Transport%20in%20Vascular%20Plants

1
Transport in Vascular Plants
2
Transport in Plants Overview

• movement of materials from one part of a plant to
  another
• involves 2 specialized tissues
• Xylem
• Phloem

3
Xylem Tissue

• Overall Structure
• made of thick cell walls
• most cells are dead
• cells are stacked up on top of another to form a
  hollow tube throughout the plant
• Overall Function
• provides structural support to the plant
• carries water and minerals from roots to leaves
• See Table 1 on pg. 555

4
Phloem Tissue

• Overall Structure
• cells are living
• cell walls are porous, allowing exchange of
  materials with neighbouring cells
• Overall Function
• carries sugars and hormones throughout the plant
• See Table 1 on pg. 555

5
Water Transport in Xylem (1 of 2)

• Roots take in water through the root hairs
  epidermal cells by osmosis
• Water flows through the epidermal cells, cortex
  and into the vascular cylinder which contains the
  xylem.
• Water is then transported in the xylem tissue up
  through the root into the stem and then branches
  into the veins of the leaf. It then moves into
  various tissues of the leaf such as the palisade
  and spongy mesophyll.

6
Water Transport in Xylem (2 of 2)

• Most water exits the plant through a process
  called transpiration
• The water diffuses into air spaces in the spongy
  cells and then diffuses out of the leaf through
  the tiny pores called stomata. As each water
  molecule exits the leaf, another one enters the
  plant through the roots

7
How does a plant move water up from its roots to
its leaves?

• 3 main theories that have been developed to
  account for the movement of water in plants
• these mechanisms are not mutually exclusive any
  or all of these may be at work in a single plant
  at any one time
• Root pressure
• Capillary action
• Cohesion-tension

8
1. Root Pressure

• Plant roots build up pressure that forces water
  upward
• Occurs normally in shorter plants
• Pressure built in roots of tall trees wont
  really push the water that far up (approx. 1
  meter at most)

9
2. Capillary Action (in narrow tubes)

• takes place because of the adhesion of water
  molecules and walls of xylem
• Adhesion intermolecular force between water and
  xylem vessel wall
• the finer the capillary or vessel, the higher
  water will climb up

10
3. Cohesion-tension

• Also known as transpiration pull
• Transpiration is the evaporation of water vapour
  from the leaves through the stomata.
• depends on the cohesive forces between water
  molecules and adhesive forces between water and
  the walls of the vessel

11
Mineral Transport

• By testing the concentration of minerals in the
  roots, scientists know that the amount exceeds
  that of diffusion
• Thus roots are actively pumping minerals and ions
  from the surroundings
• These minerals are dissolved in the water in the
  xylem or roots, which makes it more concentrated
• This increases the uptake of water into the plant

12
Translocation Transport in Phloem

• Translocation occurs through the phloem
• Phloem transport is bi-directional
• Most accepted theory mass-flow theory
• Moves from a sugar source (a place where sugar is
  produced by photosynthesis or by the breakdown of
  sugars) to a sugar sink (an organ which consumes
  or stores sugar)
• borrows water from xylem to help transport
  sugars

13
Transport in Xylem vs. Phloem (P. 569copy into
your notes)
14
Homework

• 1) Copy the translocation diagram from P. 569
  onto your handout 
• 2) Do P. 570 4, 6