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biololgy M3 > transport in plants > Flashcards

transport in plants Flashcards

1
Q

what is the function of xylem tissue

A
  • transport water and mineral ions in solution up the plant (roots to leaves)
  • gives support
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2
Q

what is the function of the phloem

A
  • transports sugars up and down the plant
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3
Q

what do the xylem and phloem make up

A
  • vascular bundle
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4
Q

why do plants need transport systems

A
  • multicellular
  • large so small SA:V
  • high metabolic rate
  • direct diffusion would be too slow to meet metabolic needs
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5
Q

what is the xylem vessel

A
  • part of the xylem tissue that transports water and ions
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6
Q

what is the structure of the xylem vessel

A
  • long, tube-like structures formed from cells joined end to end
  • no end walls
  • dead cells, no cytoplasm
  • walls are thickened with lignin
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7
Q

how is the structure of the xylem vessel adapted to its function

A
  • no end walls means the flow of water through the xylem is uninterrupted
  • the lignin means the walls won’t collapse inwards
  • water and ions move into and out of the vessels through small pits in the walls where there’s no lignin
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8
Q

what is the structure of the root

A
  • the xylem is in the centre surrounded by the phloem to provide support for the root
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9
Q

what is the structure of the stem

A
  • xylem and phloem are near the outside to provide the ‘scaffolding’ that reduces the bending
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10
Q

what is the structure of the leaf

A
  • xylem and phloem make up a network of veins which support the thin leaves
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11
Q

what are sieve tube elements

A
  • living cells that form the tube
  • they are joined end to end to form sieve tubes
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12
Q

what are sieve plates

A
  • end of the tubes which have holes in them to let solutes through
  • have no nucleus and few organelles
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13
Q

what are companion cells

A
  • they are in every sieve tube element
  • carry out the living functions for sieve cells e.g. provide energy for active transport
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14
Q

what is the method of plant dissection

A
  • use a scalpel to cut a cross section of a plant, as thin as possible
  • use tweezers to place the sample in water
  • put the sample in a dish containing stain and leave for a min
  • e.g. TBO which stains the lignin in the xylem walls blue-green to see the position of the xylem vessel
  • rinse off the sample in water and mount onto a slide
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15
Q

what is transpiration

A
  • consequence of gas exchange needed for photosynthesis
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16
Q

how is transpiration a consequence of gas exchange

A
  • a plant needs to open its stomata to let in CO2 so that it can produce glucose by photosynthesis
  • this also lets out water, water moves down the water potential gradient out of the leaf when the stomata open
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17
Q

what are hydrophilic plants

A
  • live in aquatic habitats
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18
Q

what are hyrophilic plants adapted for

A
  • low oxygen levels
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19
Q

how are hyrdophilic plants adapted

A
  • air spaces in the tissues help plants to float and act as a store of oxygen
  • air spaces in roots allow oxygen to move from floating down to parts that are underwater
  • stomata only present on the upper surface of floating leaves (maximum gas exchange)
  • flexible leaves and stems prevent damage from water currents
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20
Q

what are xerophytic plants

A
  • adapted to live in dry climates
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21
Q

how does marram grass slow down transpiration

A
  • sunk in pits so they’re sheltered from the wind
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22
Q

how do xerophytic plants reduce the water potential gradient between leaf and air

A
  • layers of hair on the epidermis traps moist air around the stomata
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23
Q

what does marram grass do to reduce their surface area

A
  • in hot or windy conditions they roll their leaves to trap moist air
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24
Q

how does light affect the rate of transpiration

A
  • the lighter it is the faster the rate of transpiration
  • the stomata open when it gets light so CO2 diffuse into the leaf for photosynthesis
25
Q

how does temperature affect the rate of transpiration

A
  • higher the temperature the faster the rate of transpiration
  • warmer water molecules have more energy so they evaporate from the cells inside the leaf faster
  • this increases the water potential gradient between inside and outside of the leaf making water diffuse out of the leaf faster
26
Q

how does humidity affect the rate of transpiration

A
  • the lower humidity the faster the rate of transpiration
  • air around the plant is dry
  • the water potential gradient between leaf and air is increased
27
Q

how does wind affect the rate of transpiration

A
  • windier it is the faster the transpiration rate
  • lots of air movement blows away water molecules from around the stomata, this increases the water potential gradient
28
Q

what is a potometer used for

A
  • estimate transpiration rates
  • measures water uptake by a plant
  • water uptake by a plant is directly related to water loss by the leaves
29
Q

what is the method of the potometer practical

A

1- cut a shoot under water (to prevent air from entering the xylem) and at a slant to increase the SA
2- assemble the potometer in water and insert the shoot underwater (no air can enter)
3- remove apparatus from the water but keep the end of the capillary emerged in a beaker of water
4- check apparatus is water and air tight
5- dry the leaves and allow the shoot to acclimatise and then shut the tap
6- remove the end of the capillary tube from the beaker of water until one air bubble has formed and then place the end back in the water
7- record starting of the position of air bubble
8- start a stopwatch and record distance moved by the air bubble per unit time

30
Q

what does the rate the air bubble has moved mean

A
  • rate of transpiration
31
Q

how many variables that affect transpiration should be implenated at a time

A
  • only 1
  • all other conditions must be kept constant
32
Q

how does water enter a plant

A
  • drawn into the root hair cells by osmosis
33
Q

where does water pass through the plant after the root hair cells

A
  • through the root cortex to reach the xylem
34
Q

how does water travel from roots to leaves

A
  • water moves from areas of higher water potential to low (down a water potential gradient)
  • soil around roots has a high water potential and leaves have a low water potential, water moves down the water potential gradient (roots to leaves)
35
Q

what are the 2 different pathways that water travels through the roots into the xylem

A
  • apoplast pathway (cell wall)
  • symplast pathways (cytoplasm)
36
Q

how does water travel through the symplast pathway

A
  • travels through the cytoplasm
  • the cytoplasm of neighbouring cells connect through plasmodesmata
  • water moves via osmosis
37
Q

how does water travel via the apoplast pathway

A
  • the cell walls are absorbent and water can simple diffuse through and pass through the spaces between them
  • moves from areas of high hydrostatic pressure to low (example of mass flow)
38
Q

what happens when water in the apoplast pathway reaches the endodermis cells in the root

A
  • its path is blocked by a waxy strip in the cell walls called the casparian strip
  • water then has to take the symplast pathway and go through a cell membrane which are partially permeable (control whether substances in the water get through to the symplast pathway)
39
Q

how does cohesion and tension help water transport

A
  • helps water move up plants against the force of gravity
  • water evaporates from the leaves at the ‘top’ of the xylem (transpiration)
  • this forms a tension which pulls the water into the leaf
  • when some water molecules are pulled to the leaf others follow (cohesion)
  • whole column of water in the xylem from roots to leaves
40
Q

how does water enter the stem

A
  • through root cortex cells
41
Q

how does adhesion help water transport

A
  • water molecules are attracted to the walls of the xylem vessels
  • helps water to rise up through the xylem vessels
42
Q

what do xylem vessels do in terms of transport of water

A
  • transports water all around the plant
43
Q

what happens in the leaves in water transport

A
  • water leaves the xylem and moves into the cells
  • water evaporates from the cell walls into the spaces between cells in the leaf
  • when the stomata open the water diffuses out of the leaf into surrounding air
44
Q

what is the first stage of the mass flow hypothesis

A

1- active transport is used to actively load the solutes into the sieve tubes of the phloem at the source, this lowers the water pot inside the sieve tubes so water enters the tubes from the xylem and companion cells by osmosis, this creates a high pressure inside the sieve tubes at the source end of the phloem

45
Q

what is the second stage of the mass flow hypothesis

A

2- at the sink end, solutes are removed from the phloem to be used up, this increases the water pot inside the sieve tubes, so water also leaves the tubes by osmosis, this lowers the pressure inside the sieve tubes

46
Q

what is the third stage of the mass flow hypothesis

A

3- results in a pressure gradient from the source to sink
- this pushes solutes along the sieve tubes to where they’re needed

47
Q

what is active loading used for

A
  • move substances into the companion cells from surrounding tissues
  • and move substances from the companion cells into the sieve tubes against a concentration gradient
48
Q

how does active loading transport substances

A
  • concentration of sucrose is usually higher in companion cells than surrounding tissues
49
Q

what is ATP used for

A
  • supply the initial energy needed for the active transport of H+ ions out of the cell and into surrounding tissue cells
50
Q

how does ATP actively transport H+ ions out of the cell and into surrounding tissue to transport sucrose

A
  • sets up a concentration gradient, more H+ ions in the surrounding tissue than in companion cell
  • H+ ion binds to a co-transporter protein in the companion cell (cc) membrane and re-enters the cc (going down conc gradient)
  • sucrose molecule binds to co-transporter protein at the same time
  • the H+ ions movement used to move sucrose molecule into the cell against the gradient
  • sucrose molecules are then transported out of the companion cells and into sieve tubes by the same process
51
Q

what is translocation

A
  • the movement of assimilates (dissolved substances)
  • moves substances from sources (where a substance is made) to sinks (where a substance is used up)
52
Q

where does translocation happen

A
  • phloem
53
Q

what is the source for sucrose

A
  • usually the leaves
54
Q

what is the sink for sucrose

A
  • other parts of the plant especially the food shortage organs and the meristems in roots, stems and leaves
55
Q

what parts of sucrose can be source and sink

A
  • during growing season it’s transported from the roots (source) to the leaves (sink)
56
Q

how do enzymes maintain a concentration gradient

A
  • changing the dissolved substances at the sink, this makes sure there’s a lower concentration at the sink than the source e.g. in potatoes sucrose is converted to starch in the sink
57
Q

what happens at other sinks with enzymes

A
  • break down sucrose into glucose and fructose for use by the plant
58
Q

why is there always a lower concentration of sucrose at the sink

A
  • makes sure there’s a constant supply of new sucrose reaches the sink from the phloem

biololgy M3 (1 decks)

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