A cell that is capable of self existence is a/an

Analyze the question: The question asks which cell can live on its own, independent of other cells. That is, which one is a complete organism by itself.

Explain the concept:

• A unicellular organism is made of only one cell. That single cell carries out all life processes: feeding, respiration, excretion, movement, reproduction, and response to stimuli.
• Cells in multicellular organisms are specialized. They depend on other cells, tissues, and organs for nutrients, oxygen, and protection, so they cannot survive independently for long.

Solution (checking each option):

• A. Amoeba: A unicellular, free-living protozoan. It feeds (by phagocytosis), respires, excretes, moves (by pseudopodia), and reproduces (by binary fission) all on its own. ✔ Capable of self-existence.
• B. Human cheek cell: An epithelial cell from the lining of the mouth. It is part of human tissue and cannot live on its own. ✘
• C. Onion epidermal cell: A cell from the outer layer of an onion bulb. It is part of a multicellular plant and depends on other tissues. ✘
• D. Ovum: A female sex cell. It is specialized and needs fertilization and the mother's body to develop. ✘
• E. Spermatozoon: A male sex cell. It is specialized for swimming to the ovum and has a very short independent life span. ✘

Exam tip: When you see "capable of self-existence" or "independent living cell," think unicellular organisms: Amoeba, Paramecium, Euglena, Chlamydomonas. Cells taken from the body or organs of plants and animals (cheek cells, onion cells, blood cells, sex cells) are always parts of a larger organism.