Biology 1020: Plant Diversity, Evolution, and Reproduction

Comprehensive vocabulary flashcards covering the evolutionary origins of land plants, alternation of generations, non-vascular plants, seedless vascular plants, gymnosperms, angiosperms, and protist outgroups based on Biology 1020 lectures.

Alternation of Generations

A reproductive life cycle characteristic of land plants in which a multicellular diploid stage ($\text{sporophyte}$) alternates with a multicellular haploid stage ($\text{gametophyte}$).

Sporic Meiosis

The life cycle mechanism where a multicellular diploid sporophyte produces haploid spores via meiosis within sporangia, which then divide mitotically to form a multicellular haploid gametophyte.

Gametic Meiosis

The sexual life cycle typical of animals in which diploid individuals undergo meiosis to produce haploid gametes directly, fusing at fertilization with no intervening multicellular haploid phase.

Zygotic Meiosis

The sexual life cycle common in fungi and some algae in which the diploid zygote immediately undergoes meiosis to produce haploid cells, with no multicellular diploid phase.

Sporopollenin

A highly durable chemical polymer that encases and protects plant spores and pollen grains from desiccation, physical damage, and microbial decay.

Embryophytes

A formal designation for land plants (Kingdom Plantae) highlighting that the multicellular diploid embryo is retained within and nourished by maternal tissues.

Phragmoplast

A specialized cytoskeletal structure consisting of microtubules and microfilaments that directs cell plate assembly during cytokinesis in land plants and charophycean algae.

Archegonium

The multicellular female gametangium found in non-vascular plants, seedless vascular plants, and gymnosperms that produces and retains a single non-motile egg cell.

Antheridium

The multicellular male gametangium found in non-seed land plants that produces and releases flagellated sperm.

Sporocyte

A specialized diploid meiocyte cell ($2n$) located within a sporangium that divides by meiosis to produce four haploid spores ($n$).

Cooksonia

An extinct genus of primitive seedless vascular land plants from the Silurian to Early Devonian, characterized by simple dichotomous branching and terminal sporangia without leaves or roots.

Aglaophyton

An Early Devonian fossil plant transitional between bryophytes and true vascular plants that possessed water-conducting tubes lacking lignin-reinforced secondary walls.

Mixotroph

An organism that combines photosynthetic autotrophy and heterotrophic nutrition depending on environmental conditions and nutrient availability.

Choanoflagellates

A group of unicellular or colonial flagellated protists with a distinctive microvilli collar surrounding a flagellum, recognized as the sister group to animals.

Laminaria

A genus of large marine brown algae (kelp) within the Stramenopiles with an analogous plant-like body plan composed of a holdfast, stipe, and blade.

Volvox

A colonial freshwater green alga (Chlorophyta) forming a hollow spherical colony of biflagellated cells that often houses internal daughter colonies produced asexually.

Bryophytes vs. Bryophyta

The term bryophytes informally describes the paraphyletic grade of all non-vascular land plants (liverworts, mosses, hornworts), whereas Bryophyta is the formal taxonomic phylum restricted to mosses.

Peristome

A ring of specialized, interlocking teeth around the opening of a moss capsule (sporangium) that expands and contracts with humidity changes to regulate spore release.

Calyptra

A protective haploid ($n$) cap covering an immature moss capsule, derived from the upper portion of the maternal archegonium.

Seta

The elongated diploid ($2n$) stalk that supports the capsule and elevates it above the gametophyte in moss and liverwort sporophytes.

Microphylls vs. Megaphylls

Microphylls are small leaves with a single unbranched vascular vein unique to Lycophytes, whereas megaphylls are leaves with a complex, highly branched vascular system characteristic of Monilophytes and seed plants.

Sorus

A cluster of sporangia located on the abaxial (underside) surface of a fertile fern frond (sporophyll); plural form is sori.

Lignin

A complex, rigid organic polymer embedded in the secondary cell walls of tracheids and vessel elements that provides structural rigidity for upright plant growth.

Lycophyta

An extant phylum of seedless vascular plants consisting of club mosses, spike mosses, and quillworts, characterized by microphyll leaves and homospory or heterospory.

Monilophyta

The clade of seedless vascular plants comprising ferns, horsetails, and whisk ferns, characterized by megaphylls and recognized as the sister group to seed plants.

Ovule

A seed plant structure consisting of a megasporangium, megaspore, and one or two protective sporophytic integuments that matures into a seed after fertilization.

Pollen Grain

The microgametophyte (male gametophyte) of a seed plant enclosed within a tough, sporopollenin-coated wall, enabling water-independent dispersal of male gametes.

Gymnosperm Seed Development Stages

The chronological maturation progression shown: Stage C (unfertilized ovule), Stage B (fertilized ovule with growing pollen tube), and Stage A (mature gymnosperm seed containing an embryo).

Gymnosperm Seed Generations

The three distinct generations present in a gymnosperm seed: the maternal sporophyte seed coat ($2n$), the nutritive female gametophyte tissue ($n$), and the new sporophyte embryo ($2n$).

Archaeopteris

An extinct Devonian progymnosperm tree that combined gymnosperm-like woody anatomy (Callixylon wood) with seedless, spore-bearing reproduction.

Heterospory

The production of two morphologically distinct types of spores: microspores that develop into male gametophytes and megaspores that develop into female gametophytes.

Homospory

The production of a single type of spore that germinates into a bisexual (hermaphroditic) gametophyte bearing both archegonia and antheridia.

Conifers

Cone-bearing gymnosperms belonging to phylum Coniferophyta; all conifers are gymnosperms, but not all gymnosperms are conifers.

Cycadophyta

An extant gymnosperm phylum with large compound leaves, prominent strobili, and ancestral flagellated sperm retained within the pollen tube.

Strobilus

A cone-like reproductive structure consisting of an axis surrounded by densely packed, modified sporangia-bearing leaves (sporophylls).

Anthophyta

The single taxonomic phylum encompassing all extant angiosperms (flowering plants), which originated in the Early Cretaceous approximately $140\text{ MYA}$.

Flower Whorls

The four concentric whorls of modified leaves forming a complete flower: calyx (sepals), corolla (petals), androecium (stamens), and gynoecium (carpels).

Double Fertilization

An angiosperm synapomorphy where one sperm nucleus fertilizes the egg to form a diploid zygote ($2n$) while the second sperm fuses with two polar nuclei to yield triploid endosperm ($3n$).

Endosperm

The triploid ($3n$) nutritive tissue in an angiosperm seed created through double fertilization to feed the developing embryo.

Embryo Sac

The mature multicellular megagametophyte of an angiosperm, formed through 3 rounds of mitotic division from a single surviving haploid megaspore to yield 7 cells and 8 nuclei.

Ragweed Pollen Grain

The microgametophyte of ragweed (shown in LM at $75\,\mu\text{m}$ and colorized SEM at $20\,\mu\text{m}$), featuring an extensively ornamented sporopollenin exine.

Dioecious vs. Monoecious

Dioecious species have separate male (staminate) and female (carpellate) individuals ('two houses'), while monoecious species bear male and female flowers (or hermaphroditic flowers) on the same individual plant ('one house').

Fruit

A ripened angiosperm ovary containing seeds that protects dormant seeds and aids in their wind, water, or animal dispersal.

Reduction of the Gametophyte

The evolutionary transition across land plant lineages from dominant, independent gametophytes in bryophytes to microscopic gametophytes dependent entirely on sporophyte tissues in seed plants (culminating in the 2-celled angiosperm pollen grain).