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NPCIL Trainee Biology — practice by topic

Browse 19 questions across 1 Biology topics. Choose what you want to revise, then open a question to check its answer and worked solution.

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The Chemical Foundation of Life (19)

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In chemistry and biology, "matter" is defined as:Read the answer and worked solution →There are 118 known chemical elements. How many of these occur naturally?Read the answer and worked solution →Isotopes of the same element are atoms that differ only in their number of:Read the answer and worked solution →The time required for half of a radioactive isotope's original concentration to decay to a more stable form is called its:Read the answer and worked solution →

Worked practice questions

In chemistry and biology, "matter" is defined as:

  1. anything that occupies space and has mass
  2. only living substances
  3. any substance carrying an electric charge
  4. any gas at room temperature
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Correct answer: A. anything that occupies space and has mass

1. The stem asks for the most fundamental definition used at the start of this topic. 2. The text states: "Matter is any substance that occupies space and has mass." 3. This definition applies equally to living and non-living material, to charged and uncharged substances, and to solids, liquids, and gases alike. 4. So matter is defined simply as anything occupying space and having mass -- not restricted to living things, charge, or a particular state. _Source: OpenStax Biology Ch 2 "The Chemical Foundation of Life", p.33 §2.1 | Atoms, Isotopes, Ions, and Molecules: The Building Blocks_

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There are 118 known chemical elements. How many of these occur naturally?

  1. 100
  2. 92
  3. 108
  4. All 118
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Correct answer: B. 92

1. The text distinguishes between the total number of known elements and the subset that occurs in nature. 2. It states: "There are 118 elements, but only 92 occur naturally. The remaining elements are synthesized in laboratories and are unstable." 3. So the elements beyond the 92nd are all laboratory-synthesized and unstable, not naturally occurring. 4. This means the correct count of naturally occurring elements is 92, not 100, 108, or all 118. _Source: OpenStax Biology Ch 2 "The Chemical Foundation of Life", p.33 §2.1 | Atoms, Isotopes, Ions, and Molecules: The Building Blocks_

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Isotopes of the same element are atoms that differ only in their number of:

  1. protons
  2. electrons
  3. neutrons
  4. valence shells
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Correct answer: C. neutrons

1. An element is defined by a fixed number of protons, so that number cannot vary between isotopes of the same element. 2. The text states: "isotopes, which are different forms of the same atom that vary only in the number of neutrons they possess." 3. Protons stay fixed (that is what makes them the same element), and while electron count can change in ions, isotopes are specifically about neutral atoms differing in neutrons. 4. So isotopes of an element differ only in their neutron count. _Source: OpenStax Biology Ch 2 "The Chemical Foundation of Life", p.34 §2.1 | Atoms, Isotopes, Ions, and Molecules: The Building Blocks_

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