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biology module 3 exchange and transport > chapter 9 transport in plants > Flashcards

chapter 9 transport in plants Flashcards

1
Q

what are the three main reasons why multicellular plants need transport systems?

A

•metabolic demands- moving substances around the plant.
•size- move substances large distances
•SA:V- leaves have high ratios but because of the overall size of lost plants they have a relatively small SA:V.

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2
Q

what is a dicotyledonous plant (dicots)?

A

they make seeds that contain two cotyledons (organs which act as food stores for the developing embryo plant and form the first leaves when the seed germinates).

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3
Q

what is a herbaceous dicot?

A

they have soft tissues and relatively short life cycles (leaves and stems that die down at the end of the growing season)

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4
Q

what is a woody (arborescent) dicot?

A

they have hard, lignified tissues and a long life cycle

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5
Q

what are the two types of vascular tissue in herbaceous dicots?

A

xylem and phloem

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6
Q

describe the stem of a herbaceous plant.

A

epidermis on outside, then cortex, then vascular bundles containing xylem(inner) and phloem(outer), parenchyma (packing tissue) on the inside

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7
Q

describe the root of a herbaceous dicot.

A

exodermis with root hair appendages on outside, epidermis, cortex, endodermis, then vascular bundles containing xylem as a star, circles of phloem and cambium containing meristems

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8
Q

deacribe the transaction of a leaf from a herbaceous dicot.

A

palisade mesophyll as darker green spots, midrib of leaf making up main body, vascular bundle sticking out containing xylem on upper side and phloem on lower side

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9
Q

describe the structure of xylem.

A

made of dead cells with no organelles and thick lignified walls, long hollow tubes made by several columns of cells fusing together end to end.

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10
Q

what is the function of xylem vessels?

A

•transport of water and mineral ions
•support

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11
Q

what is the function of the spirals of lignin running around the lumen of the xylem?

A

helps to reinforce xylem vessels so that they don’t collapse under transpiration pull

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12
Q

what does xylem parenchyma store?

A

food and tanmin deposits

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13
Q

what is tanmin?

A

bitter, astringent tasting chemical protecting plant from herbivores

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14
Q

what is the structure of the phloem?

A

living unlignified tissue made of sieve tube elements joined end to end to form a long hollow tube. cells have no nucleus and are just hollow filled with phloem sap

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15
Q

what are sieve plates?

A

perforated walls between cells letting phloem contents flow through.

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16
Q

what is the function of the phloem?

A

transports food in the form of organic solutes (sucrose, sugars, amino acids) and it can transport these in multiple directions

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17
Q

what are companion cells?

A

cells linked to sieve tube elements by many plasmodesmata that have all their organelles, they are very active cells and function as support for sieve tubes.

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18
Q

what are plasmodesmata?

A

microscopic channels through the cellulose cell wall linking the cytoplasm of adjacent cells

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19
Q

what are the supporting tissues to phloem?

A

fibres, sclereids, cells with extremely thick cell walls

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20
Q

what are some uses of water in plants?

A

•photosynthesis
•loss by evaporation cools plant
•mineral ions and products of photosynthesis transported in aqueous solution
•very strong hydrostatic pressure to drive cell expansion

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21
Q

what is a root hair cell?

A

exchange surfaces in plants where water is taken into the plant. it is a long thin extension found near the root tip

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22
Q

how are root hairs adapted as exchange surfaces?

A

•microscopic size allows them to penetrate easily between soil particles
•large SA:V
•thin surface layer
•conc of solutes in cytoplasm maintains water potential gradient

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23
Q

what are the three pathways by which water can move across the root?

A

•apoplast
•symplast
•vacuolar

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24
Q

what is the symplast?

A

continuous cytoplasm of living plant cells connected through plasmodesmata

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25
what is the symplast pathway?
the movement of water and solutes through the cytoplasm of cells via plasmodesmata by simple diffusion
26
why do root hair cells have higher water potentials than the next cell along?
it is caused by the water diffusing from the soil making the cytoplasm more dilute
27
what is the apoplast?
cell walls and intercellular spaces
28
what is the apoplast pathway?
movement of substances through cell walls and intercellular spaces by diffusion and into cytoplasm by active transport
29
describe movement of water into the xylem.
•water moves across the root in apoplast and symplast pathways until it reaches the endodermis •the endodermis has the casparian strip which contains suberin (a waxy waterproof material) •water in the apoplast pathway can go no further and it is forced into the cytoplasm of the cell joining the water in the symplast route •the endodermal cells move mineral ions into the xylem by active transport decreasing the xylems water potential causing water to be moved into the xylem by osmosis •once inside the vascular bundle water returns to the apoplast pathway to enter the xylem itself and move up the plant
30
what is root pressure?
the active pumping of minerals into the xylem by root hair cells that produces a movement of water into the xylem by osmosis
31
what are some pieces of evidence for the role of active transport in root pressure?
•some poisons affect mitochondria and ATP therefore there is no more energy supply. when scientists apply these poisons root pressure disappears •root pressure rises with a rise in temperature and falls with a fall in temperature •if levels of oxygen fall so does root pressure
32
what is a waterproof waxy cuticle important for leaves?
prevents the leaf cells losing water rapidly and constantly by evaporation
33
what are stomata?
microscopic pores in the surface of a leaf or stem that are opened and closed using guard cells
34
what are guard cells?
cells that open and close stomatal pores, controlling gaseous exchange and water loss in plants
35
how does carbon dioxide move from the air into the leaf and oxygen out of the leaf?
diffusion down concentration gradients
36
what is transpiration?
loss of water vapour from stems and leaves of a plant as a result of evaporation from cell surfaces inside the leaf and diffusion down a concentration gradient out through stomata
37
why do at least some stomata need to be open all the time?
in the day plants take in CO2 for photosynthesis and at night they need to take in O2 for respiration
38
what is the transpiration stream?
movement of water through a plant from the roots until it is lost by evaporation from the leaves
39
how does the transpiration stream occur?
•water moves by osmosis across membranes and by diffusion in the apoplast pathway from the xylem through the cells of the leaf •in the leaf it evaporates from the freely permeable cell walls of mesophyll cells into the air spaces •water vapour then moves into external air through stomata along a diffusion gradient
40
how does transpiration stream occur passively?
•water is lost from mesophyll cells which lowers the water potential of them •water moves into them from adjacent cells •this is repeated across the leaf to the xylem •water moves out of the xylem by osmosis into the cells
41
what is capillary action?
process by which water can rise up the narrow xylem vessels against the force of gravity
42
what is the transpiration pull?
water being drawn up the xylem in a continuous stream to replace water being lost by evaporation
43
how does adhesion occur in the xylem vessels?
water molecules form hydrogen bonds with the carbohydrates in the walls of the xylem
44
how does cohesion occur in the xylem?
water molecules form hydrogen bonds with each other so tend to stick together
45
what is tension and how is it created in the xylem?
•state of being stretched tight •it is created by the transpiration pull
46
what is the cohesion-tension theory?
the model of water moving in a continuous stream up the xylem and across the leaf
47
what are some pieces of evidence for the cohesion tension theory?
•changes in diameter of trees- in day transpiration is high so tension is too so diameter is a bit smaller •when a xylem vessel is broken- air is drawn into the xylem rather than water leaking out •if a xylem vessel is broken plants can no longer move water up the stem as a continuous steam because cohesive forces have been broken
48
what type of process is guard cells opening and closing?
turgor driven
49
how do guard cells open?
•when conditions are favourable guard cells pump in solutes by active transport increasing their turgor •cellulose hoops prevent it from swelling in width so they extend lengthways •inner wall is less flexible than outer wall so cells become bean shaped and open pore
50
how do guard cells close stomata?
when water becomes scarce hormonal signals from the roots can trigger turgor loss causing them to close the pore and conserve water
51
what are the factors affecting transpiration?
•light intensity •relative humidity •temperature •wind speed/air movement •soil-water availability
52
how does light intensity affect transpiration?
•in the light photosynthesis can happen so more stomata open for gas exchange •this increases the amount of water vapour lost
53
how does relative humidity affect transpiration?
•higher the humidity of air the lower the water potential gradient •this lowers rates of transpiration
54
how does temperature affect rate of transpiration?
•increases kinetic energy of water molecules therefore increases rate of evaporation from spongy mesophyll cells into air spaces of leaves •also increases conc of water vapour that external air can hold before becoming saturated so decreases humidity •both factors increase diffusion gradient and increase rate of transpiration
55
how does air movement affect rate of transpiration?
•water vapour accumulates in still air pockets around leaf •this reduces water potential gradient •therefore high wind increases transpiration and still air decreases it
56
how does soil water availability affect transpiration?
•less water available means plant is under water stress meaning transpiration rate is reduced
57
what is the most common sugar transported by phloem?
sucrose
58
what direction do phloem transport organic compounds?
from source to sink
59
what is a source in plants?
regions of a plant that produce assimilates by photosynthesis or from storage materials e.g green leaves and storage organs
60
what is a sink in plants?
regions of a plant that require assimilates to supply their metabolic needs e.g. growing roots and fruits and meristems
61
what is translocation?
movement of organic solutes around a plant in the phloem. it is an active process
62
what are assimilates?
products of photosynthesis that are transported around a plant e.g sucrose and amino acids
63
what are the two steps of translocation?
active loading and mass flow
64
describe active loading.
•companion cells pump H+ ions into the source tissue via active transport •this increase in conc of H+ ions causes them to diffuse back into companion cells by facilitated diffusion along with sucrose molecules by co transport •sucrose conc increases in companion cell •sucrose moves down conc gradient across plasmodesmata into sieve tubes by simple diffusion
65
what are 2 adaptations of companion cells?
•they have many infoldings in membrane to give increased SA for transport of sucrose •lots of mitochondria to supply the ATP needed for transport pumps
66
describe mass flow.
•loading sucrose into the sieve tubes decreases the water potential meaning water moves by osmosis from the xylem to sieve tubes •volume of liquid at source end increases also increasing hydrostatic pressure at source end of sieve tube •at sink end the sucrose leaves the sieve tube increases the water potential •water moves out of the sieve tube into the xylem by osmosis reducing hydrostatic pressure •therefore there is a hydrostatic pressure gradient from source to sink which is much faster than diffusion
67
what are some pieces of evidence that support the theory of translocation?
•advances in microscopy allow us to see the adaptations off the companion cells for active transport •if mitochondria of companion cells are poisoned translocation stops •flow of sugars in phloem is ~10k x faster than diffusion alone suggesting active process •aphids have shown that there is a positive pressure gradient from source to sink
68
what is a xerophyte?
plants with adaptations to enable them to survive in dry habitats with short supplies of water
69
what is a hydrophyte?
plants with adaptations to enable them to survive in very wet habitats such as being submerged
70
what are 3 examples of xerophytes?
•marram grass •conifers •cacti
71
what does a thick waxy cuticle do to reduce water loss?
reduces transpiration through cuticle. e.g. holly/evergreen plants
72
what does sunken stomata do to reduce water loss?
stomata being located in pits reduces air movement producing a microclimate of still humid air reducing water potential gradient which reduces transpiration. e.g. marram grass, cacti.
73
what does does reduced leaves do to reduce water loss?
greatly reduces SA reducing rate of transpiration. e.g. conifers
74
what do hairy leaves do to reduce water loss?
create microclimate of still moist air reducing water potential gradient. e.g. cacti spines
75
what do curled leaves do to reduce water loss?
confines all atoms to within a micro environment reducing diffusion of water vapour. e.g. marram grass
76
what do succulents do to reduce water loss?
store water in specialised parenchyma tissue in stems and roots. e.g. desert cacti and aloe
77
what are some root adaptations to reduce water loss?
•long tap roots to access water from deep groundwater flow/aquifers. •widespread shallow roots to collect rainwater
78
what are 3 examples of hydrophytes?
•water lillies •yellow iris •duckweeds
79
what does many always open stomata do to encourage water loss?
maximises gaseous exchange also maximises transpiration. some expamples like water lillie’s need them on the upper surface as they float on water
80
why do hydrophytes have reduced structure in plant?
water supports leaves and flowers
81
why do hydrophytes have wide flat leaves?
to capture as much sunlight as possible as water loss doesn’t matter for them
82
why do hydrophytes have lots of air sacs?
allows leaves and flowers to float on water
83
what is aerenchyma and why do hydrophytes have it?
•it is specialised parenchyma (packing) tissue that forms in leaves stems and roots. it has many large air sacs formed by apoptosis •it makes the leaves and stems more buoyant and forms a low resistance internal pathway for movement of substances

biology module 3 exchange and transport (3 decks)

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