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biology, component 3 - part 2 > plant transport > Flashcards

plant transport Flashcards

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1
Q

describe the apoplast pathway

A
  • water moves into the walls of epidermal cells

- spaces separate cellulose fibres in the cell wall which moves water through

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2
Q

describe the symplast pathway

A
  • continual pathway across the root cortex

- water moves through cytoplasm via plasmodesmata

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3
Q

how are root hair cells adapted for the uptake of water and mineral ions

A
  • large surface area
  • thousands of root hair cells provide large total surface area
  • cell wall permeable to water
  • thin cell walls
  • large numbers of mitochondria
  • large numbers of protein carriers
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4
Q

outline the features/importance of the epidermis

A
  • outer layer of root

- epidermal cells have root hairs to increase surface area

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5
Q

outline the features/importance of the xylem

A
  • dead cells contain rings of lignin to form waterproof vessels
  • water and dissolved minerals transported
  • pits in vessels allow water to move
  • water moves us tracheids which have tapered ends
  • fibres provide structural support
  • packing cells around vessels and tracheids are parenchyma
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6
Q

outline the features/importance of the phloem

A
  • living tissue

- transports sucrose around the plant

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7
Q

outline the features/importance of the endodermis

A
  • surround the pericycle

- layer of cells containing waterproof casparian strip

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8
Q

outline the features/importance of the vascular bundle

A
  • contains xylem, phloem and cambium cells
  • roots restrict pull stresses
  • stems provide flexible support but resist bending
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9
Q

outline the processes of the cohesion-tension theory

A
  • water evaporates from surface of epidermal cells
  • water diffuses from sub-stomatal chamber into atmosphere
  • water evaporates from cell walls into sub-stomatal chamber
  • water moves through leaf tissue via pathways
  • water leaves xylem and moves into apoplast due to cohesion
  • water drawn up xylem by tension
  • water enters xylem
  • casparian band prevents water movement via apoplast pathway
  • water uptake into root hair cells
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10
Q

outline the processes of investigating transpiration rate

A
  • cut shoot underwater to stop air entering xylem vessels
  • cut shoot at a slant to increase surface area
  • remove capillary tube and wait for air bubble to form
  • shut screw clip
  • remove potometer from underwater and use vaseline to ensure air tight joints around shoot
  • dry leaves because excess water slows transpiration rate
  • allow time for shoot to acclimatise
  • record position of air bubble on scale
  • start timing and calculate distance moved
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11
Q

explain how an increase in temperature effects the rate of transpiration

A
  • increases rate of transpiration

- increases kinetic energy which causes an increased rate of evaporation from mesophyll cells

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12
Q

explain the effect of increasing humidity on the rate of transpiration

A
  • decreases rate of transpiration

- lowers water potential gradient between air spaces in the leaf and the outside

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13
Q

explain the effect of increasing air movement on the rate of transpiration

A
  • increases rate of transpiration

- wind removes water vapour which increases water potential gradient

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14
Q

explain the effect of increasing light intensity on the rate of transpiration

A
  • increases the rate of transpiration
  • more open stomate
  • increases rate of photosynthesis so more water is needed
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15
Q

explain how mass flow of materials between the source and the sink would be brought about

A
  • sucrose loaded into sieve tube by diffusion which lowers water potential
  • water enters sieve tube down a water potential gradient
  • hydrostatic pressure in sieve tube increases
  • sucrose is unloaded at sink which increases water potential in sieve tube
  • water moves out of sieve tube which reduces hydrostatic pressure
  • pressure gradient means sucrose moves from source to sink
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16
Q

what is meant by translocation

A

process in which substances are moved from the site of production (source) to the place they are needed (sink)

17
Q

give two problems with the mass flow hypothesis

A
  • suggests flow is in one direction when it is actually bidirectional
  • cytoplasmic streaming can be observed
18
Q

describe the process of the ringing experiment

A
  • ring of bark is scraped away which also removes some phloem
  • sugar tries to be transported down the stem but stopped by the ring
  • bulge of sugar forms above the ring
  • suggests sugar moves down the stem in the phloem
19
Q

explain how aphids can be used to test for translocation

A
  • stylets in the mouth are used to penetrate phloem tubes
  • if anaesthetised with carbon dioxide and the stylet cut off so it remains in the phloem, pure phloem sap can be collected for analysis
20
Q

outline the structure/function of sieve tubes in the phloem

A
  • formed form sieve tube elements (parenchyma cells) - stacked on top of each other
  • cells walls a perforated where they join and form sieve plates - allow flow through and cytoplasmic strands to link cells
  • living cells however lack most organelles for easier flow
21
Q

outline the structure/function of companion cells in the phloem

A
  • found next to each sieve element
  • very dense cytoplasm containing many mitochondria and ribosomes and are very metabolically active
  • connected to sieve element via plasmodesmata
22
Q

describe how root pressure is achieved

A
  • at endodermis ions are actively taken up to by-pass the casparian strip which allows active uptake of ions
  • lowers water potential in xylem causing water to be drawn through endodermis
  • this pulling produces a positive hydrostatic pressure inside the xylem, forcing water upwards
23
Q

outline and explain the process of autoradiography as an experiment fro translocation

A
  • 14CO2 placed into bag surrounding a leaf
  • source and sink leaves are placed on photographic film for 24 hours
  • when film is developed, presence of radioactivity shows up only
  • it is concluded that sucrose is transported both up and down the stem
24
Q

how does radioactive carbon reach growing areas of the plant

A
  • plant uses the radioactive carbon for photosynthesis which incorporates it into glucose
  • glucose is converted into sucrose with the radioactive carbon
  • the sucrose is transported through the phloem to the growing buds by translocation
25
Q

describe how respiratory inhibitors can be used to provide evidence for the phloem being the tissue used for translocation

A
  • eg. cyanide

- reduces translocation of organic solutes when applied to the phloem but not the xylem

26
Q

explain how nitrogen enters the plant

A
  • enters as nitrate ions
  • diffuse into apoplast stream
  • enter symplast pathway by active transport against the concentration gradient
  • flow via the plasmodesmata into the cytoplasmic stream
27
Q

explain how the columns of water in the xylem are held up

A
  • cohesive forces between water molecules

- adhesive forces between water molecules and the hydrophilic lining of the xylem

28
Q

what is meant by transpiration

A

the loss of water through the leaves of a plant

biology, component 3 - part 2 (5 decks)

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