In certain protozoans, such as those of the genus *Paramecium*, the macronucleus is the larger of two nuclei and is responsible for directing cellular metabolism.

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The nucleus is a membrane-bound organelle that serves as the defining feature of eukaryotic cells. It houses the DNA genome within a complex nuclear membrane, controls all cellular activities, and plays an essential role in reproduction and heredity.

Nucleus

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

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In $${}1831$$, Scottish botanist Robert Brown ($${}1773$$–$${}1858$$) became the first to describe observations of nuclei, which he identified within plant cells. His findings contributed to the growing understanding of the internal structures of cells.

Robert Brown

In certain protozoans, such as those of the genus *Paramecium*, the micronucleus is the smaller of two nuclei and is specifically responsible for reproduction.

Micronucleus

Macronucleus

A heterokaryotic cell is a eukaryotic cell containing two distinct nuclei, which is formed transiently by some fungi during sexual reproduction.

Heterokaryotic Cell

A coenocyte is a cell that contains multiple nuclei because its nuclei divide during cell division but its cytoplasm does not.

Coenocyte

The cell nucleus is anchored in position within the cell by a loose mesh of intermediate filaments located outside of the nucleus.

Anchoring of the Nucleus

The nuclear membrane, or nuclear envelope, is a double membrane consisting of two contiguous lipid bilayers. Despite their physical connections, each membrane maintains unique lipids and proteins on its respective inner and outer surfaces.

Nuclear Membrane

The nucleolus is a dense region within the cell nucleus where ribosomal RNA (rRNA) biosynthesis occurs and the assembly of ribosomes is initiated.

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