Lecture XIX: Decomposers

Question 1

What is a decomposer?

Answer 1

A decomposer is:

An organism that absorbs organic nutrients from detritus, non-living organic matter (e.g. dead organisms, fallen plant matter and wastes of living organisms).

Organic macromolecules are broken down, energy harvested and inorganic nutrients are returned back to the physical environment making them available for producers to reuse.

Decomposers are the recyclers of an ecosystem.

All are heterotrophic.

Question 2

What do Decomposers do?

Answer 2

Decomposers recycle nutrients in their ecosystem and, therefore their presence is essential. All other living organisms are dependent on them.
Decomposers convert macromolecules from organic matter
into :
Simpler inorganic molecules that are released into the physical environment: PO42-, SO42-, NH3 , CO2 , etc.

Question 3

3 organisms that are decomposers:

Answer 3

Fungi

Certain Bacteria

Certain Protists

Question 4

1. Fungi

Answer 4

A Eukaryotic kingdom

General Characteristics:
Unicellular (e.g. yeast) or multicellular (e.g. mushroom producing fungi, and molds)
Cell walls made of chitin (same as arthropod exoskeletons)
Usually make up most of the mass of decomposers in their environment.
Asexual and sexual reproduction

Question 5

Fungal Ancestry

Answer 5

Fungi and animals, when compared molecularly, are more similar than when compared with other eukaryotic kingdoms. They are believed to have shared a more recent common ancestor.

Question 6

Structure of Fungi

Answer 6

Structure:
Most are multicellular

Cells join together forming filaments called hyphae (sing. hypha).

Networks of hyphae are joined together underground called mycelium.

The mycelium in the ground and fruiting bodies (e.g. mushrooms) above ground are a continuous network of hyphae.

Question 7

Mycelium of Fungi

Answer 7

The subterranean mycelium makes up the majority of the fungal organism.

Adaptation is to maximize the absorptive surface area to take in nutrients from the organic matter being decomposed.

Consequently energy is invested in increasing hyphal length and degrees of branching.

Question 8

All fungi are heterotrophic

Answer 8

Fungi cannot produce their own chemical energy (food). They must obtain energy as well as carbon from other living organisms. Unlike consumers however, they acquire them through absorption.

Fungi secrete digestive enzymes into the physical environment around them.

Enzymes break down large organic molecules into smaller soluble ones that are then absorbed by the fungus.

Question 9

Reproduction of Fungi

Answer 9

Fungi can reproduce asexually or sexually.

They produce haploid spores which are released into the environment. Each spore can grow into a new hypha.

Question 10

Asexual reproduction of Fungi

Answer 10

The cells of fungi are haploid most of the time. When they reproduce asexually it is through mitotic cell division.

Question 11

Sexual Reproduction of Fungi

Answer 11

The gametes of most fungi look just like a regular hypha.

However, when these hyphae come in contact with those of a different mycelium (another individual) that is compatible they fuse together forming a diploid cell.

This diploid cell will undergo meiosis producing genetically unique haploid spores that are released into the environment.

Question 12

Fruiting Bodies in Fungi

Answer 12

Many fungi produce fruiting bodies to aid in the dispersal of their spores formed during sexual reproduction.

They grow out of the substrate that the mycelium lives in and are therefore more obvious to us.

Fruiting bodies are adapted to different modes of spore dispersal: wind, water, or by animals

Question 13

Types of Fungi:

Answer 13

Moulds

Yeast

Club Fungi (Mushrooms, bracket fungi and puff balls)

Pathogenic fungi (plant and animal)

Mutualistic fungi (Mycorrhizal, Animal, Lichin)

Question 14

Molds:

Answer 14

Multicellular

Grow on any moist organic matter: fruit, vegetation, wood, fabric etc…

Can be highly toxic, e.g. Aspergillus, affects respiratory and nervous system

Can be very beneficial. Used to make blue cheese. Some used to make antibiotics e.g. penicillin

Question 15

Yeast:

Answer 15

Unicellular Fungi

Live in environments rich in simple sugars, fruit surfaces, flowers, guts of some organisms etc..
Used to leaven bread and make alcoholic beverages by using their ability to ferment sugars which produces CO2 and alcohol.

Question 16

Club Fungi:Mushrooms, Puffballs, Bracket fungus

Answer 16

Produce large fruiting bodies.

Some are edible, many are highly toxic! Toxins when ingested can cause symptoms ranging from hallucination to liver failure.

Never eat a mushroom you can’t identify!

Question 17

Pathogenic Fungi

Answer 17

Pathogenic fungi absorb nutrients from living organisms rather than dead organic matter.

Between 10-50% of the world’s fruit harvest is lost annually due to fungus!

Other Examples:

Dutch Elm Disease: caused by a fungus transmitted by elm bark beetles.

Mountain Pine Disease: caused by a fungus transmitted by mountain pine beetles.

Question 18

Fungal Pathogens of Animals

Answer 18

Fungal pathogens of animals also occur. Human examples are yeast infections and ringworm (athletes foot).

White Nose Syndrome:
Fungal infection of bats first detected in 2006 in North America.

Mortality estimated at over 6 million bats.

3 species of cave hibernating bats in Canada are on the endangered species list due to this fungal infection.

Question 19

Mutualistic Fungi

Answer 19

Many fungi have evolved a mutually symbiotic relationship with another organism. They gain nutrients from this association and provide something in return.
Fungus-Plant (e.g. Mycorrhizal fungi)

Fungus-Animal (e.g. Leaf cutter ants)

Fungus-Algae or Cyanobacteria (e.g. Lichen)

Question 20

Mycorrhizal Fungi

Answer 20

Mycorrhizal fungi and plant roots form a physical relationship. The fungus is better at acquiring inorganic nutrients such as phosphate ions and minerals which it provides to the plant in exchange for organic nutrients such as carbohydrates.

Question 21

Lichen

Answer 21

A symbiotic association between fungus and a photosynthetic partner (cyanobacteria or algae)

The fungus makes up the main body of the lichen and provides a safe place for the photosynthetic partner to thrive (will not dry out).

Photosynthetic partner provides the fungus with organic nutrients.

Question 22

2. Certain Bacteria

Answer 22

Bacterial decomposers in soil:

May have a typical bacterial cell shape.

Actinomycetes a genus of bacteria is colonial and resemble fungi by having branching hyphal formations.

Question 23

Actinomycetes

Answer 23

A type of bacteria that was mistaken for a fungus originally because of its cell arrangement.

They share many characteristics with fungi:

Rod shaped cells join together to form filamentous and branching shapes called hyphae.

Hyphae join together to make a network called mycelium.

Very important decomposers in soil.

Give soil it’s earthy smell.

Question 24

3. Certain Protists

Answer 24

Specialized protists called slime molds and water molds are decomposers.

They were also mistaken originally for fungi, but this time due to their ability to produce fruiting bodies for reproduction.

Question 25

Slime Moulds

Answer 25

Type of amoeba

Solitary amoebas come together to form a slug like aggregate.

Question 26

Water Moulds

Answer 26

Cells arrange into hyphae.

Decomposers of dead algae and animals in freshwater lakes, ponds streams etc… and soil habitats.

Responsible for the potato blight in Ireland in the 1900’s.