3.1.3 Transport in plants Flashcards
1
Q
what are the main reasons as to why multicellular plants need transport systems
A
- metabolic demand are high
- large size
- small SA:V ratio
2
Q
why do plants have high metabolic demands
A
- cells of chlorophyl make their own glucose + O2 by photosynthesis but internal and underground plants don’t so need to be transported
- hormones made in one part needs to travel for effect
- mineral ions absorbed by root needs transportation to cells to make proteins required for enzymes + structure
3
Q
what are 2 features of herbaceous dicots
A
- soft tissues
- relatively short life cycle
> e.g. leaves + stems die at end of growing season to soil level
4
Q
what is a vascular system
A
- series of transport vessels running through stem, roots and leaf in dicots
5
Q
what transport vessels make up the vascular system in herbaceous dicots
A
- xylem
- phloem
6
Q
how are the transport tissues found in herbaceous dicots
A
- arranged together in vascular bundles in leaves, stems and roots
7
Q
how are the vascular bundles arranged in a dicot root + why
A
- vascular bundle in middle of plant
> helps withstand tugging strains from wind - xylem in center of vb and surrounded by phloem
- layer of pericycle around then endodermis
- surrounded by cortex and then epidermis
8
Q
what is the pericycle
A
- meristematic tissue (roots)
> turns into xylem + phloem
9
Q
what is the endodermis
A
- protective layer around vascular tissue
> regulates water movement
10
Q
what is the cortex
A
- packing cells
11
Q
how are the vascular bundles arranged in a dicot stem
A
- vascular bundles around edge
> gives strength and support - xylem is inside facing + phloem is outward facing
> separated by vascular cambium - surrounded by cortex around it and then epidermis
- pith in the center
12
Q
what is pith
A
- unspecialised cells (stem)
13
Q
what is vascular cambium
A
- meristematic tissue
> separates xylem + phloem in vb
14
Q
describe how the vascular bundles are arranged in dicot leaf
A
- vascular bundles found in lower epidermis
- xylem facing downwards + phloem upwards
- separated by vascular cambium
- surrounded by spongy mesophyll
- above is palisade mesophyll then upper epidermis then waxy cuticle
15
Q
what is the main function of xylem
A
- to transport water + mineral ions
- to support
16
Q
what type of tissue is xylem
A
- non living
17
Q
how is the flow of materials in xylem
A
- up from the roots to shoots and leaves
18
Q
what are xylem made up of
A
- dead vessel elements aligned end to end to form a continuous tube called xylem vessel
19
Q
what are some features of xylem vessels
A
- hollow tube (no cytoplasm)
- thick lignified walls
- non-lignified pits
- narrow
20
Q
why is the lignified thick walls in xylem a good feature
A
- waterproofs the cells
- strong to provide structural support
> prevents xylem vessels collapsing under transpiration pull
21
Q
why are the pits in xylem a good feature
A
- allow communication between adjacent cells + lateral flow of water
> water leaves xylem and moves into other cells of plants
22
Q
why are xylem vessels being narrow a good feature
A
- allows for enhanced adhesion + cohesion of water
23
Q
how can lignin be laid down in walls of xylem vessels
A
- rings, spirals or solid tubes with many unlignified small areas called pits
24
Q
what type of tissue is phloem
A
- living tissue
25
what is the main function of phloem
- to transport organic solutes (food) around the plant from leaves where they are made by photosynthesis
26
what does the phloem supply the cells with
- sugars and amino acids needed for cellular respiration and for synthesis of all other useful molecules
> O2 needed for aerobic respiration
27
how is the flow in phloem
- flow of materials can go both up and down the plant
28
what is the main transporting vessel of the phloem
- sieve tube elements
29
what are the two main things that make up phloem tissue
- sieve tube elements
- companion cells
30
what are some features of sieve tube elements
- very little cytoplasm + no nucleus
- living cells
- end to end cells with sieve plates
31
what are some features of companion cells
- small cells
- large nucleus
- dense cytoplasm
- many mitochondria to produce ATP
32
how are companion cells linked to sieve tube elements
- linked by many plasmodesmata
33
what is the function of companion cells
- produce ATP for active loading of sucrose into sieve tube elements
34
state some of the ways water is essential to plants
- turgor pressure helps support stems + leaves
- turgor drives cell expansion
- loss of evaporative water vapour cools plants
- mineral ions + products of photosynthesis transported in aqueous solutions
- water is raw material for photosynthesis
35
where is the exchange surface in plants where water is taken into the body of the plant from the soil
- root hair cells
36
describe some of the adaptations of root hair cells that make it a good exchange surface
- small size so can penetrate between soil particles easily
- large SA:V
- thin surface layer so easier diffusion + osmosis
- conc of solutes in cytoplasm of root hair cells maintains water potential gradient between soil water and cell
37
why does water move into the root hair cell
- root hair cell has lower water potential than soil surrounding as there are many solvents such as sugars, mineral ions + amino acids
- this creates water potential gradient
- water moves in from soil (high wp) to root hair cell (low wp)
38
after the water has entered the root, what are the two pathways it can take
- symplast pathway
- apoplast pathway
39
describe the movement of water through the symplast pathway
- water moves through the continuous cytoplasm of living plant cells that are connected through plasmodesmata, by osmosis
- root hair ell has high wp than next cell along so water moves along cells down wp gradient
- this process continues until the xylem is reached
> as water eaves root hair cell, the wp of cytoplasm falls so maintains steep wp gradient allowing more water to enter from soil to cell
40
describe the movement of water through the apoplast pathway
- water moves through the cell walls and intercellular spaces
- water fills spaces between loose open network of fibres in cellulose cell wall
> water doesn't pass through any membranes so mineral ions are carried with water
41
for water to move into the root hair cell what must first happen
- mineral ions must move into root hair cells to create water potential gradient
42
how are mineral ions moved from soil to root hair cell
- by ATP (carrier proteins carry them)
43
how is ATP generated
- made from aerobic respiration
44
what 2 things does aerobic respiration need and where can that be accessed
- aerobic respiration requires oxygen + glucose
> glucose made from photosynthesis
> stored as starch + moves up and down plant as sucrose
45
what is the casparian strip
- a band of suberin (waxy material) that runs around each of the endodermal cells forming a waterproof layer
46
what happens to the water moving through apoplast + symplast when it reaches the endodermis
- as it reaches endodermis, it is met with the casparian strip
- water in apoplast pathway can't continue so forced into cytoplasm of cell, joining symplast pathway
47
what is significant about the diversion of the apoplast pathway into the cytoplasm at the casparian strip
- to move the water to the cytoplasm it has to pass through selectively permeable cell surface membranes
> this excludes any toxic solutes as membranes would have no carrier proteins to admit them
48
how does water move from the endodermal cells into the xylem
- mineral ions actively pumped into xylem, lowering wp
- water follows through due to osmosis
49
what happens to water pathway once inside the xylem
- water returns to apoplast pathway to enter xylem
50
what is root pressure
- the active transport of mineral ions into xylem creates root pressure as water is pushed up xylem and so more water enters the roots
51
how does water travel up the xylem
- as water moves into xylem, more water molecules are pulled through apoplast behind them
> this is due to the cohesion between water molecules + adhesion to wall
- cohesion + adhesion + transpiration pull create tension that allows continuous stream of water
52
how is tension created in the xylem
- the pull from water moving into xylem + up plant, along with cohesive-adhesive forces creates a tension
> this means there is a continuous flow of water through open structure of cellulose
53
what are the 3 processes that enable water to move up the stem
- root pressure
- capillary action
- transpiration pull
54
what is capillary action
- water molecules are charged and attracted to sides of xylem vessels by adhesion
- combined effects of adhesion + cohesion exhibit capillary action
> process by which water can rise up narrow tube against gravity
55
describe the transpiration stream
- water molecules are attracted by forces of cohesion which hold them in a continuous column
- as water vapour is lost from top of column (evaporation), the whole column is pulled up
> this creates tension in the lignified xylem vessel
56
describe the cohesion-tension theory
- water molecules have cohesion between them
- water molecules have adhesion between water molecules and lignified xylem vessel
> this created tension
57
what is transpiration an inevitable consequence of + why
- gaseous exchange
- the stomata open + close to allow O2 release and intake of CO2
- during this water vapour is also lost via diffusion
58
what causes stomata to open/close
- guard cells
59
how does water go to leaves + leave through stomata from the xylem
- water diffuses from xylem through cells of leaf where it evaporates from freely permeable cellulose cell walls of mesophyll cells in leaves into air spaces
- water vapour then moves into external air via stomata
60
movement of water out of xylem creates what type of pressure and thus what
- creates low hydrostatic pressure and thus tension
61
describe the transpiration pull
- water is drawn up the xylem in continuous stream to replace water lost by evaporation
62
what can be used to measure rate of water uptake
- potometer
63
when the stomata is open, what is the guard cell
- turgid
64
when the stomata is closed, what is the guard cell
- flaccid
65
state the main factors affecting transpiration
- light intensity
- relative humidity
- temperature
- wind
- soil-water availability
66
how does light intensity affect rate of transpiration
- the brighter, the more stomata open to gain light for photosynthesis + gas exchange
> more water vapour lost
> inc rate of transpiration
67
how does relative humidity affect rate of transpiration
- high humidity lowers rate of transpiration
> due to reduced wp gradient
- dry air = high rate
68
how does temperature affect rate of transpiration
- inc temp inc kinetic energy of water molecules + so inc rate of evaporation from spongy mesophyll cells into air spaces of air
- inc temp inc conc of wp that external air can hold before becoming saturates (dec humidity + wp)
69
how does wind affect rate of transpiration
- each leaf has layer of still air trapped by shape and features like hair on surface
- water vapour accumulates her
- as wind inc, water vapour is swept of surface of leaf and creating steep conc gradient so inc rate of transpiration
70
how does soil-water availability affect rate of trasnpiration
- if soil very dry then plant under water stress and rate of transpiration decrease
71
describe how stomata open
- at high light intensity, blue light stimulates ATP powered pumps to pump potassium ions into guard cells thus lowering wp
- causes water to enter guard cell from surrounding epidermal cells
- cell becomes turgid + thick inner wall curves around opening pore
72
describe how stomata close
- at low light intensity, abscisic acid (plant hormone) causes potassium ions to move out of guard cells, thus inc wp
- causes water to leave guard cells into surrounding epidermal cells
- makes cell flaccid + thick inner wall curves inward and stomata pore closes
73
what is stomatal density
- number of stomata per mm*2 (area)
74
how does water turn into water vapor when it leaves stomata
- water moves across spongy mesophyll by osmosis
- water molecules are evaporated from surface of spongy mesophyll into the sub-stomatal cavity
> now it's water vapour
- water vapour moves out of sub-stomatal cavity by diffusion
75
how does water evaporating cool the plant down
- water has a high latent heat of vaporisation
> lots of energy needed for water to evaporate so when it does lots of heat energy is removed thus cooling the plant down
76
why is it essential for plant cells to get water to become turgid
- they need support, otherwise they wilt
- if wilt, there is less SA for photosynthesis so less light absorbed
> less glucose made so less for respiration
> eventually plant dies
77
what is translocation
- the transportation of organic compounds in the phloem from sources to the sinks (tissues that need them)
78
what are assimilates
- the products of photosynthesis that are transported in translocation
79
what is the main assimilate transported around the plant
- sucrose
80
what are the main sources of assimilates in plants
- green leaves and green stems
- storage organs such as tubers + tap roots that are unloading their stores at beginning of growth period
- food stores in seeds when they germinate
81
what are the main sinks in a plant
- roots that are growing 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
82
what type of process is translocation
- in many plants it's an active process that requires energy to take place and substances can be transported up or down the plant
83
what is phloem loading
- soluble products of photosynthesis moved into the phloem from sources by an active process
84
why is sucrose the main carbohydrate transported in translocation
- it's not used in metabolism as readily as glucose so therefore less likely to be metabolised during transport process
85
what are the two main ways in which plants load assimilates into phloem
- on is a largely passive
- other is active
86
what is the apoplast route in trasnlocation
- sucrose from source traves through cell walls + inter-cell spaces to companion cell + sieve elements by diffusion down conc gradient, maintained by removal of sucrose into phloem vessels
87
describe how sucrose enters the companion cell
- H+ ions are actively pumped out of companion cells into surrounding tissue using ATP
- H+ ions return to companion cells down conc gradient via co-transport proteins
- sucrose molecule is con-transported
88
how does sucrose enter sieve tube elements
- sucrose builds up in companion cells and diffuses into sieve tube elements through plasmodesmata
89
what are some feature of companion cells to maximise sucrose transportation
- companion cells have many infoldings in cell membranes to inc SA for active transport of sucrose into cell cytoplasm
- many mitochondria to supply ATP needed for transport pumps
90
as a result of build up of sucrose in companion cells and sieve tube elements what happens next
- water moves in by osmosis
> leads to build up of turgor pressure due to rigid cell walls
> water carrying asimiliates moves into tubes of sieve elements, reducing pressure in companion cells and moves up or down plant by mass flow
91
how does phloem transport sucrose up or down the plant
- solute accumulation in source phloem leads to inc in turgor pressure + high hydrostatic pressure
> this forces sucrose to regions of lower hydrostatic pressure in the sinks
92
describe phloem unloading
- sucrose unloaded from phloem at sink
- sucrose diffuses from phloem into surrounding cells
> sucrose rapidly moves into other cells by diffusion or converted to another substance so conc gradient of sucrose is maintained between contents of phloem and surrounding cells
93
what happens to the phloem after loss of solutes from unloading
- leads to inc wp of phloem
- water moves out into surrounding cells by osmosis
- some water that carried solute to sink is drawn into transpiration stream into xylem
94
when sucrose reaches sink what can it be converted into
- glucose for respiration
- starch for storage
95
what are xerophytes
- plants living in dry habitats that have evolved in wide rage of adaptations to live + reproduce in places where water availability is low
96
what is marram grass
- a plant found widely on sand dunes + coastal areas, in dry and salty conditions
- xerophyte
97
why are plants that survive in very cold + icy conditions also xerophytes
- water in ground not freely available as it's frozen
98
name the ways of conserving water in xerophytes
- thick waxy cuticle
- sunken stomata
- reduced number of stomata
- reduced leaves
- hairy leaves
- curved leaves
- succulents
- leaf loss
99
how does thick waxy cuticle conserve water
- minimises water loss as most stomata covered
- can help survive cold + hot conditions
> example holly
100
how does sunken stomata help conserve water
- stomata located in pits
- reduced air movement
- provides a microclimate of still humid air that reduces wp gradient so reduces transpiration
101
how does hairy leaves conserve water
- microclimate of still humid air
102
how do curved leaves conserve water
- confines stomata within microenvironment of still humid air
- reduces diffusion of water vapour from stomata
103
what are succulents and how do they conserve water
- succulent plants store water in specialised parenchyma tissue in stems + roots
- swollen fleshy appearance
- water stored in plenty supply + used in times of drought
104
what are some root adaptation of xerophytes
- long roots grow deep into ground + penetrate several meters to access water that is far from surface of soil
- mass of widespread shallow roots with large SA able to absorb available water before rain shower evaporates
105
how do some xerophytes avoid the problem of less water available
- some plants lose leaves + become dormant or die, leaving seeds to germinate + grow rapidly when rain falls
- others grow as storage organs such as bulbs (onions/daffodils) and tubers
- few plants can withstand complete dehydration and recover when rain falls + due to disaccharide trehalose
106
what are some useful features of marram grass
- sunken stomata
- hairy leaves
- curved leaves
- long vertical roots penetrate sand + mat of horizontal rhizomes (modified stems) from which many more roots develop to form extensive network to help sand hold more water
107
what are some useful features of cacti
- sunken stomata
- hairy leaves
- succulents
- long roots
108
what are hydrophytes
- plants living in water and adapted to cope with growing in water or permanently saturated soil
109
what are some examples of hydrophytes
- water lilies
- water cress
110
why is important for surface water plants to have leaves that float
- to get light for photosynthesis + gas exchange
111
state the main adaptation of hydrophytes
- very thin / no waxy cuticle
- many stomata always open
- reduced plant structure
- wide flat leaves
- small roots
- large SA of stem + roots under water
- air sacs
- aerenchyma
112
why is very thin/no waxy cuticle good for hydrophytes
- don't need to conserve water as plenty available so water loss by transpiration not a problem
113
why is reduced plant structure good for hydrophytes
- water supports leaves so no need for strong supporting structures
114
why are wide flat leaves good for hydrophytes
- spread across surface of water to capture as much light
115
why do hydrophytes have small roots
- water can diffuse directly into stem + leaf tissue
> less need for uptake by roots
116
why do hydrophytes having large SA of stem + roots under water a good feature
- maximises area for photosynthesis + O2 to diffuse into submerged plants
117
why is having air sacs good for hydrophytes
- enables leaves or flowers to float to surface of water
118
what are aerenchyma
- specialised parenchyma (packing) tissue formed in leaves, stems + roots of hydrophytes
119
why are aerenchyma a good feature of hydrophytes
- many large air spaces (formed my apoptosis) in normal parenchyma
- makes leaves + stems more buoyant
- forms low-resistance internal pathway for movement of substances like O2 to tissue below water
> helps plants cope in extremely low O2 conditions (anoxic)
119
what are some features of lilies
- many always open stomata
- wide flat leaves
120
in waterlogged roots, what is in short supply to the plant + how to overcome this
- air rather than water in short supply
- special aerial roots (pneumatophores) grow upwards into air
> have many lenticel allowing entry of air into woody tissue
