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biology > C9 - Transport in plants > Flashcards

C9 - Transport in plants Flashcards

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1
Q

What are the needs of plant transport systems?

A

-Metabolic demands
-Size
-Small SA:V ratio

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2
Q

What is a dicotyledonous plant

A

Plants that produce seeds containing two cotyledons (organs that act as food stores)

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3
Q

What is the transport system in dicots

A

Vascular system

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4
Q

What is a vascular bundle?

A

Vascular system of herbaceous dicots made up of xylem and phloem tissue

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5
Q

Where are vascular bundles in the stem?

A

Edge

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6
Q

Where are vascular bundles in the root?

A

Centre

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7
Q

Where are vascular bundles in the leaf?

A

Midrib of the leaf

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8
Q

What is a a xylem

A

Plant transport tissue that carries water and minerals from root to other parts of the plant, provides support

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9
Q

What is the structure of xylem

A

-Non-living cells
-Xylem vessels which are long hollow structures made by columns of cells fusing
-Xylem parenchyma packs around xylem, storing food
-Xylem fibres which are long cells with lignified secondary walls to provide mechanical strength

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10
Q

What is the phloem?

A

Plant transport tissue that carries products of photosynthesis to all cells of plant

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11
Q

What is the structure of the phloem

A

-Sieve tube elements
-Many cells joined together forming long, hollow structure
-Perforated walls to form sieve plates

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12
Q

What are companion cells

A

Active cells found next to sieve tube elements that supply the phloem vessels with all their metabolic needs

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13
Q

How are companion cells and sieve tube elements linked?

A

By plasmodesmata- microscopic channels through cellulose walls linking cytoplasm

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14
Q

What is the importance of water in plants?

A

-Turgor pressure provides hydrostatic skeleton supporting plants
-Turgor drives cell expansion
-Loss of water cools plants
-Transport of mineral ions in solution
-Raw material for photosynthesis

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15
Q

How are root hair cells well adapted as exchange surfaces

A

-Microscopic so can penetrate between soil particles
-Large SA:V ratio
-Thin surface layer so short Diffusion distance
-Concentration of solutes in cytoplasm maintains water potential gradient

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16
Q

Why does water move into root hair cell from soil

A

Root hair cell has lower water potential than soil as root hair cell contains different solvents

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17
Q

What are the two different pathways water can take across the root

A

Symplast pathway
Apoplast pathway

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18
Q

What is the symplast pathway?

A

Movement of water and solutes through the cytoplasm of the cells via plasmodesmata by diffusion

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19
Q

How does water move through the symplast pathway

A

Root hair cell takes in water giving it a higher water potential than next door cell so water moves to that cell via osmosis
Process continues until it reaches xylem

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20
Q

What is the apoplast pathway?

A

Movement of substances through the cell walls and cell spaces by diffusion and into the cytoplasm by active transport

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21
Q

How does water move through the apoplast pathway

A

Water fills spaces between loose open network of fibres in cellulose cell wall
As water molecules move into xylem, more molecules move through apoplast due to cohesion
Creates tension causing continuous flow of water

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22
Q

How is water moved in the xylem

A

Water from apoplast pathway reaches endodermis - layer surrounding vascular tissue in roots
Water forced into cytoplasm due to waterproof Caparian strip
Passes through selectively permeable membrane
Joins water in symplast pathway
Water potential of xylem is lower, so water moves through endodermis by endodermis through symplast pathway
Returns to apoplast pathway to enter xylem
Root pressure pushes water up xylem

23
Q

What is root pressure

A

Active pumping of minerals into the xylem by root cells that produces movement of water into the xylem

24
Q

What is evidence for active transport in root pressure

A

-Some poisons affect mitochondria and prevent production of ATP, when applied to roots, there is no energy supply and root pressure disappears
-Increases with rise in pressure
-Oxygen falls, root pressure falls
-Xylem sap exudes from cut stems

25
Q

Photosynthesis

A

CO2 + H2O —> O2 + C6H12O6
Provides food for plants

26
Q

How are leaves adapted for photosynthesis

A

Large SA to catch sunlight
Waxy cuticle coating to make them waterproof

27
Q

How do gasses leave and enter the plant?

A

Stomata

28
Q

What is a stomata

A

Pores in the surface of the leaf that may be opened or closed by guard cells

29
Q

What is transpiration

A

Loss of water vapour from stems and leaves of a plant as a result of evaporation and diffusion

30
Q

What is the transpiration stream

A

Water moves by osmosis through apoplast pathway from xylem to leaf, where it evaporates

31
Q

Cohesion tension theory / transpiration model

A
31
Q

How does the transpiration stream work

A

Water molecules evaporate from the surface of mesophyll cells into air spaces in the leaf
They move out the stomata by diffusion
Loss of water lowers water potential of cell
Water moves up from adjacent cell by osmosis from symplast and apoplast pathways
Repeated across the leaf to the xylem causing water to move out into the leaf
Water molecules form hydrogen bonds with carb in wall of xylem (adhesion) and with other water molecules (cohesion) which creates capillary action effect
Water rises up xylem against gravity in continuous stream to replace water lost ( transpiration pull which causes tension )

32
Q

What is capillary action?

A

Movement of water through xylem due to difference in water potential, cohesion and adhesuom

33
Q

What is cohesion tension theory

A

Best current model explaining movement of water through a plant during transpiration

34
Q

Explain cohesion tension theory

A
35
Q

What is evidence for cohesion tension theory?

A

-When transpiration is at its height, tension in xylem is high, tree shrinks in diameter
-When xylem vessel broken, air drawn in rather than water leaving

36
Q

Why can transpiration be an issue

A

In high intensity sunlight, high rate of gaseous exchange, stomata open, water loss

37
Q

What is the opening and closing of stomata driven by

A

Turgor pressure

38
Q

What are factors affecting transpiration?

A

-Light keeps stomata open for gas exchange
-Humidity
-Temperature increases evaporation and decreases relative humidity of air
-Air movement
- Soil water availability

39
Q

What is translocation?

A

Movement of organic solutes around a plant from source to sink

40
Q

Is translocation active or passive

A

Active process

41
Q

Main sources of assimilates

A

Green leaves and green stems
Storage organs
Food stores in seeds

42
Q

What are sinks in plants

A

Roots that are growing
Meristems

43
Q

What is phloem loading?

A

Soluble products of photosynthesis being moved into phloem

44
Q

Describe how phloem loading works

A

H+ ions actively pumped out of companion cells into surrounding cells, dec conc of H+
H ions pumped back into cell via cotransport of sucrose, inc conc of sucrose in companion cells and sieve elements
Companion cells have infoldings so inc SA for transport of sucrose AND lots of mitochondria to supply ATP
Build up of sucrose in comp cell
Water moves in via osmosis, inc turgor pressure
Water carrying assimilates moves into sieve elements, moves up/down cell to lower pressure (mass flow)

45
Q

What is phloem unloading

A

Solutes diffuse out of phloem/are converted into other substances to maintain conc gradient
Inc water potential of phloem so water moves into surrounding cells via osmosis
Some water drawn into transpiration stream

46
Q

Evidence of phloem loading

A

-Microscopy shows adaptations of companion cells for active transport
-If mitochondria in companion cell poisoned, translocation stops
-Flow of sugar in phloem faster than would be possible by diffusion alone
-Aphids show pressure differences?

47
Q

What is a xerophytes

A

Plants with adaptations to help them survive in dry habitats or in habitats where water is of short supply

48
Q

Examples of xerophytes

A

Conifers
Marram grass
Cacti

49
Q

Adaptations of xerophytes

A

-Thick waxy cuticle: minimise water loss
-Sunken stomata: reduced air movement
-Reduced number of stomata: reduce water loss
-Reduced leaves: lower SA:V ratio
-Hairy leaves: humid microclimate
-Curled leaves: microclimate humid
-Succulent: store water in parenchyma tissue
-Leaf loss: prevent water loss
-Deep tap roots: access water
-Widespread shallow roots: rainwater
-Dorancy, die and drop seeds, storage organs

50
Q

What is a hydrophyte

A

Plants with adaptations to help them survive in wet conditions, submerged or on the surface of water

51
Q

Examples of hydrophytes

A

Water cress
Water lilies
Yellow iris

52
Q

Adaptations of hydrophytes

A

-Thin/no waxy cuticle: don’t need to conserve water
-Many always open stomata on upper surfaces: maximises gaseous exchange
-Reduced structure: water supports leaves
-Wide flat leaves: capture as much light
Small roots: water diffuses into stem
-Large SA of stem, roots underwater: maximises area for photosynthesis and oxygen to diffuse
-Air sacs: enables floating
-Aerenchyma: specialised parenchyma with large air spaces (buoyancy, low resistance internal pathway for transport)

biology (14 decks)

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