1. Transport

2. 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. 

3. Surface area to volume ratio

4. Transpiration
What do you remember?

5. It is a consequence of gas exchange

6. Investigating factors affecting transpiration rate
Presentations

7. Dicotyledonous plants
Distribution of xylem and phloem
Root

8. Stem

9. Leaves

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

11. Cellulose cell wall strengthened with lignin

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

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

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

15. Movement of water from soil to xylem

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

17. Apoplastic Pathway
Moves through the cell wall

18. 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.

19. 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.

20. 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.

21. Xerophytic Plants
video

22. 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.

24. 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.

25. 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.