water along the cell walls of the cells of the root cortex.
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How does it travel through the wall?
By air spaces in the cell wall due to the mesh like structure of the celluose cell walls.
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What is the symplastic pathway?
This takes place across the sytoplasm of the cells of the cortex. It is due to osmosis. Water enters by osmosis which increases the WP of the root hair cell. This causes the WP to be higher then the first cell in the cortex. Water moves via osmosis
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into this cell. This causes the 1st cells cortex to have a higher WP then the neighbour cell inside the stem. We therefore seem osmosis occur agian.Then happens agian for the 3rd cell.
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What else is happening?
As the first cell transfers it to its neighbour cell, its own WP lowers. This causes more water to move into it via osmosis, continious proccess.
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What is happening therefore?
A water potential gradient is being established across all the cells of the cortex, carrying water from the root hair cell to the endodermis.
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How is the water moving from cell to cell?
Via a thin strand of cytoplasm in a tiny opening between each cell called the plasmodemata.
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How does water pass into the xylem?
Water from the anaplastic pathway is forced into the protoplast of the endodermic cell via the casparian strip.
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The active transport of salts from the endodermis cel to the xylem, causing its WP to become lower. This causes water to move into it via osmosis.
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How does water move up the plant (1ST THEORY)?
Movement of water into the xylem via osmosis causes a force called root pressure which pushs the water up the plant.
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Evidence for root pressure? (4 REASONS)
1)pressure increases with rise in temperture/decrease in temp. 2) Metabolic inhibitors stop root pressure (active transport needed for water to move into xylem) 3)Decrease in o2 causes decrease 4) Sap exudes from cut stem at certian places at times.
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How does water move out throubh the stomata?
Humidity of the atmosphere is less then air spaces next to the stomata. Stomata open, water vapour will diffuse out of spaces into surrounding air.
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How does the water keep coming out?
Water which is diffused out into the air is replaced by water evapourating from the cell walls of the surrounding mesophyll cells.
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How does water move across the cells of the leaf?
Mesophyll lose water to the air spaces via evapouration. This causes its WP to be lower. Water enters these cells via osmosis from neighbouring cells. Loss of water lowers their WP, so they take water. Wp gradient from xylem across the leaf mesophyll
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How does water move up the stem in the xylem? (2ND THEORY).
Water evapourates from leaf due to transpiration. Water molecules have H bonds and therefore stick together.
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What is this known as?
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Therefore what does this form? What happens when water leaves into the atmopshere via diffusion?
Continious unbroken pathway across mesophyll cells and down the xylem.
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What happens when water leaves into the atmopshere via diffusion?
Water leaves the leaf. Therefore water evaporates out of the mesophyll cells to replace these and moves into the air spaces. This causes more water molecules to move up to replace these.
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What is this known as? What is the theory known as?
The Transpriation pull. The cohesion-tension theory.
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What is the evidence to support this theory? (3)
1) Change is diameter of the trunk according to rate of transpiration. During day, when transpiration at the most, more tension, so trunk has lower diameter. 2) Xylem vessel broken tree cant bring up water as continious collumn is broken.
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Why is a transport system needed (relating to cells and tissues)?
to take materials from the exchange surface to diffrent parts of the organisim. As the organisim becomes more evolved, tissues and organs more specalised and therefore more reliant upon other organs and tissues (each other).
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Why is a transport system needed? (2)
Small SA:V ratio & if the organisim is very active.
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What are the features of a transport system?
Sutiable medium to carry materials (eg:blood). A form of mass transport, closed system of vessels that contain the medium and is a branched network. Mechinisim for moving medium inside vesssels (eg heart).
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The two methods of achieving the ability to move the medium in the vessels?
Muscular contraction to cause a pressure diffrence to cause movement. Passive natural proccess, eg transpiration, used by plants.
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How does a transport system work in mammals?
Closed blood system. Muscular pump, heart, ciculates blood with its double circulatory system.
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Arterie and vein coming to/from the lungs?
Pulmonary artery/Pulmonary vein.
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Artery and vein coming to/from the heart?
Pulmonary vein and artery, vena cava and aorta.
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Arterie and vein coming to/from the Liver?
Hepatic vien and artery.
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Arterie and vein coming to/from the Stomach and intestines.
Hepatic portal vein
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Arterie and vein coming to/from the Kidneys?
Renal vein and artery.
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What are the 5 types of vessel?
Arteries, veins, capillaries, arterioles, Venules
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What is the basic structure of arteries, arterioles, veins and venules ?
Tough outer layer, Muscle layer, elastic layer, endothelium (thin layer), lumen
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Tough outer layer? Muscle layer?
Resists pressure change from both within and outside, Contracts to control flow of blood.
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Elastic layer? Endothelium? Lumen?
Maintains blood pressure by stretching and springing back, prevents friction and thin to improve diffusion rate. Central cavity which blood flows through.
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How is an artery diffrent and how does this relate to structure? Muscle layer?
Muscle layer is thick compared to veins. This allows for smaller arteries to to be contricted and dilated to control blood flow.
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To keep blood pressure high so it can reach the full body. It is streched at each systole and then springs back in diastole to maintain pressure so blood can flow in.
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Thickness of wall & no valves?
Resists the vessel bursting under pressure , (EXCEPT ONES LEAVING HEART) because Blood under High BP contstantly so does not flow backwards.
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Artiole related to function?
Muscle layer thicker then arteries to allow for constriction to give more control of movement of blood into cappilaries. Elastic thinner because pressure is lower.
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Vein structure related to function?
Muscle layer is thin (carry blood away from the tissues so cant control flow to tissues), elastic is thin (lower BP) overall thickness smaller (pressure low), valves to prevent backflow
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Why is low pressure related to low amounts of muscle, elastic etc?
Reduced risk of bursting.
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What is the function of cappilaries?
Exchange metabolic materials between the blood and the cells of the body.
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How is the blood flow in the cappliaries? Why is it like this?
Its slower because it allows for more time for exchange of materials.
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How are the cappliaries adapted?
Only a lining layer, reduces diffusion pathway. Very branched, to increase SA. Narrow diameter, so no cells are too far away. Lumen is narrow, red blood cells squeeze agianst wall, spaces between endo cells (white blood cells access tissues).
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What cant cappliaries do? What does this instead?
They cant serve every cell directly. Therefore tissue fluid that bathes each cell acts as the transport medium for metabolic materials into cells.
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What is tissue fluid?
A watery liquid which holds glucose, amino acids, fatty acid, salts, oxygen. Supplies these to tissues and recieves waste products. Means from which materials are exchanged from blood to cells.
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How is tissue fluid formed? (short version)
From blood plasma. Blood plasma is formed from various homostatic systems.
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How is hydrostatic pressure formed?
Blood pumped from heart passes down arteries, then into arterioles and then cappliaries. This forms the pressure at the arterial end of the cappariles.
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How does this form tissue fluid? What forces oppose it?
It is an outward pressure and forces tissue fluid out of the blood plasma. Opposed by hydrostatic pressure of the fluid outside cappliaries and the lower WP of the blood due to plasma protiens pulls water back in.
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What moves out? Name of this proccess?
small molecles & ultrafilteration
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How does tissue fluid move back into the circulatory system?
Loss of tissue fluid causes cappilaries to have reduced pressure. By the time blood reaches the venous end, its pressure is less then outside. Fluid moves into it. Osmostic forces also aid in this proccess.
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What else moves tissue fluid? How does it work?
Lymphatic system, Vessels begin in the tissues and merge into larger vessels that form a network throughout the body. Larger vesselss drain content into bloodstream via ducts that join veins close to the heart.
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How does their content move?
Hydrostatic pressure and contration of body muscles.
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What is the role of transpiration? Bad sides and the good?
It causes severe water loss, as the leafs have a large SA and the stomata open for gas exchange. It could be argued its needed to move water up the stem and to the leaves and also is needed tp cause ions,sugars, homromes to move around plant
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to move around the plant dissolved in the water. Therefore, transpiration causes the transfer of materials to be more rapid & for water to move moved to the plants leaves.
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What are the factors which effect transpiration?
Light intesnity, temperture, air movement and humidity.
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How does light intensity effect the rate of transpiration?
Increase in intensity causes more stomata to be open (as more photosythesis can occur so more gas needed). More area for water to leave the plant.
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How does temperture effect the rate of transpiration?
Increases the kinetic energy of the water molecules which causes them to move faster. Faster rate of movement via evapouration therefore. Faster movement of osmosis through mesophyll to replace water, which is then evapourated also.
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In addition?
Decreases the humidity.
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Increase in humidity causes there to be more water molesulces in the air. Reduces the WP gradient therefore.
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Air movement?
When water leaves via stomata, it collects in the stomata pores. This reduces the WP. Strong air movement will dissipate this water, so increasing the gradient.
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What is the name given to the plant which aims to reduce water loss?
Xerophytic plants
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How do they do this (simple)
By reducing the rate of transpiration and therefore reducing the rate water is lost.
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Why do normal plants not have to do this?
Because their rate of uptake of water is greater then their rate of transpiration. They can obtain sufficent water with transpiration still occuring.
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Give 5 examples of how they reduce water loss?
Thick cutitble, rolling up leaves, hairy leaves, stomata in pits/grooves, reduced SA:V ratio of leaves.
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Thick cuiticle?
Despite being waterproof , water can still be lost. If its thicker, this is reduced.
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Rolling up leaves?
Protects the lower epidermis from the air. This protects the stomata from the wind. Water gathers around stomata pores, reduces WP gradient. Not disrupted by the wind, so WP gradient reduced.
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Hairy? Stomata in pits/grooves? reduced SA:v of leaves?
On the lower epidermis. Cause moist air to be trapped. Lowers Wp.Same idea for the grooves.
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What is the device used to measure water uptake?
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what is it measuring?
The amount of water taken up by the plant in a given time.
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Why does this let us find the rate of transpiration?
Because 99% of water taken up is lost via transpiration.
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Stages of the experiment?
Shoot placed under water. Potometer filled with water. Using rubber tube, leaf shoot is fitted to the potometer underwater. Potometer removed from underwater and all joints
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sealed with waterproof jelly. Air bubble introduced into cappliary tube.Distance moved in given time or time taken for set distance is measured. Using this value, volume of water lost is calculated.
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Vol of water lost agianst time in minutes.
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What happens with the air bubble is close to the junction of resevoir?
Open the tap and push it back to the start of the scale.
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Card 2


What is the SA: V ratio for exchange to be effective?


High SA: V ratio.

Card 3


What organisims have this? How does volume increase as organisim size increases? Compare with SA? Therefore?


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Card 4


What are the two features larger organisms have developed to combat this?


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Card 5


What are the features of an exchange surface?


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