Lab 10 Plant Evolution and Adaptations

Plant Evolution

• Lab activities involve answering questions and sketching organisms/structures on a worksheet.
• Drawings should indicate important structures with labels, as images support studying for lab exams.

Introduction to Plant Kingdom

• Kingdom Plantae belongs to Domain Eukarya and Supergroup Archaeplastida.
• Charophytes, specifically Chara, are the closest living relatives to land plants.
• Charophyte algae inhabit shallow waters, which are subject to occasional drying.
• Selective pressure favors individuals of charophytes able to withstand periods out of water, leading to terrestrial plants.
• The terrestrial habitat had sunlight, increased CO2, and soil nutrients.
• Plants adapted to land by overcoming gravity and preventing desiccation.
• Cuticle: Is a waterproof coating found in land plants that prevents water loss.
• Stomata: These are tiny pores that extend across the cuticle that open and close for gas exchange and water conservation.
• Vascular tissue: It evolved and is composed of cells forming tubes for water and nutrient transport.
• Land plants are autotrophic, have cellulose cell walls, and exhibit a sporic life cycle involving alternation of generations.
• Alternation of generations involves a gametophyte and a sporophyte stage.
• Gametophytes produce sperm in antheridia and eggs in archegonia.
• Sporophytes produce spores in sporangia.
• Animals have diploid adults that produce haploid gametes, which are unicellular and short lived, from gamete production until fertilization.
• Plants have alternating multicellular life stages: a haploid gametophyte and a diploid sporophyte.
• In ancient plant lineages like mosses and liverworts the haploid phase is dominant, while in ferns, gymnosperms and flowering plants the diploid stage is dominant.
• Bryophytes are nonvascular plants that lack vascular tissues, and transport materials via cell-to-cell diffusion.
• Vascular plants possess specialized cylindrical cells for transporting water, minerals, and dissolved foods.
• Xylem transports water and minerals, while phloem transports carbohydrates in solution.
• Vascular plants are larger than bryophytes due to their specialized transport/support systems.
• Vascular plants include ferns, gymnosperms, and angiosperms

Classification of Living Plants

• Bryophytes (nonvascular plants) are a paraphyletic group, including:
  • Phylum Hepatophyta (Liverworts, Marchantia)
  • Phylum Anthocerophyta (Hornworts)
  • Phylum Bryophyta (Mosses, Polytrichum, Mnium)
• Vascular Plants are a monophyletic group, including:
• Seedless Vascular Plants (paraphyletic)
  • Phylum Lycophyta (Club Mosses, Spike Mosses, Quillworts)
  • Phylum Monilophyta (Whisk Ferns, Horsetails, Ferns)
• Seed Plants (monophyletic)
  • Gymnosperms
    • Phylum Ginkgophyta (Ginkgo or Maidenhair Tree)
    • Phylum Cycadophyta (Cycads)
    • Phylum Gnetophyta (Mormon Tea, Welwitschia)
    • Phylum Coniferophyta (Conifers)
  • Angiosperms
    • Phylum Anthophyta (Flowering Plants)

Bryophyte Study

• Bryophyta and Hepatophyta are two nonvascular plant phyla to study.
• "Bryophyte" is an informal term for mosses, liverworts, and hornworts, while "Phylum Bryophyta" is a formal term for mosses only.

Polytrichum Examination

• The leafy plant is the gametophyte, with male and female gametophytes.
• Male gametophytes have leaves forming a cup containing antheridia, structures that produce sperm.
• Sperm is released and swim towards a female archegonium to fertilize the egg.
• The zygote develops into an embryo or young sporophyte rising of out the archegonium.
• The archegonium's top may tear off forming a calyptra that caps the capsule on the sporophyte and lacks cup shaped leaves.

Antheridia and Archegonia

• Study male (antheridia-bearing) plants of Polytrichum and female (archegonia-bearing) plants of Mnium using prepared slides.
• Antheridia: Elongate and oval shaped with sterile jacket cells producing spermatogenous tissue that produces sperm cells, and paraphyses are support structures.
• Archegonia: Flask-shaped with a swollen base containing the egg, and an elongate neck with neck canal cells.
• The neck canal cells disintegrate leading to a neck canal, they creates a path for sperm to fertilize the egg.

Polytrichum Sporophyte

• Examine a mature sporophyte of Polytrichum and identify the calyptra, operculum, and peristome teeth.
• The operculum is a lid, while peristome teeth form the peristome that aids spore dispersal.

Hepatophyta - Liverworts

• In Marchantia, the sporophyte is retained on a female gametophyte structure called an archegoniophore that resembles a palm tree.
• Flagellated sperm is released in the presence of moisture that swim to the archegoniophore.
• Lunularia cruciata is called the crescent-cup liverwort because of crescent shaped gemma cups on the dorsal surface.
• Marchantia has round gemma cups in contrast to Lunularia.
• Gemmae are asexual, haploid tissues that will develop into independent gametophytes and disperse by rain.

Monilophyta - Seedless Vascular Plants

• Phylum Monilophyta includes whisk ferns, horsetails, and ferns.
• Seed plants evolved from monilophyte ancestors.
• Fern sporophytes produce spores that grow into gametophytes, which produce eggs and sperm.
• Water is required for sperm to swim to the egg for reproduction
• Sori, are clusters of sporangia on the undersides of fern fronds that produce clusters of sporangia.

Fern Gametophytes

• A fern gametophyte is bisexual, tiny, and heart-shaped.
• Gametangia are gamete-producing structures such as antheridia and archegonia located at the top ventral surface with rhizoids below the gametangia.
• Archegonia (egg producing) are small, dark, and are crowded just beneath the apical notch.
• Antheridia (sperm producing) are round, lighter in color and contain spermatogenous cells.

Seed Plant Characteristics

• Multicellular gametophytes have few cells and are found completely within the sporophyte, dependent on it for nutrients.
• Their megaspore is produced inside an integument-wrapped megasporangium called the ovule.
• Male gametophytes are pollen that develops from microspores that produce egg .
• A seed results from fertilization where a zygote grows into an embryo (young sporophyte).
• The embryo is wrapped in tissue layers, with outer layers forming a protective seed coat and better protection against desiccation.
• Pollen eliminates water requirement for reproduction.
• Gymnosperms: the ovule rests exposed on an ovuliferous scale.
• Angiosperms: the ovule is enclosed in sporophyte tissues.

Cycadophyta - Cycads

• Cycads: ancient plants with flagellated sperm, that resemble palm trees or tree ferns producing ovules/seeds or pollen bearing large cones.
• Each female cone scale produces two large seeds after pollination/fertilization.
• Cycads are slow-growing, rare, and found in tropical regions, known in the fossil record during the reign of dinosaurs.

Ginkgophyta - Ginkgo biloba

• Herbal supplement called Ginkgo biloba extract derives from seeds and improves memory function.
• The Ginkgo or maidenhair tree is the sole representative of Ginkgophyta.
• The plant is a heavily branched tree bearing distinctive fan-shaped leaves.
• Male trees bear small cones that produce pollen.
• Female trees bear many stalked pairs of ovules rather than female cones, which have flagellated sperm.

Coniferophyta - Conifers

• Conifers: woody plants like pines, spruces, hemlocks, junipers, redwoods, and firs.
• Conifers bear needle-like leaves and woody or papery cones.
• A pine tree produces two kinds of cones (strobili) with a central axis bearing spirally-arranged spore-bearing scales.
• Male/pollen cones are smaller and produce pollen.
• Female/seed cones are larger and produce eggs, developing seeds, with sac-like microsporangia arranged on the scales' surfaces.
• Scales, or microsporophylls, are attached spirally to the cone axis.
• Microsporangia produce microspores through mitotic division that develop into pollen grains.
• Pollen grains have "ears"

Pinus Reproduction

• Pollen grains are released at the end of May.
• Seed cones open, and pollen sifts down through the cone scales.
• Pollen lies in the chamber at the base of the micropyle (tiny hole in the ovule wall).
• Pollen grains germinate, producing a pollen tube with male gametes, which digests its way to the archegonium for fertilization.
• Fertilization: Takes place as long as thirteen months with the seed with its embryo (young sporophyte) maturing until late summer in the year after pollination.
• Female cones have, ovuliferous scales, with an ovule attached to its upper surface.
• The ovule has an inner layer of the megasporangium surrounded by the integument that surrounds the megasporangium, except for the micropyle.

Angiosperm Characteristics

• Angiosperms have ovules enclosed in ovary wall tissues.
• The ovary wall becomes the fruit containing the seeds.
• Angiosperms are successful plants with diploid sporophytes which bear the flowers.
• Haploid gametophyte is reduced to a pollen grain or an embryo sac within the ovule.
• A flower is a modified stem bearing modified leaves that attracts insects for pollination.
• Flowers and insects have a mutualistic relationship, where insects pollinate and receive pollen/nectar.
• Flowers share certain features such as circles or whorls, with the outermost being the calyx, which is composed of sepals.
• The next whorl, corolla, is composed of petals that attract pollinators.
• The third whorl is the androecium, which is composed of stamens with a pollen-bearing anther at the end of the filament.
• The innermost whorl is the gynoecium consisting of carpels or pistils, with the swollen base being the ovary containing ovules.
• The ovary will develop into the fruit, and ovules will develop into seeds.
• The stigma is the tip of the carpel that collects pollen grains leading to the style.
• The pollen grains germinate on the stigma and form a pollen tube that extends toward a micropyle.
• Two sperm nuclei: One unites with the egg to produce the zygote, and the second unites with another cell which will produce the endosperm.
• The endosperm serves as the food source for the developing embryo with double fertilization involved.
• One produces a zygote and the other producing nutritive endosperm.
• Flowers, fruits, and the endosperm are unique to angiosperms.
• Two common lineages of angiosperms are monocots and eudicots.
• Monocots: grains, grasses, lilies, palms, and orchids.
• Eudicots: oaks, maples, roses, and beans.

Flower structure

• calyx: collective term for sepals
• corolla: collective term for petals
• androecium: collective term referring to the male parts or stamens
• gynoecium: gynoecium (a collective term referring to the female parts or carpels/pistils

Monocot and Eudicot Comparison

• Monocot: one cotyledon (seed leaf) per embryo, flower parts in threes, parallel venation, one pollen grain aperture, multiple rings of vascular bundles in stem.
• Eudicot: Two cotyledons (seed leaves) per embryo, flower parts in fours/fives, net-like venation, three/more pollen grain apertures, one ring of vascular bundles in the stem.
• Monocot means "One cotyledon", and Eudicot means "two cotyledons".
• A cotyledon is the first leaf produced by the embryo and stores food that then expands.
• A seed develops from the ovule containing the embryo and endosperm.
• A fruit is the mature ripened ovary containing the seeds that serves as protection and seed dispersal.
• Fruits are dry with a hard wall to release seeds, or fleshy.