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General Biology: Chemical Basis of Life

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  • What are the four elements that make up about 96% of the weight of most living organisms?

    Oxygen, Carbon, Hydrogen, and Nitrogen make up about 96% of the weight of most living organisms.

  • Define a compound in biological terms.

    A compound is a substance consisting of two or more different elements in a fixed ratio.

  • What are trace elements and why are they important?

    Trace elements are required in small amounts to prevent disease and support health, such as fluoride added to water to reduce tooth decay.

  • What are the three subatomic particles relevant to atoms?

    Protons and neutrons are in the nucleus; electrons orbit the nucleus.

  • What determines an element's atomic number?

    The number of protons in the nucleus determines an element's atomic number.

  • What is an isotope?

    An isotope has the same number of protons but different numbers of neutrons.

  • What is the difference between atomic mass and mass number?

    Mass number is the sum of protons and neutrons; atomic mass is approximately equal to the mass number.

  • How do radioactive isotopes help in biology?

    They serve as tracers to monitor atoms in organisms and can be detected by imaging instruments.

  • What determines an atom's chemical properties?

    The distribution of electrons in electron shells determines chemical properties.

  • What is an ionic bond?

    An ionic bond is an attraction between ions of opposite charge formed by the transfer of electrons.

  • What is a covalent bond?

    A covalent bond involves sharing electrons between atoms.

  • Difference between nonpolar and polar covalent bonds?

    Nonpolar covalent bonds share electrons equally; polar covalent bonds share electrons unequally due to electronegativity differences.

  • What is a hydrogen bond?

    A hydrogen bond is a weak attraction between a hydrogen atom in one molecule and an electronegative atom in another.

  • Why is water a polar molecule?

    Water has polar covalent bonds and a bent shape, causing an unequal distribution of charges.

  • What is cohesion and adhesion in water?

    Cohesion is water molecules sticking to each other; adhesion is water sticking to other substances.

  • How does water moderate temperature?

    Water absorbs and releases heat slowly due to hydrogen bonding, stabilizing temperature.

  • Why does ice float on water?

    Ice is less dense because hydrogen bonds form a stable lattice that spaces molecules farther apart.

  • What makes water a versatile solvent?

    Its polarity allows it to surround and dissolve polar and charged solutes, forming aqueous solutions.

  • What is the pH scale?

    The pH scale measures acidity or basicity of a solution based on hydrogen ion concentration.

  • What is a buffer?

    A buffer minimizes changes in pH by accepting or donating hydrogen ions.

  • How does rising atmospheric CO2 affect coral reefs?

    CO2 dissolves in seawater, lowering pH and reducing carbonate ions needed for coral calcification.