#43
Chapter
– Plant
Reproduction
43.1 What Are the Basic Features of Plant Life Cycles?
43.2 How Is Reproduction in Seed Plants Adapted to Drier
Environments?
43.3 What is the Function and Structure of the Flower?
Terms to Know
• Haploid: having a single set of chromosomes
in each cell.
• Diploid: having two sets of chromosomes in
each cell.
• Mitosis: cell division, which produces two
genetically identical cells.
• Meiosis: reduction division, which produces
four haploid reproductive cells.
Plants and Animals
Plant Reproduction Animal Reproduction
Life cycle
Alternation of
generations
No alternation of
generations
Gametes
Haploid (n) gametes
Haploid gametes
Spores
Haploid (n) spores
No spores
Gametes made Haploid gametophyte,
by
by mitosis
Diploid organism, by
meiosis
Diploid sporophyte, by
Spores made by
meiosis
No spores
Asexual Reproduction
• Natural “cloning.” Genetically Identical.
• Fast, no mate required.
• Beneficial for plants that must compete for
scarce resources (Stable Environs).
• Part of a single plant divides by mitosis to give
rise to a new plants.
•
•
•
Spreading of runners (strawberries)
Production of bulbs (daffodils)
Sprouting of rhizomes (irises)
Sexual Reproduction
• Fusion of egg and sperm cells (haploid), from
meiosis, gamete formation and fertilization.
• May be limited to a certain season.
• Slower than asexual reproduction.
• Allows genetic mixing, increasing variability in
a population. Two parents give rise to
genetically variable offspring. Favored in
variable environments.
Alternate “Generations”
• All plant life cycles are characterized by alternating
of portions (haploid-to-diploid-to-haploid).
• Multicellular diploid plants (sporophytes) and
multicellular haploid plants (gametophytes) take turns
producing each other during the reproductive life
cycle.
• Sporophyte: diploid (2n), produce haploid spores
by meiosis.
• Gametophyte: haploid (n), produce gametes by
mitosis.
Life Cycle
Life Cycle
• Diploid sporophyte (spore-forming plant) produces
haploid spores by meiosis.
• Spore germinates (begins to grow and develop); divides
repeatedly by mitosis forming a haploid gametophyte
(gamete-forming plant).
• Gametophyte produces haploid sperm and eggs by
mitosis (gametes are produced at different times to
prevent self-fertilization).
Life Cycle
• Sperm and egg fuse to form a diploid zygote
(fertilized egg).
• Zygote undergoes repeated mitosis to form a new
diploid sporophyte plant.
Non-Flowering
Plants
• Mosses, ferns, and related plants have motile,
swimming sperm.
• Reproduction in these plants requires wet
conditions, and requires having male and
female parts close together.
• Living conditions, plant size, and genetic
mixing is limited.
Conifer Pollination
• Conifers (also non-flowering plants) have
reduced gametophytes.
• Male gametophyte is contained in a dry
pollen grain.
• Female gametophyte is a few cells inside of
the structures that become the seed.
Conifer Pollination
• Conifers are wind-pollinated plants.
• Chance allows some pollen to land on the
scales of female cones.
• Pollen germinates, grows a pollen tube into
the egg to allow sperm to fertilize the egg.
• Wind pollination is inefficient.
Pollen In-between
• Showy flowers are the
result of selection for more
efficient pollination
strategies.
• Flower parts are modified
leaves. Those that were
brightly colored attracted
insects in search of pollen.
• Pollen itself is a proteinrich food for insects. Some
plants offer other rewards,
such as nectar.
Seed Plant
Reproduction
•
43.2 How Is Reproduction in Seed Plants
Adapted to Drier Environments?
•
Seed plants (gymnosperms and angiosperms).
•
•
Gametophytes develop within sporophytes.
Reproduction can occur in dry habitats.
Seed Plant
Reproduction
•
Male gametophyte is surrounded by a protective
coat called a pollen grain.
•
The pollen grain encloses sperm cells in a
watertight packet that can be easily transported to
another plant.
•
Egg-producing female gametophyte remains moist
and protected within the sporophyte, and the pollen
grain ensures that the sperm are delivered directly
to the egg.
Seed Plant
Reproduction
•
The fertilized egg becomes enclosed in a droughtresistant seed.
•
Consists of an embryonic plant and a food
reserve encased within a protective outer coating.
•
May lie dormant up to years waiting for
conditions favorable for germination and growth.
Seed Plant
Reproduction
•
Non-flowering gymnosperms were the earliest seed
plants.
•
Gymnosperms bear male and female gametophytes
on separate cones.
•
Male cones release pollen grains that travel via wind
to female cones.