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Botany > Lecture: Phloem > Flashcards

Lecture: Phloem Flashcards

1
Q

what is the function of phloem?

A

conduction of products of Ps

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2
Q

what products of Ps does phloem conduct?

A

sugar, some amino acids

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3
Q

what are the structural elements of phloem?

A
  1. parenchyma
  2. sclerenchyma
  3. conducting sieve elements
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4
Q

what are the two types of conducting sieve elements?

A
  1. albuminous cells

2. companion cells

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5
Q

sieve cells are

A

less efficient, primitive

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6
Q

what plant groups have sieve cells?

A

ferns and gymnosperms (not angiosperms)

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7
Q

what cells are associated with sieve cells?

A

albuminous cells

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8
Q

what is the structure of sieve cells?

A

sieve areas (side walls) with pit membrane on all walls, pit fields with plasmodesmata

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9
Q

sieve-tube cells are

A

more advanced and efficient

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10
Q

what plant groups have sieve-tube cells?

A

angiosperms

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11
Q

what cells are associated with sieve-tube cells?

A

companion cells

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12
Q

what is the structure of sieve-tube cells?

A

sieve areas (side walls) and sieve plates (end walls with large pores)

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13
Q

which conducting sieve element is more efficient at transporting water with sugar and preventing air bubbles?

A

sieve-tube cells

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14
Q

how many cell walls in sieve elements?

A

only primary

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15
Q

sieve elements are ____ at maturity

A

alive, but braindead

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16
Q

what structures do sieve elements lose at maturity?

A

nuclei, ribosomes, dicytosomes, tonoplast

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17
Q

what structures do sieve elements keep at maturity?

A

plasmalemma, ER, mitochondria, some plastids, cytoplasm

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18
Q

what controls the sieve cells?

A

albuminous cells

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19
Q

what controls the sieve-tube cells?

A

companion cells

20
Q

what is the relationship between the albuminous cell and sieve cell?

A

neighbours

21
Q

what is the relationship between the companion cell and the sieve-tube cell?

A

sister

22
Q

unlike tracheary elements, the lifespan of sieve elements is __

A

short (<1 year - 5-10 years)

23
Q

what are the functions of albuminous/companion cells?

A
  1. brains of their associated cells

2. control loading / unloading

24
Q

what direction does phloem move in plants?

A

bidirectional

25
Q

by what two methods is long-distance transport of phloem carried out?

A
  1. active transport (ATP)

2. passive transport (osmosis)

26
Q

the location of source / sink for phloem will change based on

A
  1. season

2. lifestage

27
Q

what is the source / sink of phloem in summer?

A

source: site of Ps
sink: site of use/storage

28
Q

what is the source / sink of phloem in winter?

A

source: roots/storage site
sink: site of use

29
Q

how does lifestage of a plant influence the movement of phloem?

A

as plant recahes reproductive stage, it requires more phloem to be redirected to the production of reproductive structure

30
Q

how fast does phloem move through phloem?

A

50-100cm an hour

31
Q

how do we know the speed at which phloem travels?

A

aphids penetrate sieve tube cell and phloem gushes into insect, and will continue to gush if insect removed

32
Q

what is the pressure flow theory (mass flow hypothesis) for the movement of phloem?

A

long distance transport based on

  1. concentration gradient (osmotic) and turgor pressure gradient
  2. water exchange with xylem
33
Q

loading and unloading phloem is a(n) (active/passive) process?

A

active, requires ATP

34
Q

long distance transport by mass flow is a(n) (active/passive) process?

A

passive, no ATP

35
Q

what causes the bulk of the transport of phloem?

A

turgor pressure gradient

36
Q

what are the “main players” of phloem transport?

A
  1. sugar source
  2. suagr sink
  3. sieve elements
  4. associated cells
  5. tracheary elements
37
Q

what are the two routes for loading phloem?

A
  1. symplastic pressure flow

2. apoplastic loading

38
Q

where does phloem travel through in symplastic loading?

A

plasmodesmata

39
Q

where does phloem travel through in apoplastic loading?

A

cell wall

40
Q

in what order do symplastic and apoplastic loading occur? Which requires ATP?

A
  1. symplastic

2. apoplastic (ATP)

41
Q

how is sugar loaded into a sieve tube celll?

A

actively and controlled by the associated cell

42
Q

what happens once sugar has been loaded into sieve tube cell?

A

osmotic gradient is created and water from tracheary element moves to sieve tube cell, increasing turgor pressure

43
Q

what happens once water from tracheary element has increased the tugor pressure of the sieve tube cell?

A

sugar is pushed to adjacent tube (from source to sink)

44
Q

unloading sugar at the sink is a(n) (active/passive) process?

A

active (ATP)

45
Q

what controls unloading of sugar?

A

associated cells

46
Q

once sugar has been unloaded, what happens to the osmotic gradient? Turgor Pressure?

A

reverses and water moves back to tracheary element, decreasing turgor pressure

47
Q

loading and unloading phloem creates what two types of gradients?

A
  1. concentration

2. pressure

Botany (10 decks)

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