AP Biology
Chapter 3 Guided Reading Assignment
Name _________________________
This chapter is a review from your previous biology class – these concepts are critical
and repeated throughout the year. If you have not covered this material previously or
need additional assistance with the concepts please schedule time to see me.
1. Why is water considered a polar molecule?
Because oxygen is more electronegative then hydrogen, the electrons of the
molecule spend more time closer to the oxygen atom. This causes the oxygen
end to be slightly negative and the hydrogen end to be slightly positive.
2. For each of the below listed properties of water – briefly define the property and
then explain how water’s polar nature and polar covalent bonds contribute to the
water special property. Include an example in nature of each property also.
a. Cohesion- hydrogen bonds hold the substance together; helps hold cells
together because the hydrophilic outside part of cells will stick together.
b. Adhesion- the clinging of one substance to another; contributes to the
transport of water and dissolved nutrients against gravity in plants, water from
the roots reach the leaves through water- conducting cells.
c. Surface tension- measure of how difficult it is to stretch or break the surface
of a liquid. Some animals can stand, walk or run on water.
d. High specific heat- amount of heat that must be absorbed or lost for 1g of that
substance to change its temperature by 1C. Water will change its temperature
less when it absorbs or loses a given amount of heat. Heat must be absorbed
to break hydrogen bonds. This happens before molecules can move faster;
when temperature drops, more hydrogen bonds form. Water, like from lakes,
can store heat and thus cool the air.
e. Heat of vaporization- is the quantity of heat a liquid must absorb for 1g of it to
be converted from the liquid to the gaseous state. Has a high heat of
evaporation. Helps moderate earths climate and hydrogen bonds must be
broken before the molecules can make exercises from liquid.
f. Evaporative cooling- as a liquid evaporates, the surface of the liquid remains
cool. This occurs because the hottest molecules leave as gas. Helps provide
the stability temperature in lakes and ponds.
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3. What is special about water and density?
Water needs to be less dense as a solid then a liquid so ice can float, water
expands when it solidifies. More hydrogen bonds are formed. If ice sank lakes
and bodies of water it would freeze. In the winter the ice solidifies on the top
insulating heat on the bottom, preventing it from freezing.
4. Define the following terms:
a. Solute- the substance that is dissolved
b. Solvent- the dissolving agent
c. Aqueous solution- one which water is the solvent
d. Hydrophilic- whether ionic or polar, any substance that has an affinity for
water
e. Hydrophobic- substances that are non ionic and non polar, repel water
f. Colloid- a stable suspension of fine particles in a liquid
g. Hydration shell- the sphere of water molecules around each other dissolved
ion
h. Molarity- the number of moles of solute per liter of solution
5. Label the diagram below to demonstrate the dissociation of the water molecule
and then relate this diagram to pH.
This is rare, charges in concentrations
Hydronium
of hydronium and hydroxide can affect
ion (H3O+)
a cells proteins and other complex molecule.
These are pure but adding certain kinds
of solutes (acid or bases) can disrupt the balance
Hydroxide
ion (oh-)
6. What defines an acid and a base? An acid is a substance that increases the
hydrogen ion concentration of a solution. Having more H+ than OH- is acidic.
Base is a substance that reduces the hydrogen ion concentration of a solution.
7. Why are “apparently” small changes in pH so important in biology?
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One small change in H2O can disrupt the purity and make it not water. And can
vary in so many ways so it is important to have a seal.
8. What is a buffer and write and explain the carbonic acid buffer system in human
blood – yes we are back to the equation AGAIN!
Buffers are substances that minimize changes in concentrations of H+ and OHbuffer maintain the PH of human blood close to 7.4, slightly basic, it cannot drop
to 7 or rise to 7.8. Buffers accept hydrogen ions from the solution when they are
in excess and giving them when they are depicted.
9. What is acid precipitation and why is it important to living organisms?
Acid precipitation refers to rain, snow, or fog with a pH lower or more acidic than
pH 5.6. It is caused by the preference of sulfur oxides and nitrogen oxide.
Gaseous compounds that react with water in the air to form strong acids, which
fall as rain or snow. It can damage life in lakes and streams. It also washes away
minerals important to the soil.
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