BIO 201 CHAPTER 3
What is the purpose of Water?
The biological medium on Earth
All living organisms require water more than any other substance
75% of the earths surface is covered in water
Cells are about 70–95% water
The water molecule is a ?
Polar molecule: The opposite ends have opposite charges
Polarity allows water molecules to form hydrogen bonds with each other
Four of water’s properties that facilitate an environment for life are?
Cohesive and adhesive behavior
Ability to moderate temperature
Expansion upon freezing
Versatility as a solvent
Hydrogen bonds hold water molecules together, a phenomenon called ?
Cohesion helps the transport of water against gravity in plants
What is Adhesion?
An attraction between different substances, for example, between water and plant cell walls
What is Surface tension?
A measure of how hard it is to break the surface of a liquid
What is Kinetic energy?
The energy of motion
Anything that moves has kinetic energy - atoms
The faster, the more energy
What is Heat?
A measure of the total amount of kinetic energy due to molecular
Heat depends on the volume
Heat and Temperature are NOT the same
What is Temperature?
Measures the intensity of heat due to the average kinetic energy of molecules
The Celsius scale
A measure of temperature using Celsius degrees (°C)
At sea level, water freezes at 0°C and boils at 100°C
A calorie (cal)
Is the amount of heat required to raise the temperature of 1 g of water by 1°C
Specific heat of a substance
Is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC
Water’s high specific heat can be traced to ?
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form
The high specific heat of water minimizes temperature fluctuations to within limits that permit life
How does water’s high specific heat aid life on earth?
Large bodies of water can absorb and store a huge amount of heat from
Since organisms are made of water, they can resist changes in their own temperature as well
Evaporation is ?
Transformation of a substance from liquid to gas
Molecules moving very fast can enter the air as gas
Any liquid at any temperature evaporates
Increasing the temperature increases the speed
Heat of vaporization is ?
The heat a liquid must absorb for 1 g to be converted to
Double that of alcohol or ammonia
As a liquid evaporates, its remaining surface cools. this process is called ?
The fastest molecules are also the “hottest” and are most likely to
leave as a gas
Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water
Ice floats in liquid water because ?
Hydrogen bonds in ice are more “ordered,” making ice less
Water reaches its greatest density at 4°C
At 0C, water locked into a lattice
Keeps molecules of H2O far enough apart to be 10% less dense than liquid water
A solution is ?
A liquid that is a homogeneous mixture of substances
A solvent is ?
The dissolving agent of a solution
The solute is ?
The substance that is dissolved
An aqueous solution is?
One in which water is the solvent
Why is water is a versatile solvent?
Because of its polarity, which allows it to form hydrogen bonds
When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules called a hydration shell.
Water can also dissolve compounds made of nonionic polar molecules
A hydrophilic substance
is one that has an affinity for water
A hydrophobic substance
is one that does not have an affinity for water;
- Oil molecules are hydrophobic because they have relatively
Hydrophobic molecules related to oils make up cell membranes
Most biochemical reactions occur in ?
- Chemical reactions depend on collisions of molecules and therefore on the concentration of solutes in an aqueous solution
Molecular mass is ?
The sum of all masses of all atoms in a molecule.
- Numbers of molecules are usually measured in moles, where 1 mole (mol) = 6.02 1023 molecules
Molarity (M) is ?
The number of moles of soluteper liter of solution
Biologists use something called the pH scale to ?
Dscribe whether a solution is acidic or basic (the opposite of acidic)
- Adding certain solutes, called acids and bases, modifies the concentrations
An acid is ?
Any substance that increases the H+ concentration of a
When HCl is added to water H+ ions disassociate
Is acidic as there is more H+ than OH- in the solution
A base is ?
Any substance that reduces the H+ concentration of a
Sodium hydroxide in water disassociates into Na and OH-
The pH of a solution is defined by ?
The negative logarithm of H+ concentration, written as pH = –log
For a neutral aqueous solution [H+] is 10–7 = –(–7) = 7
Have pH values less than 7
Most biological fluids
Have pH values in the range of 6 to 8- Neutral = 7
Have pH values greater than 7
The internal pH of most living cells must remain close to?
- The slightest change can be deadly!
Increase or decrease by .4 – death in minutes!
Are substances that minimize changes in concentrations of H+ and OH–
in a solution
Accept hydrogen ion when in access and give hydrogen ions when they are rare