Transport in Plants (Lecture 9)
How does water transport from the roots of a tree to its top?
Plants lack the muscle tissue and circulatory system found in animals,
but still have to pump fluid throughout the plant’s body
- Passive Diffusion
- Facilitated Diffusion
Plant transport tissues: Bulk transport
Plant Transport Tissue Systems:
There are two transport systems in a plant.
One that transports water and minerals from root to all other parts.
These vessels are called xylem vessels.
Another vessels transport sugars (sucrose)
and amino acids made in leaves to all other plant parts.
These are called phloem vessels.
Xylem vessels consist of dead cells.
They have a thick, strengthened cellulose cell wall with a hollow lumen.
On the other hand, phloem consists of columns of living cells.
Plant Transport Tissue Systems:
- Tracheids (Xylem Cells)
ØElongated with pitted walls that transport materials upwards
Ølignin can be seen deposited at the cell walls
2. Xylem Vessels
ØLong continuous, nonliving hollow tube
ØWalls are strengthened by lignin
Hard and rigid substance
Named after the latin word “Lignum”, which means “Wood”
Lignin maybe deposited in different ways,
giving rise to annular, spiral or pitted xylem vessels
Organization of vascular tissue in Stem:
Organization of vascular tissue in Root:
1.Anchor the plant
2.Specialized in absorption of water & dissolved minerals
1.Long and narrow
ØIncrease surface area
2.Cells are alive
ØProvide energy for active transport
3.Root hairs have cell sap of higher concentration than surrounding soil solution
ØCell sap contains sugar, mineral salts which helps to prevent water leaking out of cell. Assist in osmosis
Transport in Plants
Three scales of plant transport
- Short distance: cell-to-cell
÷At the levels of tissues and organs
- Long distance: xylem and phloem
A variety of physical processes
Are involved in the different types of transport
How water moves into the plant.
Role of Water in plants
- Solvent for the uptake and transport of molecules
- Water is major component of cells
- Good medium for biochemical reactions
- Provide structural support via turgor pressure in leaves
- The medium for the transfer of plant gamete
- Plant movements are the result of water moving in and out of those plants
- Temperature stabilization
It is the loss of water vapour out of leaves (and stems) through stomata by diffusion.
ØEvaporation of water from the plant
1.The mesophyll cells in the leaves are covered with a thin layer of moisture
- Essential for efficient gas exchange to occur
2.Some of this moisture evaporates into the intercellular spaces which diffuses through the stomata into the air
- Water is pulled upwards through osmosis (Transpiration Pull)
3.The waterway in which the water moves from a higher water potential to a lower water potential
- Transpiration Stream
Transpiration is affected by
|Weather condition||Rate of transpiration||Why?|
|Windy||Speeds up transpiration||Moist air around the leaf is blown away|
|Humid||Slows down transpiration||Air around the leaf is already full of moisture|
|Warm||Speeds up transpiration||Evaporation occurs faster|
|Light||Speeds up transpiration||The stomata opens|
Is moving food (sucrose and amino acids) from the sources (leaf, root) to sinks (developing flowers/fruits, storage organs) through the phloem vessels.