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Special Surfaces

Candidates should be able to: a) explain, in terms of surface area:volume ratio,why multicellular organisms need specialised exchange surfaces and single-celled organisms do not (HSW1); Living organisms need : Oxygen , Glucose,Proteins ,Fats ,Water and Minerals                                                                      Waste : Carbon Dioxide, Oxygen in plants ,Ammonia, Urea and nitrogen                                     Single celled organims have a large surface area to volume ratio so diffusion is adequate        Large mullticellular organisms have a small surface area to volume ratio,Its outer surface is too small to supply the body with nutrient and oxygen quick enough to keep the cells alive also there is a greater diffusion distance.This is why they need transport sysytems

(b) describe the features of an efficient exchange surface, with reference to diffusion of oxygen and carbon dioxide across an alveolus;                      

Large surface area for molecules to pass through                                                                     Thin barrier to reduce diffusion distance                                                                                   Fresh supply of molecules                                                                                                       Removal of required molecules on the other side to maintain a steep concentration gradient

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Special Surfaces

(c) describe the features of the mammalian lung that adapt it to efficient gaseous exchange                                                                          

 Large surface area : More space for molecules to pass through.Lots and lots of alveoli that cover an area of 70 m^2                                                                                                            Barrier: The plasma membranes form the thin permeable membarane for oxygen and carbon dioxide                                                                                                                                    Diffusion Distance : Alveoli and capillaries are one cell thick each .The both contain squamos epithelium (flattened very thin).Capillaries are so small that the red blood cells are squeezed against the wall to reduce diffusione distance .The capillaries and the alveoli are in close contact. Lungs have a surfactant to reduce the cohesive forces without it the alveoli could collapse because of the cohesive forces between the water and the lining.                          

Maintaing the diffusion gradient :Blood bring co2 so that the concentration of it in the blood is higher than that in the alveoli so it moves into the alveoli from a high concentration to a low concentration.while the high concentration oxygen moves to the blood .Ventillation of the lungs allow a fresh supply of oxygen and the rapid removal of carbon dioxide, ensuring that the correct concentrations remain.         

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Special Surfaces

Describe the functions of cilia,cartillage ,goblet cells,smooth muscle and elastic tissue in the mammalian gas exhange system

Larger airways must be large enough to let air flow without obstruction, they must divide into smaller airways to get to the alveoli, they must be strong enough to prevent them from collapsing under pressure ,they must be flexible and they must stretch and recoil                         Cartillage : in c-shaped rings in trachea  and less regular in bronchi: holds the airways open to prevent collapsing during inhalation .The c-rings allow a degree of flexibilty and for the oesophagus to expand when swallowing                                                                                    Smooth muscle:contract to constrict the airway to adjust the size of the lumen especially in bronchi.This is involuntary for example people with asthma can't help to not breathe.         Elastic fibres: Recoil to to their original shape after the smooth muscle relaxes,helps dilate the airways                                                                                                                                 Goblet cells:Under the epithelium and secrete mucus, the mucus traps the particles from air such as bacteria so they can be removed to reduce the risk of infection                                   Ciliated epithelium: Consists of ciliated cells that have tiny hair like structures on the membrane (cilia),these move in a synchonised way to waft the mucus to the top of the tranchea where it can be swallowed and the bacteria in it can be killed by the acid in the stomach.

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Special Surfaces

(f) outline the mechanism of breathing (inspiration and expiration) in mammals, with  reference to the function of the rib cage, intercostal muscles and diaphragm;  Inhalation : Diaphragm contracts to become flatter and pushes digestive organs down                       External intercoastal muscles contract pushing the ribs upwards and outwards                   Volume in the chest(thorax) increases                                                                             Pressure in chest drops below atmospheric pressure so air flows into the lungs Exhalation: Diaphragm relaxes and is pushed up by the dispaced organs underneath                         External intercoastal muscles relax and the ribs fall                                                          Volume of the chest cavity decreases                                                                          Pressure in lungs increases and rises above atmospheric pressure so air moves out                     of lungs

(g) explain the meanings of the terms tidal volume and vital capacity;  Tidal Volume is the volume of air moved in and out of the lungs with each breath at rest Vital Capacity is the largest volume of air that can be moved into and out of lungs in any one breath (can be improved with exercise) Residual volume is the volume of air that always remains in lungs even after the biggest possible exhalation Inspiratoty reserve volume is how much more can be inspired over the tidal volume Expiratory reserve volume is how much air can be breathed out over the the amount breathed in a tidal volume breath

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Special Surfaces

(h) describe how a spirometer can be used to measure vital capacity, tidal volume, breathing rate and oxygen uptake; 

-has a chamber filled with oxygen that floats on a tank of water, a mouthpiece attached to a tube connected to the chamber of medical grade oxygen.                                                                 Breathing in causes the floating chamber to sink and breathing out causes it to float.                  The person's nose must be closed to avoid breathing in extra air and the mouthpiece should be  clean                                                                                                                                    To mesuree oxygen uptake a datalogger is used to to record the spirometer to produce a trace.    To avoid high levels of carbon dioxide ,soda lime is used to absorb the exhaled CO2 so the total volume of the air will go down in a spirometer trace                                                             becasue the total volume of CO2 breathed out in the same as the oxygen breathed in as the CO2 is removed the total reduction is the same as the oxygen used up so we can use this to make calculations.

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Transport in animals

(a) explain the need for transport systems in multicellular animals in terms of size, level of activity and surface area:volume ratio;                                                                            Size : large animals have several layers of cells so the sifussin of oxygen or nutriets will only be useful for the outer layers not the cells deep inside.                                                                    Surface area to volume ratio :Large animals have a small surface area to volume ratio.Diffusion is not useful to transport oxygen and nutrients for internal cells as large animals have a large volume  Level of activity : animals that a very active need a constant supply of oxygen to release the energy in food. Also so they can move around. Some animals need energy to keep themselves warm. Diffusion is too slow to meet these requirements.

(b) explain the meaning of the terms single circulatory system and double circulatory system, with reference to the circulatory systems of fish and mammals;          Single circulatory: blood passes through the heart once like in fish (heart-gills-body)               Blood pressure is reduced through the tiny capillaries of the gillsso blood will not flow quickly to the body and this limits the rate at which oxygen and nutrients are delivered   (its good for fish)    Double circulatory: Two circuits -pulmonary(to the lungs for oxygen) and systemic (to the body) mammals have this.                                                                                                                 heart increases blood pressure after coming from the lungs so it flows quickly                              systemic is at a higher pressure than pulmonary because high pressure in the pulmonary ciruit would damage capillaries in lungs.


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Transport in animals

(c) explain the meaning of the terms open circulatory system and closed circulatory system, with reference to the circulatory systems of insects and fish;

Open circulatory :blood is not always in blood vessels such as a locust.The action of muscles during movement circulate the blood.They have a long muscular heart ,blood enters it through ostia and it pumps blood toward the head by peristalsis.Some have open ended tubes that guide the blood to more active parts such as the legs and wings. Good for insects because they are small and the blood doesnt have to travel far, also they have a separate transport sysytem for oxygen and carbon dioxide.

Closed Circulatory :Blood is always contained inside vessels, tissue fluid bathes the cells. The heart can pump at a high presure so it flows quicker and oxygen and nutrients can be delivered quicker for example fish. there must be an exchange surface to allow materials to to be exchanged between surface and tissue fluid.

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Transport in animals

(d) describe, with the aid of diagrams and photographs, the external and internal structure of the mammalian heart;

structure include : aorta ,pulmonary artery, left atrium ,left pulmonary vein, left ventricle, right ventricle ,coronary arteries ,right atrium, right pulmonary vein  and vena cava .The septum is the wall that divides the left and right side of the heart.

(e) explain, with the aid of diagrams, the differences in the thickness of the walls of the different chambers of the heart in terms of their functions;

The muscle in the atria is thin because they dont need to create a lot of pressure to push blood into the ventricles.                                                                                                                    The wall of the right ventricle is thicker than atria because it needs to pump the deoxygenated blood to the lungs, longer than the distance that the atria have to pump.Not a long distance.also the blood pressure cant be too high cause it will damage capillaries.                                      The wall of the left ventrcle is thicker than both because it needs to generate enough pressure to overcome the resistance of the systemic circulation and pump blood into aorta.                                                  

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Transport in animals

(f) describe the cardiac cycle, with reference to the action of the valves in the heart; 

Diastole : both the atria and ventricles are relaxing ,blood is flowing through from the major veins so the internal volume of the heart is increasing.The atrioventricular valves are open o left blood through and the semilunar valves are closed.                                                                              Atrial Sytole; The atria contract creating pressure to push blood into the ventricles increasing the internal volume of the ventricles, ventricular walls stretch to hold as much blood as possible . Atrioventricular valves open semilunar valves closed. Blood fils the atriventrular valves so they close.                                                                                                                                      Ventricular Systole; Ventrcles contract from the apex increasing the pressure and opening the semilunar valves pushing the blood up the arteries and atriventricular valves closed                        

 Valves: ensure that blood flows in the correct direction and are opened and closed by the changes in blood pressure.With the atrioventricular valves during diastole the pressure in the ventricles drops so they open,when the ventricles contract the pressure of the blood rises above that in the atria so the valve pockets fill and they close.

Semilunar valves : when the ventricles contract the pressure in them rises above that in the aorta and pulmonary artery so the semilunar valves open.Once the pressure drops below that in the major arteries they close.

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Transport in animals

(g) describe how heart action is coordinated with reference to the sinoatrial node (SAN), the atrioventricular node (AVN) and the Purkyne tissue; 

Heart is myogenic as it can initiate its own contraction Initiation : The sinostrial node located at the top of the right atrium near the vena cava sends out a wave of excitation that quickly spreaads over the walls of both atria cause them to simultaneously contract. (atrial systole). At the top of the inter ventricular septun the atrioventricular node picks up the wave of excitation because there is a disc of non condducting tissue under the atria. The excitation is delayed at this node to allow the atria to finish contracting and for the blood to flow into the ventrcles The excitation is carried down the Purkyne tissue in the interventricular septum and at the base of the septum it is spread out to the walls of the ventrcles from the bottom up causing the ventricles to contract,pushing the blood up.

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Transport in animals

(h) interpret and explain electrocardiogram (ECG) traces, with reference to normal and abnormal heart activity; 

ECG: uses sensors to show the electrical activity of the heart                                                             P- atrial systole , QRS - ventricular systole , T - diastole                                                                      Can show arrhythmia,fibrillation, myocardial infarction, enlarged heart of non conducting Purkyne tissue . Elevation of ST - heart attack , small unclear P - atrial fibrillation, deep S - abnormal ventricular hypertrophy

(i) describe, with the aid of diagrams and photographs, the structures and functions of arteries, veins and capillaries

Arteries: Small lumen to maintain high pressure .Thick wall with collagen to help withstand the high pressure. Elastic tissue allows wall to stretch and recoil as the heart pumps, recoil maintains high pressure as heart relaxes. Smooth Muscle contacts and constrcits to adjust the lumen help direct the heart to other tissues. Endothelium that is smooth to reduce friction and can unfld when artery stretches.                                                                                                                      Veins: large lumen to ease the flow of blood. thinner layers of collagen,elastic tissue and smooth muscle as they dont need to strecth and reduce blood flow. Have valves that prevent blood from flowing in the wrong direction.                                                                                                          Capillaries : single layed of flattened endothelial cells that reduce the diffusion distance  for material. Narrow lumen ensures the red blood cells are squeezed as they pass reducing diffusin distance.

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Transport in animals

(j) explain the differences between blood, tissue fluid and lymph;

Blood - held within blood vessels and contains erythroyctes and leucocytes and platelets and  plasma that contains oxygen, carbon dioxide, salts, glucose, fatty acids, amino acids, hormones and plasma proteins.                                                                                                                            

Tissue fluid bathes the cells of individual tissues and contains some leucocytes ,some hormones , no fats , less glucose, less amino acids, less oxygen and more carbon dioxide                                    

Lymph contains lympocytes, some proteins, more fats that the blood, less glucose less amino acids , less oxygen and more carbon dioxide.

(k) describe how tissue fluid is formed from plasma; 

The blood at the arteriole end is under high hydrostatic pressure from the heart, this pushes plasma with oxygen and dissolved nutrients out of the capillaries through the small gaps . This is tissue fluid that bathes the cells and exchanges material through diffusion and facillitated diffusion.

At the venous end the blood has less hydrostatic pressure and the hydrostatic pressure in the tissue fluid and osmosis forces the fluid back into the capillary with any dissolved substances.Some of the tissue fluid is drained into the lymphatic system that eventually joins the blood in the chest cavity. Contains many lymphocytes produced at lymph nodes that filter out bacteria. Phagocytes can then ungulf these


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Transport in animals

(l) describe the role of haemoglobin in carrying oxygen and carbon dioxide;

Oxygen: haemoglobin + oxygen---> oxyhaemoglobin

haemoglobin has four haem groups with Fe2+ and they have a high affinity for oxygen so each haemoglobin can carry four molecules of oxygen.Oxygen diffuses into the haemoglobin in the red blood cells creating a diffusion gradient that allows more oxygen to enter the cells.

Carbon dioxide: Carbon dioxide diffuses into the blood and reacts with water in the presence of a catalyst - the enzyme carbonic anhydrase to make carbonic acid CO2+H20--->H2CO3.                           

The carbonic acid dissociates into H+ ions + HCO3- and the hydrogencarbonate ions diffuse out of the red blood cells into the plasma, the charge inside the red blood cells is maintained by the negative chloride ions that diffuse is as the hydrogencarbonate ions diffuse out.

Because the H+ ions are acidic haemoglobin dissociates into haemoglobin and oxygen to take up the H+ ions and make haemoglobonic acid. The haemoglobin is a buffer

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Transport in animals

(m) describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different carbon dioxide levels (the Bohr effect); 

The ability for haemoglogin to take up oxygen depends on the partial pressure or oxygen tension. The oxyhaemoglobin dissociation curve : at low partial pressures the haemoglobin does not readily take up oxygen because the haem groups are located at the center of the haemoglobin making it difficult for the oxygen to come into contact with it. This is why there is low saturation at low oxygen tensions. as the oxygen tension ises one oxygen melecule will associate with the haem group and cause a conformational change that allows more oxygen to associate with the other haemgroups.  Its difficult for the last haem group to associate so the curve levels off as saturation approaches 100% Oxygen tension in lungs is high enough to produce 100% saturation and in respiring tissue it is low enough to allow dissociation  The bohr effect: when carbon dioxide is present the hydrogen ions dispace the oxygen and it is released. At any particular oxygen tension the oxyhaemoglobin releases more oxygen when carbn dioxide is present because of the prensence of H+ions.

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Transport in animals

(n) explain the significance of the different affinities of fetal haemoglobin and adult haemoglobin for oxygen.

fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin because it must be able to pick up oxygen in an environment that makes adult haemoglobin release oxygen.Must absorb oxygen from the fluid in the mothers blood and this reduces the oxygen tension in blood fluid making maternal haemoglon release oxygen.

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Transport in plants

(a) explain the need for transport systems in multicellular plants in terms of size and surface area:volume ratio;

Every cell in a multicellular organism needs a constant supply of water and nutrints.because large plants have a small surface area to volume ration on the surface cells would gain anything from diffusion

(b) describe, with the aid of diagrams and photographs, the distribution of xylem and phloem tissue in roots, stems and leaves of dicotyledonous plants;

In roots the vascular bundle is at the center with the xylem at the center in an X shape and the pholen found between the arms od the X gives the roots strength to withstand pulling forces. this is surrouded by the endodermis(has meristem cells) , cortex and epidermis.

In the stem the vascular bundles are at the edges to withstand to bending forces . Cortex Phlem Cambium (contains meristem cells) Xylem then Pit/medulla

in the leaves the vascular bundles form the midrib of the veins with the xyem at the top and the phloem at the bottom .

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Transport in plants

c) describe, with the aid of diagrams and photographs, the structure and function of xylem vessels, sieve tube elements and companion cells; 

Xylem : transports water, long column dead cells that have been lignified with no cell contents and end walls.Good for transportation of water because its a continous column , the tubes are narrow so water column doesnt break easily. Pits formed when lignification wasnt complete allow water to move into adjacent vessels and other parts of the plant.Lignin is deposited into the walls in spiral, annular or reticulate rings allow flexibility and allows the xylem to stretch as the plant grows.

Phloem: transports sugars and is made of two parts: Sieve tube elements : cells that contain little cytoplasm and no nucleus lined up end to end with cross walls that are perforated to alllow sap to flow. Thin and six sided

Companion cells: in between the sieve tubes , larg nucleus and dense cytoplasm, a lot of mitochondria for ATP, carry out the metabolic processes such as using atp to transport sucrose into the sieve tubes through the plamodesmata.

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Transport in plants

(d) define the term transpiration;

Transpiration is the loss of water by evaporation from the aerial parts of a plant

water enters the mesophyll cells by osmosis from the xylem. Evaporation from the surface of the meseophyll cells into the intercellular spaces and then diffusion of water vapour from the intercellular spaces out through the stomata

e) explain why transpiration is a consequence of gaseous exchange; 

Transpiration is a consequence of gaseous exchange because the stoma are open in the presence of light for gaseous exchange and so the water gets out. Also the leaf must have a large surface area to get a lot of carbon dioxide so there is a larger area for water to be lost.

Water hasto move up the xylem because it is required for photosynthesis, it is required for cells to grow, keeps the cells turgid, the flow of water carries useful minerals up the plant, evaporation can keep the plant cool.

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Transport in plants

(f) describe the factors that affect transpiration rate

Number of leaves - more leaves means a larger surface area for transpiration

number, size, position of stomata- the more the stomata the more the waer that can be lost , the larger the stomata the faster the water is lost , the more the stomatat on the top of the leaf the more water that can be lost.

Cuticle : thick waxy cuticle reduces evaporation from leaf surface

Light : the stomata are open in light so water can be lost then

Temperature : at higher temperatures the rate of evaporation from cell surfaces increase and so does the water vapour potential in the leaf. Higher temperatures increase the rate of diffusion because the molecules have more kinetic energy . Higher temperatures decrease the relative water potential in the air so more diffusion out of leaf

Humidity: the more humid it is the less the transpiration because there is a small water vapour potential gradient

Wind: the more the wind the greater the transpiration because the wind will move the water vapour that has just diffused out of the leaf and mainatain a high water vapour potential gradient

Water availability : if there is little water in the soil plants cannot replace it so they shed leaves in winter for exapmle to avoid water loss

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Transport in plants

(g) describe, with the aid of diagrams, how a potometer is used to estimate transpiration rates

Potometers measure the rate of water uptake by a plant shoot, we can estimate the rate of transpiration.

Make sure there are no air bubbles so cut the shoot slanted and submerge it in the water then let it go. Meausre the position of the meniscus at regular intervals

(h) explain, in terms of water potential, the movement of water between plant cells, and between plant cells and their environment. 

Water potential is the total potentila energy of the water molecules in a system 

Pure water has the potential 0 , cells have a negative water potential beause they contain dissolved sugars and salts and water molecules move from a less negative to a more negative region.

The apoplast pathway: between the cells , water does not pass through plasma membranes so dissolved substances are carried in the water

The symplast pathway : through the cytoplasm and plasmodesmat of the cells.

The vacuolar pathway : water moves through the vacuoles of the cells


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Transport in plants

(i) describe, with the aid of diagrams, the pathway by which water is transported from the root cortex to the air surrounding the leaves, with reference to the Casparian strip, apoplast pathway, symplast pathway, xylem and the stomata; 

From thesoil : root hairs provide a large surface area for the uptake of water.The root hair use active transport to absorb minerals from the soil, this reduces the water potential in the root hair cells so water is taken up by osmosis

Across the root: Water then takes up any of the three ways to move across the root until we get to the endordemis where the casparian strip , a starch sheath blocks the apoplast pathway so it joins the symplast pathway. The endodermis cells move minerals by active transport from the cortex to the xylem and decrease the water potential in it so water moves into it by osmosis down the water potential gradient.

This in turn reduces the water potential of thecells outside the endodermis and create a water potential gradient across the whole cortex so more water is drawn up

Casparian strip : ensures that all the ions pass through the cytoplasm of the cells so that they can be activel transported into the xylem and to decrease the water potential.

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Transport in plants

(j) explain the mechanism by which water is transported from the root cortex to the air surrounding the leaves, with reference to adhesion, cohesion and the transpiration stream;

Root pressure : driving water into the xylem by osmosis due the the water potential gradient pushes the water up the xylem

Transpiration pull: water molecules are attracted to each other by cohesion forces that hold water in a column so transpiration pulls the whole column up, there is tension created in the water column . The los water is then replaced.

Capillary action : adhesion- water molecules attracted to the sides of the xylem and this puls the water up.

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Transport in plants

(k) describe, with the aid of diagrams and photographs, how the leaves of some xerophytes are adapted to reduce water loss by transpiration

Xerophytes have

Smaller leaves: needle shaped to reduce surface area for transpiration

Densely packed spongymesophyl: reduces surface area exposed to the air outside of leaves so less water will evaporate into the air spaces

Thicker waxy cuticle: reduces evaporation

Stomata : closed when water availability is low, reduce water uptake

hairs on leaf surface: Traps air close to leaf surface that can becom saturated with water vapour when transpiration occur so this reduces the water vapour potential gradient

Pits: containg stomata to trap air and moisture close to the stomata  reducin the gradient

Rolling up leaves: so the lower epidermis is not exposed to the air and trap air inside, reduce gradient

Lower water potential inside leave by maintaing a high salt concentration reducing evaporation and gradient

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Transport in plants

(l) explain translocation as an energy-requiring process transporting assimilates, especially sucrose, between sources

Translocation is the transport of assimilates in the phloem.

Source is where the sucrose enters the plane and sink is where the sucrose leaves the plant,

The companion cells use ATP to active transport H+ ions into the surrounding tissue creating a concentrtaion gradient for the H+ ions. Contransporter proteins help the H+ ions back into the companion cells with the sucrose. The sucrose diffuses into the sieve tube through the plasmodesmata down the concentration gradient

(m) describe, with the aid of diagrams, the mechanism of transport in phloem involving active loading at the source and removal at the sink, and the evidence for and against this mechanism

At the source: the sucrose entering the phloem reduces the water potential so water moves in by osmosis creating hydrostatic pressure.

At the sink : sucrose leave the phloem by diffusion or active transport to the surrounding cells and this increases the water potential of the phloem so water moves out by osmosis and decreases the hydrostatic pressure.This is mass flow as it moves the sucrose along the phloem in any direction..

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Transport in plants

Evidence: For phloem :

-Radioactively labelled CO2 supplied to the plant appears in the phloem

-Ringing a tree to remove phloem results in sugars and water collecting above the ring

-An aphid feeding on a plant stem, the mouthparts maybe used to prove its taking food from the phloem by analying the the fluid collected by the aphd or from the stylet

For metabolic energy used

Companion cells have mitochondria

-Translocation can be stopped by a metabolic poison thatbinhibits the formation of ATP

-The rate of flow of the sugars is so high that energy must be used. 10000 times faster than diffusion

For mechanism

-pH of companion cells is higher than surrounding cells

- Concentration of sucrose is higher at source than sink

Against mechanism

Not all solutes in the phloem move at the same rate, sucrose is moved to all areas of the plant at the same rate , the role of sieve plates is unclear

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