Seed Plants: Gymnosperms & Angiosperms Dr. Wendy Sera Lone Star College—University Park Biology 1409 Lab 6

Figure 19.1A—The evolution of plants involves these significant innovations. common ancestor megaphylls microphylls seeds flowers, double fertilization, endosperm, fruit Flowering plants Gymnosperms Ferns and allies Mosses Lycophytes Hornworts Vascular Nonvascular Seedless Bryophytes Seed Liverworts Charophytes PRESENT common green algal ancestor embryo protection apical growth vascular tissue Million Years Ago (MYA)

Plants have an alternation-of-generations life cycle  Two multicellular individuals alternate, each producing the other.  The sporophyte is the diploid (2n) generation.  It produces spores by meiosis.  A spore is a haploid (n) reproductive cell that develops into a new organism without needing to fuse with another reproductive cell.  A spore undergoes mitosis to become a gametophyte.  The gametophyte is the haploid (n) generation.  It produces gametes.  In plants, eggs and sperm are produced by mitosis.  A sperm and egg fuse, forming a diploid (2n) zygote that undergoes mitosis and becomes the sporophyte.

Alternations of Generations zygote (2n) Sporophyte (2n) spore (n) Gametophyte (n) (n) (n) gametes Mitosis sporangium (2n) diploid (2n) haploid (n) MEIOSISFERTILIZATION

Plants have an alternation-of-generations life cycle  Plants differ as to which generation is dominant (more conspicuous).  Sporophyte dominance was adaptive to a dry land environment.  Only the sporophyte ever has vascular tissue.  Only plants with a dominant sporophyte attain significant height.

The size of the gametophyte is progressively reduced as the sporophyte becomes more dominant. Moss Fern Gymnosperm Angiosperm roots rhizoids G a m e t o p h y t e (n) S p o r o p h y t e (2n) seed spores rhizoids

Seed Plants  Evolution of the seed was the next significant innovation in the evolution of plants.  Gymnosperms and angiosperms are seed plants.  A seed contains a sporophyte generation, along with stored food, within a protective seed coat.  The ability of seeds to survive harsh conditions largely accounts for the dominance of seed plants today.

Most gymnosperms bear cones on which the seeds are “naked”  Diversity of gymnosperms:  There are four groups of living gymnosperms: cycads, ginkgoes, gnetophytes, and conifers.  All have ovules and develop seeds that are exposed on the surface of cone scales or analogous structures.  Conifers  Consist of about 575 tree species  Many are evergreens such as pines, spruces, firs, cedars, and hemlocks.  Wood of conifers is used extensively in construction.

Gymnosperm diversity.

Pine life cycle Pollen sac Seed stored food seed coat zygote seed wing Sporophyte pollen cone scale Seed cones seed cone scale Pollen cones sperm pollen tube egg Mature female gametophyte Pollen grain Pollination Megaspores Microspores pollen grain Megaspores: Megaspore mother cell in ovule undergoes meiosis to produce megaspores.One megaspore will become the egg-producing The pollen grain: The pollen grain has two wings and is carried by the wind to the seed cone during pollination Mature male gametophyte 200 µm MEIOSIS Ovule Mitosis haploid (n) diploid (2n) FERTILIZATION The sporophyte embryo:After fertilization, the ovule matures and becomes the seed composed of the embryo, reserve food, and a seed coat. Finally, in the fall of the second season, the seed cone, by now woody and hard, opens to release winged seeds. When a seed germinates, the sporophyte sporophyte embryo Fertilization: Once a pollen grain reaches a seed cone, it becomes a mature male gametophyte. A pollen tube digests its way slowly toward a female gametophyte and discharges nonflagellated sperm. The fertilized egg is a zygote. ovule wall megaspore mother cell microspore mother cell The pollen cones: Typically, the pollen cones are quite small and develop near the tips of lower branches. The seed cones: The seed cones are larger than the pollen cones and are located near the tips of higher branches. Microspores: Microspore mother cells undergo meiosis to produce microspores. Each microspore becomes a pollen grain. Figure 19.6B

Pine Life Cycle

Carboniferous Forests Became the Coal We Use Today  Our industrial society runs on fossil fuels such as coal.  During the Carboniferous period (>300 MYA), a great swamp forest encompassed what is now northern Europe, the Ukraine, and the Appalachian Mountains in the United States.  Enormous amount of biomass  Remains became covered by sediment that changed to sedimentary rock  With pressure, the organic material became coal.

Swamp forest of the Carboniferous period. early gymnosperm club mosses horsetail seed fern fern Fossil seed fern

Angiosperms have flowers in which the seeds are “covered”  Angiosperms are flowering plants.  Evolved some 200 MYA  Innovations are flower and fruit  240,000 known species  Ovules always enclosed within sporophyte tissue  Cotyledons are seed leaves with nutrients that nourish the embryo.  Monocotyledons (or monocots) – one cotyledon  Eudicotyledons (or eudicots) – two cotyledons

Plants have a sexual life cycle called alternation of generations  Flowers are unique to angiosperms  Produce spores, protect gametophyte, attract pollinator, produce fruits  Major factor in success of flowering plants  Typical flower  Four whorls of modified leaves attached to receptacle at end of stalk (peduncle): 1.Sepals – protect bud 2.Petals – corolla 3.Stamens – anther and filament 4.Carpel – stigma, style and ovary

carpel stamen anther filament petal sepal receptacle stigma style ovary ovule Anatomy of a flower.

a. Daylilies are monocots. Monocots have flower parts usually in 3’s. b. Azaleas are eudicots. Eudicots have flower parts in 4’s or 5’s.

Alternation of generations in flowering plants mitosis diploid (2n) haploid (n) seed zygote sporophyte ovary ovule FERTILIZATION egg Female gametophyte (embryo sac) Male gametophyte (pollen grain) anther 3 4 microspore MEIOSIS megaspore sperm

Fertilization in Flowering Plants (Angiosperms) 19-19

Pollination and fertilization bring gametes together during sexual reproduction  Double fertilization is unique in angiosperms  Results in not only zygote, but also food source for developing zygote  Endosperm – nutritive tissue developing embryonic sporophyte uses as energy source  Mature seed contains: 1.Embryo 2.Stored food – endosperm  Cotyledons – seed leaves take up endosperm in eudicots 3.Seed coat – develops from ovule wall

The parts of a bean seed, a eudicot. Embryo Seed coat immature leaves hypocotyl Cotyledon (stored food) radicle

Seed Development in Flowering Plants (Angiosperms) 19-22

Fruit Development in Flowering Plants (Angiosperms) 19-23