Transport In Plants :). Flashcards
1
Q
What do plants need to get rid of?
A
Waste substances?
2
Q
How are plants like animals?
A
They’re multicellular
Small surface area to volume ratio
Relatively big
Relatively high metabolic rate
3
Q
Why can’t plants just diffuse everything they need to get and get rid of into and out of the plant?
A
Exchanging substances by direct diffusion by direct diffusion from the outer surface to the cells would be too slow to meet their metabolic needs
4
Q
What do plants need due to this issue?
A
Transport systems to move substances to and from individual cells quickly
5
Q
What does xylem tissue do?
A
Transport water and mineral ions in solution.
Substances move up plant from roots to leaves
Support the plant
6
Q
What does phloem tissue do?
A
Mainly transports sugars (also in sugars) both up and down the plant
7
Q
What do xylem and pholem make up?
A
A plants vascular system
8
Q
Where are xylem and phloem found?
A
Throughout a plant as they transport materials to all parts
Where they are found in each part is connected to the xylem’s function of support
9
Q
Describe where xylem is in a root?
A
In the centre and surrounded by phloem to provide support as it pushes through the soil
10
Q
Where are xylem and phloem found in the stems?
A
Near the outside to provide a sort of scaffolding that reduces bending
11
Q
Where are xylem and pholem found in a leaf?
A
Make up a network of veins which supports the thin leaves
12
Q
What are all the diagrams that you need to learn about xylem and phloem?
A
Transverse cross-sections
Herbaceous dicotyledonous plants (flowering plants without woody stem)
13
Q
What does transverse mean?
A
Sections cut through each structure at a right angle to its length
14
Q
Longitudinal cross-sections
A
Taken along length of structure
Shows where xylem and phloem are located in a typical stem
15
Q
What is xylem tissue made from?
A
Several different cell types
16
Q
Describe xylem vessels
A
Very long, tube-like structures formed from vessel elements
No end walls making uninterupted tube allowing water to pass through middle
Dead cells so no cytoplasm
Thickened walls with lignin (increases as plant ages)
17
Q
Lignin
A
Woody substances
Supports xylem vessels and stops them collapsing inwards
Can be deposited in xylem walls in different ways in spiral or distinct rings
Water and ions move into and out of vessel through small pits in wall where’s no lignin
18
Q
What does phloem transport?
A
Solutes (dissolved substances) mainly sugars like sucrose round plants
19
Q
How is phloem formed?
A
Like xylem from cells arranged in tube
20
Q
Function of phloem tube?
A
Transport tube not support
21
Q
What does phloem tissue contain?
A
Phloem fibres
Phloem parenchyma
Sieve tube elements
Companion cells
22
Q
What are the most important cells in phloem for transport?
A
Sieve tube elements
Companion cells
23
Q
What are sieve tube elements?
A
Living cells that form the tube for transporting solutes through the plants
24
Q
How are sieve tube elements joined?
A
End to end to form sieve tubes
25
What are the sieve part of sieve tube elements?
End walls which have lots of holes in them allowing solutes to pass through them
26
What is unusual about sieve tube elements for living cells?
No nucleus
Very thin layer of cytoplasm
Few organelles
27
How are cytoplasms between sieve tube elements cells connected?
Cytoplasm of adjacent cells is connected through holes in sieve played
28
Companion cells purpose?
Sieve tube elements lack of nucleus and other organelles means they can't survive in their own so 1 companion cell for 1 sieve tube element
Carry out living functions for both themselves and sieve cells e.g. Provide energy for active transport of solutes
29
How do you look at plant tissue?
Dissect and prepare section of tissue
Look under microscope
Draw it
30
How to dissect and prepare a section of a tissue? Step 1
Use scalpel/ razor blade to cut cross-section of stem transverse or longitudinal. Cut sections thinly as possible thin sections are better for viewing under a microscope
31
How to dissect and prepare a section of a tissue? Step 2
Use tweezers to gently place cut sections in ester until you come to use them stopped my them from drying out
32
How to dissect and prepare a section of a tissue? Step 3
Transfer each section to dish containing stain e.g. Toluidine blue O(TBO) and leave for 1 minute. TBO stains lignin in walls of xylem vessels blue-green. See position of xylem vessels and examine their structure
33
How to dissect and prepare a section of a tissue? Step 4
Rinse off section in water and mount each one onto a slide
34
What do plants need?
Substances like water, minerals and sugars to live
| Need carbon dioxide but it enters at leaves where it's needed
35
How does water enter a plant?
Through its root hair cells
36
What does a water get from and to to be transported around the plant?
From the soil
Through the roots
Into the xylem
37
Where does water go to reach the xylem?
Enters through root just cell
| Through the root cortex including the endodermis to reach the xylem
38
How is water drawn into the roots?
Via osmosis
| Travels down a water potential gradient
39
What's osmosis?
Diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential
40
How does water always move?
From areas of higher water potential to areas of lower water potential
Goes down a water potential gradient
41
What does the soil around the roots generally have?
A higher water potential (lots of water down there)
42
Leaves have?
Lower water potential (because water constantly evaporates from them)
43
What do these two things mean for water potential gradient?
Creates a water potential gradient keeping water moving through the plant in the right direction from roots (high) to leaves (low)
44
How many paths does water travel through the root via the root cortex into the xylem?
Two
45
Two xylem paths?
Symplast pathway
Apoplast pathway
Vacoluar pathway
46
What does the symplast pathway go?
Through the living parts of the cell-the cytoplasm. The cytoplasm of neighbouring connect through plasmodesmata
47
What are plasmodesmata?
Small channels in the cell wall
48
How does water move through symplast pathway?
Via osmosis
49
Apoplast pathway goes where?
Through non-living parts of cells-the cell walls.
50
Why can the apoplast pathway go through the cell wall?
Walls are very absorbent and water can simply diffuse through them as well as pass through spaces between them
51
What can the water in the apoplast pathway carry?
Solutes and move from areas of high hydrostatic Pressure to areas of low hydrostatic pressure. (Along pressure gradient)
Example of mass flow
52
What happens when water in the apoplast pathway gets to endodermis cell?
It's path is blocked by a waxy strip in the cell walls (Casparian strip). Now water takes symplast pathway
53
Why is this useful?
Water has to go through a cell membrane
| Cell membranes are partially permable and are able to control whether or not substances in the water get through
54
What happens once the water gets past the casparian strip?
Water moves into the xylem
55
Which of the two pathways is used?
Both pathways are used but apoplast pathway is the main one because it provides the least resistance
56
What do xylem vessels do?
Transport water all around the plant
57
What happens at the leaves with the xylem?
Water leaves the xylem and moves into the cells mainly by the apoplast pathway
58
Where does water evaporate?
From the cell walls into spaces between cells in the leaf
59
What happens when the stomata opens?
The water diffuses out of the leaf down the water potential gradient into surrounding air
60
What's the stomata called?
Tiny pores in the surface of the leaf
61
What's transpiration?
The loss of water from a plants surface
62
What is the movement of water from root to leaves called?
Transportation stream
63
What do the mechanisms that move water include?
Cohesion
Tension
Adhesion
64
What do cohesion and tension help to do?
Water move up plants from roots to leaves against the force of gravity
65
Where does water evaporate?
At the leaves at the top of the xylem (transpiration)
66
What does water evaporating from leaves do?
Create a tension (suction) which pulls more water up the leave
67
Water are molecules are?
Cohesive so when some are pulled into the leaf others follow meaning a whole column of water in the xylem from leaves down to roots moves upwards
68
Where does water enter?
The stem through the root cortex cells
69
Cohesive is?
Stick together
70
What is adhesion also partly responsible for?
The movement of water
71
How is adhesion responsible for the movement of water?
As well as being attracted to each other, water molecules are attracted to the walls of the xylem vessels
Helping water to rise up through the xylem vessels
72
What does cohesion and tension allow?
The mass flow of water over long distances up the stem
73
Why does transpiration happen?
A result of gas exchange
74
Why does the plant open the stomata?
Needs to let in carbon dioxide so it can produce glucose (by photosynthesis)
75
What also happens when the stomata is opened?
Water is let out so there's a higher concentration of water inside the leaf than in the air outside so water moves out of the leaf down the water pore beak fragment
76
What's transpiration a side effect of?
Gas exchange needed for photosynthesis
77
How does water move?
From areas of higher water potential to areas of lower water potential
Down the water potential gradient
78
What are the four main factors affecting transpiration rate?
Light
Temperature
Humidity
Wind
79
How does light affect rate of transpiration?
The lighter it is the faster the transpiration
This is because the stomata when it's light so CO2 can diffuse into leaf for photosynthesis. When dark the stomata are usually closed so little transpiration
80
How does temperature affect transpiration rate?
The higher the temperature the faster the transpiration rate
Warmer water molecules have more energy so evaporate from cells inside leaf faster increasing water potential gradient between inside and outside of leaf making water diffuse out of leaf faster
81
Humidity transpiration rate?
Lower humidity the faster the transpiration rate
| If air around plant is dry the water potential gradient between leaf and air is increased increasing transpiration
82
Wind transpiration rate?
The windier it is the faster the transpiration rate. Lots of air movement blows away water molecules from around the stomata increasing water potential gradient increasing rate of transpiration
83
What's a potometer?
A special piece of appartus used to estimate transpiration rate
84
What does a potometer actually measure?
Water uptake by the plant but it's assumed that water uptake is directly related to water loss by leaves
85
How do you estimate how different factors affect transpiration rate? Step 1
Cut shoot underwater to prevent air from entering the xylem. Cut it at a slant increasing surface area available for water uptake
86
How do you estimate how different factors affect transpiration rate? Step 2
Assemble potometer in water and insert shoot underwater so no air can enter
87
How do you estimate how different factors affect transpiration rate? Step 3
Remove appartus from water but keep end of capillary tube submerged in a beaker of water
88
How do you estimate how different factors affect transpiration rate? Step 4
Check that the appartus is watertight and airtight
89
How do you estimate how different factors affect transpiration rate? Step 5
Dry leaves allow time for shoot to acclimatise and then shut the tap
90
How do you estimate how different factors affect transpiration rate? Step 6
Remove end of capillary tube from beaker of water until one air bubble was formed then put the end of the tube back into the water
91
How do you estimate how different factors affect transpiration rate? Step 7
Record starting position of the air bubble
92
How do you estimate how different factors affect transpiration rate? Step 8
Start a stopwatch and record distance moved by bubble per unit time e.g. Per hour. The rate of air bubble movement is an estimate of the transpiration rate
93
How do you estimate how different factors affect transpiration rate? Step 9
Remember only change one variable (temperature... at a time) all other conditions (light, humidity...) must be kept constant
94
Air bubble called?
Air-water meniscus
95
Potomotor things to remember
Rervoir of water used to return bubble to start for repeats
As plant takes up water air bubble moves along scale
Tap shut during experiment
Capillary tube with scale
bubble moves
Beaker of water underneath
96
What are xerophytes?
Plants like cacti and marram grass (grows on sand dunes)
Adapted to dry climates
Adaptations that prevent them losing too much water by transpiration
97
Marram grass adaptations
Stomata sunk into pits
A layer of hair on epidermis
In hot or windy conditions, marram grass plants roll their leaves
Thick waxy layer on epidermis
98
How is the marram grass having stomata that are sunk in pits a good adaptation?
They are sheltered from the wind
| Helps slow transpiration down
99
How is the marram grass having a layer of hairs on the epidermis a good adaptation?
Traps moist air round stomata reducing water potential gradient between leaf and air slowing transpiration down
100
How is the marram grass rolling their leaves in hot or windy conditions a good adaptation?
Traps moist air
Slowing down transpiration
Reduces exposed surface area for losing water and protects stomata from wind
101
How is the marram grass having a thick waxy layer on epidermis a good adaptation?
Reduces water loss by evaporation because the layer is waterproof (water can't move through it)
102
Cacti adaptations
Thick, waxy layer on the epidermis reducing water loss by evaporation (waterproof layer)
Spines instead of leaves reducing surface area for water loss
Closes their stomata at the hottest times of the day when transpiration rates are the highest.
103
Hydrophytes are?
Plants like water lilies which live in aquatic habitats. As they grow in water they don't need adaptations to reduce water loss but they need adaptations to help them cope with low oxygen level
104
Hydrophytes adaptations
Air spaces in tissues help plant float and act as a store of oxygen for use in respiration
Stomata usually only present on upper surface of floating leaves
Often have flexible leaves and stems
105
Air spaces in tissues help plant float and act as a store of oxygen for use in respiration explain more?
E.g. Water lilies have large air spaces in their leaves allowing the leaves to float on the surface of the water increasing the amount of light they receive. Air spaces in roots and stems allow oxygen to move from floating leaves down to parts of plant underwater
106
Stomata usually only present on upper surface of floating leaves why is this a good adaptation?
Helps maximise gas exchange
107
Often have flexible leaves and stems a good feature for hydrophytes?
Supported by water around them so don't need rigid stems for support
Flexibility helps prevent damage by water currents
108
What's translocation?
Movement of assimilates (dissolved substances e.g. Sugars like sucrose, and amino acids) to where they're needed in a plant.
Energy requiring process that happens in the phloem
109
What does translocation do?
Move substances from sources to sinks.
110
Source
Substance where it's made at high concentration
111
Sinks
Area where used up
| At low concentration there
112
Why are sugars transported as sucrose?
It's not soluble and metabolically inactive so doesn't get used up during transpiration
113
Source for sucrose?
Leaves (where it's made)
114
Sink for sucrose?
Other parts of the plant especially the food storage organs and the meristem (areas of growth) in the roots, stem and leaves
115
What are roots sources or sink?
Sucrose can be stored in the roots
During growing season, sucrose is transported from roots to leaves to provide the leaves with energy for growth. In this case, roots are the source and the leaves are a sink.
So both as some parts of the plant can be
116
What do enzymes do to do with concentration gradient?
Enzymes maintain a concentration gradient from source to sink by changing the dissolved substances at the sink (by breaking them down or making them into something else) this makes sure that's always a lower concentration at the sink than at the source
117
What happens in potatoes?
Sucrose is converted to starch in sink areas, so there's always a lower concentration of sucrose at sink than inside the phloem. Making sure there's a constant supply of new sucrose reacted the sink from the phloem. In other sinks, enzymes such as invertase break down sucrose concentration into glucose (and frutose) for use by plants. Again make sure there's a lower concentration of sucrose at the sink
118
How are scientists thinking translocation happens?
Scientists aren't certain exactly how dissolved substances (solutes) are transported from source to sink by translocation. Best supported theory is mass flow hypothesis
119
Step 1 of the mass flow hypothesis
Active transport is used to actively load solutes (sucrose from photosynthesis) into sieve tubes of phloem at source (leaves)
120
Step 2 of translocation
This lowers the water potential inside the sieve tubes so water enters the tubes by osmosis from xylem and companion cells
121
Step 3 translocation
This created a high pressure inside the sieve tube at the source end of the phloem
122
Step 4 of translocation
At sink end, solutes are removed from the phloem to be used up increasing water potential inside the sieve tubes so water also leaves the tube by osmosis lowering the pressure inside the sieve tubes
123
Step 5 of translocation
The result is a pressure gradient from source end to sink end.
Gradient pushes solutes along sieve tubes to where they're needed
124
Active loading is used for what?
To move substances into companion cells from surrounding tissues and from companion cells into sieve tubes against a concentration gradient
125
What is the concentration of sucrose higher?
In the companion cells then the surrounding tissue cells and higher in the sieve tube cells than companion cells
126
What happens as a result?
Sucrose is moved to where it needs to go using active transport and co-transporter proteins.
127
Active transport
Uses energy to move substances against their concentration gradient
128
Step 1 active loading
In companion cell, ATP is used to actively transport hydrogen ions (H+) out of the cell and into surrounding tissue cells
129
Step 2 active loading
This sets up a concentration gradient- there are more H+ ions in the surrounding tissue than in the companion cell
130
Step 3 active loading
An H+ ion bonds to a co-transport protein in the companion cell membrane and re-enters the cell (down the concentration gradient)
131
Step 4 of scuba loading
A sucrose molecule binds to the co-transport protein at the same time. The movement of the H+ ions is used to move the sucrose molecule into the cell against its concentration gradient
132
Step 5 active loading
Sucrose molecules are then transported out of the companion cells and into the sieve tubes by the same process
133
What is ATP?
One of the products of respiration
134
What does the breakdown of ATP supply?
Initial energy needed for active transport of H+ ions
