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Biology a level - ocr a > Chapter 9 - Transport In Plants > Flashcards

Chapter 9 - Transport In Plants Flashcards

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1
Q

Name three reasons why multicellular plants need transport systems

A

Metabolic demands
Size
Surface are : volume

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2
Q

Metabolic demands for plant transportation

A

Internal and underground parts of the plant need to transport

  • Oxygen and glucose for photosynthesis
  • Remove waste products from metabolism reactions
  • Hormones to areas where they have an affect
  • Mineral ions around the body from the root, to make proteins for enzymes and cell structure
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3
Q

Size demands for plant transportation

A

Large plants need effective transport systems that will transport substances (assimilates) from the roots to the leaves

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4
Q

Surface area: volume demands for plant transportation

A

Quite a small sa:v

So can’t rely solely on diffusion to supply cells with everything they need

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5
Q

Function of xylem

A

Transport of mater and mineral ions in solution from bottom to top

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6
Q

Describe the xylem

A
  • Made from columns of vessel elements fusing together end to end
  • Non living tissue, dead cells
  • Walls thickened with lignin - support, structure, waterproof (spirals, rings)
  • Bordered pits - water ions move into and out of
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7
Q

What does xylem tissue contain:

A

Parenchyma

  • packs around xylem vessels
  • stores food
  • contains tannin (protects from attack)

Fibres

  • long cells with lignified secondary walls
  • provide extra mechanical strength
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8
Q

Function of phloem

A

Transports organic solutes such as sugars and amino acids , needed for cellular respiration and synthesis, around the plant from the leaves where they are made by photosynthesis

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9
Q

What are the main transporting vessels of the phloem

What does the phloem tissue consists of

A

Phloem sieve tube elements

  • no nucleus, thin layer of cytoplasm, few organelles
  • many cells joined end to end to form hollow structure
  • sieve plates let solutes pass through

Companion cells

  • carry out living function for both of them
  • provide the energy for the active transport of solutes

Fibres, parenchyma and sclereids
- support and provide strength

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10
Q

Positioning of transport tissue in herbaceous dicot

Stems

Roots

Leaves

A

Near the outside
- strength and support, reduces bending

Xylem in centre (x)surrounded by phloem
- gives strength against tugging forces

Large central vein containing vascular bundle
- support for thin leaves

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11
Q

Similarities between phloem and xylem

A

Transport materials around plant

Made up of cells joining end to end forming long hollow structures

Sieve tube elements and xylem vessel elements don’t have nucleus

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12
Q

Differences between phloem and xylem

A

Xylem is non living tissue
Xylem transports water and supports plant - phloem transports organic solutes
Xylem transports only up - phloem does up and down
Phloem doesn’t have lignified walls

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13
Q

Uses of water in plants

A
  • turgor pressure supplies support for leaves, stem and drives cell expansion
  • loss of water keeps plant cool
  • raw material for photosynthesis
  • mineral ions and products of photosynthesis transported in it
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14
Q

How are root hairs adapted as exchange surfaces

A
  • small size so can penetrate easily between soil particles
  • large SA:V
  • thousands of hairs
  • thin surface layer - easy diffusion
  • concentration of solutes in cytoplasm maintains a water potential gradient (sugars, mineral ions, amino acids)
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15
Q

What is the symplast pathway

What causes continuous flow

A

Travels through cytoplasm and plasmodesmata (small channels in cell walls)

Via osmosis

  • root hair cell has higher WP than the next cell
  • result from water diffusing in from cell
  • made cytoplasm more dilute
  • continues to the other cells by diffusion
  • when water leaves root hair cell, WP in cytoplasm falls
  • creating WP concentration gradient
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16
Q

What is the apoplast pathway

What causes continuous flow

A

Goes through cell walls

Move from high hydrostatic pressure to low hydrostatic pressure
Mass flow

  • as water enters xylem, water is drawn through apoplast pathway
  • due to cohesive forces that creates tension
  • meaning there is a continuous flow
17
Q

How does water travel from the roots hair to endodermis layer

A
  • water enters root hair cell
  • passes through the root cortex by both symplast and apoplast pathways
  • when apoplast reaches endodermis it is blocked by the waxy casparian strip
  • forces water to take symplast route so it has to pass through the selectively permeable cell surface membrane, filtering out toxic solutes as there is no carrier protein
18
Q

Travelling from endodermis to xylem

A
  • xylem is more concentrated in solutes, so active transport is required to pump minerals
  • water travels by osmosis
  • producing root pressure - this gives water a push up the xylem
19
Q

Evidence for active transport in endodermis

A
  • cyanide (prevent atp production) causes root pressure to disappear
  • root pressure increases with temperature
  • if levels of respiratory substances fall so does root pressure
20
Q

Differences between symplast and apoplast

A

Apoplast composed of non living parts of plant - symplast is living

Apoplast water movement occurs by passive diffusion - symplast occurs by osmosis

Apoplast shows less resistance to the water movement

Apoplast movement is rapid

21
Q

Process of transpiration

A

Plant opens stomata for gaseous exchange

This let’s out water vapour by diffusion

22
Q

Factors that affect transpiration

A

More Light
- stomata open more because photosynthesis increases

Higher Temperature
- water molecules have higher energy so evaporate from cells faster

Lower humidity
- water potential gradient between leaf and air increased

Faster wind
- blows away water molecules around stomata

More Soil water availability

23
Q

How water moves from xylem and out at leaves

A
  • xylem transports water around plant
  • water leaves xylem and moves into cells by apoplast pathway
  • water evaporates from mesophyll cells into air space
  • water leaves into external air when stomata open
24
Q

Transpiration definition

A

Loss of water from a plants surface

25
Q

Transpiration stream

A

Movement of water through a plant

26
Q

How does water move up against the force of gravity

A

Adhesion

  • water forms hydrogen bonds with carbohydrates in the walls of narrow xylem vessels
  • helps water rise up through xylem

Cohesion

  • water molecules form hydrogen bonds with each other and move as a mass
  • water follows up the xylem

Tension

  • transpiration pull produces tension
  • pulls more water into the leaf
27
Q

Evidence for cohesion tension theory

A

Tree diameter decreases when tension in xylem is highest

When xylem is cut, air is drawn into xylem instead of water leaking out

28
Q

How does a stomata open and close

A
  • when conditions are favourable, guard cells actively pump solutes, to increase turgor pressure.
  • because the inner wall of the guard cell is less flexible than the outer, the cell swells and opens the pore
  • when water less water, hormonal signals from root close the cell
29
Q

What is translocation

A

The movement of dissolved substances from sources to sinks

30
Q

Differences between source and sink

A

Source

  • the supplier of carbohydrates needed by cells of plant
  • e.g : leaves, provide sucrose

Sink

  • area of plant that needs assimilates in phloem
  • e.g : roots, meristems
31
Q

The apoplast route from source to sink

A
  • sucrose moves into companion cells and sieve tube elements by active transport
  • hydrogen ions are pumped out of companion cells using ATP
  • they return down a concentration gradient via a co-transport protein carrying sucrose as well
  • build up of sucrose in sieve and companion draws water in by osmosis
  • causing a build up of turgor pressure
  • assimilates move into sieve tube elements and are carried to the sink
  • assimilates leave by diffusion
32
Q

Phloem unloading

A
  • leaves by diffusion

- converted into another substance to maintain a concentration gradient

33
Q

What are the limitations of the use of a photometer

A

Not all water is lost by transpiration

  • photosynthesis
  • maintain turgid

The plant is dying so might not take up as much water

34
Q

Using a photometer

A

Cut the shoot under water and at a slant
Assemble the photometer under water
Take photometer out of water - leave capillary in water beaker
Make sure it is air tight
Dry the leaves
Allow for plant to acclimatise
Shut the tap
Bring capillary tube out of water until an air bubble has formed then put back
Record starting position

35
Q

Adaptations of marram grass to reduce water loss

A

Sunken stomata
- sheltered from wind

Hairs on epidermis
- traps moist air - reduces wp gradient

Roll their leaves

  • traps moist air
  • protects stomata from wind

Thick waxy cuticle
- reduces evaporation

36
Q

Adaptations of cacti to reduce water loss

A

Have spines instead of leaves
- reduces SA of water loss

Close their stomata

37
Q

Adaptations of water lilies to survive in water

A

Air spaces in tissues

  • can float obtain maximum light for photosynthesis
  • act as oxygen store

Stomata on upper leaf
- maximise gas exchange

Have flexible leaves
- prevent damage by water current

Biology a level - ocr a (11 decks)

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