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AS BIOLOGY > 10 - Plant Transport (C3) > Flashcards

10 - Plant Transport (C3) Flashcards

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1
Q

What is the vascular tissue in plants?

A

Xylem and phloem, found in vascular bundles

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2
Q

What is the vascular tissue in animals?

A

Blood

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3
Q

What is the vascular bundle made up of?

A

Xylem, cambium, phloem, sclerenchyma

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4
Q

How does the structure of the star shaped xylem benefit the plant?

A

It resists vertical stresses (pull) and anchors the plant in the soil

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5
Q

How does the structure of the vascular bundle in stems benefit the plant?

A

It gives the stem flexible support and resists bending

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6
Q

What are the two main cell types in xylem?

A

Vessels and tracheids

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7
Q

What are the two functions of xylem?

A
  • Transport of water and dissolved minerals

- Providing mechanical strength and support

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8
Q

What happens if the water potential in the soil is higher than the WP in the root hair cell?

A

Ions will be actively transported into the root hair cell to lower the WP and increase the WP gradient

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9
Q

What are the 3 ways that water moves through the roots?

A
  • Apoplast pathway (80%)
  • Symplast pathway (15%)
  • Vacuolar pathway (5%)
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10
Q

What pathway does water usually use to travel through the roots?

A

The apoplast pathway

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11
Q

Where does the water move in the apoplast pathway?

A

Along the cellulose cell wall

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12
Q

Where does the water move in the symplast pathway?

A

Through the cytoplasm and plasmodesmata

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13
Q

Where does the water move in the vacuolar pathway?

A

Through vacuoles and cytoplasm

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14
Q

What is the waxy material on the walls of the endodermis?

A

The casparian strip, made of suberin

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15
Q

What does the casparian strip do?

A

It is selective and prevents water movement through the apoplast pathway and directs it through the endodermis via the symplast pathway

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16
Q

How is the WP of the xylem made more negative than the WP of the endodermal cells?

A
  • The WP of the endodermis cells is raised by water being driven in by the Casparian strip
  • The WP of the xylem is decreased by AT of mineral salts, mainly sodium ions, from the endodermis and pericycle into the xylem
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17
Q

What is cohesion tension theory?

A

The theory of the mechanism by which water moves up the xylem, because of the cohesion and adhesion of water molecules and the tension in the water column

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18
Q

What causes water to be sucked up the xylem to the leaves?

A
  • When water is lost by transpiration, water moves via osmosis up the xylem
  • There is positive hydrostatic pressure (root pressure)
  • Water molecules are cohesive and adhesive
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19
Q

What is the definition of cohesion?

A

Attraction between water molecules, seen as hydrogen bonds, resulting from the dipole structure of the water molecule

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20
Q

What is the definition of adhesion?

A

Attraction between water molecules and hydrophilic molecules in the cell walls of the xylem

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21
Q

What is the definition of transpiration?

A

The evaporation of water vapour from the leaves or other areas of the plant, out through stomata into the atmosphere

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22
Q

What does the rate of transpiration depend on?

A
  • Genetic factors controlling the number, distribution + size of the stomata
  • Environmental factors e.g temp, humidity + air movement
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23
Q

How is a continuous flow of water able to move through the xylem?

A
  • They’re made of dead cells aligned end to end
  • No end walls
  • No cell contents including no nucleus or cytoplasm
24
Q

What does thickened lignified walls in the xylem do?

A
  • Prevents walls from collapsing

- Waterproof

25
Q

What do tracheids do?

A

They have tapered ends which fit together and pits which allow transfer of water between cells

26
Q

Why do xylem and phloem contain fibres?

A

For support

27
Q

Why do xylem and phloem contain parenchyma cells?

A

For packing tissue

28
Q

How does nitrogen enter the plant?

A
  • As nitrate/ammonium ions
  • They diffuse along the conc. gradient into the apoplast stream but enter symplast by AT and then flow via plasmodesmata in the cytoplasmic stream
29
Q

What does xylem carry?

A

Water and mineral ions up the plant

30
Q

What does phloem carry?

A

Dissolved organic materials e.g sucrose around the plant

31
Q

What is the cortex?

A

A layer of packing tissue between epidermis and vascular tissue

32
Q

What is the endodermis?

A

A layer of cells that contains a waterproof casparian strip to control movement of ions into xylem

33
Q

What is the outer cell layer of the vascular tissue in the dicotyledon called?

A

Epidermis

34
Q

What is a potometer used to measure?

A

Rate of transpiration (altho it actually measures the rate of uptake of water + some of this is used in photosynthesis)

35
Q

How do you set up a potometer?

A
  • Cut shoot under water (to stop air entering xylem vessels)
  • Cut shoot at a slant (to increase SA)
  • Check apparatus is full of water
  • Insert shoot into apparatus under water (to prevent air locks in xylem)
  • Shut screw clip
  • Remove potometer from water and ensure airtight joints around shoot
  • Dry leaves
  • Keep condition(s) constant
  • Allow time for shoot to acclimatise
  • Keep ruler fixed and record position of air bubble on scale
  • Start timing and measure/calculate distance moved per unit time
36
Q

Why does an increase in temperature increase the rate of transpiration?

A
  • Increase in kinetic energy of water molecules

- Increase in rate of evaporation from stomata

37
Q

Why does an increase in humidity decrease the rate of transpiration?

A
  • Increase in humidity = increase in water vapour in the air
  • Therefore WP gradient between air and leaf decreases
  • So less water is lost by evaporation
38
Q

Why does an increase in air movement increase the rate of transpiration?

A
  • Increase in air movement = increase in WP gradient between the leaf and air as the boundary layer of air and water vapour around the stomata is removed quicker
39
Q

Why does an increase in light intensity increase the rate of transpiration?

A
  • More stomata open as there will be an increase in GE of CO2 to increase the rate of photosynthesis
  • Therefore there is a greater SA where transpiration can occur
40
Q

What is translocation?

A

The movement of soluble materials, such as glucose and amino acids, through the phloem from source to sink

41
Q

Where do mesophytes grow?

A

In areas of adequate water supply

42
Q

Where do xerophytes grow?

A

In areas of scarce water supply (including deserts, cold regions where soil is frozen, and windy places)

43
Q

Where do hydrophytes grow?

A

Partially or fully submerged in water

44
Q

What feature do mesophytes have to reduce water loss?

A
  • Shed leaves before winter, so water not lost by transpiration
  • Stomata close at night, and can close during day
  • Most annual mesophytes survive winter as dormant seeds
45
Q

What features do xerophytes have (e.g. marram grass) to reduce water loss?

A
  • Rolled leaves - reduces SA of leaf exposed for transpiration
  • Sunken stomata - trap water vapour in pits outside stomata, reducing WP gradient
  • Hairs - trap water vapour
  • Thick cuticle - waterproof, reduces water loss
46
Q

What features do hydrophytes have?

A
  • Little or no lignified tissue as supported by water
  • Little or no cuticle
  • Xylem poorly developed as not needed to transport water
  • Stomata on upper leaf
  • Stems and leaves have large air spaces for O2 and CO2 for buoyancy
47
Q

In what directions can phloem transport materials?

A

Up, down and sideways

48
Q

How are sieve tube elements in phloem adapted for transporting materials?

A

They lose their nucleus and most of their organelles during their development

49
Q

What were the ringing experiments used to prove translocation through phloem?

A
  • Ring of outer bark tissue (phloem) removed from tree trunk
  • After time, a bulge was seen above cut ring
  • This proves the sucrose is transported through the plant in the phloem, so couldn’t move past this point
50
Q

How are radioactive tracers used to prove translocation through phloem?

A
  • Plant photosynthesises in presence of radioactive isotope e.g. 14CO2
  • Sucrose made from 14CO2 in photosynthesis
  • Stem section placed on photographic film, which produces an autoradiograph, which replicates the positions of phloem in the stem
51
Q

How are aphids used to prove translocation through phloem?

A
  • Aphid inserts stylet into sieve tube
  • Removes sap of phloem
  • Aphid removed with stylet remaining, sap collected and analysed
52
Q

What about translocation does the mass flow hypothesis not explain?

A
  • Rate of phloem transport is much faster than if substances were moving by diffusion
  • Sieve plates with small pores would obstruct mass flow
  • Sucrose and AAs move at different rates + directions in same tissue
53
Q

What are other theories which suggest translocation through phloem?

A
  • An active process may be involved
  • Protein filaments pass through sieve pores so perhaps different solutes are carried along different routes through the same sieve tube element
  • Cytoplasmic streaming could be responsible for movement in different directions in individual sieve tube elements
54
Q

Why do sieve tube elements have a thin layer of cytoplasm?

A

For less resistance / ease of transport

55
Q

What is the role of the sieve plates?

A
  • Connect elements

- Let solutes through

56
Q

What is mass flow hypothesis of translocation at the source?

A
  • H+ ions pumped out of companion cells into source cells by AT
  • H+ ions return to companion cell with sucrose down diffusion gradient
  • Sucrose loaded into sieve tube by diffusion via companion cells and plasmodesmata - reduces sieve tube WP
  • Water enters sieve tube by osmosis from surrounding tissue down WP gradient
  • Increases hydrostatic pressure in sieve tube
57
Q

What is mass flow hypothesis of translocation at the sink?

A
  • Sucrose unloads from sieve tube at sink via diffusion or AT - increases sieve tube WP
  • Water moves out sieve tubes by osmosis. Reduces hydrostatic pressure in sieve tube

AS BIOLOGY (13 decks)

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