Transport in plants Flashcards
1
Q
Reasons why plants need a transport system
A
- high metabolic demands
- large size
- small surface area: volume
2
Q
What is a dicotyledonous plant, differences between herbaceous and arborescent
A
- make seeds containing 2 cotyledons (food stores)
- herbaceous= soft tissue, shorter life cycle
- arborescent= hard, lignified tissue, longer life cycles
3
Q
Structural features of xylem
A
- 1 way transport, upwards
- made up of mainly dead cells
- main feature= xylem vessels, long hollow structures formed of several columns of cells fusing
- contain thick walled parenchyma (contain tannin)
- xylem fibres with lignified walls, provide mechanical strength, contain bordered pits
4
Q
Role of parenchyma and tannin
A
- parenchyma store food and tannin
- tannin provides protection from herbivores
5
Q
What are bordered pits
A
- unlignified areas of xylem fibres
- where water leaves the xylem and moves into other cells
6
Q
Key functions of xylem
A
-transport water and mineral ions
- provide plant support
7
Q
Structural features of phloem
A
- living tissue
- flow 2 way, up and down
- sieve tube elements
- sieve plates
- companion cells
- plasmodesmata
8
Q
What are sieve tube elements and sieve plates
A
- elements= main transporting vessel, made up of cells joined together to form hollow tubes, not lignified
- plates= perforated areas of sieve tube elements, let phloem contents flow through
9
Q
What are plasmodesmata
A
- microscopic channels through the cellulose cell walls
- link cytoplasms of adjacent cells
10
Q
What is turgor, what does it do
A
- pressure as a result of osmosis in plant cells
- provides hydrostatic skeleton to support the stems and leaves
- drives cell expansion- enables plants to force way through concrete
11
Q
How does water move into root hair cells
A
- soil water has a low concentration of dissolved materials so has a high water potential
- cytoplasm and sap of root hair cell contain many solvents so low water potential
- moves into root hair cell by osmosis
12
Q
Adaptations to root hair cells
A
- microscopic size
- each hair has a large sa:vol
- each hair has thin surface layer
- maintain a water potential gradient
13
Q
Features of the symplast pathway
A
-moves through cells by osmosis
- water potential higher in cell than the adjacent one, water moves along until it reaches the xylem
14
Q
Features of the apoplast pathway
A
- water moves through cell walls and intercellular spaces
- water fills spaces between cells, cohesive forces mean water pulls other water molecules with it
15
Q
What is the endodermis
A
-a layer of cells surrounding the vascular tissue of roots
- where water travels to via the symplast/apoplast pathway
16
Q
What is the casparian strip
A
- a band of waxy material that runs around each endodermal cell forming a waterproof layer
17
Q
How water moves into the xylem from the endodermal cells
A
- solute concentration in endodermal cells dilute compared to xylem
- xylem water potential much lower than endodermal cells
- increased rate of osmosis of water flow into xylem, down a water potential gradient
18
Q
Role of root pressure, how is it produced
A
- produced by the active pumping of materials into the xylem
- gives water a small ‘push’ up the xylem
19
Q
Transpiration
A
The loss of water vapour from plant stems and leaves
20
Q
Process of transpiration
A
- C02 needs to move into the leaf, O2 needs to move out for photosynthesis in the light, needs O2 in the dark for respiration
- stomata have to be open for this, and when they are water moves out the leaf by DIFFUSION
21
Q
What is the transpiration stream
A
- the flow of water from being taken up to the roots , transported up the xylem to the leaves, where it evaporates
22
Q
Process of the transpiration stream
A
- water evaporates from the surface of mesophyll cells into air spaces in the leaf, move out stomata into air
- loss of water lowers water potential of cells, causing water to move in from adjacent cells by osmosis
- process repeated across all the cells in the leaf to the xylem
- water molecules form hydrogen bonds with carbs in the xylem vessels- adhesion
- water molecules also have cohesive forces, so form bonds with each
other - cohesive and adhesive forces results in water exhibiting capillary action, resulting in transpiration pull
- water moves in a continuous stream= cohesion-tension theory
23
Q
What is capillary action
A
- process by which water can rise up against a narrow tube against gravity
24
Q
What is the transpiration pull
A
- water is drawn up the xylem in a continuous stream to replace water lost by evaporation/transpiration
- it results in tension in the xylem, which helps water move across roots from soil
25
What is the cohesion-tension theory
- the model of water moving from the soil in a continuous stream up the xylem and along the leaf
26
Evidence for the role of active transport processes in root pressure
- if cyanides applied to plant, root pressure disappears
- root pressure increases with a rise in temperature and vice versa
- if levels of oxygen or respiratory substances fall, root pressure falls
-xylem sap elude from cut end of stems
27
Evidence for the cohesion tension theory
- tree diameters shrink when transpiration highest
- if xylem vessel broken, air is drawn in rather than water leaking out
28
How to measure the rate of water uptake from a potometer
distance moved by air bubble/ time taken to move distance
29
Roles of the stomata for controlling transpiration
- turgor driven process
- when turgor low, asymmetric figuration of guard cells closes stomatal pores
- guard cells pump solutes in by active transport when environment conditions favourable
- cellulose hoops prevent cells swelling in width- extend lengthways
- when water sparse, hormonal signals from roots can trigger turgor loss from guard cells which close the stomatal pore to conserve water
30
Factors affecting transpiration and why
- LIGHT= more stomata open, so more evaporation- higher light intensity means higher transpiration
- RELATIVE HUMIDITY= high humidity lowers rate of transpiration (lower water potential gradient between air and inside of the leaf)
- TEMPERATURE = temperature increase increases the kinetic energy of molecules so more evaporation, or a temperature increase increases the concentration of water vapour (decreases relative humidity), both ways increase diffusion gradient between air inside and outside leaf, so increase the rate of transpiration
- AIR MOVEMENT= each leaf has a still layer of air trapped around it, water vapour accumulates here , increasing water vapour potential , so reduced diffusion gradient- increased rate of transpiration (wind/air movement increases, still air decreases)
31
What is relative humidity
A measure of the amount in water vapour in the air compared to the total concentration of water the air can hold
32
What is glucose converted to to be transported around plants
Sucrose
33
What is translocation
- the transport of materials in a plant from source to sink
34
What are assimilates
- the products of photosynthesis that are transported
35
Main sources of assimilates in plants
- green leaves and stems
- food stores in seeds when the germinate
- storage organs e.g. tubers and tap roots
- (some sources transport up, some down)
36
Main sinks in a plant
- roots growing and/or actively absorbing mineral ions
- meristems that are actively dividing
- parts of the plant that are laying down food stores e.g. developing seeds, fruits or storage organs
