The basic unit of life is:
A. Atom
B. Water
C. Cell
D. Chemical level of organisation
Correct Answer:- C. Cell
Explanation:- The basic unit of life is the cell.
This is a foundational principle in biology, known as the **cell theory**, which states:
1. All living organisms are composed of one or more cells.
2. The cell is the basic structural, functional, and biological unit of all known living organisms.
3. All cells arise from pre-existing cells (via cell division).
Key points:
• Even the simplest organisms (like bacteria) are made of at least one cell.
• Complex organisms (like humans, plants, or animals) are made of trillions of specialized cells.
• Viruses are not considered living organisms by most biologists because they cannot carry out life processes independently and lack cellular structure.
So, universally accepted answer: the cell.
Other Options Details:
Here is a clear description of each option in the context of levels of biological organization (typically asked in biology questions):
A. Atom
• Smallest basic unit of matter (e.g., carbon, hydrogen, oxygen, nitrogen).
• Not a level of biological organization by itself, but the starting point of all matter.
• Atoms combine to form molecules.
• Example: Oxygen atom (O), Carbon atom (C).
B. Water
• A specific type of molecule (H₂O), not a complete level of organization.
• Water is one of the most important inorganic molecules in living organisms.
• It is formed when hydrogen and oxygen atoms chemically bond.
• Essential for life, but it belongs to the molecular level, not a separate level.
C. Cell
• The basic structural, functional, and biological unit of all living organisms .
• It is the smallest unit of life that can replicate independently.
• Represents the cellular level of organization.
• Example: Red blood cell, neuron, bacterial cell.
• Cells are made up of many molecules (like proteins, DNA, water, lipids).
D. Chemical level of organization
• Also called the molecular level.
• The lowest level in the biological hierarchy.
• Includes atoms → molecules → macromolecules (e.g., proteins, carbohydrates, lipids, nucleic acids).
• All biological structures and functions begin at this level.
Example: DNA molecule, glucose, hemoglobin, water, ATP.
Summary of the hierarchy (starting from the lowest):
1. Chemical level (atoms → molecules → macromolecules) → D
2. Cellular level(cells) → C
3. Organelle level
4. Tissue level
5. Organ level
6. Organ system
7. Organism
So:
• A. Atom → part of the chemical level
• B. Water → a molecule (belongs to chemical level)
• C. Cell → cellular level (first level considered truly “living”)
• D. Chemical level of organization → the entire first level (atoms + molecules)
The most precise answer for the lowest level of biological organization is usually D. Chemical level of organization.
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Writer: Vandita Singh, Lucknow (GS India Nursing Group)