2.3 adaptations for transport (plant) Flashcards
1
Q
what is the function of the root hair cell?
A
- absorb water, to balance out the water loss out of the stomata
2
Q
how are the root hair cells adapted to their function?
A
- large surface area for the absorption of water via osmosis
- thin cell walls (short diffusion pathway)
3
Q
how do the root hair cells absorb the water?
A
- its vacuole has a high solute potential (cell sap) and therefore there is a concentration gradient between the high watee potneital in the soil and water is taken up
4
Q
what does the xylem transport?
A
- water and minerals
5
Q
what three ways can water be transported?
A
apoplast ( through the cell wall)
symplast ( through cytoplasm and plasmodesmata)
vacuolar (from vacuole to vacuole)
6
Q
what is the endodermis?
A
- surrounding the xylem
- contains a waterproof casparian strip, preventing further transport via apoplast
6
Q
what is the structure of the xylem?
A
- xylem tissue in the centre
- surrounded by the endodermis
just goes down
7
Q
what is the function of the phloem?
A
transport the products of photosynthesis (amino acids/sucrose)
goes up and down
8
Q
how is the casparian strip waterproof?
A
- impregnated with super in (waterproof and structure) and therefore makes a casparian strip
9
Q
how does the casparian strip prevent apoplast transport?
A
it is waterproof and therefore the apoplastic transport of water transport needs to enter the symplast pathway instead
10
Q
how does root pressure lead to the uptake of water?
A
- salts are actively pumped into the vascular tissue, FROM THE ENDODERMIS making the xylems water potential negative
- therefore water enters the xylem through osmosis
- this is root pressure
11
Q
how are minerals taken up?
A
- these are taken up by active transport ( as large and polar) then the minerals move along the apoplast pathway in the transpiration stream
-once reached the casparian strip, cannot move via apoplast pathway and have to enter via active transport - then they move into the symplastic pathway against the concrete gradient to by-pass the casparian strip
12
Q
what is the apoplast pathway?
A
water moves through the cell walls
13
Q
what is the symplastic pathway?
A
water moves through the cytoplasm and plasmodesmata
14
Q
what is the vacuolar pathway?
A
water moves from vacuole to vacuole
15
Q
where does the xylem take water?
A
transports water and minerals from the root to the leaves
16
Q
where does phloem transport products of photosynthesis?
A
- from the leaves to other parts of the plant
17
Q
what cells are the xylem made up of?
A
dead cells form a tube
- vessels
- tracheids
- fibres
- xylem parenchyma
18
Q
what is the function of the vessels and tracheas in the xylem?
A
- form a system of impermeable tubes through which water can travel
- give the cell strength/support
- they are insoluble due to ligin in their cell walls
19
Q
what is the xylem vessels main function?
A
- to transport water and mineral salts
20
Q
where are xylem found in the stem?
A
peripheral vascular bundles, gives them flexible support and resistance to strain
21
Q
where are the xyklem found in the leaves?
A
- vscular tissue arranges into a network of veins
22
Q
where is the xylem found in the root?
A
- central arrangement as it helps with any stresses
- anchors the plant
23
Q
what is a dicotyledon stem?
A
a stem with a vascular bundle in the centre
24
what is transpiration?
- the loss of water from the surface of the leaves by evaporation through evaporation through the stomata
25
what is transpiration pull?
as water molecules leave the cells in the leaf, it pulls out other water molecules
26
why does transpiration pull occur?
cohesion-tension theory -
- due to the large cohesive forces between the water molcules
- due to the adhesive properties of the water against the hydrophilic lining of the xylem vessel
27
what is the rate of transpiration affected by?
- temperature
- humidity
- air movement
- light intensity
27
how does temperature affect the transpiration rate?
- rise in temperature provides kinetic energy for the movement of water molecules
- increased rate of evaporation from the walls of the mesophyll
- if stomata is open, it speeds rate of diffusion of water vapour into the surrounding air
- water potential of surrounding air gets lower as temp increases so it can hold more transpired water
28
how does humidity affect the rate of transpiration?
- greater the humidity, the lower the rate of transpiration
- this is because the air inside the leaf is saturated with water vapour and the outside air has less water vapour
therefore when the stomata is open water vapour rapidly diffuses out of the leaf
29
how does air movement affect the rate of transpiration?
- water vapour accumulates around the leaf surface which decreases the water potential gradient - therefore a decreased transpiration rate
- movement of the surrounding air removs the accumulated layer of saturated air and increased the water potential gradient - higher rate of transpiration
29
how does light intensity affect rate of transpiration?
- higher the light intensity leads to stomata opening which increases the rate of transpiration
30
how is a potometer set up?
- cut shoot under water
- keep leaves dry
- set up apparatus underwater
- ensure airtight
30
how is the sieve tube adapted for the movement of products?
- the sieve plates have pores which allows for multi-directional flow of the products
- thin cytoplasmic filaments with no large organelles which allows the products of photosynthesis to flow with no obstruction
- plasmodesmata allows for the transport of ATP into the sieve tube from companion cells
30
what is a cytoplasmic strand?
- these extend from one sieve cell to the next through the pores in the sieve plate
- contains phloem protein
30
what are the four types of cells in the phloem tissue?
- sieve tubes
- companion cells
- phloem fibres
- phloem parenchyma
30
what is the function of the sieve tube?
- transport of products of photosynthesis
- formed of sieve elements and placed end-to-end
- the sieve cells have pores which are the sieve plates they products go through this
- no nucleus/organelles
30
what are the products of photosynthesis used for after being translocated in the phloem?
used for growth or storage
30
what is translocation?
- where the products of photosynthesis are transported in the phloem away from the leaf
30
how can the rate of transpiration be measured?
- potometer which measures the rate of water absorption by the air bubble movement (highlights the volume of water taken up by the shoot - air released as it is taken up )
31
what is a companion cell?
- connected to the sieve tub via the plasmodesmata
- contains all organelles (nuclei, rough ER, mitochondria..)
- makes proteins and ATP for the sieve tube
31
what is a form of evidence to support the translocation of products in the phloem?
- ringing experiments which removed cylinders of bark ( just the outside) which removed the phloem
32
how did the presence of sucrose prove that translocation of the products of photosynthesis was occuring?
- sucrose was found above the cut ring which proves that phloem is found on the outside of the vascular bundle
- as the tissues swell due to the decreased water potential in the phloem so water moves into the phloem cells from the xylem
- no sucrose below the ringed line
32
where is the xylem/phloem located in the stem?
xylem - periphery
phloem - in the centre
32
where is the phloem located in the vascular bundle?
on the outside, smaller
32
what is a sink?
- any region of the plant that uses the products of photsynthesis ( storage...)
32
where is the xylem/phloem located in the root?
xylem - in the centre
phloem - periphery
32
how do aphids support translocation in the phloem?
- aphids have a stylet ( needle-like mouthpart) which insert into the sieve tube
- the stylet can be cut off and the sap produced form the stylet contains products of photosynthesis
-proving translocation occurs in the sieve tubes
32
how do autoradiographs prove the translocation in the phloem?
- carbon dioxide labelled with radioactive carbon and given to an illuminated plant leaf
-the radioactive carbon is fixed to the sucrose (produced by photosynthesis)
- the sucrose then gets translocated to other parts of the plant and can be traced by autoradiography
- then, the leaves and sink tissues are placed and analysed for the presence of radioactivity and proving that sucrose goes up and down
33
what direct does transport move in the phloem?
- biodirectional (goes both ways)
34
what is the mass flow theory?
this is main theory to explain translocation
- there is passive flow of sugars from the phloem of the source leaf (highest concentration) to the sink (lowest concentration)
35
explain the mass flow theory?
- sugars made at the source (leaf), the water potential gets more negative and water moves into the cells by osmosis
- therefore, the hydrostatic pressure increases and forces the products of photosynthesis into the sieve tubes (they are now loaded for translocation)
- therefore the products of photosynthesis are forced along the sieve tubes by the high pressure water moving to lower pressures
- hydrostatic pressure is lower at the sink as sugars are stored as starch hence reducing the water potential/pressure
- water passes into the xylem to be transported back to the source
36
what are the arguements against the mass flow theory?
- the rate of transocation is too fst for it to be a passive process
- sieve plates have pores which stop flow
- does not give a role for the companion cells and for them to be producing ATP
36
what are the three classifications of plants according to water availability?
hydrophytes
xerophytes
mesophytes
37
what is a hydrophyte?
- water plants
- they grow submerged or partially submergd in water
- ( e.g. waterlily)
37
what is a xerophyte?
- plants live in conditions very sparse of water
- e.g. marram grass in sand dunes
37
what is a mesophyte?
- adequate water supply
- these are the majority of plants
- close stomata during night to prevent water loss
- underground orans survive winter
38
how is the waterlily (hydrophyte) specialised?
SWAX
- no/thin waxy cuticle as water loss is not a problem
- stomata on upper side as underside is underwater
- larger air spaces to help with buoyancy and oxygen reserves
- poorly developed xylem as abundance of water
38
how is marram grass specialised? (xerophytes)
- rolled leaves from shrinking of the cell wall to reduce the area exposed to air to reduce transpiration and conserve water
- stiff, interlocking hairs to conserve water vapour and reduce the graident for transpiration
- thick waxy cuticle to reduce water loss by evaporation
- highly developed xylem with lignin impregnated
39
what is the structure of the guard cells?
- ends of guard cells are thinner as it expand and become turgid when water moves in - CLOSE STOMATA
- middle part is thicker as to not allow water to diffuse in
40
describe how sugars move down the phloem?
- leaves photosynthesise and make sugars which get loaded into the phloem/sieve tube
- water potential falls in the phloem
- the sugars are drawn down from high pressure to low pressure in sieve tubes
41
where is lignin?
the cell walls of the xylem, making it impermeable and so the contents don’t leave and the surrounding cells are dead
42
what is the role
of the casparian strip?
to control where water enters (symplastic pathway)
43
how do you find the rate?
y2 - y1
divorced by
x2 - x1
