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BIO A-level > Transport in Plants > Flashcards

Transport in Plants Flashcards

1
Q

Compare 5 features in xylems and phloems

A

Xylem:
-Dead cells
-Bordered pits
-Lignin
-Transport water & MI
-Direc: up

Phloem:
-Living cells
-No bordered pits
-No lignin
-Transport sucrose, AA, organic compounds
-Direc: up & down

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2
Q

Define the term water potential

A

Tendency of water to move from 1 location to another across PPM

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3
Q

What water potential does pure water have?

A

0 kPa

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4
Q

Is the water potential in the xylem higher or lower than pure water?

A

Lower

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5
Q

What is the pressure exerted by water inside a cell called?

A

Hydrostatic

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6
Q

Explain how a root hair cell changes the water potential inside the cell, including how this affects osmosis

A

↓ ψ by ↑ing no. MI to ↑ osmosis

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7
Q

Describe the apoplast pathway

A

-Water passes through spaces in cell walls & between cells
-Doesn’t pass through plasma membrane so moves by MASS FLOW
-Carries MI

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8
Q

Describe the symplast pathway

A

-Water enters cytoplasm & passes through plasmodesmata to ADJACENT CELLS
-Water moves by osmosis

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9
Q

Describe the vacuolar pathway

A

Same as symplast but water can also pass through vacuoles in cell

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10
Q

Describe the movement of water into the xylem

A

-Ions actively transported into xylem
-ψ ↓ -> water moves into xylem by OSMOSIS (from symplast)
-Water also pulled from apoplast pathway (water may move by apoplast pathway after Casparian strip)

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11
Q

Name what the casparian strip is made of

A

Suberin

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12
Q

Describe how water leaves the xylem near the leaf and exits via transpiration

A

-Xylem -> spongy mesophyll tissue via apoplast pathway (mesophyll cell walls)
-Also symplast pathway (cytoplasm & plasmodesmata of spongy mesophyll cells). Osmosis
-Evaporates from surface of spongy mesophyll cells
-Water vapour diffuses down its conc gradient through open stoma out of plant
-Water also moves via osmosis into palisade mesophyll layer

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13
Q

Describe how water is transported up the xylem

A

-Transpiration stream: water lost by transpiration causing transpiration pull
-Pull creates tension (hence lignin needed)
-Cohesion forces strong enough to hold water molecules in long column
-This is cohesion tension theory

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14
Q

Define the term transpiration

A

-Loss of water vapour
-From upper parts of leaf (particularly stomata)
-By evaporation
-Down conc gradient

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15
Q

State 10 factors affect the rate of transpiration. Split these into 5 environmental and 5 plant factors

A

Environmental
-Light intensity
-Temp
-Humidity
-Wind
-Water availability
Plant
-No. stomata
-Stomata distribution
-No. leaves
-Leaf SA
-Cuticle thickness

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16
Q

Explain how light intensity affects the rate of transpiration

A

-↑ intensity = ↑ rate
-↑ stoma open -> ↑ light absorbed by chloroplast for ↑ photosynthesis

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17
Q

Explain how temperature affects the rate of transpiration

A

-↑ temp = ↑ rate
-Water molecules have ↑ KE -> ↑ rate of diffusion out of stomata

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18
Q

Explain how the relative humidity affects the rate of transpiration

A

-↑ humidity = ↓ rate
-For water to evaporate need ψ gradient between air in leaf & atmosphere
-↑er humidity -> ↑er ψ of air -> ↓er ψ gradient
-So rate = ↓er in ↑ humidity

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19
Q

Explain how the air movement (wind) affects the rate of transpiration

A

-↑ wind = ↑ rate
-In still air, humid air diffuses out of each stomata
-Air movement replaces humid air w/ drier air
-Maintains ψ -> ↑ rate

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20
Q

Explain how water availability affects the rate of transpiration

A

-↑ availability = ↑ rate
-↑ stoma open to take in water
-↑ water vapour loss

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21
Q

Define the term biotic and abiotic

A

-Biotic: Living
-Abiotic: Non-living

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22
Q

State 6 precautions that need to be taken when using a potometer

A

-Cut shoot underwater & keep there -> avoid air bubbles in xylem which would break continuous column of water
-Assemble apparatus under water -> avoid air bubbles
(these 2 are same mark)
-Cut shoot at slant
-Seal all joints w/ vaseline -> making it as airtight as possible
-Use healthy plant w/ xylem intact -> Ensures transpiration stream functions
-Air tight seals -> avoids air bubbles

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23
Q

State the function of the reservoir in a potometer

A

Resets air bubble

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24
Q

Define the term xerophyte

A

Plants evolved to live in dry habitats & ↓ water availability

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25
Give 2 examples of xerophytes
-Cacti -Marram grass
26
Define the term hydrophytes
Plants evolved to live in water
27
Give an example of a hydrophyte
Water lily
28
Describe and explain 4 adaptations of cacti
-Leaves reduced to spines -> ↓ SA -> ↓ stomata -> ↓ evaporation & diffusion -> ↓ transpiration -Succulents -> store water in parenchyma (packing tissue) -Green stem for photosynthesis -> it's ok that they have smaller SA bc ↑ temp speeds up enzyme reaction & ↑ light intensity = ↑er rate photosynthesis -Widespread roots -> Absorb rainwater before water drains out
29
Describe and explain 5 adaptations of marram grass
-Dense spongy mesophyll -> ↓ air spaces ->↓ evaporation-> ↓ diffusion-> ↓ transpiration -Rolled leaf -> trap water vapour-> ↓ water potential gradient ->↓ transpiration -Thick waxy cuticle -> ↓ evaporation from leaf surface -Leaf hairs -Sunken stomata
30
Describe and explain 4 adaptations of water lilies
-Large flat leaves -> ↑ SA -> ↑ photosynthesis -Stomata = on upper epidermis -> ↑ gas exchange -Large air spaces in leaf -> ↑ gas exchange -> float -↑ large air spaces in leaf stem -> float
31
What is translocation?
-Movement of assimilates throughout plant -From source to sink -Involving active loading of sucrose -& mass flow of sap
32
What is a source? Give an example
-Place in plant where assimilates produced & loaded into phloem -photosynthesising green leaves and stems
33
What is a sink? Give an example
-Place of active growth/storage where assimilates needed -Meristematic tissue (bc cell division)
34
Describe the process of active loading of sucrose
-H+ ions pumped out of companion cells by active transport (w/ E from hydrolysis of ATP) -H+ & sucrose move by facilitated diffusion through a co-transport -Sucrose moves from companion cell to sieve tube element (simple diffusion) through plasmodesmata
35
In active loading, where does energy come from to pump hydrogen ions
Hydrolysis of ATP
36
In active loading, where is there a higher concentration of hydrogen ions?
Out of the companion cell
37
Why is pH higher in the companion cell than in the surrounding tissue?
-↑er conc H+ ions out of companion cells compared to tissue bc they're pumped out
38
Explain the stages of translocation from active loading at the source to unloading at the sink
-Sucrose = actively loaded -Means H+ ions pumped out of companion cell, H+ & sucrose co-transported into companion, sucrose diffuses into sieve tube -Lowers ψ in sieve tube near source cells -Water moves into phloem from xylem by OSMOSIS -This increases hydrostatic P in phloem at source -Sap moves to lower hydrostatic P -Sucrose diffuses into companion cell -> transported to sink cells -Increases ψ in sieve tube at sink -Water leaves phloem by OSMOSIS into xylem -Keeps hydrostatic P low at sink
39
Explain why multicellular plants need transport systems
-Move substances to and from individual cells quickly -Low SA:V -> can't rely on diffusion -Remove waste products -High metabolic rate
40
Describe the structure of a vascular bundle
-Root hair -Epidermis -Cortex -Endodermis -Phloem -Xylem
41
Describe the structure of the vascular system
-Xylem tube -Phloem tube --Sieve tube elements --Companion cells
42
Function of all parts of the vascular system
43
What is transpiration a consequence of?
Gas exchange
44
Define the term transpiration stream
-Movement of water from roots -Through stem -Out of plant into air
45
a) Explain why the xylem is surrounded by lignin and b) why this lignin is spiralled
a) -Reinforces xylem vessels -So don't collapse under transpiration pull b) -So it's flexible -e.g. for wind
46
Describe 5 structures of the xylem including their functions
-Thick cell wall containing lignin -> prevents collapse & adhesion of water -Non-lignified pits (gaps in cell wall) -> lateral flow of water to leave to adjacent vessels or living parts -Hollow tube w/ no cytoplasm -Remains of end wall where it has been lost -Xylem parenchyma -> store food
47
State where ATP is released from for active loading in the phloem
Mitochondria in companion cell
48
Describe the structure of the phloem
-Companion cell -Sieve tube element -Sieve plate -Plasmodesmata between companion cells and sieve tube (NOT between companion cells)
49
State 4 control variables for the potometer experiment?
-Same age -Same species -Same nutrients -Same soil
50
Describe the effect that number of stomata has on the rate of transpiration
More stomata = Higher rate of transpiration
51
Explain the effect that cuticle thickness has on the rate of transpiration
-Thicker cuticle = less water loss (waterproof layer) -Reduced rate of evaporation from top of leaf
52
Explain the effect that the surface area of the leaves has on the rate of transpiration
-Higher SA=more stomata -Faster rate of diffusion -Faster rate of transpiration
53
Explain the effect that the number of leaves has on the rate of transpiration
-Higher SA=more stomata -Faster rate of diffusion -Faster rate of transpiration
54
Explain the effect that stomata distribution has on the rate of transpiration
-If more are on top of leaf higher rate of diffusion & evaporation -Bc upper surface more exposed to environment
55
State 3 adaptations of guard cells and explain why they are useful
-Cell wall thicker on 1 side than the other (thicker on side facing pore) Causes cell to bend & open stomata -Mitochondria Generates ATP for active transport -Vacuole Take up water -> become turgid
56
Describe the function of lignin in plants
-Provide strength/support -Prevent collapse due to pressure from transpiration -Make waterproof -Create hollow tube -> continuous column of water + limit lateral flow of water -Adhesion between water molecules & wall
57
Explain the purpose of carrying out replications in an experiment
-Results more reliable -Help identify anomalies
58
Explain why potometers only provide an estimate for the rate of transpiration
-Measures water uptake -But not all water is lost -> some used in photosynthesis/making cells turgid
59
State 4 adaptations of sieve tubes that enable mass flow to occur
-Elongated elements -Elements joined end to end (form column) -Sieve plates -Little cytoplasm -No nucleus/few organelles
60
Why would a student take readings from 8 different leaves in an experience designed to test the rate of transpiration in plants
To assess repeatability of data
61
Explain why starch is not transported in the sap
-Not soluble -Cannot enter/leave cells -Does not affect osmosis
62
Suggest why sucrose is a more suitable transport molecule than glucose
-Sucrose less likely to diffuse out of sieve tubes -Non-reducing -> less reactive (/likely to be used in resp by mitochondria for E) (no immediate reactions occur as it is being transported) -It's loading/unloading is controlled w/ transport proteins
63
State the process by which water moves up the xylem and sucrose up the phloem
Mass flow

BIO A-level (13 decks)

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