Transport

Why do multicellular organisms need transport systems? Too big so not all of their cells have contact with the external environment.  All organisms need to exchange substances with their environment - take in needed molecules and get rid of waste. 

Surface area to volume ratio

Transpiration What do you remember?

It is a consequence of gas exchange

Investigating factors affecting transpiration rate Presentations

Dicotyledonous plants Distribution of xylem and phloem Root

Stem

Leaves

Xylem Transports water Supports plant Two types: Vessels – no end walls Tracheids – pits in end walls

Cellulose cell wall strengthened with lignin

Phloem Transporting organic substances Sieve tube elements join end to end Sieve plates between Nucleus and cytoplasm pushed to side

Kept alive by companion cells Lots of mitochondria Connected to sieve tube by plasmodesmata

Movement of water From cell to cell – down a water potential gradient. From cell to environment - first by osmosis then diffusion

Movement of water from soil to xylem

Symplastic pathway Through the cytoplasm and the vacuole Entering adjacent cells through plasmodesmata or cell walls

Apoplastic Pathway Moves through the cell wall

Casparian strip In the stele the cells have a thick, waterproof band of suberin in cell wall Apoplastic pathway stopped. This helps with root pressure.

Roots to leaves Mass flow due to cohesion and adhesion Hydrostatic pressure (transpiration decreases pressure at top) Root pressure (increases pressure at bottom) – active secretion of solutes in to the xylem.

Role of ions in plants Nitrates Magnesium Nitrates provide the nitrogen plants need to construct such vital molecules as amino acids and nucleic acids (DNA and RNA). Also some of the vitamins. Lack of nitrates means stunted growth, low yields, yellow leaves.  Magnesium is the ion that's vital to chlorophyl function and photosynthesis. Without it leaves turn yellowish and/or red orange in colour, shrivel and die.

Xerophytic Plants video

Translocation Food is transported from source to sink Mainly sucrose Actively pumped into the sieve tubes at the source Water follows by osmosis, creating high pressure. Sugar is then removed by active transport, and water again by osmosis, lowering the pressure in the sieve tube at the sink.

Sugar Loading and Unloading There are two known mechanisms In one, it then enters the phloem by attaching to sucrose transporter proteins embedded in the plasma membranes of the sieve elements and companions cells. In the second mechanism, sucrose enters through plasmodesmata they unload from the phloem either through plasmodesmata or by crossing from one cell to another across the cell walls.

Loading Hydrogen ions are pumped out of the companion cell in to the source cell Hydrogen ions flow back by diffusion through a carrier protein that also carries sucrose. High concentration of sucrose in companion cell causes sucrose to flow into phloem through plasmodesmata.