Transport in Plants Flashcards
(91 cards)
1
Q
Reasons why plants need transport system
A
Size, metabolic rate, surface area to volume ratio
2
Q
Why size affects a plant’s need for a transport system
A
Large plants need to move substances up and down the entire length
3
Q
Why metabolic demand affects a plant’s need for a transport system
A
Internal and underground plant parts need oxygen and glucose to get to them, hormones need transporting to where they have an effect, mineral ions need transporting to make proteins for enzymes
4
Q
Why surface area to volume ratio affects a plant’s need for a transport system
A
Plants have a low surface area to volume ratio so diffusion is not enough to supply the plant cells with everything they need
5
Q
Arrangement of vascular bundles in the stem
A
Around the edge for strength and support
6
Q
Arrangement of vascular bundles in the root
A
In the middle to help withstand the tugging strains from the wind
7
Q
Arrangement of vascular bundles in the leaf
A
Midrib of a leaf supports the structure of the leaf
8
Q
Dicotyledonous plants
A
Plants that make seeds that contain two cotyledons
9
Q
Cotyledons
A
Organs that act as food stores for developing embryos
10
Q
Types of dicots
A
Herbaceous, woody
11
Q
Structure of the xylem
A
Long hollow structures made of columns of cells fused together end to end, thick-walled parenchyma around the xylem vessels, lignified secondary walls, bordered pits
12
Q
Role of thick walled parenchyma
A
To store food, to store tannins
13
Q
Role of lignin in xylem
A
To provide mechanical strength
14
Q
Arrangement of lignin in the xylem
A
Rings, spirals, solid tubes
15
Q
Role of pits in the xylem
A
To be where the water leaves the xylem for other cells in the plant
16
Q
Function of the xylem
A
To transport water and mineral ions, to support the plant
17
Q
Structure of sieve tube elements
A
Many cells joined end to end to form a hollow structure, not lignified, sieve plates
18
Q
Function of sieve tube elements
A
Main transporting vessels of organic solutes
19
Q
Function of sieve plates
A
To let phloem contents flow through
20
Q
Why mature phloem cells have no nucleus
A
Large pores appear in the cell walls, tonoplast and nucleus and other organelles break down, phloem fills with phloem sap
21
Q
Structure of companion cells
A
Linked to sieve tube elements by plasmodesmata, nucleus and organelles present
22
Q
Function of companion cells
A
To act as the life support system for the sieve tube cells
23
Q
Structure of the phloem
A
Sieve tube elements, companion cells, fibres, sclereids
24
Q
Sclereids
A
Cells with very thick cell walls
25
How to dissect stems to observe xylem
Put material in water containing a strongly coloured dye for 24 hours, rinse it, make clean transverse cut with a sharp blade on a white tile, xylem show up as spots, make a clean longitudinal cut, xylem show up as coloured lines
26
Limitations of dissection of stem to observe vascular bundles
Can't be adjusted to see phloem, dependent on sharp blade and steady hand, if they aren't cut in the right place you won't see any xylem
27
Process of transpiration
Water evaporates from the surface of mesophyll cells into air spaces in the leaf and moves out of the stomata by diffusion, evaporation lowers water potential of the cell, water moves into cell by osmosis through apoplast and symplast pathways, repeated across the leaf to the xylem, water moves out of xylem by osmosis, water molecules form hydrogen bonds with each other resulting in cohesive forces causing capillary action, water drawn up the xylem to replace water lost by evaporation by the transpiration pull, transpiration pull causes tension in xylem
28
Theory related to transpiration
Cohesion-tension theory
29
Capillary action
Water moving up a narrow tube against the force of gravity
30
What is transpiration an inevitable consequence of?
Gaseous exchange for photosynthesis
31
Evidence for the cohesion-tension theory
Trees shrink in diameter when transpiration is at its highest because of the higher tension in the xylem, broken xylem vessels take up air rather than letting water out, broken xylem vessels can't move water because the continuous stream has broken
32
How to measure transpiration rate
Potometer
33
Why is it difficult to measure transpiration directly?
Hard to condense and collect all water that evaporates from leaves without collecting water from the soil, hard to separate water from transpiration and water vapour from respiration
34
Precautions when setting up a potometer
All joints sealed with waterproof jelly, airtight, calibrated, cut the shoot at a slant, set up underwater
35
Which wall of the guard cell is more flexible?
Outer layer
36
Factors which will affect the rate of transpiration
Light intensity, relative humidity, temperature, air movement, soil-water availability
37
How does light intensity affect the rate of transpiration?
Increased light intensity opens more stomata, increases evaporation from the surfaces of the leaf
38
How does relative humidity affect the rate of transpiration?
High relative humidity will lower the rate of transpiration, reduced water potential gradient
39
How does temperature affect the rate of transpiration?
Increased temperature increases the kinetic energy of water molecules and increases rate of evaporation, increased temperature increases concentration of water vapour that the external air can hold
40
How does air movement affect the rate of transpiration?
Air movement blows away diffusion shells, increases water potential gradient
41
How does soil-water availability affect the rate of transpiration?
Dryness will put the plant under water stress and the rate of transpiration will be reduced
42
Things water is used for in plants
Turgor pressure, cell expansion due to turgor, cooling by evaporation, transport medium, photosynthesis
43
Adaptations of root hair cells
Microscopic size so can penetrate between soil particles, high surface area to volume ratio, thin surface layer, high concentration of solutes in the cytoplasm of root hair cells
44
Names of water pathways through the root
Symplast, apoplast, vacuolar
45
Symplast pathway
Water moves though continuous cytoplasm of plant cells through plasmodesmata by osmosis
46
Apoplast pathway
Water moves through the cell walls and intercellular spaces between cellulose fibres, water entering xylem pulls a thread of water through the cell walls through cohesive forces
47
Vacuolar pathway
Water moves through the vacuoles
48
How water moves into the xylem
Reaches endodermis and Casparian strip, apoplast pathway diverges with symplast pathway, water passes through selectively permeable membranes, water potential in xylem is lower than that of endodermal cells, returns to apoplast pathway, root pressure results in water being pushed up xylem
49
Why it is good that water must move through selectively permeable membranes before reaching the xylem
Removes toxic solutes because of lack of transport proteins for them
50
Thing endodermal cells do to maintain water potential gradients
Pump mineral ions into the xylem by active transport
51
Evidence for the role of active transport in root pressure
Cyanide causes root pressure to disappear, root pressure increases with a rise in temperature which suggests chemical reactions are involved, low levels of oxygen or glucose decreases root pressure, guttation
52
Guttation
The forcing of xylem sap out of the ends of cut stems or from special pores at the ends of leaves
53
Xerophytes
Plants that have adapted to be able to live and reproduce in places where there is little water availability
54
Adaptations of xerophytes
Thick waxy cuticle, sunken stomata, fewer stomata, reduced leaf area, hairy leaves, curled leaves, succulents, leaf loss, long roots, shallow roots with large surface area, dormancy, disaccharide trehalose
55
How a thick waxy cuticle reduces water loss
Prevents water loss through the cuticle
56
How sunken stomata reduce water loss
Reduces air movement, reduce water potential gradient
57
How fewer stomata reduces water loss
Reduce water loss by transpiration
58
How reduced leaf surface area reduces water loss
Reduced surface area to volume ratio
59
How hairy leaves reduce water loss
Trap water lost by transpiration, reduce water potential gradient
60
How curled leaves reduce water loss
Confines stomata to microclimates
61
How succulents are good for xerophytes
Water stored in specialised parenchyma tissue
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How losing leaves reduces water loss
Water can't be lost through the leaves
63
How long roots reduce water loss
Allow them to reach water that is further down
64
How shallow roots with a large surface area work for xerophytes
Can absorb any available water before a rain shower evaporates
65
Adaptations of marram grass
Vertical and horizontal roots, stomatal pits, hairs, curled leaves
66
Adaptations of cacti
Vertical and horizontal roots, sunken stomata, reduced leaves, succulent
67
Hydrophytes
Plants that live in water and need adaptations to cope with growing in water
68
Why hydrophytes need to get rid of water
Need to float to get to light, air spaces need to be full of air
69
Adaptations of hydrophytes
Very thin or no waxy cuticle, lots of stomata, stomata always open, reduced structure, wide flat leaves, small roots, large surface area of stems and roots under the water, air sacs, aerenchyma, pneumatophores
70
How having a very thin or no waxy cuticle will help a hydrophyte
Water can be lost through the cuticle
71
Why can hydrophytes have their stomata open all the time?
No worries about loss of turgor
72
How wide, flat leaves help hydrophytes
Can capture more light
73
How small roots help hydrophytes
Water can diffuse directly into stem and leaf tissue
74
How having large surface areas of stem and root under water helps hydrophytes
Maximises the area for photosynthesis, maximises area for oxygen diffusion
75
How having air sacs helps hydrophytes
Enables leaves to float to the surface of the water
76
How aerenchyma helps hydrophytes
Makes leaves and stems more buoyant, low resistance internal pathway for movement of substances
77
How pneumatophores help hydrophytes
Roots that grow upwards to get to the air
78
Adaptations of water lilies
Wide flat leaves, stomata on the upside of the leaf, flexible stems
79
Main substance transported by translocation
Sucrose
80
Example of a source
Leaves
81
Example of sinks
Roots, meristems
82
Translocation
An energy requiring process that transports assimilates in the phloem between sources and sinks
83
Assimilates
Transported products of photosynthesis
84
Process of translocation
Hydrogen ions pumped out of companion cell using ATP, hydrogen ions return to companion cell via cotransport protein, sucrose cotransported, sucrose diffuses out of companion cell through plasmodesmata, water moves in by osmosis, carries assimilates, moves to areas of low pressure
85
Adaptations of companion cells
Infoldings in cell membranes to increase surface area for active transport, lots of mitochondria
86
How water and solutes are transported through a plant
Solute accumulation in phloem increases turgor pressure to force sap to regions of lower pressure, pressure differences transport the stuff
87
How the phloem is unloaded
Diffusion of sucrose into surrounding cells, sucrose moves rapidly to maintain concentration gradient, loss of solute in phloem increases water potential of phloem, water moves into surrounding cells by osmosis, surrounding cells can be xylem
88
Evidence for process of translocation
Microscopes show adaptations of companion cells, poisoned mitochondria stop translocation, flow is 10000 times faster than it would be if just done by diffusion, aphid's stylet show there is a positive pressure
89
Questions about translocation
Not all solutes move at same rate, role of sieve plates
90
What do potometers measure?
Water uptake
91
Why may potometer measurements not be representative of the rate of transpiration?
Not all of water uptaken is lost, uptake by a detached shoot is not the same as a whole plant
