Transcript LP-PartTwo - Warren`s Science Page


Gymnosperms: vascular seed bearing
plants with a naked seed coat
› No fruit around the seed
Conifers: seeds develop in a female
cone while male cones develop pollen
 Most are evergreens with needle or
scale-like leaves that have thick cuticles
 They make up the most abundant
(pines), tallest (redwoods), and oldest
(bristlecone pine) trees


Cycads: palm-like trees that flourished
during the Mesozoic era
› Only about 130 species still exist- confined to
tropics and subtropics
› They bear massive cone-shaped strobili that
produce either pollen (transferred by air
currents) or ovules

Ginkgos: reduced in
diversity from the
Mesozoic to only one
surviving species today
› Unusual in being
deciduous
› Hardy, showing resistance
to insects, disease, and
air pollutants
Bonsai Ginkgos

Gnetophytes: most unusual
gymnosperms
› Live in tropical and desert areas

The pine tree (sporophyte) produces two
kinds of cones
› Male cones produce sporangia that yield
microspores that develop into pollen grains
(male gametophyte)
› Female cones produce ovules that yield
megaspores (female gametophyte)
Pollination is the arrival of a pollen grain
on the female reproductive parts, after
which a pollen tube grows toward the
egg
 Fertilization, which is delayed for up to a
year, results in zygote that develops into
an embryo within the conifer seed


Angiosperms: vascular seed plants that
make flowers and fruits
› After fertilization, the ovule becomes the
seed and the ovary becomes the fruit

Most angiosperms develop rapidly and
produce seeds quicker than
gymnosperms

Development of the
flower lead to the
attraction of insects,
birds, and other
animals that helped
reproduction occur
rapidly
› Lead to a great deal of
coevolution in flower
development and
pollinators

When buffeted by severe environmental
challenges, the flowering plants did well
› Thanks to their protective seeds and help
from pollinators

Flowering plants arose from 3 lineages
and comprise a tremendous diversity

Three major groups:
1. Magnolids: include magnolias, avocados,
nutmeg and black pepper plants
2. Eudicots: include familiar shrubs, trees
(except conifers), and herbaceous plants
3. Monocots: include grasses, lilies, and major
food-crop grains
Magnolids
Eudicots
Monocots
The female gametophyte forms the
ovary
 Pollen forms inside stamens
 Pollination leads to double fertilization:
one sperm fertilizes the egg, the second
sperm fertilizes a cell that becomes the
endosperm
 Ovary tissue develops into the fruit that
covers the seeds
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Table 23.1
 Table 23.2
 Page 388
