Fungi Evolution and
Diversity
Grade 10
Term 3
Fungi
 There are 100,000 species of fungi at
the moment but mycologists
(scientists who study fungi) think
there are many more.
 Fungi are mostly multicellular
eukaryotes.
 Fungi are saprotrophs – they send out
enzymes that break down dead and
decaying organic matter. Nutrients
are then absorbed by the fungi.
 Figure 10.1 shows how the 6 groups of fungi are related.
 Microsporidia and chytrids are single-celled.
 Chytrids are aquatic and have flagellated spores and gametes.
Evolution of
Fungi
 Zygospore fungi, sac fungi and club fungi have similar structures.
 Protists evolved 1.5 billion years ago.
 Animals and plants are descendent from these but animals show
more recent links.
 Animals and fungi from the super group Opisthokonta are more
closely related to each other than to plants.
 It is thought that they share an aquatic, flagellated, single-celled
ancestor.
 Multicellular forms came later after animals and fungi divided into
different groups.
 Fungi don’t fossilize‫ تتحجر‬well so it is harder to date their
evolution.
 The earliest fungi fossil found is 460 million years old but we think
fungi may be older than that.
 Mycorrhizae are evident in plant fossils.
 Mycorrhizae are fungus that grow on plant roots.
 It is thought that fungi were so successful because of adaptive
radiation when organisms began to colonise the land.
 Some fungi are single-celled.
Example: yeast.‫خميرة‬
 Most are multicellular.
Structure of
Fungi
 The body of most fungi are
known as mycelium (fungus
filaments).
 The mycelium is made up of
filaments called hyphae (web).
 This structure allows a high
surface-to-volume ratio which
maximizes the absorption of
nutrients.
 Hyphae‫ خيط فطري‬grow from their tips.
 Some have septa‫ حاجز‬which are walls that break
the hyphae into cells.
 Fungi with septa are called septate.
 Pores in the septa allow cytoplasm and some
organelles pass through from one cell to another.
 Septa that separate reproductive cells are nonporous.‫غير قابل لإلختراق‬
 Aseptate fungi ‫الفطريات المطهرة‬are not divided into
cells and have many nuclei in one hyphae.
 Some hyphae can ‫اخترق‬penetrate/break through
rigid‫ جامد‬substances like plant tissue.
 When a fungus reproduces, a specific part becomes a reproductive
structure and the rest of the mycelium nourishes/feeds it.
 Fungal cells don’t have chloroplasts.
 They have a cell wall made of chitin.
 Chitin is made of glucose microfibrils and each glucose has a
nitrogen-containing amino acid attached.
 Chitin is also found in insects and crustacea so it shows the link to
animals.
 Fungi store energy as glycogen which is the same as animals.
 Except for chytrids, fungi are not motile as they lack basal bodies
and flagella.
 They find food by growing hyphae – hyphae can grow up to 1 km a
day.
 Fungi reproduce both sexually and asexually.
 Sexual reproduction of terrestrial‫ نبات‬fungi occurs in 3 stages.
 Hyphae from 2 different mating fungi make contact and fuse.
 This can happen immediately or take months or years.
Reproduction
of Fungi
 The nuclei divide until every cell in the hyphae has one of each
nuclei.
 A hyphae with paired haploid nuclei is called dikaryotic.
 The nucleus fuse and the zygote undergoes meiosis before spore
formation.
 Fungi usually produce nonmotile spores that are windblown – this
ensures the offspring are spread to new locations.
 Spores are produced during sexual and
asexual reproduction.
 Spores are reproductive cells that
develop into new organisms without
needing to fuse with another
reproductive cell.
 Large mushrooms can produce billions
of spores in a few days.
 When the spore lands on a food
source, it germinates and grows.
 Asexual reproduction usually occurs
when spores are produced by a
specialized part of the mycelium.
 It can also occur by fragmentation and
by budding.