PLANTS, CELLS AND WATER

 

WATER IS THE MOST ABUNDANT CONSTITUENT OF LIVING ORGANISMS

 

WATER AND HYDROGEN BONDS

 

1. WATER CONSISTS OF A SINGLE

   OXYGEN ATOM COVALENTLY BONDED

   TO TWO HYDROGEN ATOMS

 

2. THE OXYGEN ATOM IS STRONGLY

   ELECTRONEGATIVE SO IT ATTRACTS

   ELECTRONS

 

3. THE ELECTRONS ATTRACTED ARE

   CLOSER TO THE OXYGEN NUCLEUS   THAN THE HYDROGEN NUCLEUS SO,     THE OXYGEN ATOM CARRIES A        PARTIAL NEGATIVE CHARGE AND       THE HYDROGEN ATOMS CARRY A        PARTIAL POSITIVE CHARGE.

 

   THIS ARRANGEMENT MAKES WATER A

   POLAR MOLECULE

 

4. ADJACENT WATER MOLECULES ARE

   ATTRACTED TO ONE ANOTHER

   BECAUSE OF THE UNEQUAL   POSITIONING OF THE ELECTRONS.

   THIS ATTRACTION IS CALLED

   A HYDROGEN BOND.

 

5. THE HYDROGEN BOND IS WEAKER

   THAN EITHER A COVALENT OR

   IONIC BOND.

 

6. THE HYDROGEN BOND IS   RESPONSIBLE FOR THE MANY   UNIQUE PROPERTIES OF WATER

 

   a. LOW MELTING TEMP.(0OC)

   b. HIGH BOILING TEMP.(1000C)

   c. HIGH HEAT OF VAPORIZATION

      (2452J/gm)

   d. ATTRACTION OF WATER TO

      OTHER MOLECULES OR SURFACES

   e. FORMING HYDRATION SHELLS

      AROUND PROTEINS

 

 

 

 

PHYSICAL AND CHEMICAL PROPERTIES

OF WATER

 

1. LIQUID OVER THE RANGE OF

   TEMPERATURES COMPATIBLE WITH

   LIFE

 

2. HAS A HIGH SPECIFIC HEAT (CAN

   ABSORB LOTS OF ENERGY BEFORE

   THERE IS A TEMPERATURE RISE)

 

3. HAS A HIGH THERMAL CONDUCTIVITY (CONDUCTS HEAT

   AWAY FROM POINT OF APPLICATION)

 

4. HAS A HIGH HEAT OF FUSION

   (HIGH ENERGY IS REQUIRED TO

   CONVERT ONE GRAM OF ICE TO ONE

   GRAM OF WATER)

 

5. HAS ITS MAXIMUM DENSITY IN THE

   LIQUID STATE.

 

 

 

6. HAS A HIGH HEAT OF VAPORIZATION (THE AMOUNT OF

   ENERGY NEEDED TO CONVERT ONE

   MOLE OF LIQUID WATER TO ONE

   MOLE OF WATER VAPOR).

 

7. WATER IS CLOSE TO BEING THE

   UNIVERSAL SOLVENT BECAUSE SO

   MANY THING CAN DISSOLVE IN IT.

 

   a. DUE TO HYDROGEN BONDING

   b. POLAR THINGS DISSOLVE IN

      POLAR SOLVENTS.

  

8. WATER MOLECULES ARE ATTRACTED

   TO EACH OTHER (COHESION)

  

   a. GIVES WATER SURFACES A HIGH

      SURFACE TENSION

 

   b. GIVES WATER COLUMNS A HIGH

      TENSILE STRENGTH

 

 

 

 

9. WATER MOLECULES ARE ATTRACTED

   TO SURFACES (ADHESION)

     

   a. IMPORTANT FOR CAPILLARY

      RISE OF WATER IN THE XYLEM

 

TRANSLOCATION OF WATER

 

TRANSLOCATION - MOVEMENT OF

SUBSTANCES FROM ONE REGION TO ANOTHER

 

SOIL --> PLANT --> ATMOSPHERE

 

TRANSLOCATION CAN BE ACTIVE (ENERGY REQUIRED) OR

PASSIVE (NO ENERGY REQUIRED)

 

IN THE CASE OF WATER, TRANSLOCATION IS PASSIVE

 

 

 

 

 

 

THE TWO TYPES OF PASSIVE MOVEMENT ARE:

 

   1. BULK FLOW (MASS FLOW)

 

   2. DIFFUSION

 

      a. OSMOSIS

 

BULK FLOW IS PRESSURE DRIVEN

(ie. GRAVITY)

 

   EXAMPLES:  WATER IN A HOSE

              WATER COLUME IN A

                 PLANT

              WATER IN A STREAM

 

DIFFUSION IS DIRECTED MOVEMENT IN RESPONSE TO A CONCENTRATION GRADIENT

 

OSMOSIS IS THE DIFFUSION OF WATER OVER A SELECTIVELY PERMEABLE MEMBRANE

 

 

OSMOSIS CAN BE DEMONSTRATED USING AN OSMOMETER

 

 

 

 

 

 

 

 

 

 

WHEN TWO DIFFERENT CONCENTRATION SOLUTIONS ARE SEPARATED BY A

DIFFERENTIALLY PERMEABLE MEMBRANE, WATER WILL MOVE FROM THE SIDE HAVING THE LOWEST CONCENTRATION TO THE SOLUTION HAVING THE HIGHEST CONCENTRATION (THE SOLUTION HAVING A HIGH CONCENTRATION OF SOLUTES HAS A LOW CONCENTRATION OF WATER.  THE SOLUTION HAVING A LOWER CONCENTRATION OF SOLUTES HAS A LOW CONCENTRATION OF WATER)

 

THE PRESSURE NECESSARY TO PREVENT THE MOVEMENT OF WATER FROM A SOLUTION HAVING A LOW SOLUTE CONCENTRATION TO A HIGH SOLUTE CONCENTRATION IS CALLED

OSMOTIC PRESSURE

 

FACTORS INFLUENCING OSMOSIS:

 

   1. CONCENTRATION

   2. PRESSURE