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Module 3 > Transport in plants > Flashcards

Transport in plants Flashcards

1
Q

Why do large plants need a transport system

A

have a small SA:V
Plants not active and have low respiration so demand for O2 is low
Large demand for sugars and water

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2
Q

What do plants need a transport system to move

A

water and minerals from the roots to the leaves
sugars from the leaves to the rest of the plant

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3
Q

What does the vascular tissue consist of

A

xylem - water and soluble mineral ions travel upwards
Phloem - assimilates (sucrose) travel up and down

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4
Q

How is vascular tissue distributed

A

xylem and phloem are found together in vascular bundles
- may also contain other types of tissues i.e. collenchyma/ sclerenchyma) that give bundle strength and help support the plant

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5
Q

How is the xylem and phloem arranged in a young root

A
  • at the centre
  • central core of xylem often shaped in an ‘X’ where the phloem is found in between the arms of the ‘X’ shaped tissue
    arrangement provides strength and support to pulling forces to which root is exposed
    -around vascular bundle is endodermis which plays key role in getting water into the xylem vessels
  • in endodermis is layer of meristem cells (can divide) called the pericycle
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6
Q

How is the xylem and phloem arranged in a stem

A

Vascular bundle found near the outer edges of the stem
Non woody: bundles separate and discrete
Woody: separate in young stems but becomes continuous rings in older stems
Arrangement provides strength and flexibility to withstand pulling forces stems and branches are exposed
- xylem towards inside of vascular bundle and phloem towards the outside
- in between xylem and phloem is a layer of cambium tissue

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7
Q

What is the cambium

A
  • in between xylem and phloem vessels
  • layer of meristem cells hat divide to produce new xylem and phloem
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8
Q

How is the xylem and phloem arranged in a leaf

A
  • vascular bundles form the midrib and veins of a leaf
  • dicotyledonous leaf had branching network of veins that gets smaller as spread away from mid-rib
  • with in each vein the xylem is located at the top of the phloem
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9
Q

What is the structure and function of the xylem

A

vessel used to transport water and mineral ions from roots up to the leaves and other parts of the plant
Consists of:
-vessels to carry water and dissolved mineral ions
- fibres to help support the plant
- living parenchyma cells which act as packing tissue to separate and support vessels

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10
Q

What does lignin do to the xylem

A
  • as xylem develops lignin impregnates the walls of the cells making them waterproof
  • this kills the cells - end walls and contents of the cells decay leaving long tube of dead cells with no contents (xylem vessel)
  • lignin strengthens the walls and prevents from collapsing - keeps vessel open even when there is short water supply
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11
Q

What does the lignin thickening cause in the xylem wall

A

forms patterns in the wall
- may be spiral, annular (rings) or reticulate (a network of broken rings)
prevents the vessel becoming too rigid and allows some flexibility of the stem/branch

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12
Q

What happens where lignification is incomplete

A

leaves gaps in the cells
- gaps form pits/ bordered pits which in two adjacent vessels that are aligned allows water to leave one and pass on to the next vessel
Allows water to leave the xylem and pass into he living parts of the plant

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13
Q

Adaptations of the xylem to its function

A
  • made from dead cells aligned end to end to form a continuous column
  • tubes are narrow so water column does not break and capillary action is effective
  • bordered pits in lignified walls allows water to move sideways from one vessel to another
  • lignin deposited in the walls spiral, annular, reticulate patterns allow xylem to stretch as plant grows and enables the stem/branch to bend
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14
Q

What is the structure and function of the phloem

A

Phloem is a vessel used t transport assimilates (sucrose and amino acids i.e.) around the plant
- sucrose is dissolved in water to form a sap
Consists of sieve tubes made up of sieve tube elements and companion cells

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15
Q

Features of the sieve tube elements

A

-elongated sieve tube elements are lined up end to end to form sieve tubes
- contain no nucleus and little cytoplasm leaving space for mass flow pf sap to occur
- at end of the sieve tubes elements are perforated cross walls called sieve plates
- perforations into the sieve plates allow movements of the sap from one element to the next
- sieve tubes have very thin walls

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16
Q

Features of the companion cells

A

In between sieve tube elements are small cells which with large nucleus and dense cytoplasm
- numerous mitochondria to produce ATP needed for active processes
- carry out metabolic activities needed to load assimilates into sieve tubes

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17
Q

How are plant cells linked

A

Many plant cells joined by cytoplasmic bridges, where the cytoplasm of cells is connected to the cytoplasm of another cell through a gap in their walls.

These gaps are called plasmodesmata

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18
Q

What are the three different pathways water can take into a plant

A

apoplast pathway
symplast pathway
vacuolar pathway

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19
Q

How does the Apoplast pathway work

A

Water passes through spaces in the cell wall and between the cells
DOES NOT pass through any plasma membranes into cells
- water moves my mass flow rather than by osmosis
- dissolves mineral ions and salts can be carried with the water

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20
Q

How does the Symplast pathway work

A

Water enters the cell cytoplasm through the plasma membrane
- can pass through the plasmodesmata from one cell to the next

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21
Q

How does the Vacuolar pathway work

A

Similar to the Symplast pathway but water is not confined to the cytoplasm of the cells
- able to pass through the vacuoles as well

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22
Q

What is the Casparian Strip

A

impermeable waterproof substance in the wall of endodermal cells of plant roots
- creates water tight steal between cells preventing water from entering the xylem via the apoplast pathway
-ensures dissolved minerals and ions pass into cell cytoplasm through plasma membrane

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23
Q

What is the purpose of root hair cells

A

cells with long extension that increase the SA of the root

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24
Q

Movement of water through the root

A

Root hairs absorb minerals
Water moves across cortex down WP to endodermis
Enters symplast pathway as apoplast pathway blocked by Casparian strip

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25
Q

The role of the endodermis

A
  • endodermis layer of cells between medulla and xylem
  • water movement across the root occurs by active process at the endodermis
26
Q

How does water move from the cortex cells into the medulla and xylem

A

-plasma membrane contains transport proteins that actively pump mineral ions from the cytoplasm of the cortex cells into the medulla and xylem
- this makes WP in xylem and medulla more negative than cortex cells
- water moves down WPG

27
Q

What stops water passing back into the cortex cells once in the medulla

A

apoplast pathway is blocked by casparian strip

28
Q

What are the three processes that help water up the stem

A
  • root pressure
  • transpiration pull
  • capillary action
29
Q

How does root pressure move water up the stem

A

-endodermis moving minerals into medulla and xylem draws water in by osmosis
- pressure in root medulla builds up and pushes water into the xylem
- can only push a small way as only a small amount of pressure

30
Q

How does transpiration pull move water up the stem

A
  • loss of water from leaves replaced by water from xylem
  • water molecules attracted by cohesion - strong so holds in chain
    -as molecules lost at one end the whole chain is pulled upwards
31
Q

What is cohesion/adhesion

A

cohesion - attraction between water molecules caused by hydrogen bonds
adhesion - attraction between water molecules and the walls of the xylem vessel

32
Q

Why must the walls of the xylem be strengthened with lignin

A

pull from above as water is pushed up the xylem creates tension and lignin strengthens the wall to stop it from collapsing

33
Q

What is the theory of cohesion an tension being in action with one another called

A

The cohesion tension theory

34
Q

What happens if the chain of one water column is broken within one xylem column

A

Can be replaced by another via the bordered pits

35
Q

How does capillary action move water up the stem

A
  • adhesion - water being attracted to the side of the xylem column and because xylem vessels are narrow it pushes water upwards
36
Q

How does water leave the leaf

A
  • through water vapour via the stomata
    Some through the waxy cuticle
    Water evaporates from the guard cells lowering WP and causing water to enter through to neighbouring cells
37
Q

What is transpiration

A

Loss of water from the upper parts of the plant

38
Q

What is the pathway for water leaving the leaf

A

1) enter xylem and moves by osmosis to spongy mesophyll/ may also enter the cell walls via apoplast pathway
2)Water evaporates from cell walls of spongy mesophyll
3) water vapour moves out of the leaf via open stomata reliant on the Water Vapour potential gradient

39
Q

What must be the Water Vapour potential gradient be

A

Higher in the leaf then outside

40
Q

What is the importance of transpiration

A

As water lost must be placed with water from below: this movement:
- transports useful mineral ions up the plant
- maintains cell turgidity
- supplies water for growth/ cell elongation and photosynthesis
- supplies water that as evaporates can keep plant cool on a hot day

41
Q

Environmental factors that affect transpiration rate

A
  • light intensity
  • temperature
  • relative humidity
  • air movement (wind)
  • water availability
42
Q

How does light intensity affect transpiration rate

A

Stomata open in day for photosynthesis - where water vapour lost through gaseous exchange

43
Q

How does temperature affect transpiration rate

A

1) increases rate of evaporation so WP in leaf rises
2) rate of diffusion through stomata
3) decrease relative WVPG in air - more rapid diffusion

44
Q

How does relative humidity affect transpiration rate

A

If higher in air less water lost - small WVPG gradient between air spaces in leaf and outside

45
Q

How does air movement affect transpiration rate

A

air will carry water away = HWVPG

46
Q

How does water availability affect transpiration rate

A

insufficient water - stomata will close ad leaves wilt

47
Q

Hydrophyte/xerophyte

A

Hydrophyte - a plant adapted to living on ground that is very wet
Xerophyte- a plant adapted to living in very dry conditions

48
Q

Main structural and behavioural adaptions of terrestrial plants

A

-Waxy cuticle recues water loss to evaporation in epidermis
-Stomata are under the surface - reduces loss from direct heating of the sun
-Stomata = closed at night
-Deciduous plants - lose leaves in the winter

49
Q

Marram grass - sand dunes

A

1) Leaf rolled longitudinally so air trapped inside - air humid reduces water loss
2) Thick waxy cuticle on upper epidermis to reduce evaporation
3) Stomata inner side of rolled leaf, protected by enclosed airspace
4) Stomata in pits in LE, folded and covered in hairs - recue air movement - water loss
5) Spongy mesophyll - dense - less SA for evap of water

50
Q

Cacti

A

1) Succulents - store water in stems, ribbed and fluted so can expand
2) Leaves = spines, recues SA, less water lost in transpiration
3) Green stem for photosynthesis
4) Widespread roots - rainfall

51
Q

Other xerophytic features

A
  • Closing stomata when H20 is low
  • LWP in leaf (high salt conc in cells) recues evaporation as WPG reduced
  • Long tap root = reach water underground
52
Q

Hydrophytes e.g

A

Water lillies - face issues with getting O2 and sunlight

53
Q

Hydrophytes adaptions

A

1) Many large air spaces in leaf
2) Stomata - UE so exposed to air
3) Leaf stem - large air spaces - buoyancy and O2 diffuse quickly

54
Q

Hydathodes

A

Release water droplets that can evaporate from leaf surface if water cannot leave the plant due to high humidity

55
Q

What is translocation

A

The transport of assimilates throughout the plant

56
Q

Source/ Sink

A

Source - A part of the plant that loads assimilates into the phloem sieve tubes
Sink - Removes

57
Q

Active loading

A

1) ATP in companion cells provides energy to actively transports hydrogen ions out
2) Creates a concentration gradient
3) Hydrogen ions diffuse (facilitated) back into CC through co-transport proteins only if accompanied by sucrose (secondary active transport)
4) As concentration of sucrose in CC increases it diffuses through the plasmodesmata into the sieve tube element

58
Q

How is the sucrose transported around the plant by mass flow

A

By a difference in hydrostatic pressure between the two ends of the tubes = a pressure gradient

Water enters at the source increasing pressure and leaves at the sink decreasing pressure
- Water enters at source and leaves at the sink

59
Q

Movement of sap along the phloem

A

1) Sucrose actively loaded into the sieve tube element and lowers WP
2) Water follows by osmosis and increase hydrostatic pressure
3) Sap moves from high to low hydrostatic pressure
4) Sucrose removed from sieve tube by surrounding cells and increases the WP in the sieve tubes
5) Water moves out of the sieve tube and reduces the hydrostatic pressure

60
Q

Benefits of carbohydrates being dissolved in sucrose

A

Sucrose is soluble so can be transported in sap
-Metabolically inactive so not used up by cells as it is being transported

Module 3 (3 decks)

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