transport in plants Flashcards
(100 cards)
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
2
Q
Direction of flow in phloem and xylem
A
xylem - up
phloem - up or down as needed
3
Q
What is the role of collenchyma and sclerenchyma?
A
to provide mechanical strength and support plant
4
Q
Where is sclerenchyma and collenchyma found?
A
in the vascular bundles
5
Q
Describe the vascular bundle in the young root
A
Bundle in centre, xylem x shaped and phloem between arms of x shape
6
Q
Where is the endodermis in the young root?
A
surrounds the vascular bundle and medulla
7
Q
Where is the pericycle found?
A
Layer cells just inside the endodermis in young root
8
Q
Where are vascular bundles located in the stem?
A
Found around the outside of the stem
9
Q
What happens to vascular bundles in stem in woody plants?
A
will fuse to create a continuous ring
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
11
Q
How are tissues organised in the stem?
A
vascular bundles and sclerenchyma around outside of stem, medulla in centre, surrounded by collenchyma
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
13
Q
Where is the phloem located in the stem?
A
On outside of vascular bundles
14
Q
Where is xylem located in stem?
A
on inside of vascular bundles
15
Q
Where is sclerenchyma located in stem?
A
sclerenchyma on outer edge of vascular bundle
16
Q
Where is collenchyma located in the stem?
A
layer on outer edge of the stem
17
Q
Where is the cambium located in the stem?
A
between phloem and xylem
18
Q
What is the role of the cambium?
A
meristem cells, can differentiate to create new xylem/phloem
19
Q
How are vascular bundles organised in the leaf?
A
xylem on top, phloem on bottom
20
Q
Describe lignification
A
lignin impregnates and kills xylem cells, waterproofs and strengthens cell wall.
contents decay leaving hollow tube, xylem vessel
21
Q
How is lignin shaped in the xylem cell walls?
A
in spirals for flexibility
22
Q
Why does lignin form spiral shapes?
A
for flexibility of the stem
23
Q
How does lignin help xylem perform function?
A
prevents collapse, makes hollow, creates tube, waterproofs it
24
Q
What are bordered pits?
A
places in xylem vessel walls where lignification is not complete
25
What is the role of bordered pits?
allow water to pass between xylem vessels or to tissues
26
Adaptations of xylem to its function (5)
aligned dead cells, continuous column;
thin tubes;
bordered pits;
lignification
no walls/contents to obstruct water
27
How is capillary action maintained in the xylem?
thin tubes, water column doesn't break easily - adhesion
28
What are assimilates?
mainly sucrose and amino acids, dissolved in water to form sap, products of photosynthesis
29
Describe the structure of the phloem (3)
sieve tube elements elongated;
perforated sieve plates between them;
companion cells between tubes
30
What do companion cells do?
load assimilates into phloem
31
Describe the walls of the phloem
thin, 5/6 sided
32
How are sieve tube elements adapted for mass flow?
no nucleus and little cytoplasm
33
How are companion cells adapted?
dense cytoplasm and large nucleus, many mitochondria for active processes
34
What are plasmodesmata?
gaps in cell wall connecting cells by their cytoplasm
35
Name three pathways taken by water
apoplast, symplast and vacuolar
36
Describe the apoplast pathway
Moves through molecules in cell walls by mass flow, does not enter cell
37
Describe the symplast pathway
Water moves through cells and their cytoplasm and through plasmodesmata
38
Describe the vacuolar pathway
Moves through cells cytoplasm and plasmodesmata and vacuole
39
What is water potential?
Tendency of water molecules to move from one area to another
40
How does water move between water potential?
from area of high potential to low
41
What happens if plant cell placed in pure water/higher potential?
water moves in by osmosis until becomes turgid, cell wall prevents bursting, pressure potential between water and cell wall
42
What does turgid mean?
plant cell intake lots of water, swells and cell membrane exerts pressure on cell wall
43
What happens if plant cell placed in lower water potential?
water leaves by osmosis, cytoplasm and vacuole shrink, membrane will pull away from cell wall
44
What does flaccid plant cell mean?
cell lost lot of water, cell membrane does not exert pressure on cell wall
45
Term when plant tissue/cell loses a lot of water
flaccid
46
What does plasmolysed mean?
cell membrane detached from cell wall due to water loss
47
What is transpiration?
loss of water (vapour) from plant via leaves
48
How is water lost from a plant?
from leaves through stomata, some lost through waxy cuticle
49
Describe the pathway taken by water through the leaf
into cells of spongy mesophyll from xylem,
evaporates from cell walls and diffuses out of open stomata
50
Loss of water out of the stomata depends on what?
Must be lower water vapour potential outside of the leaf
51
Why is transpiration important? (4)
water moves transports minerals up plant;
maintains turgidity;
supplies water for growth, photosynthesis;
evaporation keeps plant cool
52
Five factors which affect transpiration rate
temperature;
wind;
humidity;
light intensity;
water availability
53
How does increased temperature affect the rate of transpiration?
higher = increase;
increased evaporation rate, water vapour potential in leaf rises;
thermal->kinetic energy increases diffusion rate;
potential gradient cause rapid diffusion
54
How does high light intensity affect the rate of transpiration?
higher light intensity causes stomata to open and water to leave, increases rate
55
How does humidity affect the rate of transpiration?
humidity increases water potential outside leaf reducing rate transpiration, reduces concentration/potential gradient
56
How does air movement affect the rate of transpiration?
Air carries away water vapour in the air, increasing potential gradient, quicker transpiration
57
How does water availability affect the rate of transpiration?
More water can replace lost water, if low supply stomata close and leaves wilt - more water, increased transpiration
58
Role of root hair cells
absorb mineral ions and water from soil
59
Adaptations of root hair cells
long and large SA
60
Describe the pathway of water across root and into the xylem
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
How do water and minerals cross casparian strip?
transporter proteins pump minerals into medulla/xylem, water follows by osmosis due to lower water potential in xylem
62
Role of the endodermis and casparian strip
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
Three processes which help water move up the stem by mass flow
root pressure;
transpiration pull;
capillary action
64
Describe how root pressure helps water move through the xylem
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
Describe how the transpiration pull helps water move up the xylem
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
What is the cohesion tension theory?
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
What is cohesion in water?
water molecules are attracted to each other by weak forced due to its polar nature
68
Describe how capillary action helps water move up the xylem
water molecule attracted to walls of xylem by adhesion;
narrow tubes allow forces to pull water up vessel
69
How does water move through the leaf using water potential gradient? (3)
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
Why is water loss an issue for terrestrial plants?
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
How are terrestrial plants adapted to reduce and replace water lost? (4)
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
How does losing leaves at winter help with water loss in terrestrial plants?
temperature too low and water frozen so cannot photosynthesise;
no reason to keep leaves which allow water to escape, prevents water loss
73
Why does marram grass need to adapt to sand dunes?
harsh conditions, water drains quickly, sand salty, windy conditions
74
What kind of plant is marram grass?
xerophyte
75
How is marram grass adapted to survive in dunes? (5)
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
How does a dense spongy mesophyll reduce transpiration?
less SA in leaf for water to evaporate from
77
How do rolled leaves reduce water loss?
traps air in gap, very humid, prevents water loss by increasing water vapour potential in air around stomata, stomata on inside of leaf
78
How do sunken pits protect stomata?
stomata hidden from air movement which reduces humidity in the air and increases transpiration
79
How are cacti adapted to survive in arid conditions?
succulents;
leaves just spines;
stem green for photosynthesis;
roots widespread
80
How do spines prevent transpiration?
type of leaf, smaller surface area, lose less water by transpiration
81
What is a succulent?
a plant which stores water in stem, sometime ribbed so they can expand
82
Three other xerophytic adaptations
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
What are hydrophytes?
plants which live in water
84
How are water lilies adapted to living in water? (4)
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
Why do water lilies have large space in the leaf?
to keep the plant afloat for air and sunlight
86
Why do water lilies have large air spaces in the stem?
buoyancy, allow oxygen to diffuse quickly to roots for aerobic respiration
87
What is translocation?
Movement of assimilates around the plant
88
What is a sink and a source?
source - part of plant which loads assimilates into phloem,
sink - part of plant which removes assimilates from phloem
89
How are assimilates loaded into the phloem? (4)
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
What is active loading?
the process of loading sucrose into the sieve tube elements by active transport of hydrogen ions in companion cells
91
Describe facilitated diffusion in companion cell
protons actively pumped out causing concentration gradient, diffuse back into companion cell along with a sucrose molecule by facilitated diffusion via cotransporter proteins
92
Where are assimilates loaded into phloem?
at source, by companion cells
93
Which cell loads assimilates into the phloem?
companion cell
94
Describe the movement of sap in the phloem (2)
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
State two sources of a plant
mainly leaves - sucrose transported to growing meristems and roots for storage;
roots - in spring, stored starch converted to sucrose and transported around plant
95
Explain why the hydrostatic pressure is high at the source (3
Assimilates are loaded in, decreasing water potential;
water moves in by osmosis;
increasing the hydrostatic pressure
96
Explain why the hydrostatic pressure is low at the sink (3)
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
What is the pericycle?
layer meristem cells able to differentiate
98
Why is the xylem X shaped in the root?
provides strength to withstand pulling forces on the roots
99
What is a xerophyte?
A plant adapted to living in arid conditions
