Fungi

Page
2

plasma

membrane

Plant cell

Fungal hypha

Hyphae

25 µm

Slide 9

Fungi produce spores through sexual or asexual life cycles

Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually.

Fungal nuclei are normally haploid.

Sexual reproduction requires the fusion of hyphae from different mating types.

Fungi use sexual signaling molecules called pheromones to communicate their mating type.

Slide 10

Life Cycle of Fungi

Spores

Spore-producing

structures

GERMINATION

ASEXUAL

REPRODUCTION

Mycelium

Key

Heterokaryotic

(unfused nuclei from

different parents)

Haploid (n)

Diploid (2n)

SEXUAL

REPRODUCTION

KARYOGAMY

(fusion of nuclei)

PLASMOGAMY

(fusion of cytoplasm)

Heterokaryotic

stage

Zygote

2n

Spores

GERMINATION

MEIOSIS

Slide 11

Plasmogamy is the union of two parent hyphae, mycelia.

In most fungi, the haploid nuclei from each parent do not fuse right away; they coexist in the hyphae, this mycelium is called a heterokaryon.

In some fungi, the haploid nuclei pair off two to a cell; such a mycelium is dikaryotic.

During karyogamy, the haploid nuclei fuse, producing diploid cells: n + n = 2n.

Slide 12

Hours, days, or even centuries may pass before the occurrence of karyogamy, nuclear fusion.

The diploid phase is short-lived and undergoes meiosis, producing haploid spores.

Slide 13

Asexual Reproduction

In addition to sexual reproduction, many fungi can reproduce asexually.

Molds produce haploid spores by mitosis and form visible mycelia.

Other fungi that can reproduce asexually are yeasts, which inhabit moist environments.

Instead of producing spores, yeasts reproduce asexually by budding: simple cell division and pinching of “bud cells” from a parent cell.

Slide 14

Penicillium: a mold that decomposes food. Mold produce spores asexually by mitosis.

2.5 µm

Slide 15

The yeast Saccharomyces cerevisiae in several stages of asexual reproduction by budding.

10 µm

Parent

cell

Bud

Slide 16

Concept 31.3: The ancestor of fungi was an aquatic, single-celled, flagellated protist