Carbon is central to organic molecules because it

Answer: Forms four covalent bonds, allowing diverse skeletons Four valence electrons → four covalent bonds → chains, rings, and branches that produce the structural diversity of life.

Approximately what percentage of living matter (by mass) is composed of just C, H, O, and N?

Answer: 96% These four elements account for 96% of biomass; trace elements (P, S, Ca, K, etc.) make up the rest.

Which property makes carbon ideal as the central atom of organic molecules?

Answer: Carbon forms 4 stable covalent bonds, allowing diverse 3D skeletons With four valence electrons, carbon forms four covalent bonds and assembles into chains, rings, and branches - the basis for biomolecular diversity.

AP Biology · Topic 1.2

Elements of Life Practice

Part of Chemistry of Life.(SYI-1.B)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$Carbon is central to organic molecules because it$
- A
  $Carries a permanent positive ionic charge$
- B
  $Forms ionic bonds, allowing rigid skeletons$
- C
  $Forms four covalent bonds, allowing diverse skeletons$
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- D
  $Has six valence electrons available for bonding$
Why
$Four valence electrons \to four covalent bonds \to chains, rings, and branches that produce the structural diversity of life.$
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Sample 2difficulty 1/5
$Approximately what percentage of living matter (by mass) is composed of just C, H, O, and N?$
- A
  $96%$
  check_circle
- B
  $20%$
- C
  $75%$
- D
  $50%$
Why
$These four elements account for ~96% of biomass; trace elements (P, S, Ca, K, etc.) make up the rest.$
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Sample 3difficulty 2/5
$Which property makes carbon ideal as the central atom of organic molecules?$
- A
  $Carbon forms 4 stable covalent bonds, allowing diverse 3D skeletons$
  check_circle
- B
  $Carbon dissociates easily in water$
- C
  $Carbon donates protons to acids$
- D
  $Carbon can only form linear single bonds$
Why
$With four valence electrons, carbon forms four covalent bonds and assembles into chains, rings, and branches - the basis for biomolecular diversity.$
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