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Biology Year 12 > 9 - Transport in plants > Flashcards

9 - Transport in plants Flashcards

1
Q

Why do multicellular plants need a transport system?

A
  • substances such as glucose and oxygen need to be transported to cells that do not photosynthesise.
  • waste products of cell metabolism need to be removed.
  • small SA:V ratio
  • relatively big with high metabolic rate.
  • exchange by diffusion alone would be too slow to meet metabolic needs.
  • hormones need to be transported to where they are required.
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2
Q

What two types of tissues are part of the vascular system?

A
  • xylem

- phloem

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3
Q

How are the vascular bundles arranged in a stem?

A
  • phloem outside
  • xylem inside
  • cambium in between

vascular bundle around edge to give strength and support.

cambium layer contains meristem cells.

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4
Q

How are the vascular bundles arranged in a root?

A
  • xylem in x structure in middle
  • phloem in 4 sections around xylem
  • root hair surrounding

vascular bundle in middle to help plant withstand tugging strains (e.g wind).

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5
Q

How are the vascular bundles arranged in a leaf?

A
  • xylem on top
  • phloem on bottom

midrib (largest middle part of leaf) is the main vein carrying the vascular tissue.

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6
Q

Function of xylem

A
  • Transports water and dissolved mineral ions
  • one direction movement (upwards). Water moves from roots towards leaves.
  • provides structural support
  • passive process
  • TRANSPIRATION
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7
Q

Functions of phloem

A
  • Transports organic solutes and dissolved sugars.
  • bidirectional movement.
  • from leaves to rest of plant.
  • active process
  • TRANSLOCATION
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8
Q

what cells are present in xylem?

A
  • xylem vessels
  • xylem fibres
  • xylem parenchyma
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9
Q

what cells are present in phloem?

A
  • sieve tube elements
  • companion cells
  • parenchyma
  • phloem fibres
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10
Q

explain the structure of the xylem

A
  • xylem vessels are long hollow structures formed from cells (dead) joined end to end.
  • no end walls between the cells, forming a continuous hollow tube.
  • thick lignified walls (lignin) help to support the xylem vessels and prevent them from collapsing inwards under the transpiration pull.
  • lignin deposited in walls as spirals or distinct rings.
  • water and mineral ions move in and out of xylem vessels through non-lignified pits.
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11
Q

explain the structure of phloem

A

sieve tube elements:
living cells joined end to end to form a long, hollow structure.
- sieve plates are between the cells, and are perforated to allow phloem contents through.
- no nucleus, very thin cytoplasm, very few organelles (unusual for a living cell).

Companion cells

  • 1 companion cell for every sieve tube element.
  • they are linked by many plasmodesmata.
  • they have a nucleus and organelles.
  • they carry out the living functions for both themselves and the sieve tube cells.
  • e.g provide energy for active transport of solutes.
  • no lignified walls
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12
Q

Sieve tube cells are living cells. Why are they unusual?

A
  • no nucleus
  • very thin layer of cytoplasm
  • vey few organelles.
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13
Q

What is the phloem filled with?

A
  • phloem sap
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14
Q

Which kind of plants have a vascular system consisting of xylem and phloem?

A

herbaceous dicotyledonous plants

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15
Q

Why do plants need water?

A
  • to transport mineral ions and sugars in aqueous solution.
  • water is a reactant photosynthesis
  • cooling effect by transpiration
  • turgor pressure.
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16
Q

What are the adaptations of a root hair cell?

A
  • microscopic means they can penetrate between soil particles.
  • large SA:V ratio as they are microscopic in size.
  • thin surface layer provides a short diffusion and osmosis distance.
  • concentration of solutes in cytoplasm of root hair cells maintains a water potential gradient between soil water and cell.
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17
Q

What is osmosis?

A

the movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane.

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18
Q

What are the 3 different pathways water can take from the root to the xylem?

A
  • symplast pathway
  • apoplast pathway
  • vacuolar pathway
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19
Q

Symplast pathway (cytoplasm)

A
  • water travels through the living parts of cells (cytoplasm)
  • the cytoplasm of neighbouring cells are connected by plasmodesmata.
  • osmosis
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20
Q

apoplast pathway (cell wall)

A
  • water travels through the non-living parts of cells (cell walls).
  • water can from carry solutes and move area of high hydrostatic pressure to areas of low hydrostatic pressure.
21
Q

vacuolar pathway

A

through vacuoles as well as cytoplasm.

22
Q

Explain the casparian strip

A
  • water travels through symplast, apoplast, vacuolar pathways and reach the endodermis.
  • path is blocked by the casparian strip.
  • it is a waxy (suberin) strip which is impenetrable.
  • water is forced through the symplast pathway.
  • useful as water has to go through partially permeable cell surface membrane.
  • controls which substances get through to xylem.
  • toxic solutes are removed and water moves on to the xylem.
23
Q

How does water leave the plant?

A
  • water leaves xylem and move into mesophyll cells by apoplast pathway.
  • water evaporates from the cell walls to large air spaces between cells in the leaf.
  • when stomata in the leaf open, water diffuse out of the leaf (down water potential gradient).
  • loss of water from a plant’s surface is called transpiration.
24
Q

How does water move up the plant against gravity?

A

Cohesion and tension:

  • as water evaporates from the leaves, this creates tension, which pulls up more water into the leaves.
  • cohesion means that when some water molecules are pulled into the leaf, other water molecules follow.
  • means that water moves up the xylem in a continuous stream.

Adhesion:

  • water molecules are attracted to the walls of the xylem vessels.
  • this helps water molecules to rise up the xylem vessels..
25
Q

evidence for cohesion tension theory

A
  • changes in tree diameter (high transpiration rates during day diameter decreases due to increased tension) and vice versa
  • broken xylem vessel: stops drawing up water as air is drawn in breaks the transpiration stream.
26
Q

Factors affecting transpiration rate

A
  • Light intensity
  • Relative humidity
  • temperature
  • Wind
  • soil-water availability
27
Q

How does light intensity affect transpiration rate

A
  • at higher light intensity
  • more stomata open
  • evaporation from leaf increases
  • rate of transpiration increases
28
Q

How does relative humidity affect transpiration rate

A
  • at higher relative humidity
  • water potential gradient between inside leaf and surroundings becomes shallower
  • rate of transpiration decreases
29
Q

How does temperature affect transpiration rate

A
  • at higher temperatures
  • kinetic energy of water molecules increases, so water evaporates from the leaves quicker.
  • water potential gradient between inside leaf and surroundings increases.
  • rate of transpiration increases.
30
Q

How does wind affect transpiration rate

A
  • at higher wind speeds
  • when water is lost from a leaf, a thin layer of water forms outside the leaf around stomata. This decreases the water potential gradient.
  • wind blows this layer away, increasing the water potential gradient between the inside of leaf and surroundings.
  • rate of transpiration increases.
31
Q

How does soil-water availability affect transpiration rate

A
  • at higher soil-water availability

- rate of transpiration increases.

32
Q

In a potometer, how do you work out the volume of water taken in by the plant?

A

πr²h

33
Q

In a potometer, how do you work out the rate of transpiration and units?

A

mm3min-1

πr²h (mm3) / time taken (mins)

34
Q

What are xerophytes and examples?

A

plants adapted to living in dry conditions

  • cacti
  • marram grass
35
Q

What are hydrophytes and examples?

A

plants that live in or on water.

  • water lilies
36
Q

How are xerophytes adapted to their environments?

A
  • sunken stomata: sheltered from wind.
  • hairs and pits: traps moist air. Reduces the water potential gradient between the inside and outside the plant.
  • rolling leaves: traps moist air (reduces water potential between outside and inside plant), reduces exposed surface area for transpiration to occur.
  • thick waxy cuticle
  • densely packed mesophyll
37
Q

How are hydrophytes adapted to their environments?

A
  • very thin or absent waxy cuticle. (don’t need to conserve water)
  • many always-open stomata on upper surfaces.
  • reduced structure of plant (water supports the leaves and flowers)
  • wide, flat leaves: to increase surface area for photosynthesis.
38
Q

Define transpiration

A

Transpiration is the passive process of the loss of water vapour by evaporation from the surface of leaves and stems of a plant.

39
Q

Define translocation

A

Translocation is the active process to transport assimilates, especially sucrose, in the phloem between sources and sinks.

40
Q

what is the sugar transported as in translocation

A

glucose is transported as sucrose.

41
Q

source examples?

A
  • green leaves (can be both source and sink) and green stems
  • tubers and tap roots
  • food stores in seeds during germination
42
Q

sink examples?

A
  • growing roots

- meristems

43
Q

adaptations of companion cells for translocation?

A
  • lots of mitochondria to provide ATP for active pumping of H+ ions and sucrose across its membrane
  • nucleus to control the activities of itself and the sieve tube element.
44
Q

two routes which assimilates are loaded into the phloem?

A
  • symplast route (passive - through plasmodesmata)

- apoplast (active)

45
Q

What are the three stages of translocation?

A
  • active loading
  • mass flow
  • unloading at the sink
46
Q

Stages of active loading

A
  • hydrogen ions are actively pumped by proton pumps from the companion cells into the source by active transport (ATP provides energy).
  • hydrogen ion concentration increases outside the companion cell.
  • hydrogen ions re-enter companion cells along with sucrose molecules via carrier proteins by facilitated diffusion (passive).
  • sucrose molecules then diffuse into phloem sieve tube elements via the plasmodesmata.
47
Q

Stages of mass flow

A
  • increase in solute concentration in the sieve tube decreases water potential.
  • water enters sieve tube by osmosis from xylem.
  • hydrostatic pressure inside sieve tube at the source increases.
  • water and solutes move towards sink down a hydrostatic pressure gradient along the phloem.
48
Q

stages of unloading at the sink

A
  • solutes leave the sieve tube at sink by diffusion
  • water potential inside sieve tube increases.
  • water moves out of sieve tube by osmosis to xylem.
  • water potential and hydrostatic pressure decreases. Creates a low hydrostatic pressure at sink compared to high hydrostatic pressure at source.
49
Q

evidence of mass flow theory

A
  • advances in microscopy
  • if mitochondria in companion cell are poisoned, translocation stops.
  • feeding aphids
  • rate of flow of sugars in phloem (10000 times faster than if diffusion alone, suggesting an active process for mass flow).

Biology Year 12 (11 decks)

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