Which of these is an odd one out?

Correct — C. ATP, glucose and NADH all work in energy metabolism, and DNA does not.

Glucose is the fuel. Glycolysis splits it into pyruvate, yielding ATP and NADH.

NADH carries electrons to the electron transport chain, where their energy makes more ATP.

ATP is the energy currency the cell spends. DNA stores hereditary information instead, so option (c) is the odd one out.

Why the others are wrong

• (a)
  ATP — ATP is the energy currency of the cell, which respiration makes from glucose, much of it by way of NADH. It sits inside the energy group.
• (b)
  Glucose — Glucose is the starting fuel: glycolysis breaks it down and yields ATP and NADH. It heads the energy chain the other two belong to.
• (d)
  NADH — NADH is the reduced form of NAD, a carrier that takes electrons from glucose breakdown to the electron transport chain, where ATP is made. It belongs with the energy molecules.

An odd-one-out item turns on the grouping rule, so find what three options share before judging the fourth.

Here the rule is energy. Glucose is broken down in respiration, NADH carries the electrons it releases, and ATP holds the energy the cell then spends.

DNA is a polymer of deoxyribonucleotides that stores hereditary information. Its job is information, not energy.

Key facts

• ATP (adenosine triphosphate) is the energy currency of the cell.
• Glycolysis breaks one glucose into two pyruvate, with a net gain of 2 ATP and 2 NADH.
• NAD is a dinucleotide: an adenine nucleotide joined to a nicotinamide nucleotide through their phosphates. NADH is its reduced form.
• In aerobic respiration the electron transport chain, fed by NADH, makes most of the cell's ATP.

Common traps

• Grouping by structure and picking glucose, the one option with no nucleotide, when the key groups by role in energy metabolism.
• Setting ATP apart as a nucleotide like DNA's building blocks, when its role here is energy.

No directly related past PYQ was found.