Asexual Reproduction in Multicellular Organisms > Spore Formation

A special reproductive structure formed by simple plants and fungi that germinates directly to form a new individual is called a spore.

Spores that possess flagella and are capable of movement in water are called motile spores or zoospores.

Spores that lack flagella and are incapable of movement are called non-motile spores.

Non-motile spores with a typical cell wall and without flagella are called aplanospores.

Asexual spores produced inside a sporangium are called sporangiospores.

Non-motile asexual spores produced externally and not inside a sporangium in many fungi are called conidia or conidiospores.

Spores are reproductive bodies that can develop into new organisms. In simple plants such as algae, spores may be motile or non-motile. In fungi, asexual spores commonly occur as sporangiospores or conidia.

• Seen in lower plants (algae) and fungi.
• It explains how many lower plants and fungi reproduce rapidly.
• A spore can be compared to a tiny, ready-to-grow reproductive particle - a miniature survival capsule that begins a new organism when conditions become suitable.

Spore Formation in Algae:

General features: Simple plants, such as algae, reproduce by specialised reproductive structures called spores. These may be:

• Motile spores are called zoospores.
• Non-motile spores, such as aplanospores and hypnospores.
• These spores germinate directly to form new individuals.

Chlamydomonas (Algae):

• The parent cell enters a reproductive phase under favourable conditions.
• The flagella are withdrawn, and the cell becomes non-motile.
• The protoplast divides longitudinally into 4 to 8 or more uninucleate parts within the parent cell wall.
• Each part develops a wall and flagella, becoming a zoospore (similar to the parent but smaller in size).
• Zoospores are released from the parent cell.
• Each zoospore increases in size and grows into a new individual.

Formation of zoospores in Chlamydomonas

Fungi commonly reproduce asexually by two major types of spores: sporangiospores and conidia.

(A) Sporangiospores:

• Formed inside a structure called a sporangium.
• In lower fungi (e.g., Pythium), they are motile and called zoospores - fungal zoospores lack a cell wall and possess one or two flagella.
• In members of Mucorales (e.g., Rhizopus), they are non-motile and called aplanospores - these have typical cell walls around them.
• The sporangiospore germinates by forming a germ tube to initiate the assimilatory phase of the fungus.

(B) Conidia (Conidiospores):

• Non-motile asexual spores are produced externally (exogenously) on specialised hyphae called conidiophores.
• They are not formed inside a sporangium.
• Common examples include Aspergillus and Penicillium.
• They help fungi reproduce and spread efficiently.

A-D. Asexual reproduction in fungi: A. liberation of zoospores from sporangium in Pythium; B. liberation of aplanospores in Rhizopus; C and D. conidia formation on conidiophore in Aspergillus and Penicilium, respectively

• A spore is a reproductive structure in simple plants and fungi that germinates directly into a new individual; it may be motile (zoospores) or non-motile (aplanospores).
• In algae like Chlamydomonas, the protoplast divides into 4–8 parts, each forming a zoospore that grows into a new individual.
• Fungi reproduce asexually by two spore types - sporangiospores and conidia.
• Sporangiospores form inside a sporangium: motile zoospores (e.g., Pythium) and non-motile aplanospores (e.g., Rhizopus).
• Conidia are non-motile spores formed externally on conidiophores, as in Aspergillus and Penicillium.