AP Biology:: Chemistry Of Life

What are the FOUR elements that make up the vast majority (roughly 96%) of living organisms' mass?

- **A)** Carbon, Hydrogen, Oxygen, and Nitrogen
- **B)** Calcium, Potassium, Sodium, and Iron
- **C)** Oxygen, Nitrogen, Argon, and Neon
- **D)** Carbon, Silicon, Gold, and Helium

Why is CARBON considered especially well-suited to form the 'backbone' of the large, complex molecules found in living things?

- **A)** Carbon can form FOUR stable covalent bonds simultaneously, allowing it to bond with many other atoms (including other carbon atoms) to build large, complex, and diverse molecular structures, including chains, branches, and rings
- **B)** Carbon is chemically identical to oxygen in every respect
- **C)** Carbon never actually forms chemical bonds with any other element
- **D)** Carbon can only ever form a single bond with one other atom, limiting it to very small molecules

What is a COVALENT BOND?

- **A)** A chemical bond formed when two atoms SHARE one or more pairs of electrons
- **B)** A bond formed when one atom completely TRANSFERS an electron to another atom, with no sharing involved
- **C)** A synonym for a hydrogen bond
- **D)** A bond that can only ever form between two identical atoms of the exact same element

What is an IONIC BOND, and how does it differ from a COVALENT bond?

- **A)** An ionic bond forms when one atom essentially TRANSFERS an electron to another atom, creating oppositely charged ions that attract each other, whereas a covalent bond involves atoms SHARING electron pairs rather than transferring them
- **B)** Ionic bonds can only ever form within a single, isolated atom
- **C)** An ionic bond involves sharing electrons, while a covalent bond involves transferring them (the reverse of the truth)
- **D)** Ionic and covalent bonds are always exactly identical, with no meaningful difference

What is a HYDROGEN BOND, and how does its STRENGTH compare to a COVALENT bond?

- **A)** A hydrogen bond is a relatively WEAK attraction between a slightly positive hydrogen atom (already covalently bonded to an electronegative atom like oxygen or nitrogen) and a nearby slightly negative atom -- considerably weaker than a covalent bond
- **B)** A hydrogen bond can only ever form between two hydrogen atoms directly bonded to each other
- **C)** A hydrogen bond is always significantly STRONGER than any covalent bond
- **D)** Hydrogen bonds and covalent bonds are always exactly equal in strength

Why is WATER's POLARITY (having a slightly positive end and a slightly negative end) so important for many of its unique, biologically relevant properties?

- **A)** Polarity prevents water from ever forming any bonds with other water molecules
- **B)** Water molecules are completely nonpolar, with no charge distribution of any kind
- **C)** Water's polarity has no actual relationship to any of its physical or chemical properties
- **D)** Water's polarity allows individual water molecules to form HYDROGEN BONDS with each other (and with other polar or charged molecules), which underlies properties like cohesion, high specific heat, and its ability to dissolve many other polar/ionic substances

What is COHESION, as a property of water molecules?

- **A)** A synonym for water's boiling point
- **B)** Cohesion refers only to how water interacts with non-water substances, never with other water molecules
- **C)** The tendency of water molecules to actively repel each other with no attraction whatsoever
- **D)** The tendency of water molecules to STICK TOGETHER with each other, due to hydrogen bonding between them

What is ADHESION, as a property relevant to water, and how does it differ from COHESION?

- **A)** Adhesion refers only to water sticking to other water molecules, identical to cohesion
- **B)** ADHESION is water's tendency to stick to OTHER (non-water) surfaces or substances, while COHESION is water's tendency to stick to ITSELF (other water molecules)
- **C)** Neither adhesion nor cohesion has any relationship to water's interactions with any surface
- **D)** Adhesion and cohesion are always exactly the same phenomenon, with no meaningful distinction