Plant transport Flashcards
What does the xylem tissue transport?
Transports water and mineral ions in a solution. They move up the plant from the roots to the leaves.
What does the phloem tissue transport?
Mainly transports sugars both up and down the plant.
How are xylem vessels adapted to their function?
No end walls; uninterrupted tube allows water to pass through easily. End walls are dead no cytoplasm. Thickened with lignin stops walls from collapsing.
How do water and ions leave the Xylem Vessel?
Through small pits in the walls where there is no lignin.
Sieve tube elements
- Living cells form tube for transporting solutes throughout the plant
- Joined end to end to form sieve tubes
- No nucleus,very thin layer of cytoplasm
- Cytoplasm of adjacent cells connected through holes in sieve plates
SIEVE in sieve tubes
These are the end walls that have lots of holes to allow solutes to pass through like sucrose.
Companion cells
For every sieve tube element, there is a companion cell for each as they cannot survive on their own
- Provides energy for active transport of solutes
Symplast pathway
This goes through the living part of the cell the cytoplasms of neighbouring cells connect through plasmodesmata. Moving via osmosis
Apoplast pathway
Goes through the non-living parts of the cell walls are very absorbant and water can diffuse through it .
Transpiration
The evaporation of water from a plants surface
Consequence of gas exchange when the stomata opens to allow co2.
- Water moves down a potential gradient to move out the leaf
Translocation
The movement of dissolved substances to where there needed in a plant known as assimilates
- Requires energy and happens in the phloem
Factors affecting the rate of transpiration
Light, Temperature, Humidity, Wind
How is marram grass adapted to reduce water loss? (xerophytic)
Stomata sunken in-wall pits to shelter themselves from the wind lowering the rate of transpiration. They also have a layer of hairs on the epidermis which traps moisture.
What does translocation do?
Transports substances from the sources to the sinks
What is a sink?
This is the area where a substance is used up
What is a source?
This is where something is made.+
How do substances enter the phloem?
Through Active Loading; used to move substances into the companion cells from surrounding tissues, and from the companion cells to the sieve tubes against a conc gradient.
Process of Active loading
hydrogen ions / H* / protons, pumped out of companion
cells;
2 increases, hydrogen ion / H* / proton, concentration
(gradient) (outside companion cell) ;
3 hydrogen ions, re-enter / flow back into,
companion cells:
4 sucrose / sugar, moves with hydrogen ions / AW;
5 down concentration gradient ;
6 ref. cotransporter proteins / cotransport(ation);
7 by facilitated diffusion ;
8 sucrose / sugar, diffuses into sieve tube (element) ;
9 through plasmodesmata;
Where is the xylem found on a stem cross section and a root cross section?
- On the inside of both phloem is on the outside
How does water get into the plant?
- Drawn into roots via osmosis
- Soil around roots has a higher water potential and leaves have a lower one which creates a water potential gradient that keeps water moving through the plant in the right direction from roots to leaves
Cohesion and tension theory
- Water evaporates from leaves at top of xylem
- Creates a tension which pulls more water into the leaf
- Water is cohesive so when some are pulled others follow meaning the water in the xylem moves upwards
- Water enters through root cortex cells
Adhesion
- Water also attracted to the walls of the xylem vessels
- Helps water rise up through the vessels
Adaptations of hydrophytes
- Air spaces in tissues to help plant float can also be a store for oxygen
- Stomata only present on upper surface of floating leaves maximising gas exchange
- Flexible leaves and stems
