Transport in plants and transpiration Flashcards
What is the stele?
Vascular cylinder containing xylem and phloem (vascular tissue)
What does xylem transport?
Water and mineral salts
What does phloem transport?
Sugars e.g. sucrose
What are some characteristics of xylem vessels?
Highly specialised for transport of water and minerals
No end walls
No cell contents
Are dead
Secondary walls are thickened with lignin
What is the purpose of pits?
Allows movement of water between adjacent vessels and surrounding cells
What are 2 important properties of lignin?
Strength - prevents vessels from collapsing under the pressure of transpiration
Waterproof - prevents leakage of water
What is the definition of transpiration?
Evaporation of water from the mesophyll surface and subsequent diffusion of H2o vapour through the stomata and into the atmosphere.
What are the 3 main stages of transpiration?
Into and across the root
Up the root and stem into the xylem
Through the leaf and evaporation of water from the leaf
Explain the movement of water through roots:
Vast majority plants are terrestrial
Need to conserve water - waxy cuticle
Cannot absorb water over general surface
What helps root absorb water?
Root hairs
What does a root hair look like?
Long
thin
extension of a root epidermal cell
How long will a root hair be functional?
A few weeks
What is the main function of root hair cells?
Exchange surfaces in plants responsible for absorption of mineral ions and water
Why are root hairs efficient exchange surfaces?
A large surface area - occur in thousands of each root branch
Thin surface layer - substances can move easily
Does the soil have a low or high water potential and why?
High - soil solution is mostly water
Do root hair cells have a low or high water potential and why?
Low water potential - contain solutes such as sugars, amino acids and mineral ions
What direction will the water move in relation to root hair cells?
From the soil solution into root hair cells -
from high water potential to low water potential
What are the two pathways water moves once it has entered the root hair cells?
Apoplastic pathway
Symplastic pathway
Where does water move in the apoplastic pathway?
Along the cellulose microfibrils of the cell wall
What is special about microfibrils and what does this mean for the movement of water?
They are parallel
Water moves between the layers rather than through them
What is the movement of water within the apoplastic pathway?
cell wall - cell wall
What is meant by cohesive?
The water molecules stick to each other
When water is drawn into the endodermal cells what happens?
More water is pulled along behind it
How does water move in the Symplastic pathway?
From cytoplasm to cytoplasm
Where does the water pass through?
Through tiny openings in the cell wall
What are these tiny openings called?
Plasmodesmata
What does each plasmodesmata contain?
filled with a thin strand of cytoplasm
What does water entering by osmosis do within the symplastic pathway?
Increases the water potential in the root hair cell
What does this therefore mean?
Has a higher water potential than the first cell in cortex
In what way does water move in the symplastic pathway?
Water moves from root hair cell to first cell in cortex by osmosis
What way will water move by osmosis?
Moves from cell to cell by osmosis along water potential gradient
How do ions enter root hair cells?
By facilitated diffusion/ active transport
Either along or against the concentration gradient
What is the first step of water moving into xylem?
When water reaches the endodermis by the apoplastic pathway - waterproof casparin strip prevents it from progressing along the cell wall
Where is water forced during the symplastic pathway?
Into the living protoplast where it travels along the symplastic pathway
What does the endodermal cells transport?
Actively transports salt in the xylem
What does this process require?
Energy
Where is the only place this process can occur?
In living tissue
What must water enter first to get into the xylem?
Must enter the cytoplasm of endodermal cells
