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?

Chapter #43 – Plant

Reproduction

• 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.

Terms to Know

Plant Reproduction

Animal Reproduction

Life cycleAlternation of generations

No alternation of generations

GametesHaploid (n)

gametesHaploid gametes

SporesHaploid (n)

sporesNo spores

Gametes made by

Haploid gametophyte, by

mitosis

Diploid organism, by meiosis

Spores made by

Diploid sporophyte, by

meiosisNo spores

Plants and Animals

• 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)

Asexual 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.

Sexual Reproduction

• 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.

Alternate “Generations”

Life Cycle

• Diploid sporophyte (spore-forming plant) produces haploid spores by meiosis.

Life Cycle

• 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).

• Sperm and egg fuse to form a diploid zygote (fertilized egg).

• Zygote undergoes repeated mitosis to form a new diploid sporophyte plant.

Life Cycle

• 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.

Non-Flowering Plants

• 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.

Conifer Pollination

• 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 protein-rich food for insects. Some plants offer other rewards, such as nectar.

Pollen In-between

• 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 drought-resistant 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.

Seed Plant Reproduction