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transport in plants Flashcards

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1
Q

Why do plants need a transport system?

A

to get water and minerals from the roots up to the rest of the plant;
to carry assimilates made at the leaves down through the plant

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2
Q

Direction of flow in phloem and xylem

A

xylem - up
phloem - up or down as needed

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3
Q

What is the role of collenchyma and sclerenchyma?

A

to provide mechanical strength and support plant

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4
Q

Where is sclerenchyma and collenchyma found?

A

in the vascular bundles

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5
Q

Describe the vascular bundle in the young root

A

Bundle in centre, xylem x shaped and phloem between arms of x shape

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6
Q

Where is the endodermis in the young root?

A

surrounds the vascular bundle and medulla

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7
Q

Where is the pericycle found?

A

Layer cells just inside the endodermis in young root

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8
Q

Where are vascular bundles located in the stem?

A

Found around the outside of the stem

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9
Q

What happens to vascular bundles in stem in woody plants?

A

will fuse to create a continuous ring

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10
Q

How is the ring of vascular bundles important to woody plants?

A

complete ring of vascular bundles provides strength and flexibility to withstand bending forces on stems and branches

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11
Q

How are tissues organised in the stem?

A

vascular bundles and sclerenchyma around outside of stem, medulla in centre, surrounded by collenchyma

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12
Q

How are vascular bundles organised in the stem?

A

phloem on outside, xylem inside, cambium layer between them. sclerenchyma on outer edge of vascular bundle

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13
Q

Where is the phloem located in the stem?

A

On outside of vascular bundles

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14
Q

Where is xylem located in stem?

A

on inside of vascular bundles

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15
Q

Where is sclerenchyma located in stem?

A

sclerenchyma on outer edge of vascular bundle

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16
Q

Where is collenchyma located in the stem?

A

layer on outer edge of the stem

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17
Q

Where is the cambium located in the stem?

A

between phloem and xylem

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18
Q

What is the role of the cambium?

A

meristem cells, can differentiate to create new xylem/phloem

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19
Q

How are vascular bundles organised in the leaf?

A

xylem on top, phloem on bottom

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20
Q

Describe lignification

A

lignin impregnates and kills xylem cells, waterproofs and strengthens cell wall.
contents decay leaving hollow tube, xylem vessel

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21
Q

How is lignin shaped in the xylem cell walls?

A

in spirals for flexibility

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22
Q

Why does lignin form spiral shapes?

A

for flexibility of the stem

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23
Q

How does lignin help xylem perform function?

A

prevents collapse, makes hollow, creates tube, waterproofs it

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24
Q

What are bordered pits?

A

places in xylem vessel walls where lignification is not complete

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25
Q

What is the role of bordered pits?

A

allow water to pass between xylem vessels or to tissues

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26
Q

Adaptations of xylem to its function (5)

A

aligned dead cells, continuous column;
thin tubes;
bordered pits;
lignification
no walls/contents to obstruct water

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27
Q

How is capillary action maintained in the xylem?

A

thin tubes, water column doesn’t break easily - adhesion

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28
Q

What are assimilates?

A

mainly sucrose and amino acids, dissolved in water to form sap, products of photosynthesis

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29
Q

Describe the structure of the phloem (3)

A

sieve tube elements elongated;
perforated sieve plates between them;
companion cells between tubes

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30
Q

What do companion cells do?

A

load assimilates into phloem

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31
Q

Describe the walls of the phloem

A

thin, 5/6 sided

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32
Q

How are sieve tube elements adapted for mass flow?

A

no nucleus and little cytoplasm

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33
Q

How are companion cells adapted?

A

dense cytoplasm and large nucleus, many mitochondria for active processes

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34
Q

What are plasmodesmata?

A

gaps in cell wall connecting cells by their cytoplasm

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35
Q

Name three pathways taken by water

A

apoplast, symplast and vacuolar

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36
Q

Describe the apoplast pathway

A

Moves through molecules in cell walls by mass flow, does not enter cell

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37
Q

Describe the symplast pathway

A

Water moves through cells and their cytoplasm and through plasmodesmata

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38
Q

Describe the vacuolar pathway

A

Moves through cells cytoplasm and plasmodesmata and vacuole

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39
Q

What is water potential?

A

Tendency of water molecules to move from one area to another

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40
Q

How does water move between water potential?

A

from area of high potential to low

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41
Q

What happens if plant cell placed in pure water/higher potential?

A

water moves in by osmosis until becomes turgid, cell wall prevents bursting, pressure potential between water and cell wall

42
Q

What does turgid mean?

A

plant cell intake lots of water, swells and cell membrane exerts pressure on cell wall

43
Q

What happens if plant cell placed in lower water potential?

A

water leaves by osmosis, cytoplasm and vacuole shrink, membrane will pull away from cell wall

44
Q

What does flaccid plant cell mean?

A

cell lost lot of water, cell membrane does not exert pressure on cell wall

45
Q

Term when plant tissue/cell loses a lot of water

A

flaccid

46
Q

What does plasmolysed mean?

A

cell membrane detached from cell wall due to water loss

47
Q

What is transpiration?

A

loss of water (vapour) from plant via leaves

48
Q

How is water lost from a plant?

A

from leaves through stomata, some lost through waxy cuticle

49
Q

Describe the pathway taken by water through the leaf

A

into cells of spongy mesophyll from xylem,
evaporates from cell walls and diffuses out of open stomata

50
Q

Loss of water out of the stomata depends on what?

A

Must be lower water vapour potential outside of the leaf

51
Q

Why is transpiration important? (4)

A

water moves transports minerals up plant;
maintains turgidity;
supplies water for growth, photosynthesis;
evaporation keeps plant cool

52
Q

Five factors which affect transpiration rate

A

temperature;
wind;
humidity;
light intensity;
water availability

53
Q

How does increased temperature affect the rate of transpiration?

A

higher = increase;
increased evaporation rate, water vapour potential in leaf rises;
thermal->kinetic energy increases diffusion rate;
potential gradient cause rapid diffusion

54
Q

How does high light intensity affect the rate of transpiration?

A

higher light intensity causes stomata to open and water to leave, increases rate

55
Q

How does humidity affect the rate of transpiration?

A

humidity increases water potential outside leaf reducing rate transpiration, reduces concentration/potential gradient

56
Q

How does air movement affect the rate of transpiration?

A

Air carries away water vapour in the air, increasing potential gradient, quicker transpiration

57
Q

How does water availability affect the rate of transpiration?

A

More water can replace lost water, if low supply stomata close and leaves wilt - more water, increased transpiration

58
Q

Role of root hair cells

A

absorb mineral ions and water from soil

59
Q

Adaptations of root hair cells

A

long and large SA

60
Q

Describe the pathway of water across root and into the xylem

A

moves through root hair cells across root cortex;
at endodermis, apoplast path blocked by casparian strip, forces water through plasma membrane into cells, transporter proteins actively pump minerals into medulla and xylem;
lowers water potential in xylem, water moves in by osmosis

61
Q

How do water and minerals cross casparian strip?

A

transporter proteins pump minerals into medulla/xylem, water follows by osmosis due to lower water potential in xylem

62
Q

Role of the endodermis and casparian strip

A

forces water and minerals into cells through membrane for active transport of mineral ions, contains granules of starch for energy, prevents backflow of water

63
Q

Three processes which help water move up the stem by mass flow

A

root pressure;
transpiration pull;
capillary action

64
Q

Describe how root pressure helps water move through the xylem

A

pumping of minerals and movement of water from root into the xylem causes build up of pressure;
forces water into and up the xylem

65
Q

Describe how the transpiration pull helps water move up the xylem

A

cohesion-tension theory - lost water must be replaced. Water held together by cohesion forces, strong enough to maintain column of water which is pulled up xylem;
pull at top creates tension, lignin prevents collapse

66
Q

What is the cohesion tension theory?

A

as water is lost from the plant, forces of cohesion pull water molecules up the xylem in a long chain, creating tension, aka transpiration pull

67
Q

What is cohesion in water?

A

water molecules are attracted to each other by weak forced due to its polar nature

68
Q

Describe how capillary action helps water move up the xylem

A

water molecule attracted to walls of xylem by adhesion;
narrow tubes allow forces to pull water up vessel

69
Q

How does water move through the leaf using water potential gradient? (3)

A

Water evaporates from cavity above guard cells, lowers water potential;
water moves into cells from those with higher potential;
water drawn into cells from xylem down potential gradient

70
Q

Why is water loss an issue for terrestrial plants?

A

must photosynthesise and keep stomata open to remove oxygen from photosynthesis which allows water to leave;
have to adapt to replace lost water and minimise water lost

71
Q

How are terrestrial plants adapted to reduce and replace water lost? (4)

A

thick waxy cuticle on leaf reduces water loss
stomata on underside avoids heat of sun;
stomata close at night when cannot photosynthesise;
lose leaves in winter, will not lose water when water is frozen/temperature too low

72
Q

How does losing leaves at winter help with water loss in terrestrial plants?

A

temperature too low and water frozen so cannot photosynthesise;
no reason to keep leaves which allow water to escape, prevents water loss

73
Q

Why does marram grass need to adapt to sand dunes?

A

harsh conditions, water drains quickly, sand salty, windy conditions

74
Q

What kind of plant is marram grass?

A

xerophyte

75
Q

How is marram grass adapted to survive in dunes? (5)

A

leaves rolled, can roll tighter when conditions dry;
thick waxy cuticle;
stomata on inner side of leaf;
stomata in sunken pits;
dense spongy mesophyll

76
Q

How does a dense spongy mesophyll reduce transpiration?

A

less SA in leaf for water to evaporate from

77
Q

How do rolled leaves reduce water loss?

A

traps air in gap, very humid, prevents water loss by increasing water vapour potential in air around stomata, stomata on inside of leaf

78
Q

How do sunken pits protect stomata?

A

stomata hidden from air movement which reduces humidity in the air and increases transpiration

79
Q

How are cacti adapted to survive in arid conditions?

A

succulents;
leaves just spines;
stem green for photosynthesis;
roots widespread

80
Q

How do spines prevent transpiration?

A

type of leaf, smaller surface area, lose less water by transpiration

81
Q

What is a succulent?

A

a plant which stores water in stem, sometime ribbed so they can expand

82
Q

Three other xerophytic adaptations

A

closure of stomata when water availability low;
high salt concentration causes low water potential inside leaf, reduces water loss;
long tap root reaching deep underground

83
Q

What are hydrophytes?

A

plants which live in water

84
Q

How are water lilies adapted to living in water? (4)

A

large air spaces in the leaf;
stomata on upper epidermis for gas exchange;
stem large air spaces;
hydathodes on leaves create water droplets for transpiration in humid air

85
Q

Why do water lilies have large space in the leaf?

A

to keep the plant afloat for air and sunlight

86
Q

Why do water lilies have large air spaces in the stem?

A

buoyancy, allow oxygen to diffuse quickly to roots for aerobic respiration

87
Q

What is translocation?

A

Movement of assimilates around the plant

88
Q

What is a sink and a source?

A

source - part of plant which loads assimilates into phloem,
sink - part of plant which removes assimilates from phloem

89
Q

How are assimilates loaded into the phloem? (4)

A

at companion cells, protons actively pumped out of cell to surrounding tissues;
increased concentration protons outside cell, diffuse back in via cotransporter proteins;
only allow diffusion if accompanied by sucrose molecule;
increased concentration of sucrose in companion cell causes diffusion into phloem via plasmodesmata

90
Q

What is active loading?

A

the process of loading sucrose into the sieve tube elements by active transport of hydrogen ions in companion cells

91
Q

Describe facilitated diffusion in companion cell

A

protons actively pumped out causing concentration gradient, diffuse back into companion cell along with a sucrose molecule by facilitated diffusion via cotransporter proteins

92
Q

Where are assimilates loaded into phloem?

A

at source, by companion cells

93
Q

Which cell loads assimilates into the phloem?

A

companion cell

94
Q

Describe the movement of sap in the phloem (2)

A

mass flow - from high to low hydrostatic pressure;
loaded at source, increase in hydrostatic pressure, removed at sink, lower hydrostatic pressure - from source to sink

95
Q

State two sources of a plant

A

mainly leaves - sucrose transported to growing meristems and roots for storage;
roots - in spring, stored starch converted to sucrose and transported around plant

95
Q

Explain why the hydrostatic pressure is high at the source (3

A

Assimilates are loaded in, decreasing water potential;
water moves in by osmosis;
increasing the hydrostatic pressure

96
Q

Explain why the hydrostatic pressure is low at the sink (3)

A

assimilates diffuse or are actively moved into tissues at sink;
makes water potential higher in phloem than in sink tissues, water move out phloem by osmosis;
hydrostatic pressure decreases

97
Q

What is the pericycle?

A

layer meristem cells able to differentiate

98
Q

Why is the xylem X shaped in the root?

A

provides strength to withstand pulling forces on the roots

99
Q

What is a xerophyte?

A

A plant adapted to living in arid conditions

Biology (18 decks)

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