Download File

Transport in Plants
SECTION 3.4
UNIT C
Objectives
 distinguish between cohesion and adhesion, giving
examples
 describe water transport from root to leaf including
different processes used
 relate tonicity of plant environment to movement of
water in and out of the cell
 summarize the process of sugar transport in plants
Review
 What is osmosis?
 What is diffusion?
 What is active transport?
 What is transpiration? Where does it take place?
Plant Transport of Water: 3 Main Steps
 1) Water uptake in roots – root pressure
 2) Cohesion & Adhesion in Xylem
 3) Leaf transpiration
Animation:
http://www.biology.ualberta.ca/facilities/multimedia/uploads/alberta/transport.
html
Root Pressure
 Movement of water from roots to leaves
 Pressure built up in xylem
 Dissolved minerals in root cells due to active
transport
 Water enters cell, creating positive pressure, forcing
fluid up the xylem
 Water forced from area of higher pressure in roots to
area of lower pressure in leaves
Root Pressure
 When would root pressure not be the complete
explanation for water movement in plants?

When the plant is very large (maximum of a few metres)
 Overall process affected by transpiration
Cohesion and Adhesion
 Cohesion
 Attraction of water molecules to other water molecules
 Due to polar nature of water (slightly positive end attracts
slightly negative end of another water molecule)
Cohesion and Adhesion
 Adhesion
 Attraction of water molecules to molecules of other substances
 Usually polar interactions
Cohesion & Adhesion in the plant
 Cohesion and adhesion are two properties
of water that helps it to travel from roots to
leaves.
 Cohesion

Causes water molecules to cling to each other
 Adhesion
 allows water to pull itself up
the plant
 Video:
http://www.youtube.com/watch?v=EKyHbanzYnI&feature
=related
 Trees & Capillary Action:
http://www.davidlnelson.md/Cazader
o/Trees&CapillaryAction.htm
Transpiration
 Evaporation of water through stomata and lenticels
through transpiration creates a tension or
transpiration pull.
 When combined with cohesion, adhesion, and root
pressure, water is able to be drawn up the xylem.
 Transpiration is dependent on temperature. Higher
temperatures increase the rate of evaporation and
cause rapid movement in xylem.
Video: Plant Transport - Summary
 http://www.youtube.com/watch?v=U4rzLhz4HHk
&feature=related
 Why would the carnation/celery change color?
 How is it related to root pressure and transpiration?
 Transpiration causes the loss of water through the stem and
leaves.
 This water must be replaced, drawing water up from the roots
 Note that only certain cells in the celery are stained
Which cells might these be?
 Xylem

Do Now
 Individually, write a story of water transport in a
large plant using the information on p. 317-318. You
are writing it from the point of view of the water
molecule.
 Explain in your story how the plant uses adhesion
and cohesion properties of water to its advantage
 Include the different transport mechanisms used at
different parts of the plant

Root Pressure, Adhesion, Cohesion, Transpiration
Tonicity & its Effect on the Plant
 Tonicity  concentration of solute particles in an
solution

Related to hypertonic and hypotonic (which one would have a
higher tonicity?)
 What will happen to a plant cell that is placed in a
concentrated salt solution?
Water leaves the plant cell by osmosis
 Effect = plasmolysis (cell looks shrunken)
 Water leaves vacuole, cell contents pull into center,
cell membrane becomes visible

Hypertonic solution
Hypotonic solution
Question
 What would happen to a plant that was placed in a
hypertonic solution (salt solution)?

Becomes flaccid
 What would happen to the plant when it was moved
from this solution to a hypotonic environment?

Becomes turgid
Sugar Transport
 Phloem is essential
 Removal causes plant death
 Takes sugar from source (leaves) to place to be
used/stored (sink)
 Composed of sieve tube cells



Need companion cells to control its activity
Why?
Uses carrier proteins and active transport to take in sugar
molecules
Sugar Transport
 If sugar is being moved into the cells, what else will
follow it?

Water!
 Increased pressure pushes water and sugars through
phloem to rest of plant
 Called the pressure-flow theory
Sugar Uses
 Actively transported from sieve cells in phloem to
adjacent cells
 Use:



Growth
Respiration
Other life processes
 Stored in roots, stems, or leaves
 Water follows movement of sugar and can:
 Increase turgidity of other cells
 Leave through transpiration
 Move into xylem