A1.1: Water

Is water polar or non-polar? What is the significance of this?

Polar: this makes it an excellent solvent and allows the formation of hydrogen bonds.

Why is it important to have intra- and extra- cellular water?

All chemical communication in and out of cells require water environments.

Properties of water

• Polar (pro)

• Provides buoyancy (pro)

• Provides stable thermal properties - high specific heat capacity (pro)

• Higher viscosity than air (con)

Polarity of molecules depends on:

Equal or unequal sharing of electrons

Covalent bonds

Two atoms share electrons

Water molecule polarity diagram

Hydrogen bonds

Ephemeral (short-lived) attraction between water molecules. The oxygen bonds to one of the hydrogens.

Cohesion

Molecules of the same type are attracted to each other

Hydrogen bonds below freezing point

Molecular motion slows until it stops, hydrogen bonds become locked into place, ice crystal forms

Surface tension cause

Water molecules at the surface face have stronger cohesion with the molecules below them, causing inward tension. This is what allows water surface to be a habitat for some organisms.

Water column (cohesion)

Evaporation and cohesion (hydrogen bonds) in water molecules causes tension which pulls on water molecules further down in the xylem where water is evaporating from, and cohesion causes all the water molecules to move upwards in a “water column.” Water is replaced in the xylem within the roots.

Adhesion

Attraction and hydrogen bonding between two different types of molecule. Found in: water column in the xylem, capillary action in soil

Water column (adhesion)

When the water column is not actually being “pulled up,” adhesion between water molecules and cellulose in the plant cell wall allows the column to not fall back down again.

Cuticle (plant)

Wax layer preotecting the leaf from excessive evaporation

Capillary action

Water entering small spaces resisting gravity (for example moving up through soil and into plants) due to adhesion

Cytoplasm soluble molecule examples

• Cytoplasmic enzymes

• Glucose

• Ions

• Amino acids

• Proteins

Cytoplasm insoluble molecules examples

• Steroid hormones

• Membrane-bound proteins (can stay attatched to membrane and still interact with other molecules.

• Fats/lipids

• Cholesterol

The first cells originated in water: true or false?

True

Water importance to living organisms:

• Makes up the cytoplasm

• Makes up intracellular/tissue fluid

• Makes up fluid found in all organelles

• Facilitates transport in and out of the cell

• Is essential to blood and other fluids

• Is the medium for life in bodies of water

Polar covalent bonds:

Electrons are unequally shared. This is what causes hydrogen bonds in water.

Non-polar covalent bonds

Electrons are equally shared

Hydrophobic/insoluble molecules exp.

• Steroid hormones

• Membrane-bound proteins

• Epidermal cells (cuticle)