Biology 102 Chapter 30
The Evolution of Seed Plants
1. Define seed and list those groups of plants that produce
seed.
---seed is fertilized, ripened ovule of gymnosperm or angiosperm
---seed consists of embryo, food supply, and seed coat
2. Explain how each of the following is significant in the
progression from nonseed to the seed plants which are the
dominant plants on Earth today.
TERRESTRIAL HABITAT
---support
---water supply (access/conservation) and nutrients
---solving the “hanky-panky” problem
SIZE AND DEPENDENCY OF GAMETOPHYTE/SPOROPHYTE
---let’s review the proposed evolutionary scheme once more
---Bryophytes have dominant gametophyte and reduced sporophyte
--sporophyte dependent on gametophyte
---ferns have dominant sporophyte and reduced gametophyte
--are nutritionally independent of each other
---gymnosperms have dominant sporophyte and further reduced
gametophyte
---angiosperms have even further reduced gametophyte
---in seed plants, gametophyte nutritionally dependent on
sporophyte
HOMOSPOROUS VS. HETEROSPOROUS
---homosporous plant produces single type spore that develop
into single type gametophyte that bears both male and female
reproductive organs
---heterosporous plant produces two distinct types of spore
--megaspore develops into larger female gametophyte (mega)
--microspore develops into smaller male gametophyte (micro)
---Bryophyta is homosporous
---most ferns are homosporous (always exceptions)
---seed plants (gymno/angio) are heterosporous
SPORES AS MEANS OF DISPERSAL
---spore (haploid reproductive structure) shed for dispersal by
mosses and ferns
---seed plants retain the megaspore and female gametophyte
develops within megasporangia and depend on sporophyte for
food and water
---microsporangium produces male gametophyte (pollen), which is
distributed by wind, insect, bird, plant breeder, etc.
--pollen grain that reaches appropriate surface, develops
further
MECHANISM BY WHICH SPERM REACHES THE EGG
---mosses and ferns still dependent on moisture for sperm to
swim to egg
---seed plants depend on pollen (male gametophyte) dispersal
--appropriate location, pollen grain grows pollen tube
--when tip of tube reaches megagametophyte, two sperm
are released
3. Explain the difference between:
POLLINATION AND FERTILIZATION
---pollination is transfer of pollen to appropriate structure
--ovule/carpel/pistil
---fertilization is union of sperm and egg to produce single
cell called zygote
---time for an Estesism
CONES, FLOWERS, AND FRUITS
---cone is axis bearing tight cluster of scales or leaves
specialized for reproduction
---flower is total reproductive structure of angiosperms
--Dr. Richard’s favorite was “modified leaf with carpels”
---fruit is a ripened and mature ovary (or groups of ovaries)
--sometimes applied to reproductive structures of other
groups of plants
NAKED SEED AND COVERED SEED
---gymnosperms are said to have “naked seeds”
---ovules and seeds are NOT protected by flower or fruit tissue
---angiosperms are said to have covered seeds
---ovary of flowering plant (with seeds it contains) develops
into fruit after fertilization
--hence, the term “covered seeds”
4. Describe the life cycle of a pine tree.
---pollen falls onto ovulate cone and enters ovule through
micropyle
---germinates in ovule, forms pollen tube that digests its
way through nucellus
---megaspore mother cells undergoes meiosis = 4 haploid
megaspores (one survives)
--it grows and divides repeatedly by mitosis = immature
female gametophyte
---2 or 3 archegonia, each with egg, develop within
multicellular gametophyte
---after 1 year = eggs ready for fertilization, 2 sperm
cells have developed & pollen tube has grown through
nucellus to female gametophyte
---fertilization occurs when one sperm nuclei unites with
the egg nucleus
--all eggs in ovule may be fertilized, but only one
zygote develops into an embryo (usually)
---pine embryo (new sporophyte) has rudimentary root and
several embryonic leaves
--embedded in female gametophyte
--nourishes the embryo until capable of photosynthesis
---ovule has developed into pine seed
--embryo (2n), food source (n), surrounding seed coat
(2n)
---scales of ovulate cone separate (about 1 more year), and
winged seeds are carried by wind (usually) to new
locations
5. Describe the structure of pollen and seed cones and
distinguish between the two.
---multicellular gametophyte generation is reduced &
develops from haploid spores that are retained within
sporangia
---male gametophyte is the pollen grain (no antheridium)
---female gametophyte consists of multicellular nutritive
tissue and an archegonium that develops within an ovule
---conifer life cycles are heterosporous
--male and female gametes develop from different types
of spores produced by separate cones
---pollen cones have microsporangia
--cells undergo meiosis = haploid microspores
--these small spores develop into pollen grains
--pollen grains = male gametophyte
---ovulate cones have megasporangia
--cells here undergo meiosis = large megaspores that
develop into the female gametophyte
---each ovule initially includes a megasporangium
(nucellus) enclosed in protective integuments
--has single opening called micropyle
6. Identify the parts of a flower and describe a function for
each.
---chalk talk time on flowers
7. Distinguish between perfect and imperfect flowers.
---flower containing both male and female reproductive parts is
called “perfect”
--has both megasporangia and microsporangia
---flower with only megasporangia OR microsporangia called
“imperfect”
--either stamens or carpels nonfunctional or absent in
given flower
8. Distinguish between monoecious and dioecious flowering
plants.
---monoecious means “one-housed”
--megasporangiate and microsporangiate flowers occur on
same plant (corn/birch)
---dioecious means “two-housed”
--given plants produces either flowers with stamens or
flowers with pistils but NEVER both
--willows, date palms, and wacky-backy