Chapter 2 Part B Homework

What is the primary energy-transferring molecule in cells?

Answer: ATP Why: When broken (cleaved), the high-energy phosphate bonds in the ATP molecule release the energy used to do cellular work.

In a covalent bond,

Answer: Atoms share one or more pairs of electrons. Why: In covalent bonds, atoms share ("co") their valence electrons ("valent"). These bonds are strong because to maintain stability the atoms must stay close enough together to continue sharing their electrons.

Which of the following is an exchange reaction?

Answer: HCl+NaOH→NaCl+H2O Why: The reactants exchange parts to produce new chemical combinations.

Which of the following statements is true regarding the enzyme-catalyzed reaction (B) compared to the uncatalyzed reaction (A)?

Answer: Less energy input is required to start the reaction in the presence of enzyme. Why: Enzyme-catalyzed reactions require less activation energy and therefore are initiated with a lower input of energy. This activation energy represents the energy necessary for driving the early stages of the reaction: creating contact between properly oriented substrates, breaking original bonds, and so on.

Which of the following is an example of a decomposition reaction?

Answer: MgO2 → Mg + O2 Why: A decomposition reaction occurs when a larger molecule is broken down into smaller molecules or its constituent atoms.

Atoms of oxygen have a total of 8 electrons. Are these atoms stable, and why or why not?

Answer: No, because the atoms have only 6 valence electrons, but need 8 for stability. Why: To be stable, by the Octet Rule an atom must have 8 electrons in its outermost orbital. With only 6 valence electrons, oxygen atoms are unstable and will seek ways to get or share two more electrons to become stable.

Which of the following distinguishes hydrogen bonds fro covalent bonds?

Answer: Only hydrogen bonds can form between molecules Why: Because hydrogen bonds are not true bonds, they do not always join atoms together within a single molecule. In water, for example, hydrogen bonds link water molecules together. This is referred to as an intermolecular attraction—it is between different atoms.

Each specific amino acid has a unique ______.

Answer: R group Why: The identity of each unique amino acid is determined by the structure of its R group (note differences within the green rectangular area in amino acids (b) through (e)).

Which of the following is true of polar covalent bonds? Which of the following is true of polar covalent bonds?

Answer: The electrons are shared unequally. Why: Because the electrons are shared unequally, they spend more time around one atom than the other, causing a slight negative charge where they tend to hang out the most, and a slight positive charge where they spend the least time.

Which of the following is TRUE regarding the pH of a solution?

Answer: The more hydrogen ions in a solution, the more acidic the solution is. Why: The more hydrogen ions in a solution, the more acidic the solution is.

Which of the following is not a result of hydrogen bonds?

Answer: Two hydrogen atoms join together to form a molecule of hydrogen gas. Why: Hydrogen bonds occur when there are polar covalent molecules present, but hydrogen atoms join with each other through nonpolar covalent bonds.

Which of the following best describes dehydration synthesis?

Answer: Two smaller molecules join together after a water molecule is removed from between them. Why: This is a common way for organic molecules to combine.

Water acts to dissolve molecules in the body. How does water dissolve the salt (NaCl) in your mouth from a salty pretzel?

Answer: Water acts as a solvent because the partial negative charge on the oxygen in water attracts sodium, while the partial positive charge on hydrogen attracts chloride. This results in the separation of sodium from chloride, thus breaking the ionic bond. Why: Yes, salt (NaCl) is an ionic compound that can be separated by the polar water molecule.

Carbon atoms have four valence electrons. Are they likely to react with other atoms, and why or why not?

Answer: Yes, because they can become more stable by doing so. Why: Atoms react with other atoms to gain stability, typically by gaining, losing, or sharing electrons to attain a full outermost orbital. Atoms with full outermost electron orbitals are less likely to react and are referred to as being inert.

In plasma, a typical body fluid, protein floating around would be considered to be which of the following?

Answer: a solute, specifically both a colloid and an electrolyte Why: Yes, colloids are large particles dispersed in body fluids. Since most proteins have a negative charge, they are also considered to be electrolytes.

What is the classification of a solution with a pH of 8.3?

Answer: alkaline solution Why: A pH between 0.0 and 7.0 is acidic. A pH between 7.0 and 14.0 is basic. Therefore, a solution with a pH of 8.3 is an alkaline (or basic) solution.

All amino acids (such as the four represented in the figure) contain ______.

Answer: an amine group and carboxyl group Why: The oval area shown in each of the amino acids highlights the amino group, carboxyl group, and central carbon found in all amino acids.

Which of the following is not produced through chemical bonding?

Answer: atoms Why: Atoms react through chemical bonding to form larger structures. Chemical bonding begins with atoms; it does not produce them. All of the structures that we cover in A&P are made from atoms through chemical bonding.

Water ________.

Answer: can form hydrogen bonds Why: Due to its polar nature, water is able to form hydrogen bonds. In fact, many of the special properties of water derive from its extensive hydrogen bonding capacity. In addition, water has a high heat capacity and is considered a universal solvent since it dissolves more substances than any other known solvent.

Electrolytes are charged particles called ions that are dissolved in body fluids. Which of the following ions would be considered a major anion in the body?

Answer: chloride Why: Yes, chloride is a major extracellular anion (negative ion).

Which of the following correctly ranks chemical bonds, in order, from strongest to weakest?

Answer: covalent, ionic, hydrogen Why: In covalent bonds, electrons are shared between atoms; in ionic bonds electrons are lost or gained; but hydrogen bonds are not true chemical bonds—they are weak attractions due to slight electrical imbalances. No electrons are directly involved.

Hydrolysis is an example of which type of reaction?

Answer: decomposition Why: Most chemical digestion is done by hydrolysis reactions.

Which of the following is NOT one of the three major types of chemical reactions? Which of the following is NOT one of the three major types of chemical reactions?

Answer: hyperbolic Why: Most chemical reactions exhibit one of three recognizable patterns. They are either synthesis, decomposition, or exchange reactions.

Covalent bonds:

Answer: involve the sharing of one to three pairs of electrons. Why: In single covalent bonds, one pair of electrons is shared; in double covalent bonds two pairs are shared; and triple covalent bonds involve sharing of three pairs of electrons. Double covalent bonds are common between carbon atoms in some organic molecules.

Which pH is more acidic, a pH of 3, a pH of 7, or a pH of 9?

Answer: pH of 3 Why: Yes, the lower the pH, the more acidic the fluid. pH is inversely related to the number of H+ ions. As the number of H+ ions increases (and thus the acidity increases), the pH decreases. Therefore, a pH of 3 is the most acidic of the three values given.

Formation of hydrogen bonds requires hydrogen atoms and what else?

Answer: polar covalent bonds Why: Hydrogen gets a slight positive charge from the unequal sharing of electrons in polar covalent bonds, and it bonds to another atom with a slightly negative charge, again resulting from unequal electron sharing due to a polar covalent bond.

A molecule of water (H2O) is formed by what type of bond?

Answer: polar covalent bonds Why: The unequal electron distribution produces a slight negative charge on the oxygen and a slight positive charge on the hydrogens. These slight charges give water many unique characteristics that make it ideal for many physiological processes.

In a chemical equation, what are the chemicals on the left side of the arrow called?

Answer: reactants Why: The chemicals on the left side of the arrow will react with each other.

Cortisol is a type of lipid hormone. Which type of lipid would cortisol be classified as?

Answer: steroid Why: Yes, cortisol is a steroid hormone synthesized from cholesterol.

Which of the following are especially important for growth and repair processes?

Answer: synthesis reactions Why: Synthesis reactions combine smaller molecules to make larger ones.

Which parts of atoms can interact (react) to form chemical bonds?

Answer: valence electrons Why: Only the outermost parts of atoms interact (react) with each other, and those are the valence electrons. If the outermost orbital is full, the atom is stable and less likely to react with another atom.

What is the most abundant and important inorganic compound in living material?

Answer: water Why: Water is the most abundant and important inorganic compound because of its high heat of vaporization, polar solvent properties, high heat capacity, reactivity, and cushioning properties.

Foods are broken down into their building blocks by adding water. This would be an example of which characteristic of water?

Answer: water as a reactant Why: Yes, water molecules are necessary for salivary amylase to hydrolyze starch to glucose in your mouth. Thus, water acts as an important reactant.