Biology Chapter 3 - Water and Life

Importance of water

Cells are 70-95% water

Covers 75% of Earth’s surface

Structure of water

Polar covalent

Partial positive an negative ends

Tetrahedral shape

4 Emergent properties of water

1. Cohesion

2. Moderation of temperature,

3. Expansion upon freezing

4. Versatile solvent

Cohesion of water

Due to hydrogen bonds

High surface tension

Attracts to other polar molecules

Imperious

Water cannot wet something

Capillary action

Adhesion and cohesion

Moderation of temperature by water

Acts as temp buffer

Specific heat of water, heat of vaporization, evaporative cooling

Thermal engery

Random movement of atoms and molecules

Temperature

Measure of average kinetic energy of molecules in matter

Heat

Thermal energy transfer from 1 body to another

Calorie

Unit of heat; amount needed to raise temperature of 1g of water by 1C

Kilocalorie

Unit of heat; amount needed to raise temperature of 1kg of water by 1C

Joule

Unit of heat; 1J = .239 cal; 1 cal = 4.184J

Specific heat

Amount of heat that must be absorbed or lost by 1g of substance to change its temp by 1C

How well as substances resists change in temp as it absorbs or releases heat

Specific heat of water

Water has high specific heat due to H-bonds, lots of energy needed to raise or lower temp

Evaporative cooling

Process of cooling down a surrounding area by absorbing heat from it as the liquid evaporates

Vaporization

Liquid to gas; molecules moving fast enough leave liquid → becomes gas

Why does temperature drop as something evaporates?

Average kinetic energy decreases

Moderating climate

Water evaporating absorbs heat, water condensing releases heat

Heat of vaporization

Amount of heat needed to change 1g of substance from liquid to gas

Water has high heat of vaporization due to H-bonds

Floating ice on liquid water

Above 4 C water expands when heated and contracts when cooled

Water is most dense at 4 C

At 0 water molecules form into crystal lattice

Water: solvent of life

Versatile solvent becasue of its polarity

Solution

Homogenous mixture of 2+ substances

Solvent

Dissolving agent

Solute

Substance that is dissolved

Aqueous solution

Solution where water is solvent

Hydration shell

Sphere of water molecules around each dissolved ion

Water-soluble

Ability of a compound to dissolve when water molecules surround each solute molecule forming H-bonds with them

Hydrophilic

Affinity for water

Hydrophobic

No affinity for water

Non-polar or nonionic

Molar mass

Sum of masses of all the atoms in a molecule

Molarity

Number of moles of solute per liter of solution

Mole

Avogadro’s number = 6.02 * 10²³

Water is a reversible reaction

H₂O ←→ H⁺ + OH^-

Pure water at equilibrium

[H⁺] = [OH^-] = 1 × 10^-7 M

Acid

Substance that increases [H⁺]

Base

Substance that reduce [H⁺] in a solution

Strong acid or base

Dissociates completely in water

The pH scale

[H⁺][OH^-] = 1 × 10^-14 M

pH calculation

-log[H⁺]

pH scale

0 to 14

pH range of biological fluids

6-8

Range of pH of living cells

7-7.4

Buffers

Substance that minmizes changes in [H⁺] and [OH^-] by reacting with added H⁺ or OH^-

Buffer system in blood

Carbonic acid/bicarbonate

H₂CO₃ ←→ HCO₃^- + H⁺

Bicarbonate ion balance addition of H⁺

Hydrogen ion balances addition of OH^-

Buffering system

Homeostasis

Acidification

Threat to water quality

Ocean acidification

CO₂ dissolves in seawater → forms carbonic acid → breaks down to H⁺ + HCO₃^- → lowers pH

Acid percipitation range

pH < 5.6

Acid rain

Harmful minerals dissolve and absorbed by plants