Electrons carry a negative charge and contribute almost nothing to an atom's mass.
Correct Answer
True
True. An electron has a charge of -1 and a mass so small that it is treated as negligible. An atom's mass comes almost entirely from its protons and neutrons.
Category: Atoms and Ions
Question 2
Isotopes of an element have the same number of neutrons but different numbers of protons.
Correct Answer
False
False. Isotopes have the same number of protons, which is what makes them the same element, but different numbers of neutrons. Carbon-12 and carbon-14 both have 6 protons but 6 and 8 neutrons.
Category: Atoms and Ions
Question 3
Radioactive isotopes are unstable and break down over time, giving off particles or energy.
Correct Answer
True
True. Unstable isotopes decay by releasing particles or energy. This steady decay is what makes isotopes such as carbon-14 useful for dating fossils.
Category: Atoms and Ions
Question 4
Carbon-14 has a half-life of about 50 years.
Correct Answer
False
False. Carbon-14 has a half-life of about 5,730 years. Because of that long half-life, it can date remains up to about 50,000 years old.
Category: Atoms and Ions
Question 5
A chloride ion carries a negative charge because it has one more electron than it has protons.
Correct Answer
True
True. A chlorine atom has 17 protons and gains an electron to have 18 electrons. The extra negative charge gives the chloride ion a charge of -1, making it an anion.
Category: Atoms and Ions
Question 6
Covalent bonds form when one atom completely transfers electrons to another atom.
Correct Answer
False
False. Covalent bonds form when atoms share electrons. A complete transfer of electrons produces ions, which are then held together by an ionic bond.
Category: Chemical Bonds
Question 7
Hydrogen bonds between paired bases help hold the two strands of a DNA double helix together.
Correct Answer
True
True. The bases on the two strands face inward and pair with each other through hydrogen bonds. Each one is weak, but together they hold the strands firmly.
Category: Chemical Bonds
Question 8
Oils dissolve easily in water because oil molecules are polar.
Correct Answer
False
False. Oils are nonpolar and hydrophobic, so they cannot form hydrogen bonds with water and do not dissolve in it. Polar and charged substances are the ones that dissolve in water.
Category: Properties of Water
Question 9
Water can absorb a large amount of heat before its temperature rises much, because much of the energy goes into breaking hydrogen bonds.
Correct Answer
True
True. Water's high heat capacity comes from its hydrogen bonds, which must be broken before the molecules can move faster. This property helps keep the temperature of organisms and bodies of water stable.
Category: Properties of Water
Question 10
A solution with a pH of 4 is basic.
Correct Answer
False
False. A pH below 7 is acidic, so a pH of 4 is acidic. Basic, or alkaline, solutions have a pH above 7.
Category: pH and Buffers
Question 11
Buffers help keep pH stable by absorbing excess hydrogen ions or hydroxide ions.
Correct Answer
True
True. A buffer takes up extra hydrogen ions or hydroxide ions so the pH of a solution changes very little. The bicarbonate system in blood is an example.
Category: pH and Buffers
Question 12
Acids are substances that release hydroxide ions and raise the pH of a solution.
Correct Answer
False
False. Acids release hydrogen ions and lower pH. Bases are the substances that release hydroxide ions or take up hydrogen ions, raising pH.
Category: pH and Buffers
Question 13
Glucose, fructose and galactose all have the same chemical formula, C6H12O6.
Correct Answer
True
True. These three monosaccharides are isomers: they have the same atoms but arranged differently. That difference in arrangement gives each one different chemical properties.
Category: Carbohydrates
Question 14
Humans can easily digest cellulose to obtain the sugar it contains.
Correct Answer
False
False. Humans lack the enzymes needed to break the bonds in cellulose, so it passes through the digestive tract as fiber. Cows and termites depend on microbes in their guts to digest it.
Category: Carbohydrates
Question 15
Chitin, a nitrogen-containing polysaccharide, forms the exoskeletons of arthropods such as insects and crabs.
Correct Answer
True
True. Chitin is a tough structural polysaccharide containing nitrogen. It makes up arthropod exoskeletons and is also found in the cell walls of fungi.
Category: Carbohydrates
Question 16
A triglyceride is made of one glycerol molecule joined to two fatty acids.
Correct Answer
False
False. A triglyceride is one glycerol joined to three fatty acids, and three water molecules are released as the bonds form. The two-fatty-acid structure, with a phosphate group in place of the third, is a phospholipid.
Category: Lipids
Question 17
Phospholipids have hydrophilic heads and hydrophobic tails, which lets them form the double layer of cell membranes.
Correct Answer
True
True. In water, phospholipids arrange themselves with their tails pointing inward away from the water and their heads facing outward. This arrangement forms the lipid bilayer of the plasma membrane.
Category: Lipids
Question 18
Unsaturated fats such as olive oil are usually solid at room temperature.
Correct Answer
False
False. Unsaturated fats are usually liquid at room temperature because the double bonds put kinks in their chains so they cannot pack tightly. Saturated fats, such as butter, tend to be solid.
Category: Lipids
Question 19
A protein's primary structure is its sequence of amino acids.
Correct Answer
True
True. Primary structure is the order of amino acids in the chain, determined by the gene that codes for the protein. This sequence in turn determines how the protein folds into its higher levels of structure.
Category: Proteins and Nucleic Acids
Question 20
Denaturing a protein with heat changes its amino acid sequence.
Correct Answer
False
False. Denaturation changes a protein's three-dimensional shape, which can destroy its function, but the amino acid sequence stays the same. Cooking an egg white is a familiar example.
Category: Proteins and Nucleic Acids