Along with terrestrial plants and animals, fungi are eukaryotes with a huge range of body designs and are one of the main evolutionary lineages to occupy land. Although there are roughly 100,000 known species of fungi, there are about 1.5 million different types of fungi on Earth. Fungi include things like edible mushrooms, yeasts, black mold, and Penicillium notatum, which makes the antibiotic penicillin. A fungus is presently the biggest (and maybe the oldest) living thing on Earth’s surface.
In general, how old are fungi? It has unfortunately been challenging to build much of a fossil record for fungus because the majority of fungal structures do not fossilize efficiently. The origin of fungi has undergone various changes as a result of the development of new molecular techniques, and it is still a subject of intense controversy.
Fungi are thought to have either arisen significantly earlier (1300 million years ago) or at the same time as the earliest land plants in the Pre-Cambrian, according to the two most popular hypotheses. The main distinction is whether fungi originated in water before spreading to land and coexisting with plants, or whether their evolutionary origins occurred simultaneously with the plant invasion of land. About either theory, there is proof that by 420 million years ago, fungus and plants were developing at the same time on land, millions of years before the first vertebrates crawled out of the sea.
Characteristics of Fungi
The following are some important characteristics of fungi:
- Fungi are eukaryotic, non-vascular, non-motile and heterotrophic organisms.
- They could have filaments or only one cell.
- They reproduce with the use of spores.
- Fungi exhibit the phenomenon of alternation of generation.
- Because they lack chlorophyll, fungi cannot carry out photosynthesis.
- Starch is the form in which fungi store their food.
- Fungi perform chitin biosynthesis.
- The fungi’s nuclei are quite small.
- No embryonic stage exists in the fungi. They emerge from spores.
- Reproduction can be sexual or asexual.
- A few types of fungus can infect their hosts as parasites.
- Pheromone, a substance that fungi make, is what triggers sexual reproduction in fungi.
Structure of Fungi
The following points can be used to illustrate how fungi are structured:
- Except for yeast cells, almost all fungus are composed of filaments.
- They could be multicellular organisms or single-celled ones.
- The long, thread-like structures that make up fungi are called hyphae. Mycelium is the term for the structure made up of these hyphae.
- The cell wall of fungi is composed of carbohydrates and chitin.
- A protoplast makes up the cell wall; this protoplast then differentiates into other cell components such the cell membrane, cytoplasm, organelles, and nuclei.
- The nucleus is transparent and packed with chromatin filaments. Nuclear membranes are used to enclose the nucleus.
Growth
Although some fungus, known as dimorphic fungi, can transition from a single cell to a multicellular form depending on their environment, most fungi are multicellular organisms. They exhibit the vegetative and reproductive morphological stages separately. While the reproductive stage can be more obvious, the vegetative stage is composed of a tangle of thin, thread-like structures called hyphae (plural, hypha).
Despite being minuscule, fungal hyphae enable the quick movement of nutrients and small molecules throughout the fungal body. Numerous fungi arrange these hyphae into networks to form a mass known as a mycelium. The mycelium can develop on a surface, in a liquid, on living tissue, or on soil or decomposing matter. The mycelium of a fungus can be very large, even though individual hyphae are very small; some species genuinely are “the fungus humongous.” The enormous Armillaria solidipes (honey mushroom), which occupies more than 2,000 acres of subterranean earth in eastern Oregon, is regarded as the largest creature on Earth and is thought to be at least 2,400 years old.
Fungi can grow with or without light and oxygen and prefer moist, slightly acidic environments. The majority of fungi are obligate aerobes, meaning they need oxygen to survive. However, some species, like the Chytridiomycota found in the rumen of cattle, are obligate anaerobes, meaning they can only breathe under anaerobic conditions because oxygen would otherwise kill them or disrupt their metabolism. similar to those used in wine, yeast like those used in wine or beer-making, are intermediates: facultative anaerobes. They grow best in the presence of oxygen using aerobic respiration, but can survive using anaerobic respiration when oxygen is not available.
Mode of Reproduction in Fungi
Fungi have both sexual and asexual reproduction methods. The so-called “imperfect” fungi can only reproduce asexually, in contrast to the “perfect” fungi, which can reproduce both sexually and asexually (by mitosis). Due to the diversity of reproductive strategies, fungi can be divided into different phyla (subgroups) by the unique structures they develop for reproduction, including Basidiomycota, Ascomycota, Glomeromycota, and Chytridiomycota.
Fungi reproduce both sexually and asexually by producing a large number of tiny, light-weight spores that leave the parent organism by either floating on the wind or hitching a ride on an animal. The possibility of spores landing in environment that will support growth increases with the massive amount discharged.
Asexual Reproduction
Asexual reproduction is possible for fungi by spore production, budding, or fragmentation. During budding, a bulge forms on the side of the cell, the nucleus splits mitotically, and the bud eventually separates from the mother cell. By contrast, fragments of hyphae can establish new colonies. Asexual spores, which can only be produced by one parent (by mitosis) and are genetically identical to that parent, are the most typical kind of asexual reproduction. Fungi can spread out and colonize new surroundings owing to spores. They can be discharged either externally or inside a unique reproductive sac known as a sporangium.
Sexual Reproduction
A community of fungi gains genetic diversity through sexual reproduction. Sexual reproduction takes place in mushrooms in a number of ways, usually in reaction to unfavorable environmental circumstances. We will give a general description of this process, but keep in mind that the specifics substantially vary by fungus species. During sexual reproduction, two mating types (rather than discrete “sexes,” such as male and female) are formed.
The following three steps are present in all fungal sexual reproductive processes, notwithstanding their numerous variations. First, two haploid cells merge during plasmogamy, which is defined as “the marriage or union of cytoplasm”; this results in the dikaryotic stage, in which two haploid nuclei coexist in a single cell. The haploid nuclei combine during karyogamy (also known as “nuclear marriage”) to create a diploid zygote nucleus. In the gametangia (plural, gametangium) organs, where gametes of various mating kinds are produced, meiosis finally occurs. At this point, the cycle can restart because the spores have now spread across the environment.
Nutrition and Metabolism
Because they employ complex organic compounds as a source of carbon rather than fixing atmospheric carbon dioxide like some bacteria and the majority of plants, fungi are heterotrophs, just like animals. Additionally, like animals, fungi must get nitrogen from their surroundings because they cannot fix it from the atmosphere. However, fungus carry out these actions in the reverse order unlike many mammals, who swallow food before digesting it inside in designated organs.
As a result, digestion takes place outside the body. Exoenzymes are initially carried outside of the hyphae in multicellular fungus, where they are used to break down environmental nutrients. The larger surface area of the mycelium is then used to absorb the smaller molecules created by this external digestion.
The majority of fungi are decomposers that obtain nutrients from dead or decomposing organic materials (usually plants). Insoluble polysaccharides, such the cellulose and lignin of decaying wood, can be broken down by fungal exoenzymes into easily absorbed glucose molecules. Other fungi take on unique tasks, such as those in mutualistic relationships with plants, where they exchange plant sugars for water and essential nutrients.
Others are parasitic and infect either plants or animals; for instance, smut and Dutch elm disease impact plants, whereas athlete’s foot and candidiasis (thrush) are serious fungal infections in people. Some fungus even turn to predatory behavior in nitrogen-deficient conditions, catching other tiny animals like nematodes using constricting rings within their hyphae.
Uses of Fungi
Fungi are among the most significant groups of living things since they are essential to the biosphere and have significant economic value due to both their beneficial and detrimental effects.
The following are some significant applications for fungi:
- They have a significant impact on the recycling of decomposing and dead waste.
- Food – The cultivated species of mushrooms are edible and are consumed by people.
- Medicines – A variety of fungi are used to make antibiotics and treat illnesses in both people and animals. The common fungus Penicillium is the source of the antibiotic penicillin.
- Fungi are biocontrol agents that use insects and other tiny worms as food and aid in pest control. fungus spores are used as a spray on crops.
- Food spoilage – Fungi play a major role in recycling organic material and are also responsible for major spoilage and economic losses of stored food.