Chapter 9- Plant Bio Flashcards
Transpiration
The loss of water vapour from the leaves and stems of plants
Stomata formed from?
2 specialized guard cells.
When it’s light what happens to the stoma and why?
It opens because plant need carbon dioxide to photosynthesise.
At night what happens to the stoma and why?
It closes to prevent excessive water loss! Don’t photosynthesise at night (cuz there’s no light!)
The active process of drawing water into the stomata
Protein pumps (K+ ion pumps) in guard cell membrane = accelerates opening of the stomata by pumping in ions
* reduces the water potential
therefore water enters
Abiotic factors influencing Transpiration
- Lots of stomata allows more transpiration than less big ones
- Wind blows away evaporated water = reduces humidity around stomata
(Evaporation is more difficult in higher humidity, as air is more saturated with water) - Hotter temps = cause more evap = more transpiration
- More light = stimulates stomata opening and leaf warming
Characteristic of Xylem
- Hollow dead cells joined end-end
- continuous tubes (narrow) = strengthened with lignin (polymer)
- Rigid structure = prevents them from collapsing under low-pressure
- Pits in the wall = allows movement across
- No cell content, no nucleus, no cytoplasm, no end wall!
Xylem only function when they’re___?
dead
Cohesion of water, and what it allows to happen in plants?
When one water molecule is attracted by other ones by Hydrogen bonding.
Allows water to be pulled up from the xylem in a continuous stream.
Adhesion of water, and what it allows to happen in plants?
When water = attracted to hydrophilic parts of cell walls of xylem.
Causes water to be drawn through the cell wall from the nearest available supply to replace water loss from evap.
Adhesive property and evap, generates what?
Tension force in the leaf cell wall.
Transpiration pull is caused by?
The low pressure, generating a pulling force that goes up from the roots through the xylem.
*Strong enough to move water upwards, against the force of gravity.
Is transpiration passive or active?
PASSIVE. With all the energy needed coming from the thermal energy that causes transpiration.
What does the active process of minerals in roots cause?
Absorption of water by OSMOSIS.
Where is the vascular bundle in the roots, and why is it in that position?
In the middle = to support the root and prevent it from being pulled out.
Where is the vascular bundle in the stem, and why is it in that position?
Scattered = cuz the stem needs to be able to bend.
Is the concentration of mineral ions in soil or roots higher?
Roots (can be up to 100x higher!)
How do the minerals (positively charged so stick onto soil) that are stuck onto soil particles (negatively charged) taken into plants?
+ Root hairs pump out H+ ions to knock out (displaces) the minerals stuck onto the soil particles.
+ so that the plants can suck the minerals up through the roots through PUMP PROTEIN.
Symplastic pathway
When water moves from Cytoplasm - Cytoplasm
* Through the PLASMODESMATA (holes in the cellulose wall to make cytoplasm continuous!)
Apoplastic pathway
When water moves by capillary through CELLULOSE CELL WALL.
* Cohesion occurs between water molecules also adhere to cellulose fibres.
What does the Casparian Strip do?
Acts as a barrier to the movement of water and minerals by the APOPLASTIC pathway.
Xerophytes
Plants adapted to growing in deserts + other dry habitats.
Strats for Xerophyte survival?
+ increase rate of water uptake from soil
+ decrease rate of water loss by transpiration
Ephemeral Xerophytes
+ Have a v. short life cycle that’s completed in brief period when water is available after rainfall
+ Then remain dormant as embryos inside seeds until the next rain
Perennial Xerophytes
+ Rely on the storage of water in specialized leaves, stems or roots!
What are the adaptations of Cactus? (3)
1) Leaves reduced to spines
2) Stems = contain water storage tissues and become swollen after rain
3) Epidermis = thick waxy cuticle
Halophytes
Plants adapted to Saline conditions
Adaptations of Halophytes (3)
1) structures for removing salt build up
2) Water storage structure develops in leaves
3) Thick cuticle and multiple layer epidermis
Mass Flow
When Phloem uses water from the xylem to help move sugars
Phloem can also travel through cell walls, how?
+ From mesophyll cells → cells walls of companion cells and sometimes sieve cells
= where sucrose transport protein actively transports sugars in
Symplastic moving of sucrose on phloem
+ Travels betw/ cells through plasmodesmata
Once the sucrose reaches the companion cell when transported in symplastic route what happens?
Converted to oligosaccharide to maintain sucrose concentration
Water will flow from an area of what?
High pressure → low pressure
Water potential
The measure of the tendency of water to move from one area to another
Water potential Ψw
Ψw = Ψp + Ψs
Water potential = pressure potential + Solute potential
Pure water’s solute potential is
0
The more negative the solute potential?
The more solute there is dissolved in the water
Phloem: Sieve tube elements
+ living!
→ They depend on the membrane to help maintain the sucrose and organic molecules conc. est. by active transport
+ Have reduced cytoplasm and NO nucleus
Phloem: Companion cell
+ share the same parental cell as sieve tube el.
+ perform many genetic and metabolic funct. of sieve tube cell and maintain ability to survive!
+ Has lots of mitochondria = active transport
Phloem: Plasmodesmata
+ connects the cytoplasm of comp. cell and sieve tube cell
→ hv. smaller diameter than plasmodesmata found in other parts
+ facilitate movement of oligosaccharides and genetic material betw/ cells
Evidence of translocation (2)
1) By giving plants radioactive CO2 (carbon 14)
→ Make radioactive nutrients
→ can be seen by radioactive detectors
2) Aphids = suck nutrient rich phloem
→ cutting stylet the phloem can be analysed
→ The closer the stylet is to the sink the slower the phloem will flow so the slower the phloem sap will come out through stylet
Totipotent
Cells that can differentiate into any cell type including embryo and placenta
Meristem
Composed of undifferentiated cells undergoing active cell division
What do cells in meristem do?
+ They’re small and undergo cell cycle repeatedly to produce more cells by mitosis and cytokinesis
With each division of cells in the shoot apical
+ 1 cell remains in the meristem
+ The other increases in size and differentiates as it is pushed away from the meristem region
Leaf primordia
youngest dev. leaf
Axillary bud
Dev. bud
Apical meristem (2)
+ shoot apical
+ root apical
IAA
Indole-3-Acetic Acid
+ most abundant Auxin
+ controls growth in shoot apex
+ promotes elongation of cells
+ synthesised in apical meristem of shoot
→ transported down stem to stimulate growth
What can v. high conc. of Auxin do?
INhibit growth
