Ch3-Water and Plant Cell

Dr. Huseyin Tombuloglu

GBE310 Spring, 2015

Why do we start with water?

• Water is critical for plants functionally andstructurally• Water relations are fundamental to plantgrowth and function

What roles does water play in plants?1. The universal solvent2. The largest constituent of all cells, and plant cells in

particular 80 to 90% water by weight3. Acts as medium for macromolecular structure, 4. Participates in biochemical reactions 5. Medium for transport6. Evaporative cooling, moderates the rate of temperature

changes7. Hydrostatic support, helps provide structure for plants8. Driving force for movement9. Driving force for growth10. And more . . .

“(there is) no doubt that water has thelargest 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 Properties1. Partial polarity

Water Properties2. 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 Properties3. 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/gWater 540

Ethanol 204

Acetone 125

Chloroform 59

Water Properties4. 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

Low surface tension

High surface tension

Unit I Opener Light micrograph of a soybean root stele

Water movementALWAYS PASSIVE!

There are only two ways water can move

1- Diffusion

2- Bulk flow

Water movement1- 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 Plants1- Water

2- Mineral