Water, acids, bases and buffers

What does it mean to be Alive?Remember Bio 11?1. are made up of cells2. grow and maintain structure by taking in

chemicals and energy from their environment3. respond to the external environment4. reproduce and pass on their organization

(genetic information) to their offspring5. at the species level, evolve/change, and

adapt to the environment

The function of our body systems:HOMEOSTASIS: all the things living organisms

do that cause it to maintain a relatively constant, stable internal environment regardless of the external environment. There are countless examples in the human body: Guesses?

blood pH =7.4body temp. = 37°Cblood pressure = 120/80blood [glucose] = 0.1% 

How is homeostasis controlled? Positive/Negative FeedbackIt relies on FEEDBACK MECHANISMS.Brain control centers (e.g. in the hypothalamus)

monitor and control body conditions (e.g. pH, temperature, blood pressure glucose levels)

Sensors all over body detect unacceptable levels and signal the appropriate brain center

control center directs body to behave in such a way that normal state is regained

Once normal state is regained, the sensor stops signaling the brain center (this the “negative feedback part”), so adaptive response stops.

Negative Feedback Continued:results in a FLUCTUATION between two

levels. e.g. the concentration of glucose in your blood is almost never exactly 0.1%. It’s usually a little bit above or a little bit below. Over the course of a day, though, it would average out to be exactly 0.1%.

The EssentialsLife needs water!

Organic vs. Inorganic Organic means it contains carbon.

Water moleculescomposed of two hydrogen (H) atoms and one larger

oxygen (O) atom. Each outside hydrogen atom is bonded to the middle

oxygen atom by a covalent bond. A sharing of electrons.The oxygen atom attracts the electrons in these bonds

more strongly than the hydrogen atoms. This unequal sharing of electrons causes each oxygen atom to be slightly negative in charge (-) and each hydrogen atom to be slightly positive in charge (+).

These partial charges make the water molecule polar in nature with oxygen acting as a negative pole and hydrogens acting as positive poles.

The oxygen atom also has two lone pair of electrons associated with it that adds to its partial negative charge and results in the bent nature of the water molecule.

A note about sharing: ElectronsCovalent bond: sharing of electrons between

atomsPolar Covalent bond: Unequal sharing (water)Ionic bond: when atoms donate (do not share)

electrons with each other.Hydrogen bonds: weak bond between hydrogen

and other molecules because of polarity.

The Unequal sharing of electrons as well as hydrogen bonds gives water its unique properties.

Covalent vs. Ionic

Models:Page 1 of text.

Waters RoleHydrogen bonding gives water a strong

affinity for itself and explains things like the formation of water droplets, the movement of water to the tops of tall trees, and the ability of water striders to get around.

Water has many properties and functions useful to living organisms. These include acting as a solvent, temperature regulator and a lubricant. More on that next.

Water as a solvent

A solvent is a fluid that makes up the majority of the volume in a solution. The solvent will have other substances dissolved in it that are called solutes. Water is an ideal solvent for many things that are found in our bodies as solutes. These substances include salts like sodium chloride that are ionic in nature and are attracted to the partial charges in water. Once dissolved in water, these molecules are transported throughout the body in blood and lymph (tissue fluid).

Polar molecules like carbohydrates, proteins, and nucleic acids are soluble in water and very important in the functioning of our cells. Lipids or fats are non-polar molecules and do not dissolve readily in water. This creates a hydrophobic effect due the hydrogen bonding in water and is important for the formation of cell membranes. Water also makes up the main component of our blood (92%) with many types of cells and molecules dissolved in it. The fluid in our tissues is composed mainly of water and exchanges materials with our blood. These ideas will become important later in the course.

Water as a temperature regulator

Water in our bodies acts to moderate changes in our temperature much like large bodies of water moderate temperature changes in coastal communities (called the Lake Effect). The numerous hydrogen bonds in water help it resist temperature changes as a lot of energy must be added to raise the temperature of water. The opposite is also true as water tends to hold onto heat energy very well resisting falling temperature. Water protects us from rapid temperature changes and helps us maintain our normal body temperature. In situations where we overheat, such as during strenuous exercise, sweating removes large quantities of heat as water evaporates from our skin.

Water as a lubricant

Water molecules cling together due to hydrogen bonding yet flow freely as a fluid. These characteristics allow water to act as a transport medium and to keep many of our internal structures moving. Water dissolves numerous chemicals and allows them to be transported effectively in our bodies by our circulatory system. The role of water as a lubricant is seen in sites where our body surfaces interact with the dry environment we live in. Examples include tears, mucus in the lungs, throat, and nose, and sinovial fluid in the joints.

Water in different states: Big QOne very cool thing about water is that it

floats as a solid (Ice!)Think about how important this property is to

life on earth.What would happen if it sunk?

How do you think the future of fresh water will shape economies of the future?

Must check-outs!http://environment.nationalgeographic.com/e

nvironment/freshwater/http://www.unwater.org/statistics.html

Acids Bases and Buffers….and pHThe pH scale is used to describe the relative

acidity or alkalinity (‘Basic-ness’) of solutions. The number scale is from 0 to 14 and represents the number of H+ ions in a solution

A pH of 0 represents an extremely acidic solution such as concentrated hydrochloric acid.

A pH of 14 represents an extremely basic solution like concentrated sodium hydroxide found in oven cleaner. A pH of 7 describes a neutral solution like pure water that contains an equal concentration of hydronium (H+) and hydroxide (OH-) ions.

Acidsare molecules that produce Hydronium Ions

(H+) when added to water. Strong acids, like hydrochloric acid (HCl -> H+ and Cl-), produce large concentrations of H+ ions, while weak acids, like acetic acid found in vinegar, produce low concentrations of H+ ions.

Acidic solutions contain more acid (H+) than base (OH-) and have a pH less than 7.

Bases

Bases are molecules that produce Hydroxide Ions (OH-) when added to water. Strong bases, like sodium hydroxide (NaOH -> Na+ and OH-), produce large concentrations of OH- ions, while weak bases like sodium bicarbonate (baking soda), produce small concentrations of OH- ions.

Basic or alkaline solutions contain more OH- ions than H+ ions and have a pH greater than 7. Basic solutions are often called alkaline solutions.

Bufferscompound or combination of compounds (often

a weak acid or base and a related salt) that keeps the pH of a solution constant.

Buffers resist changes in pH by reacting with any added acids (H+) or bases (OH-). A common buffer system in our bodies that keeps our blood pH at about 7.4 involves the weak acid, carbonic acid (H2CO3) and bicarbonate ion (HCO3-).

Carbonic acid and bicarbonate ion are both in the blood creating an equilibrium system.

Why do we need buffers?All living things need to maintain a

constant pH (e.g. human blood pH = 7.4). Why is pH so important? If pH

changes, it can cause enzymes – the chemical helpers that run the chemical reactions essential to life - to “denature” (i.e. change shape - more on this later!).

potential Hydrogen!The numbers in the pH scale can seem

misleading, because the pH scale is a logarithmic scale. That means each number on the pH scale represents a difference in magnitude of 10.

For example, a pH of 2 is ten times more acidic than a pH of 3.

A pH of 2 is 100 times more acidic than a pH of 4.

A pH of 13 is 1000 times more basic than a pH of 10, and so on.

Macromolecules. There are a few basic molecules that help

make up life in general. These four basic components are:

Carbohydrates, Proteins, Lipids and Nucleic Acids.

VocabAcid, acid (carboxyl) group, adenine, adenosine

triphosphate (ATP), alpha helix, amine group, amino acid, base, beta pleated sheet, bonding, buffer, carbohydrate, cellulose, complementary base pairing, cytosine, dehydration synthesis, deoxyribonucleic acid (DNA), deoxyribose, dipeptide, disaccharide, double helix, glucose, glycerol, guanine, glycogen, hemoglobin, hydrogen bonding, hydrolysis, lipid, lubricant, maltose, monomer, monosaccharide, neutral fat, nitrogenous base, nucleic acids, nucleotide, organic, peptide bond, pH, phosphate, phospholipid, polarity, polymer, polypeptide, polysaccharide, primary structure, protein, quaternary structure, R-group, ribonucleic acid (RNA), ribose, saturated fatty acid, secondary structure, solvent, starch, steroid, sugar-phosphate backbone, temperature regulator, tertiary structure, thymine, unsaturated fatty acid, uracil