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AS2 Biology > Transport In Plants > Flashcards

Transport In Plants Flashcards

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1
Q

What is the vascular tissues specialised for?

A

Transport of water and ions (xylem) and organic molecules such as sugar and aa (phloem)

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2
Q

What is the epidermis?

A

The outer layer of the root

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3
Q

Stele

A

The vascular tissue that is conc in epidermis- composed of phloem and xylem tissue

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4
Q

Endodermis

A

single layer of cells immediately outside the stele

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5
Q

Cortex

A

Layer of undifferentiated cells between the epidermis and the endodermis. Cells in the cortex have small air spaces between them and the cells themselves may be rich in starch grains

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6
Q

What is the funct of the xylem?

A

Highly spec for transport of water and ions from the root to the leaf

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7
Q

What 3 ad does the xylem tissue have?

A

No end walls
No cell contents
Dead when fully formed

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8
Q

What in the xylem is ideal for water transport?

A

The column of vessels that prod a long continuous tube

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9
Q

What lines the sec c.w?

A

Specially thickened with an impermeable subst called lignin

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10
Q

What are protoxylem?

A

First formed xylem

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11
Q

What pattern does protoxylem have?

A

Annular/ spiral thickening

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12
Q

What is the metaxylem?

A

Xylem vessels in more mature parts of the root

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13
Q

What pattern does metaxylem have?

A

Pitted/ Reticulate

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14
Q

What is an ad of pitted vessels?

A

Almost complete covering of lignin some small pits are present that allows the movement of water between adj vessels and surrounding cells

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15
Q

State 2 v important jobs of lignin:

A

1: Prov great strength that prevents vessels from collapsing when under pressure by the transp stream “sucking” water up the plant. This also provides structural support
2: Waterproof which prevents the leakage of water

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16
Q

Where are new xylem cells produced?

A

In the cambium between the xylem and the phloem

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17
Q

Where is the protoxylem pushed to in the roots?

A

Pushed to the outer edge of the stele as the metaxylem forms behind it

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18
Q

What does the phloem transport?

A

Sucrose and aa made in phs- active process needs en to work

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19
Q

What is translocation?

A

Movement of subst such as sugars and ions thru the phloem

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20
Q

Which cells are concerned with translocation?

A

Sieve tube elements

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21
Q

How are the sieve tube elements aligned?

A

Aligned end to end to form a continuous row called the sieve tube

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22
Q

How are sieve plates formed?

A

Cells have end walls perforated with sieve pores

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23
Q

What happens to cell contents in sieve tubes as it matures?
What is the adv of this?

A

Loses the nucleus and cytoplasm is reduced in volume and displaced to the side of the sieve tube el
This allow mat to flow more easily

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24
Q

What are the microtubules in sieve tubes inv in?

A

Inv in the process of translocation of solutes (sugars and ions)

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25
Q

What are the dif of companion cells vs normal?

A

Have many more mitochondria and ribosomes and have a high met rate

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26
Q

How are companion cells linked to sieve el?

A

By numerous plasmodesmata

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27
Q

What are the funct of companion cells?

A

Act as supporting cells, carrying out many metabolic activities for the highly spec sieve tube el

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28
Q

How is the vasc arranged?
What is an adv of this?

A

Vasc bundle around the outside of the stem
Creates greater support necessary in stems to support branches and leaves

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29
Q

How does the vasc bundle branch into the leaf?

A

Cont into the leaf as the midrib, which branches to form smaller veins that are distributed throughout the leaf. Veins are found in the spongy mesophyll just below the palisade layer.

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30
Q

What is transpiration?

A

The process of water loss by evaporation in plants

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31
Q

What are the 3 distinct phases for the movement of water and ions into the plant?

A

1: Transp of water (and ions) into and across the root
2: Transport up the root and stem into the xylem
3: Transport thru the leaf and the ev of water from the leaf

32
Q

What facilitates the uptake of water into the cell root?

A

RHC have lsa

33
Q

How does water enter into the cell root?

A

Osmosis- water in soil has a higher water potential than RHC due to sugars and other compounds present in the cells. Cell surf membr of RHC is effective exch surf as c.w is perm, thin and has a lsa

34
Q

What are the 2 main pathways of water into the cell?

A

Apoplast and Symplast

35
Q

Apoplast Pathway inv

A

Inv water moving along the cel microfib of the c.w

36
Q

What is apoplast movement helped by?

A

Helped by parallel arr of microfib in cellulose wall, allows water to pass easily between the dif layers rather than thru them
As the water moves thru the wall, cohesive properties of water helps pull water column along
Due to the lim res to water movement by apoplast pathway- most water moves by this method

37
Q

What does Symplast involve?

A

Involves water moving thru the cytoplasm of adj cells across the cortex by osmosis

38
Q

What is the symplast pathway water moved by?

A

Movement of water across root creates water pot gradient necessary for this to take place (from high to low conc)
Water moves from soil and into the RHC, these cells therefore have a higher water pot. Water then flows from these cells and across the cortex by osmosis
Water moves from cell to cell thru the plasmodesmata that links the cytoplasm of cells of the cortex together.

39
Q

How do ions enter the RHC?

A

Fac dif/ a.t dpeending on conc grad
Intake of ions is often by at causing the build up of ions in plant cells, thereby requiring ions to be moved against the conc grad

40
Q

What sort of waterproof layer does the endodermis have?

A

Waterproof layer formed of suberin called the Casparian strip embedded in the cel cell wall that encircles each cell.

41
Q

What happens to the transp syst at the Casparian strip?

A

All water being transp by apoplast pathway now joins water being transp by the symplast pathway. This means all water moving into the stele is by the symplast pathway.

42
Q

What does the crossover from apoplast to symplast ensure?

A

Ensures movement of water from this point is under metabolic control

43
Q

What does the pos of Casparian strip prev?

A

Prev movement of water thru the endodermis via the apoplast pathway

44
Q

What does endodermis cells do?

A

Pumps ions into the xylem cells, a process that inv en expenditure

45
Q

What does the pumping of ions in the endodermal cells do?

A

Creates a water potential grad that draws water from the endodermis into the xylem. Movement of water osmotically into the base of the xylem tissue creates a root pressure force that helps to move water up the plant.

46
Q

What is the function of the cohesive pull of transp stream?

A

Helps move water from the endodermis into the xylem

47
Q

What happens as water evaporates out of the stomata?

A

Creates a negative pressure that pulls the water column up thru the xylem as a mass flow movement

48
Q

What process is needed for water evaporating out of the stomata?

A

Req water column to form a continuous unbroken pathway thru the xylem called the transp stream

49
Q

What does cohesion do?
State the cohesion-tension theory

A

Water mol form H2 bonds between one another and this tends to stick the water mol together. Allows water to be sucked up the xylem in a continuous column as the water at the top evaporates out of the leaf

50
Q

What does cohesion theory do?

A

Ev (transp) of water out of the leaves, resulting in the transp pull

51
Q

What are the two pieces of evidence for the cohesion-tension theory?

A

1: If water column in the xylem is broken and an air gap appears, water below the gap content cannot be pulled up
2: During day, when transp is at its greatest there is much more tension or heg pressure in the xylem. This neg pressure tends to pull the walls of the xylems vessels in and can reduce the diameter of a tree trunk

52
Q

What 2 imp prop does lignin give the xylem?

A

It is waterproof to avoid water loss
It is v strong allowing the xylem to withstand the pressure exerted on them by the transp pull

53
Q

State the 3 mech inv in the movement of water up the stem

A

1: Cohesion Tension theory
2: Root Pressure
3: Capillarity (Adhesion)

54
Q

Descr root pressure:

A

Endodermal cells actively pump ions into the xylem creating a water potential gradient that causes water to flow into the xylem in osmosis

55
Q

Dscr capillarity

A

If straw is placed in water water will move up due to adhesive properties of water

56
Q

Adhesion

A

Attr between unlike materials e.g water mol and the xylem cells. Adhesive forces between the water column and xylem walls may reduce the forces nec for the transp pull

57
Q

How does water enter the leaf? What does it do from there?

A

Midrib which splits into numerous veins that distribute water across the leaf

58
Q

Where does water pass from the veins of the midrib?

A

Passes to surrounding cells. Water travels across the leaf from the xylem to the spongy mesophyll cells by apoplast and symplast pathways

59
Q

What causes transp losses?

A

Due to water ev from cell surf membr of the s.m cells into the intracellular air spaces with the water vapour diffusing out of the stomara down the conc grad

60
Q

What is translocation?

A

Movement of organic substances in the phloem. Phloem transp org subst from the leaves to the growing parts.

61
Q

What is the main subst tranl in phloem?

A

SUCROSE

62
Q

What are the 2 key features of translocation?

A

Energy requiring
2-way transp system- sucrose can move up and down the sieve tubes

63
Q

Descr how companion cells are inv in the ev for en expenditure

A

C. cells have v high met activity. En output is linked to processes in the sieve tubes. Also inv in uptake of sucrose from adj phs cells and loading of sucrose into the sieve tube elements via plasmodesmata b4 being transp around the plant.

64
Q

Descr how met inhibitors are inv in ev for en expenditure

A

Stop resp in plant cells also disrupts the process of translocation

65
Q

What is ev for the 2-way movement in phloem?

A

Use of radioact labelled sucrose (14CO2) shows that a leaf on a branch half way down a stem may send sucrose both up a plant to growing shoot tip regions and also down to the roots for storage as starch.
Rad. sucr can be show moving down in one sieve tube and moving up in another.
The build up of sucrose helps create a hydrostatic grad between some parts of plant and sink where sucr levels are lower

66
Q

How does stomatal density effect rate of transp?

A

No. stomata per unit area of leaf. the more stomata the more ev and therefore the more transp

67
Q

How does the leaf sa effect rate of transp?

A

The greater the area, the more stomata present- more ev- more transp

68
Q

Cuticle Thickness

A

Thicker- less ev- less transp
Cuticle thicker on u.ep b/c higher light intensity and temp on upper surf so more ev occurs

69
Q

Light Intensity

A

Little effect on transp
Rate of transp and ev greater during day in light vs dark b/c stomata closed

70
Q

Wind Speed on transp

A

Incr wind speed inc rate of diffusion- wind moves away dif shells from the stomata. These are layers of humid air that can build up outside the stomata- reduce conc grad between inside of leaf and outside so reduce dif and transp

71
Q

Wind Speed on Ev

A

Moves humid air in dif shells away from stomata- ensures a steep water pot grad between inside and outside leaf. This increases rate of ev of water from s.m cells into the intercellular spaces and then dif of water vapour out of the stomata

72
Q

Temp on Ev

A

Higher the temp the faster rate of ev of water from s.m cells and faster rate of diffusion of water vapour thru the stomata

73
Q

Humidity on Ev and Transp

A

Incr hum decreases rate of ev so transp. Decreases water pot grad inside and outside leaf. Inside leaf, sub-stomatal air spaces become v humid due to the build up of water vapour, reducing ev from s.m cells

74
Q

Soil Water Avail on ev and transp

A

v. dry- v low due to lack of water in soil. Also, if plant is dehydrated the stomata will close. Defensive mech to conserve water when little water is avail

75
Q

State some ad of xerophytes:

A

Low water avail
Rolled leaves, stomata w/i enclosed area, sunken stomata in pits, layer of leaf hairs (on lower ep), layer of humid air trapped, dif grad increases, reduces rate of transp, thick cuticle, increased waterproofing so reduced cuticular transp, spines/ needles replace typical leaves, small leaves, reduced sa for transp/ fewer stomata/ succulent tissue/ large stores of water within tissue can be used in droughts, deep roots reach water deep in soil

76
Q

Ad of hydrophytes

A

Wet habitats, stomata found mainly on upper surf of leaf, allows ge to take place between leaf and air, prevents water entering air spaces and submerging leaf, large air spaces, allows plant to float so obtaining max light for phs

AS2 Biology (6 decks)

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