Question 1

What is the name of a molecule composed of one or more sugars?

Accepted Answer

Carbohydrates are molecules composed of one or more sugars. Lipids, nucleic acids, and polypeptides are not composed primarily of sugars.

Question 2

What type of chemical bond connects the complementary strands of a DNA molecule to each other?

Accepted Answer

Hydrogen bonds connect the complementary strands of DNA together.

Question 3

Which of the following are found in the nucleus of an atom?

Accepted Answer

The nucleus of an atom contains two types of subatomic particles: protons and neutrons. Electrons exist in the electron cloud surrounding the nucleus.

Question 4

Because the electrons in a water molecule are shared unequally between hydrogen and oxygen, water is said to be

Accepted Answer

Water is a polar molecule because the electrons in the covalent bonds between hydrogen and oxygen are shared unequally, with the electrons spending more time closer to the oxygen nucleus than the hydrogen nuclei. This creates a partial negative charge around the oxygen atom and a partial positive charge around the hydrogen atoms, giving water a polar nature.

Question 5

Each of the following is a feature of all known living things EXCEPT

Accepted Answer

While genes are made up of nucleic acids (DNA or RNA), not all genes are made up of proteins. Some genes, such as ribosomal RNA genes, are made up of RNA molecules. However, all living things do exhibit growth, homeostasis, and metabolism.

Question 6

Nonliving things include fire, water, and viruses. Many features of living things are also found in nonliving things. Of the following features, which is most likely to be absent in nonliving things?

Accepted Answer

Homeostasis, the ability to maintain a stable internal environment, is a feature typically absent in nonliving things.

Question 7

What kind of bond holds the atoms of a single water molecule together?

Accepted Answer

A single water molecule is held together by covalent bonds that are polar. This is because oxygen has a greater electronegativity than hydrogen, causing the shared electrons in the covalent bond to be pulled closer to the oxygen atom, giving it a partial negative charge and the hydrogen atoms partial positive charges.

Question 8

Imagine a newly discovered biological molecule that is mostly hydrophobic in its structure. This new molecule will most likely be classified as a

Accepted Answer

Hydrophobic molecules repel water and tend to be nonpolar. Carbohydrates, nucleic acids, and proteins are polar and do not have a significant hydrophobic component, making lipids the best choice for a new biological molecule described as hydrophobic.

Question 9

A molecule that is composed only of chains and rings of hydrogen and carbon is called a

Accepted Answer

A molecule composed only of hydrogen and carbon is called a hydrocarbon. Carbohydrates are composed of carbon, hydrogen, and oxygen and include sugars and starches. Polypeptides are chains of amino acids that make up proteins. Polysaccharides are complex carbohydrates made up of long chains of sugar molecules.

Question 10

What kind of bond holds two water molecules to each other?

Accepted Answer

Two water molecules are held together by hydrogen bonds.

Question 11

What is the pH of a neutral solution?

Accepted Answer

The pH of a neutral solution is 7. This means that the concentration of hydrogen ions (H+) and hydroxide ions (OH-) are equal, resulting in a balance between acidity and alkalinity. A pH of 1 is extremely acidic, a pH of 5 is slightly acidic, and a pH of 9 is slightly alkaline.

Question 12

Which term best describes the sugar in a sugar-water solution?

Accepted Answer

The sugar in a sugar-water solution is the solute. The solute is the substance that is dissolved in a solution, in this case being sugar. A solvent is the substance that dissolves the solute, which in this case is water. The terms product and reactant refer to substances involved in a chemical reaction.

Question 13

Which term best describes the water in a sugar-water solution?

Accepted Answer

The solvent is the substance in a solution that dissolves the solute. In a sugar-water solution, water is the solvent and sugar is the solute.

Question 14

Which of the following pairs of molecules can be held together by a hydrogen bond?

Accepted Answer

Hydrogen bonding occurs between molecules that have a partial positive charge on a hydrogen atom bonded to a strongly electronegative atom (such as nitrogen, oxygen, or fluorine) and a partial negative charge on another electronegative atom in a nearby molecule. This is commonly found in polar molecules, so the pair of polar molecules can be held together by a hydrogen bond.

Question 15

An atom will be least likely to form chemical bonds with other atoms when

Accepted Answer

When the valence shell (the outermost electron shell) is full of electrons, the atom is stable and does not need to form bonds with other atoms. This is because a full valence shell indicates that the atom has achieved a stable electron configuration similar to the noble gases.

Question 16

The atomic number of an element refers to the number of ________ in one atom of that element.

Accepted Answer

The atomic number of an element refers to the number of protons in one atom of that element.

Question 17

If life on Mars is fundamentally like life on Earth, its macromolecules will be based on which element?

Accepted Answer

Carbon is the element that forms the backbone of all organic molecules on Earth. If life on Mars is similar to Earth, it is likely that the macromolecules will also be based on carbon.

Question 18

How do the concentrations of H⁺ and OH^- compare to each other in an acidic solution?

Accepted Answer

In an acidic solution, the concentration of H⁺ is higher than the concentration of OH⁻. This is because acids are substances that release H⁺ ions when they are dissolved in water, leading to an excess of H⁺ ions in the solution. This results in a decrease in pH, making the solution acidic. On the other hand, the concentration of OH⁻ ions is low because the H⁺ ions combine with water molecules to form H₃O⁺ ions, reducing the availability of OH⁻ ions in the solution.

Question 19

Which macromolecule has a sugar-phosphate backbone?

Accepted Answer

The sugar-phosphate backbone is a characteristic feature of nucleic acids, which include DNA and RNA. The backbone is composed of alternating deoxyribose or ribose sugars and phosphate groups. Lipids have a glycerol backbone, proteins have an amino acid backbone, and polysaccharides have a chain of sugar molecules as the backbone.

Question 20

In general, what makes one kind of amino acid different from other amino acids?

Accepted Answer

Amino acids all have the same basic structure, including an amino group and a carboxyl group, but the side group (also known as the R group) is unique to each amino acid. This side group determines the physical and chemical properties of the amino acid, which in turn affects its role in proteins and other biological processes. Therefore, the answer is the side group.

Quiz 2: Are We Alone in the Universe? Water, Biochemistry, and Cells