Chapter 9 - Transport in plants Flashcards

Question 1

Q

the 3 main elements a plant needs are?

Question 2

Q

position of xylem and phloem within vascular bundles?

Answer

A

phloem: outside, xylem: inside facing centre of cell/stem

Question 3

Q

what do sclerenchyma fibres do?

Answer

A

tend to lie on the outside of VB and in between diff vessels, provide additional support to the VBs and plants as a whole + help to keep vessels upright and open

Question 4

Q

what do parenchyma fibres do?

Answer

A

living cells that act as a packing tissue to separate the xylem vessels from phloem, and provide them w support

Question 5

Q

structure of xylem vessels?

Answer

A

ded cells stacked end to end
xylem cells have no cytoplasm or organelles and no cell walls at their ends (only at sides) that would slow the flow of water
lined w lignin - a waterproof polysaccharide

Question 6

Q

in VBs, xylem vessels are?

Answer

A

continuous hollow tubes that run through the plant

Question 7

Q

formation of xylem vessels?

Answer

A

immature xylem vessels are waterproofed when lignin is deposited on the inside of their cell walls + in a spiral pattern
the process of lignification kills the cells and allows for max. flow

Question 8

Q

adaptations of xylem ?

Answer

A

holes in the xylem w no lignin - bordered pits - allow H2O to move between vessels to get to diff leaves e.g.
vessels are narrow enough to ensure water travels upwards in an unbroken column
no end walls or organelles to impede water flow

Question 9

Q

H2O movement?

Answer

A

in xylem vessels: mass movement

- between plant tissues: osmosis

Question 10

Q

root hair cells are adapted spec for the uptake of water and mineral ions:

Answer

A

mineral ions are actively transported from the soil into the root hair cell
these minerals reduce the water potenial of the root hair cell cytoplasm
water enters the root hair cell by osmosis

Question 11

Q

where does the cortex lie?

Answer

A

between epidermis (outside) and endodermis (inside)

Question 12

Q

inside the endodermis,…

Answer

A

is the Medulla - means centre/ middle - xylem is here

Question 13

Q

Purposes of the Casparian Strip?

Answer

A

creates a checkpoint for plant immune systems b4 transport thru the rest of the plant - acts as a barrier to pathogens
blocks water from passing back into the cortex from the xylem

Question 14

Q

where does the water exit xylem vessels?

Answer

A

the xylem vessels located in the spongy mesophyll where the xylem vessel finishes

Question 15

Q

how does water vapour diffuse out of the stomata?

Answer

A

down a water vapour potential gradient

Question 16

Q

what is transpiration?

Answer

A

the loss of water through the aerial parts of the plant mainly thru stomata in the leaves

Question 17

Q

what is the transpiration stream?

Answer

A

there is a constant stream of water travelling from the roots, through the stem and out of the leaves. Water diffusing out of the roots is replaced by water from the xylem vessels

Question 18

Q

importance of transpiration?

Answer

A

a constant supply of water to the leaves has benefits:

main being maintenance of turgidity - gives support & strength to the cell
water for metabolic processes
transport of mineral ions - if water wasn’t present, the ions wouldn’t be able to dissolve in any solution, need to dissolve so they can flow freely & b delivered to cells
evap H2O keeps plant leaves cool in the sun - maintains temp

Question 19

Q

evidence for transpiration - - pressure?

Answer

A

the column of water pulled up is under - pressure
leaf = - pressure, drawn up in roots = + pressure
if there was a + pressure in leaf and trans wasn’t happening, the water would just stay in the leaf and build up, push back down on the xylem vessel, water wouldn’t have any gradient to be sucked up the xylem vessel

Question 20

Q

what is - pressure?

Answer

A

where something is being pulled to an area where its under less pressure

Question 21

Q

what does - pressure do?

in day and night

Answer

A

squeezes the xylem vessels in the day (sunlight -> transpiration) and relaxes in the night (less trans)

Question 22

Q

what happens if xlem vessels are broken evid)

Answer

A

air gets sucked in and they fail to carry water -> air enters causing bubbles, adding to the pressure of the vessels, and so H2O can’t be carried as there are air blockages in the vessels.
if xylem vessels r broken, the plant loses it’s ability to draw up water

Question 23

Q

what in the xylem do water molecules adhere to?

Answer

A

hydrophilic polysaccharides (not lignin - hydrophobic)w

Question 24

Q

what allows water to travel long distances up the xylem ?

Answer

A

the combination of cohesion and adhesion

Question 25

Q

capillary action?

Answer

A

the forces of adhesion push H2O along narrow vessels
each xylem vessel only has a thin cross section but packing thin xylem vessels at high density max. this effect
overall this force is quite weak and is more useful in V short plants w a high amount of xylem vessels

Question 26

Q

why are phloem necessary?

Answer

A

Plants need to be able to transport water from their roots upwards and sugars and other assimilates both upwards and downwards

Question 27

Q

Phloem tissue consists of 2 types of cell:

Answer

A

sieve tube element which are lined end to end to allow flow of sap & they have little cytoplasm and no nucleus to max. Space for sap but they r still alive, and companion cells which control transport in the sieve tube elements

Question 28

Q

Companion cells contain many mitochondria bc ?

Answer

A

the phloem requires active transport to move sap in translocation

Question 29

Q

Translocation is?

Answer

A

the transport of assimilates through a plant

Question 30

Q

outline the process of active loading?

Answer

A

Step 1: H+ ions are pumped out from the companion cells to the surrounding leaf tissue creating a diffusion gradient of H+

2: H+ ions diffuse back into the companion cells thru cotransporter proteins bringing sucrose w them
3: High concs of sugar in companion cells cause sucrose to diffuse into the sieve tube elements

Question 31

Q

what is active loading?

Answer

A

The process of loading sucrose into the sieve tube elements

Question 32

Q

what are sources in plants?

Answer

A

Sources are parts of plants that load materials into the transport system (can be where something is absorbed or created)
The leaves are a source of assimilates that are transported in the phloem

Question 33

Q

what are sinks in plants?

Answer

A

Sinks are parts of the plant where materials are removed from a transport system
The roots are a common e.g. of a sink in plants - they remove the sucrose from the phloem to use it in their own cells

Question 34

Q

The sources and sinks of plants are connected by ?

Answer

A

the phloem allowing assimilates to be transported to where they are needed

Question 35

Q

the process of translocation

Answer

A

When the assimilates are actively loaded into the sieve tube element, the water potential at the source decreases
Water from the xylem vessels in the source then follows into the sieve tube element by osmosis
Loading of assimilates and water at the source creates a high hydrostatic pressure
Sucrose removed at the sink reduces the water potential of the surrounding cells
Water then leaves the sieve tube element by osmosis
Unloading of assimilates and water reduces the hydrostatic pressure at the sink
The difference in HP between source and sink creates a pushing force hat moves sap to the location it is needed
This whole process is known as mass flow - bc we’re talking about moving the sugar and water in large amounts from areas of high to low pressure

Question 36

Q

what are xerophytes?

Answer

A

Xerophytes are plants adapted to living in dry conditions

Question 37

Q

what do xerophyte leaves tend to be like?

Answer

A

Leaves tend to be small or needle shaped -> reduces their SA:V -> less area for water to be lost from

Question 38

Q

why do some xerophytes have hair on their leaves?

Answer

A

Hair on leaves = slows air movement around the top of the leaf, traps air around top of leaf which means more humid air so less strong water vapour potential gradient

Question 39

Q

adaptations of cacti?

Answer

A

have many additional adaptations to help them cope w extremely dry conditions:
fleshy body for water storage,
spines that protect the cactus against animals who might eat it for water,
slow growth & very little flowering = V low metabolic rate so lower demand for water,
thick stems = reduces SA:V
Water collection: wide & extensive roots = inc SA for them to gather water

Question 40

Q

Marram grass adaptations?

Answer

A

most obvious feature it has evolved is the rolled leaf = reduced SA:V -> less water loss due to transpiration
& in the rolled up area can maintain humidity = reduced water vapour potential gradient
Other: sunken stomata, hairs, thick waxy cuticle

Question 41

Q

hydrophytes adaptations?

Answer

A

Are plants that are spec adapted to live in water rather than soil

Question 42

Q

Challenges faced by hydrophytes?

Answer

A

have to get O2 to submerged tissues,
have to keep afloat to get sunlight,
high humidity above the surface of the water (water is constantly evaporating) greatly reduces the rate of transpiration

Question 43

Q

adaptations of hydrophytes?

Answer

A

large air spaces in spongy mesophyll to give buoyancy (ability to float in water),
leaf stems have many air spaces to allow O2 to diffuse to roots,
many hydrophytes increase their transpiration rates by using hydathodes

Question 44

Q

what are hydathodes?

Answer

A

structures in plants that release water droplets which then may evaporate from the leaf surface

Question 45

Q

The transport system in plants is divided into 2 types of vascular tissue:

Answer

A

xylem tissue and phloem tisSue

Question 46

Q

xylem function is?

Answer

A

Function is to transport water and dissolved ions from the roots up the stem and into the leaves of plants.

Question 47

Q

Xylem structure?

Answer

A

Made of 2 main cell types: xylem vessels and xylem parenchyma, but also tracheids.
Xylem parenchyma are living ‘packing cells’ found in between the xylem vessels.
Xylem vessels are formed from dead cells that have lost their top and bottom cell walls forming long, hollow tubes.
The vessel walls become lignified - spirals or rings of a hydrophobic biopolymer called lignin are deposited within the cell walls. This gives the vessels mechanical strength

Question 48

Q

how does water flow thru xylem?

Answer

A

Sideways movement of water and ions through pits which connect vessels laterally.
Allows the movement of water from soil to leaves by mass flow, not diffusion.

Question 49

Q

phloem tissue is made up of?

Answer

A

2 main cell types:

sieve tube elements and companion cells.

Question 50

Q

Sieve tube elements?

Answer

A

Sieve tube elements (STEs) distribute the assimilates of photosynthesis around the plant. This is translocation.
STEs are living cells forming continuous columns.
A modified cell wall called a sieve plate is found at each end of each STE..
Very little cytoplasm and few organelles, leaving room for the transport of sugars.

Question 51

Q

companion cells?

Answer

A

Companion cells are ‘normal’ plant cells.
Many mitochondria and ribosomes - very active.
Give metabolic support to STEs.
Closely associated with STEs.
Involved in loading and unloading sucrose into and out of STEs.

Question 52

Q

how are STEs and companion cells connected?

Answer

A

Many plasmodesmata connecting STEs and companion cells.

Question 53

Q

what are the assimilates of photosynthesis?

Answer

A

The assimilates of photosynthesis are the organic molecules made from the sugars the plant makes during photosynthesis. Sucrose is the main transport sugar, but amino acids, hormones and other organic molecules are also transported.

Question 54

Q

where are VBs fouund in a root?

Answer

A

If you look at a micrograph of a section of a plant’s root, the vascular tissue is central - in the middle, in a structure called the stele

Question 55

Q

where are VBs found in the stem?

Answer

A

If you look at a micrograph of a section of a plant’s stem, the vascular tissue is peripheral - round the outside, in structures called the vascular bundles

Question 56

Q

Epidermis? (root)

Answer

A

The outer layer of cells is the epidermis.

In the root, many epidermis cells are specialised and have root hairs to increase SA for absorption.

Question 57

Q

cortex? (root)

Answer

A

The thick layer of unspecialised cells between the epidermis and the stele is the cortex - a ‘packing’ layer made of parenchyma cells

Question 58

Q

Endodermis? (root)

Answer

A

The outer layer of the stele is the endodermis. These cells control the entry of ions into the xylem

Question 59

Q

where is phloem tissue found in a plant? (root)

Answer

A

In between the ‘arms’ of the cross is phloem tissue.

Question 60

Q

where is xylem found in a root?

Answer

A

Xylem tissue forms a cross shape in the centre of the stele

Question 61

Q

pericycle? (root)

Answer

A

The pericycle is a layer of cells between the endodermis and the phloem.

Question 62

Q

(stem) collenchyma cells?

Answer

A

just behind the epidermis are a few layers of strengthening cells called collenchyma cells.

Question 63

Q

(stem) cortex?

Answer

A

The thick layer of unspecialised cells in the centre of the stem is the cortex - made of parenchyma cells.

Question 64

Q

(stem) each VB has?

Answer

A

Each vascular bundle has 4 distinct regions.

Answer 64

A

Sclerenchyma cells are mechanically strong, supporting the stem.

Answer 65

A

xylem ➡ cambium ➡ phloem ➡ sclerenchyma

Answer 66

A

The lignified fibres are sclerenchyma.

The pith is loosely packed parenchyma cells.

Answer 67

A

Minimises water loss from top surface of leaf.

Answer 68

A

Structural cells forming top surface of leaf.

Answer 69

A

Main site of photosynthesis. Packed with chloroplasts.

Answer 70

A

Gas exchange and evaporation of water vapour.

Answer 71

A

Form part of spongy mesophyll tissue.Continuous with atmosphere.

Answer 72

A

Structural cells forming under surface of leaf.

Answer 73

A

Work in pairs, changing turgidity to open and close stomata.

Answer 74

A

Pores allowing CO2 in, O2 out and water vapour out of leaf.

Answer 75

A

Transports sugars away from the leaf, to other plant cells.

Answer 76

A

Transports water and ions to leaf cells.

Answer 77

A

On a bright, sunny day, the rate of photosynthesis within the leaf > the rate of respiration.
This means more O2 is being produced in the leaf than being used and more CO2 is being used than being produced.
So, to allow photosynthesis to happen (which is essential for the plant to make respiratory substrate for its cells), the stomata have to be open, allowing CO2 into and O2 out of the leaf.
Because of this, evaporation of water from the spongy mesophyll cells, into the air spaces, and the loss of water vapour through stomata into the atmosphere is inevitable.
This (transpiration) maintains a constant stream of water through the plant, ensuring photosynthesising cells are supplied with water, and all cells have a high water potential outside them, maintaining their turgidity and therefore support for the plant
Only when light intensity is very low (eg at night), or the plant is under ‘water stress’ will the stomata close.

Answer 78

A

For photosynthesis but they don’t need much for this compared to…
- To ensure a constant stream of water through the plant, ensuring all cells have a high water potential outside them, maintaining their turgidity and therefore supporting the plant.

Answer 79

A

If a plant runs out of water, then this stream stops and cells lose their turgidity. The whole plant wilts. Leaves lose their orientation to light so photosynthesis become less efficient. Eventually the plant will die.
If the plant is watered, cells can recover their turgidity quite quickly.

Answer 80

A

A key point is that a plant must control the entry of ions into its xylem - eg NO3-, PO43-, K+
Too few ions, and the plant will not be able to synthesise molecules like proteins and nucleic acids, and too many may be toxic, interfering with metabolic reactions in ce

Answer 81

A

The only way a plant can control ion entry is when ions cross a membrane. This means ions can be prevented from getting into cells by closing channel or carrier proteins, or actively transported into cells through carrier proteins.

Answer 82

A

There is a Ψ gradient from the water in the soil, into root hair cells, through the cells of the root, to the xylem vessels at the centre of the root.
So, water moves down this Ψ gradient from the soil, into the xylem.

Answer 83

A

The symplast route

- The apoplast route

Answer 84

A

water and ions crossing the membrane of a root hair cell (therefore controlling ion entry), moving though the cytoplasm of cells and the plasmodesmata between cells, all the way to the xylem vessels.

Answer 85

A

The apoplast route involves the water and ions moving between cells, through the cell walls between the cells and not crossing a membrane.
This means ion entry cannot be controlled.
This continues until the endodermis cells, which have a strip of a waxy material called suberin in their cell walls - the Casparian strip.
This forces the water and ions across the membrane of the endodermis cells, into the symplast route - therefore controlling ion entry.

Answer 86

A

The Casparian strip ‘forces’ water and ions across a membrane, from apoplast into the symplast route.

Answer 87

A

water and ions move through the cell walls without entering cells and crossing a membrane

Answer 88

A

water and ions cross a membrane, enter the cytoplasm of cells and move from cell to cell through plasmodesmata

Answer 89

A

an active process ‘pushing’ water and ions from the roots of a plant, upwards.

Answer 90

A

= If a plant’s stem is cut just above the ground, water will ooze out of the cut surface, forced up from the roots.
- Some plants show guttation, where pressure from the roots forces water through xylem vessels, up the stem and out of openings at the tip of leaves

Answer 91

A

Cells in the endodermis actively transport ions from their cytoplasm into the xylem vessel
this lowers the water potential in the xylem and steepens the water potential gradient between endodermis cells and xylem vessels
this means more water moves by osmosis from endodermis cells into xylem vessels, increasing the pressure in xylem vessels in the roots
which results in root pressure

Answer 92

A

the movement of water into and up the xylem vessels

Answer 93

A

they are adapted to survive in salty environments where the soil water surrounding their roots has a lower water potential than the cytoplasm of their root hair cells.

Answer 94

A

Water now moves from the roots, up the stem, into the leaves, and evaporates from the leaves through stomata, into the atmosphere. This process is transpiration

Answer 95

A

root pressure, transpiration, cohesion-tension

Answer 96

A

Water is ‘pushed’ up plants from the roots, as you have recently learned. This is actually pretty insignificant - the other 2 factors are much more imp

Answer 97

A

In the leaves, water moves down a water potential gradient from xylem into spongy mesophyll cells.
Water evaporates from the cell walls at the surface of these cells into the air spaces.
Energy for this is provided by heat energy from the sun, and the environment.
Water vapour molecules diffuse out of the leaf via stomata, into the atmosphere.
This is transpiration, and provides a ‘pull’ for water from the top of a plant - water that is lost from here needs to be replaced by water below, in the xylem vessels.
This causes a continuous stream of water through the plant - the transpiration stream.

Answer 98

A

Water molecules H bond with each other - they show cohesion.
Water molecules ‘stick’ to the inside of xylem vessels - this is adhesion.
Because water is being pulled from the top of the plant, this means the columns of water in the xylem vessels are stretched a bit - they are in tension.
These ideas are summarised as the cohesion-tension model.

Answer 99

A

As xylem vessels have such a small diameter (~50μm), adhesion and cohesion are very significant at this small scale, causing capillary action. This helps to ensure water moves up the vessels.

Answer 100

A

Water is pulled from the top of a plant by transpiration - the evaporation of water from the leaves
columns of water in the xylem vessels maintain a constant transpiration stream, because water has the properties of cohesion and adhesion
water is pushed from the roots of the plant by the active process of root pressure.

Answer 101

A

rate of transpiration

Answer 102

A

Temperature
Humidity
Wind speed
Light intensity

Answer 103

A

Higher temp = 🡩 kinetic energy of water molecules in liquid water on surface of spongy mesophyll cells.
This 🡩 rate of evaporation, adding water molecules to the air spaces inside the leaf.
Water potential in air spaces of leaf 🡩.
Ψ gradient between air spaces and atmosphere gets steeper, 🡩 rate of water loss from leaf.`

Answer 104

A

🡩 humidity adds water molecules to atmosphere outside leaf.
This 🡩 Ψ outside leaf.
Ψ gradient between air spaces and atmosphere gets less steep, 🡫 rate of water loss from leaf.

Answer 105

A

🡩 wind speed removes water molecules from atmosphere outside leaf.
This 🡫 Ψ outside leaf.
Ψ gradient between air spaces and atmosphere gets steeper, 🡩 rate of water loss from leaf.

Answer 106

A

Does not affect the rate of transpiration directly.

- At low light intensities, stomata close, preventing water loss from the leaf, slowing the rate of transpiration.

Answer 107

A

potometer

Answer 108

A

a cut shoot is placed in the potometer and, as water evaporates from the leaves, it is replaced by water from the potometer.
The rate of this movement of water can be measured as the water moves in the capillary tube.
Different conditions can be set up to investigate the effect of different factors: a fan, a hairdryer, a plastic bag, etc…

Answer 109

A

Precautions need to be taken to ensure the apparatus is completely air and watertight - if a tiny bubble gets into a xylem vessel, the vessel will become blocked, slowing transpiration.

Answer 110

A

Another key point is that the plant cells are alive, so are producing water from respiration. Leaf cells are also photosynthesising, so are using water for this process. This means that the water movement in the capillary tube is only an estimation of the water being lost through transpiration.

Answer 111

A

Data from a potometer is usually expressed as ‘volume of water lost per unit time per unit of leaf area’ for example:

mm3 min-1 cm-2

Answer 112

A

used to be living, now dead
walls made of cellulose + lignin
end walls disappear - continuous tube
sideways movement of water and ions through pits

Answer 113

A

allows movement of H2O from soil to leaves by mass flow
flow of materials is roots➡ shoots + leaves
parenchyma cells store food + contain tannin deposits - protects plant tissue from attacks from herbivores

Answer 114

A

transport the assimilates of photosynthesis

- translocation

Answer 115

A

‘life support system’ for STEs

- very active

Answer 116

A

‘packing cells’

Answer 117

A

strong, lignified cells

Answer 118

A

root: xylem is +/ x shaped
stem: eggs around outside
leaf: near palisade mesophyll

Answer 119

A

ions cross membranes of root hair cells for entry

Answer 120

A

Water evaporates from the leaves.
Replaced by water from the apparatus.
Air / water meniscus moves along the capillary tube.
Movement measured and timed.
Different conditions can be set up with eg a fan, humidifier / plastic bag, light, radiant heater.`

Answer 121

A

Potometer measures the water being taken up by the shoot.
Not all this water is lost from the leaves / transpired.
Some of this water is used for photosynthesis.
Also, some water produced by respiring cells.

Answer 122

A

Allow the apparatus to settle by leaving for at least 5 minutes.
Take measurements of distance and time from the capillary tube. Make sure replicate readings are taken.
Measure SA of leaves and convert data to mm3 min-1 cm-2 to enable comparison of data between groups.
Investigate 1 factor as the IV at a time, and make sure other factors are controlled.
Ideally, set up a control potometer, identical in every way apart from no leafy shoot.

Answer 123

A

Set the device up underwater to ensure there are no air bubbles in the tubing.
Ensure an airtight seal between the shoot and the rubber by using vaseline.
Cut the shoot underwater to eliminate air bubbles from the xylem vessels at the bottom of the shoot.
Cut the shoot at an angle so any bubbles don’t enter the xylem vessels.
Ensure the leaves are dry so as not to block stomata.

Answer 124

A

thick, waxy cuticle
stomata in pits or deep grooves, and reduced numbers of stomata
leaves reduced to spines
hairs
curled leaves
swollen, succulent stems
leaf loss
other adaptations: root, avoiding…

Answer 125

A

in most plants, up to 10% of the water loss by transpiration is thru the cuticle
helps min H2O loss
common in evergreen plants

Answer 126

A

by ⬇ leaf area, H2O loss can be greatly ⬇
the leaves of conifers are greatly reduced to thin needles. These narrow leaves, which r almost circular in cross section have greatly reduced SA:V, min. H2O loss in trans

Answer 127

A

create a microclimate of still, humid air, reducing the water vapour potential gradient and ⬇ loss of H2O by trans from the surface of the leaf
some plants e..g marram grass even have micro hairs in the sunken stomata pits

Answer 128

A

greatly ⬇ H2O loss by Trans, espec in combination w other adaptations
confines all of the stomata within a microenvir, of still humid air to ⬇ diffuciom of H2O vapour from the stomata e.g. marram grass

Answer 129

A

store water in specialised parenchyma tissue in their stems & roots
often have a swollen/ fleshy appearance hence name
H2O stored when it’s in plentiful supply 7 used in times of drought
e.g. aloe Vera

Answer 130

A

some plants prevent water loss thru their leaves by simply losing their leaves when water is not available,.
e.g. palo verde

Answer 131

A

root adaptations - long tap roots, widespread shallow toots w a large SA
avoiding the prblms - plants may lose leaves & become dormant, die, leaving seeds behind to germinate & grow rapidly when rain falls again, others survive as storage organs
a few plants can withstand complete dehydration and recover ➡ linked to disaccharide thehalose.

Answer 132

A

many xerophytes have their stomata located in puits, which ⬇ air movement, producing a micro climate of still, humid air that ⬇ the water vapour potential gradient so ⬇ Trans, e.g. in Marram Grass
⬇ no. of stomata which reduce their water loss by transpiration but also reduce their gas exchange capabilities.

Answer 133

A

Lignin can be laid down in the walls of the xylem vessels in several different ways. It can form rings, spirals or relatively solid tubes with lots of small unlignified areas called bordered pits. This is where water leaves the xylem and moves into other cells of the plant.

Answer 134

A

Like xylem, the phloem sieve tubes are made up of many cells joined end to end to form a long, hollow structure. Unlike xylem tissue, the phloem tubes are not lignified. In the areas between the cells, the walls become perforated to form sieve plates, which look like sieves and let the phloem contents flow through. As the large pores appear in these cell walls, the tonoplast (vacuole membrane), the nucleus and some of the other organelles break down. The phloem becomes a tube filled with phloem s^> and the mature phloem cells have no nucleus.

Answer 135

A

microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells

Answer 136

A

Phloem tissue also contains supporting tissues including fibres and sclcreids, cells with extremely thick cell walls.

Answer 137

A

This is the movement of water through the apoplast - the cell walls and the intercellular spaces.
Water fills the spaces between the loose, open network of fibres in the cellulose cell wall.
As water molecules move into the xylem, more water molecules are pulled through the apoplast behind them due to the cohesive forces between the water molecules.
The pull from water moving into the xylem and up the plant along with the cohesive forces between the water molecules creates a tension that means there is a continuous flow of water through the open structure of the cellulose wall, which offers little or no resistance.

Answer 138

A

At CS, water in the apoplast pathway can go no further and it is forced into the cytoplasm of the cell, joining the water in the symplast pathway. This diversion to the cytoplasm is significant as to get to get there, water must pass through the selectively permeable cell surface membranes, this excludes any potentially-toxic solutes in the soil water from reaching living tissues, as the membranes would have no carrier proteins to admit them. Once forced into the cytoplasm the water joins the symplast pathway.

Answer 139

A

• Some poisons, such as cyanide, affect the mitochondria and prevent the production of ATP. If cyanide is applied to root cells so there is no energy supply, the root pressure disappears.
• Root pressure increases with a rise in temperature and falls with a fall in temperature, suggesting chemical reactions are involved.
• If levels of oxygen or respiratory substrates fall, root pressure falls.
• Xylem sap may exude from the cut end of stems at certain times.
In the natural world, xylem sap is forced out of special pores at the ends of leaves in some conditions - for example overnight, when transpiration is low. This is known as guttation.

Answer 140

A

Water molecules evaporate from the surface of mesophyll cells into the air spaces in the leaf and move out of the stomata into the surrounding air by diffusion down a concentration gradient.
The loss of water by evaporation from a mesophyll cell lowers the water potential of the cell, so water moves into the cell from an adjacent cell by osmosis, along both apoplast and symplast pathways.

Answer 141

A

Water molecules form hydrogen bonds with the carbohydrates in the walls of the narrow xylem vessels.

Answer 142

A

Water is drawn up the xylem in a continuous stream to replace the water lost by evaporation.

Answer 143

A

Changes in the diameter of trees.
When a xylem vessel is broken - for example when you cut flower stems to put them in water - in most circumstances air is drawn in to the xylem rather than water leaking out.
If a xylem vessel is broken and air is pulled in as described in the previous bullet, the plant can no longer move water up the stem as the continuous stream of water molecules held together by cohesive forces has been broken.

Answer 144

A

When transpiration is at its height during the day, the tension in the xylem vessels is at its highest too. As a result the tree shrinks in diameter. At night, when transpiration is at its lowest, the tension in the xylem vessels is at its lowest and the diameter of the tree increases. This can he tested by measuring the circumference of a suitably sized tree at different times of the day.

Answer 145

A

because of the practical difficulties with condensing and collecting all of the water that evaporates from the surfaces of the leaves and stems of a plant without also collecting water that evaporates from the soil surface. It is also very difficult to separate water vapour from transpiration and water vapour produced as a waste product of respiration

Answer 146

A

act on the opening/closing of the stomata, the rate of evaporation from the surfaces of the leaf cells or the diffusion gradient between the air spaces in the leaves and the air surrounding the leaf

Answer 147

A

— An increase in temperature increases the kinetic energy of the water molecules and therefore increases the rate of evaporation from the spongy mesophyll cells into the air snares of the leaf
—An increase in temperature increases the concentration of water vapour that the external air can hold before it becomes saturated (so decreases its relative humidity and its water potential).

Answer 148

A

very thin/ no waxy cuticle
many always open stomata on upper leaf surface
reduced structural tissue
wide flat leaves
small roots
large SA of stems and roots underwater
air sacs
aerenchyma

Answer 149

A

very thin/ no waxy cuticle
many always open stomata on upper leaf surface
reduced structural tissue
wide flat leaves
small roots
large SA of stems and roots underwater
air sacs
aerenchyma

Answer 150

A

hydrophytes do not need to conserve water as there is always plenty available so water loss by Trans is not an issue.

Answer 151

A

⬆ no. of stomate ⬆ gas exchange

- no risk of loss of turgor, so stomata usually open for gas exchange & the guard cells are inactive

Answer 152

A

the H2O supports the leaves and flowers so there is no need for strong supportive structures.

Answer 153

A

some hydrophytes, inclu. water lilies have leaves that spread cross the surface of the water to capture as much light as possible

Answer 154

A

water can diffuse directly into stem and leaf tissue so there is less need for uptake by roots

Answer 155

A

this max. the area for photosynthesises and for O2 to diffuse into submerged plants.

Answer 156

A

enable the leaves and/or flowers to float to teh surface of the water

Answer 157

A

specialised parenchyma tissue forms in the leaves, stems, roots of hydrophytes.
has many large air spaces, seemed to be formed by apoptosis in normal parenchyma
functions: making the leaves and stem more buoyant & forming a low resistance internal pathway for the movement of substances such as O2 to tissues below the H20 ➡ helps plant cope w anoxic conditions in the mud by transporting O2 to the tissues

Answer 158

A

plant tissue found in the stems and roots of some hydrophytes, which allows oxygen to get down into the roots, which could be in poorly oxygenated water or waterlogged soil.

Answer 159

A

Translocation is the transport of the assimilates of photosynthesis (particularly the sugar sucrose) form source cells to sink cells.

Answer 160

A

Source cells are where sugars are produced.

Sink cells are where sugars are used.

Answer 161

A

aphid can be used to take a sample of phloem sap.
Aphids naturally use their mouthparts (stylets) to penetrate phloem STEs and feed on the sugars.
If the aphid is removed, leaving the stylet, the phloem sap can be collected from the stylet and analysed.

Answer 162

A

During the day - source, because leaf cells photosynthesise, making sugars - at a faster rate than they respire, which uses sugars.
At night - sink, because at night cells don’t photosynthesise, but they still respire, which uses sugars.

Answer 163

A

Sink. No photosynthesis, but always respiration, using sugars.

Answer 164

A

Flowers don’t photosynthesise, but their cells respire, so sink. Also some flowers produce nectar to attract insects, which is formed from phloem sap, so definitely sink.

Answer 165

A

In the spring / summer - sink. Because sugars are being converted to starch for storage in the tubers.
In early spring, starch is converted back to sugars which are used to synthesise molecules to produce a new plant, so source.

Answer 166

A

Source cells produce sucrose molecules from photosynthesis, or from the breakdown of storage molecules like starch.
Sucrose is actively loaded into companion cells by cotransport with H+ ions.
Sucrose diffuses from companion cells into phloem STEs through plasmodesmata.
4 . The high concentration of sucrose lowers the water potential in the STEs, and water moves by osmosis from the xylem into the STEs. This raises the hydrostatic pressure in the STEs close to the source cells.
5 .Sucrose is used by sink cells, either as a respiratory substrate, or to synthesise storage molecules like starch, or both.
Sucrose passively unloads from companion cells by diffusing out, into sink cells which are using the sucrose.
Sucrose diffuses down a concentration gradient from STEs into companion cells near to the sink cells.
The lowering of sucrose concentration raises the water potential in the STEs, and water moves by osmosis from STEs into the xylem. This lowers the hydrostatic pressure in the STEs close to the sink cells.
Phloem sap moves by mass flow from high to low hydrostatic pressure from source to sink cells in the phloem STEs.
Water and dissolved ions also move by mass flow down the hydrostatic gradient in the xylem vessels. This can contribute to the transpiration stream.

Answer 167

A

• green leaves and green stems
• storage organs such as tubers and tap roots that are unloading their stores at the beginning of a growth period
• food stores in seeds when they germinate.
Some of these need to transport resources downwards, and some need to move materials up the plant.

Answer 168

A

roots that are growing and/or actively absorbing mineral ions
meristems that are actively dividing
any parts of the plant that are laying down food stores, such as developing seeds, fruits or storage organs.

Answer 169

A

Water-logging is a major problem for all hydrophytes. The air spaces of the plant need to be lull of air. not water, for the plant to survive.

Answer 170

A

• green leaves and green stems
• storage organs such as tubers and tap roots that are unloading their stores at the beginning of a growth period
• food stores in seeds when they germinate.
Some of these need to transport resources downwards, and some need to move materials up the plant.

Answer 171

A

roots that are growing and/or actively absorbing mineral ions
meristems that are actively dividing
any parts of the plant that are laying down food stores, such as developing seeds, fruits or storage organs.

Answer 172

A

there is a pressure pushing water upwards up xylem vessels from the roots
caused by active transport of ions from endodermis cells into xylem vessels
water movies down water potential gradient into xylem vessels and thfr ‘pushes’ up the plant

Answer 173

A

flowering plants which are naturally found in saline habitats, such as coastal swamps, sand dunes, inland sand flats…. They have evolved a no. of strategies to survive and reproduce under highly saline conditions where most plants cannot.

Answer 174

A

salt tolerance - ‘salt accumulators’ which involves
accumulating salt in plants cells (⬆ conc, thfr WP⬇) & salt avoidance
‘salt excludes’ which involves adaptations to min the concs of salts in the cells or adaptations to bar salts from entering through plant roots

Answer 175

A

+ adaptations of companion cells seen thru advances in microscopes
+ if Mitochondria in companion cells poisoned, translocation stops
+ flow of sugars is faster than would be from diffusion alone, suggesting active
+ Aphid studies - + pressure in Phloem, conc of sucrose is higher near source than sink
+ sucrose moves at same rate regardless of conc at sink

Answer 176

A

not all solutes move at same rate

- sieve plates role?

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Chapter 9 - Transport in plants Flashcards

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