Chapter 2_ Water the Medium of Life

Question 1

Life originated, evolved, and thrives in the

Answer 1

sea

Question 2

Water and its ionization products,
hydrogen ions and hydroxide
ions, are

Answer 2

critical determinants of
the structure and function of
many biomolecules, including
amino acids and proteins,
nucleotides and nucleic acids,
and even phospholipids and
membranes.

Question 3

What Are the Properties of Water?

Answer 3

-Water has a substantially higher boiling point, melting point, heat of vaporization, and surface tension
-its maximum density is found in the liquid (not the solid) state, and it has a negative volume of melting (that is, the solid form, ice, occupies more space than does the liquid form, water)

Question 4

• occur when two atoms in a molecule
  have substantially different electronegativity: One atom attracts electrons more than another, becoming more negative, while the other atom becomes more positive.

Answer 4

Permanent Dipoles

Question 5

Water’s ability to surround ions in dipole interactions and diminish their attraction for each other is a measure of its dielectric constant, D.

Answer 5

(1) Water has a high dielectric constant.

Question 6

excellent solvent properties of water stem from its ability to readily form hydrogen bonds with the polar functional groups on these compounds, such as hydroxyls, amines, and carbonyls

Answer 6

(2)Water Forms H Bonds with Polar Solutes

Question 7

• apparent affinity of nonpolar structures for one another
  -Because nonpolar solutes must occupy space, the random H-bonded network of water must reorganize to accommodate them.

Answer 7

(3)Hydrophobic Interactions

Question 8

(Compounds containing both strongly polar and strongly nonpolar groups)

Answer 8

(4) Interaction with amphiphilic molecules

Question 9

Enumeration: Properties of water

Answer 9

1) Water has a high dielectric constant.
2)Water Forms H Bonds with Polar Solutes
(3)Hydrophobic Interactions
(4) Interaction with amphiphilic molecules

Question 10

The presence of dissolved substances disturbs the structure of liquid water, thereby changing its properties.

Answer 10

Colligative Properties

Question 11

Colligative Properties

Answer 11

▪ Freezing point depression
▪ boiling point elevation
▪ vapor pressure lowering
▪ Osmotic pressure effects

Question 12

The pressure necessary to push water back through the membrane at a rate exactly equaled by the water influx is

Answer 12

the osmotic pressure of the solution

Question 13

states that when equilibrium is disturbed, the rates of the forward and reverse reactions change to relieve that stress and reestablish equilibrium.

Answer 13

Le Châtelier’s principle

Question 14

Oxygen–Hemoglobin Equilibrium and Hypoxia

Answer 14

The transport of oxygen involves an equilibrium between hemoglobin (Hb), oxygen, and oxyhemoglobin (HbO2).

Question 15

We define an aqueous solution as being

Answer 15

neutral when the [H+] = [OH-]
acidic when [H+] > [OH-]
basic when [H+] < [OH-]

Question 16

is called ionization constant of water and is very small.

Answer 16

-Kw
Kw = [H+][OH-]

Question 17

The Swedish chemist Svante Arrhenius proposed the first definition of acids and bases

Answer 17

Arrhenius Definition

Question 18

Arrhenius Definition

Answer 18

“Acids are substances that dissociate in water to produce H+ ions and bases are substances that dissociate in water to produce OHions”

Question 19

Arrhenius Definition:
But what if the acid/base is not dissolved in water?

Answer 19

• The Arrhenius definition for acids and bases only refers to compounds dissolved in water.

Question 20

Johannes Brønsted and Thomas Lowry revised Arrhenius’s acid-base theory to
include other solvents besides water.

Answer 20

Brønsted-Lowry Definition

Question 21

Brønsted-Lowry Definition

Answer 21

“An acid is a hydrogen containing species that donates a proton. A base is any substance that accepts a proton.”

Question 22

Brønsted-Lowry acids and bases always exist as conjugate acid-base pairs.
Their formulas differ by only one proton.

Answer 22

Conjugate Pairs

Question 23

What are buffers and what do they do?

Answer 23

Buffers are present to prevent large fluctuations in pH

Question 24

is one where complete dissociation of the
compound occurs.

Answer 24

A strong acid

Question 25

is one where incomplete dissociation of the compound occurs.

Answer 25

A weak acid

Question 26

First Line of Defense against pH:
Chemical Buffer system

Answer 26

• Bicarbonate Buffer system
• Phosphate Buffer system
• Protein Buffer system

Question 27

Second line of defense against pH:
Physiological Buffer system

Answer 27

• Respiratory Mechanism
• Renal Mechanism

Question 28

Bicarbonate Buffer system

Answer 28

Maintain a 20:1 ratio : HCO3-
:H2CO3 (bicarbonate to carbonic acid)
-Catalyzed by the enzyme carbonic anhydrase (enzyme found in red blood cells, gastric mucosa, pancreatic cells, and renal tubules)
-Functions with respiratory and urinary systems :to lower pH, kidneys excrete HCO3, to raise pH, kidneys excrete H+ and lungs excrete CO2

Question 29

is very effective but not found in high
concentrations in extracellular fluid.

Answer 29

Phosphate Buffer

Question 30

Phosphate Buffer

Answer 30

-Important in the intracellular fluid (ICF) and renal tubules.
-where phosphates are more concentrated
and function closer to their optimum pH of 6.8
– constant production of metabolic acids creates pH values from 4.5 to 7.4 in the ICF, avg. 7.0

Question 31

Protein Buffers

Answer 31

a) Amino Acids
b) Hemoglobin

Question 32

a) Amino Acids

Answer 32

free and terminal amino acids
– Respond to pH changes by accepting or releasing H+
-If acid comes into blood, hydronium ions can be neutralized by the –COO- groups
-If base is added, it can be neutralized by the –NH3+ groups

Question 33

b) Hemoglobin

Answer 33

-Binds CO2
-Binds and transports hydrogen and oxygen
-Maintains blood pH as hemoglobin changes from oxyhemoglobin to deoxyhemoglobin

Question 34

Physiologic Buffer Systems

Answer 34

Lungs
Kidneys

Question 35

Physiologic Buffer Systems:
RESPIRATORY REGULATION

Answer 35

-Exhalation of carbon dioxide
* Powerful, but only works with volatile acids
* Doesn’t affect fixed acids like lactic acid
* CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-
* Body pH can be adjusted by changing rate and depth of breathing
* Provide O2 to cells and remove CO2

Question 35

Ventilation Rates & Effect on pH Balance

Answer 35

It’s all about CO2 and the bicarbonate buffering system
* Increased ventilation rate causes

Question 36

Hyperventilation

Answer 36

drives the reaction to the left, causing removal of H+, pH goes up

Question 37

Hypoventilation

Answer 37

drives the reaction to the right, causing additional H+, pH goes down

Question 38

Physiologic Buffer Systems:
RENAL REGULATION

Answer 38

-Can eliminate large amounts of fixed acid
* Can also excrete base
* Can conserve and produce bicarbonate ions
* Most effective regulator of pH
* If kidneys fail, pH balance fails
* Only the kidneys can rid the body of acids generated by cellular metabolism (nonvolatile or fixed acids), while also regulating blood levels of alkaline substances and renewing chemical buffer components.

Question 39

Base Excretion

Answer 39

• Only regulated by the kidney.
• Primary base in the body is HCO3
• The kidney can retain or excrete HCO3- as needed.

Question 40

Importance of Renal Regulation

Answer 40

-For every hydrogen ion buffered by bicarbonate – a bicarbonate ion is consumed.
-To maintain the capacity of the buffer system, the bicarbonate must be regenerated

Question 41

Importance of Renal Regulation

Answer 41

◻ Bicarbonate formation can only continue if these hydrogen ions are removed
◻ This process occurs in the cells of the renal tubules where hydrogen ions are secreted into the urine and where bicarbonate is generated and retained in the body

Question 42

Renal Responses to Acidosis

Answer 42

A. increased reabsorption of the filtered HCO3 −
B. increased excretion of titratable acids, and
C. increased production of ammonia.

Question 43

Renal Responses to Acidosis: A. increased reabsorption of the filtered HCO3 −

Answer 43

(1)CO2 within renal tubular cells combines with water in the presence of carbonic anhydrase.
(2)The carbonic acid (H2CO3) formed
rapidly dissociates into H+ and HCO3−
(3)Bicarbonate ion then enters the bloodstream
(4)while the H+ is secreted into the renal tubule,
(5)where it reacts with filtered HCO3 − to form H2CO3.
.

Question 44

Renal Responses to Acidosis: B. Increased Excretion of Titratable Acids

Answer 44

After all of the HCO3− in tubular fluid is
reclaimed, the H+ secreted into the tubular lumen can combine with HPO4 2− to form H2PO4− (the latter is not readily reabsorbed because of its charge and is eliminated in urine). The net result is that H+ is excreted from the body as H2PO4−, and the HCO3−
that is generated in the process can enter the bloodstream.

Question 45

Renal Responses to Acidosis: C. Increased Formation of Ammonia

Answer 45

In the proximal tubules of the nephrons within the kidneys, glutamine, an amino acid, can be metabolized to produce ammonia. This process is enhanced in response to acidosis. The enzyme responsible for this conversion is glutaminase, which breaks down glutamine into ammonia and other byproducts.

Question 46

Regulation of Plasma pH - Alkalosis

Answer 46

-When the body is in alkalosis, tubular
cells secrete bicarbonate ions and
reclaim hydrogen ions and acidify the
blood.
-The mechanism is the opposite of
bicarbonate ion reabsorption process