Multiple choice Which of the following is the most abundant protein in the whole of the biosphere? Collagen Keratin Ribulose bisphosphate Carboxylase-Oxygenase Glucose-6-phosphatase Inulin Reveal answer Fill a bubble to check yourself C Correct answer Explanation Ribulose bisphosphate Carboxylase-Oxygenase (RuBisCO) is the most abundant protein in the whole of the biosphere.