BIOLOGY 101 - Modesto Junior College

BIOLOGY 101

CHAPTER 3: Water and Life:

The Molecule that supports all Live

Water and Life:

The Molecule that Supports all Life

CONCEPTS: ? 3.1 Polar covalent bonds in water molecules result in hydrogen bonding ? 3.2 Four emergent properties of water contribute to Earth's suitability for life ? 3.3 Acidic and basic conditions affect living organisms

Water and Life:

The Molecule that Supports all Life

OVERVIEW:

? The physical properties of water are dictated by the laws of thermodynamics

The First Law of Thermodynamics Energy cannot be created or destroyed, it can only be transformed

The Second Law of Thermodynamics The total entropy of an isolated system always increases over time

or... High energy systems spontaneously change to lower energy systems

Water and Life:

The Molecule that Supports all Life

3.1 Polar covalent bonds in water molecules result in hydrogen bonding:

? A water molecule is shaped like a wide V, with two hydrogen atoms joined to an oxygen atom by single polar covalent bonds.

? Because oxygen is more electronegative than hydrogen, a water molecule is a polar molecule in which opposite ends of the molecule have opposite charges. Polar molecules have a separation of charges, having both positively and negatively charged regions

Water and Life:

The Molecule that Supports all Life

3.1 Polar covalent bonds in water molecules result in hydrogen bonding:

? A water molecule is shaped like a wide V, with two hydrogen atoms joined to an oxygen atom by single polar covalent bonds.

? Because oxygen is more electronegative than hydrogen, a water molecule is a polar molecule in which opposite ends of the molecule have opposite charges. The oxygen region of the molecule has a partial negative charge (-), and the hydrogen regions have a partial positive charge (+).

Water and Life:

Organisms depend on the cohesion of water molecules

3.2 Four emergent properties of water contribute to Earth's suitability for life:

1. Cohesion of Water Molecules (Surface Tension and Transpiration) ? Many organisms depend on surface tension and the cohesion of water

2. Moderation of Temperature (Specific Heat & Heat of Vaporization) ? Properties of water reduce large temperature changes in the environment

3. Ice Floats and Insulates (Density of Ice) ? Because ice floats, lakes and oceans do not freeze

4. Effective Solvent (polar substance) ? The polar nature of water allows biological molecules to be transported and stored in living organisms

Water and Life:

The Molecule that Supports all Life

3.2 Four emergent properties of water contribute to Earth's suitability for life:

? Water has a variety of unusual properties because of the attraction between polar water molecules. The slightly negative regions of one water molecule are attracted to the slightly positive regions of nearby water molecules, forming hydrogen bonds.

? When water is in its liquid form, its hydrogen bonds are very fragile, about one-twentieth as strong as covalent bonds.

? Hydrogen bonds form, break, and re-form with great frequency

? Each hydrogen bond lasts only a few trillionths of a second, but the molecules continuously form new hydrogen bonds with a succession of partners.

? At any given instant, a substantial percentage of all water molecules are hydrogen-bonded to their neighbors

Water and Life:

The Molecule that Supports all Life

1

3.2 Four emergent properties of water contribute to Earth's suitability for life:

? Collectively, hydrogen bonds hold water together, a phenomenon called cohesion.

? Cohesion among water molecules plays a key role in transporting water and dissolved nutrients against gravity in plants.

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download