1. Lesson Overview Lesson OverviewFungi Lesson Overview 21.4 Fungi

2. Lesson Overview Lesson OverviewFungi What Are Fungi? Many fungi grow from the ground, but fungi aren’t plants. Instead of carrying out photosynthesis, fungi produce enzymes that digest food outside their bodies. Then they absorb the small molecules released by the enzymes. Many fungi feed by absorbing nutrients from decaying matter in the soil. Others live as parasites, absorbing nutrients from their hosts.

3. Lesson Overview Lesson OverviewFungi What Are Fungi? The cell walls of fungi are composed of chitin, a polymer made of modified sugars that is also found in the external skeletons of insects. The presence of chitin is one of several features that show fungi are more closely related to animals than to plants.

4. Lesson Overview Lesson OverviewFungi Structure and Function Yeasts are tiny fungi that live most of their lives as single cells. Mushrooms and other fungi, on the other hand, grow much larger. Their bodies are made up of cells that form long, slender branching filaments called hyphae.

5. Lesson Overview Lesson OverviewFungi Reproduction Fungi can reproduce asexually, primarily by releasing spores that are adapted to travel through air and water. Breaking off a hypha or budding off a cell can also serve as asexual reproduction.

6. Lesson Overview Lesson OverviewFungi Reproduction Most fungi can also reproduce sexually. The life cycle of the bread mold Rhizopus stolonifer is shown.

7. Lesson Overview Lesson OverviewFungi Diversity of Fungi More than 100,000 species of fungi are known. Biologists have placed fungi into several distinct groups. The major groups of fungi differ from one another in their reproductive structures.

8. Lesson Overview Lesson OverviewFungi Diversity of Fungi

9. Lesson Overview Lesson OverviewFungi Decomposition Many fungi feed by releasing digestive enzymes that break down leaves, fruit, and other organic material into simple molecules. These molecules then diffuse into the fungus. Many organisms remove important trace elements and nutrients from the soil. Fungi recycle these essential elements and nutrients. If these materials were not returned, the soil would quickly be depleted.

10. Lesson Overview Lesson OverviewFungi Plant Diseases A number of parasitic fungi cause diseases that threaten food crops. Corn smut, for example, destroys corn kernels. Some mildews, which infect a wide variety of plants, are also fungi.

11. Lesson Overview Lesson OverviewFungi Animal Diseases Fungal diseases also affect insects, frogs, and mammals.

12. Lesson Overview Lesson OverviewFungi Animal Diseases Parasitic fungi can also infect humans.

13. Lesson Overview Lesson OverviewFungi Lichens Lichens are extremely resistant to drought and cold. Therefore, they can grow in places where few other organisms can survive—on dry bare rock in deserts and on the tops of mountains.

14. Lesson Overview Lesson OverviewFungi Lichens Lichens are often the first organisms to enter barren environments, gradually breaking down the rocks on which they grow. In this way, lichens help in the early stages of soil formation. Lichens are also remarkably sensitive to air pollution: They are among the first organisms to be affected when air quality deteriorates.

15. Lesson Overview Lesson OverviewFungi Mycorrhizae The presence of mycorrhizae is essential for the growth of many plants. The seeds of orchids, for example, cannot germinate in the absence of mycorrhizal fungi. Many trees are unable to survive without fungal symbionts.