Evolution of multicellular plants
Evolution of a multicellular
organism from a unicellular protist
Fig 16.27
Going from unicellular to multicellular
Going from unicellular to
multicellular
Advantages
Organization and specialization of plant parts
Permanent colonization of land becomes possible
Disadvantages
Loss of mobility – evolution of specialized plant parts
is essential for nutrition and reproduction
Reduction in individual plant growth rate
Challenges
“Communication” between cells
The development of tissue systems
Photos of slime moulds by Clive Shirley
Organisms with both unicellular and multicellular stages
Photos of slime moulds
http://www.hiddenforest.co.nz/slime/intro.htm
Slime moulds have structural adaptations and life cycles
that enhance their ecological role as decomposers
Slime moulds have structural adaptations
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.
Characteristics of Dictyostelium
Up to 100,000 cells signal each other by releasing a chemoattractant 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 celltype regulation are common to Dictyostelium and metazoans.
A model organism for bio-medical research.
Alternation of Generations
Alternation of Generations
Origin of alternation of generations?
Relative sizes and general morphology of
gametophyte and sporophyte generations in
bryophytes, ferns and seed plants
Sizes and morphology of generations
The life cycle of Ulva
The life cycle of Ulva
Fig 16.26C
Evolution of a multicellular
organism from a unicellular protist
Fig 16.27
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