Transport in Plants (Lecture 9)

Plant Transport

—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

Transport Mechanisms

—Passive transport                                 

• Passive Diffusion
• Facilitated Diffusion
• Osmosis

—Active transport

—Plant transport tissues: Bulk transport

• Xylem
• Phloem

 

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:

1. Tracheids (Xylem Cells)

ØElongated with pitted walls that transport materials upwards         

ØAt maturity,

Ølignin can be seen deposited at the cell walls

Øno cytoplasm

2. Xylem Vessels

ØLong continuous, nonliving hollow tube

ØNo cytoplasm

ØWalls are strengthened by lignin

 

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

 

 

Plant Transport:

Organization of vascular tissue in Stem:

Organization of vascular tissue in Root:

Functions

1.Anchor the plant

2.Specialized in absorption of water & dissolved minerals

Adaptations

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 Structures

Transport in Plants

—Three scales of plant transport

• Intracellular

÷Epidermal cells

• 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

Transpiration

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

Translocation

Is moving food (sucrose and amino acids) from the sources (leaf, root) to sinks (developing flowers/fruits, storage organs) through the phloem vessels.