Evolution of multicellular plants

Fig 16.27

Evolution of a multicellular organism from a unicellular protist

Going from unicellular to multicellular

Advantages

Disadvantages

Challenges

Going from unicellular to multicellular

“Communication” between cells

The development of tissue systems

Loss of mobility – evolution of specialized plant parts is essential for nutrition and reproduction

Organization and specialization of plant parts

Reduction in individual plant growth rate

Permanent colonization of land becomes possible

Photos of slime moulds

http://www.hiddenforest.co.nz/slime/intro.htm

Photos of slime moulds by Clive ShirleyOrganisms with both unicellular and multicellular stages

Slime moulds have structural adaptations

Slime moulds have structural adaptations and life cycles that enhance their ecological role as decomposers

Two main groups.1 - Plasmodial slime moulds or true slime moulds, are a large single-celled mass with thousands of nuclei called a plasmodium formed when individual flagellated cells swarm together and fuse into one large bag of cytoplasm with many diploid nuclei.

2 - Cellular slime moulds spend most of their lives as separate single-celled amoeboid protists, but upon the release of a chemical signal, individual cells aggregate into a great swarm, known as a pseudoplasmodia and eventually muticellular slugs.

http://www.wvonline.com/myxo/intro.htm

The life cycle of a cellular slime mold, Dictyostelium

The life cycle of a cellular slime mold, Dictyostelium

Film of Dictyostelium

Dictyostelium amoebae grow as separate, independent cells but interact to form multicellular structures when challenged by adverse conditions such as starvation.

Up to 100,000 cells signal each other by releasing a chemo-attractant and aggregate to form a mound.

Subsequent processes depend on cell-cell communication.

Many of the underlying molecular and cellular processes appear to have arisen in primitive precursor cells and to have remained fundamentally unchanged throughout evolution.

Basic processes of development such as differential cell sorting, pattern formation, stimulus-induced gene expression, and cell-type regulation are common to Dictyostelium and metazoans.

A model organism for bio-medical research.

Characteristics of Dictyostelium

Alternation of Generations

Alternation of Generations

Origin of alternation of generations?

Sizes and morphology of generations

Relative sizes and general morphology of gametophyte and sporophyte generations in bryophytes, ferns and seed plants

The life cycle of Ulva

Fig 16.26C

The life cycle of Ulva

Fig 16.27

Evolution of a multicellular organism from a unicellular protist

Sections you need to have read

16.21 16.22 16.23 16.24 16.25 16.26 16.27 16.28

Courses that deal with this topic

MICROM 435 Microbial Ecology