Fungi - An Overview PDF

Fungi- An Overview Dr. Basma Samir (MD) 2  Fungi (singular: fungus) are a kingdom of multicellular eukaryotic organisms that are heterotrophs (cannot make their own food) and have important roles in nutrient cycling in an ecosystem. This means they are not animals, plants, or bacteria. U...

Fungi- An Overview Dr. Basma Samir (MD) 2  Fungi (singular: fungus) are a kingdom of multicellular eukaryotic organisms that are heterotrophs (cannot make their own food) and have important roles in nutrient cycling in an ecosystem. This means they are not animals, plants, or bacteria. Unlike bacteria, fungi have complex eukaryotic cells like animals and plants. Fungi reproduce both sexually and asexually, and they also have symbiotic associations with plants and bacteria. 3  Not Bacteria Not Animal Cell 4 Not Plants Unlike plants, fungi do not contain the green pigment chlorophyll and therefore are Not capable of Photosynthesis. That is, they cannot generate their own food by using energy from light. Fungi need to absorb nutrients from organic substances that contain carbon, like carbohydrates, fats, or proteins. 5  Plant cell walls are made of cellulose. Fungal cell walls have chitin, like some members of the animal kingdom, the exoskeletons, or the outer hard shell of various insects, and crustaceans like crabs and lobsters are made of chitin. Chitin is a distinctly non-plant substance. 6 Fungal characteristics 7  Cells Fungi are eukaryotes. They have a well-organized cell, characteristic of all eukaryotes. They have a body (thallus) composed of microscopic tubular cells called hyphae. DNA is encapsulated in a central structure “the nucleus”-some cells can have multiple nuclei. They also have organelles that perform various functions such as energy production and protein transport. 8 Cell Wall & Cell Membrane Fungal cells have: An inner cell membrane and an outer cell wall. These two layers have more in common with animals. Cell membranes of fungi are made of proteins and lipids like animal cell. They also contain a unique steroid called ergosterol as animal cell membranes which contain varying amounts of cholesterol. 9 Structure Fungi can be made up of: a single cell as in the case of yeasts, or multiple cells, as in the case of mushrooms. The bodies of multicellular fungi are made of cells that band together in rows that resemble the branches of trees. Each individual branched structure is called a hypha (plural: hyphae). Several hyphae mesh together to form the mycelium, which constitutes the fungal body. Hyphae expand their surface area in order to: take in food, facilitate digestion and also to reproduce. 10 Spores A spore is a survival or dispersal unit, consisting of one or a few cells, that is capable of germinating to produce a new hypha. Fungal spores lack an embryo, but contain food reserves needed for germination. Many fungi produce more than one type of spore as part of their life cycles. Fungal spores may be formed via an asexual process involving only mitosis, or via a sexual process involving meiosis. Fungi frequently reproduce by the formation of spores. 11 Nutrition Fungi cannot conduct photosynthesis. They need to absorb nutrients from various organic substances around them. (Heterotrophs). When they find food, they secrete their enzymes out on to the food, and digestion takes place outside their body. These specialized digestive enzymes are known as exoenzymes, and are secreted from the tips of growing hyphae onto their surroundings. As a result of exoenzyme activity, large food molecules are broken down into smaller ones, which are brought into the hyphae. Cellular respiration then takes place inside fungal cells. That is to say, organic molecules such as carbohydrates and fatty acids are broken down to generate energy. 12 How Do Fungi Obtain Their Food Saprotrophic fungi obtain their food from dead organic material and are ecologically useful decomposers. Parasitic fungi feed on living organisms (usually plants), thus causing disease. Symbiont or a Mutualist: a fungus derives sustenance from a live host without harming it. Necrotrophs infect a living host, but kill host cells in order to obtain their nutrients. 13 Reproduction Various fungi are capable of reproducing asexually or sexually. Both processes can generate spores. These are special cells, which when released into a suitable environment, can give rise to a new fungal body. Spores can be carried to new environments by air or water. 14 Asexual reproduction occurs through mitosis, when a fungal cell divides and produces identical genetic copies of itself. In simpler, single-celled fungi like yeast, this process is known as budding. In this case, a small bud emerges from the parent cell, slowly growing in size. The nucleus divides into two and the bud splits off once it is the same size as the parent cell. On the other hand, multicellular fungi such as molds reproduce through the formation of asexual spores. 15 Sexual reproduction Sexual reproduction in fungi produces spores through Meiosis. As a result, these spores contain half the number of parental chromosomes. Once released, the spores germinate into tree-like mycelia and are ready to "mate." 16  Sexual reproduction (cont.,) Mating takes place when two primary mycelia come into contact with one another and form a secondary mycelium. Each segment of the secondary mycelium has 2 nuclei: one from each original segment. The individual nuclei still have half the number of chromosomes as the parent cell. In the course of several steps nuclei fuse, giving rise to cells with the original number of chromosomes. After this point, the sexual reproductive cycle begins again: meiosis occurs and spores are produced. 17  Fungus and us Fungi are inextricably linked to our lives. They affect our health, food, industry and agriculture in both positive and negative ways. 18 Beneficial Fungi Fungi are sources of important medications. The antibiotics penicillin and cephalosporin as well as; The drug cyclosporine, which helps to prevent transplant rejection are all produced by fungi. Yeast (Saccharomyces cerevisiae) is essential to the fermentation of alcohol and to the baking of raised, fluffy bread. The characteristic azure hue of blue cheeses is due to the sporulation of the fungus Penicillium roquefortii." Mushrooms are tasty additions to meals. 19 Beneficial Fungi Important scientific discoveries have been made using fungi as model organisms. Scientists George Beadle and Edward Tatum won the Nobel Prize in 1958 for their work in discovering that; genes control the expression of enzymes. Yeast has also been used as a model organism for answering questions in the field of genetics. There are 75,000 known fungal species. But this number is believed to represent only 5 % of the species that exist in nature. 20 Harmful Fungi Yet, fungi produce toxins called mycotoxins that are harmful to us. "Almost all mycotoxins are produced by molds,". For example, Aspergillus fungi that grow on corn and peanuts produce aflatoxins. This mycotoxin is considered a carcinogen and has been linked to liver cancer. Smut and Rust fungi (named for the coaly and rust like appearance of their spores) routinely destroy food crops and plants like beans, barley and pine trees. 21  Bread Mold If left in a warm, dark and moist environment, bread may grow mold. Common bread molds appear black or blue-green. Causes Spores from mold floating through the air, land on bread and activate when moisture and temperature conditions are right. Bread mold prefers warm, moist and dark environments. Types The type of mold that afflicts bread is the dry, cotton-textured mold, which grows in threads through the bread. 22 Colors Each species of mold exhibits its own color. The Rhizopus stolonifer species appears black, whereas the penicillium species appears blue- grayish-green with a white border. Fact Penicillium species of bread mold is the same species from which scientists extract penicillin, an antibiotic that kills bacterial infections within the body. Reproduction Bread mold reproduces by releasing spores into the air, asexually. When the spores land on an object with the correct environmental conditions (light, heat, water and nutrition), they will germinate, then grow roots, mature and then release spores of their own. 23 Discussed Items What are Fungi? Plant or Animal?? Characteristics of Fungi Structure of a fungal cell Spores Nutrition Reproduction Fungi and Us.. Beneficial fungi Harmful fungi 24 25