Topic 7 Transport in plants Flashcards
Xylem
- structural support
- non-living
- thick walls made of cellulose
- cell wall contain lignin
- no end walls
- large lumen
- have pits
- carries waters and minerals
- from roots to parts above ground
Phloem
- Sieve tube elements (living cells)
- have companion cells
- many plasmodesmata
- strong cellulose wall
- peripheral cytoplasm
- have sieve plates
- carries organic compounds made by photosynthesis (particularly sucrose)
- can move in different directions
Types of ground tissue
Parenchyma
- thin cell wall
- cortial, pith and mesophyll cells
- photosynthesis, cell division and storage of nutrients
Collenchyma
- thicker cell wall
- outer cortial cells
- structural support
Sclerenchyma
- Thickest
- contain lignin
- cortial cells or harder stems
- non-living
- only for strucural support
Types of specialised tissues
- Dermal tissue
- Ground tissue
- Vascular tissue
Specialised tissue: Dermal tissue
epidermis
- continuous outside layer of plant
- 1 cell thick
cuticle
- dead cells
- stem and leaves covered with cuticles
stomata
- leaves has pored for gas exchange
Specialised tissue: Ground tissue
(Parenchyma)
Thin walled cells
function:
- photosynthesis
- storage
- support
- gas exchange
- structure
- transport
palisade meophyll (column shaped)
spongy mesophyll (more air space)
(Collenchyma)
- provide flexibility and support
(Sclerenchyma)
- thick lignified cell wall
- often die when mature
Specialised tissue: Vacsular tissue
- Xylem
- Phloem
Transport Mechanism
Apoplastic pathway
- through cell wall/ intercellular space
(Cortex -> endodermis)
= Endodermis has casparian strip (suberised cell wall)
->impermeable to water (apoplastic pathway blocked)
Symplastic pathway
- through cytoplasm/ vacuole/ plasmodesmata
Transpiration (Via..)
Loss of water vapour from leave
1. Via stomata
- diffusion of water vapour from airspace to atmosphere
- Via Cuticle
- loss of water vapour through cuticle on leaf surface
- vary small amount of water loss
Transpiration
- Transpiration pull (cohesion and adhesion)
- water vapour diffuses out via stomata
- water evaporates from mesophyll cell wall surface
- lowers water potential gradient at leaves
- water moves up xylem from roots to leaves - root pressure
- casparian strip at the endodermis blocks apoplastic pathway
- water & ions must pass endodermial cells
- xylem vessels in root increases in solute concetration
- lowers water potential gradient
= more water uptake from soil (increase hydrostatic pressure at roots)
Factors affecting rate of Transpiration
- Humidity
- wind speed
- water availability
- temperature
- light intensity
- stomatal aperture
Xerophytes
plants living in areas with short water supply
Adaptations:
1. Rolled leaves
2. hair/trichomes
3. sunken stomata
4. Stomata only present ion lower/ innder surface
5. reduced number of stomata
6. leaves reduced to spines/ needles/ small leaves
7. thick, waterproof, waxt cuticle
8. multi-layered epidermis
Translocation (source and sink)
Transport of assimilates within plants
source:
- site of photosynthesis
- loading of sucrose into sieve tube
sink:
- site where assimilated are stored
- unloading of sucrose from sieve tube
- phloem sap able to flow upwards/ downwards in a sieve tube sink
Loading sucrose into Sieve tubes
Active transport (requires ATP):
1. H+ ions in companion cells are pumped out (by proton pump)
2. H+ ions gradient build up
3. H+ ions re-enter companion cells down the concentration gradient
4. H+ ions are transported via facilitated diffusion
5. Sucrose is transported via secondary active transport
