Module 3.3 Flashcards
1
Q
What does a single celeb algae do
A
It takes in carbon dioxide and water and carries out photosynthesis
- as it has a very large surface area to volume ratio it can rely on diffusion for the transport of molecules .
2
Q
Multicellular plants transport ?
A
Multicellular plants are large , and trees very large .
They also have a low surface area tovoile ratio
Therefore they CANNOT rely on diffusion alone for the transport of molecules .
3
Q
What does the green parts of multicellular plants do ?
A
They can carry out photosynthesis producing oxygen and glucose
- the glucose and oxygen can then be used in aerobic respiration .
4
Q
Many parts of multicellular plants cannot carry out photosynthesis for sample tissues int eh roots .
A
…
5
Q
What do the cells in root tissues do ?
A
They absorb mineral ions by active transport
Therefore they have a high metabolic reactions . Including aerobic respiration
6
Q
Due to their high metabolic rate …
A
Sugars must be transported to these tissues
7
Q
What other molecules do multicellular plants transport b
A
For example , mineral ions are transported from the roots to other parts of the plant .
- a good demo Lee is the nitrate IOKE which is used by plants to make amino acids .
8
Q
What else do plants transport ?
A
Hromones from where they are synthesised to their target tissues .
9
Q
Seeds contain an embryonic lead called a what is it called and what does it do
A
Cotyledon , when a seed germinates , the cotyledon unfurls allowing the seedling to carry out photosynthesis .
10
Q
Example of a plant that has only one cotyledon what are they called
A
Grass scientists call this MONOCOTYLEDONOUS plants
11
Q
Example of plants that have two cotyledons
A
Trees , scientists call these dicotyledonous plants .
12
Q
Transport system in dicotyledonous and monocotyledonous arrange in different way
A
Only need to know dicotyledonous
13
Q
Teees are example of what type of dicotyledonous?
A
Woody dicotyledonous
Often long growing and long lived
14
Q
In contrast , what a geraniums examples of ?
A
Herbaceous dicotyledonous plants
Herbaceous plants are often fast growing and can be short lived
- unlike woody plants , herbaceous plants do not have a woody stem .
15
Q
Plants have two different transport systems , what are they called ?
A
Xylem and phloem
16
Q
Function of xylem
A
Xylem carries water and mineral ions from the roots of the plant , up the stem to the leaves .
17
Q
Function of phloem tissue
A
Phloem tissue transports organic molecules such as sugars produced by photosynthesis in the leaves .
- these melcljes can move in the phloem down the plant to the roots or up the plant to the flower
18
Q
What are the xylem vessels and phloem vessels grouped together in ? ROOT
A
Vascular bundles .
-the arrangement of vascular Burnell’s is different in the roots the stem and the leaves. .
19
Q
where do root hair cells fire from ROOT
A
A layer of external tissue called the epidermis .
- we then have a thick layer called the cortex .
20
Q
What is inside the cortex ? ROOT
A
The cortex contains parenchyma cells which are found extensively in plants .
21
Q
What is in the center of the rlly and what is this surrounded by ? ROOT
A
Vascular bundle which is surrounded by a layer of cells called the endodermis .
22
Q
Where are the xylem vessels in the basic slr bundle ROOT
A
In the center with the phloem vessels around the xylem .
23
Q
Adaptations of xylem vessels ROOT
A
They are mechanically strong
-Because they are grouped together in the center of the root , this helps to prevent the root form being pulled out of the soil , for example by strong winds.
24
Q
Vascular bundles STEM how are they arranged ?
A
They are arranged in a ring around of the stem
- the center of the plant stem is called the PITH and consists of parenchyma cells
Around the edge we have epidermis and correct
25
What is within the vascular dbinfles known as the STEM
The phloem vessels are located around the edge of the stem . the xylem vessels are found closer to the center .
- ASA THE BUNDLES are around the EDGE AOF THE STEM , fhis helps the stem tk withstand the bending due to the wind .
26
LEAF Vascular bundles
Main vascular bundles in the center .
- fhis part of the leaf is called the midrib .
27
Function of midrib LEAF
It provided transport and support to the leaf .
- the lead is also supported by smaller vascular bundles connected to the main one , .
28
Completion of Vasculwr bundle LEAS
- the xylem is at the upper part of the vascular bundle. .
- phloem is at the lower part. .
29
Where doenspjtoeynejsis mainly take part in the leaf ?
Palisade mesophyll which is in the upper half of the leaf .
30
Key : xylem consists of two main types of tissue which is ?
Xylem vessels and xylem fibres
31
Xylem vessels
- xylem vessels start as a series of plant cells , running up the stem from the roots to the leaves.
- at a certain point , the carbohydrate lignin forms within the cell walls , .
32
Lignin is impermeable , what does fhis mean !
It prevents substances from passing through the cell wall .
- the living contents of the cell die
And the end walls between the cels break down . HWOEBER , regions of the cell wall remain free of ligning these are called pits .
33
What do pits do in the xylem !
These allow water and dissolved substances to pass between vessels .
- so the final xylem vessels consist of non living hollow tubes ,
34
What happens when a xylem vessel is blocked or damaged !
Then water cna move thru light he lord to different vessels .
- the pits also allow water to move out of the xylem , for example to cels in the leaves
35
How is ligning arranged
Spirals or rings
Kn other xylem vessels ligning scan be continuous apart form the pit .
36
Function of lignin
Helps to support the structure of the xylem vessel. .
37
What happens when water is pulled up the xylem vessels ?
Causing the pressure in the vessels to fall slightly .
- the lignin in the vessel walk held tk orevent the vessels from collapsing .
38
What are xylem fibres ?
Xylem Finrws aee formed form long narrow cells .
- very large amount of ligning forms in these cells
Jus liek xylem bellies the itneiror contents of cells kes
HOWWVE UNLIKE XYLEM VESSELS. Xylem fives are not used to transport water instead they provide mechanical support for plant. .
39
What does xylem also contain - parenchyma cells what do they do zb
Parenchyma cels can act as a store of starch .
Parenchyma cells can also Cornish tannins which are bitter compounds that DETER HERBIVORES FORM ESTING THE PLANT
40
In the leaves what process happens
Plants carry out photosynthesis which produces the sugar GLUCOSE .
41
What is glucose used for
To form
Other compounds such as different sugars and aminos did a
- these compounds are called ASSIMILATES .
42
Job of phloem ?
Transport assimilated from the leaves to other parts of plant such as roots or flowers .
- meaning , molecules cna be transported, both up and down the phloem. .
43
Whay is the fluid moving the phloem referred to as ?
Phloem sap .
44
In contrast to xylem , phloem is …
A living tissue
45
Phloem consists of two types of tissue. Number one and what if consist of
- sieve tube element which consists of a long line of cells arranged end to end ,.
-inside thsr cells almost all of the organelles have been lost. , including the nucleus and vacuole.
- levaing the interiors of these cells almost entirely free . To transport phloem sap .
46
What do the end walls of these cells ahve ?
They have been modified to contain large pores .
- scientists call these modified end walls a sieve plate .
47
What do sieve plates do ?
They allow the phloem sos to move brteeen the cells .
48
Sieve tube element cells ahve lost most of their organelles , what is a disvavdabgev bevwuse of this !
This means that they cannot produce large amounts of essential molecules like atp
HWOEBER , Next to the sieve tube element cells there are companion cells .
49
What do compaction cels contain ?
Companion cells contain a nucleus as wel as large amounts of mitochondria . .
MICROSCOPIC channels link the companion cells to the sieve tube element cells , thsr channels are called plasmodesmafa
50
Function of plasmodesmafa
Molecules such as ATP and proteins can move through the plasmodesmwrs into the sieve tube element cells. .
51
So what is the role of the companion cells
To provide essential molecules to the sieve tube element cells. X
52
Unlike xylem .. phloem tubes do not contain what in their cell walls zb
Lignin .
HWOEBER phloem contains two ghped of tissue which provide support.
FIBRSS AND SCLEREIDS
53
Function of fibres and scleroses in phloem
They both contain thickened cell walls containing lignin .
/ fibres are king and narrow .
Sclerosis have a variety kf shapes. .
54
Roots are covered in root hairs , where do root hairs grow from zb
The cells in the epidermis of the root . On other words outer layer z s
55
Water moves into root hair cells jow ? And how are they separated to this rapidly
Osmosis .
1. Densely packed root hairs , massively increases fhe surface area to volume ratio of the root .
2. Surface of the root hair consists of only the cell wall and cell membrane . - making the surface dxgdmdly thin increasing the rate of osmosis
56
Third adaptation of root hair cells
The water in the soil contains dissolved mineral ions for example magnesium . Which plant uses to make chlorophyll .
HOWBEER , The concentration of these mineral ions is lower in the soil than in the root ahir
SO ROOT HAIR CELLS AUSE ACTIVE TRAMPSORT O MVOE THESEMINERAL IONS INTO THE CELL AZ
57
Root hair cells also contain other dissolved compounds like sugars how does this effect water potenital
Therefore the water potenitalINSIDE the root hair cell is LOWER ATHAN IN THE SOIL .
So wayer makes intl the rlly hair cell by osmosis down the wayer potenital gradient. .
58
Where does water love form the root hair cell ?
Through the root forest to the xylem
59
There are Toledo ways in which water can move through the cortex
Symplast pathway asymplast pathway
60
First way water moves they direct sumplast pathway
Water moves from the cytoplasm of one cell to the cytoplasm of the adjacent cell .
- to do this wayer moves through the plasmodesmata , linking the cells .
61
Plasmodesmafa are whay ?
Microscopic channels through the cell wall connection the cytoplasm of cells .
62
How is the sumplast pathway driven !
By the water potenital gradient between the root hair cells and xylem .
- water continually moves into the root hair cells by osmosis from the soil .
THIS MAKES the water potenital of the root hair cells frayed than the forest cells
63
What is the water potenital like in the xylem and what is the Chevy of this
The water potential is relatively low . So wayer moves by osmosis across the forest down the water potential gradient .
64
Speed of symplast pathway ?
Pathway is relatively slow ,
Thay is bevause the pathway for water in the cytoplasm is obstructed by the organelles .
65
Other path way thay wayer
Moved by
Apoplast pathway
66
How does water move in the apoplast pafheay
Water moves within the cell walls and the spaces between the cells ,
- the cellulose cell walls have a relatively open structure allowing water to lvoe easily between the cellulose fibres .
- remember , water orlcuecl are attracted to each other aNknoes as cohesion Sadie to hydrogen bond to rsjfoth
67
As water moves into the fulll and is carried away
More water moves along the apoplast pathway due to cohesion.
- the apoplast pathway offers much less resistance to water flow than the sumplast pathway
68
Before the water passes through the xylem , what does it have to pass though
Layer of cells called endodermis
69
Adaptations of cells in the endodermis
They have an unusual featfue
- a band of waterproof material called Suberin runs around the cell wall .
scientists call this rhetorical casparism strip .
70
What is the effect of the capsariam strip ?
Water can no longer move through the apoplast pathway .
instead , the water now pssses though the cell meme brand and into the cytoplasm becoming part of the symplat pathway
71
What happens if we force all water into the cytoplasm ?
This allows the fell emergence to contorl which substances can enter the xylem
72
What type of transport do cels in the endodermis use ?
They use active transport to pump mineral ions into the xylem.
- this lowers the water potential of culem , triggering water tk move into the xylem vessels by osmosis . Scientists call this effect ROOT PRESSURE
73
Is root pressure an active process ?
Yes it is an active process reuwiring respiration
-
74
What happens if we inhibit respiration
By using a metabolic poison like cyanide . The hen root pressure stops
75
When else do root pressure sfop
If we prevent aerobic respiration by excluding oxygen .
76
Water passes into the leaf how ?
Through the xylem vessels in the vascular bundle .
77
What is the surface of the lead covered in and what is its job ?
A waterproof layer called the waxy cuticle .
- the job of the waxy cuticle is to reduce water loss from the surface of the lead by evaporation .
78
Apart from water , what else does photosynthesis need and how does the plants get this ?
The gas carbon dioxide , this carbon dioxide diffused into the lead from the external air .
79
What does photosynthesis reproduce and what happens to it ?
It produced the gas oxygen which diffuse out of the leaf .
80
What do we find on the lower surface of the leaf photosynthesis sexplain ?
We find thousands of tiny pores called stomata .
- when the plant photosynthesises the stomata are open , allowing carbon dioxide to diffuse into the leaf and oxygen to diffuse out .
81
Internal structure of the les fkeybidrs
The surface of the cells in the leaf are covered with a thin layer of water . This water evaporates from the surface of the cells . Because of this , the internal leaf spaces contain a high concentration of water vapour .
82
Generally . What is the level of water vapour like in the external air , link this to stomata .
It is relatively low .
So when the stomata are open the water vapour diffuses out of the leaf into the eyxnernal air .
- this evaporation of water followed by the diffusion of water vapour is called TRANSPIRATION
83
Why does the water potential of the cells in lead decrease in transpiration ?
Because of the continuous evaporation fromtheir surface .
/ this causes water to move by osmosis from adjacent cells .
- this now lowers the water potential of these cells , causing water to move in to them .
84
Why does the water potential of the cells in lead decrease in transpiration ? Part 2
At some point , this reaches the xylem , with water passing out of the xylem to adjacent lm cells .
85
So when transpiration is taking place …
Water is continuously
Being pulled out of the xylem vessel .
- scientists call this pulling effect TENSION
86
What is the transpiration stream ?
The movement of water form the roots up the xylem and out of the lead
87
What is cohesion ?
Water molecules form hydrogen bonds to eachother .
88
Where does water form hydrogen bonds in plants ?
They form hydrogen bonds to molecules in the xylem vessel walls . For example , carbohydrates . This is called ADHESION
89
What is one effect of cohesion and adhesion ?
Is that water can move up very thin tubes against the force of gravity . Scientists refer to this as capillary action .
- so when water is removed from the top ox the xylem vessels due to transpiration . More water loved uo the fullest vessels by capillary action to twke its place .
- this whole process is referred to as transpairtoom pull
90
What is the combined effect of transpiration pull coupled with cohesion and adhesion ?
Is that water is drawn into the roots. Moved up the stem and passed out of the leaves .
Scientists call this whole process cohesion - tension theory .
91
First Piece of evidence that supports cohesion tension theory
1. If a plants stem is cut , then air is sucked into the xylem , suggesting that the xylem vessels are under tension .
HOWEVER , air prevents the cohesion between water molecules , so water movement stops ,
92
Second piece of evidence that supports cohesion tension theory
If we measure the diameter of a tree trunk , we can see that this reduces when transpiration is at its maximum .
- this supports the idea that transpiration pull is generating NEGATIBE PRESSURE or tension in the xylem .
93
How can we measure the rate of water uptake in a plant ?
By using a bubble potometer
94
What does a bubble potometer conists of
A fine capillary tube filled with water
- tube come fed to
Plant which is cut at the stem
A- tube also also connected to syringe w water
Finally we as use a needle to place small bubble at end of capillary tube
95
Stage one or bubble ptopemrter
As water evaporates from the leaves of the plant , water is drawn into the stem .
- this causes air bubble to move towards the plant
96
Stage two of bubble potometer
By measuring how far the air bubble moves in a given time ,
- we can calculate the rate of water uptake into the plant .
- we can fhen see how the rate of water uptake changes if we change the conditions .
97
How would we change the conditions of Hubble potometer
Carry out the experiment under different light intensities .
/ investable the effect of wind by using a fan .
- invetween experiments , RESDY position of air bubble by adding more water from the syringe .
98
Key of the bubble potometer
It only measures the water uptake into the plant .
- not all of this water will take part in transpiration .
R.g small amt will be used as a reactant in photosynthesis .but vast majority for trajsiepario
99
Things to consider when setting up bubble potometer pronlem 1
- 1. Firstly when we take cutting from parent plant , air will be sucked into t the xylem vessel
- these air gals would prevent water from being taken up the stem .
100
Bubble potometer p1 solution
- to correct for this , we now place the cut stem of our plant into water . And cut off the last 1 cm .
- water will now flow into the xylem and we shall avoid any air gaps . .
- place the potometer under water , inser fut end to avoid any air gaps
Carefully do otherwise damages plant and avoid water on underside of leaves as that’s were most stomata are found .
101
Why is it important that the potometer is fully sealed ?
Use petroleum jelly around connection between stem and tube
- allow plant to adapt to its surroudnings for ten mins before starting edpiemenr
102
How does a mass potometer work ?
Place our plant in its pot on a balance , as the plant loses water through trsnspifafiom , the total mass decreases .
103
Key about mass potometer
We have to prevent evaporation of water from the soil .
- otherwise , this would contribute to mass loss giving a false reading for transpiration . This is done by covering the soil with plastic wrap .
104
Two advantages to the mass potometer
1. Firstly , this directly measures the rate of transpiration rather than the rate of water uptake .
2. Must less disruptive to the plant , as it does not involve cutting the stem .
105
How does water evaporate ?
From the moist surfaces of the cells inside the leaf .
The water vapour then diffuses out of the leaf to the external air through tiny pores called stomata . This is called TRANSPIRATION
106
Stomata are central to why process ?
Transpiration .
107
Stomata is plural WHAT is singular stoma
108
What is each stoma surrounded by and what do they do ?
Guard cells and the shape of the guard cells determines whether the stoma is open or closed .
109
What is rhe first key features of guard cells ?
Firstly the cellular cell wall on the inner side of the guard cell is thicker than one the rest of the cell .
110
What is the second key feature of a guard cell ?
Sill some of the cellulose microfibrils in the cell wall are arranged in ring shapes .
111
What does stomata have to do in relation to photosynthesis
Plants harness light energy to produce sugar glucose and for this to occur
Carbon dioxide must diffuse into the lead through the stomata .
112
What happens to stomata in light conditions ? Part one
Stomata open - allowing carbon dioxide to diffuse into the leaf. . WHY ?
- light conditions trigger solutes such as the potassium ion to be transferred into the guard cells .
-.
113
What happens to stomata in light conditions part two
this LOWERS the water potenital of the interior of the guard cells . Water now moves into the guard cells by osmosis causing the guard cells to swell .
- scientists say that the guard cells become turgid
114
What happens to stomata in light conditions part rheee
However , as water enters , the rings of cellulose prevent the guard cells from expanding width wise .
INSTEAD , guard cells expand lengthwise .
115
What is the purpose for he thickened cell walks (ref to card 114)
The thickened cell walls prevent the guard cells from expanding evenly . Forcing guard cells to make a CURVED SHAPE
- fhis curved shape allows the stoma to open between the guard cells .
116
What can diffuse out of the leaf when stomata are open zv what is the porblem w this
Water vapour
- this loss of water could cause the plant to dry out .
117
Why do the stomata close at night time
- plant no longer carries out photosynthesis , they clsoe to reduce wate loss
118
In what conditions can the level of water in the soil fall
Drought
119
What does a plant do when there is a drought (1)
The roots send a hormonal signal to the leaves , this hormone triggers the guard cells to lose their turgidity causing stomata to close.
120
What does a plant do in drought contains (2)
By closing their stomata under drought conditions this reduces water loss from the plant .
- closing their stomata prevents plant from carrying out photosynthesis , HWOEBER this is a small rocie to pay to prevent plant from dying from water loss
121
Cells on the inside of leaves are covered with a thin layer of water what happens to his water
…
- this water vapour can diffuse out of the stomata down the conecentrafion gradient to the external air . Aka transpiration
122
First factor that affects transpiration and why
LIHHT INTENSITY ,
For transpiration to take place drowned misf be open and they open in LIGHT conditions to allow carbon dioxide to diffuse into the leaf and take part in photosynthesis .
123
What happens to trabspirarion as we increase light intros itt and WHY
The rate of transpirariln increases . Because increasing light intensity increases the number of open stomata , allowing more water vapour to diffuse out of the leaf .
124
What at high light intensities the rate of transpiration no longer increases ?
At high light intensities almost all of the stomata will be open .
125
Second factor that affects transpiration
Relative humidity
(Water vapour diffuses out of the lesf down a conc gradient )
- BECAUSE , Fhe conc of water vapour outside lesf is generally lower then inside .
126
What does relative humidity tell us ?
The concentration of water vapour in the air . As a percentage of the maximum
Possible .
100% humidity means concentration of water vapour is high as it possibly could be
127
If the reliable humidor outside leaf increases …
Smaller concentration graidnebf befweeen inside the leaf and outside .
- so increasing the relative humidity ourside the leaf reduces the rate of transpiration .
128
How is the rate of transpiration increased by Temperatuee
TEMPERATURE
1. at higher temperatures , water molecules a have more kinetic energy . Meaning there is a greater rate of evaporation of water from the internal surfaces of the leaf .
129
How does temp increases transpiration part 2
At higher temperatures , the relative humidity of the external air decreases ,
- due to these two effects , the concentration gradient of water vapour between the inside of the leaf and the external air increases at higher temperatures .
- this increases the rate of transpiration
130
Another thing that affects the rate of transpiration third thing (movement of air ) explain
- when water vapour moves out of the stomata during transpiration ,
- that water vapour can build up around the EXTERNAL surface of the leaf .
EFFECT OF TJIS , Is to reduce the concentration gradient for water vapour , between the inside kf the lead and the outside / this reduces the rate of transpiration as
131
What does the air movement eo the the water vapour
Aka wind , it removes the water vapour as it diffuses out of the leaf ,
BECAUSE air movement increases the cofnentraidon gradient of of age rvpaour the effect of fhis is to INCREASE the rate of transpiration
132
Transpiration falls on still days as what
There is little air movement
133
Fifth factor that affects transpiration !
The level of water in the soil (droughts stomata close reducing water loss yeah the card we did girl ..
134
Plant have adpaptions to reduce wate loss
Closing stomata at night where no photosynthesis
135
Whay does a waxy cuticle do ?
It reduces water loss by evaporation
136
What are xerophytes
Plants fhag have evolved to live in dondutions where water is very scarce
137
Cacti adaptations
Costco leaves have been replaced with fibrous spines , shift photosynthesis taking place in the stem of the cactus .
- In these cacti the stomata are found on the surface of the stem .
138
Cacti adaptations , what does replacing the leaves with spines do ?
Replacing the leaves with spines deuce the surface area to volume ratio of the Cactis , which then reduces water loss
139
What is another adaptation of spines in cacti
The spines also trap moisture air near the catctis reducing the rate of transpiration . As well as providing some shade for the stem from the heat of the sun .
140
Adaptations of cacti - explain thick waxy cuticle
To reduce evaporation kf water .
141
In cacti where are the stomata sunken into and why ?
Pits , this traps the layer of moist air around the stomata , reducing water loss by transpiration .
142
When do cacti open their stomata ?
At night , to absorb the carbon dioxide , when conditions are relatively cool .
- carbon dioxide is then used during the day for photosynthesis .
Only open at night reduces water loss in cacti during heat dk daytime
143
Cacti adaptations - extensive shallow roots
This allows the cacti to absorb water after a rain shower before the water evaporates .
- cacti can also have very deep roots do access water from lower levels of the soil .
144
Where can cacti store water ?
In their stem ,
Plants which can store water like this are called succulents
145
Where is marram grass found ?
In san dunces
Here water is scarce and windy conditions increase evaporation of water form plants .
146
How are the leaves of marram grass evolved
They can roll into a tube with the stomata on the inside ,
- moist air is trapped within the tube rather than being blown away by the wind .
147
Where is stomata found in marram grass ?
In sunken pits , with fine hairs projecting inwards towards the centre .
- these adaptations ensure that moist air is trapped around the stomata . THIS reduces the concentration gradient for water vapour , between the air and ilrhe internal spaces between the leaf cells .
- this reduces the rats of diffusion of water vapour out of the stomata .
148
Why do marram grass have a thick waxy cuticle v
A very thick waxy cuticle , to deuce evaporation from the surface .
149
What are the roots of marram gras like ?
Very long , extending deep into the sand to find water .
- marram grass also have extensive roots which are closer to the surface , these roots help the sand to retain water ,
150
Why do parts of the plant require glucose
For respiration .
-
151
What is the glucose produces in the leaves first converted to ?
The disaccharide sucrose
- sucrose is LESS reactive than glucose and is LESS LIKELY ATO REACT WITJ OTHER molecules
152
What are assimilates ?
Molecules , such as sucrose , which are made as a result of photosynthesis, .
- assimilated can also include amino acids .
153
How are assimilates like sucrose transported ?
Around the plant in the phloem .
- the transport of assimilates in the phloem is referred to as translocation .
154
Key assimilated like sucrose are transpired from sources to sinks .
…
155
What are sources ? Give examples
Where the assimilates are produced for example photosynthesising leaves
- other sources include storage organs such as tubers which can release their carbohydrate stores when they are needed .
156
What are sinks ? Give examples
Sinks are regions where assimilates are required .
These include roots which carry out active transport n therefore have a high rate of respiration .
157
Give two more examples of sinks
Storage organs can also be sinks when they are refilling their carbohydrate stores .
- other sinks include growing regions such as shoots , which contain dividing meristem tissue .
158
How assimilate such as sucrose are transpired in the phloem …
Is not well understood - but there is an active model for this process to understand this need to understand structure of phloem z
159
Imagine source - in this case photosynthesising leaf
The source is connected by the PHLOEM to a sink , in this case a root .
Key ; at the source sucrose is loaded into the phloem by an ACTIVE process , f
160
PART ONE Close up of cell membrane of phloem companion cell what does a protein do B
A protein on the cell membrane of the companion cell uses ATP , to pump hydrogen ions out of the cytoplasm and into the spaces of the cell wall . This process is active transport , this creates a concentration gradient for hydrogen ions .
161
Part TWO
With more hydrogen ions on the outside of the cell membrane , .
- the hydrogen ions now can flow through a cotransporter protein doen the concentration gradient back into the cell
- this INWARD AFLOW OF HYDROGEN ions is coupled to an inward flow of sucrose into the companion cell .
162
Adaption of companion cells I. Terms of translocation in phloem
They have a large number of mitochondria which provide the ATP needs for the active transport of hydrogen ions.
163
Part THREE
FOLEING on the cell membrane also increase the surface area for the proteins involved .
164
What is the concentration of sucrose like because of the transport process
The concentration of sucrose in the companion cells is high .
165
Transport process part four
The sucrose can now diffuse through the PLASMODESMAA form the companion cells to the sieve tube element cells .
- meaning we have a high concentration of aSucrose Is the siege tube element cells .
166
Transport professionals five what so the effect of high cocn of sucrose is sieve tube
it’s to LOWER THE WATER POTENTIAL inside the sieve tube element ,
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Part five of transport
Water now makes into the sieve tube element by osmosis from nesrbh tissues including XYLEM VESSELS
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Pert fibe transport
This now increases the hydrostatic pressure inside the sieve tube element .
- ASA REUSLT AFHE LHLLEM SAP NKW MLVES Up or down DOWN THE SIEVE TUBE ELEMENT. .
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Part six
This bull movement of phloem sap is called MASS FLOW
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Part 7 of mass flow
At the sink , sucrose moves out of the sieve tube element. /!: is converted to glucose for use in respiration
- or in the case of storage organs the sucrose is converted into starch .
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Part 8 of mass flow
As the sucrose leaves , this increases the water potenital in the sieve tube element .
- causing water to move out of the river tube element by osmosis .
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Part 9 of mass flow
Some do this water will go back into the xylem . And join the transpiration stream .
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There are several lines of evidence that support this active model of movement in the phloem
Example , the rage of flow of sucrose in the phloem , is much fwtser then could take place by diffusion alone. .
- if we inhibit the companion fell mitochondria , translocation stops ,
