C3: Adaptations for transport in plants Flashcards
Describe the structure of a dicotyledon root
From outer layer to Inner:
Root hair
Epidermis (outer layer)
Parenchyma (Cortex)
Endodermis (layer surrounding pericycle and the vascular bundle)
pericycle (layer surrounding the vascular bundle)
Phloem (circles next to X)
Xylem (X shape)
what is the cell called that that uptakes water and how is it adapted to its function
The root hair cell:
Has a large survace area
large vacuole containing cell sap that lowers the water potential within the cell
Describe the uptake of water and ions into root hair cells
Soil solution has a higher water potential than the vacuole so water moves in by osmosis down the water potential gradient.
If there is a higher concentration of ions (eg: nitrates) in the soil than in the root hair cell, the ions are transported into the cell by facilitated diffusion through channel and carrier proteins, but if there is a lower concentration of these ions in the surrounding soil the ions are actively transported into the cell by carrier proteins using energy from ATP.
What are the two main pathways in which water travels through the plant to the xylem
Apoplast pathway - water moves through the cell walls but is not continuous as the Casparian strip in the endodermis forces water into the cytoplasm
Symplast pathway - water moves through the cytoplasm and plasmodesmata(strands of cytoplasm through pits in the cell wall joining adjacent cells so the pathway is continuous)
What is the endodermis
A single layer of cells around the pericycle and vascular tissue of the root.
Describe how the structure of the endodermis is suited to its role
Endodermis’ cell wall has the casparian strip which is the impermeable band of suberin in the cell wall this blocks the movement of water in the apoplast driving it into the cytoplasm
Describe the movement of water and minerals into the xylem
Water has to move into the xylem by osmosis
therefore the water potential of the endodermis has to be higher than in the xylem, this is maintained by:
The movement of water into the cytoplasm via the apoplast pathway
The active transport of minerals and ions into the xylem lowering the water potential in the xylem
Describe the structure of a dicotyldon stem
6 points
From outer layer to inner:
Epidermis
Collenchyma
Parenchyma (cortex)
Phloem
Xylem
Medulla
Describe the structure of the xylem and two of its roles and an adaptation.
consists of:
* Vessels
* Tracheids
* Fibres
* Parenchyma (living)
Xylem are dead cells that transport water and minerals up the plant and provide mechanical strength and support as they are strengthened by waterproof lignin
Name two factors in how water moves through the xylem (transpiration stream)
Cohesion-tension theory
Rootpressure
Describe the cohesion tension theory
as water molecules leave the xylem cells in the leaf by evaporation they pull up other water molecules behind them because they have cohesion(hydrogen bonds between them) this pull produces tension in the xylem
Water molecules also have adhesion which is the attraction to the hydrophilic cells in the xylem which contributes to water movement in the xylem.
Describe root pressure in the xylem
operates over small distances in living plants and is a consequence of osmotic movement of water into the xylem down the water potential gradient acrooss the root and into the base of the xylem pushing water molecules already in the xylem up it.
Describe transpiration
The evaporation of water vapour from the leaves and shoots of the plant out through the stomata into the atmosphere
What environmental factors effect the rate of transpiration
Temperature
Humidity
Air movement
Light intensity
Describe the difference between mesophytes, hydrophytes and xerophytes
Mesophytes - plants living in environments where Water is adequate
Hydrophytes - plants living in a water rich environment
Xerophytes - plants living in environments where water is scarce
Name adaptations of hydrophytes
4 pounns
Little/no waxy cuticle as no need to conserve water.
Stomata on upper surface as lower surface submerged.
Poorly developed xylem as no need to transport water.
Large air spaces (aerenchyma) provide buoyancy and act as
reservoirs of gas.
Name adaptations of Mesophytes
3 piints
Close stomata at night to decrease water loss.
Shed leaves in unfavourable conditions, e.g. winter.
Underground organs and dormant seeds survive winter.
Name adaptations of Xerophytes
4 points
Thick waxy cuticle reducing water loss by evaporation from epidermal tissue.
Sunken stomata increasing humidity in an air chamber above the stomata, reducing diffusion gradient and therefore water loss by transpiration.
Rolled leaves - reduces area of leaf exposed directly to air.
Stiff interlocking hairs trap water vapour inside rolled leaf, reduces water potential gradient and therefore water loss.
Describe the structure of the phloem
Phloem sieve tubes carry sucrose and
amino acids.
Sieve elements end in sieve plates containing pores through which cytoplasmic filaments extend linking cells. (plasmodesmata)
No other organelles are in the sieve elements.
Companion cells contain many mitochondria for ATP and ribosomes for protein synthesis.
Proteins and ATP are passed to the sieve elements through plasmodesmata.
Define translocation
The active movement of solutes of photosynthesis (sucrose and AA) through the phloem from source to sink.
this movement can be any direction (up,down,sideways) unlike the xylem which is only up
Describe the for and against of the mass flow hypothesis
1 point for , 4 points agaist
For:
Sucrose made at source
lowers water potential. Water
enters cells and sucrose is
forced into phloem (loading).
This increases hydrostatic
pressure and therefore mass
flow occurs along the phloem
to the root where sucrose
is stored as starch, water
potential is less negative and
water moves into the xylem.
Against:
Sieve plates impede flow.
Translocation is faster than expected
with diffusion.
This theory does not explain
bidirectional flow or different rates of
flow of sucrose and amino acids.
Does not explain companion cell
mitochondria, high O2 intake or
stopping of translocation by cyanide.
