Biology · Biomolecules · NEET
Water is the most abundant MOLECULE in a cell (about 70-90% of cell mass). Protein is the most abundant ORGANIC molecule or the most abundant biomacromolecule. These are two different questions. If NEET asks for the most abundant molecule overall, the answer is water. If it asks for the most abundant protein, the answer is collagen (in animals) or RuBisCO (the most abundant enzyme). Read the exact wording of the question.
Almost every chemical reaction of life happens in water. Water acts as the main solvent, so ions, sugars, amino acids and other small molecules can dissolve and move around. Because so much of the cell is a water-based fluid (cytoplasm), water molecules simply outnumber every other type of molecule. That is why water sits at the top of the abundance list.
NCERT lists water as the most abundant chemical in living organisms when discussing the chemical composition of the cell. Water is not a carbon-based organic biomolecule like protein or DNA, but it is still the most abundant molecule present. So for NEET, remember: most abundant molecule = water; most abundant ORGANIC biomolecule = protein.
Do not mix molecules and elements. Water (H2O) is the most abundant MOLECULE in a cell. Oxygen is the most abundant ELEMENT by weight in the human body, largely because water itself is full of oxygen atoms. So oxygen (element) and water (molecule) are both 'most abundant' but in two different lists.
Water is far more abundant than carbohydrate. In a living cell water is about 70-90% of the mass, while all carbohydrates together are only a small percentage. Among carbon-based (organic) molecules, protein usually comes first, then carbohydrate and lipid, then nucleic acid. Water still beats all of them as the single most abundant molecule.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Water. It makes up roughly 70 to 90 percent of the total mass of a cell, more than any other single molecule.
Protein. Among carbon-containing biomolecules, protein comes first, followed by carbohydrate, lipid and then nucleic acid.
Because it is the main solvent of life. Nearly all cellular reactions occur in a water medium, so water molecules greatly outnumber every other molecule.
Oxygen by weight, mostly because water (H2O) contains large amounts of oxygen atoms. This is an element question, not a molecule question.
Yes. Different cells and tissues have different water content, and metabolically active cells generally hold more water. But water still stays the most abundant molecule overall.
