The life cycle of
How does this life
cycle compare with your own? Where do meiosis and syngamy occur in
the life cycle of vertebrates, or of some brown algae (e.g. Fucus)?
for an image of Fucus from the University of British Columbia. Images of Fucus male
gametangia are also available. What components of the plant life cycle
shown at the left are missing in the vertebrate life cycle? For more information
on life cycles, as well as stimulating ideas about their evolution, see
Plants are distinguished
from the other kingdoms of living things by photosynthetic energy capture,
multicellularity, as well as by their common life cycle with
of spore- and gamete-producing generations (sporophyte, gametophyte,
- sporic meiosis,
in contrast to gametic meiosis, as in life cycle of vertebrates
Evidence from biochemistry
strongly suggests that the life cycle shown here was inherited from green
algae (such as Ulva, mentioned in class as an example of an isomorphic alternation of
Life cycle terminology
and related notes
- The gametophyte
is the gamete-producing plant, or stage of the life cycle.
- The sporophyte
is the spore-producing plant, or stage of the life cycle.
- Spores and
gametes are both single cells, but they are differ in how they
function. A spore develops into a new individual following germination.
A gamete functions only by fusing with another gamete of the
opposite mating type to form a zygote (the single-celled product
of gamete fusion).
- Development of
the sporophyte from a zygote involves production of an embryo (hence
the name "Embryophyta"),
i.e. an immature stage of the sporophyte that is nutritionally dependent
on and (or) enclosed by gametophyte tissue.
- Separation of plants
into pigeonholes (Bryophyta, Pteridophyta, seed plants,
etc.) is based to a considerable extent on the increasing degree to
which the sporophyte is the dominant phase of the life cycle, with:
- presence of
- increased stature,
independence from the gametophyte;
- more complex
organization (stem, leaves, roots);
- shift from
dispersal via spores to dispersal of embryo sporophytes (seeds);
- enclosure of
embryos in increasingly complex sporophytic structures (fruits)
so as to maximize dispersal and establishment.
- So as to evoke
the extent of the shift from a dominant gametophyte to a dominant sporophyte,
a moss gametophyte may be compared with pollen grains of a flowering
plant (e.g. ragweed or other Asteraceae); although the latter may consist
of only two or three nuclei these are equivalent to the moss in having
developed from a spore and in giving rise to (male) gametes.
are plant families? | How do we distinguish
them? | How and why do we study them? |
Selected vascular plant families of Ontario
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last updated 14-Sep-2008
2008 Department of Ecology & Evolutionary Biology and 2000-2006 Botany Department, University of Toronto.