Fungus Worksheet

FUNGUS WORKSHEET

Name______Class______Date ______

Read this passage from the lesson and answer the questions that follow.

Nutrition

Fungi get their nutrition by absorbing organic compounds from the environment. Fungi are heterotrophic; they rely solely on carbon fixed by other organisms for their metabolism and nutrition. Fungi have evolved in a way that allows many of them to use a large variety of organic substrates for growth, including simple compounds as nitrate, ammonia, acetate, or ethanol. Their mode of nutrition defines the role of fungi in their environment.

Fungi obtain nutrients in three different ways:

They decompose dead organic matter. A saprotroph is an organism that obtains its nutrients from non-living organic matter, usually dead and decaying plant or animal matter, by absorbing soluble organic compounds. Saprotropic fungi play very important roles as recyclers in ecosystem energy flow and biogeochemical cycles. Saprophytic fungi, such as shiitake (Lentinulaedodes) and oyster mushrooms (Pleurotusostreatus), decompose dead plant and animal tissue by releasing enzymes from hyphal tips. In this way they recycle organic materials back into the surrounding environment.
They feed on living hosts. As parasites, fungi live in or on other organisms and get their nutrients from their host. Parasitic fungi use enzymes to break down living tissue, which may causes illness in the host. Disease-causing fungi are parasitic. Recall that parasitism is a type of symbiotic relationship between organisms of different species in which one, the parasite, benefits from a close association with the other, the host, which is harmed.
They live mutualistically with other organisms. Mutualistic fungi live harmlessly with other living organisms. Recall that mutualism is an interaction between individuals of two different species, in which both individuals benefit.

Both parasitism and mutualism are classified as symbiotic relationships, but they are discussed separately here because of the different effect on the host.

Fungal hyphae are adapted to efficient absorption of nutrients from their environments, because hyphae have high surface-area-to-volume ratios, shown in Figure 5. These adaptations are also complemented by the release of hydrolytic enzymes that break down large organic molecules such as polysaccharides, proteins, and lipids) into smaller molecules. These molecules are then absorbed as nutrients into the fungal cells. One enzyme that is secreted by fungi is cellulase, which breaks down the polysaccharide cellulose. Cellulose is a major component of plant cell walls. In some cases, fungi have developed specialized structures for nutrient uptake from living hosts, which penetrate into the host cells for nutrient uptake by the fungus.

A mycorrhiza (Greek for fungus roots) is a symbiotic association between a fungus and the roots of a plant. In a mycorrhizal association, the fungus may colonize the roots of a host plant by either growing directly into the root cells, or by growing around the root cells. This association provides the fungus with relatively constant and direct access to glucose which the plant produces by photosynthesis. The mycelia of the fungi increase the surface area of the plant’s root system. The larger surface area improves water and mineral nutrient absorption from the soil.

Questions

1. What are some of the simple organic compounds that fungi use for their growth?

2. What are the three ways that fungi obtain nutrients?

3. How do the saprophytic fungi, such as the shiitake and oyster mushrooms, decompose dead plant and animal tissue?

4. How are fungal hyphae adapted for efficient absorption of nutrients from their environments?

5. In a mycorrhizal association, what is the benefit to the fungus?

Circle the letter of the correct choice.

1. The characteristics of fungi include

A. heterotrophy.

B. most fungi being multicellular.

C. cell walls containing chitin.

D. all of the above

2. Chitin makes up

A. the cell walls of fungi.

B. the cell walls of plants.

C. the cell walls of bacteria.

D. all of the above

3. A mycorrhiza is a symbiotic association between a fungus and what structures of a plant?

A. leaves

B. stems

C. roots

D. none of the above

Read this passage from the lesson and answer the questions that follow.

Release of Spores

The spores of fungi are released in many different ways. Some are spread by wind, and others are spread by water. Certain species have evolved “spore cannons” which can shoot spores up to 30 cm away. This ensures the offspring fungus will not be in competition for resources with its parent or “siblings” Others rely on mechanical force; for example, puffballs, such as the one shown at left in Figure 13 (see FlexBook), can burst when knocked or disturbed. Other fungi attract insects to carry spores away. Stinkhorns, like the one shown at right in Figure 13 (see FlexBook), attract flies to their fruiting structures, by having bright colors and an odor like rotting meat, which flies love. When the spores reach a suitable substrate, they germinate, form new hyphae, and so restart their life cycle.

Phylum Chytridiomycota

Living chytrids are mostly aquatic. They live in fresh water, in marine waters, and on land. Their name refers to the chytridium (from the Greek chytridion, meaning "little pot"): the structure containing unreleased spores. Chytrids also have flagellated gametes; no other fungi have flagellated cells. Chytrids secret enzymes that can break down cellulose, chitin, and keratin, which makes them important decomposers. However, they can also be parasitic.

Recently, a chytrid species, Batrachochytriumdendrobatidis, was discovered to cause a serious and highly contagious disease in amphibians. This fungus, shown in Figure 14 (see FlexBook), is considered to be one of the main reasons for the decline in worldwide amphibian populations. The disease caused by chytrids is called Chytridiomycosis.

The oldest fossil fungi known are chytrids. Studying the living chytrids can help scientist understand how fungi have evolved.

Questions

1. What is the advantage of “spore cannons”?

2. How do stinkhorns attract flies to their fruiting structures?

3. What makes chytrids important decomposers?

4. What is one of the main reasons for the decline in worldwide amphibian populations?

5. What can studying living chytrids help scientists do?

Circle the letter of the correct choice.

2. Yeasts belong to which phylum?

A. Zygomycota

B. Ascomycota

C. Basidiomycota

D. Chytridiomycota

Read this passage from the lesson and answer the questions that follow.

Symbiotic Relationships of Fungi

Another major ecological role of fungi is in the mutualistic relationship they have with plants. A mycorrhiza (Greek for fungus roots) is a symbiotic (or occasionally weakly pathogenic) association between a fungus and the roots of a plant. In a mycorrhizal association the fungus may colonize the roots of a host plant either intracellularly or extracellularly. It is estimated that about 95 percent of plant families live in symbiosis with a mycorrhizal fungi. Figure 1 (see FlexBook) shows the fruiting bodies of the bicolored deceiver mushroom that is often associated with tree roots.

This mutualistic relationship provides the fungus with easy access to carbohydrates such as glucose which are made by the plant in photosynthesis. The carbohydrates are translocated from the site of photosynthesis to the root tissues and then to the fungal partners. In return, the plant gains the use of the mycelium's very large surface area to absorb water and mineral nutrients from the soil, thus improving the mineral absorption capabilities of the plant roots.

Plant roots alone may not be able to take up phosphate ions in alkaline soils. The mycelia of the mycorrhizal fungus can access the phosphate ions, and make them available to the plants they colonize. Mycorrhizal mycelia are much smaller in diameter than the smallest root, and can explore a greater volume of soil, providing a larger surface area for absorption. Mycorrhizae are especially beneficial for its plant partner in nutrient-poor soils.

Mycorrhizal plants are often more resistant to diseases, such as those caused by microbial soil-borne pathogens, and are also more resistant to the effects of drought. These effects are perhaps due to the improved water and mineral uptake in mycorrhizal plants.

Studies have shown that plants grown in sterile soils and growth media often grow poorly without the addition of fungal spores or hyphae of mycorrhizal fungi to the soil. The mycorrhizal fungi colonize the plant roots and aid in the uptake of soil mineral nutrients. The absence of mycorrhizal fungi can also slow plant growth in early succession or on disturbed soil.

Lichens

Lichens are not single organisms, but are symbiotic associations of a fungus (the mycobiont) with a photosynthetic partner (the photobiont), shown in Figure 3 (see FlexBook). The photobiont is usually either green alga or cyanobacterium that produces food from sunlight. A few lichens are known to contain yellow-green algae or, in one case, a brown alga. The fungus surrounds the algal or bacterial cells, often enclosing them within special fungal tissues that are unique to lichen symbioses.

The fungus usually makes up the majority of the body mass of the lichen. Lichens take the shape of the fungal partner and so are named after the fungus. The fungus in a lichen is usually an Ascomycete, and more rarely a Basidiomycete. A lichen is either called an ascolichen or a basidiolichen. The photobiont provides sugars and other carbohydrates, while the fungus provides minerals and water. The functions of both symbiotic organisms are so closely intertwined that they function almost as a single organism.

Lichens do not have roots and do not need to have access to water like most higher plants do. They can therefore grow in locations impossible for most plants, such as bare rock, sterile soil or sand, and various artificial structures such as walls, roofs and monuments. Lichens can survive very harsh conditions, and live in the Arctic, the Antarctic, deserts and mountaintops, and can withstand extreme temperatures. Many lichens also grow as epiphytes (epi- on the surface, phyte- plant) on other plants, particularly on the trunks and branches of trees. When growing on other plants, lichens are not parasites; they do not consume any part of the plant, or kill it.

Lichens are sensitive to environmental pollutants, and have been used as “indicator organisms” in studies on environmental pollution. They are also important pioneer species; they are usually one of the first eukaryotic organisms to colonize disturbed ecosystems in the process of succession. To read more about pioneer species and ecological succession, read the Biomes, Ecosystems, and Communities chapter.

The European Space Agency has discovered that lichens can survive unprotected in space. In an experiment, two species of lichen – Rhizocarpongeographicum and Xanthoriaelegans, shown in Figure 4 (see FlexBook) – were sealed in a capsule and launched on a Russian Soyuz rocket on May 31, 2005. Once in orbit the capsules were opened and the lichens were exposed directly to the vacuum of space as well as to the large temperature changes and cosmic radiation of open space. After 15 days the lichens were brought back to Earth and were found to be alive, and did not have any observable damage.

Questions

1. What does the fungus gain in a mycorrhiza?

2. What is the advantage to a mycorrhizal plant of the mycorrhizal mycelia having a smaller diameter than the plant’s root?

3. In a lichen, the photobiont is usually which of two organisms?

4. Why can lichens grow in locations impossible for most plants?

5. How is it known that lichens are important pioneer species?