This document discusses the physiology of fungi. It covers their nutrition and metabolism, noting that most fungi are saprophytes that feed through absorption after excreting enzymes to break down food. It also discusses fungal growth, noting the four basic phases and factors like nutrients, temperature, and pH that influence it. The document outlines both asexual and sexual reproduction in fungi. Asexual reproduction occurs through mechanisms like fission, budding, and spore production. Sexual reproduction involves the fusion of compatible nuclei through various processes like gamete fusion or gametangial contact and copulation.

1. 3.1. Nutrition and metabolism
3.2. Reproduction
3.3. Growth
3.4. The physical environment and growth
 Unit -4. Fungal Physiology

2. Nutrition and Metabolism
• Most fungi are saprophytes.
• live as decomposers and symbionts.
• Excrete Exoenzymes, powerful hydrolytic enzymes, break down
food----into simpler compounds----absorb and use.
• Fungi feed by absorption of nutrients.
• Parasitic fungi absorb nutrients from the cells of living hosts.
• Glycogen is the primary storage polysaccharide.
• Most are aerobic.
• can use a variety of carbon sources to derive cellular energy.
• Simple molecules (e.g., glucose) easily diffuse through the
membrane/cell wall.

3. Nutrition and Metabolism cont.
• Soluble carbohydrates must enter hyphae by diffusion, and
this is followed by active uptake across the fungal
membrane.
• Most fungal carbohydrate metabolism is via glycolysis and
the tricarboxylic acid cycle.

4. Mineral requirements
Biogeochemical Cycles -The flow of chemical
elements and compounds between living organisms
and the physical environment.

5. 3.3. Growth
• Hyph al Growth- predominantly grow by the process of hyphal chain
elongation (e.g., elongation at the tip, also called apical growth) and
branching.
• NB: The length of a hyphal chain depends on the growth environment. If
left undisturbed, as on an agar surface, the chain can become quite
long.

6. Figure 6.14
There are four basic phases of growth.

7. 3.4. The physical environment and growth
• The concentration and available nutrients in the
medium, temperature , pH, oxygen and osmotic
potential are determines the growth of fungi.

8. Reproduction
Asexual reproduction-occurs by several mechanisms.
• Fission / Transverse fission.
• Budding.
• Direct spore production.
• Hyphal fragmentation-component cells behave as
arthrospores or chlamydiospores and oidia (if enveloped
in thick cell wall before separation).
• Sporangiospores are produced in sporangium (sac) at
the end of an aerial hypha (sporangiophore).
• Conidiospores are unenclosed spores produced at the tip
or on the sides of aerial hypha.
• Blastospores are produced when a vegetative cell buds
off.

9. Budding
Fission

12. Sexual reproduction
• Involves the union of compatible nuclei.
• Some fungi are self-fertilizing (male and female gametes produced
on the same mycelium (homothallic/ monoecious), while others
require outcrossing between different but sexually compatible
mycelia (heterothallic).
• Zygote formation proceeds by one of several mechanisms.
• Fusion of gametes .
• Fusion of gamete-producing bodies (gametangia) .
• Fusion of hyphae .
• Sometimes there is immediate fusion of nuclei and cytoplasm;
however, more common is a delayed fusion of nuclei, resulting in the
formation of a cell with two haploid nuclei (dikaryotic stage).
• Zygotes can develop into spores (zygospores, ascospores, or
basidiospores); spores are used for identification purposes and
also aid fungal dissemination.
Conti.

13. Sexual fusion in fungi is of different types, as follows
A. PLANOGAMETIC COPULATION
. Here motile gametes called planogametes undergo
fusion.
•

14. B. GAMETANGIAL CONTACT
• Here, gamete bearing structures called gametangia come
closer to each other and develop a fertilisation tube through
which the male gamete migrates into the female
gametangium.
• Eg. : Phytophthora infestans-potato blight, British,1845;ireland,
obligate parasite, cellulase, haustorium.

15. C. GAMETANGIAL COPULATION - the gametangia fuse with each
other, lose their identity and develop into a zygospore.
Eg.: Mucor, Rhizopus

16. D. SPERMATISATION- In some fungi like Puccinia, tiny unicellular spore like
structures called spermatia are formed. They get transferred to female
gametangia through various agencies.
E. SOMATOGAMY-In examples like Agaricus, fusion occurs between two
somatic cells and involves only plasmogamy. This results in the formation of
dikaryotic hyphae. Hence, the process is called dikaryotization.