Lab 5 Plant Diversity 2: Seed Plants
September 20, 2011
Seed: A seed consists of an embryo and food supply surrounded by a
protective coat. Seed provide a number of advantages. They are able to
resist harsh conditions and persist for long times in the environment. These
features allow for greater dispersal.
In seed plants the gametophytes are more reduced and the Gametophytes
now retained in sporangia
All seed plants are heterosporous. That is they produce microspores and
megaspores which develop into the male and female gametophytes.
Integument: The female gametophyte is surrounded by a protective layer
of sporophyte tissue called the integument. This layer develops into the seed
coat. The female gametophyte remains inside the sporophyte tissue for it
entire lifecycle.
Pollen: The microspore develops into a pollen grain which consists of a
male gametophyte enclosed in a pollen wall. These are able to survive in
the environment and be transported to another plant by either wind or by
an animal pollinator. When pollen germinates, it grows a pollen tube which
transports the sperm inside the plant ovule. These sperm no longer require
flagella, however they are retained in a few gymnosperms.
Gymnosperm: Gymnosperm means naked seed. This group consists of
plants that have no seed coverings.
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Refer to your text book to study the lifecycle of a gymnosperm. Make
sure to note that the seed coat is diploid, the embryo is diploid, and that the
food source is haploid.
Gymnosperm Phyla
• Cycandophyta
– These plants have large cones, palm like leaves.
– 130 know species left
• Ginkophyta
– This phylum has only one extant (surviving) species, Ginko biloba
(the ginko tree).
• Gnetophyta
– This group has about 35 extant species.
– Ephedra (Morman tea) is an example. The compound ephedrine
is used in some cold medicines.
• Coniferophyta
– This group includes about 600 species. It contains the pines,
spruces, cedars, and others.
Angiosperms: Angiosperm means covered seed. These are the plants with
fruits and flowers. They are the most abundant and diverse group of plants
today. Flowers are structures for sexual reproduction. Many have features
for the attraction of animal pollinators. Fruits protect the seeds and many
have features to aid in their dispersal. You should be able to label the parts
of the flower shown on the figure below.
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Cotyledons: Angiosperm embryos have one or two cotyledons or seed
leaves. These cotyledons store food for the embryo but to not do photosynthesis. Plants have been traditionally grouped by the number of cotyledons
that the embryo possesses. Monocots have embryos with one cotyledon. Dicots have two cotyledons. Dicots are not a monophyletic group and have now
been broken into the groups: Eudicots, Magnoliids, and Basal Angiosperms.
There are several features that differ between eudicots and monocots. You
should be familiar with the traits below to distinguish between a eudicot and
a monocot.
Embryos
Leaves
Stems
Roots
Pollen
Flowers
Monocots
1 cotyledon
parallel veins
vascular tissue scattered
fibrous root system
pollen grain with one opening
organs in multiples of 3
Eudicots
2 cotyledons
netted veins
vascular tissue in rings
tap root
pollen grain with 3 openings
organs in multiples of 4 or 5
For Your Quiz:
• Know the life cycles of gymnosperms and angiosperms
• Be able to label the parts of a flower
• Know the characteristics of Monocots and Eudicots
• Be able to list the 4 phyla of gymnosperms
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