Transport in Plants

Introduction What are plants made of?

Introduction What are plants made of? Plants require at least 17 elements

Introduction What are plants made of? Plants require at least 17 elements Hydrogen (H) & Oxygen (O 2 )  water Carbon Dioxide (CO 2 )  air Other nutritional elements  soil

Introduction What are plants made of? Plants require at least 17 elements Hydrogen (H) & Oxygen (O 2 )  leaves Carbon Dioxide (CO 2 )  leaves Other nutritional elements  roots Transport System for movement of molecules between roots and leaves is necessary.

Molecular movement across membranes Some molecules that are imported or exported from plant cells: – Water – Potassium, phosphorus, etc.

Transport in Plants Symplastic Transport: Apoplastic Transport:

Transport in Plants Symplastic Transport:  Plasmodesmata : microscopic channels connecting cytoplasm between two cells. Apoplastic Transport :

Transport in Plants Symplastic Transport:  Plasmodesmata: microscopic channels connecting cytoplasm between two cells. Apoplastic Transport:  Free diffusional space outside the plasma membrane is called apoplast.  Movement of molecules within the cell walls

Symplastic transport Diffusion Facilitated Diffusion Active Transport Exocytosis and Endocytosis Osmosis

Diffusion Diffusion:  Movement of particles of a substance through a concentration gradient,  Results in equilibrium: the uniform distribution of the substance.

Facilitated Diffusion Transport proteins are involved.  One protein acts alone  Gated channels Size is controlled by channel diameter.  Passive transport

Active transport Moves molecules up a concentration Gradient.  Requires ATP

Transport of Molecules Across Membrane

Osmosis Net movement of a solvent across a partially permeable membrane.  Water is always the solvent in plants Aquaporins Osmosis and diffusion are different…

Osmotic potential (ψ O ): –The measurement of water’s tendency to move across a membrane as a result of solute concentration Pressure potential (ψ P ): –The pressure of the surrounding cell wall. Water potential: Ψ w = ψ O + ψ P

Movement and Uptake of water and Solutes in Plants Vascular System Xylem Phloem Water evaporation from leaves pulls water through xylem from roots.

Some of the water characteristics which help in the transportation process: –Water is a polar molecule –Adhesion: the attraction between water and cell wall molecules –Cohesion: attraction between water molecules –Tension: negative pressure on water

Tension Cohesion Theory Water enters the xylem in the roots by Osmosis. Once in the xylem the water molecules hydrogen bond forming a continuous string of water molecules up to the leaf. Water is constantly lost by Transpiration in the leaf. When one water molecule is lost another is pulled along. Transpiration pull is the main cause of water movement

Gas Exchange and Water Loss in Plants Cuticle: waxy layer outside of most epidermal cells Controlled by stomata  90% of water loss is through stomata Sufficient water Internal CO 2 concentration High winds Low humidity ABA: is produced in roots in response to dry soil

Phloem Responsible for sugar and organic molecule transportation  Sugar Source  Sugar Sink

Transport of Sugars Symplastic  Plants from warm environment Apoplastic  Plants from temperate or cold environments Do you know why??

Pressure-Flow Hypothesis H + ions are pumped out the cell H + + Sugar enter cell by cotransporters When water leaves sieve-tubes it takes the solutes with it.