Lesson Explainer: Kingdom Fungi Biology

In this explainer, we will learn how to recall the characteristics of organisms belonging to the kingdom Fungi.

There is a huge variety of life on Earth. When studying living organisms, scientists classify them into distinct groups based on their appearance, characteristics, and evolutionary history. Examples of these groups are kingdoms, as shown in Figure 1; kingdom Fungi is an example of these kingdoms.

Organisms belonging to kingdom Fungi all share some characteristics. All fungi are heterotrophic, which means they are unable to synthesize their own food (like plants), so they must consume organic matter as food. Many species of fungi are decomposers, which means they break down dead and decaying material and use that as a source of nutrition. This form of nutrition is known as “saprophytic.” This process is incredibly important for nutrient cycles in ecosystems—think about all the dead organisms that would be left lying around if fungi were not there to break them down!

Definition: Heterotroph

A heterotroph is an organism that obtains food from consuming other organisms or organic matter.

Definition: Saprophyte

A saprophyte is an organism that obtains nutrition from dead or decaying matter.

Example 1: Recalling the Method of Nutrition for Fungi

Organisms belonging to kingdom Fungi are heterotrophic. How do the majority of organisms in the kingdom Fungi obtain their nutrition?

  1. They absorb nutrients from organic matter in their environment, such as dead tissues.
  2. They produce it themselves through the process of photosynthesis.
  3. They act as parasites and enter the bloodstream of animals to obtain nutrients.
  4. They ingest and digest other organisms, obtaining nutrients from the breakdown of their tissues.

Answer

Heterotrophic organisms are those that cannot produce their own nutrition (unlike plants) and so must obtain it from other organisms or organic matter. Although some species of fungi are parasitic, they do not usually infect animals to obtain nutrients from the blood. Fungi are small, immobile organisms, so they cannot prey upon other organisms to consume them, and they do not have a specialized digestive system to digest them. However, many species of fungi act as decomposers in an ecosystem, helping to break down dead or decaying organic matter and absorbing any useful nutrients. Most fungi are known as saprophytes, which identifies them as organisms that rely on dead or decaying matter for the majority of their nutrition.

Therefore, the correct answer is that they absorb nutrients from organic matter in their environment, such as dead tissues.

Fungi share some characteristics with those organisms belonging to the plant kingdom. Organisms belonging to both kingdoms are immobile, so unlike animals, they cannot freely move themselves around. The cells of both fungal and plant species are surrounded by a cell wall; however, in fungi the main component of the cell wall is chitin, whereas in plants it is cellulose.

Organisms belonging to this kingdom are eukaryotic. This means that their cells, whether the organism is unicellular or multicellular, contain a membrane-bound nucleus and other membrane-bound organelles. The nucleus is very important, as this is where the genetic material is stored.

Definition: Eukaryotic Cell

A eukaryotic cell is a cell that contains a membrane-bound nucleus and other membrane-bound organelles.

Example 2: Recalling the Characteristics Shared by All Fungi

The Venn diagram provided shows some key characteristics of the phyla of kingdom Fungi. What other characteristic is shared by all members of the fungi kingdom?

  1. Being immobile
  2. Being mobile
  3. Being parasitic
  4. Cytoplasm containing chloroplasts
  5. Cell membrane containing peptidoglycan

Answer

Kingdom Fungi is a taxonomic group that includes a wide variety of fungal species. All individuals belonging to this kingdom share some characteristics; they are all eukaryotic organisms, so their cells will contain a membrane-bound nucleus. Their cells will be surrounded by a cell wall, and the major component of this wall will be the polymer chitin. They are heterotrophic, which means they must consume organic matter to obtain their nutrition. Unlike other heterotrophic organisms (namely, animals), fungi are immobile and are not able to move around to find organisms to consume. Many fungi act as decomposers, so they break down dead or decaying matter to obtain their nutrition. As we can see from the Venn diagram, the only missing characteristic that is not outlined is that fungi are not able to move.

Therefore, the other characteristic shared by all members of the fungi kingdom is being immobile.

Figure 2 provides a simple outline of a typical fungus. The structures highlighted are the network of hyphae within the body of the fungus and the mycelium that spreads through the soil.

Hyphae are tiny filaments that form a network in the body of the fungus. The cell walls of the hyphae are strengthened by chitin, a flexible but strong polysaccharide. These filaments can be undivided or divided into cells by internal walls called septa.

Key Term: Hyphae

Hyphae are the long, branching filaments of a fungus.

In the soil or surrounding food, wood, or other substrates, the hyphae form mycelium. This is a network of branching hyphae that spread through the soil to absorb nutrients for the fungus. The mycelium has a very large surface-area-to-volume ratio, which makes it ideal for this function, and can spread rapidly through the surrounding substrate.

Key Term: Mycelium

Mycelium consists of a mass of branching hyphae, which allow the fungus to absorb nutrients from its environment.

Another defining characteristic of organisms belonging to kingdom Fungi is their reproductive methods. The large majority of fungal species can reproduce sexually and asexually by producing small, haploid cells called spores.

Definition: Spores

Spores are special reproductive cells that contain half the genetic material of the cells of the parent organism. Spores can be used in asexual and sexual reproduction.

These spores can be produced by asexual reproduction, which will create new organisms identical to the parent organism, or by sexual reproduction, which will create genetically different organisms by combining genetic material from two parent organisms. A basic outline of both of these methods in a typical life cycle of a fungus is summarized in Figure 3.

Definition: Haploid

A haploid cell is a cell that only has a single set of chromosomes (n).

Definition: Diploid

A diploid cell contains two sets of chromosomes (2n).

Kingdom Fungi is a large taxonomic group, containing many species. To help understand these species, biologists have further divided this group into smaller groups, known as phyla. Let's take a look at these phyla and their defining features, given in Table 1 below.

Fungi are classified into phyla based on their differing reproductive structures: the sporangia, asci (singular: ascus), and basidia. Figure 4 outlines the difference between the three and where they are found on a typical fungus.

Example 3: Classifying Organisms into Fungal Phyla

A list of phyla belonging to the kingdom Fungi is provided:

  1. Zygomycota
  2. Ascomycota
  3. Basidiomycota

An organism is found that has divided hyphae and that produces spores by sexual reproduction on a club-shaped structure. Which phylum of Fungi is it most likely to belong to?

Answer

To answer this question, we need to recall the defining characteristics of each of the fungal phyla listed. Organisms belonging to phylum Zygomycota are characterized by having undivided hyphae, and they produce spores via sexual or asexual reproduction inside structures called sporangia. Phylum Ascomycota contains organisms that have divided hyphae and produce spores by asexual or sexual reproduction in sac-like structures called asci. Organisms belonging to phylum Basidiomycota also have divided hyphae, but they produce spores mainly via sexual reproduction on club-like structures called basidium.

Based on the information provided, we can eliminate the possibility of the organism belonging to the Zygomycota phylum, as it has divided hyphae. The key piece of information is the shape of the structure that produces spores, which is described as being “club shaped.” This is referencing the shape of the basidium, which is used by organisms belonging to the Basidiomycota phylum to produce spores.

Therefore, the organism being described is most likely to belong to the Basidiomycota phylum.

Fungi can be incredibly useful for humans. Rhizopus nigricans (bread mold) naturally produces an enzyme that can be extracted to be used in the production of cheese. Penicillium is a naturally occurring fungus that produces the antibiotic penicillin, which is used to treat a range of bacterial diseases. Common mushrooms provide a nutritional food source for humans and other organisms. Saccharomyces cerevisiae, more commonly known as baker’s yeast, is a fungus that is regularly used in bread-making as the carbon dioxide it releases when it ferments allows the bread to rise!

However, some species of fungi can be parasitic. Cryphonectria parasitica is a species of fungi that causes chestnut blight, a disease that kills large amounts of chestnut trees. Histoplasma capsulatum is a species of fungi that can cause pulmonary infections within humans. Other species of fungi are responsible for infecting and damaging crops and spoiling stored food.

Let’s summarize the key points we have learned about kingdom Fungi.

Key Points

  • Organisms belonging to kingdom Fungi are eukaryotic, heterotrophic, and immobile.
  • Fungi can be unicellular or multicellular.
  • Fungi are largely saprophytic, but some can be parasitic.
  • Fungi contain a network of specialized filaments called hyphae, and these hyphae extend through the surrounding medium to form mycelium.
  • Kingdom Fungi can be further divided into the phyla Zygomycota, Ascomycota, and Basidiomycota, based on the organisms’ reproductive structures.
  • Organisms within the same phyla share similar characteristics and methods of producing spores.

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