Chemical Composition of Living Organisms — NEET Biology
📚 Practice ConceptAlthough there is a bewildering diversity of living organisms, their chemical composition and metabolic reactions appear to be remarkably similar. The elemental composition of living tissues and non-living matter appear also to be similar when analysed qualitatively. However, a closer examination reveals that the relative abundance of carbon, hydrogen and oxygen is higher in living systems when compared to inanimate matter. The most abundant chemical in living organisms is water. There are thousands of small molecular weight (<1000 Da) biomolecules. Amino acids, monosaccharide and disaccharide sugars, fatty acids, glycerol, nucleotides, nucleosides and nitrogen bases are some of the organic compounds seen in living organisms. There are 20 types of amino acids and 5 types of nucleotides. Fats and oils are glycerides in which fatty acids are esterified to glycerol. Phospholipids contain, in addition, a phosphorylated nitrogenous compound.
Assertion (A): Carbon and hydrogen are more abundant in living organisms than in earth’s crust. Reason (R): Living organisms contain organic molecules with high carbon and hydrogen content.
View solution & NCERT explanation
Correct answer: B — If both assertion and reason are true but reason is not the correct explanation of the assertion.
NCERT states “However, a closer examination reveals that the relative abundance of carbon and hydrogen with respect to other elements is higher in any living organism than in earth’s crust.” The Assertion removes the crucial qualifier “relative abundance” making it false - in absolute terms, earth’s crust has more carbon and hydrogen. The Reason is true from NCERT’s discussion of organic molecules in living systems.
What does NCERT say about Although there bewildering diversity?
Has this concept appeared in NEET?
Which chapter is this from?
Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
176/180MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.