1. Transportation in Plants
Section 4.2

2. Learning Goal
To enhance our knowledge of plant systems by looking at now water and minerals are transported within them

3. Introduction
Plants have a system to transport fluids and nutrients from 1 part of the plant to another
Basically – a plant is a tube with its base embedded in the ground, where the base of the tube is the root system, and the leaves are at the top of the tube

4. Introduction A plant needs 2 kinds of transportation
Job One – move sugars
Sugars made in the leaves by photosynthesis must be carried to all other living cells in the plant
So WATER that carries these dissolved sugars must move up and down the tube
Cells in the Phloem do this
Job Two – move water up
Water and dissolved nutrients must be taken up by the roots and sent to cells, so water moves up the tube
Cells in the Xylem do this

5. How things move in / out
Particles move based on concentration gradients – the amount of a substance on one side versus the other
This happens because of DIFFUSION
Where substances move from a HIGH concentration to a LOW concentration

6. How things move in / out
Similarly, water also moves from a HIGH [ ] to a LOW [ ]
This more specific type of diffusion is called OSMOSIS
Diffusion and Osmosis occur naturally and allow water, sugars, and nutrients to be transported throughout the plant

7. Transport in the Xylem
The root cells have a higher [ ] of dissolved nutrients than the surrounding soil
So water moves INTO the roots by Osmosis, where:
Water moves through the root cells or intercellular spaces within the root and enters the Xylem
The water is then transported in the Xylem up through the root into the stem
Inside the stem, water moves by Osmosis into other tissues

8. Transport in the Xylem
As the xylem tissue carrying water and minerals enters the leaf, the conducting vessels branch into the many veins
From the end of each vein, water and minerals can diffuse into the cells of the leaf
Unfortunately, more than 90% of the water that reaches the leaf evaporates out through the stomata through a process called transpiration

9. Transport in the Xylem

10. Transport in the Xylem
But how does water from the ground reach the tops of a 30 foot tree?
Well there are 2 processes that let this happen:
Root Pressure –positive pressure (pushing mechanism)that pushes water up through the xylem
Transitional Pull – negative pressure (pulling mechanism) help move water move up through the xylem

11. Transport in the Xylem

12. Transport in the Xylem Root Pressure
Is created under certain conditions, like at night time when there isn’t so much transpiration and the soil is moist
As root cells bring minerals into the xylem, the mineral [ ] in the xylem increases
This high [ ] of minerals increases the tendency of water to diffuse into the root xylem by OSMOSIS
As water flows in, the pressure in the roots builds up in the xylem and push water upwards in the plant
However, this root pressure is not enough to force to move water alone – so plants also use Transpiration Pull
Water entering the roots create a POSITIVE Pressure that pushes water UP
Minerals move from the soil into the xylem against their [ ] gradients by Active Transport
The now added minerals in the xylem makes MORE water move up by OSMOSIS
This process is added by the adhesion (sticking) of water molecules to the cell walls of the xylem tissue

13. Transport in the Xylem Transpirational Pull
Looks at pulling water up AGAINST Gravity
Negative pressure (Pulling) from above is the Strongest force for long-distance heights
The COHESION-TENSION MODEL accounts for the majority of water and minerals moving from the roots all the way up in the leaves of the tallest trees
Since more than 90% of water that is absorbed from the roots is lost via Transpiration, water from the leaves creates a negative pressure that PULLS water up to replace its loss in evaporation

14. Transport in the Xylem Transpirational Pull
There are 3 Main Factors that make this process work:
Transpiration – the evaporation of water molecules from the shoot system, is responsible for the movement of water and dissolved minerals upward in a plant stem. Dry air, heat, and wind cause this to take place, as water exits through the stomata

15. Transport in the Xylem Transpirational Pull
Cohesion – the columns of water in the xylem have a property called cohesion, where the force of attraction between water molecules keeps them together in the xylem

16. Transport in the Xylem Transpirational Pull
Adhesion – causes the water molecules to stick to the xylem walls. Adhesion works with cohesion to keep water from separating and keeps on being pulled up in the plant

17. Transport in the Xylem

18. Nutrient Transport in Phloem
How does the sugar made in the leaves through photosynthesis get to the other plant cells for food?
Phloem, carries sugars from the leaves to other parts of the plant that need the nutrients.  

19. Nutrient Transport in Phloem
Within the phloem, sugars travel from areas of high sugar concentration and high water pressure, called sources (like a leaf cell)
To regions of low sugar concentration and low water pressure, called sinks (like a root cell)
(Osmotic concentration refers the concentration of solutes, or sugars in this case; where the concentration of solutes is highest, so is the osmotic concentration).
*High [ ] to Low [ ] = Diffusion!*

20. Nutrient Transport in Phloem
This movement of sugar molecules from high [ ] to low [ ] is called Translocation
Translocation allows other cells in the plants to receive the nutrition it needs (sugars) to survive

21. Nutrient Transport in Phloem
A perfect example of this movement is seen when you collect sap from a tree!
During the spring, lots of new leaves begin to grow, for this to happen they need nutrition (sugar)!
Sap contains lots of sugar that is converted into starch, and moves throughout the tree to where its needed
Once the new leaves have grown, they make their own sugar via photosynthesis and provide nutrition to other cells in the plant

22. Review (6) https://www.youtube.com/watch?v=xGCnuXxbZGk Pg. 69 # 3, 5