Who is credited with first observing cells?
Robert Hooke
Anton van Leeuwenhoek
Robert Koch
Louis Pasteur
Carolus Linnaeus
The Correct Answer is A
A. Robert Hooke: Robert Hooke is credited with the first observation and description of cells in 1665. Using a compound microscope, he examined a thin slice of cork and noted small, box-like structures, which he termed "cells" because they reminded him of the small rooms in a monastery. His work laid the foundation for the development of cell theory in biology.
B. Anton van Leeuwenhoek: Anton van Leeuwenhoek made pioneering contributions to microbiology by observing living microorganisms, including bacteria and protozoa, using single-lens microscopes of his own design. Although he observed “animalcules,” he was not the first to describe cells as structural units of organisms.
C. Robert Koch: Robert Koch was a 19th-century physician and microbiologist known for identifying specific bacteria as causative agents of diseases such as tuberculosis and anthrax. His work advanced germ theory but did not involve the initial discovery of cells.
D. Louis Pasteur: Louis Pasteur made critical contributions to microbiology and immunology, including disproving spontaneous generation and developing vaccines. While he studied microorganisms, he is not credited with the first observation of cells.
E. Carolus Linnaeus: Carolus Linnaeus was a botanist and zoologist who developed the binomial nomenclature system for classifying organisms. He did not work with microscopes or the discovery of cells.
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Related Questions
Correct Answer is B
Explanation
A. Discovery of ribosomes as non-membranous organelles: Ribosomes are intracellular structures responsible for protein synthesis and are not surrounded by membranes. While their discovery expanded understanding of cellular components, it did not contradict classical cell theory, which focuses on cells as the basic structural and functional units of life.
B. Identification of multinucleated skeletal muscle fibers: Classical cell theory posits that a cell has a single nucleus and functions as an autonomous unit. The presence of multinucleated skeletal muscle fibers, also called syncytia, challenged this notion This observation revealed that some cells can deviate from “one nucleus per cell” concept, prompting refinement of the theory.
C. Observation that all living organisms metabolize ATP: While ATP metabolism is a universal feature of living cells, this observation supports rather than challenges cell theory. It reinforces the concept that cells are the basic functional units responsible for life-sustaining biochemical processes.
D. Recognition that membranes are composed of phospholipid bilayers: Identifying the phospholipid bilayer structure of membranes clarified how cells maintain compartmentalization and selective permeability. This structural insight complements classical cell theory and does not contradict the fundamental principles regarding cellular organization.
Correct Answer is A
Explanation
A. Glycocalyx: The glycocalyx is a sticky, gelatinous layer found external to the cell wall in some bacteria and eukaryotic cells. It is primarily composed of polysaccharides and sometimes proteins. This structure functions in adherence to surfaces, protection against desiccation, and evasion of host immune responses, making it essential for colonization and virulence in pathogenic microbes.
B. Capsule: A capsule is a well-organized, dense form of glycocalyx that surrounds certain bacterial cells. While all capsules are glycocalyx, not all glycocalyx is a capsule; the term “capsule” specifically refers to a structured, tightly bound layer that provides enhanced protection and virulence.
C. Membrane: The membrane, including the plasma or cytoplasmic membrane, is a lipid bilayer that controls selective permeability and transport. It is not the sticky, gelatinous external layer.
D. Viroid: A viroid is an infectious, small circular RNA molecule that infects plants. It is unrelated to cellular coatings or structural layers and does not consist of polysaccharides or proteins.
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