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biology module 3 > transport in plants + exchange surfaces > Flashcards

transport in plants + exchange surfaces Flashcards

1
Q

mass flow definition

A

the bulk movement of fluids down a pressure or concentration gradient

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2
Q

3 reasons why plants need specialised transport systems

A
  • to move products of photosynthesis, water and O2 from source to sink
  • most plants are large and substances have to travel huge distances from root to tip
  • SA:V is very low overall
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3
Q

outline the process of phloem loading

A
  • sucrose is actively loaded into phloem companion cells
  • sucrose can diffuse through plasmodesmata into sieve tube elements
  • as sucrose conc increases in phloem, water potential decreases causing water to move in laterally from xylem via osmosis
  • this increases hydrostatic pressure causing phloem sap to move towards sink via mass flow
  • at the sink sucrose moves back into companion cells + is used up, maintaining conc gradient
  • water rejoins xylem
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4
Q

source definition

A

where a substance is made or stored

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5
Q

sink definition

A

where a substance is needed e.g. roots which cannot photosynthesise, storage organs, growing regions

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6
Q

how is sucrose actively loaded into companion cells

A

a protein in companion cell membrane uses ATP to pump H+ out of cytoplasm into cell wall, then H+ reenters through cotransporter proteins with sucrose

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7
Q

why is sucrose used to transport sugars around plants

A

glucose is too reactive, sucrose isn’t so ensures all glucose makes it to sink where it is needed

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8
Q

what happens when sucrose gets to the cells where it is needed

A

it is usually converted into:
- glucose for respiration
- starch for storage

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9
Q

what is the function of the phloem

A

facilitates the transport of assimilates from source to sink, either up or down the plants

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10
Q

assimilates definition

A

substances made in plants as a result of photosynthesis, e.g. dissolved ions, sugars, etc

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11
Q

how are assimilates transported in phloem

A

assimilates dissolve in water to form sap which moves through phloem

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12
Q

outline the structure of the phloem

A

made of living cells
- sieve tube elements
- companion cells
- phloem fibres / sclerenchyma
- parenchyma

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13
Q

3 functions + structure of sieve tube elements

A
  • main conducting cells so have strong cellulose walls
  • also have a very thin layer of cytoplasm and few organelles which provides more space for assimilates
  • have pores on end plates which allows liquid to easily flow
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14
Q

4 functions + structure of companion cells

A
  • provides metabolic support so linked to sieve tube elements by plasmodesmata
  • also has very dense cytoplasm with many organelles
  • provides ATP for movement so contain many mitochondria
  • also lots of proteins in plasma membrane, allow for the creation of conc gradients + supplying substances to sieve tube elements + receiving substances from neighbouring cells
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15
Q

3 functions + structure of phloem sclerenchyma

A
  • made of dead cells with tapered ends
  • provides structural support so reinforced with lignin in walls which is water proof
  • also prevents wilting but costly to make
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16
Q

3 functions + structure of phloem parenchyma

A
  • storage cells for food, etc so have a dense cytoplasm and a large vacuole
  • thin cellulose wall allows them to closely pack together
  • elongated + tapered + cylindrical
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17
Q

what is the function of the xylem

A

facilitates the transport of water around the plant

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18
Q

transpiration definition

A

the evaporation of water from the xylem out of the leaves

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19
Q

how does water leave the plant

A

through the stomata

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20
Q

how is water loss in plants controlled

A

the stomata can open and close, this is controlled by guard cells (found in pairs)

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21
Q

how do the guard cells control the opening + closing of the stomata

A

through turgor pressure
- epidermal cells surrounding guard cells pump in K+ ions to lower water potential, these can also diffuse back out to increase water potential
- when guard cells fill with water, they swell and become turgid, inner wall next to stomata is thicker than outer wall, causing the thicker wall to bend, opening the stomata
- when guard cells lose water they become flaccid, and stomata close

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22
Q

what is important about guard cell walls

A

the inner wall next to stomata is thicker than the outer wall

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23
Q

4 ways plants conserve water

A
  • waxy cuticle
  • stomata on underside of leaf
  • closeable stomata
  • roots that grow down to water in soil
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24
Q

what 4 main factors affect the rate of transpiration

A
  • humidity
  • temperature
  • light intensity
  • air movement
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25
Q

how does humidity affect the rate of transpiration

A

high air humidity decreases rate
this is because there is more water in the air which decreases the water potential gradient

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26
Q

how does temperature affect the rate of transpiration

A

high temp increases rate
this is because molecules have more kinetic energy, increasing rate of evaporation
also at high temps the concentration of water held by air increases

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27
Q

how does light intensity affect the rate of transpiration

A

high light intensity increases rate
this is because rate of photosynthesis increases so there is more water in guard cells which causes stomata to open so more evaporation can occur

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28
Q

how does air movement affect the rate of transpiration

A

lots of air movement increases rate
this is because wind moves air away from stomata which maintains a steep water potential gradient

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29
Q

outline the structure of the xylem

A

made of dead cells
- vessel cells
- tracheids
- xylem fibres / sclerenchyma
- parenchyma

30
Q

5 functions + structure of xylem vessel cells

A
  • water conducting cells so have open rounded edges and no end plates so mass flow of water in uninhibited
  • also ensures that cohesive/adhesive forces of water aren’t disrupted
  • walls are reinforced with lignin as must withstand high hydrostatic pressure
  • large and multicellular
  • pits in walls allow for lateral movement of water between xylem and phloem
31
Q

functions + structure of tracheids

A
  • water conducting cells
  • must withstand hydrostatic pressure so reinforced with lignin in walls
  • lots of lignin in walls means there is a narrow lumen, maintaining pressure?
  • tapered + closed ends
  • small and unicellular
  • pits in walls allow lateral movement of water between xylem and phloem
32
Q

function of xylem sclerenchyma

A

structural support

33
Q

function of xylem parenchyma

A

storage cells for food, etc

34
Q

an advantage of the xylem being a bundle of very narrow vessels rather than one wide vessel

A
  • greater heights of liquid are achieved due to capillarity
  • smaller tubes mean grater contact with vessel walls so greater adhesive forces
35
Q

outline adaptations of lignin

A

lignin is made up of fibres arranged in a spiral
this provides the plant with flexibility to grow + allows it to cope with external pressures e.g. wind

xylem vessels aren’t completely lignified, which allows stem to flex and move slightly e.g. in the wind

36
Q

what are the 3 pathways water takes through roots

A
  • apoplast pathway
  • symplast pathway
  • vacuolar pathway
37
Q

outline the apoplast pathway

A

water travels through plant cell walls
- this is possible due to the open structure of cellulose
- cohesion means water molecules stick together, so as water is carried away by xylem vessels water molecules move along apoplast pathway

38
Q

outline the symplast pathway

A

water moves through cell cytoplasm and plasmodesmata
- as water potential of root cells > water potential of xylem, water moves down water potential gradient
- this pathway is quite slow as organelles obstruct pathway

39
Q

outline the vacuolar pathway

A

water moves through plasmodesmata and through cortex cell vacuoles
- water travels down water potential gradient from soil to xylem via osmosis

40
Q

why is the water potential in the xylem so low

A

this is because cells in the root endodermis actively pump mineral ions into xylem to decrease water potential, allowing water to passively move towards/in xylem via osmosis - THIS IS ROOT PRESSURE
- this also increases pressure which forces water upwards
- as this is an active process, if respiration is inhibited e.g. by cyanide or lack of O2 root pressure will completely stop

41
Q

what is the casparian strip

A

a band of suberin which runs around the walls in the endodermis
- suberin is a waterproof material
- this means water from apoplast pathway must switch to symplast pathway
- allows water moving inot xylem to be regulated by cell membrane

42
Q

once water has entered the xylem how does it move

A

as a continuous stream due to forces of cohesion + adhesion

43
Q

what 3 processes are involved in the movement of water up the stem of a plant

A
  • root pressure
  • capillarity
  • cohesion-tension theory/capillary action
44
Q

capillarity definition

A

the tendency of liquid in a tube to rise or fall due to surface tension

45
Q

what causes capillarity

A

adhesive forces between xylem vessels and water molecules, which allows water to be pulled up xylem

46
Q

outline cohesion tension theory

A

the cohesive force between water molecules pulls other molecules upwards as in the xylem it is a continuous stream
this puts an inwards pressure on the column of water, called tension
- this tension produces a narrower column of water

47
Q

capillary action definition

A

the process of a liquid flowing in a narrow space in opposition to or without the assistance of external forces like gravity

48
Q

what happens if a xylem vessel is broken

A

the continuous stream of water is broken so no water can be taken up

49
Q

can water still reach the leaves if a xylem vessel is blocked

A

yes
this is because pits in the xylem allow for lateral movement of water, it can travel through phloem

50
Q

vascular bundle definition

A

the arrangement of xylem + phloem tissues + sometimes cambium that form fluid-conducting channels in herbaceous dicots

51
Q

vascular system definition

A

a system of transport vessels in plants + animals

52
Q

what makes up the vascular bundle in stem from outside to in

A

sclerenchyma
phloem
cambium
xylem

53
Q

cambium definition

A

meristematic tissues that can differentiate into xylem and phloem as the plant grows

54
Q

herbaceous definition

A

having a fleshy or soft stem

55
Q

dicotylendonous definition

A

plants that produce 2 seed leaves

56
Q

what is the difference between mono- or di-cotylendonous plant leaves

A

mono - vessels are parallel to the leaves
di - vessels branch out from a central vessel

57
Q

5 reasons why plants need water

A
  • to maintain turgidity of cells
  • to transport nutrients around plant
  • to create an aq environment for reactions to occur
  • to cool plants by evaporation
  • for photosynthesis
58
Q

from outside to inside what tissues are present in a dicot root section

A

epidermis + root hair cells
exodermis
cortex
endodermis
pericycle
phloem
xylem

59
Q

what is the pericycle

A

the part of the root where lateral roots grow, made up of meristematic tissue

60
Q

what is the function of the endodermis

A

contains a ring of suberin which is impermeable to water - casparian strip

61
Q

what is the function of the cortex

A

stores a large amount of starch

62
Q

what shape is the xylem tissue

A

star shaped

63
Q

what is the function of root hairs

A

uptake of water from roots, lots of root hairs have a high SA:V which increases rate of water uptake by osmosis

64
Q

what must water potential of soil be relative to roots for water uptake to occur

A

soil water potential must be less negative / greater than root water potential
remember pure water has a water potential of 0

65
Q

how does the plant ensure water potential of roots is more negative/less than soil

A

mineral ions from soil are actively pumped into root

66
Q

1 example of what plants use glucose for

A

respiration

67
Q

1 example of what plants use lipids for

A

cell membranes

68
Q

1 example of what plants use proteins for

A

enzymes for reactions

69
Q

1 example of what a plant uses nucleic acids for

A

DNA replication

70
Q

do all plant cells contain chloroplasts

A

no
root cells don’t, as there is no light underground so cannot photosynthesise

71
Q

what 3 conditions could cause stomata to close

A
  • high temperatures
  • high CO2 concentration
  • water stress
72
Q

how are palisade cells adapted for their function

A

contain lots of chloroplasts + packed tightly together to maximise light absorption for photosynthesis

biology module 3 (7 decks)

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