A researcher studies a syncytial tissue in which multiple nuclei share a common cytoplasm. Which principle of classical cell theory is most directly questioned by this finding?
All cells arise from pre-existing cells
The cell is the basic unit of structure and function
All organisms are composed of one or more cells
Cells contain hereditary information
The Correct Answer is B
A. All cells arise from pre-existing cells: This principle, articulated by Rudolf Virchow, emphasizes that cellular reproduction occurs through division of existing cells. The existence of a syncytium does not contradict this principle because the multinucleated structure can arise from the fusion of multiple cells or nuclear division without cytokinesis.
B. The cell is the basic unit of structure and function: Classical cell theory defines the cell as an autonomous, discrete unit of life with its own cytoplasm and nucleus. In syncytial tissues, multiple nuclei share a common cytoplasm, blurring the boundaries of individual cellular units. This challenges the notion of cells as independent structural and functional entities.
C. All organisms are composed of one or more cells: Syncytial tissues still meet this principle because they are formed by cellular components and exist within multicellular organisms. The organism-level composition remains consistent with classical cell theory.
D. Cells contain hereditary information: The presence of multiple nuclei within a shared cytoplasm does not negate that nuclei house DNA or hereditary material. Each nucleus maintains genetic information, so this principle is upheld even in syncytial structures.
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Correct Answer is B
Explanation
A. Yeasts are multicellular fungi that reproduce by spore fragmentation: Multicellular fungi, such as molds, have hyphal structures and can reproduce via spore formation or fragmentation of mycelia. Yeasts, however, are unicellular and do not form multicellular hyphae under normal conditions.
B. Yeasts are unicellular fungi that reproduce by budding: Yeasts are single-celled eukaryotic fungi that reproduce primarily through asexual budding, where a new daughter cell forms as an outgrowth from the parent cell. Their unicellular structure and budding reproduction distinguish them from filamentous fungi.
C. Yeasts are prokaryotic organisms that divide by binary fission: Prokaryotic organisms, such as bacteria, lack a nucleus and organelles and reproduce primarily by binary fission. Yeasts are eukaryotic, containing a true nucleus and membrane-bound organelles, and although some yeast species may divide by fission, they are classified as eukaryotes.
D. Yeasts are photosynthetic eukaryotes with chloroplasts: Photosynthesis is carried out by plants and certain protists possessing chloroplasts. Yeasts lack chloroplasts and do not perform photosynthesis; they obtain energy through fermentation or aerobic respiration, depending on environmental conditions.
Correct Answer is A
Explanation
Viral genomes consist of either DNA or RNA, but never both at the same time. This is a fundamental principle in virology and is used to classify viruses into DNA viruses and RNA viruses. The genome may be single-stranded or double-stranded and can exist in linear, circular, or segmented forms, depending on the specific virus. Unlike human and other living cells, which contain both DNA (as genetic material) and RNA (for protein synthesis), viruses rely on only one type of nucleic acid for replication. This distinction is important because the type of genome determines the virus’s replication strategy, mutation rate, and response to antiviral therapies.
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