+ ap biology mrs. valdes chapter 3: water and fitness in the environment

+

AP Biology

Mrs. Valdes

Chapter 3:Water and

Fitness in the Environment

+ Overview: The Molecule That Supports All of Life Water = biological medium on Earth

All living organisms require water more than any other substance

Cells: Most cells surrounded

by water Cells are about 70–95%

water Abundance of water =

main reason Earth is habitable Why?

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

+Fig. 3-UN6

Surface of EarthSurface of Mars

+Concept 3.1: The polarity of water molecules results in hydrogen bonding• Water molecule is a polar molecule:

• The opposite ends have opposite charges Polarity water molecules form hydrogen bonds with each

other

• Four of water’s properties that facilitate an environment for life are: Cohesive behavior Ability to moderate temperature Expansion upon freezing Versatility as a solvent


Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for life

+Fig. 3-UN7

+ Cohesion Cohesion: Hydrogen bonds hold water molecules together

helps the transport of water against gravity in plants Adhesion: attraction between different substances

water and plant cell walls Surface tension: measure of how hard it is to break the

surface of a liquid; related to cohesion


+ Moderation of Temperature

Water absorbs heat from warmer air; releases stored heat to cooler air

Kinetic energy: the energy of motion• Heat: measure of the total amount of kinetic energy due to

molecular motion• Temperature: measures the intensity of heat due to the

average kinetic energy of molecules Celsius scale: measure of temperature using Celsius degrees

(°C) Calorie (cal): amount of heat required to raise the

temperature of 1 g of water by 1°C “Calories” on food packages are actually

kilocalories (kcal) 1 kcal = 1,000 cal

Joule (J): another unit of energy 1 J = 0.239 cal, or 1 cal = 4.184 J


+ Water’s High Specific Heat Specific heat: amount of heat that must be absorbed or lost

for 1 g of that substance to change its temperature by 1ºC Specific heat of water = 1 cal/g/ºC Water’s high specific heat resists changing temperature

better for LIFE

Hydrogen bonding water’s high specific heat Heat absorbed when

hydrogen bonds break Heat is released when

hydrogen bonds form


+ Evaporative Cooling Evaporation: transformation of a substance from liquid to gas Heat of vaporization: heat a liquid must absorb for 1 g to be

converted to gas Evaporative cooling: as a liquid evaporates, its remaining

surface cools helps stabilize temperatures in organisms and bodies of water

Hydrogen bonds in ice more “ordered” = ice less dense Ice floats

Water reaches its greatest density at 4°C If ice sank, all bodies of water would eventually freeze solid,

making life impossible on Earth


Insulation of Bodies of Water by Floating Ice

+ The Solvent of Life Solution: liquid that is a homogeneous mixture of substances Solvent: dissolving agent of a solution Solute: substance that is dissolved Aqueous solution: one in which water is the solvent Water = versatile solvent due to its polarity Hydration shell: When an ionic compounds dissolve

in water, each ion is surrounded by a sphere of water molecules

Even large polar molecules like proteins can dissolve in water if they have ionic and polar regions

+Hydrophilic and Hydrophobic Substances

Hydrophilic: has an affinity for water; “water-loving” Hydrophobic: does not have an affinity for water; “water-

fearing” How can you tell if a molecule is hydrophobic? Colloid: stable suspension of fine particles in a liquid

Most biochemical reactions occur in water Chemical reactions depend on collisions of molecules thus on

the concentration of solutes in an aqueous solution Lots of chemical reactions would occur in…?

Molarity (M): number of moles of solute per liter of solution


Solute Concentration in Aqueous Solutions

+Concept 3.3: Acidic and basic conditions affect living organisms

Hydrogen atom in hydrogen bond between two water molecules can shift from one to the other: Hydrogen atom leaves electron behind transferred as a proton or

hydrogen ion (H+) Molecule with the extra proton is = hydronium ion (H3O+) The molecule that lost the proton is now a hydroxide ion (OH–) Water is in a state of dynamic equilibrium in which water

molecules dissociate at the same rate at which they are being reformed

Water in state of dynamic equilibrium Rate of water molecules dissociate = rate of water molecules

reformed RARE but changes in concentrations of H+ and OH– can

drastically affect the chemistry of a cell How?


+ Acids and BasespH Scale: Scientists us to determine whether solution is acidic or basic

Most biological processes within pH range 6-8Acid: any substance that increases the H+

concentration of a solution pH less than 7

Base: any substance that reduces the H+ concentration of a solution

pH more than 7[ H+ ] = [ OH– ] in pure water

Any aqueous solution at 25°C the product of H+ and OH– is constant [H+][OH–] = 10–14

pH of a solution is defined by the negative logarithm of H+ concentration

pH = –log [H+]Neutral aqueous solution

[H+] is 10–7 = –(–7) = 7

+Fig. 3-UN5

Bases donate OH–

or accept H+ inaqueous solutions

Acids donate H+ inaqueous solutions

Acidic[H+] > [OH–]

Neutral[H+] = [OH–]

Basic[H+] < [OH–]

14

7

0

+ Buffers Internal pH of most living cells

MUST remain close to pH 7 Buffer: substances that

minimize changes in concentrations of H+ and OH– in a solution

Most buffers consist of acid-base pair


+ Threats to Water Quality on Earth Acid precipitation: rain, snow, or fog with a pH lower than

5.6 can fall far from pollutant source can damage life in lakes and streams Effects on soil chemistry are contribute

to decline of some forests Pollutants + water in air = Acid Rain Burning fossil fuels Poor water

quality CO2 is released by fossil fuel

combustion: “Greenhouse effect” Acidification of the oceans

this decrease in the ability of corals to form calcified reefs


+Fig. 3-11

EXPERIMENT

RESULTS

Cal

cif

icat

ion

rat

e(m

mo

l C

aCO

3

per

m2 p

er d

ay)

[CO32–] (µmol/kg)

150 200 250 3000

20

40

+ You should now be able to:

1. List and explain the four properties of water that emerge as a result of its ability to form hydrogen bonds

2. Distinguish between the following sets of terms: hydrophobic and hydrophilic substances; a solute, a solvent, and a solution

3. Define acid, base, and pH

4. Explain how buffers work


+ ap biology mrs. valdes chapter 3: water and fitness in the environment

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