Video Transcript
In this video, we will learn 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 plant, animal, protist, fungi, and monera. The members of kingdom monera are prokaryotic organisms, while the members of all of the other four kingdoms are eukaryotic organisms. This means that the cells of these organisms possess a nucleus that contains and protects the 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 and 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 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 nutrients from inorganic substances. All species of fungi are heterotrophic organisms. Fungi absorb nutrients from their surroundings.
Plants and other autotrophs are what we consider producers. They use energy from the Sun to convert inorganic materials into nutrients. Animals like humans are considered to be consumers. They consume plants and other organisms to get the nutrients that they need. When these organisms die, they’re broken down by heterotrophs called decomposers. Bacteria and fungi are examples of decomposers. They are heterotrophs, like animals, but they get their nutrients by breaking down 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. 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 structure similar 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 plant cells possess a rigid material called cellulose, while the cell walls of fungi 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. Some species of fungus possess incomplete septa, and some have no divisions at all. And unlike plant cells, which are heterotrophs 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 appear 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 that their cell walls possess 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 from 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, since two parents are involved.
When a fungus is ready to reproduce by releasing spores, the hyphae underground grow upward into what’s commonly called a fruiting body. The mushrooms and molds that we 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 basidium, which produce their spores. These basidium are where the phylum gets its name.
Fungi in phylum Zygomycota include many of the species we commonly call mold that grow on bread and fruit. The hyphae of Zygomycota are completely undivided except for during reproduction or when blocking off dead or damaged sections. Many 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. The sporangia are tiny structures filled with spores.
Fungi in the phylum Ascomycota are also commonly called sac fungi. The species within Ascomycota that make spores produce them in sacks called asci. These asci are where Ascomycota get their name. Members of this phylum include baker’s and brewer’s yeast, some edible fungi like morels and truffles, and even the antibiotic mold penicillin. 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 people, animals, or 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 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. When I picture members of the fungus kingdom, I imagine mushrooms sprouting from a dead fallen tree. By thinking of mushrooms as an example of a member of the fungus kingdom, I’m able to quickly recall some key things. This mushroom is multicellular. It reproduces by making spores. It gets its nutrition from dead and decaying material. And it doesn’t move around on its own.
Now we can add to this information some other things that we know are true about fungi. We know that some fungi are unicellular because we know that yeast are also a member of the fungus kingdom. We know that fungi can reproduce sexually or asexually because spores can be produced using one parent or two. We know that fungi are heterotrophic organisms because they absorb their nutrients from their surroundings. And we know that, like immobile plants, the cell walls of fungi are surrounded and supported by a cell wall, even though the cell wall of fungi is different than the cell wall of plants.
So now we’re ready to choose the best answer. Two of our answer choices state that members of kingdom fungi have no cell walls. So we know that these two answers are incorrect. Another choice states that fungi are mobile, which is also incorrect. We know that fungi do not 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 may be parasitic or saprophytic. A parasite is an organism that lives on or in a host and causes the host harm. And saprophytic means an organism that breaks down decaying matter and absorbs nutrients from it. Well, we know that fungi are heterotrophic decomposers. And the fact that they may be parasites is not surprising. And finally, this answer choice states that fungi have cell walls, a fact which we’ve already confirmed. So the answer choice that best describes members of kingdom fungi is “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. We learned that fungi can be unicellular or multicellular. They reproduce sexually or asexually. They are heterotrophs. They have chitin in their cell walls. They are eukaryotic organisms. We learned that fungi are immobile or sessile. And we also examined some examples. Then we looked at the characteristics of three phyla within the fungi kingdom: Zygomycota, Ascomycota, and Basidiomycota.