Phycomycetes

Biological classification can be defined as the method used to categorize and group living organisms based on their features and functions, also known as taxonomy. The first biological classification is done by Aristotle, who classified living organisms based on morphological characteristics. According to the classification of Aristotle, organisms can be classified as Organisms that have red blood cells and Organisms that don’t have red blood cells. After that, Carolus introduced the system of kingdoms. According to him, there are two kingdoms, Animalia and Plantae. But still, there are some organisms that didn’t get any categorization from this classification. Then R.H. Whittaker classified organisms. R.H. Whittaker classified living organisms into 5 kingdoms based on their cell structure, complexity, reproduction, mode of nutrition, and phylogenetic relationships. The five kingdoms are Monera, Protista, Fungi, Animalia, and Plantae.

Fungi

Fungi are found everywhere across the world. They are heterotrophic organisms and get nutrients from dead substrates by absorption. Most of the fungi are multicellular except yeast. Their cell walls are composed of fungal or chitin cellulose. Their bodies are long and have thread-like structures called hyphae. A bunch of hyphae forms mycelium. They depend on living animals and plants and are called parasites.

Fungi are further classified into 4 classes based on the structure of mycelium and mode and type of spore formation:

1. Phycomycetes
2. Ascomycetes 
3. Basidiomycetes
4. Deuteromycetes

Phycomycetes 

Phycomycetes are known as the lowest class of true fungi. Phycomycetes organisms are located all over the world in soil, animal manure, and on fruits. Frequently, the fungi of this class are found in refrigerators and are commonly called bread molds.

Characteristics

• They are called algal fungi, and they are found in aquatic habitats, damp places, and on decaying wood in moist or as an obligate parasites on plants.
• They can be parasites or saprophytes.
• Mycelium is coenocytic and aseptate
• The wall of the hyphae is made up of cellulose.
• Asexual reproduction takes place by zoospores (motile) or aplanospores(non-motile).
• Sexual reproduction takes place by gametangial contact, in which male gamete is transferred from the antheridium to the oogonium.
• At the end of sexual reproduction, oospores will be produced.
• Common examples are- Rhizopus, Mucor, and Albugo.

Classification of Phycomycetes

Phycomycetes are further classified into 3 subclasses based on the method and result of sexual reproduction, and their somatic structures:

Archimycetes

• The non-mycelial thallus will be round or lob-shaped because of the enlargement of zoospores.
• They sometimes possess rhizoids.
• Their higher forms may be developed into rudimentary mycelium.
• Includes 3 orders:
  • Chytridiales: They are often known as chytrids. They include both soil and aquatic inhabiting species. They are an order of water molds.
  • Ancylistales: They are an unusual member of aquatic Phycomycetes. Sporophores are generally unbranched or rarely branched, having one conidium per branch.
  • Protomycetales: They are spore sac compounds. They are a small group of plant-parasitic Archimycetes.

Oomycetes

• They have well-developed coenocytic mycelium.
• Oogamy is their mode of sexual reproduction.
• Mostly motile zoospores are the accessory spores formed in most of them.
• Includes 5 orders:
  • Blastocladiales: They have a thallus that consists of branched and single basal cells with sporangia at one end and rhizoids at the other. The genus of Blastocladiales are Blastocladia and the family is Blastocladiaceae.
  • Monoblepharidales: They have simple and unbranched filamentous thallus. They can reproduce through autospores and zoospores. Sometimes oogamous sexual reproduction can occur.
  • Leptomitales: They are an order of water molds. They contain the Apodachlya genus.
  • Saprolegniales: They are an order of freshwater mold. 
  • Peronosporales: many diseases of plants are sometimes classified under this order. They are an order of water molds.

Zygomycetes

• They have well-developed mycelium.
• Conjugation of two gametangia is their mode of sexual reproduction.
• Here accessory spores are non-motile aplanospores, and they are known as sporangiospores and formed within the sporangium.
• It Includes 2 orders-
  • Mucorales: They are typically fast-growing. Their hyphae don’t have septa. These are saprotrophic. A few of them cause animal and human diseases also.
  • Entomophthorales: Most species are the pathogens of insects. Production of ballistic asexual spores is observed in most species. When they don’t land on a suitable host, they make one for themselves.

Life cycle 

• Phycomycetes have a simpler life cycle than ascomycetes and basidiomycetes. 
• It has distinct asexual and sexual cycles.
• The somatic body will produce sporangium throughout the asexual cycle, from which spores are produced asexually. Each spore will then produce the somatic body upon germination. The asexual cycle is therefore finished. To facilitate the growth of new individuals, this procedure is repeated.
• During the sexual cycle, the somatic body may participate in sexual reproduction directly, or it may produce gametangia, from which gametes mature and zygotes are created through the gametic union.
• Again, the gametangia may engage in sexual activity directly even though they do not produce well-organized gametes. When the suitable nuclei are brought together by plasmogamy, the zygote is created by karyogamy nearly immediately, establishing diplophase. Meiosis occurs after the diplophase, producing spores or germ tubes from which the somatic body develops.
• The zygote may also have tight walls and only become active after some downtime. Thus, meiosis might be postponed. In Phycomycetes, the haplophase makes up the major portion of the sexual cycle. In contrast, the dikaryophase is very short and may often be absent.

Economic Importance 

• Phycomycetes include numerous varieties of species that attack the leaves and shoots of angiospermous plants and cause plant diseases.
• Some terrestrial species of Phycomycetes are destructive parasites of plants and certain insects.
• Other species of Phycomycetes cause food spoilage, including fruits and vegetables.
• Some species are used in industries for the fermentation purpose of various products.
• Many species of soil-inhabiting cause serious root troubles to economic plants, and others destroy the seedlings.
• Aquatic species of Phycomycetes are susceptible to Hydrogen ion concentration, which is why with the rise of temperature and falling of water level, these species decreased with the decrease in several hydrogen-ion concentrations. 

FAQs on Phycomycetes

Question 1: Define biological classification.

Answer:

Biological classification can be defined as the method used to categorize and grouping of living organisms based on their features and functions.

Question 2: Write the classification of living organisms according to R.H Whittaker.

Answer:

R.H. Whittaker classified living organisms into 5 kingdoms based on their cell structure, complexity, reproduction, mode of nutrition, and phylogenetic relationships.Five kingdoms are:

1. Monera
2. Protista
3. Fungi
4. Animalia
5. Plantae

Question 3: Write a short note on Phycomycetes.

Answer:

They are called algal fungi, and they are found in aquatic habitats, damp places, and on decaying wood in moist or as an obligate parasite on plants. Common examples are- Rhizopus, Mucor, and Albugo.

Question 4: Write subclasses of Phycomycetes.

Answer:

Phycomycetes are classified into 3 subclasses based on the method and result of sexual reproduction, and their somatic structures:

1. Archimycetes
2. Oomycetes
3. Zygomycetes

Question 5: Write 5 orders of oomycetes.

Answer:

1. Blastocladiales
2. Monoblepharidale
3. Leptomitales
4. Saprolegniales
5. Peronosporales