Chapter 9

Question 1

Three reasons why transport system needed in plants

Answer 1

1) metabolic demands and transport
- leabes stem photosynthesis but roots don’t, they need the assimlated similarly they got mineral ions but leaves don’t = need to be trsndportrer . Waste proeuctsof cell need to be transported too, horomknes lroducedine area need to be transported to place where they need to affect

2) Size = so big some that they need transport system to move thing sallnthe way up and down effienctky
3) SA:V nit consistent, keaves have good . But rest of plant not, stems trunks roots have low SA:V ratio and this too low means diffusion nit effienc teniugh ti diffuse substances at a rate that sustains their life processes. So transport needed

Summary

1) metabolic demands and trsnsoort (things made here need to gonthere, hormones, assimialted ions)
2) size some are so big need transport
3) sa: b not constant snd too low to survive

High metabolic rate even tho still, so low as : v not enough ti survive

Question 2

Structure of leaf

Answer 2

- waxy cuticle
Upper epidermis 
- palisade mesopjyll
Spring lesolyll 
Lowered epidermis = stomata and guard cells
- waxy cuticle 

Waxy at top and bottom, then epidermis
Palisade spongy lower epidermis guard etcbsnd cuticle

Spongy impotent sencrested air spaces so more SA for gas exchange to take place

Question 3

Dicotyledonous plants

Answer 3

These are plants whose seeds make Two Cotyledons , which are organs that act as food stores for embryo plant

Cotyledon = organ that provides food store for when it first germinates, dicots have two in each seed

Question 4

Two types

Answer 4

From these dicots there are herbaceous dicots and woody aborescent dicots

Herbaceous dicots Have soft tissues and short life fyfke. Where leaves and stem die at end of season, woody dicots have hard kiani died tissues and lint life cycle so tree,but we only look at simple herbaceous dicots

Question 5

Vascular bundles

Answer 5

Vadualr system is transport system finromplsnts , here this made of xylem and phloem ARRANGED IN VASCUALR BUNDLES with different patrerne

Question 6

How are vascualr bundles arranged in roots stems and keaves in herbacueos dicots?

Answer 6

First of all xylem always in centre, and phloem on outside

In stems
- on the outside like a ring
Root
- in the middle with xylem star shaped and phloem around its
Leaves = midrib of lead is the main vein carrying vadcuakr bundle, which helps for structures, but there are also many branching off veins too which help inn bith steufture snd supoirt (think about veins on lead)

• root = star shaped xylem
• stem = ring like
• leaf, midrib main vein with branches

Question 7

Why

Answer 7

Stem = is ring shaped with xylem inside phloem outside
- this is because it gives strength and support

Root = inside star shaped xylem
- in the middle help plant withstand tugging strains due ti blowing winds

Leaf - just midrib main vein with branches, and these give suporit and help with transport , midrib Mersin vein

The Venetian in herbaceous leaves are NETTED rather than long and narrow

So stem = ring like to give suporit like scaffold, xylem inside
Leaf midrib main vein acts as suporit snd structure with many others
Riit star like middle suporit agsisnt wind

Question 8

Dicot vs monocots

Answer 8

Mono to not cotyledon organ for food for germinating plant
Benstion in dicots is scattered vs narrow and straight
Petsls in dicots 4s or 5s comaoref to 3s

For ting vsciuskr bundle otuside fir suporit

Question 9

Xylem function and structure

Answer 9

Xylem function = to transfer water and mineral ions from roots in ONE DIRECTION to the rest of the plant AND supports

Structure

• dead xylem cells packed end to end to make columns which fuse together
• this makes hollow tube
• no end walls
• walls strengthened with lignin to give mechanical strength
• in between xylem vessels are xylem PARENCHYMA tissue which store food and contain tannin
• tannin is a bitter chemical that protects plants form herbivores

And water leaves the xylem to go into other cells through non LIGNIFIED BIRDERED PITS

Summary
Xylem function ti transfer water snd mineral ions one way to rest of plant snd suporit

• xylem vessels made from dead cells hoined end to end thatbhave fused to make hollow tube allows ease of passage
• these have no end walls
• strengthened by kiani which guves mechsnicsl strength and support p
  Another tissue xylem have is xylem parenchyma, this dtored food but also had tannin Encinitas is bitter chemical to orient herbivores

There are also non kignified oitd which are holes water and ions can escape from to get to cells

Question 10

Function of phloem

Answer 10

Phloem function is to transfer assimilated produced from photodythendid bith ways to the rest of the plant , organic solutes

Question 11

Structure of phloem

Answer 11

Phloem made from cells called sieve tube elements which are alive that have no cell contents , not even nucleus.

• these joined end to end to make a hollow tube
• they have end walls but these are perforated to form SIEVE PLATES , this was word
• due ti being alive they have companion cells next to them which carry out life processes for them and the phloem cell too. Theee are linked by PLASMODESMATS (which is cintinius cytoplasm )
• they DONT HAVE LIGNIN

Summary

• phloem vessels also made from cells joined end to end to make a hollow like tube, these cells are called sieve tube elements
• cells are alive , and have end walls, up these perforated to make SIEVE plates . This REDUCES RESISTANCE TO THE flow of assimilated
• cells have no cell contents , to reduce OBSTRUCTION to flow of sddimialred
• no lignin
• companion cells, connected d y plasmidesmate

Question 12

Oh yh how can king in loom like in octried?

Answer 12

Sometimes doirslk, rings or soldi tube

Logo in gived mechsncisl dtrngth ti Reddit trnsdlirstjin lull snd like in stem for bending snd roots for tugging

Question 13

How to view vascular bundle bith transverse and long tofu skin

Answer 13

For example celery , cut hordintslly to make as thin strip as possible to see through light microcode
- leave in water for s bit snd stain it with TOLUIDINE BLUE
- rinse stained out ti slide with water as a fixing agent
You should be able to see the vascular bundle as rings, here the tiki dune blue stained the lignin so this should be xylem

But for rhubarb, do lontifunskm

1’ take a few out and push apart, add a drop of methylene blues

• get excess out , drop of glycerol and view
• you should see striaght lines or rings, this is lignin seem horizontally and lignin deposited as rings

Summary celery transverse die tolkduine blue rings . Rhubarb longtifunsk stsightnlined

Question 14

Why water needed for plants.

Answer 14

Turgor oresdure gived STRUCTURE + drives expansion for roots
Water in transpiration acts to cool plant due to high SHC
Water in transpiration provided plants with mineral ions form ground
Raw material for photosynthesis to make glucose for respiration and other functioned

But yh it makes a hydrostatic skeleton such that it is held srroshjr

Question 15

Okay so water moves in from root hair cells which sinexchnsge survive

What is this and what ways is it adapted for this role , what is a ROOT HAIR

Answer 15

Root hair is a thin extension from root hair cell

Rootnhair fell sdslted in 4 different ways

1) large SA:V , means efficient diffusion and osmosis of water + more area for active transport of mineral ions
2) has THIN DIFFUSION DISTANCE , just cell wall and membrsne, which makes diffusion more effienct
3) microscopic size means Dan penetrate between soil particles
4) CONCENTRATION GRADIENT ALWAYS HIGH

Question 16

How is a high concentration gradient maintained for root hair cells?

Answer 16

High cytoplasmic solute concentration means there is always a higher water original in soil than in cell, so osmosis happens

This is kept high by
- there is low sokute in soil water anyways, but active trsnort makes sure mormions in cell, as well as PROTON PUMPS
As well water moves into vacuole which drevreade water potential of the cell too

Thid why water kofed in by osmiodis

Summary how is root hair cell sfsltedfor osmsis

• high sa:v
• microscopic size can penetrate throihgh gaps and soil
• small diffusion distance = cell wall and membrsne
• high cytoplasmic colute concentration ensures high cinentrstiin gradient , done by active transport, protein pumps

Question 17

After it enters root hair cells , it moves

Answer 17

It moves from cell to cell until it reaches xylem in two ways

Symolsts method (simple so cytoplasm
)
Apoplasr method cellukose

Question 18

Describe the simplest methid

Answer 18

Thidnid the movement of the water through the cintiniud cytoplasm of each xylem cell, joined by PLASMODESMATA

Basically as next cell lower water potential, it just moved along and along snd along

Finally the fist root hair cell water potential decreases again, which allows water to move in again from roots from soil

This is actually the movement of SOIL SOLUTION, not strictly water, thid is mixture of everything disdioved in wster until endodermis is mite

Question 19

Apolast pathway?

Answer 19

Slightly harder
- movement of water through apoplasr which is the cell walls and intracellukar spaces between the, .

This is movement of water through cell walls and spaces between them, and as water move throihgh thr,, more is dragged along due to cohesive priority of water and adhesions with cell walls, which means the lull creates a tension so that water is continuously pulled.

This is done by hydrostatic oresdure

Question 20

Apolast snd shmolsdt psthay

Answer 20

Dynolst is movement of water by osmosis through continuous cytoplssm of cell to cell until reach xylem through plamsodemssts, ss next cell always shows e lower water print is, snd thid rested root hair cell water oeitnisl too

Apoplasr pathway is movement of water through cellulose snd intrevullar spaces between them . As water moves, there is a pull due to cohesion and adhesive forced of water, creating a tension that pulse the water along thisnoahtway, which offers no resistance

Question 21

What happens once the water reaches close to the xylem , endodermis

Answer 21

As cell by cell eventually it reaches at the endodermis , which is a grouo or cells that surround the vascular tiddue
2) the endodermis has a band called the CASPARIAN STRIP , which is a band of waxy material called SUBERIJNthat forms a waterproof layer around the endodermis

3) at this stage , water from thr apolast pathway is BLOCKED by cadparaij strip and thus it is FIRCED to join the symolsdt pathway
4) yet I’m doing so it passed through SELECTIVELY OERMEABLE CELL SURFACE MEMBRSNES TO GET TI CYTOPLSSM , which blocks any potentially toxic solutes from reschijg the living ridden

Plant protected from djsger, if there wasn’t any there, it would accumulate over time and cause disease

Okay again
After moving by symolsdt snd apolast pathway cell by cell it reaches a band of cells surrounding the bsscisuk tissue called the endodermis. The endodermis has a band of waxy material waterproof made from Suberin , called the caspairain strip. The faspsiraj strip is waterproof , and prevents the apoplasr pathway from tunuign such that it had to join symolsdt pathway l yet in doing so it is forced to go through deletivelyboermabke plasma membrane ti job shmokst osthwsy in the cytoplasm,so which fikterd out any potential toxic solutes that if left there would accumulate and potentially cause harm to living tiddue. This way Acaspiarin strip so important

Question 22

What else does endodermis ensure

Answer 22

That any solutes that have accumulated into thr xylem don’t go back into thr water solution and get water

So basically any solutes that are in xylem good don’t accidentally leave and go back int o root hair cells

Question 23

So how does the water enter the xylem for the first time then?

Answer 23

Once last the cssparian strip, water enters the vascular bundle via symolsdt , but once inside it can regrant to apoplasr pathway

How does this haooen tho?
Through osmosis , and the effectd of thid is increased :
- to start the cytoplasm of the endodermis cells have low concentration anyways , which means HIGH water potential. On the other hand xylem has higher concentration of ions which means low water portnisl, and so water moves by osmosis into the vessel
BUT lIT APPEARS that the endodermis cells actively pump ions Into the XYLME vessel too, which also artifisllynloerd its water pirtnisl .

This increases concentration brsident snd allows for more efficient osmosis and rate of water movement into xylem

Summarised

• after strip, symolsdt , but once in vsdcuakr then apolast too
• here xylem seems to have high conc solute then ednodemrls cells, which means low water original vsbjigh so osmosis, yet on other hand ti seem active trnsdlirt ions haooend in to surgically increase this

Question 24

What is rhis

Answer 24

This is known as ROOT PRESSURE and gives water a bit of a kick into the xylem, but it is INDEPENDENT OF ANY effect sir trsnduporwtiojl here, it id not the main fsctor of water kofijt into the xylem or through , but it helps and can be through if an external factor to say when in night when transpiration not happening because stomata closed, then water still moves up anyways

Question 25

What is evidence for active transport in creatin of root pressure?

Answer 25

poisons like cyanide affect the mitochondria and prevent the production of ATP , remember it is a ninnrevsieble non competive inhibitor, and affects cytochrome c oxidase which stops respiration from happening. If this is aookied to the root cells, no more ATP happens, so no more active transport, and that means that articulated pressure can’t be made. THIS ADTUALLY HAPPENS= root pressure dissapeaes , suggesting active transport has something f to play with root oresdure

• root pressures increase with rise in temp and decrease with fall in temp, suggesting chemical resctions arejnvikved which are boosted due to enxyme activity
• if level or oxygen or respiratory substsnce levels fall suddenly root oresdur falls too = not enough atp being made in repsirsiton = not enough active transport = not enough root oresdure
• xylem sap exudes from pores of stems or lesvedst night, known as GUTTINATION, the fact that this happens , indeed net of transpiration , suggests something like root pressure is present which still allows water to be moved up

Guttinstion hsppens due to a build up of oresdure forcing it out, but we nintrnsdlristjinnscrife princess must happen to push water against gravity snd force it out

Summary 4 evidence
+- cyanide prevents atp = root pressure gone
- inc temp = inc root oresdure suggest chemical activity snd ensyme involved so active
- decrease oxygen if repsirstiry substance = decrease atp = decrease root pressure
- fact that guttinstion happens which is excess pressure when trnslirsiton low suggests some active process forcing water up still,
-

Question 26

Redos how water enter xylem

Answer 26

First through soil, root hair cells adapted sa: v, thin distance, microscopic so csn go into any washer, high conc grsdient crested by active transport snd water going tin vacuole
- then cell by cell until endodermis, band of cells sround vsducakr bundle containing waxy material called capsaicin strip which waterproof.
- does this by apoplasr celluksoe fibre and symolsdt cintunius cytoplasm linked by plsdmidesmate
-once at endodermis, cslsairsn stionblocks apolast pathway from continuing sonfirce to merge ympladt,here go through membrane filter toxic hilly days
-enter xylem through symolsdt , later join apolast sgsin, but how so essilky?
- alresdy low conc endodmeral high xylem, but known that iOS actively transported to serifsally increase grsdient snd rate if diffusion
+ evidence for this = cyanide stop atp stop root pressure temp inc increase root oresdure, oxygen decrease decrease root oresdure and guttinstion , without transpiration still build of pressure force water out

Root oresdure independent of trnsorisjton stream , not the main thing pulling up but helps

Question 27

What is transpiration and why does it happen

Why is some stomata need to be openna t nights

Answer 27

How gases move in and out

To complete ohotodtynetheis not only water but also co2

Csbrihdyrste. Dioxide Kobe’s in and oxygen out of a life by diffusion through tiny pores cslled stomata which are in lower under is controlled by guard cells.

HOWEVER problem, when stomata open co2 and oxygen exchange, but water vapour is also lost by diffusion.

This loss of water is cslled transpiration and it is an inevitable ocnsewuency of gas exchange

Transpiration is the loss of water vapour through stomata due to stomata opening for gas exchange
Here water esfporsrwd into vapour and stays between hooes spongy snd when open then diffuse

Stomata regulate by keeping closed much as possible , but in night even tho no hoot happens some stomstaneed to be open to allow oxygen to enter so respiration can continue to take place

Question 28

Translisrwjton stream

Answer 28

This is the movement of water from the soil into root hair cells, into the xylem , into cells in leaves where it evapirsted into the gaps between spongy medolphylk cells snd leaves by diffusion due to opening of stomsta

Question 29

Okay so how does transpiration stream carry water form ground ;ignoring root pressure), start by working back to the xylem ?

Answer 29

To start, water enters the cells in a leaf or something through xylem by both pathways remember, thede move to cells, where they efporwteinto air spadednanddiffuse into surroundings down a concentration gradient when stomata open

• the removal of water from one cell now lowers its potential, causing water to move in by osmosis into that cell by symolsdt and apoplast too
• this is repeated cell by cell until the xylem is reached Where water moves ournof xylem to the cells

So basic water in cell evaporate diffuse down cocn gradient reduce potential, moves forms djscent cell higher water original by bith pathways, continued until water enters cells from xylem

Question 30

And how does transpiration stream carry water from ground up?

Answer 30

Water molecules from hydrogen bond weigh each other’s meaning it pulls on water molecules , and this is cohseive forced . It also forms hydrogen bonds with xylem walls which is adhesion
- combined effect if these is what allows water to exhibit cappislrybsction, the movement of water against a NARROW tube against gravity. Water is drawn up in a CONTINOUS STREAK to replace water lost by evpoarwtuoj , thid is the TRANSPIRSRIOJNPULL (pull of water due to loss of water by evaporation and cohesive and adhesive forces it has edchniting capillary action

The loss of wwter and trnsdpristiojnoulk helps create tendioj in the xylem and helps pull water from roots and across from soil too.

Model of water moving from thr soil in a continuous streak up the xylem across the leaf is called the cohesion tension theiryb

Question 31

Cohesion’s tension again

Answer 31

Bsdiscally afeternwater pulled from xylem due to cohesive snd adhesive forced it dns exhibit cspislry section di ride against narrow tube against gravity, thid is trnsdlirstjin lull, which caused tension in xylem, and thus helps of eater along from roots and adross soil even easier too, this is the cohesion tension theory , movement if water from roots to leaf due to continue stream

Question 32

Evidence for cohesion tension theory (3)

Answer 32

1) changes in diameter to tree
- at day when trnsdlirstjin is st highest tension in xylem also at highedt, so trunk is shrunk and diameter / circumeferenc lowest
- yet at night when transpiration at lowest due ti guard cells, the tension is at lowest too, so trunk can expand and circumference is highest thid cns be measured knowing
- shown by as time increases too kidday, rate trnsdlirstjin increase, so sicujfeende decreases inverted growth

2) when you cut xylem vessel , air is drawn in rather than water leaking - this because if high tension it already in
3) if this dies haooen adn air drawn in , then continuous stream of water broken , and chefs be forced gone so water can’t be drawn up the stem anymore no l this because cohesion is only with Water, air comes in and less so bruh

Question 33

Advnategs if trnsodirsiojt

Answer 33

• helps deliver minerals from ground due ti cintinisu Luke

- cools down the plant

Question 34

Problem transpiration

Answer 34

L amount of water bailable in environments one of most low available thing, so when high light itnensity available andnohodytnridd can happen a lot , a lot of water lost too, so it is limited and supply csnt meet demand

Question 35

How to invesitgste trnsdlirstjin, come back to do tins

Answer 35

Very hard to directly measure exactly how much water kesved the plants, only way to do this is use fraud bag methid but even this very hard
- the fact that 99% of water uptaken by plant is lost in trnsdlirstjin mesns using rate of water loss is a good enough model to determine rstebif trnsodirsitonl only limtistionis that 1z used in transport snd onosytnrehdid

Thus any factors thst increase or decrease jots KE in okant you can basically say directly increase decrease trnsoirsitok
This can be done using photometer

Question 36

How to setup promote effectively and ensure no air bubbles introudced

Answer 36

DONT want air bubble because this could ruin results and make you think more lost than it should

1) first cut your stem UNDERWATER so no air bubble introduce . Do at angle so more SURFSCE area for uptake
2) set up everything underwater , attach the stem underwater, connect all apparatus of post-mortem itself
3) ensure that junctions are AIRTIGHT, using rubber bung or Vaseline between joints for smooth and airtight fit
3) now take out , make sure three way head closed , and you will have to ensure the leaves dry first or it won’t give good indication due to conc gradient
4) ensure tank full. Now introduce an air bubble by removing capillary tube for a second quick and use syringe to draw water to tank (not plant)
5) now measure how far it knifed in time
6) finally reset bubble using syringe again ti restart, ensure tank is full

Question 37

Prevent air specially

Answer 37

Cut underwater, set up and attach understatement use Vaseline or bunt q, ensure apparatus ruck with water

Keep other ifneitonnfisntsnt and use rule or scale, allow time for it to ACCLIMATE

Question 38

How do guard cells control thr stomata

Answer 38

Turgor

When turgor low the non symmetrical configuration of the guard cells makes it close

2) when environmental conditions goodnthi such as sunlight, guard cells will actively pump ions to increase their turgor pressure
- this causes the cells the swell lengthways
- because the inner cell wall is THICKER than outer cell wall, cells befoke bean shaped an open the pore

When water becomes scarce, hormonal signals trigger loss of trig or , which caused it to change shape assynetirflslg and close

Summary

• turgor low ti fhsnges shape assymtrifslkt snd closes pore
• when conditions like light goof, ions pumped in to increase tiger pressure . As inner cell wall thicker than outer, it extends length ways into shape of bean and opens up

When tigirnlow again hormones remove turgor ptreedure Faustino it to dlow wgwinne

Question 39

Factors affecting transpiration ?

Answer 39

• light intensity
  Light is needed for photosynthesis and so in the light the stomata open so co2 and oxygen can exchange and products needed for photosynthesis obtained, thus increase light intensity increases smoiunt of stomata open so that max photo achieved, but this also inc rate of transpiration, but only to a certain point, after that it max as max stomata open
• temperature
  Increase temp means more water evaporate from inside cell, creating more diffusion (as more evaporates = higher gradient etc)
• but also increase temp increases max water can be held outside, so decrease humidity and thus increase concentration gradient
• humidity
  Conc grsdient , inc this decrease trnsoirsitoj k decrease this increase rate
• wind movement
  Again cind gradient k increase this and more molecules justndiffused leave inc grsdient
• water available ?
  If not Anouilh in soil then not enough turgor snd stomata close so transpiration decrease

Summarynfor temp fire t
Two ways
1) inc temp means in kinetic energy means more evaporation happens , this in diffusion as more con grsdient between two and so more transpiration
2) also inc max water held otuside so humidity diecrese including gradient

1) soil water k less v less open
3) light intensity k more light intensity ire dtonats open so photosytnehsinhaooen faster rate to get co2 but to limit ince all open that is max
Wind and hudmith

Humidity measure or water concentration compared to max water it fan hold

Question 40

What is translocation

What is asidjniaktedn

Answer 40

The transport of orgsnud compounds from source ti sink is known as translocation, done by phloem. Active process requires energy to do so

Products if onitdyntrhid are transported and this is assimilated

Main one trnsoirtrris sucrose
- this bead use metabolically jnsctive so not used up as energy source when trans ported
- sokubken
C

Summary l- transport or assimilated from source to sink, active process require energy can be up or down and asidjiaktednsrenorieuce ohitodybtheid main is sucrose

Question 41

What can be sourced and sink

Answer 41

Source can be leaves stems m but also storage organs like tubers and roots in winter , where sink is leaves and rest of plant like growing at winter

Sinks are storage organs like tubers and roots in summer , where source are like green leaves

Anything growing can be a sink , a route Dan be food store , cotyledon , in seeds too

Question 42

What’s is cind of thr sssmilatemoinke at sink and how

Answer 42

Always kower so the assimilate fan end up here, and this is controlled by enzymes who make sure to cinverbtssimislre into another polymer like starch so that it reeucedncojcen, and thst doesn’t effect wise rpotentisl grsdient

Question 43

Okay assimilated can be loaded either ossicles by symolsdt route Ron

Answer 43

Either psssively by symolsdt route or actively by solar routr

Question 44

How is it loaded osssively via symolsdt route first

Answer 44

• simply moves through cytoplasm of medppjyll cells where lroruced through plasmodesmats and into sieve tube elements like thst. This is passive and diffusion,msnd the rest hsppens by mass flow (incresse cocn of sucrose in phloem at source decrease water potential so water move in fromxylem etc)

Question 45

Apolast part? Ignore icl , sssume to get close to the sieve tube

Answer 45

Basically travels through celluksoenfibres and itnrackekkusr spaces until it reaches comosndiojncellsnof thr sieve tube elements

Question 46

Okay so explain active loading at the source

Answer 46

Sucrose molecules in surrounding medophyll cells make way by apoplast till they reach companion cells

As low concentration in medophyll and higher in companion active transport hsppens

Bsdislly comosnion cells get sucrose molecules actively pumped into them :

• H+ ions are actively pumped out into the surrounding tissue VIA A PROTON PUMP CARRIER PROTEIN , requiring ATP
• now there a higher concentration of H+ ions on the outside of the comosnion celk thsn inside, creating sn electrochemical grsdient
• energy here is used to COTRANSPORT THE SUCROSE MOLECUKES INTO THE comosnion cell via a cotrsnsoorter and fscikated fifudsuoj , against its concentration gradient but with H+ conc gradient
• now sucrose in comosnion cell and this can be actively transported exact same way inti the phloem, or move here by apopkast osthwsy , or diffusion, but say sctiventrnsdpirtn

Question 47

Next

Answer 47

Once sucrose molecules increase in cocn at ohloem, this decreases water oirtniskndue to less free water molecules, and so water moves in by osmosis from the xylem as it is higher water oritnisknhere. This increases hydrdtaticoresdureat the souce
At the sink, unloading happens . Here as there is a high concentration in phloem than comosnion cells, sucrose simply moves in via diffusion , and is then converted into a stosgre thignlike starch to ensure this condition grsdient is maintiendd. The removal of sucrose into the comosnion cells mesnd an increase ifwaternpeitnislnst the sink. This leads to water KEAFINF by osmosis into xylem because lower water or risk, and this reduces hydrostatic oresdure st the sink

Finally , due to a oresdure grsdient , the assimilated move by mass flow from area of high pressure to low oresdure, source ti sink. Whole process repeats again

Enxumes at sink ensure low concentration in cells so thstsucrise always diffuses in o

Question 48

Summarise translocation

Answer 48

Phloem loading can happen

• passively by symolst pathway to reach the phloem first through plasmodemata
• actively by apoplast

Here sucrose molecules from surrounding tiddue are ACRIFEKY pumped in to the comosnion cells. This happens by a proton pump csrrier protein actively transporting h+ ions into thr surrounding tissue resuming atp, but this now created highe con h+ outside thsn inside snd so electrochemical grsdient esdrbskished, snd sucrose emielcuked use this ekectichemicslngrsdiejt energy to be contrsndoorter bybcitrsnodter inti thr comosnion cells sgsisnt its icnentrstiin grsdient (by fsciskted diffusion). The same thing happens again ti get into phloem, or some moves passively by apoplast ti get their
That was active loading

Once loaded , inc solute dec water , so water move in inc oresdure
At sink cocn solute in cell always kept low by endyme ckbvert, so move in diffuse, inc water potential, means water leave to xylem by osmosis, low hydrstaticoresdurllaismialtes move by amssflwo down orsduregesdirnr

Question 49

How are comosnion cells adapted for translocation?

Answer 49

Well needatp to do active transport, so got a lot of mtihvindris
- and also highly folded member snd ti increase SURFSCE area so that more active transport can take place kesdign ti more movement

Question 50

Evidence for ACTIVE LOADING AND mass flow (4)

Answer 50

1) microscopy advancement means can see adaprsjoje of comosnion cell (membrsne area snd mitochondria) and link this to active transport
2) if mitochondria of companion cell stop working , active transport will stop and mass flow is no longer observed (showing it is necsssry )
3) the flow in sugar is too fast if it was just diffusion , suggesting some sort of active process needed
4)
- aphid different pressured
Aphid was used to show translocation of solutes, aphid beak was used snd when implemented all the way into ohloem , water with solute would come out , due to pressure regardless of aphid
- could test this by using different alhidntube at sifferent points, and where oresdure lower expected it was, showing pressure changes were needed for ksss flow , and this caused by scrife

Summary l
Poison stop atp stop sctife stop mass flow
Faster than diffusionnalone suggests something’s active
Sdvancemtn mesmerised dna see sdsltsjton comosnion cell
Aphid beak used snd proved oresdure change needed

Question 51

Singh Vance between diffusion and as ; v on karge plants

Answer 51

Large plants have large kwave hoof high s ;p: v , so more water leaves due ti trnsoririsojnsnd so more adaptions are needed for tree tinsufe

Question 52

Rest of diffusion?

Answer 52

Distance /2

Question 53

Active vs fsciskted

Answer 53

Active actuskky used energy ti cause transport, fsciksited still depends on the nstualnnegeyr snd movement of moelfukenossidivlr y

Active is against fraduemr , fsciskted is skijg

Fsciskted hsooens in active thin