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biology module 3 > Transport in plants > Flashcards

Transport in plants Flashcards

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1
Q

Reasons why plants need a transport system

A
  • high metabolic demands
  • large size
  • small surface area: volume
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2
Q

What is a dicotyledonous plant, differences between herbaceous and arborescent

A
  • make seeds containing 2 cotyledons (food stores)
  • herbaceous= soft tissue, shorter life cycle
  • arborescent= hard, lignified tissue, longer life cycles
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3
Q

Structural features of xylem

A
  • 1 way transport, upwards
  • made up of mainly dead cells
  • main feature= xylem vessels, long hollow structures formed of several columns of cells fusing
  • contain thick walled parenchyma (contain tannin)
  • xylem fibres with lignified walls, provide mechanical strength, contain bordered pits
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4
Q

Role of parenchyma and tannin

A
  • parenchyma store food and tannin
  • tannin provides protection from herbivores
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5
Q

What are bordered pits

A
  • unlignified areas of xylem fibres
  • where water leaves the xylem and moves into other cells
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6
Q

Key functions of xylem

A

-transport water and mineral ions
- provide plant support

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7
Q

Structural features of phloem

A
  • living tissue
  • flow 2 way, up and down
  • sieve tube elements
  • sieve plates
  • companion cells
  • plasmodesmata
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8
Q

What are sieve tube elements and sieve plates

A
  • elements= main transporting vessel, made up of cells joined together to form hollow tubes, not lignified
  • plates= perforated areas of sieve tube elements, let phloem contents flow through
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9
Q

What are plasmodesmata

A
  • microscopic channels through the cellulose cell walls
  • link cytoplasms of adjacent cells
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10
Q

What is turgor, what does it do

A
  • pressure as a result of osmosis in plant cells
  • provides hydrostatic skeleton to support the stems and leaves
  • drives cell expansion- enables plants to force way through concrete
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11
Q

How does water move into root hair cells

A
  • soil water has a low concentration of dissolved materials so has a high water potential
  • cytoplasm and sap of root hair cell contain many solvents so low water potential
  • moves into root hair cell by osmosis
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12
Q

Adaptations to root hair cells

A
  • microscopic size
  • each hair has a large sa:vol
  • each hair has thin surface layer
  • maintain a water potential gradient
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13
Q

Features of the symplast pathway

A

-moves through cells by osmosis
- water potential higher in cell than the adjacent one, water moves along until it reaches the xylem

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14
Q

Features of the apoplast pathway

A
  • water moves through cell walls and intercellular spaces
  • water fills spaces between cells, cohesive forces mean water pulls other water molecules with it
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15
Q

What is the endodermis

A

-a layer of cells surrounding the vascular tissue of roots
- where water travels to via the symplast/apoplast pathway

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16
Q

What is the casparian strip

A
  • a band of waxy material that runs around each endodermal cell forming a waterproof layer
17
Q

How water moves into the xylem from the endodermal cells

A
  • solute concentration in endodermal cells dilute compared to xylem
  • xylem water potential much lower than endodermal cells
  • increased rate of osmosis of water flow into xylem, down a water potential gradient
18
Q

Role of root pressure, how is it produced

A
  • produced by the active pumping of materials into the xylem
  • gives water a small ‘push’ up the xylem
19
Q

Transpiration

A

The loss of water vapour from plant stems and leaves

20
Q

Process of transpiration

A
  • C02 needs to move into the leaf, O2 needs to move out for photosynthesis in the light, needs O2 in the dark for respiration
  • stomata have to be open for this, and when they are water moves out the leaf by DIFFUSION
21
Q

What is the transpiration stream

A
  • the flow of water from being taken up to the roots , transported up the xylem to the leaves, where it evaporates
22
Q

Process of the transpiration stream

A
  • water evaporates from the surface of mesophyll cells into air spaces in the leaf, move out stomata into air
  • loss of water lowers water potential of cells, causing water to move in from adjacent cells by osmosis
  • process repeated across all the cells in the leaf to the xylem
  • water molecules form hydrogen bonds with carbs in the xylem vessels- adhesion
  • water molecules also have cohesive forces, so form bonds with each
    other
  • cohesive and adhesive forces results in water exhibiting capillary action, resulting in transpiration pull
  • water moves in a continuous stream= cohesion-tension theory
23
Q

What is capillary action

A
  • process by which water can rise up against a narrow tube against gravity
24
Q

What is the transpiration pull

A
  • water is drawn up the xylem in a continuous stream to replace water lost by evaporation/transpiration
  • it results in tension in the xylem, which helps water move across roots from soil
25
Q

What is the cohesion-tension theory

A
  • the model of water moving from the soil in a continuous stream up the xylem and along the leaf
26
Q

Evidence for the role of active transport processes in root pressure

A
  • if cyanides applied to plant, root pressure disappears
  • root pressure increases with a rise in temperature and vice versa
  • if levels of oxygen or respiratory substances fall, root pressure falls
    -xylem sap elude from cut end of stems
27
Q

Evidence for the cohesion tension theory

A
  • tree diameters shrink when transpiration highest
  • if xylem vessel broken, air is drawn in rather than water leaking out
28
Q

How to measure the rate of water uptake from a potometer

A

distance moved by air bubble/ time taken to move distance

29
Q

Roles of the stomata for controlling transpiration

A
  • turgor driven process
  • when turgor low, asymmetric figuration of guard cells closes stomatal pores
  • guard cells pump solutes in by active transport when environment conditions favourable
  • cellulose hoops prevent cells swelling in width- extend lengthways
  • when water sparse, hormonal signals from roots can trigger turgor loss from guard cells which close the stomatal pore to conserve water
30
Q

Factors affecting transpiration and why

A
  • LIGHT= more stomata open, so more evaporation- higher light intensity means higher transpiration
  • RELATIVE HUMIDITY= high humidity lowers rate of transpiration (lower water potential gradient between air and inside of the leaf)
  • TEMPERATURE = temperature increase increases the kinetic energy of molecules so more evaporation, or a temperature increase increases the concentration of water vapour (decreases relative humidity), both ways increase diffusion gradient between air inside and outside leaf, so increase the rate of transpiration
  • AIR MOVEMENT= each leaf has a still layer of air trapped around it, water vapour accumulates here , increasing water vapour potential , so reduced diffusion gradient- increased rate of transpiration (wind/air movement increases, still air decreases)
31
Q

What is relative humidity

A

A measure of the amount in water vapour in the air compared to the total concentration of water the air can hold

32
Q

What is glucose converted to to be transported around plants

A

Sucrose

33
Q

What is translocation

A
  • the transport of materials in a plant from source to sink
34
Q

What are assimilates

A
  • the products of photosynthesis that are transported
35
Q

Main sources of assimilates in plants

A
  • green leaves and stems
  • food stores in seeds when the germinate
  • storage organs e.g. tubers and tap roots
  • (some sources transport up, some down)
36
Q

Main sinks in a plant

A
  • roots growing and/or actively absorbing mineral ions
  • meristems that are actively dividing
  • parts of the plant that are laying down food stores e.g. developing seeds, fruits or storage organs

biology module 3 (1 decks)

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