Fungi are eukaryotic organisms, which means their cells contain a nucleus and other membrane-bound compartments. A fungal cell is therefore more structurally complex than a bacterial cell, but it also has features that distinguish it from plant and animal cells.
The most important structural difference is the cell wall. Fungal cell walls are built primarily from chitin and glucans, rather than the cellulose found in plant cell walls. Inside the wall, a plasma membrane encloses the cytoplasm, nucleus, organelles, and cytoskeleton that carry out the cell’s essential functions.
Although fungi include very different organisms—from single-celled yeasts to filamentous molds and large mushrooms—their cells share a basic structural plan.
The main layers of a fungal cell
A fungal cell can be understood from the outside inward: the cell wall, plasma membrane, and cytoplasm containing organelles and the nucleus.
The cell wall provides mechanical strength and helps the cell maintain its shape. Just inside it is the plasma membrane, a selectively permeable barrier that controls what enters and leaves the cell. The interior contains the cytoplasm, where the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, vacuoles, ribosomes, and other structures perform specialized tasks.
The exact appearance varies with fungal species and cell type. A budding yeast cell, for example, looks very different from a cell within a long fungal hypha, but the underlying cellular machinery is broadly similar.
The fungal cell wall
The cell wall is one of the defining features of fungal cells. It surrounds the plasma membrane and protects the cell from physical stress while helping it retain its shape.
Its structural framework contains chitin, a tough carbohydrate polymer, along with glucans, which are chains of glucose molecules. Other wall components, including various proteins and sugars, contribute to the wall’s organization and properties.
Chitin is also found in the exoskeletons of arthropods, but that does not mean fungal walls and insect exoskeletons are structurally identical. In fungi, chitin is integrated into a larger network of wall materials.
The wall is not simply a rigid shell. It is a dynamic structure that must be remodeled as the cell grows. A growing fungal tip, for instance, has to extend its wall while maintaining enough strength to prevent the cell from rupturing.
This remodeling is especially important in hyphae, the microscopic filaments that make up the bodies of many fungi. Hyphal growth occurs predominantly at the tip, where new cell-wall material is deposited and incorporated into the existing wall.
Why the cell wall matters
The fungal cell wall has several important roles:
- It gives the cell mechanical support and helps determine its shape.
- It protects the plasma membrane and cellular contents.
- It helps the cell withstand changes in its surrounding environment.
- It provides a framework that can be remodeled during growth and development.
The wall is also biologically important because its components differ from those of human cells. This difference is one reason fungal cell-wall components and the enzymes involved in making them are important targets in antifungal research and medicine.
The plasma membrane
Immediately inside the cell wall is the plasma membrane, a thin, flexible membrane made primarily of lipids and proteins.
The membrane separates the cell’s interior from its surroundings and regulates the movement of substances across it. Nutrients must enter, metabolic waste must leave, and ions must be carefully distributed between the cytoplasm and the external environment.
Fungal membranes contain ergosterol, a sterol that performs important structural and regulatory functions in the membrane. Ergosterol is broadly analogous in function to cholesterol in animal cell membranes, although the molecules are chemically different.
Because ergosterol is characteristic of fungal membranes and is absent from human cell membranes, it is an important target for several classes of antifungal drugs.
The plasma membrane also contains proteins that act as transporters, receptors, enzymes, and channels. Together, these components allow the fungal cell to sense its environment, acquire nutrients, communicate internally, and maintain stable conditions inside the cell.
The nucleus stores and regulates genetic information
Like other eukaryotic cells, fungal cells have a nucleus enclosed by a nuclear envelope. The nucleus contains the organism’s chromosomes, which are made of DNA associated with proteins.
The nuclear envelope separates the genetic material from the surrounding cytoplasm while allowing controlled exchange through nuclear pores. Genes in the DNA provide instructions for producing RNA and proteins that support the cell’s structure, metabolism, growth, and reproduction.
Many fungi have more than one nucleus in a cell or within a continuous section of a filament. This is particularly relevant in filamentous fungi, whose hyphae may contain multiple nuclei. Some fungal cells can therefore have a cellular organization quite different from the single-nucleus model often used in introductory diagrams.
Mitochondria supply usable energy
Mitochondria are membrane-bound organelles that carry out most of the cell’s aerobic energy production.
They break down molecules derived from nutrients and use the released energy to produce ATP (adenosine triphosphate), a molecule that cells use to power many processes. These include biosynthesis, transport across membranes, movement of cellular components, and growth.
Fungal mitochondria have their own small genomes, inherited from ancient bacterial ancestors through a process known as endosymbiosis. Their internal membranes provide surfaces for the reactions involved in cellular respiration.
The endoplasmic reticulum builds proteins and lipids
The endoplasmic reticulum (ER) is an interconnected membrane system within the cytoplasm.
The rough endoplasmic reticulum is covered with ribosomes and is involved in producing proteins destined for secretion, insertion into membranes, or delivery to certain cellular compartments.
The smooth endoplasmic reticulum lacks ribosomes and participates in lipid production and other metabolic processes.
For fungi, the ER is particularly important because many proteins that ultimately become part of the cell wall or are secreted outside the cell must first pass through the secretory pathway.
The Golgi apparatus modifies and sorts cellular products
The Golgi apparatus consists of flattened membrane-bound compartments that process, modify, and sort molecules produced in the secretory pathway.
Proteins and other molecules can be chemically modified as they move through the Golgi and then directed to their appropriate destinations. Some are transported to the plasma membrane or outside the cell, while others are delivered to internal compartments.
This system allows a fungal cell to coordinate the production and distribution of materials needed for growth, membrane maintenance, and cell-wall construction.
Vacuoles store materials and help regulate the cell
Fungal cells commonly contain vacuoles, membrane-bound compartments that perform several functions rather than serving merely as storage containers.
Vacuoles can store ions, metabolites, and other substances and participate in the breakdown and recycling of cellular material. They also contribute to regulation of internal ion concentrations and osmotic balance, which is the control of water movement associated with differences in solute concentration.
Fungal vacuoles share some functional similarities with lysosomes in animal cells, although the organization of these compartments differs among organisms.
Ribosomes make proteins
Ribosomes are molecular machines that translate genetic information carried by messenger RNA into proteins.
They are found both free in the cytoplasm and attached to the rough endoplasmic reticulum. Free ribosomes generally produce proteins that function within the cytoplasm or certain internal compartments, while ribosomes associated with the ER produce proteins entering the secretory pathway.
Ribosomes themselves are not enclosed by membranes, so they are not technically organelles in the same sense as mitochondria or the nucleus.
The cytoskeleton organizes the fungal cell
The cytoskeleton is a network of protein filaments that provides structural organization and helps move materials within the cell.
Two particularly important components are actin filaments and microtubules. Actin contributes to cell shape, membrane organization, and transport. Microtubules help organize chromosomes during nuclear division and provide tracks along which certain cellular cargoes can move.
In filamentous fungi, cytoskeletal systems are essential for directing materials toward the growing hyphal tip. This allows the cell to extend in a highly organized way rather than expanding uniformly.
Hyphae give many fungi their filamentous form
Many fungi grow as networks of microscopic filaments called hyphae. A mass of interconnected hyphae is called a mycelium.
A hypha is essentially a long, tubular cellular structure. Depending on the fungal group, hyphae may be divided by cross-walls called septa or may contain a continuous cytoplasmic compartment with multiple nuclei.
Septa can contain openings that allow cytoplasm and certain cellular components to move between neighboring sections. In some fungi, therefore, the boundary between one cellular compartment and another is more flexible than the boundaries between typical animal cells.
Hyphal growth depends on coordinated delivery of membrane, cell-wall components, proteins, and other materials to the growing tip. Vesicles carrying these materials move through the cell and contribute to construction at the apex.
This organization allows fungi to grow through soil, wood, food, and other substrates while maintaining an extensive surface area for acquiring nutrients.
Yeast cells show a different fungal growth strategy
Not all fungi grow as hyphae. Yeasts are fungi that commonly exist as individual cells.
A familiar example is Saccharomyces cerevisiae, the yeast used in breadmaking and fermentation. It generally reproduces by budding: a new daughter cell develops as an outgrowth of the parent cell and eventually separates.
The same fundamental structures found in other fungal cells—cell wall, plasma membrane, nucleus, mitochondria, ER, Golgi apparatus, vacuoles, ribosomes, and cytoskeleton—support this different growth pattern.
Some fungi can switch between yeast-like and filamentous forms depending on environmental conditions. This ability, called dimorphism when it involves two distinct growth forms, can be an important part of fungal biology.
How fungal cells differ from plant and animal cells
Fungal cells share their basic eukaryotic organization with plants and animals, but several characteristics distinguish them.
| Feature | Fungal cells | Plant cells | Animal cells |
|---|---|---|---|
| Nucleus | Present | Present | Present |
| Cell wall | Usually present; rich in chitin and glucans | Present; primarily cellulose-based | Absent |
| Plasma membrane | Present; contains ergosterol | Present; contains characteristic plant sterols | Present; contains cholesterol |
| Chloroplasts | Absent | Present in photosynthetic cells | Absent |
| Mitochondria | Present | Present | Present |
| Vacuoles | Common | Common, often prominent | Present in some forms but generally less prominent |
| Typical nutritional strategy | Absorbs nutrients after external digestion | Produces organic compounds through photosynthesis or obtains them from the environment | Ingests or absorbs nutrients |
The absence of chloroplasts means fungi do not obtain energy by photosynthesis. Instead, they generally secrete enzymes into their surroundings, break complex materials into smaller molecules, and absorb the resulting nutrients.
Why fungal cell structure is biologically important
Fungal cells are built to support a distinctive way of life. Their cell walls provide strength, their membranes regulate exchange with the environment, and their secretory systems allow them to release enzymes and other substances outside the cell.
The combination of these features is especially effective for absorptive nutrition. Rather than taking food into an internal digestive system, fungi can digest materials externally and absorb the resulting molecules across their cell surfaces.
In filamentous fungi, the elongated shape of hyphae further extends the organism’s contact with its environment. Growth at the hyphal tip allows fungi to explore new territory while continuously producing and transporting the cellular materials needed to maintain the expanding structure.
Understanding these structures also explains why fungal cells are important in medicine, agriculture, ecology, and biotechnology. The differences between fungal and human cells provide opportunities for selectively targeting fungi, while the specialized growth and secretion systems of fungi make them valuable producers of enzymes, organic compounds, and other biological products.
