Cell water content — typical percentage in active protoplasm In actively metabolizing cells, approximately what fraction of protoplasm is water by mass?

Introduction / Context:
Water is the universal solvent of life and dominates the mass of living cells. Knowing the typical water content in active protoplasm is important for understanding diffusion, enzyme kinetics, osmotic balance, and thermal properties of cells.

Given Data / Assumptions:

• The question refers to active protoplasm, not dehydrated or dormant states.
• Values are approximate and commonly reported in cell biology references.
• Protoplasm includes the living content of the cell.

Concept / Approach:

Most actively growing cells contain a very high proportion of water. While the exact percentage can vary across organisms and cell types, values near nine parts water to one part solute mass are commonly cited. High water content supports rapid biochemical reactions and effective transport of metabolites and ions within the cytosol and organelle matrices.

Step-by-Step Solution:

Verification / Alternative check:

Histological and biochemical analyses consistently place cellular water content between roughly 70% and 90%, with actively metabolizing tissues often near the upper end, validating the selection of 90% for this question.

Why Other Options Are Wrong:

10% and 40% are far too low for living cells. 70% may fit some tissues but is less representative of highly active protoplasm. 55% is typical of some macromolecular mixtures, not whole active cells.

Common Pitfalls:

Confusing whole-organism water content with cellular protoplasm, or assuming a single universal value without considering metabolic state.

Final Answer:

90%