AP Biology Chapter 3


The biological medium on Earth required by all living organisms more than any other substance.


Most cells are surrounded by water, and cells themselves are about ___-___% water.

Abundance of water

The main reason the Earth is habitable.

Polar molecule (Water)

What type of molecule is a water molecule?

Polar molecule

Opposite ends have opposite charges


Allows water molecules to form hydrogen bonds with each other


Collectively, hydrogen bonds hold water molecules together, a phenomenon called ________.

transport; gravity

Cohesion helps the _______ of water against ________ in plants.


An attraction between different substances, for example, between water and plant cell walls.

Surface tension

A measure of how hard it is to break the surface of a liquid

Related to cohesion

What is surface tension related to?

warmer; cooler

Water absorbs heat from ______ air and releases store heat to ______ air.


What can absorb or release a large amount of heat with only a slight change in is own temperature?

Kinetic energy

The energy of motion


A measure of the total amount of kinetic energy due to molecular motion


Measures the intensity of heat due to the average kinetic energy of molecules

Specific heat

A substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1 degree C.

High specific heat

Water resists changing its temperature because of its _____ _________ _______.

Hydrogen bonding

What water's high specific heat can be traced to?

Heat is absorbed

When hydrogen bonds break, _____ ___ _________.

Heat is released

When hydrogen bonds form, ______ ____ _________.

temperature fluctuations

What does the high specific heat of water minimize to within limits that permit life?


Transformation of a substance from liquid to gas

Heat of vaporization

The heat a liquid must absorb for 1 g to be converted to gas.

Evaporative cooling

A process by which as a liquid evaporates, its remaining surface cools. It helps water stabilize temperature in organisms and bodies of water.

ordered; less dense

Ice floats in liquid water because hydrogen bonds in ice are more "________," making ice _____ ________.

4 degrees C

Water reaches its greatest density at how many degrees Celcius?

If ice sank

What would eventually make all bodies of water freeze solid, thus making life impossible on earth?


A liquid that is a homogeneous mixture of substances.


The dissolving agent of a solution


The substance that is dissolved

Aqueous solution

One in which water is the solvent

Polarity (versatile)

What makes water a versatile solvent and allows it to form hydrogen bonds easily?

Hydration shell or sphere of hydration

When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules called a

Nonionic polar molecules

Water can also dissolve compounds made of what?

ionic and polar regions

Large polar molecules such as proteins can dissolve in water if they have _____ and ______ _______


A substance that has an affinity for water


A substance that does not have an affinity for water

relatively nonpolar bonds

Oil molecules are hydrophobic because they have _________ _________ ________.

Hydrogen ion

The hydrogen atom leaves its electron behind and is transferred as a proton

Shift from one to the other

A hydrogen atom in a hydrogen bond between two molecules can ______ _______ ______ to the ________.

Hydronium ion

The molecule with the extra proton in now a _________ _____, and is often represented at H+

Hydroxide ion

The molecule that lost the proton

Dynamic equilibrium

Water is in a state of what in which water molecules dissociate at the same rate at which they are being reformed.

H+ and OH-

Changes in concentrations of _____ and _____ can drastically affect the chemistry of a cell.

Pure water

Concentrations of H+ and OH- are equal in _______ _______.

Acids and bases

Adding what solutes modifies the concentrations of H+ and OH-?

pH scale

Biologists use something called what to describe whether a solution is acidic or basic (the opposite of acidic).


Any substance that increases the H+ concentration of a solution


Any substance that reduces the H+ concentration of a solution

25 degrees C

In any aqueous solution at how many degrees is the product of H+ and OH- constant.


A solution is defined by the negative logarithm of H+ concentration


Solutions have pH values less than 7


Solutions have pH values greater than 7

6 to 8

Most biological fluids have pH values in the range of ___ to ____.


A stable suspension of fine particles in a liquid.


The higher the concentration the higher the _________.