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as bio unit2 > 2.3 Adaptations for Transport: Plants > Flashcards

2.3 Adaptations for Transport: Plants Flashcards

1
Q

What are vascular bundles?

A

Part of a transport system that exits within vascular plants that is used to transport water and other biological molecules between sections of a plant
—> two types: xylem and phloem

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2
Q

What is the role of the xylem?

A

Transport of water and dissolved minerals

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3
Q

What is the role of the phloem?

A

Translocation of sucrose and amino acids

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4
Q

Outline the structure of the xylem

A
  • elongated dead cells arranged to form continuous vessels
  • no cytoplasm
  • impermeable to water
  • tough walls of lignin
  • 2 types: vessels (angiosperms) and tracheids (ferns, conifers, angiosperms)
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5
Q

2 functions of xylem

A
  • transport of water and dissolved minerals
  • providing mechanical strength and support
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6
Q

What is cotyledon?

A

Embryonic leaf in seed bearing plants, one or more of which are the first leaves to appear from a germinating seed

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7
Q

3 types of tissues found in plant stems and leafs

A
  • parenchyma: thin cellulose layer
  • collenchyma: thick cellulose layer
  • sclerenchomyma: lignified tissue
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8
Q

Describe the structure of the stem

A
  • xylem inside to provide support and flexibility, phloem on outside
  • collenchyma tissue in the cortex to support the stem
  • layer of cambium between xylem and phloem in which meristem cells are involved in production of new xylem and phloem
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9
Q

What is cambium?

A
  • layer of actively dividing cells between xylem and phloem responsible for the secondary growth of stems and roots
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10
Q

What is pericycle?

A

A unique layer of cells in plants encircling vascular tissue in stems and roots
—> essential for lateral root initiation

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11
Q

Describe the structure of the roots

A
  • xylem is central and star shaped with phloem between groups of xylem cells to resist vertical stresses and anchor plant to the sol
  • surrounded by endodermis
  • inner layer of meristem called the pericycle ( lateral root initiation, secondary growth )
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12
Q

Describe the structure of the leaves

A
  • vascular tissue in midrib and a network of veins, giving flexible strength and resistance to tearing
  • light capture on adaxial surface (upper)
  • gas exchange on abaxial surface (lower)
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13
Q

Describe uptake of water by the roots

A
  • soil water contains a very dilute solution of mineral salts and has a high water potential
  • vacuole and cytoplasm of root hair cell contain a concentrated solution of solutes and have a lower water potential
  • water passes into root hair cell by osmosis, down a water potential gradient
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14
Q

3 methods of movement of water through the root

A
  1. Apoplast pathway - water moves in cell walls (fastest)
  2. Symplast pathway - water moves through cytoplasm and plasmodesmata, continual pathway across the root cortex
  3. Vacuolar pathway - water moves from vacuole to vacuole
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15
Q

Endodermis

A

A single layer of cels around the pericycle and vascular tissue of the root. Each cell has an impermeable waterproof barrier in its cell wall

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16
Q

Casparian strip

A

The impermeable band of Suberin in the cell walls of endodermal cells, blocking the movement of water in the apoplast so it moves into the cytoplasm

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17
Q

Water moves from the root endodermis into the xylem across the endodermal cell membranes. What are the 2 explanations for this?

A
  1. Increased hydrostatic pressure in root endodermal cells pushes water into the xylem. HP increased by:
    —> active transport of ions into endodermal cells reduces water potential
    —> diversion of water into endodermal cells from apoplast pathway by the casparian strip
  2. Decreased water potential in the xylem draws water by osmosis across endodermal cell membranes. Water potential deceased by:
    —> water being diverted into the endodermal cells by the Casparian strip
    —> active transport of mineral salts from endodermis and pericycle into the xylem
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18
Q

What are the 3 main mechanisms for movement of water from roots to leaves?

A
  • cohesion-tension
  • capillarity
  • root pressure
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19
Q

Explain the cohesion-tension mechanism

A
  • in transpiration water evaporates which draws water across the cells of the leaf n the apoplast, symplast and vacuolar pathways from the xylem
  • as water molecules leave xylem cells they pull up other water molecules
    —> occurs as water molecules show cohesion and the continuous pull produces tension in the water column
  • COHESION-TENSION THEORY: theory of the mechanism by which water moves up the xylem as a result of the cohesion and adhesion of water molecules and tension in the water column, all resulting from the waters dipole structure
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20
Q

Explain the capillarity mechanism

A
  • movement of water up narrow tubes by capillary action
  • cohesion between water molecules generates surface tension and this combined with adhesion draws the water up
  • capillarity only operates over short distances
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21
Q

Explain the root pressure mechanism

A
  • operates over short distances in living plants and is a consequence of movement of water from the endodermal cells into the xylem pushing water further up
  • caused by the osmotic movement of water down water potential gradient across the root and into the base of the xylem
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22
Q

Source of energy that moves water through a plant

A

Sunlight

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23
Q

Explain how water moves up the xylem

A

Molecules of water pulled up xylem due to cohesion of water molecules resulting in adhesion of water molecules to walls of xylem

24
Q

How to increase transpiration

A
  • lower humidity
  • increase temp
25
Q

What is meant by cohesion

A

Strong attraction that water molecules exert on one another

26
Q

Explain how tension is generated

A

Water molecules evaporating through the stomata and due to cohesion this creates an upward force (tension) throughout the whole column

27
Q

How is root pressure generated

A

Active transport of ions into root xylem creates an osmotic water potential gradient so water is drawn in

28
Q

State the function of the sieve tube cells

A

Translocation of sucrose and amino acids

29
Q

State the function of companion cells

A

Carry out respiration to supply sieve cells with ATP

30
Q

Define transpiration

A

Loss of water vapour by evaporation through stomata in leaves

31
Q

Benefit of transpiration

A
  • cool down plant
  • encourage transpiration stream
32
Q

Disadvantage of transpiration

A
  • plant wilt and die if unregulated as too much water loss
33
Q

Factors that influence transpiration

A
  • light: higher intensity of light = higher rate of transpiration. Stomata close at night to reduce water loss
  • temperature: higher temp = faster transpiration. More KE so evaporate from mesophyll quicker
  • humidity: lower humidity = faster transpiration. Greater conc gradient so more diffusion
  • wind: more wind = more transpiration. Increased conc gradient so more water out of stomata
34
Q

How to measure rate of transpiration

A

Potometer (measure water uptake as the 2 are near proportional)

35
Q

Why do you cut plants under water?

A

Stop air getting into xylem which impacts cohesive forces between H2O molecules, impacting transpiration stream

36
Q

Rate of transpiration equation

A

vol of water
——————
time

37
Q

Mesophytes

A

Plants living in conditions of adequate water supplies

38
Q

Xerophytes

A

Plants living in conditions where water is scarce

39
Q

Hydrophytes

A

Water plants

40
Q

Features of mesophytes

A
  • shed leaves before winter
  • aerial parts of non-woody plants die off so not exposed to cold
    —> perennials survive underground
    —> annuals survive as dormant seeds
  • annuals have low metabolic rate so water not required
  • extensive fibrous roots
41
Q

Features of xerophytes

A
  • rolled leaves: large thin walled epidermal cells become plasmolysed during excessive transpiration. Reduces leaf area exposed to air
  • sunken stomata: occur on adaxial surface. Reduces water potential gradient so reduces diffusion rate
  • hairs: stiff, interlocking hairs trap water vapour and reduce water potential gradient
  • thick cuticle: reduces water loss, thick cuticle = lower transpiration rate
  • fibres of sclerenchyma: stiff so maintain shape even when flaccid
42
Q

Features of hydrophytes

A
  • little to no lignified support tissue
  • little need for transport so poorly developed xylem
  • no cuticle as no need to prevent water loss
  • stomata on upper surface
  • stems and leaves have large air spaces forming a reservoir of oxygen and carbon dioxide for buoyancy
43
Q

What happens to glucose once it’s produced in photosynthesis

A
  • turned to sucrose
  • back into glucose for meristem and roots
  • sucrose sometimes put into starch for storage
44
Q

What is meant by assimilates?

A

Sucrose and amino acids that move up and down the phloem

45
Q

Process of loading sucrose in phloem

A
  • sucrose made in photosynthesis in source cell
  • H+ ions actively transported from companion to source cell
  • sucrose join to H+, both co-transported by FD from source cell to companion cell
  • sucrose diffuses from companion cell into phloem sieve tube element through plasmodesmata
  • due to low water potential in phloem, water molecules diffuse from xylem into phloem and create the push to deliver sink
46
Q

Outline mass flow (diagram inc)

A
  • sucrose make water potential very negative in leaf cells and water passes into cells by osmosis.
  • hydrostatic pressure builds up forcing sucrose solution through phloem to the sink
    —> mass flow
  • in the sink, sucrose is removed in respiration
47
Q

3 pieces of evidence for translocation

A
  • bark ringing experiments
  • analysis of aphid feeding
  • radioactively labelled CO2
48
Q

Explain bark ringing experiments

A
  • remove cylinder of bark tissue that contains phloem
  • swell above ring due to large volumes of sucrose
49
Q

Explain radioactive labelled CO2

A
  • C14 in CO2
  • stem section in film, exposed to radiation source
  • position of exposure coincides with position of phloem
    —> indicates phloem translocates sucrose mass in photosynthesis
50
Q

Explain aphid feeding analysis

A
  • insert stylet into sieve tube
  • cut off stylet and analyse fluid - found sucrose
51
Q

How do we know ATP is used in translocation?

A
  • companion cells packed w mitochondria
  • translocation can be stopped by metabolic inhibitors
  • very high rate of flow - 10000x higher than for diffusion
52
Q

Other theories of translocation/mass flow

A
  • active process may be involved
  • protein filaments pass through sieve pores so diff solutes are carried along diff route through same sieve tube
  • cytoplasmic streaming could be responsible for movement in diff directions in individual sieve tube elements, providing there is a mechanism to transport solutes through sieve plates
53
Q

Two structural features of guard cells that differ from epidermal

A
  • chloroplast
  • unevenly thickened cell walla
54
Q

How does water move into vascular tissue from root

A
  • endodermal cells w Casparian strip forces water into symplast by blocking apoplast as made of Suberin that is waterproof
  • active transport of ions into xylem decreases water potential
  • water enters xylem by osmosis
55
Q

Conclusions from distribution of radioactivity in leaves of plant

A
  • high levels in young leaves so young leaves must be sinks
  • sucrose to young leaves as an energy source for growth
  • lack of radiation in older leaves implies they’re a source or can produce own sucrose

as bio unit2 (7 decks)

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