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

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.

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.

Nucleolus

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.

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University of Wisconsin - Madison

Eukaryotes have membrane-bound organelles, each with their own structure and function. Organelles commonly found in eukaryotes include:
- Nucleus
- Endoplasmic Reticulum
- Golgi Apparatus
- Lysosome
- Vacuole
- Mitochondria
- Chloroplast
- Peroxisomes

Organelles Commonly Found in Eukaryotes

https://openstax.org/details/books/microbiology/

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.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Nucleus

The Golgi apparatus is an organelle within the endomembrane system that consists of a series of stacked, flat membranous disks. It receives proteins and lipids from the endoplasmic reticulum and uses enzymes to modify them, frequently by adding carbohydrate components to produce glycoproteins, glycolipids, or proteoglycans.

The Golgi Apparatus

Lysosomes are membrane-bound organelles belonging to the endomembrane system that contain digestive enzymes. They function to break down external particles, such as food, microorganisms, and immune complexes, as well as internal debris like damaged organelles, while keeping these enzymes compartmentalized to protect the cytoplasm.

Lysosomes

Vacuoles are formed off of the plasma membrane in a process called phagocytosis.

Vacuole

The mitochondria is responsible for aerobic respiration in eukaryotes. It contains two lipid membranes which are the inner and outer membranes. The inner membrane is the site for the electron transport chain for aerobic respiration. The mitochondrial matrix is also an important site for metabolic enzymes and the mitochondrial DNA.

Mitochondria

Peroxisomes are membrane-bound eukaryotic organelles that produce hydrogen peroxide to break down molecules such as uric acid, amino acids, and fatty acids. They contain the enzyme catalase to degrade hydrogen peroxide, and they function alongside the smooth endoplasmic reticulum (SER) in lipid biosynthesis, while protecting the cytoplasm from oxidative damage through compartmentalization.

Peroxisome

A multi-membrane organelle where photosynthesis occurs in eukaryotes

Chloroplast

The endoplasmic reticulum (ER) is a network of membranous tubules and flattened sacs called cisternae, all bounded by a single lipid bilayer. The ER is continuous with the nuclear envelope, and it is divided into two structurally and functionally distinct regions—the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER)—which serve as sites for synthesizing different cellular molecules.

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