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Biology OCR A Level > Plant Transport > Flashcards

Plant Transport Flashcards

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1
Q

Why do we need plant transport systems?

A
  • High Metabolic Demand
  • Low SA: V Ratio
  • Long Distance from external surface to cells
  • Ensures molecules reach all tissues
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2
Q

Explain how water enters the endodermis in root cells?

A
  • Ions enter via active transport
  • Lower water potential
  • Water moves in by osmosis
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3
Q

Why do we need plant transport systems?

A
  • High metabolic demand
  • Low SA:V Ratio
  • Diffusion rate is not sufficient
  • Long distance from external surfaces to cells
  • Ensures nutrients/molecules reach all parts of the plant
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4
Q

Why do plants need water?

A
  • Evaporation to keep them cool
  • Nutrients/Molecules travel in aqueous medium
  • Turgor pressure for cell expansion
  • Raw material for photosynthesis
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5
Q

What is the parenchyma?

A

Support tissue

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6
Q

Adaptations of root hair cells?

A
  • High SA: V Ratio
  • Lots of them!
  • Microscopic size: penetrate between soil particles easily
  • Maintain water potential gradient
  • Thin CSF
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7
Q

Adaptations of xylem?

A
  • Immature cells produce lignin which kills the cells.
  • Lignin for mechanical strength and support
  • No end cell walls to allow for continuous stream of water
  • Dead
  • Non lignified boarder pits to allow for lateral movement of water
  • Lignin to reinforce the plant wall against the transpiration pull
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8
Q

Where is a companion cell located?

A

Vascular tissue

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9
Q

What does a companion cell transport?

A

H+, Assimilates e.g sucrose

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10
Q

What does a root hair cell transport?

A

Mineral ions e.g Nitrate Ions

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11
Q

How does the Casparian Strip prevent ions from reaching the xylem of the plant by the apoplast pathway?

A
  • Strip is impervious to water/ solutions
  • Forces water to pass through cell surface membrane
  • Phospholipid bilayer repels ions (hydrophilic molecules due to its hydrophobic core)
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12
Q

Explain why water molecules can form hydrogen bonds with nitrate ions.

A
  • Water is a polar molecules
  • Nitrate ion is charged
  • Hydrogen bonds form between H on water and O on nitrate ion
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13
Q

A group of students want to observe the xylem, how should they go about this?

A
  • Put leaf in dye
  • Cut a transverse section
  • Observe under low power under a light microscope
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14
Q

How do xeropohytes xylem differ to hydrophytes xylem?

A
  • Hydrophytes have no lignin (water provides turgor pressure for strength)
  • Xerophytes have thinner walls
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15
Q

A similarity between xylem and phloem?

A
  • Both made up of cells joined end to end
  • Xylem vessels and phloem sieve tube elements both lack nuclei
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16
Q

Differences between xylem and phloem?

A
  • Lignified
  • Sieve tube elements
  • Companion cell
  • End Walls
  • Bordered pits
  • Cytoplasm
  • Vessels
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17
Q

What is the function of the bordered pits?

A

Lateral movement of water

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18
Q

What are the precautions when using a potometer?

A
  • Do not allow air to enter to ensure continuous stream of water
  • Keep abiotic factor constant as it affects the rate of transpiration
  • Keep screw clip closed to prevent entry of water whilst measuring
19
Q

Describe how a potometer can be used to achieve a more accurate transpiration rate.

A
  • Potometer airtight
  • Dry leaves
  • Cut shoot under water/ Slanted cut
  • Measure distance air bubble travels during a fixed time interval
  • Constant conditions
20
Q

Suggest three ways in which students could improve their tree sampling method.

A
  • Same / similar, size / age, trees/ leaves
  • Repeat and calculate mean
  • Record at same time of day/year
  • Evenly distributed around the tree
  • Systematic sampling / sample at set distances
21
Q

The students concluded that there is a positive correlation between distance of the tree from
the river and mean leaf hair density.
Suggest reasons for this positive correlation.

A
  • Further away from river there is less water available
  • Transpiration causes water loss
  • Hairs trap water vapour
  • Reduced water potential gradient inside and outside the leaf
22
Q

Suggest how water is being lost from the cut stem when all the leaves have been treated with
petroleum jelly.

A
  • Evaporation from upper leaf surfaces.
  • Epidermis/ Cuticle
23
Q

State what assumption is made when using this apparatus to measure the rate of
transpiration.

A

Transpiration equals uptake.

24
Q

Symplast Pathway

A
25
Q

Apoplast Pathway

A
26
Q

Vacuolar Pathway

A
27
Q

Cohesion

A
28
Q

Adhesion

A
29
Q

Plasmodesmata

A
30
Q

How are hydrophytes adapted?

A
  • No thin waxy cuticle (wax production is a waste)
  • Large SA:V Ratio to increase photosynthesis as transpiration is not an issue
  • Many stomata to maximise gas exchange
  • Stomata on the top surface
31
Q

Why is sucrose used as an assimilate?

A
  • Sucrose is soluble so can be transported in sap
  • Metabolically inactive so none is used
32
Q

How does phloem unloading work?

A

Sucrose diffuses from phloem to surrounding cells. Sucrose is then converted to glucose and is either used in respiration or converted into starch for storage. The concentration of sucrose/glucose is maintained. Loss of sucrose increases water potential of phloem. Water leaves phloem to surrounding cells and results in a lower hydrostatic pressure.

33
Q

Is phloem loading an active or inactive process via the apoplast pathway?

A

Active Process

34
Q

What are the structural adaptations of companion cells?

A
  • Many mitochondria (ATP for PPs)
  • Increase SA:V Ratio
35
Q

What is mass flow?

A

Bulk movement/ transport of phloem sap caused by hydrostatic pressure gradient from source to sink.

36
Q

In the modified plants, the unloading of sucrose is increased in the tubers compared with those that were not modified. The transport of sucrose to the tubers was also increased in the modified plants.

Deduce a possible mechanism to account for the increased unloading and transport of sucrose in the modified plants.

A
  • Sucrose unloaded at sinks and invertase converts sucrose into glucose /
    monosaccharide
  • Increases sucrose concentration gradient
    between phloem and sink
  • Causes increased unloading of sucrose from
    phloem
  • Increases solute gradient between source
    and sink
  • Removal of water from phloem increases pressure gradient between source and sink
  • Contributes to increased movement in
    phloem
37
Q

Why is starch not used as an assimilate?

A
  • Not soluble so does not affect water potential gradient/ osmosis
  • Cannot enter/leave cells
  • Makes sap viscous
38
Q

Describe adhesion.

A

Water molecules are attracted to the impermeable xylem walls.

39
Q

Describe a hydrogen bond.

A

The electrostatic force of attraction between the electropositive H atom of one water molecule and the electronegative O atom on an adjacent water molecule.

40
Q

Which way are materials transferred in a plant?

A

Sources to Sinks!

41
Q

What are some examples of translocation from sources to sinks?

A
  • Substances transferred from storage organs like tubers to shoot tips
  • Substances transferred from leaves to developing fruit
42
Q

What are the key features of the mass flow hypothesis (does this evidence support the mass flow hypothesis…?)

A
  • Water moves in and out of the phloem by osmosis
  • Pressure moves the sucrose solution
  • It involves active processes that use ATP
43
Q

Which three features undermine the mass flow hypothesis?

A
  • Speed substances travel (glucose travels faster than amino acids, if they travel by pressure then there shouldn’t be a difference)
  • Sucrose delivery (does not always go to the area with the lowest sucrose)
  • Sieve plates (wouldn’t they hinder mass flow?)

Biology OCR A Level (18 decks)

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