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Alevel Biology > 3.3 > Flashcards

3.3 Flashcards

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1
Q

Dicotyledonous plants

A

Plants with two seeds and a branching pattern of veins in the leaf

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2
Q

Meristem

A

A layer of diving cells

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3
Q

Phloem

A

Transports dissolved assimilates

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4
Q

Vascular tissue

A

Consist of cells specialised for transporting fluids by mass flow

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5
Q

Xylem

A

Transports water and minerals

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6
Q

Companion cell

A

Cells that help to load sucrose into sieve tubes

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7
Q

Sieve tube elements

A

Makes up the tubes in phloem tissue that carry sap up and down plant, sieve tubes separated by sieve plates

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8
Q

Xylem vessels

A

Tubes which can carry water up the plant

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9
Q

Plasmodesmata

A

Gaps in cell wall containing cytoplasm that connects two cells

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10
Q

Potometer

A

A device that can measure rate of water uptake as a leaf stem transpires

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11
Q

Transpiration

A

Loss of water vapour from aerial parts of a plant, mostly through stomata in the leaves

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12
Q

Adhesion

A

Attraction between water molecules and walls of xylem vessel

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13
Q

Cohesion

A

Attraction between water molecules caused by hydrogen bonds

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14
Q

Why do plants need a transport system

A

All living things need to take substances and return waste to their environment

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15
Q

Why do larger plants need specialised exchange surfaces and transport systems

A

Have a smaller SA:V ratio

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16
Q

What does every cell of a multicellular plant need

A

Regular supply of oxygen, water, nutrients and minerals

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17
Q

Why is plants oxygen demand low

A

Plants aren’t very active and their respiration rate is low

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18
Q

How can plants need for oxygen be met

A

By diffusion

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19
Q

Is plants need for water and sugars high or low

A

High

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20
Q

What can plants absorb from their roots and what can’t they

A

Can absorb water and minerals but can’t absorb sugars from the soil

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21
Q

What function can leaves perform

A

Can perform gaseous exchange and manufacture sugars by photosynthesis

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22
Q

What function can leaves not perform

A

Can’t absorb water from the air

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23
Q

What do plants needs a transport system to move and from where to where

A

Water and minerals form roots to leaves, and sugars from leaves to rest of the plant

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24
Q

What do transport systems in plants consist of

A

Specialised vascular tissues

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25
Q

What does they xylem transport and in what direction

A

Water and soluble mineral ions travel up the plant

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26
Q

What travels in the phloem vessel and what direction

A

Assimilates such as sugars and they can travel up or down the plant

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27
Q

How is plants specialised transport system different to humans

A

There is no pump(heart) and respiratory gases aren’t carried by these tissues

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28
Q

What are dicotyledonous plants

A

Plants with 2seed leaves, and a characteristic distribution of vascular tissue

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29
Q

How is vascular tissue distributed in dicotyledons

A

Throughout the plant

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30
Q

Where are phloem and xylem found in dicotyledons

A

Found together in vascular bundles, bundles also contain other tissue types

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31
Q

What tissues are in a dicotyledons vascular bundle

A

Xylem, phloem, …

collenchyma, sclerenchyma)

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32
Q

What is collenchyma and sclerenchyma role in vascular bundle

A

Gives bundle strength and helps support the plant

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33
Q

what is structure of vascular bundle in dicotyledons roots

A

At the centre of a young root, central core is xylem (often in X shape)

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34
Q

What does xylems X shape provide root with

A

Strength to withstand pulling forces to which roots are exposed

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35
Q

What is around the vascular bundle

A

A special sheath of cells called endodermis

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36
Q

What role does the endodermis of a dicotyledon root

A

Key role of getting water into xylem

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37
Q

What is just on the inside of endodermis

A

A layer of meristem cells (unspecialised cells) called pericycles

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38
Q

What is in each section of a X shape xylem

A

Phloem

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39
Q

What is another name for the whole vascular bundle

A

Root stele

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40
Q

What is the layer outside of the endodermis called in roots

A

Cortex

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41
Q

What is the outside layer of the plant root called

A

Epidermis

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42
Q

In dicotyledons stem where is the vascular bundle found

A

Near the outer edge of the stem

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43
Q

What is the difference between woody plants and non woody plants vascular bundles in the stem

A

In non-woody plants they are separate and clear and in woody plants they are less clear

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44
Q

What do vascular bundles look like in woody plants stem

A

They are separate in young stems but become continuous rings in older stems, meaning there is a complete ring of vascular tissue just under the bark a tree

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45
Q

What does the arrangement of dicotyledons vascular bundles in stem mean

A

Arrangement provides strength and flexibility to withstand bending forces which stems and branches are exposed to

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46
Q

Where is the xylem, and phloem found in vascular bundle of stem

A

Xylem found towards the inside and phloem towards the outside

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47
Q

What is in between the xylem and phloem in a stem vascular bundle

A

A layer of cambium

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48
Q

What is cambium

A

A layer of meristem cells that divide to produce new phloem and xylem

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49
Q

What is the area in the middle of the stem and all the vascular bundles called

A

The pith

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50
Q

What is found on the outside of the phloem near the epidermis of a stem

A

Sclerenchyma

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51
Q

Where is collenchyma located in a stem of a dicotyledons

A

In a ring round the outside of all the vascular bundles to provide strength

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52
Q

Where do vascular bundles form in a leaf

A

In the midrib and leaves veins

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53
Q

What type of veins does a dicotyledon have

A

A branched network of veins that get smaller as they spread away from the midrib

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54
Q

Where are the xylem and phloem vascular bundle located in leaves

A

The xylem is on top of the phloem, closer to the upper epidermis of the leaf and phloem is closer to the lower epidermis

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55
Q

What does dissection of a plant to examine its distribution of vascular tissue need

A

Staining

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56
Q

What plant is usually used the examine the distribution of vascular tissue

A

Celery stick

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57
Q

How would you carry out an experiment to look at vascular bundles in a celery

A

Cut a thin section and view it at low power, allow the leafy stem to take up water by transpiration, the stem can then be cut longitudinally or transversely and examined with a microscope

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58
Q

What is xylem

A

A tissue used to transport water and mineral ions from the roots to the leaves and other parts of the plant

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59
Q

What does xylem tissue consist of

A

Vessels to carry water and dissolved mineral ions, fibres to help support the plant, living parenchyma cells which act as packing tissue to separate and support the vessel

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60
Q

What happens as the xylem vessel develops

A

Lignin impregnates walls of cells, making them waterproof

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61
Q

What happens once lignin impregnates xylem

A

It is waterproof which kills it and so the end walls and contents of the cells decay, leaving a long column of dead cells with no contents- creating the xylem vessel

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62
Q

What is lignin role in the xylem

A

Strengthens the vessel walls and prevents them from collapsing which keeps vessel open even when water is in low supply

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63
Q

What does lignin thickening form

A

Patterns in the cell wall (may be spiral, annular(rings) or reticulate (network of broken rings) which prevents vessel from being too rigid and allows stem/branches some flexibility

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64
Q

What happens in some places where lignification isn’t complete

A

Leaves gaps in the cell wall, these gaps form boarded pits

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65
Q

What is the name of the process of lignin thickening

A

Lignification

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66
Q

What are bonded pits

A

Pits in 2 adjacent vessels which are aligned to allow water to leave the xylem and pass into living parts of the plant

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67
Q

How can xylem vessels carry water and mineral ions from the roots to the top of the plant

A

They are made from dead cells aligned end to end to form a continuous column, tubes are narrow so water column doesn’t break easily and capillary action can be effective, bordered pits in lignification walls allow water to move sideways from one vessel to another, lignin deposited in walls in spiral, annular or reticulate patterns allow xylem to stretch as plant grows enabling stem/branches to bend

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68
Q

Why is flow of water in xylem not impeded

A

As there are no cross walls, there are no cell contents (nucleus or cytoplasm), lignin thickening prevents walls from collapsing

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69
Q

What is there in xylem lumen

A

Nothing expect water and minerals

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70
Q

Where is parenchyma located around the xylem

A

On the outside in bundles

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71
Q

What is phloem

A

A tissue used to transport assimilates(sucrose and amino acids) around plant

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72
Q

What is sucrose dissolved in to form what in plants

A

Dissolved in water to form sap

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73
Q

What does phloem tissue consist of

A

Sieve-tubes made up of sieve tube elements and companion cells

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74
Q

How do sieve tube elements form sieve tubes

A

Elongated sieve tube elements are lined up end to end to form sieve tubes

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75
Q

What do sieve tube elements contain and what don’t they

A

Contain no nucleus and very little cytoplasm, leaving space for mass flow and sap to occur

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76
Q

What are at the end of each sieve tube element

A

Perforated cross-walls called sieve plates

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77
Q

What do perforations on sieve plates allow

A

Movement of sap from one element to the next

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78
Q

What are sieve tubes walls like

A

Very thin and when seen in transverse sections they are usually 5-6 sections

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79
Q

What are the small cells found between sieve tubes

A

Companion cells

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80
Q

What is components of companion cells

A

Each have a large nucleus and dense cytoplasm, they have numerous mitochondria to produce ATP needed for active processes

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81
Q

What is companion cells function

A

Carry out metabolic processes needed to load assimilates actively into sieve tube

82
Q

Are cellulose cell walls fully permeable to water

A

Yes

83
Q

How to water molecules move between cellulose cell wall and gaps in between cells

A

Can move freely

84
Q

How can water also pass into the cytoplasm or even vacuole

A

It can pass across the cell wall and through partially permeable plasma membrane into cells cytoplasm/vacuole

85
Q

How are many plants cells joined

A

Cytoplasmic bridges

86
Q

What are cytoplasmic bridges

A

Cell junctions at which cytoplasm of one cell is connected to another through a gap in their cell walls

87
Q

What are gaps in the cell wall connecting plant cells together called

A

Plasmodesmata

88
Q

What are the three pathways for water molecules to travel cell to cell

A

Apoplast pathway, symplast pathway, vacuolar pathway

89
Q

What is the apoplast pathway

A

Water passes through spaces in cell walls and between cells in intercellular space, doesn’t pass through any plasma membrane, water can move by mass flow instead of osmosis, dissolved mineral ions and salts can be carried with the water

90
Q

What is the symplast pathway

A

Water enters cell cytoplasm through plasma membrane, it can then pass through plasmodesmata from one cell to the next

91
Q

What is the vacuolar pathway

A

Similar to symplast pathway but water isn’t confined to the cytoplasm of cells, it can enter and pass through the vacuole too

92
Q

What is water potential

A

Is a measure of the tendency of water molecules to move from one place to another

93
Q

What way does water always move on a gradient

A

From a region of higher water potential to a region of lower water potential

94
Q

What is the water potential of pure water

A

0kPa

95
Q

What reduces the water potential in plants and how

A

Cells cytoplasm has mineral ions and sugars which reduce water potential as fewer free water molecules are available than in pure water

96
Q

In plants what is always the value of water potential

A

Below 0 (negative)

97
Q

What happens when a plant cell is placed in pure water and why

A

It will take up water molecules by osmosis as water potential in cell is lower blood than water potential of pure water, water molecules will move down a water-potential gradient into the cell

98
Q

When a plant cell is placed in a solution with higher water potential will it fill to its burst

A

No as cells have strong cellulose cell wall, when cells are full of water they become turgid

99
Q

What is it called when a turgid water in plant cell exerts pressure on cell wall

A

Pressure potential

100
Q

What happens as pressure potential builds up

A

It reduces the influx of water

101
Q

What happens when plant cell is placed in a salt solution with very low water potential

A

It will loose water by osmosis as water potential in the cell is higher than that of the salt solution, so water moves down the concentration gradient out of the cell

102
Q

What happens as water leaves a plant cell

A

Cytoplasm and vacuole shrink and eventually cytoplasm no longer pushes against cell wall and cell is no longer turgid

103
Q

What happens when water continuously leaves a plant cell

A

The plasma membrane will loose contact with the cell wall, this is known as plasmolysis and the tissue is now flaccid

104
Q

What happens when plant cells touch each other

A

Water molecules can pass cell to cell, water molecules will move from the less negative water potential to the more negative one, known as osmosis

105
Q

What is transpiration

A

Loss of water vapour from the upper parts of a plant, mostly leaves

106
Q

Where does some water evaporate from on a plant and how is it prevented

A

Some evaporates through upper leaves surfaces but loss is limited by waxy cuticle

107
Q

Where is most water lost by on plants

A

Through the stomata which open to allow gaseous exchange from photosynthesis

108
Q

Why is most water vapour lost during the day

A

As photosynthesis occur only when there is sufficient sunlight (in the day)

109
Q

What is a typical pathway taken by water leaving the leaf (osmosis)

A

Water enters xylem and moves by osmosis into cells of spongy mesophyll, it may also pass along cell walls via apoplast pathway

110
Q

What is a typical pathway taken by water leaving the leaf (evaporates)

A

Water evaporates from cell walls of spongy mesophyll

111
Q

What is a typical pathway taken by water leaving the leaf (diffusion)

A

Water vapour moves by diffusion out of the leaf through open stomata which relies on a difference in the concentration of water vapour molecules in the leave compared to outside the leaf

112
Q

What is the difference in concentration of water vapour in to leaf to outside known as

A

Water vapour potential gradient, there must be a less negative water vapour potential inside the leaf than outside

113
Q

Is transpiration good or bad

A

Transpiration may be inevitable consequence of gaseous exchange but also essential for plant survival

114
Q

What happens as water vapour lost from leaf

A

It must be replaced from below, plant draws up water from roots to stem as a transpiration stream

115
Q

What does the movement of water from roots to leaves provide

A

Transports useful mineral ions up the plant, maintains cell turgidity, supplies water for growth, cell elongation and photosynthesis, supplies water that, as it evaporates, can keep the plant cool on a hot day

116
Q

How does light intensity effect water loss of a plant

A

When it’s light, stomata open to allow gaseous exchange for photosynthesis, so higher light intensity increases transpiration rate

117
Q

How does temperature effect transpiration rate

A

Higher temp will increase rate of transpiration in 3ways, increase rate of evaporation for cells surfaces so water potential in leaf rises, increases rate of diffusion through stomata as water molecules have more kinetic energy and decreases relative water vapour potential in air, allowing a more rapid diffusion of molecules out of the leaf

118
Q

How does relative humidity effect transpiration rate

A

Higher the relative humidity in the air the lower the rate of water loss we there will be a smaller water vapour potential gradient between the air spaces in the leaf and the air outside

119
Q

How does air movement (wind) effect transpiration rate

A

Air moving outside of the leaf will carry away water vapour that has just diffuser which maintains a high water vapour potential gradient

120
Q

How does water availability effect transpiration rate

A

Is there is little water in the soil, then the plant can’t replace lost water, if the water in the soil is insufficient, then stomata close and leaf wilts

121
Q

What is a potometer

A

Device to measure rate of transpiration, but looking at how much water a plant uptakes in a certain time at certain conditions

122
Q

What is the transpiration stream

A

Movement of water from the soil through the plant to air surrounding the leaves

123
Q

What is the main driving force of transpiration stream

A

The water potential gradient between the soil and the air in leaf air spaces

124
Q

What does the outermost layer of a root (epidermis) have

A

Root hair cells

125
Q

What are root hair cells

A

Cells with long extensions that increases the SA of the root, these cells absorb mineral ions and water from soil

126
Q

What happens once root hair cells absorb water and mineral ions from the soil

A

Water then moves across the root cortex down water-potential gradient into epidermis of the vascular bundle

127
Q

After water and minerals been absorbed by root hair cell it may also take the apoplast pathway as far as the endodermis but can’t go further. Why?

A

As apoplast pathway is blocked by casparian strip so it must enter symplast pathway

128
Q

What happens after mineral ions pass casparian strip via symplast pathway

A

They actively transport into the medulla making the water potential lower so water follows by osmosis

129
Q

Are mineral ions actively or passively taken up by roots

A

Actively

130
Q

How does water move across roots cortex

A

By osmosis

131
Q

What is the role of the endodermis

A

The movement of water across the root is driven by an active process that occurs at the endodermis

132
Q

What is the endodermis

A

The layer of cells surrounding medulla and xylem such as starch sheath as it contains starch granules which is a sign energy is being used

133
Q

What is casparian strip

A

Blocks the apoplast pathway between cortex of roots and the medulla which ensures water and dissolved mineral ions(esp nitrates) have to pass into cell cytoplasm via cell membrane

134
Q

What does the roots plasma membranes contain and what does this mean

A

Transporter proteins which actively pump mineral ions from cytoplasm of cortex cells into the medulla and xylem which makes water potential of medulla and xylem more negative, so water moves from cortex cells into medulla and xylem by osmosis

135
Q

What happens once water has entered the medulla

A

It can’t pass back into cortex as apoplast pathway of endodermal cells is blocked by casparian strip

136
Q

How does water move through the xylem

A

By mass flow- a flow of water and mineral ions in the same direction

137
Q

What are the 3 processes to help water move up the stem

A

Root pressure, transpiration pull and capillary action

138
Q

What is root pressure

A

Action of the endodermis moving minerals into medulla and xylem by active transport draws water into medulla by osmosis, pressure in root medulla then builds up forcing water into xylem, root pressure can push water a few meter up the steam but not to the top of a tall tree

139
Q

What is transpiration pull

A

Loss of water by evaporation from leaves must be replaced by water coming up from xylem, water molecules are attracted to each other by forces of cohesion, these cohesive forces are strong enough to hold water molecules together in a long chain/column

140
Q

What happens as molecules are lost at the top of the column of a xylem due to transpiration pull

A

The whole column is pulled up as one chain and the pull from above creates tension in the column of water, so the xylem must be strengthened by lignin which prevents vessel collapsing under tension

141
Q

What is another way of calling transpiration pull and why

A

Cohesion tension theory as this mechanism involves cohesion between water molecules and tension in the column of water

142
Q

What does cohesion tension theory rely on and what happens is this isn’t the case

A

Plant maintaining an unbroken column of water all the way up the xylem, if the water column is unbroken in one xylem vessel then water column can still be maintained through other vessels via bordered pits

143
Q

What is capillary action

A

Same forces that hold water molecules together also attract water molecules to sides of the xylem vessel known as adhesion

144
Q

How does adhesion work in capillary action

A

As xylem vessels are narrow these forces of attraction can pull water up the sides of the vessel

145
Q

What happens to pressure when water leaves xylem at the leaves

A

It creates a low hydrostatic pressure so there is tension

146
Q

In what state does most water leave the leaf in

A

Most water that leaves the the leaf exists as vapour through stomata, only a small amount leave through the waxy cuticle

147
Q

Where does water most evaporate the leaves from

A

From cells lining the cavity immediately above the guard cells known as sub-stomatal air space

148
Q

What does water evaporating from sub-stomatal air space cause

A

Lowers the water potential in these guard cells causing water to enter them by osmosis from neighbouring cells, so in turn water drawn from xylem in leaf by osmosis but water may also reach these cells by apoplast pathway from xylem

149
Q

What are terrestrial plants

A

Plants living on land

150
Q

What do most land plants have as their main problem

A

There is often limited access to water

151
Q

How is water lost from a terrestrial plant

A

Lost by transpiration as plants exchange gases with the atmosphere via their stomata

152
Q

What happens to a plant during the day to do with gas exchange

A

Plants take up lots of CO2 for photosynthesis and remove oxygen which is a bi-product of photosynthesis, so the stomata must be open during the day and while the stomata are open there is an easy route for water loss

153
Q

Lost water must be replaced in plants, what must terrestrial plants be adapted to

A

Reducing water loss and replace lost water by

154
Q

How can most terrestrial plants reduce their water loss by structural and behavioural adaptation

A

A waxy cuticle on leaf will reduce water loss due to evaporation through epidermis, stomata often under leaf surface which reduces evaporation from direct heat from sun, most stomata close at night when no light for photosynthesis, deciduous plants lose their leaves in winter when ground may be frozen and less water available and when temp may be too low for photosynthesis

155
Q

How is marram grass specialised

A

Specialises living in sand dunes where conditions are particularly harsh as any water in the sand drains away quickly and sand may be salty and leaves often exposed to very windy conditions

156
Q

What is marram grass

A

A xerophyte

157
Q

What is an xerophyte

A

A plant adapted to living in arid conditions

158
Q

What are marram grasses adaptations so it can survive arid conditions

A

Leaves rolled longitudinally so air trapped inside comes humid which reduces water loss from leaves, they can roll tighter in dryer conditions. has thick waxy cuticle in outer side of rolled leaf to reduce evaporation. Stomata on inter side of rolled leaf (lower epidermis) so they are protected by enclosed air space. stomata are in pits in lower epidermis which is also folded and covered by hairs, this helps reduce air movement, spongy mesophyll is dense with few air spaces so less SA for water to evaporate

159
Q

How are cactus adapted to living in arid conditions

A

They are succulents-store water in their stems which becomes fleshy and swollen. Stem is often ribbed or fluted so it can expand when water is available. Leaves reduced to spines which reduces SA so less water lost by transpiration, stem green for photosynthesis, roots widespread to take advantage of any rainfall

160
Q

What are other adaption of other xerophyte plants

A

Closing stomata when water availability is low to reduce water loss and reduce need to uptake water, some have low water potential in their leaf cells by having high salt concentration in their cells which reduces evaporation of water from cells surfaces as water potential gradient between cell and leaf air spaces is reduced, some have a very long tap root that can reach water deep underground

161
Q

What are hydrophytes

A

Plants what live In water such as water lilies

162
Q

What is hydrophytes problems

A

They have access to water but struggle to get oxygen into their submerged tissues and keeping afloat

163
Q

Why do hydrophytes need to keep afloat

A

They need to keep their leaves in sunlight for photosynthesis

164
Q

What are adaptations of water lilies

A

They have many large air spaces in the leaf which keeps leaves afloat so they are in the air and can absorb sunlight, stomata are on upper epidermis so they are exposed to air to allow gas exchange, leaf stem has many large air spaces, which helps with buoyancy and also allows oxygen to quickly diffuse into the roots for aerobic respiration

165
Q

What happens to transpiration if the surrounding water or air is too humid

A

Water won’t evaporate, so water can’t leave the plant so the transpiration stream stops and plant can’t transport mineral ions to the leaves

166
Q

How do plants deal with the issue of high humidity

A

Many plants have specialised structures at the tip/margins of their leaves called hydathodes which can release water droplets which may then evaporate from leaf surface

167
Q

What is translocation in plants

A

Occurs in the phloem and is the movement of assimilates throughout the plant

168
Q

What are assimilates

A

Substances made by plant using substances absorbed by the environment usually include sugars which are mostly transported as sucrose and amino acids

169
Q

What is a source

A

Part of the plant that loads assimilates into phloem sieve tubes

170
Q

What is a sink

A

A part of the plant that removes assimilates from phloem sieve tube

171
Q

How is sucrose loaded into sieve tube

A

By an active process, involving use of energy from ATP in companion cells

172
Q

What is used to actively transport hydrogen ions out of companion cells

A

Energy

173
Q

Why are hydrogen ions actively transported out of companion cells in translocation

A

It increases their concentration outside the cell and decreases their concentration inside the companion cells so a concentration gradient is created

174
Q

How do hydrogen ions diffuse back into companion cells in translocation

A

Through special cotransporter proteins which allow movement of hydrogen ions into a cell if they are accompanied by a sucrose molecule

175
Q

What is hydrogen ions being allowed into companion cell if they are accompanied by a sucrose called

A

Cotransport or secondary active transport as it results from active transport of hydrogen ions out of cell and moves sucrose against its concentration gradient

176
Q

What happens a sucrose concentration in companion cell increases

A

It can diffuse through plasmodesmata into sieve tube

177
Q

How is sucrose moved along phloem

A

By mass flow

178
Q

What solution is in the phloem

A

Sap- a solution of sucrose, amino acids and other assimilates

179
Q

What direction does sap flow in in the phloem

A

Can be made to flow in either direction depending on where it’s required

180
Q

What is flow in phloem caused by

A

Flow is caused by a difference in hydrostatic pressure between 2 ends of the tube, producing a pressure gradient

181
Q

Why does sap flow from source to sink

A

Water enters tube at the source increasing the pressure and leaves tube at the sink reducing the pressure

182
Q

What happens as sucrose enters sieve tube element at the source

A

It makes the water potential inside sieve tube more negative (lower) which results in water molecules moving into sieve tube element by osmosis from surrounding tissue which increases hydrostatic pressure in the sieve tube at the source

183
Q

What is the source of a plant

A

Any part of the plant that leads sucrose into sieve tube

184
Q

In early spring what are examples of a source in plants

A

Roots-where energy stored as starch is converted to sucrose and moved to other part of the plant in order to enable growth in spring

185
Q

What is an example of a source in late spring, summer and early autumn

A

The leaf-sugars made during photosynthesis are converted to sucrose and loaded into phloem sieve tubes, occurs when leaves are green

186
Q

Where in the plant is sucrose transported in translocation

A

Sucrose is transported to other areas of the plant that may be growing such as meristems or to roots for storage

187
Q

What is a sink in a plant

A

Anywhere that removes sucrose from the phloem sieve tube

188
Q

What are examples of things sucrose is used for in a plant

A

Sucrose could be used for respiration and growth in meristem or it could be converted to starch for storage in a root

189
Q

Where sucrose is being used in cells how does it move out of the phloem

A

It diffuses out sieve tube via plasmodesmata or removed by active transport

190
Q

What does removal of sucrose from sap do to the water potential

A

Increases saps water potential, so water moves out of sieve tube into surrounding cells which reduces the hydrostatic pressure in phloem at the sink

191
Q

What does water entering sieve tube at the source increases

A

Increases the hydrostatic pressure in the phloem

192
Q

What does water leaving the sieve tube at the sink reduce

A

Reduces the hydrostatic pressure in the phloem

193
Q

What does the difference in hydrostatic pressure in the phloem create

A

Pressure gradient is set up along sieve tube and sap flows from higher to lower pressure, could be in either direction depending on where sucrose is being produced and where it is needed

194
Q

Is it possible for sap to be flowing in different directions in different sieve tubes

A

Yes

195
Q

Why is sap described as moving in mass flow

A

As sap in one tube is all moving in the same direction

196
Q

What is the process of translocation

A

1.sucrose actively loaded into sieve tube element and reduces water potential, 2.water flows by osmosis and increases hydrostatic pressure in sieve tube elements, 3.sap moves down sieve tube from higher hydrostatic pressure at the source to lower at the sink, 4.sucrose removed from sieve tube by surrounding cells and increases water potential in sieve tube, 5.water moves out of sieve tube and reduces hydrostatic pressure

197
Q

What is stoma doing when it’s cells are turgid

A

Open

198
Q

What happen when stoma cells are flaccid

A

Shut

199
Q

How do you measure rate of transpiration

A

Volume of cylinder, V=pi x r^2 x h, then divide volume by time, V/T= mm s-1

200
Q

How would you carry out a potometer experiment

A

Cut the shoot under water so no air enters the xylem and cut stem diagonally for larger SA, dry leaves before experiment and make sure potometer is air tight, if you want air bubble back to 0 you open up the reservoir

Alevel Biology (25 decks)

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