Ch3Water and Plant Cell
Dr. Huseyin Tombuloglu
GBE310 Spring, 2015
Why do we start with water?
• Water is critical for plants functionally and
structurally
• Water relations are fundamental to plant
growth and function
What roles does water play in plants?
1.
The universal solvent
2.
The largest constituent of all cells, and plant cells in
particular 80 to 90% water by weight
3.
Acts as medium for macromolecular structure,
4.
Participates in biochemical reactions
5.
Medium for transport
6.
Evaporative cooling, moderates the rate of temperature
changes
7.
Hydrostatic support, helps provide structure for plants
8.
Driving force for movement
9.
Driving force for growth
10. And more . . .
“(there is) no doubt that water has the
largest collection of anomalous
properties of any common substance”
Kramer and Boyer (1995):
Water Relations of Plants and Soils
How water molecules goes up to the
higgest parts of a plant?
Water Properties
1. Partial polarity
Water Properties
2. Hydrogen bonding
FIGURE 3.4 (A) Hydrogen bonding between water molecules results in local aggregations of
water molecules. (B) Because of the continuous thermal agitation of the water molecules, these
aggregations are very short-lived; they break up rapidly to form much more random
configurations.
Water Properties
3. Highly stable
•High specific heat & latent heat of vaporization
•Resistant to compression and tension
(>-30 MPa)
Latent heat of vaporization
is the energy needed to separate molecules from the liquid phase
and move them into the gas phase at constant temperature—a
process that occurs during transpiration.
For water at 25°C, the heat of vaporization is 44 kJ mol –1
—the highest value known for any liquid.
Most of this energy is used to break hydrogen bonds between
water molecules
Liquid
Latent heat of vaporization cal/g
Water
540
Ethanol
204
Acetone
125
Chloroform
59
Water Properties
4. Displays adhesion
•Attraction to surfaces
5. Displays cohesion
•Attraction to other water molecules
Capillary action = adhesion + cohesion + surface tension
Contact angle (A) and capillarity (B) of
water
High surface tension
Low surface tension
Unit I Opener Light micrograph of a
soybean root stele
Water movement
ALWAYS PASSIVE!
There are only two ways water can
move
1- Diffusion
2- Bulk flow
Water movement
1- Diffusion
• Movement down a concentration gradient
• Driven solely by a concentration gradient
• A slow process
Water movement
2- Bulk (or mass) flow
– Driven solely by a pressure gradient
– A faster process
Examples:
•Water movement through aquaporins
Cellular examples of water transport
•Diffusion through membranes
•Bulk flow through aquaporins
Nutrition of Plants
1- Water
2- Mineral