Plant transport Flashcards
1
Q
what are the two major groups of flowering plants?
A
- dicotyledons
- monocotyledons
2
Q
why do plants need transport systems?
A
- small SA:VR so diffusion is not enough
- water and minerals travel upwards in the xylem
- sugars travel up and down in the phloem
- phloem and xylem are vascular tissues and together they form vascular bundles
3
Q
what do the root hairs provide?
A
a large surface area, which allows absorption of water
4
Q
where is the vascular tissue?
A
the vascular tissue occurs in the centre of the root
5
Q
what is the shape of the xylem?
A
The xylem is usually a star shape with phloem found between the arms of the xylem.
6
Q
what three things does the root provide to counteract pulling forces?
A
- strength
- support
- anchorage
7
Q
where is the endodermis in the root?
A
surrounding the vascular tissue
8
Q
what is the casparian strip?
A
The Casparian strip, made of suberin, is a waterproof strip in the endodermis.
9
Q
what is located inside the endodermis?
A
Inside the endodermis is the pericycle, a layer of meristem cells between the endodermis and the vascular tissue (stele).
These cells are still able to divide.
10
Q
what is the cambium?
A
The cambium is made of meristem cells – forms the new xylem and phloem. The structure gives strength and flexible support to the stem and also resistance to bending
11
Q
what cells is the xylem made of?
A
- vessels
- tracheids
- fibres
- xylem parenchyma
12
Q
what do the vessels do and what are they?
A
- Vessels transport the water and minerals.
- Vessels are dead cells, aligned end to end, forming narrow tubes
13
Q
what adaptations do the xylem have?
A
They are lignified which gives strength, flexibility and allows the plant to grow
14
Q
if lignification is incomplete in xylem vessels, what happens ?
A
leaves pores in the wall of the vessels – pits
Allows water to leave or enter the vessel
15
Q
what is the phloem made up of?
A
- sieve tubes
- companion cells
- phloem fibres
- phloem parenchyma
16
Q
is the phloem Alive or dead?
A
alive
17
Q
what do the sieve tubes do?
A
transport the sucrose and amino acids
18
Q
what is a sieve plate on sieve tubes?
A
The ends of each sieve element are perforated with pores – sieve plate.
19
Q
what do sieve elements not have?
A
nuclei or other organelles
20
Q
what are the sieve tube elements associated with?
A
companion cells
21
Q
what do companion cells have?
A
Have dense cytoplasm, large central nucleus, many mitochondria
22
Q
how are the companion cells connected to the sieve element?
A
connected to the sieve element by plasmodesmata.
23
Q
what is transpiration?
A
Transpiration is the loss of water vapour from the leaves of a plant due to evaporation.
24
Q
what is the transpiration stream?
A
Movement of water through the plant
25
what is the definition of osmosis?
The movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
26
how does a solute affect the water potential?
Solutes lower the water potential.
27
how does water uptake by the roots occur?
- Water moves in by osmosis due to lower water potential inside the epidermal root cells.
- Minerals taken up by active transport by the root hair cells.
- This lowers the water potential of these cells and water moves in.
28
what are the three pathways that water can take across the root tissues?
- apoplast pathway
- symplast pathway
- vacuolar pathway
29
what is the apoplast pathway?
water moves through the cell walls
30
what is the symplast pathway?
water moves through the cytoplasm and plasmodesmata
31
what is the vacuolar pathway?
water travels from vacuole to vacuole
32
what does the casparian slip block?
the apoplast pathway between the cortex and the xylem
33
what does the casparian strip do?
Ensures water and dissolved minerals have to pass through the plasma membrane.
34
how are minerals and nitrate ions transported into the xylem from the cytoplasm of the cortex?
Minerals and particularly nitrate ions are actively transported by transporter proteins, into the xylem from the cytoplasm of the cortex.
35
what does the transported minerals etc. in the xylem do and what occurs as a result?
This lowers the water potential in the xylem so water enters the xylem from the cortex, by osmosis.
therefore Once water enters the xylem it can not pass back into the cortex as the apoplast pathway is blocked.
36
transport of water into and across the roots procedure?
1. Water enters root hair by osmosis down a water potential gradient
2. water potential of root hair cell increases surrounding cells have a ore negative wp
3. water moves into surrounding cells. Some by symplast pathway and vacuolar pathway and Some by apaoplast pathway, along the cell walls. UNTIL water reaches the epidermis
4. Casparian strip prevents movement of water by this pathway. Casparian strip prevents movement of water by this pathway
5. Water enters xylem from the surrounding cells. As minerals are actively transported into the xylem. Which reduces water potential in xylem of root
6. water moves up in root xylem
37
what are the 3 processes that helps water move up the stem?
- root pressure
- transpiration pull
- capillary action
38
how does root pressure work?
- Active transport of minerals into the xylem.
- Water then moves across the cortex and into the xylem via the water potential gradient produced.
39
how does transportation pull occur?
Transpiration pull is produced by the loss of water by evaporation from the leaves.
40
how does transpiration pull work?
The cohesion between water molecules is strong enough to hold the molecules together in a long chain or column.
As molecules are lost at the top of the column, the whole column is pulled up as one chain – transpiration stream.
The pull from above i.e. evaporation from the leaves, creates a tension in the column of water.
41
what theory also relate to the transpiration pull theory?
This is known as the cohesion-tension theory.
42
how does capillary action work?
-Water molecules are attracted to the sides of the xylem vessel - adhesion.
- The xylem vessels are narrow, so this can pull the water up the sides of the vessel.
43
what is adhesion?
-Water molecules are attracted to the sides of the xylem vessel
44
how does water move across the leaf?
Water enters the leaf in the xylem and moves across the mesophyll cells.
It evaporates into air spaces
Water molecules will diffuse down a water vapour potential gradient through the stomata.
45
how does water move from the xylem?
Water will move from the xylem through cells in the leaf down the water potential gradient.
Water moves through cells by the apoplast, symplast and vacuolar pathways.
46
why do plants lose so much water?
Stomata are open during the day to allow gaseous exchange for photosynthesis. Therefore plants will always lose water while stomata are open, hence transpiration.
47
why is the transpiration stream useful to plants?
- Water is required by the leaves for photosynthesis
- Water keeps cells turgid
- Water is required to enable cells to grow and elongate
- Contains dissolved minerals which are useful to the plant
- Evaporation of water keeps plant cool.
48
what is used to measure transpiration?
potometer
49
what is translocation?
transport of soluble organic substances (assimilates) in the phloem sieve tube.
50
what are assimilates?
substances, such as sucrose, that have been made in the plant.
51
what is the source?
releases sucrose into the phloem
52
what is the sink?
removes sucrose from the phloem
53
what direction does translocation occur?
up and down
54
where does translocation occur?
Translocation occurs in the phloem sieve tube cells.
55
how does sucrose in solution move into the phloem?
moves in the phloem by MASS FLOW.
It moves from source to sink
56
how does water availability affect water vapour loss?
If there is little water in the soil, then the plant cannot replace the water that is lost. Water vapour loss in plants is reduced when stomata are closed or when the plants shed leaves in winter.
57
how does number of leaves affect water vapour loss?
More leaves larger surface area over which water vapour can be lost
58
how does Number, size, position of stomata after water vapour loss?
Many large stomata, water vapour lost more quickly. Stomata on lower surface, water vapour loss is slower
59
how does presence of cuticle affect water vapour loss?
Waxy cuticle reduces evaporation of water vapour from leaf surface
60
how does temperature affect water vapour loss?
Higher temperature will increase rate of water
vapour loss:
Increase rate of evaporation from cell surface so water vapour potential in leaf rises
Increase rate of diffusion through stomata as water vapour molecules have more kinetic energy
Decrease relative water vapour potential in the air, allowing more rapid diffusion of H20 vapour molecules out of leaf.
61
how does relative humidity affect water vapour loss?
Higher relative humidity in air will decrease rate of water loss - smaller water vapour potential gradient between air spaces in leaf and outside
62
how does air movement or wind affect the water vapour loss?
Air moving outside of leaf will carry away water vapour that just diffused out of leaf. This will maintain a high water vapour potential gradient.
63
how does light intensity affect water vapour loss?
Stomata open to allow gaseous exchange for photosynthesis – CO2 in/O2 out
64
what is the process of loading of sucrose at source?
Hydrogen ions (H+) are pumped out of the companion cell
This requires ATP
There is a higher concentration of H+ outside the cell
H+ move back into the cell down a concentration gradient using a carrier protein.
Sucrose molecules are carried into the companion cell using the same carrier protein.
It is called a CO-TRANSPORTER.
Sucrose diffuses from the companion cell to the sieve tube element through the plasmodesmata
65
what is the mass flow hypothesis?
- Water potential is lowered in the sieve tube element due to entry of sucrose.
- Water moves in by osmosis.
- Increases hydrostatic pressure.
- Sucrose diffuses out at sink.
- Hydrostatic pressure lower at sink, as water also moves out.
- Hydrostatic pressure gradient produces flow along phloem.
- This is MASS FLOW
66
why is sucrose unloaded at the sink?
Sucrose moves out into the tissues by diffusion. There are two reasons:
It is converted to:
a) glucose to be used in respiration
b) a storage compound e.g. starch
67
how does sucrose in solution move?
by mass flow in the phloem
68
Evidence for sucrose being carried in the phloem
- When a plant is supplied with radioactively labelled carbon dioxide (used in photosynthesis), the labelled carbon appears in the phloem
- Ringing a tree to remove the phloem results in sugars collecting above the ring.
- An aphid feeding on a plant stem can be used to show that the mouthparts are taking food from the phloem.
68
Evidence For Movement of Solutes Through the Phloem By Mass Flow Hypothesis
- Positive pressure inside the phloem
- Concentration of sucrose is higher in sources than sinks
- Movement of sap 10 000x faster than expected by diffusion alone
- An increase in sucrose at sources is followed a little later by an increase in sinks
- Aerobic respiration poisons inhibit translocation of sucrose (inhibits ATP production)
- Companion cells contain lots of mitochondria (ATP production.)
- Phloem sap has a high pH of 8 (accounts for H+ being pumped out)
- High difference in electrical potential across cell membrane suggests more H+ outside than inside
- Reduced flow at night
69
Evidence Against Movement of Solutes Through the Phloem By Mass Flow Hypothesis
What is the role of the sieve plate in this mechanism? Wouldn’t its presence hinder liquid flow?
- Act as support to prevent collapse
- Allow the phloem to seal rapidly if damaged to prevent loss of sucrose and entry of pathogens
- Not all dissolved solutes move at the same speed
Sucrose is delivered at the same rate everywhere You might expect sucrose transport to be quicker to sinks with low sucrose concentrations ( as there would be a higher pressure difference along the phloem
70
how is a potometer set up?
- Cut a shoot underwater
- place the shoot in the tube under water
- full of water/ no extra bubbles
- Make sure it is airtight, using vaseline to seal any gaps
- Dry the leaves of the shoot
- Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water
- Set up the environmental factor you are investigating
- Allow the plant to adapt to the new environment for 5 minutes
- Record the starting location of the air bubble
- Leave for a set period of time
- Record the end location of the air bubble
- Change the light intensity or wind speed or level of humidity or temperature (only one - whichever factor is being investigated)
- Reset the bubble by opening the tap below the reservoir
- Repeat the experiment
- The further the bubble travels in the same time period, the faster transpiration is occurring and vice versa
70
How would you compare the results from two separate experiments?
- set up in the same optimum conditions
- calculate the rate of bubbles per unit area of leaf
- run for the same length of, submerge plants at the same time etc.
