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IB Biology > 9.2 Transport in the phloem of plants > Flashcards

9.2 Transport in the phloem of plants Flashcards

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1
Q

What is translocation?

A

Translocation is the movement of organic compounds from sources to sinks

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2
Q

What is a source?

A

Where the organic compounds are synthesised

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3
Q

What is a sink?

A

Where the compounds are delivered to for use or storage

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4
Q

What are the sources in plants?

A

Photosynthetic tissue aka leaves

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5
Q

What are the sinks in plants?

A

Roots
Fruits
Seeds

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6
Q

How are organic compounds transported from sources to sinks?

A

Via the phloem

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7
Q

What is the phloem?

A

A vascular tube system

It is responsible for transporting organic compounds from sources to sink

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8
Q

How are sugars transported and why?

A

They are transported as sucrose because it is soluble but metabolically inert

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9
Q

What is nutrient- rich viscous fluid of the phloem?

A

Plant sap

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10
Q

What are the two types of cells phloem sieve tubes composed of?

A

Sieve element cells and companion cells

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11
Q

In addition to sieve element cells and companion cells, what cells does the phloem also have and what do they do?

A

Sclerenchymal and parenchymal cells which fil additional spaces and provide support

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12
Q

What are sieve element cells?

A

They are long and narrow cells that are connected together to form the sieve tube

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13
Q

How are sieve elements connected?

A

By sieve plates at their transverse ends which are porous to enable flow between cells

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14
Q

What do sieve elements lack and how is it helpful?

A

They lack a nuclei and have reduced organelles to increase flow rate

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15
Q

What helps sieve elements withstand hydrostatic pressure?

A

Thick and rigid cell walls

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16
Q

What do companion cells do?

A

Provide metabolic support for sieve element cells and facilitate the loading and unloading of materials at source and sink

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17
Q

Why do companion cells have an infolding plasma membrane?

A

It increases surface area to volume ratio to allow more material exchange

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18
Q

Why do companion cells have many mitochondria?

A

To fuel the active transport of materials between the source and sink and the sieve tube

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19
Q

What do companion cells have to move materials in and out of the sieve tube?

A

Transport proteins

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20
Q

If the sieve element did not have the support of a companion cell what would it not be able to do and why?

A

Sustain independent metabolic activity because sieve elements have no nuclei and fewer organelles

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21
Q

What exists between sieve elements and companion cells in relatively large numbers?

A

Plasmodesmata

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22
Q

What does plasmodesmata do?

A

Connect the cytoplasm of companion and sieve element cells and mediate the symplastic exchange of metabolites

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23
Q

What does the phloem transport?

A

Transports food and water

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24
Q

How many ways is the movement in phloem?

A

Two ways

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25
Q

What do connecting sieve cells share?

A

A highly perforated sieve plate

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26
Q

What mediates the movement of sap?

A

Hydrostatic pressure from the xylem

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27
Q

How can you usually differentiate xylem and phloem cells in a microscopic image?

A

By the diameter of their cavity

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28
Q

Does the xylem or the phloem have a larger cavity?

A

The xylem

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29
Q

What are xylem and phloem grouped into?

A

Bundles that extend from the roots to the shoots in vascular plants

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30
Q

Where can you find differences in between plant types?

A

Distribution and arrangement

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31
Q

What are two different plant types?

A

Monocotyledones and Dicotyledons

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32
Q

In monocotyledons roots how does the stele present itself?

A

The stele is large and vessels will form a radiating circle around the central pith

33
Q

When talking about the vessels surrounding the stele in roots, where are xylem vessels located?

A

More internally

34
Q

When talking about the vessels surrounding the stele in roots, where are phloem vessels located?

A

More externally

35
Q

In dicotyledons roots how does the stele present itself?

A

The stele is very small and the xylem is located centrally with the phloem surrounding it

36
Q

In dicotyledons roots how do xylem vessels form?

A

They form a cross shape

37
Q

In dicotyledons roots where are phloem situated?

A

In the surrounding gaps

38
Q

In monocotyledons stems, where are the vascular bundles found?

A

In a scattered arrangement throughout the stem

39
Q

In monocotyledons stems, where are the phloem vessels positioned?

A

Positioned externally towards the outside of the stem

40
Q

In dicotyledons stems, how are vascular bundles arranged?

A

In a circle around the centre of the stem

41
Q

In dicotyledon stems what separates phloem and xylem vessels and in which order are they separated?

A

The cambium

Xylem on the inside and phloem on the outside

42
Q

How does the organic compounds produced at the source loaded into phloem sieve tubes?

A

Actively by companion cells

43
Q

How can materials pass into the sieve tube?

A

Via interconnecting plasmodesmata

44
Q

How can materials travel across the intervening cell wall?

A

They can be pumped by membrane proteins

45
Q

What describes the transport of apoplastic loading of sucrose into the phloem sieve tubes?

A

Active transport that requires ATP expenditure

46
Q

What are actively transported out of phloem cells and how?

A

Hydrogen ions are actively transported out of phloem cells by proton pumps

47
Q

How is a proton gradient created?

A

The concentration of hydrogen ions consequently builds up outside of the cell

48
Q

How do hydrogen ions diffuse back into the phloem cell?

A

Via a co transport protein which requires sucrose movement

49
Q

What does the diffusion of hydrogen ions back into the cell result in?

A

A build up of sucrose within the phloem sieve tube for subsequent transport from the source

50
Q

What makes the sap solution at the source to become hypertonic?

A

The active transport of solutes into the phloem by companion cells

51
Q

What does hypertonic sap solution at the source result in?

A

Water to be drawn from the xylem via osmosis

52
Q

Why does hydrostatic pressure at the source increase?

A

The incompressibility of the water that has built up in the phloem

53
Q

What does the increase in hydrostatic pressure force?

A

It forces the phloem sap to move towards areas of lower pressure

54
Q

What does the phloem sap moving towards areas of lower pressure cause?

A

Phloem transports solutes away from the source and to the sink

55
Q

What happens to the solutes that are unloaded from the phloem?

A

They are transported into sinks

56
Q

What do companion cells unload from the phloem?

A

Solutes

57
Q

What is the sap solution at the sink?

A

Hypotonic

58
Q

What does the sap solution being hypotonic then cause?

A

Water being drawn out of the phloem and back into the xylem via osmosis

59
Q

What does water being drawn out of the phloem and back into the xylem via osmosis ensure?

A

That the hydrostatic pressure at the sink is always lower than the hydrostatic pressure at the source

60
Q

What does a low hydrostatic pressure at the sink mean?

A

Phloem sap will always move from the source towards the sink

61
Q

What are organic molecules when they are transported into the sink?

A

Either metabolised or stored with the tonoplast of vacuoles

62
Q

What are aphids?

A

A group of insects which feed mainly on sap from phloem

63
Q

What is a stylet?

A

A mouthpiece of aphids which pierces the plants sieve tube to allow sap to be extracted

64
Q

What aids the penetration of the stylet into the sieve tube?

A

Digestive enzymes that soften the intervening tissue layers

65
Q

What happens if the stylet is severed and why?

A

Sap will continue to flow from the plant due to the hydrostatic pressure within the sieve tube

66
Q

Why are aphids good for providing a measure of phloem transport rates?

A

Because aphids collect sap at various sites along a plants length

67
Q

When measuring phloem transport using aphids, where is the plant grown?

A

Within a lab with the leaves sealed within a glass chamber containing radioactively labelled CO2

68
Q

When measuring phloem transport using aphids, what will the leaves convert the CO2 into?

A

Into radioactively labelled sugars which are transported by the phloem

69
Q

When measuring phloem transport using aphids, where are the aphids placed and then what happens?

A

Along the plants length and are then encouraged to feed on the phloem sap

70
Q

When measuring phloem transport using aphids, what happens once the feeding has commenced?

A

The aphid stylet is severed and sap continues to flow from the plant at the selected positions

71
Q

When measuring phloem transport using aphids, why is the sap analysed?

A

For the presence of radioactively labelled sugars

72
Q

When measuring phloem transport using aphids, how can it be calculated?

A

Based on the time taken for the radioisotope to be detected at different positions along the plants length

73
Q

What is phloem transport also known as?

A

Translocation rate

74
Q

What determines the translocation rate?

A

The concentration of dissolved sugars in the phloem

75
Q

What affects the concentration of dissolved sugars in the phloem sap?

A

The rate of photosynthesis
The rate of cellular respiration
The rate of transpiration
The diameter of the sieve tubes

76
Q

What affects the rate of photosynthesis?

A

Light intensity
CO2 concentration
Temperature

77
Q

What affects the rate of cellular respiration?

A

Any factor which physically stresses the plant

78
Q

What does the rate of transpiration determine?

A

How much water enters the phloem

79
Q

What does the diameter of sieve tubes affect?

A

Hydrostatic pressure but it may differ between plant species

IB Biology (57 decks)

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