Plant Evolution, Diversity, and Reproduction

Comprehensive practice flashcards defining core vocabulary on serial endosymbiosis, protistan lineages, non-vascular bryophytes, seedless vascular plants, and seed plant anatomy from Biology tutorials 5, 6, and 7.

Serial Endosymbiosis

The evolutionary process explaining how eukaryotic cells arose from simpler prokaryotic organisms, wherein mitochondria and plastids descended from formerly free-living prokaryotes engulfed in sequential steps.

Primary Endosymbiosis ($1^\circ\text{ ES}$)

The engulfment of a photosynthetic cyanobacterium by a eukaryotic host cell to produce the first chloroplast (plastid); an event that occurred once in evolutionary history.

Secondary Endosymbiosis ($2^\circ\text{ ES}$)

The process wherein a non-photosynthetic eukaryotic cell engulfs a red or green alga that had already undergone primary endosymbiosis, giving rise to chloroplasts in various protist lineages multiple times independently.

Diatoms

Unicellular, non-motile photosynthetic stramenopiles characterized by a rigid silica cell wall that can withstand immense amounts of pressure.

Dinoflagellates

Alveolate protists reinforced with cellular plates that possess two flagella and are known for producing toxic red tides.

Sporic Meiosis (Alternation of Generations)

A life cycle in which a diploid ($2n$) sporophyte produces haploid ($n$) spores via meiosis, which mature into a multicellular haploid gametophyte via mitosis before producing gametes.

Gametic Meiosis

A life cycle in which meiosis produces haploid germ cells (egg and sperm) that unite in fertilization to form a diploid ($2n$) embryo, which develops into the mature organism via mitosis.

Zygotic Meiosis

A life cycle where the single-celled diploid ($2n$) zygote is the only diploid stage, undergoing meiosis immediately to produce haploid ($n$) cells that develop into a mature organism.

Phragmoplast

A plant cell division structure involved in cytokinesis, shared as an ancestral synapomorphy between charophytes and land plants (embryophytes).

Sporopollenin

A durable polymer that coats plant spores to protect them from desiccation and environmental damage within the sporangia.

Peristome

A specialized ring of tooth-like structures on the moss (Bryophyta) sporangium/capsule that opens and closes to control spore dispersal.

Operculum

The protective lid covering the opening of the moss capsule (sporangium) that detaches to expose the peristome and release spores.

Calyptra

A protective cap of haploid gametophyte tissue that encloses and shields the immature operculum and sporangium.

Archegoniophore and Antheridiophore

Umbrella-like gametophyte projections found in Hepatophyta (liverworts); archegoniophores bear female archegonia containing eggs, while antheridiophores bear male antheridia containing sperm.

Gemmae Cups

Cup-like asexual reproductive structures situated on the dorsal surface of liverwort (Hepatophyta) gametophytes that produce dispersing vegetative fragments called gemmae.

Microphylls

Small, spine-shaped leaves supported by a single unbranched strand of vascular tissue, unique to the Lycophyta lineage.

Megaphylls

Leaves with a highly branched vascular network of veins, found in Monilophyta and seed plants.

Homospory

Spore production in which a single type of spore develops from a sporangium to produce a typically bisexual gametophyte bearing both antheridia and archegonia.

Heterospory

Spore production characterized by two distinct types of spores: megaspores that yield female gametophytes and microspores that yield male gametophytes.

Sporocyte

A diploid ($2n$) spore mother cell located inside a sporangium that divides meiotically to produce haploid ($n$) spores.

Strobilus

A cone-like reproductive cluster composed of aggregated sporophylls (leaves that bear sporangia), found in lycophytes and gymnosperms.

Three Generations of a Seed

The tri-generational structure comprising the parent sporophyte ($2n$) seed coat, the female gametophyte ($n$) food reserve in gymnosperms, and the new sporophyte embryo ($2n$).

Gymnosperm Microgametophyte

A four-celled pollen grain consisting of a tube cell, a generative cell, and two sterile cells, developed within microsporangia on pollen cones.

Angiosperm Microgametophyte

A two-celled pollen grain consisting exclusively of a tube cell and a generative cell, developed within microsporangia located in anthers.

Embryo Sac

The reduced female gametophyte of angiosperms, typically consisting of seven cells (one egg cell, two synergids, three antipodal cells, and one central cell containing two polar nuclei).

Double Fertilization

An angiosperm reproductive mechanism where one sperm ($n$) fertilizes the egg ($n$) to form a zygote ($2n$), and a second sperm ($n$) unites with two polar nuclei ($2n$) to form triploid endosperm ($3n$).

Synergids

Two specialized cells flanking the egg cell in an angiosperm embryo sac that guide the pollen tube to the egg and are thought to represent remnants of the archegonium.

Ovule

A structure consisting of the integument(s), megasporangium (nucellus), and megasporocyte, which develops into a seed following fertilization.

Serial Endosymbiosis

The evolutionary theory explaining that eukaryotic mitochondria and plastids descended from formerly free-living prokaryotes engulfed in successive events and passed down through protist, animal, and plant lineages.

Primary Endosymbiosis

The evolutionary event occurring only once where a eukaryotic host engulfed a photosynthetic cyanobacterium, leading to the formation of the first chloroplast (plastid).

Secondary Endosymbiosis

The process occurring independently multiple times where a non-photosynthetic eukaryote engulfed a red or green alga that had already undergone primary endosymbiosis, retaining the plastid in a symbiotic relationship.

Diatoms

Unicellular, non-motile Stramenopiles with a silica cell wall capable of withstanding immense amounts of pressure.

Dinoflagellates

Alveolates with two flagella reinforced with cellular plates that are known to cause toxic red tides.

Gametic Meiosis

A life cycle in which meiosis directly produces the germ cells (egg and sperm), which unite during fertilization to form a diploid ($2n$) embryo that develops into a mature organism via mitosis.

Sporic Meiosis (Alternation of Generations)

A life cycle in which meiosis occurs within the diploid ($2n$) sporophyte to produce haploid ($n$) spores, which then divide by mitosis to form a haploid ($n$) gametophyte.

Zygotic Meiosis

A life cycle where the single-celled zygote is the only diploid ($2n$) stage, immediately undergoing meiosis to generate haploid ($n$) cells that form the mature organism.

Charophytes

A group of green algae that forms the sister taxon to Embryophytes (land plants), sharing rings of cellulose-synthesizing proteins, flagellated sperm structure, and phragmoplast formation.

Green Algae

A paraphyletic group of photosynthetic organisms that comprises Chlorophytes and Charophytes.

Bryophytes

Non-vascular land plants characterized by a dominant gametophyte generation, flagellated sperm requiring water for reproduction, lack of vascular tissue, and absence of true roots and leaves.

Hepatophyta

The phylum comprising liverworts, which feature a lobed and liver-shaped gametophyte, rhizoids only, gemmae cups, archegoniophores, antheridiophores, and an absence of stomata.

Archegoniophores and Antheridiophores

Umbrella-like gametophyte projections in liverworts (Hepatophyta); archegoniophores bear egg-containing archegonia, while antheridiophores bear sperm-containing antheridia.

Bryophyta

The phylum comprising true mosses, featuring a leafy gametophyte, an elevated sporophyte containing stomata, an operculum, a peristome, and a capsule.

Anthocerophyta

The phylum comprising hornworts, characterized by a dominant gametophyte, stomata, and a horn-shaped sporophyte.

Operculum

A cap or lid covering the sporangium (capsule) in mosses that opens to expose the peristome teeth for spore release.

Peristome

A specialized ring of tooth-like structures on the rim of the capsule in mosses (Bryophyta) that aids in spore dispersal.

Gemmae Cups

Cup-like asexual reproductive structures located on the gametophyte thallus of liverworts (Hepatophyta).

Homospory

The production of a single type of spore from a sporangium on a sporophyll, which typically grows into a bisexual gametophyte producing both eggs and sperm.

Heterospory

The production of two distinct types of spores: megaspores from megasporangia that become female gametophytes, and microspores from microsporangia that become male gametophytes.

Microphylls

Small leaves supported by a single unbranched strand of vascular tissue, unique to Lycophyta.

Megaphylls

Leaves with a highly branched vascular system, characteristic of Monilophyta and seed plants.

Strobili

Cone-like clusters composed of sporophylls (leaves bearing sporangia), found in Lycophyta and gymnosperms.

Monilophyta

Seedless vascular plants including ferns, exhibiting megaphylls (large fronds), a heart-shaped bisexual prothallus gametophyte, and sori with an annulus on the underside of fronds.

Ovule

A diploid ($2n$) seed plant structure consisting of a megasporangium (nucellus), a megaspore, and one or two integuments, which receives pollen through the micropyle and matures into a seed.

Ovuliferous Scale

A woody scale of a female gymnosperm cone that directly bears two ovules on its upper surface.

Carpel

The female reproductive organ of angiosperms enclosing one or more ovules inside an ovary, which later develops into a fruit.

Gymnosperm Microgametophyte

A pollen grain composed of four cells: one tube cell, one generative cell, and two sterile cells, retained inside pollen cones.

Angiosperm Microgametophyte

A pollen grain reduced to two cells: one tube cell and one generative cell, produced and retained in floral anthers.

Double Fertilization

A fertilization event unique to angiosperms in which one sperm ($n$) fertilizes the egg to produce a diploid ($2n$) zygote, while the other sperm ($n$) fuses with two polar nuclei ($2n$) to form a triploid ($3n$) endosperm.

Endosperm

A triploid ($3n$) nutritive tissue created by double fertilization in angiosperms that supplies nutrients to the developing embryo sporophyte.

Gymnosperm Seed

A seed containing three generations: a diploid ($2n$) embryo, a haploid ($n$) female gametophyte food reserve, and a diploid ($2n$) parent sporophyte seed coat.

Angiosperm Seed

A seed containing three generations: a diploid ($2n$) embryo, a triploid ($3n$) endosperm food reserve, and a diploid ($2n$) parent sporophyte seed coat.

Synergids

Two accessory cells flanking the egg inside the angiosperm embryo sac that attract and guide the pollen tube and sperm before disintegrating.

Micropyle

A pore opening in the integument(s) of an ovule through which the pollen tube or pollen grain enters to deliver sperm.