CK-12 Life Science

by CK-12 Foundation

  Fungi are Good Eaters

  Fungi can grow fast because they are such good eaters. Fungi have lots of surface area and this large surface area “eats.” Surface area is how much exposed area an organism has compared to their overall volume, and in the mushroom for example, most of that surface area is actually underground. They also have special enzymes that they can squirt into their environment. These enzymes help them digest large organic molecules. In some ways similar to your cutting up your meat or vegetables before eating, fungi “cut up” large molecules such as sugars, proteins, and lipids into smaller molecules. Then the fungi absorb the nutrients into their cells.

  Fungi Body Parts

  Fungi have a cell wall, hyphae, and specialized structures for reproduction. The hyphae are thread-like structures which interconnect and bunch up into mycelium. Ever see mold on a damp wall or on old bread? The things that you are seeing are really mycelia. The hyphae and mycelia help the fungi absorb nutrients from living hosts. Other specialized structures are used in sexual reproduction. One example is a fruiting body. A mushroom is a fruiting body, which is the part of the fungus that produces the spores. Those spores are the basic reproductive units of fungi.

  Fungi Reproduction

  Reproduction of fungi is different for different fungi. Many fungi reproduce both sexually or asexually, while some reproduce only sexually and some only asexually. Asexual reproduction takes only one parent and sexual reproduction takes two parents.

  Asexual Reproduction

  Fungi reproduce asexually through three methods: spores, budding, and mycelial fragmentation. Asexual spores are formed by the fungi and released to create new fungi. Have you ever seen a puffball? A puffball is a kind of fungus that has thousands of spores in a giant ball. Eventually the puffball bursts and releases the spores in a huge “puff”. In budding, the fungus grows part of its body which eventually breaks off. The broken-off piece becomes a “new” organism. Many fungi can reproduce by mycelial fragmentation or splitting off of the mycelia. A fragmented piece of mycelia can eventually produce a new colony of fungi.

  Asexual reproduction is faster and produces more fungi than sexual reproduction. For some species of fungi, asexual reproduction is the only way possible to reproduce. Asexual reproduction is controlled by many different factors, including environmental conditions such as the amount of sunlight and CO2 the fungus receives, as well as the availability of food.

  Sexual Reproduction

  Almost all fungi can reproduce with meiosis. Meiosis is a type of cell division where haploid cells are produced (discussed in chapter titled Cell Division, Reproduction and DNA). But meiosis in fungi is really different from sexual reproduction in plants or animals.

  Meiosis occurs in diploid cells and is a process that produces haploid cells. A diploid cell is a cell with two sets of chromosomes--one from each parent. A haploid cell has one set of chromosomes. In meiosis, the chromosomes duplicate once, and then after two more divisions, four haploid cells are produced. Each haploid cell has half the chromosome number of the parent cell. However, in fungi, meiosis occurs right after two haploid cells fuse, producing four haploid cells. Mitosis then produces a haploid multicellular "adult" organism or haploid unicellular organisms. Mitosis is cell division that results in two genetically identical offspring cells.

  Other Sexual Processes

  Some species of fungi exchange genetic material by parasexual processes. This means that some haploid nuclei in the fungi cells may fuse and form diploid nuclei. These nuclei rarely exist and are usually very unstable. Chromosomes are lost during later mitotic divisions which can make the offspring fungus genetically different from the parents.

  Classification of Fungi

  Scientists used to think that fungi were members of the Plant kingdom. They thought this because fungi had several similarities to plants. For example, fungi and plants are usually sessile with a leaf or flower that is attached to a stem. Also:

  Both fungi and plants have similar morphology or structure.

  Plants and fungi live in the same kinds of habitats, such as growing in soil.

  Plants and fungi both possess a cell wall; animals cells do not have cell walls.

  Scientists now consider fungi to be a separate Kingdom that is nearly one billion years old.

  Physiological and Morphological Traits

  There are a number of characteristics that distinguish fungi from other eukaryotic organisms.

  Fungi cannot make their own food like plants can since they do not have any of the right equipment for photosynthesis. Fungi are more like animals and some bacteria in that they have to obtain their food from outside sources.

  The cell walls in many species of fungi contain chitin. Chitin is a nitrogen-containing material found in the shells of animals such as beetles and lobsters. The cell wall of a plant is not made of chitin but rather a carbohydrate called cellulose.

  Unlike many plants, most fungi do not have a well-developed vascular system. A vascular system is necessary for the transportation fluids such as water and nutrients. In all plants, the vascular system is made up of structures called xylem and phloem. Fungi do not have xylem or phloem which, again, distinguishes them from plants.

  One characteristic that is unique to fungi is the presence of hyphae, which combine in groups called mycelia, as described above.

  The Evolution of Fungi

  Fungi appeared during the Paleozoic Era, a geologic time period lasting from about 570 million to 248 million years ago, and the time when fish, insects, amphibians, reptiles, and land plants appeared. The first fungi were most likely aquatic, and had flagellae that released spores. The first land fungi probably appeared in the Silurian period (443 million years ago to about 416 million years ago), a geologic period during which land plants also first appeared.

  Roles of Fungi

  Fungi are found all over the globe in many different kinds of habitats. Fungi even thrive in deserts. Most fungi however are found on land rather than in the ocean, but some species live only in marine habitats. Fungi are extremely important to these ecosystems because they are one of the major decomposers of organic material in most terrestrial ecosystems. Scientists have estimated that there are nearly 1.5 million species of fungi.

  Importance of Fungi for Human Use

  Humans use fungi for food preparation or preservation and other purposes. For example, yeasts are required for fermentation of beer, wine and bread (Figure below). Some fungi are used in the production of soy sauce and tempeh, a stable source of protein, like tofu, found in South East Asia. Mushrooms are used in the diet of people all over the globe. Other fungi are producers of antibiotics, such as penicillin. The chitin in the cell walls of fungi, has been said to have wound healing properties.

  Figure 9.11

  , a single-celled fungus called Brewer's or Baker's yeast, is used in the baking of bread and in making wine and beer through fermentation. There are several other species of yeast used in brewing beer. Each can impart a distinctive taste.

  Edible and Poisonous Fungi

  Some of the best known types of fungi are mushrooms--both edible and poisonous (Figure below). Many species are grown commercially, but others must be harvested from the wild. When you order a pizza with mushrooms or add them to your salad, you are most likely eating Agaricus bisporus, the most commonly eaten species. Other mushroom species are gathered from the wild for people to eat or for commercial sale.

  Have you ever eaten blue cheese? Do you know what makes it blue? You guessed it. Fungus. For certain types of cheeses, producers inoculate milk curds with fungal spores to promote the growth of mold which makes the cheese blue. Molds used in cheese production are safe for humans to eat.

  Many mushroom species are poisonous to humans—some mushrooms will simply give you a stomach ache while others may kill you. Some mushrooms you can eat when they are cooked but are poisonous when raw.

  Figure 9.12

  Some of the best known types of fungi
are the edible and the poisonous mushrooms.

  Fungi in the Biological Control of Pests

  Some fungi work as natural pesticides. For example in agriculture, some fungi may be used to limit or kill harmful organisms like mites, pest insects, certain weeds, worms, and other fungi that harm or even kill crops.

  Lesson Summary

  Fungi are in their own kingdom based on their structures, ways of obtaining food, and on their means of reproduction.

  Fungi live with other organisms in symbiotic relationships.

  Fungi reproduce asexually, sexually and parasexually.

  Fungi appeared during the Paleozoic Era.

  Fungi are widely used in industry and medicine.

  Review Questions

  What two characteristics distinguishes fungi from plants?

  How many species of fungi exist?

  Define mycorrhizal symbiosis.

  Describe the symbiotic relationship of a lichen.

  How was Beatrix Potter important to the scientific world?

  Describe the relationship between the ambrosia beetle and fungi.

  Name two human diseases caused by fungus.

  When you see mold what body part of the fungus are you observing?

  Describe asexual reproduction in fungi.

  Describe sexual reproduction in fungi.

  Further Reading / Supplemental Links

  Money, Nicholas, The Triumph of Fungi: A Rotten History. Oxford University Press, 2006.

  Webster, Robert and Weber, Roland, Introduction to Fungi. Cambridge University Press, 2007.

  Moore-Landecker, Elizabeth, Fundamentals of Fungi. Benjamin Cummings, 1996.

  http://www.tolweb.org/Fungi

  http://www.ucmp.berkeley.edu/fungi/fungi.html

  http://www.perspective.com/nature/fungi

  http://en.wikipedia.org/wiki/Image:DecayingPeachSmall.gif

  (http://waynesword.palomar.edu/trfeb98.htm)

  Vocabulary

  asexual reproduction

  Reproduction involving only one parent; fungi reproduce asexually through three methods: spores, budding, and mycelial fragmentation.

  budding

  Asexual reproduction in which the fungus grows part of its body which eventually breaks off; the broken-off piece becomes a new organism.

  chitin

  A nitrogen-containing material found in the cell wall of fungi; also found in the shells of animals such as beetles and lobsters.

  fruiting body

  Specialized structure used in sexual reproduction; part of the fungus that produces the spores.

  heterotroph

  Organism which obtains carbon (“food”) from outside of themselves.

  hyphae

  Thread-like structures which interconnect and bunch up into mycelium; helps bring food, such as a worm, inside the fungus; : the “arms and legs” of a fungus.

  lichen

  A symbiotic relationship between a fungus and a bacteria or algae; each organism provides nutrients for the other.

  meiosis

  A type of cell division where haploid (one set of chromosomes) cells are produced.

  mycelial fragmentation

  Asexual reproduction involving splitting off of the mycelia; a fragmented piece of mycelia can eventually produce a new colony of fungi.

  mycelium

  Help the fungi absorb nutrients from living hosts; composed of hyphae.

  mycorrhizal symbiosis

  A relationship between fungi and the roots of plants where both benefit; the plant provides glucose and sucrose to the fungus that the plant makes through photosynthesis; the fungi provides minerals and water to the roots of the plant.

  parasite

  The organism that benefits in a relationship between two organisms in which one is harmed.

  spores

  The basic reproductive units of fungi.

  Points to Consider

  Plants are fascinating organisms and are widely diverse. Although scientists used to think that fungi were plants, we now know that plants are fungi are separate. In this lesson we have discussed fungi. Now think about what sets plants apart from fungi?

  Chapter 10: Plants

  Lesson 10.1: Introduction to Plants

  Lesson Objectives

  Describe the major characteristics that distinguish the Plant Kingdom.

  Describe plants’ major adaptations for life on land.

  Explain plants’ reproductive cycle.

  Explain how plants are classified.

  Check Your Understanding

  What are the major differences between a plant cell and an animal cell?

  What is photosynthesis?

  Introduction

  Plants have adapted to a variety of environments, from the desert to the tropical rain forest to our lakes and oceans. In each environment, plants have become crucial to supporting animal life. First, plants provide animals with food. In a forest, for example, caterpillars munch on leaves while birds eat berries and deer eat grass. Furthermore, plants make the atmosphere friendly for animals. Plants absorb animals’ “waste” gas, carbon dioxide, and release the oxygen all animals need for cellular respiration. Finally, plants provide cover and shelter for animals. A bird can take refuge from predators in a shrub and use twigs to make a nest high in a tree (Figure below). Without plants, animals would not be able to survive.

  Figure 10.1

  These bird eggs are benefiting from the cover of a plant; plant materials make up the nest, and when the eggs hatch, the young birds will eat plant products like seeds and berries.

  What Are Plants?

  From tiny mosses to extremely large trees (Figure below), the organisms in the Plant Kingdom have three main distinguishable features.

  They are all:

  eukaryotic

  photosynthetic

  multicellular

  Recall that eukaryotic organisms also include animals, protists, and fungi; eukaryotic cells have true nuclei that contain DNA and membrane-bound organelles such as mitochondria. As discussed in the Cell Functions chapter, photosynthesis is the process by which plants capture the energy of sunlight and use carbon dioxide from the air to make their own food. Lastly, plants must be multicellular. Recall that some protists, like diatoms, are eukaryotic and photosynthetic; however, diatoms are not considered plants. Diatoms are a major group of algae, and are mostly unicellular.

  Figure 10.2

  There is great diversity in the plant kingdom, from tiny mosses to huge trees.

  Adaptations For Life On Land

  Much evidence suggests that plants evolved from freshwater green algae (Figure below). For example, green algae and plants both have the carbohydrate cellulose in their cell walls and they share many of the same pigments. (For a review of plant cells, see the Cells and Their Structures chapter.) So what separates green algae, which are protists, from green plants?

  Figure 10.3

  The ancestor of plants is green algae. This picture shows a close up of algae on the beach.

  One of the main features that distinguishes plants from algae is the retention of the embryo during development. In plants, the embryo develops and is nourished in the female reproductive structure after fertilization. Algae do not retain the embryo. This was the first feature to evolve that separated the plants from the green algae. Plant reproduction will be discussed in the following section.

  Although the retention of the embryo is the only adaptation shared by all plants, over time other adaptations for living on land also evolved. In early plants, a waxy layer called a cuticle evolved to help seal water in the plant and prevent water loss. However, the cuticle also prevents gases from entering and leaving the plant easily. Recall that the exchange of gasses - taking in carbon dioxide and releasing oxygen - occurs during the process of photosynthesis. Therefore, along with the cuticle, small pores in the leaves called stomata also evolved (Figure below). The stomata can open and close depending on weather conditions; when it's hot and dry the
stomata can stay closed to conserve water. The stomata can open again to permit gas exchange when the weather cools down.

  Figure 10.4

  Stomata are pores in leaves that allow gasses to pass through, but they can be closed to conserve water.

  A later adaption for life on land was the evolution of vascular tissue. Vascular tissue is specialized tissue that transports water, nutrients, and food in plants. In algae, vascular tissue is not necessary since the entire body is in contact with the water. But on land, water may only be present deep in the ground. Vascular tissue delivers water and nutrients from the ground up and food down into the rest of the plant. The two vascular tissues are xylem and phloem. Xylem is responsible for the transport of water and mineral nutrients from the roots throughout the plant. It is also used to replace water lost during transpiration and photosynthesis. Phloem mainly carries the sugars made during photosynthesis to the parts of the plant where it is needed.

  Plant Reproduction and Life Cycle

  Alternation of generations describes the lifecycle of a plant (Figure below). In alternation of generations, the plant alternates between a sporophyte that has two sets of chromosomes (diploid) and a gametophyte that has one set of chromosomes (haploid). Briefly, alternation of generations can be summarized in the following four steps: follow along in Figure below as you read through the steps.