Transport in plants Flashcards

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1
Q

why do plants need a transport system?

A

small surface area to volume ratio
relatively large – high metabolic rate
exchange of substances by direct diffusion is too slow
need transport system as roots can obtain water and minerals but not all sugars
leaves can produce sugars but not get all water from air

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2
Q

what does the xylem and phloem do?

A

xylem tissue- transports water and soluble minerals upwards
phloem tissue- moves sugars up or down

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3
Q

where is the location of the xylem and phloem in the roots?

A

they are in the centre to provide support for the root as it pushes through the soil

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4
Q

where is the location of the xylem and phloem in the stem?

A

near the outside to provide ‘scaffolding’ that reduces bending
found together in vascular bundles

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5
Q

where is the location of the xylem and phloem in the leaves?

A

make-up a network of veins which support the thin leaves

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6
Q

what are the adaptations of xylem vessels?

A

hollow dead cells
no end walls- water passes up through the middle easily
pits (small holes) in the sides of the walls allow water and minerals to move into neighbouring cells
strengthened with lignin
ring or spiral structures allow flexibility

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7
Q

what are the adaptations of phloem tissue?

A

composed of sieve tube elements and companion cells
sieve tube elements have very few organelles- (no nucleus) thin layer of cytoplasm
At either end they have a sieve plate- lots of holes to allow solutes to pass through
companion cells have organelles to support themselves and the sieve tube elements

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8
Q

what is osmosis?

A

movement of water down a water potential gradient across a partially permeable membrane

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9
Q

what is the symplast pathway?

A

water enters the root hair cell via osmosis
travels through the cortex via the living parts of the cells (cytoplasm) until it reaches the xylem vessels
water moves down a water potential gradient
cytoplasms are connected via plasmodesmata

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10
Q

what is the apoplast pathway?

A

water is absorbed in the cell walls of the root hair cell
travels through the cortex via the non-living parts of the cell (walls and spaces between them) until it reaches the endodermis layer
moving via mass flow from an area of high hydrostatic pressure too low hydrostatic pressure

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11
Q

what is the casparian strip?

A

waxy waterproof layer

stops the water from travelling any further

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12
Q

what is the movement of water from roots to leaves called?

A

the transpiration stream

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13
Q

why does transpiration happen?

A

it happens as a result of gas exchange
a plant needs to open it stomata to let in carbon dioxide so it can produce glucose by photosynthesis
it also lets water out – higher concentration of water inside the leaf than in the air outside so water moves out of the leaf down the water potential gradient when the stomata open

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14
Q

how is water transported from the soil to the leaves?

A

minerals actively transported into root hair cells, lowering water potential in root hair cells
water moves from soil into root hair cells through osmosis, down WP gradient
water moves from cell to cell down WP gradient via symplast OR apoplast pathway
in symplast pathway, water moves through cytoplasm and between cells through plasmodesmata
in apoplast pathway, water moves between spaces in cellulose cell wall
at the casparian strip in the endodermis, water is forced out of apoplast and into symplast pathway
minerals are actively transported from endodermis cells to xylem, lowering WP gradient in xylem
water vapour leaves stomata by diffusion down concentration gradient
water moves up xylem via mass flow / capillary action (cohesive and adhesive)
water is pulled by xylem because of tension created by loss of water vapour via transpiration

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15
Q

why isn’t transpiration rate the same as rate of water uptake?

A

some water is used for photosynthesis
some water is used to create turgor pressure
some water is also produced by respiration

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16
Q

what are the factors affecting rate of transpiration?

A
light intensity
temperature
air movement
humidity
number of stomata
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17
Q

how does light intensity affect rate of transpiration?

A

increasing light intensity- more stomata will open, rate of photosynthesis is greater so more gas exchange occurs
rate of transpiration increases until all stomata are open- allows more water to evaporate out of the leaf
rate of transpiration stays constant

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18
Q

how does temperature affect rate of transpiration?

A

increasing temperature- the faster water vapour molecules will move because they have more kinetic energy
water evaporates from leaf faster
WP inside the leaf increases compared to outside (steeper WP gradient) so water diffuses out of leaf faster
rate of transpiration increases

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19
Q

how does air movement affect rate of transpiration?

A

the windier it is, the faster the transpiration rate
lots of air movement blows away water molecules from around the stomata
increases the WP gradient (maintains steep gradient) which increases the rate of transpiration

20
Q

how does humidity affect the rate of transpiration?

A

the more humid the air, the more water vapour there is
this reduces the WP gradient between inside and outside of leaf
water molecules diffuse more slowly, decreasing the rate of transpiration

21
Q

how do you measure rate of transpiration?

A

using bubble potometer

a bubble is incorporated in the setting up so that the movement of water can be tracked

22
Q

how do you use a potometer?

A

1) cut shoot underwater to prevent air being introduced into the xylem
2) insert shoot into potometer underwater so no air can enter system
3) check system is air and water tight
4) dry both sides of the leaves
5) allows shoot to acclimatise- rate will be constant
6) introduce an air bubble into the capillary tube
7) record start position of bubble, start timer
8) record distance and time taken for the bubble to move
9) use these values to calculate rate (D/T)
10) only alter one variable at a time - keep other factors which affect transpiration constant
11) repeat to eliminate anomalous result
12) calculate mean result and/or carry out statistical analysis

23
Q

what are the limitations of using a potometer?

A

cutting plant shoot may damage plant

plant has no roots so no resistance to water being pulled

24
Q

how do you calculate transpiration rate?

A

rate = volume / time
you need to calculate the volume of a cylinder ( length of capillary tube)
V=πr2h

25
Q

what are xerophytes?

A

plants that have adapted to live in very dry, hot and breezy conditions e.g. cacti and marram grass

26
Q

what is marram grass?

A

lives on sand dunes
conditions are harsh as water drains quickly and can often be salty
windy conditions

27
Q

describe the adaptation ‘rolled up leaves’

A

stomata tend to be on lower epidermis
rolling up leaves traps moist air near the stomata
reduces WP gradient between the leaf and the air so transpiration greatly reduces
reduces air movement around stomata

28
Q

describe the adaptation ‘thick cuticle’

A

some transpiration occurs through waxy cuticle
cuticle is impermeable to water
thick - Less water can escape via evaporation

29
Q

describe the adaptation ‘stomata in pits or grooves’

A

traps moist air near to leaf surface
reduces WP gradient
reduces air movement near stomata

30
Q

describe the adaptation ‘dense spongy mesophyll’

A

this leaves few air spaces

therefore there is less SA for evaporation of water

31
Q

what is cacti?

A

live in deserts

have additional features to overcome harsh conditions

32
Q

describe adaptations that cacti have

A

store water in their stems- they become fleshy and swollen
stem is often ribbed or fluted so that it can expand when water is available
leaves are reduced to spines- reduces surface area of the leaf and thus transpiration
used to protect the plant from predation
green stems- for photosynthesis
widespread roots-take advantage of any rain that does fall

33
Q

what are hydrophytes?

A

plants adapted to living in water or where the ground is very wet

34
Q

what are hydrophytes’ problems?

A

getting oxygen to submerged tissues is problematic
needs to keep afloat
needs to keep leaves in sunlight

35
Q

what are hydrophyte adaptations?

A

thin/ no waxy cuticle- not needed
large air spaces in the leaf- keeps the leaves afloat so that they can absorb sunlight
always open stomata on upper epidermis- they are exposed to air to allow gaseous exchange
stem has large air spaces- helps with buoyancy, allows oxygen to diffuse quickly to the roots for aerobic respiration

36
Q

what is translocation?

A

move substances (assimilates) from the source to the sink by mass flow in the phloem

37
Q

what does translocation mainly transport and why?

A

sucrose

it’s soluble like glucose but it is metabolically inactive so it won’t get used up during transport

38
Q

what is the source and the sink?

A

source of a substance is where it’s made (high concentration)
sink is the area where it’s used up (low concentration)

39
Q

what happens at the source during translocation?

A

active transport is used to actively load the solute into the sieve tubes of the phloem
lower the WP inside the sieve tube
water enters tube by osmosis from xylem and companion cells
creates a high pressure inside the sieve tubes at the source end of the phloem

40
Q

what happens at the sink during translocation?

A

solutes are removed from the phloem to be used up- happens by diffusion because solutes are at a higher concentration in the phloem than in the sink
removal of solute increases the water potential inside the sieve tubes
water leaves the tube by osmosis
this lowers the pressure inside the sieve tubes

41
Q

what happens during the flow?

A

there is a pressure gradient from the source end to the sink end
gradient pushes solutes along sieve tubes towards the sink
when they reach the sink, solutes will be used (e.g. in respiration) or stored (e.g. as starch)

42
Q

describe the relationship between concentration of sucrose and rate of translocation

A

the higher the concentration of sucrose at the source, the higher the rate of translocation

43
Q

what is active loading?

A

used at the source to move substances into the companion cells from surrounding tissues and from companion cells into sieve tubes against concentration gradient
concentration of sucrose usually higher in companion cells than the surrounding tissue cells and higher in sieve tube cells than companion cells

44
Q

how is sucrose moved?

A

using active transport and co transport proteins

45
Q

what are co transport proteins?

A

a type of carrier protein that binds to 2 molecules at a time

46
Q

describe the steps of active loading

A

in the companion cell, ATP is used to actively transport H+ ions out of the cell and into surrounding tissue cells
sets up a concentration gradient- more H+ ions in the surrounding tissue then in companion cell
H+ ion bind to co transporter protein in the companion cell membrane and re-enter the cell (down the concentration gradient)
sucrose molecule binds to the cold transport proteins at the same time
movement of H+ ions is used to move the sucrose molecules into the cell against it’s concentration gradient
sucrose molecules are then transported out of companion cell and into sieve tubes using the same process