Kingdoms Protista & Fungi Ch. 17

The Origin of Eukaryotic Cells Eukaryotic cells appeared first around 1.7 billion years ago eukaryotic cells possess an internal structure called a nucleus

The Origin of Eukaryotic Cells The endosymbiotic theory is a widely accepted explanation for the origin of mitochondria and chloroplasts in eukaryotes from bacteria present-day mitochondria and chloroplasts still contain their own DNA this DNA is remarkably similar in size and character to the DNA of bacteria

The theory of Endosymbiosis

The Evolution of Sex A profound difference between prokaryotes and eukaryotes is that eukaryotes have the capacity for sexual reproduction sexual reproduction involves two parents contributing gametes to form the offspring gametes are usually formed by meiosis and are haploid the resulting offspring are diploid But sexual reproduction is not the only way that eukaryotes can reproduce many eukaryotes reproduce by asexual reproduction, which is reproduction without forming gametes the offspring of asexual reproduction are genetically identical to the parents many eukaryotes reproduce mainly by asexual reproduction, switching to sexual reproduction only during environmental stress

The Evolution of Sex A different asexual strategy in eukaryotes is parthenogenesis, the development of an adult from an unfertilized egg Many plants and marine fishes undergo a form of sexual reproduction that does not involve partners this is called self-fertilization and involves one individual providing both male and female gametes

The Evolution of Sex Sexual reproduction is one of the most important evolutionary innovations of eukaryotes it provides a means of shuffling genes, creating genetic diversity genetic diversity is the raw material of evolution the greater the genetic diversity, the more rapid the evolutionary pace

General Biology of Protists, the Most Ancient Eukaryotes Protists are eukaryotes united on the basis of a single negative characteristic they are not fungi, plants, or animals in all other respects, they are highly variable with no uniting features

Figure 20.5 A unicellular protist

Figure 20.8 The major protist clades

A Diverse Kingdom Euglenozoa: Euglenoids Euglena is a representative euglenoid two flagella contractile vacuole to help regulate the osmotic pressure within the organism a light-sensitive stigma which helps this photosynthetic form find light asexual reproduction Figure 20.9 Euglena

A Diverse Kingdom Stramenopila: Brown algae (phylum Phaeophyta) are the longest, fastest-growing, and most photosynthetically productive living things all are multicellular and most are marine their life cycle has alternating generations Figure 20.11(a) Brown algae

A Diverse Kingdom Stramenopila: Diatoms (phylum Chrysophyta) photosynthetic encased by unique double wall of silica abundant in both oceans and freshwater habitats Figure 20.11b Diatoms Fossilized deposits of diatom shells are mined as “diatomaceous earth.”

A Diverse Kingdom Alveolata: Ciliates (phylum Ciliophora) Complex and unicellular possess large numbers of cilia have a defined cell shape and two nuclei per cell the pellicle is a proteinaceous scaffold, found inside the plasma membrane, that confers flexible support asexual reproduction is by fission while sexual reproduction is by conjugation Figure 20.12 A ciliate

A Diverse Kingdom Alveolata: Dinoflagellates (phylum Pyrrhophyta) photosynthetic unicellular protists usually bear two flagella of unequal length a stiff outer coating of cellulose and silica, giving them unique shapes

Dinoflagellates

A Diverse Kingdom Alveolata: Dinoflagellates (continued…) some dinoflagellates produce bioluminescence or powerful toxins that cause “red tides” “red tides” are population explosions of these kinds of dinoflagellates Figure 20.14 Red tide

A Sporozoan Life cycle Plasmodium : malaria

Chapter 21 Fungi Invade the Land

A Fungus is Not a Plant The fungi are a distinct kingdom of organisms, comprising about 74,000 species mycologists are scientists who study fungi There are many significant differences between fungi and plants, including fungi are heterotrophs fungi have filamentous bodies fungi have nonmotile sperm fungi have cell walls made of chitin fungi have nuclear mitosis

A Fungus Is Not a Plant fungi exist mainly in the form of slender filaments called hyphae (singular, hypha) each hypha is basically a long string of cells different hypha can associate with each other to form much larger structures a mass of hyphae is called a mycelium the main body of a fungus is not a mushroom but the extensive network of fine hyphae that penetrate the soil, wood, or flesh in which the fungus is growing the mycelium may contain many meters of hyphae

Masses of hyphae form mycelia The dense interwoven mat you see here growing through leaves on a forest floor is a mycelium made up of microscopic hyphae.

A Fungus Is Not a Plant Fungal cells can intercommunicate because fungal cells are separated by incomplete septa (singular, septum) cytoplasm can flow freely among the cells of the hypha many nuclei may be connected together by the shared cytoplasm proteins synthesized throughout the hyphae can be carried to hyphal tips all parts of the fungal body are metabolically active

Figure 21.3 Septum and pore between cells in a hypha

Reproduction and Nutrition of Fungi Fungi reproduce both asexually and sexually all fungal nuclei, except for the zygote, are haploid often in sexual reproduction of fungi, different “mating types” must participate when two hyphae of different mating types come into contact, the hyphae fuse

Reproduction and Nutrition of Fungi Spores are a common means of reproduction among the fungi Spores are well suited to the needs of an organism anchored to one place Spores are small and light and remain suspended in the air for long periods of time and may be carried great distances When a spore lands in a suitable environment, it germinates and begins to divide, forming a new fungal hypha

Many fungi produce spores

Reproduction and Nutrition of Fungi All fungi perform external digestion they secrete digestive enzymes into their surroundings and then absorb back into their bodies any organic molecules many fungi are able to break down the cellulose in wood some fungi are carnivores for example, the oyster fungus attracts nematode worms and then feeds upon them

Figure 21.5 The oyster mushroom

Table 21.1 Fungi

Ecological Roles of Fungi Fungi, together with bacteria, are the principal decomposers in the biosphere Fungi are virtually the only organisms capable of breaking down lignin in wood Fungi, by breaking down substances, release critical building blocks from the bodies of dead organisms and make them available to other organisms

Fungi as Parasites Cause series plant and animal diseases Examples: Corn smut Mildew Wheat rust Cordyceps Cause some human disease Athletes foot Ringworm Thrush

Ecological Roles of Fungi Fungi often act as disease-causing organisms for both plants and animals

Ecological Roles of Fungi Fungi have many important commercial uses the manufacture of bread, beer, wine, cheese and soy sauce all depend on fungi many antibiotics are derived from fungi some fungi can be used to clean up toxic substances from the environment

Ecological Roles of Fungi Some fungi are edible, others contain poisonous toxins

Ecological Roles of Fungi Fungi are involved in a variety of intimate symbiotic associations with algae and plants the fungus contributes the ability to absorb minerals and other nutrients from the environment the photosynthesizer contributes the ability to use sunlight to power the building of organic molecules

Ecological Roles of Fungi Two kinds of mutualistic associations between fungi and autotrophic organisms are ecologically important mycorrhizae are symbiotic associations between fungi and the roots of plants lichens are symbiotic associations between fungi and either green algae or cyanobacteria

Ecological Roles of Fungi In most mycorrhizae, the fungal hyphae actually penetrate the outer cells of the plant root and extend far out into the soil these are called endomycorrhizae In some mycorrhizae, the fungal cells grow between but do not penetrate the roots these are called ectomycorrhizae

Figure 21.16 Endomycorrhizae and ectomycorrhizae

Ecological Roles of Fungi A lichen is a symbiotic association between a fungus and a photosynthetic partner most of the visible body of the lichen consists of its fungus, but interwoven between hyphal layers are cyanobacteria, green algae, or both lichens can invade harsh habitats but are sensitive to pollutants

Lichens growing on a rock