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biology > transport in plants (9) > Flashcards

transport in plants (9) Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

what are dicotyledonous plants

A

these are plants that make 2 cotyledons (food stores) in their seeds.

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1
Q

what are the 3 reasons for a transport system in plants/ why do multicellular plants need transport systems

A

high metabolic demands - underground parts of plant don’t photosynthesise so they need waste substances removed and o2 and glucose transported to them. mineral ions need to be transported to all cells to make proteins.
size - bigger, taller plants need efficient transport systems to move substances up and down plant.
SA - plants have a large SA: volume ratio so they cant solely rely on diffusion to supply cells w everything

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2
Q

what are cotyledons

A

food stores

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3
Q

what are the 2 types of dicotyledonous plants. and give an example of each

A

herbaceous - soft tissues, short life cycle (little plants)
woody - lignified tissues, long lived (trees)

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4
Q

how are the xylem and phloem arranged in the stems, roots, leaves

A

vascular bundles

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5
Q

where in the stem are the vascular bundles located and why are they there

A

around the edge to give support and strength

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6
Q

where in the roots are the vascular bundles located

A

in the middle to help plant withstand tugging strains from the wind blowing the stem and leaves

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7
Q

where are the vascular bundles in the leaves and why there

A

in the midrib of a dicot leaf. helps support structure of leaves.

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8
Q

in a vascular bundle where are the phloem and xylem located

A

phloem on outside and xylem on inside

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9
Q

function of xylem tissue

A

structural support and transports water + minerals up plant.

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10
Q

what is the function of the spiral band of lignin in the xylem vessel

A

spiral bands allow vessels to elongate, thus allowing tissues to expand w/o breaking the vessel walls

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11
Q

what is the function of the bordered pits in the vessel

A

they act as channels for the transport of h20 +minerals between the adjacent cells

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12
Q

is their lignin in the phloem

A

no

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13
Q

are their bordered pits in the phloem

A

no

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14
Q

what is plasmodesmata

A

gaps in cell wall between companion cells + sieve tube elements

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15
Q

what feature would not be found in mature xylem vessels

A

cytoplasm

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16
Q

xylem vessels contain lignin carbohydrate. what is this for

A

allows water to pass into adjacent vessels

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17
Q

a feature of the sieve tubes

A

contains perforated cross walls

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18
Q

what roles does water have within plants

A

turgor pressure - provides a hydrostatic skeleton to support stems + leaves.
evaporation- keeps plants cool.
turgor drives cell expansion -
the force that enables plant roots to force their way thru tarmac + concrete.
transport - mineral ions + products of photosynthesis are transported in aqueous solutions
raw material - h20 is raw material for plants

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19
Q

adaptations of the root hair cell

A

they are microscopic so can penetrate easily between soil and branches.
large SA: V ratio
thin surface layer for fats diffusion =osmosis
the concentration of solutes in the cytoplasm of root hair cells maintains a water potential gradient between the soil water and cell

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20
Q

talk about soil water

A

has a very low concentration of dissolved minerals so has a high water potential. while RHCs have a high conc of solvents so the water potential in rhc is lower this drives more water into the RHCs by osmosis

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21
Q

what is another reason for the lignin in the xylem

A

lignin reinforces the xylem so it doesn’t collapse under the transpiration pull

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22
Q

how are sieve plates formed and what are they for

A

in the areas between the cells the cell walls become perforated = sieve plates.
they let the phloem contents flow through

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23
Q

as large pores appear in the phloem what happens

A

the tonoplast, nucleus and other organelles break down. so mature phloem cells have no nucleus

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24
Q

after the water is in the RHC how does it travel to the xylem. what are the 2 pathways water moves thru the plant to the xylem

A

apoplast + symplast pathways

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25
Q

explain symplast pathway

A

symplast is the continuous cytoplasm of the living plant cells that is connected thru the plasmodesmata - by osmosis.
the RHC has a higher water potential than the next cell along cos pf water diffusing in from the soil making the cytoplasm more dilute, so water moves from the RHC into the next cell by osmosis.
this process repeats cell to cell until the water has reached the xylem.
as water leaves a RHC the water potential of cytoplasm drops again, this maintains a a steep water potential gradient

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26
Q

explain apoplast pathway

A

this is the movement of water through cell walls + intercellular spaces. water fills the spaces between the open network of fibres in the cellulose cell wall. as water molecules move into the apoplast more are pulled behind due to cohesive forces between the water molecules. the pull from water moving up into the xylem and from the cohesive forces creates a tension that makes a continuous flow of water through the xylem w little resistance

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27
Q

describe pathway of water after reaching the root

A

the water moves across the route via symplast or apoplast pathway until it reaches endodermis.
the water runs around the apoplast strip, the apoplast strip is made of suberin so the water is forced into the cytoplasm (symplast pathway). to get into cytoplasm the water crosses the selectively permeable cell surface membranes. the endodermal cells move mineral ions into the xylem by active transport, this lowers the water potential of the xylem , lower than of the endodermal cells. creates root pressure. this increases the rate of water moving into the xylem by osmosis down a conc gradient from the endodermis down the symplast pathway

28
Q

what is the endodermis

A

a layer of cells that surrounds xylem + phloem

29
Q

what is suberin and what does it prevent

A

a strip of waxy material that runs around each of the endodermal cells - the apoplast strip. it prevents the movement of water thru the cell walls (apoplast pathway)

30
Q

1st evidence for active transport

A

poisons (cyanide) affect the mitochondria, so the root pressure disappears. root pressure needs energy, mitochondria produce ATP . no ATP no energy.

31
Q

2nd evidence for active transport

A

root pressure increases with a rise in temp, this suggest chemical reactions are involved cos increasing temp increase chemical reactions (partucles move faster and collide more often, so chemcal reaction rate increases)

32
Q

3rd evidence for active transport

A

if levels of oxygen or respiratory substrate fall root pressure falls. oxygen is needed for respiration

33
Q

4th evidence for active transport

A

root pressure and transpiration are independent of eo - when water transpiration is low xylem sap can still be seen exuded from the tips of leaves.

34
Q

what is ttranspiration

A

loss of water. when the stomata open for gas exchange, water moves out of the leaf by diffusion

35
Q

why does stomata close at night (dont forget some stomata stay open allthetime)

A

reduces water loss. no photosynthesis at night so demand for o2 is low

36
Q

what do guard cells do

A

when conditions are optimal they pump in solutes by active transport which increases the turgor.

37
Q

2 features of guard cells

A

guard cells have cellulose rings around them, so they cannot swell but can lengthen.
inner wall not as flexible so the cells curve becoming bean shaped, creating a pore.

38
Q

when water is scarce what happens with the guard cells

A

a hormonal signal is sent from the roots and trigger turgor loss in the guard cells thus closing the stomata

39
Q

what are the 5 stages of the transpiration stream

A

1 - water enters root by osmosis
2 - water transported up xylem up to leaves
3 - water moves by osmosis and diffusion across membranes along the apoplast pathway from the xylem
4 - water evaporates from freely permeable cellulose cell walls of the mesophyll cells into the air spaces
5 - water vapour moves out of the leaves thru the stomata down a concentration gradient/diffusion gradient

40
Q

what is cohesion tension theory

A

driving force for water movement up from the roots to the leaves

41
Q

adhesion + cohesion = ?

A

water exhibiting capillary action, the process by whuch h20 can rise up a narrow tube agianst gravity

42
Q

what is the transpiration pull

A

where water is drawn up xylem in a continuos stream to replace h20 lost by evaporation

43
Q

evidence for cohesion tension theory

A

changes in tree diameter - when transpiration as at its height during the day tension in xylem is at a highso the tree shrinks in diameter. at night are the lowest rates of transpiration so diameter increases.
breaking a xylem vessel - cut a flower stem, put in water and air will be drawn into the xylem rather than water as the continuous stream of water molecules held tg by cohesive forces has been broken

44
Q

limitations to transpiration?

A

in high intensity light, rate of photosynthesis is fast so stomata must beopen to supply the co2 but then the plant will lose alot of water, in some case too much water is lost
water availability is often limited

45
Q

we measure transpiration with a …

A

potometer

46
Q

rate of water uptake calculation (potometer experiment)

A

rate of water uptake = distance moved by air bubble/time taken for air bubble to move that distance

47
Q

for the potometer experiment where should the stem be cut

A

underwater so no air bubbles go into the stem

48
Q

a control of this experiment?

A

all joints must be sealed w waterproof jelly to ensure any water loss measured is as a result of transpiration from the stem/leaves

49
Q

5 factors affecting transpiration?

A

light, humidity, temp, air movement, soil water availability

50
Q

how does light affect transpiration

A

increased light intensity=increase photosynthesis. increased light intensity= more stomata open for gas exchange, this increases the rate of water vapour diffusing out + therefore increasing the evaporation from the surfaces of the leaf

51
Q

how does humidity affect transpiration

A

high humidity lowers rate of transpiration cos of reduced water vapour potential gradient between the inside of the leaf + outside air. dry air has opposite effect + increases rate of transpiration.

52
Q

how does temperature affect transpiration

A

increase temp increases KE of water molecules, so increases rate of evaporation from spongy mesophyll cells into air spaces of the leaf. higher temp increases conc of water vapour that the external air can hold before becoming saturated (so decreases its relative humidty and its water potential)

53
Q

how does air movement affect transpiration

A

each leaf has a layer of still air around it trapped and little hairs on the leaf to decrease air movement close to the leaf. water vapor that diffuses out of the leaf accumulates here, so the water potential around the stomata increases in turn reducing the diffusion gradient. lomg period of still air will reduce transpiration

54
Q

hoe does soil water availability affect transpiration

A

if soil is dry the plant will be under water stress and so raate of evaporation will be reduced

55
Q

when diffusion gradient is increased what else increases

A

rate of transpiration

56
Q

what is translocation

A

the transport of organic compounds ususally in the form of sucrose (produced in leaves in paliisade mesophyll))

57
Q

why is sucrose transported instead of glucose

A

increases energy storage. its an efficient energy transfer

58
Q

transport occurs from a source to a sink, true or false

A

true

59
Q

what is a source

A

regions of plant that produce assimilates by photosynthesis or form storage materials (leaves)

60
Q

what is a sink

A

regions of a plant that require assimilates to supply their metabolic needs (roots, fruits)

61
Q

what is the phloem loading

A

the movement of sucrose into the phloem to be transported. its an active process, requires ATP

62
Q

what are the 2 main ways that sucrose is loaded

A

symplast and apoplast route

63
Q

how are companion cells adapted for this loading

A
  • many infoldings
  • many mitochondria
    see kerboodle for further detail
64
Q

what is phloem unloading

A

kerboodle pg 209

65
Q

evidence for mass flow in phloem

A

kerboodle pg 209 for further detail
phloem sap can be exuded from hole usig aphids.
flow of sugars 10000x faster than if just diffusion was responsible
if mitochondria of companion clells are poisones w cyanide translocation stops
microoscopy allows us to see adaptations of the companion cells

66
Q

what is apoplast route

A

kerboodle pg 208

67
Q

2 adaptations of sieve tubes that enable mass flow

A

theyre stacked and their end walls (sieve plates) have lrg pores thru which their cytoplasm can flow

68
Q

how are assimilates loaded into the phloem

A

biology (19 decks)

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