January 7 ~Feb1 2013
Midterm date: Monday Febuary 4 2013. 5-7pm
Module 2: Begins on Tuesday Feb 5 . th
Total: 12 lectures
1-2: Tree of life-plants
3-4 Plant cells and plant tissues
5-6. From seed to tree
7-8. From tree to seed
9. Transport in plants
10. Plant nutrition and soils
11. Plant defense
12. Plant life on the edge.
Lecture 9 notes Transport in plants
Basic plant needs: sugar=carbon dioxide + light +water, water, oxygen, minerals
A) Water transport through xylem
i) Hypotheses on mechanisms of water transport.
How does water move through xylem?
Answer: 3 hypotheses: capillary action, root osmotic push, transpiration.
1] capillary action- travels 1 m up xylem
water move upward xylem through adhesion (water & tube walls) and cohesion
(water & water molecutes).
Adhesion is stronger than cohesion.
Capillary action is not strong enough for trees because it travels for 1 meter! 2) Root osmotic push- travels 3 m up xylem
Osmosis (osmotic pressure) is where water diffusion through semipermeable
membrane such as the cell wall from a low concentration to a high concentration
until both concentration are equal.
Plant actively pump ions into root cells with ATP . water moves into cells by osmosis
when oot hair have greater osmotic pressure (high ion_ than surrounding soil.
But his only pushes the xylem by 3meters!
3) Transpiration-travels 100 +m up xylem.
Use of cohesion.
Sun turns liquid water into gas > gas moves from parenchyma into intercellular leaf
space> cohesion pulls water from veins into parenchyma>gas diffuse out of stomata.
ii) Synthesis, total plant water transport
soil to root hair; osmosis
into xylem: osmosis & transpiration pull (from leaves)
up xylem between root and stem: transpiration
root to leaves: cohesion
angiosperms have more efficient trachieds and vessel elements-have perforation
entering of water into roots:
Apoplastic transport:water flows through cell walls, more rapid, faster, less
resistant to water flow
Symplastic transport: water flows through cell and pits of parenchymas.
Casparian strip: waxy layer that makes apoplastic transport impassable.
So it’s: root hair> epidermis>cortex> endodermis> Casparian strip>
stele.(middle/vascular cambium)>xylem parenchyma>xylem vessels
o Endodermis: control layer to what substances can enter xylem.
o So when apoplastic cannot pass, they active transport into symplastic