Structure and Reproduction of Fungi | Botany Optional for UPSC PDF Download

What is Fungi?

Fungi constitute a group of eukaryotic organisms encompassing microorganisms like yeasts, molds, and mushrooms. They are categorized within the kingdom Fungi.
Organisms within the Fungi kingdom possess cell walls and have a widespread presence. They are classified as heterotrophs among living organisms, meaning they obtain nutrients by consuming other substances.

Examples of fungi include the formation of black spots on bread left outdoors for a period, the growth of mushrooms, and the yeast cells commonly used in the production of beer and bread. Fungi are also frequently associated with skin infections and various fungal diseases.
It's notable that many of these examples thrive in environments with sufficient moisture. Therefore, we can conclude that fungi typically flourish in conditions that are both moist and warm enough to support their growth.

Structure of Fungi

The structure of fungi can be described as follows:

• Filamentous Structure: The majority of fungi exhibit a filamentous structure, except for yeast cells.
• Single-Celled or Multicellular: Fungi can exist as single-celled or multicellular organisms.
• Hyphae: Fungi are composed of long, thread-like structures called hyphae. These hyphae collectively form a network-like structure known as the mycelium.
• Cell Wall: Fungi possess a cell wall made primarily of chitin and polysaccharides. This cell wall provides structural support and protection.
• Protoplast: Within the cell wall, there is a protoplast that contains various cell components, including the cell membrane, cytoplasm, cell organelles, and nuclei.
• Nucleus: The nucleus in fungi is characterized by its density and clarity, with visible chromatin threads. It is enveloped by a nuclear membrane.

Characteristics of Fungi

The key characteristics of fungi are as follows:

• Eukaryotic: Fungi are eukaryotic organisms, meaning they have cells with a defined nucleus and membrane-bound organelles.
• Non-Vascular and Non-Motile: Fungi lack vascular tissues for transporting water and nutrients, and they are non-motile, meaning they do not have the ability to move on their own.
• Heterotrophic: Fungi are heterotrophic, relying on external sources for nutrients as they cannot perform photosynthesis.
• Unicellular or Filamentous: Fungi can exist as single-celled or filamentous structures.
• Spore Reproduction: Fungi reproduce through the formation and dispersal of spores.
• Alternation of Generation: Some fungi exhibit an alternation of generation in their life cycles, involving both haploid and diploid stages.
• Lack of Chlorophyll: Fungi do not contain chlorophyll and are incapable of photosynthesis.
• Starch Storage: They store their food reserves in the form of starch.
• Chitin Biosynthesis: Fungi produce chitin, a structural component of their cell walls.
• Small Nuclei: The nuclei of fungi are typically small in size.
• Lack of Embryonic Stage: Fungi do not have an embryonic developmental stage and instead develop from spores.
• Reproduction: They reproduce through both sexual and asexual means.
• Parasitism: Some fungi can be parasitic and infect other host organisms.
• Pheromone Production: Fungi produce pheromones, which play a role in their sexual reproduction.
• Examples: Common examples of fungi include mushrooms, molds, and yeast.

Classification of Fungi

Fungi are classified into different groups based on various characteristics:

Based on Mode of Nutrition

• Saprophytic Fungi: These fungi obtain their nutrition by decomposing dead organic matter. Examples include Rhizopus, Penicillium, and Aspergillus.
• Parasitic Fungi: Parasitic fungi derive their nutrition by living on other living organisms, such as plants or animals, and absorbing nutrients from their host. Examples include Taphrina and Puccinia.
• Symbiotic Fungi: These fungi establish mutually beneficial relationships with other species. Examples are lichens and mycorrhiza. Lichens involve an association between fungi and algae, where both benefit. Mycorrhiza is the symbiotic relationship between fungi and plants, where fungi aid in nutrient uptake by plants, and plants provide organic molecules like sugar to the fungus.

Based on Spore Formation

Kingdom Fungi are classified into different groups based on the formation of spores:

• Zygomycetes: These fungi form spores through the fusion of two different cells. Sexual spores are called zygospores, and asexual spores are known as sporangiospores. They lack septa in their hyphae. An example is Mucor.
• Ascomycetes: Also known as sac fungi, they can be found in various ecological roles, including coprophilous, decomposers, parasites, or saprophytes. Sexual spores in ascomycetes are called ascospores, and asexual reproduction occurs through conidiospores. Saccharomyces is an example.
• Basidiomycetes: This group includes mushrooms and often includes parasites. Sexual reproduction in basidiomycetes involves basidiospores, while asexual reproduction can occur through conidia, budding, or fragmentation. Agaricus is an example.
• Deuteromycetes: Also known as imperfect fungi, deuteromycetes do not follow the regular fungal reproduction cycle, including sexual reproduction. Asexual reproduction typically occurs through conidia. Trichoderma is an example.

These classifications are based on key characteristics, such as nutrition and spore formation, and help in categorizing and understanding the diversity of fungi in the kingdom Fungi.

Reproduction in Fungi

Reproduction in fungi encompasses both sexual and asexual methods. The sexual form of reproduction is referred to as "teleomorph," while the asexual form is referred to as "anamorph."

• Vegetative Reproduction in Fungi: Vegetative reproduction occurs through various processes, including budding, fission, and fragmentation.
• Asexual Reproduction: Asexual reproduction in fungi involves the formation and dispersal of spores known as conidia, zoospores, or sporangiospores.
• Sexual Reproduction: Sexual reproduction in fungi occurs through the production of specialized spores, including ascospores, basidiospores, and oospores.

It's important to note that the conventional mode of sexual reproduction is not universally observed in all fungi within the kingdom Fungi. In some cases, the fusion of two haploid hyphae does not immediately result in the formation of a diploid cell. Instead, an intermediate stage known as the "dikaryophase" is observed, followed by the eventual formation of diploid cells. This variation highlights the diversity in fungal reproductive strategies.

Uses of Fungi

Fungi have diverse and significant roles in the environment and economy, with various uses, both beneficial and harmful:

• Recycling: Fungi play a crucial role in breaking down and recycling dead and decaying organic matter, contributing to nutrient cycling in ecosystems.
• Food: Certain mushroom species that are cultivated are edible and serve as a source of nutrition for humans.
• Medicines: Many fungi are used in the production of antibiotics and are essential in controlling diseases in humans and animals. The famous antibiotic penicillin is derived from the fungus Penicillium.
• Biocontrol Agents: Fungi are employed as biocontrol agents to combat pests and insects. Fungal spores are used in the form of sprays to manage pest populations in agriculture.
• Food Spoilage: While fungi contribute to organic material decomposition, they are also responsible for food spoilage, leading to economic losses in stored food products.

These varied roles of fungi highlight their importance in nature and agriculture, as well as their influence on human health and the environment.

Examples of Fungi

Following are the common examples of fungi:

• Yeast
• Mushrooms
• Moulds
• Truffles