Phycomycetes, Definition, Characteristics, Types and Structure

Phycomycetes, also known as lower fungi or algal fungi, play an essential role in the study of fungi and are fundamental to understanding the diversity and complexity of fungal organisms. In the NEET biology syllabus , studying Phycomycetes provides students with foundational knowledge of fungal types, structures, and reproductive methods.

Definition of Phycomycetes

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Characteristics of Phycomycetes

• Habitat: They are typically found in moist, damp environments, which provide optimal conditions for their growth.
• Thallus Structure: The body of Phycomycetes is usually a mycelium composed of hyphae that lack septa (cross walls), meaning they are coenocytic. This structure allows for efficient nutrient transport and distribution within the fungal body.
• Cell Wall Composition: While most fungi have cell walls composed of chitin, many Phycomycetes have cell walls that contain cellulose, especially in Oomycetes.
• Nutrition: Phycomycetes can be saprophytic, deriving nutrients from decaying matter, or parasitic, feeding on living hosts. Parasitic species often cause diseases in plants and animals.
• Life Cycle : These fungi exhibit both sexual and asexual reproductive cycles, which vary between species, contributing to their ability to adapt to diverse environmental conditions.

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Types of Phycomycetes

• Oomycetes (Water Molds) : Oomycetes thrive in water and moist conditions, and their structure is more plant-like than typical fungi. They are known for causing diseases in plants, such as late blight in potatoes, caused by Phytophthora infestans. Their cell walls are primarily composed of cellulose.
• Zygomycetes : These fungi are primarily terrestrial and thrive on decaying organic matter. Zygomycetes include many molds, such as Rhizopus stolonifer, which is commonly found on bread. They are characterized by the formation of zygospores during sexual reproduction, which are thick-walled spores that provide durability.

Structure of Phycomycetes

• Hyphae: Phycomycetes possess aseptate (non-segmented) hyphae that form a network called mycelium. These hyphae are coenocytic, containing multiple nuclei within a shared cytoplasm.
• Spores : Asexual reproduction in Phycomycetes often involves the formation of spores, such as zoospores (motile) in aquatic fungi or sporangiospores in terrestrial fungi. These spores are usually enclosed within a sporangium, a structure that helps protect the spores until they are ready to be released.
• Cell Wall: As previously mentioned, Phycomycetes may have cell walls made of cellulose rather than chitin, especially in Oomycetes, which further highlights their plant-like properties.

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Reproduction of Phycomycetes

• Sporangiospores: The most common mode of asexual reproduction in Phycomycetes is through sporangiospores, which are produced in a sac-like structure called a sporangium. When the sporangium matures, it releases the spores into the environment, where they germinate and form new mycelia.
• Zoospores: In water molds, zoospores are flagellated, motile spores that enable the fungus to disperse in aquatic environments. These spores can move towards favorable conditions, settle, and develop into new individuals.

• Zygospores in Zygomycetes : During sexual reproduction, compatible hyphae come together to form thick-walled, diploid zygospores, which undergo meiosis and eventually germinate to form new hyphal structures. This process ensures genetic diversity.
• Oospores in Oomycetes: In Oomycetes, sexual reproduction involves the formation of oospores, which are also thick-walled and result from the fusion of male and female gametangia (structures that produce gametes). These oospores serve as a survival mechanism in harsh conditions.

MCQs of Phycomycetes

Q1. In-class Phycomycetes, the mycelium is;

1. coenocytic and aseptate.
2. coenocytic and septate.
3. unicellular and aseptate.
4. multicellular and septate.

Q2. Which of the following fungi does NOT belong to phycomycetes?

1. Rhizopus
2. Mucor
3. Albugo
4. Agaricus

Answers of MCQs of Phycomycetes