Lesson Video: Kingdom Fungi Biology • First Year of Secondary School

Video Transcript

In this video, we will learn how to describe the common characteristics of organisms belonging to kingdom Fungi. We will learn about their cell structure, how they obtain nutrition, and how they reproduce. Then, we’ll learn about selected phyla of Fungi and how to classify these organisms.

In 1969, a scientist named Robert Whittaker classified all of life into five kingdoms. These kingdoms are Plantae, or plants; Animalia, or animals; Protista, which are otherwise known as protists; Fungi; and Monera. The members of kingdom Monera are prokaryotic organisms, while the members of all the other four kingdoms are eukaryotic organisms. You might remember that one of the main differences between the cells of eukaryotic and prokaryotic organisms is that eukaryotic cells possess a nucleus, which contains and protects their genetic material, or chromosomes. Fungi is one of the five kingdoms in Whittaker’s system. The Fungi kingdom is extremely diverse and is estimated to possess between two to four million total different species.

A kingdom is a general classification, so it contains many different species. But all of these species will have some characteristics in common. All fungi are eukaryotic organisms. Fungi can be unicellular or multicellular. Species of fungi may reproduce sexually or asexually. Like plants, fungi are generally considered to be sessile, or immobile, organisms. They generally don’t move around from place to place on their own. Also like plants, the cells of fungi possess a rigid cell wall. But unlike plants, fungi cannot make their own food from inorganic substances. All species of fungi are heterotrophic organisms as they absorb all the nutrients they need from their surroundings.

Plants and other autotrophs are what we consider producers. They use light energy, usually from the Sun, to convert inorganic material into organic material, like sugar. Animals, like humans, are heterotrophs, and they’re considered to be consumers. They consume plants and other organisms to get the nutrients they need. When these organisms die, they are broken down by heterotrophs called decomposers. Bacteria and fungi are examples of decomposers. They are heterotrophs like animals, as they gain their nutrition from another organism. But they get these nutrients by breaking down or decomposing dead and decaying organic materials.

Organisms that absorb nutrition from decayed organic matter are also called saprophytic organisms. In this process, the decomposers make many necessary materials available to the producers again. This process is sometimes called the nutrient cycle. Decomposers like fungi play an essential role in our planet’s ecosystems. When we think of fungi, we commonly think of the mushrooms that humans sometimes eat. However, fungi spend most of their lifetime growing below the surface as threadlike filaments called hyphae. A single one of these filaments is called a hypha. The hyphae secrete digestive enzymes, which break down the materials around them. They are then able to absorb the broken-down organic compounds as nutrients.

Hyphae form huge networks. Just one cubic centimeter of soil could contain up to a kilometer of hyphae. In fact, almost all of what we consider to be soil is actually the remains of organisms after they’ve been broken down by decomposers like fungi. Hyphae are threadlike structures made of fungal cells. The cells in hyphae have a similar structure to that of plant cells. Both plants and fungi are eukaryotic, so their cells possess a nucleus that stores DNA. They also both have an inner cell membrane that is supported and surrounded by an outer cell wall. The cell walls of most plant cells possess a rigid material called cellulose, while the cell walls of fungal cells are strengthened by a material called chitin. Chitin is also found in the exoskeletons of bugs and other arthropods.

The hyphae of some species of fungus possess complete divisions between each cell. These dividing walls are called septa, or a singular septum. Some species of fungus possess incomplete septa, and some have no divisions at all. Unlike the cells of plants, which are autotrophs and carry out photosynthesis, you will not find any chloroplasts within the cells of fungi.

Because of similarities between their cell structures and because they both appeared to grow from the ground, fungi were initially classified with plants. The classification of organisms based only on observable characteristics is called artificial classification. Later, the fact that fungi are heterotrophs and their cell walls possessed chitin led scientists to place them into their own kingdom. Later genetic analysis has shown that fungi are even more closely related to animals than they are to plants. The use of genetic and evolutionary relationships to classify organisms is called natural classification.

Most species of fungi are able to reproduce either sexually or asexually. They are able to reproduce asexually by fragmentation, which is when a part of an organism breaks off and grows into another individual. Single-celled fungi like yeast can also reproduce asexually by budding.

Many fungi can also reproduce by making and releasing spores. Spores can be made asexually by just one parent organism. Sometimes the hyphae of two individuals from the same species merge and share genetic material. This method of producing spores is a form of sexual reproduction, as two parents are involved. When a fungus is ready to reproduce by producing spores, the hyphae underground grow upward into what’s commonly called a fruiting body. The mushrooms and molds that we tend to picture when we think of fungi are actually just their reproductive parts. This is similar to how flowers are the reproductive parts of many plants.

The fruiting bodies of different species of fungi have different appearances and produce spores in different ways. The spores disperse, carried by wind, water, or animals. And when they land on a suitable surface, they grow into a new network of hyphae. And the life cycle begins again.

The Fungi kingdom is a large general taxonomic group. The many different species in the Fungi kingdom can be classified into several different phyla. Let’s take a look at three of these phyla and their characteristics. The phylum Basidiomycota contains many of the species that we think of as mushrooms. Most of the species within this phylum reproduce sexually. The fruiting bodies of Basidiomycota grow special structures called basidia, which in the singular form is called a basidium. These basidia produce spores, and they are how the phylum gets its name.

Fungi in the phylum Zygomycota include many of the species that we commonly call mold that grow on bread and fruit, for instance, on this orange. The hyphae of Zygomycota are completely undivided, except for during reproduction or when blocking off dead or damaged sections. Many of the species within the Zygomycota phylum are used in important industrial processes and even some food production. The fruiting bodies of species within Zygomycota are called sporangia, or a singular sporangium. The sporangia are tiny structures filled with spores.

Fungi and the phylum Ascomycota are commonly called sac fungi. The species within Ascomycota that make spores produce them in sacks called asci, or a singular ascus. These asci are where Ascomycota get their name. Members of this phylum include bakers’ and brewers’ yeast, some edible fungi like morels and truffles, and even the fungi from which the antibiotic penicillin is derived, more commonly known as penicillium. Ascomycota is the largest phylum in the Fungi kingdom, and it contains both unicellular and multicellular species. Some unicellular species of Ascomycota are pathogens, which can cause infections in animals like humans or in plants.

Now that we’ve learned the characteristics of the organisms within the Fungus kingdom as well as some of the phyla within it, let’s try a practice question.

Which of the following best describes members of kingdom Fungi? (A) They are heterotrophic organisms which are only parasitic and have no cell walls. (B) They are free-living heterotrophic organisms which have no cell walls and reproduce by binary fission. (C) They are mobile heterotrophic organisms which may be parasitic or saprophytic and have cell walls. Or (D) they are heterotrophic organisms which may be parasitic or saprophytic and have cell walls.

This question is asking us to recall what we know about the members of the Fungus kingdom and then to choose the answer that best describes their characteristics. So we’ll start with what we already know about fungi. Often when we picture members of the Fungus kingdom, we might imagine mushrooms sprouting from a dead fallen tree. By thinking of mushrooms as an example of a member of the Fungus kingdom, we’re able to recall some key characteristics. This mushroom is multicellular. It reproduces by making spores. It gets its nutrition from dead or decaying material by decomposing it. And it doesn’t move around on its own, so it can be described as immobile.

Now, we can add to this information with some other things that we know about fungi. We know that some fungi are unicellular, as we know that yeast are also a member of the Fungus kingdom. We also know that fungi can reproduce sexually or asexually, since spores can either develop into a new organism on their own or be used in sexual reproduction with a spore from another fungus. We know that fungi are heterotrophic organisms because they absorb their nutrients from living or once-living organisms in their surroundings. And we know that, like immobile plants, fungal cells are surrounded and supported by a cell wall, even though the cell wall of fungi is different from the cell wall of plants.

So now we’re ready to choose the best answer. Two of our answer choices state that the members of kingdom Fungi have no cell walls, so we know that these two options are incorrect. Another answer choice states that fungi are mobile, which we know is also incorrect. Fungi are immobile, which means they cannot move around on their own. So we’ve been able to eliminate three of the four options. But let’s check the fourth one to make sure that it’s correct.

The remaining answer choice states that fungi are heterotrophic organisms, which we’ve already stated is true. It goes on to state that fungi maybe parasitic or saprophytic. A parasite is an organism that lives in or on a host and causes that host harm. And a saprophytic organism is one that breaks down decaying matter and absorbs nutrients from it. Well, we know that fungi are heterotrophic decomposers. And the fact they may be parasites is not surprising. Finally, this answer choice states that fungi have cell walls, which is a fact that we’ve already confirmed.

So, the answer choice that best describes the members of kingdom Fungi is that they are heterotrophic organisms which may be parasitic or saprophytic and have cell walls.

Let’s wrap up our lesson by taking a moment to review what we’ve learned. In this video, we learned about the characteristics of organisms within the kingdom Fungi. For example, we learned that fungi can be unicellular or multicellular. They reproduce either sexually or asexually. They are heterotrophs. They have chitin in their cell walls. They are also eukaryotic organisms. We learned that fungi are immobile or sessile, which means they cannot easily move around on their own. We also examined some examples of fungi. We then looked at the characteristics of three phyla from the Fungi kingdom: Zygomycota, Ascomycota, and Basidiomycota.