Early atomphere is rich in hydrogen, sulphur and nitrogen, until the evolution of photosynthetic
organisms that were capable to of:
2. Releasing oxygen in the process
A protective layer ozone began to form to protecing the terrestrial life from the ultraviolet rays of the
Photosynthesis, through the release of oxygen into the atmosphere, created a more hospitable
Major groups: bryophytes t lack trie vascular tissues
Tracheophyte t have treu roots, stems and leaves as well as vasular tissues.
Both groups lifecycle consists of an alternation between a diploid sporophyte generation and a haploid
Design of plant body compromise of 2 parts t requirement of photosynthesis (max surface area to
absorb light energy and carbon dioxide) and the requirement of reducing the evaporation of water (min
Part of the Descendant species adapt to new habitate, result in two different species t divergent
Some unrelated groups evolved into similar afaptations t converggent evolution
Plant attract the pollinator t two catrgories of attractants; primary and secondary
Primary attractants t satisfy a physiological demand t eg. Feeding
Secondary attractant t used to draw the pollinators attention to thw presence of the primary attractant.
Both primary and secondary attractants must work together for pollinator to occur.
Evolution of flower and pollinator t ist generalists pollinator, flower small and simple t then, more
effective pollinator, flower evolve to attract pollinator t now, specilists pollinators, flowers adapt to
attract certain pollinators.
Evolution trends towards flower specialization include the reduction in the number of floral part , and a
change from radical to bi lateral symmetry.
Some vertabrates can be pollinators as well t birds, bats, rodents~
On eof the most diverse group of plants
Small simple plants
Commonly found in moist environments
Lacking true leaves, stems or roots
Must absorb water for water transport t the life cycle of bryophytes requires an external source of
Fertilization reaquies water so that sperms can swim to eggs
Alternation of generation t haploid gametophyte is the dominant
Diploid sporophyte is short lived and is physically attached to and nutritionally dependent on the
Sex organs develop at the tips of a gametophyte: the antheridium contaion motile spetm
Archegonium contains a single egg cell! When they both moistented -- they ruputre and release the
sperm and the egg t the sperm will swim to the archrgonium and fertilize the egg t grow a sporophyte
and will arrached to the gamtophyte until its spores have been dispersed t then it dies, it has a stalk and
a sporangium which containing the spores t the spores will grow into new game tophytes and the life
cycle is repeated