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Plant Classification

Terms

Angiosperm - A vascular flowering plant in which seeds are enclosed inside of protective ovaries.

Apical meristem - Regions located at the tips of roots and shoots, wherein cells undergo rapid mitotic division and allow for the vertical, primary growth of the plant.

Apoplast - The pathway from the root surface to the core by which water moves along cell walls and through intercellular spaces, bypassing the cells themselves.

Archegonium - The female sex organ of terrestrial plants; where egg cells are produced.

Bryophyte - A lower terrestrial plant (often a moss or liverwort) that lacks a vascular system and is dependent on environmental moisture for reproductive and nutritive functions.

Companion Cell - A cell, found in the phloem of vascular plants, that is closely associated with one or more sieve elements.

Cork Cambium - Along with vascular cambium a type of lateral meristem, the cork cambium is located just inside the cork (bark)covering of a woody stem. As the plant shoot or root grows in width, the cork cambium produces more cork to serve as protective covering for the plant.

Cotyledon - An leaf characteristic of angiosperm embryos; monocot embryos have one, and dicot embryos have two.

Cross-pollination - The process, occurring in most angiosperms, by which the male gametes of one plant (carried by pollen grains) fertilize the eggs of another.

Dicot - A flowering plant (angiosperm) that possesses two cotyledons during embryonic development.

Diploid - Having two sets of chromosomes, one from each parent.

Double Fertilization - The mechanism of angiosperm fertilization that involves the joining of haploid gametes to create a diploid zygote, and the simultaneous joining of a second sperm cell with a fusion nucleus to create a triploid nucleus (which becomes the endosperm).

Endosperm - A substance, formed from a triploid nucleus in angiosperm reproduction, that nourishes a developing embryo within a seed.

Epidermal - Refers to the cells that lie on the outer surface of an organism.

Fibrous Roots - A system of many small, branching roots (none of which predominates) that spread out in the top few centimeters of soil; characteristic of monocots.

Fusion Nucleus - The diploid product formed by the joining of the two polar nuclei in the angiosperm ovule.

Gamete - A haploid sex cell (either an egg or sperm cell); male and female gametes join during fertilization to create a diploid zygote.

Gametophyte - A haploid plant or plant structure that produces haploid gametes through mitosis.

Gemmae - Specialized liverwort cells that allow the plants to reproduce asexually; when broken off from the parent plant, these cells can grow independently into new gametophyte plants.

Gymnosperm - A vascular non-flowering plant (commonly known as a conifer) in which seeds are not protected by an ovary.

Haploid - Having only one set of chromosomes.

Heartwood - In contrast to sapwood, a term for the dead, clogged xylem cells near the center of a tree. Heartwood is the tree's main column of support.

Heterospory - The reproductive phenomenon, characteristic of gymnosperms and angiosperms, whereby spores of two distinct sexes are produced; these spores develop into sex-specific gametophytes.

Lateral Meristem - A term for the two types of tissue, vascular cambium and cork cambium. These tissues produce a vascular plant's secondary growth, which is a growth in width.

Megaspore - Female spore; gives rise to a female gametophyte.

Microspore - Male spore; gives rise to a male gametophyte.

Monocot - A flowering plant (angiosperm) that possesses one cotyledon during embryonic development.

Ovary - In plants, the protective structure that holds the ovules and surrounds the angiosperm seed; after fertilization, develops into a fruit.

Ovule - Structure that contains the female gametophyte and gametes; after fertilization, develops into a seed.

Phloem - Vascular tissue composed of cells (sieve elements and companion cells) that are living at maturity; transports the essential products of photosynthesis throughout the plant body.

Photosynthesis - The process by which plants and other autotrophic organisms convert light energy into vital organic materials.

Polar Nuclei - Two nuclei, contained within the same cell, that are created from the mitotic division of the megaspore during angiosperm reproduction. The Polar nuclei unite in the ovule to form a fusion nucleus, which gives rise to endosperm when fertilized.

Pollen Grain - The male gametophyte of gymnosperms and angiosperms.

Pollen Tube - The outgrowth of a pollen grain that creates a path through the female sex organ in order to penetrate to the egg cells.

Primary Growth - The vertical growth of the plant that takes place in the apical meristems.

Root - The part of a plant beneath the soil; responsible for collecting water and minerals from the soil, storing nutrients, and securing the plant to the ground.

Root Hair - An outgrowth of a plant root that provides an increased surface area for the absorption of water and dissolved minerals from the soil.

Sapwood - In contrast to heartwood, the part of a tree closer to the periphery that is comprised of the functioning xylem cells. It is important to remember that "functioning" xylem cells does not equate to "living" xylem cells. All xylem cells are dead at maturity.

Secondary Growth - A plant's growth in width, which takes place in the lateral meristems.

Self-pollination - The process by which the male gametes of a plant fertilize the eggs of the same plant.

Sieve Element - A living conductive cell of phloem.

Sporangium - The part of a plant where spores are produced.

Spore - Haploid cell from which a gametophyte is produced.

Sporophyte - A diploid plant or plant structure that produces haploid spores through meiosis.

Symplast - The pathway from the root surface to the root core, by which water enters the root hair membrane and travels through the cytoplasm of adjacent cells via channels that connect the contents of those cells.

Taproot - A single dominant root (often with several smaller secondary roots branching off of it) that extends deep into the soil; characteristic of dicots.

Tracheid - A conductile xylem cell characteristic of gymnosperms. They are longer and thinner than vessel elements, lower on the evolutionary ladder, and not quite as efficient in terms of transport.

Tracheophyte - A terrestrial plant with a vascular system.

Triploid - Having three sets of chromosomes.

Vascular Cambium - The lateral meristem located between the phloem and xylem in vasacular plants. On its inside surface, vascular cambium produces new xylem cells, on its outside new phloem cells.

Vessel Element - A conductile xylem cell characteristic of angiosperms. They are shorter and wider than a tracheid, higher on the evolutionary ladder, and more efficient in terms of transport.

Vascular System - Mechanism of internal water and nutrient transport, made up of the vascular tissues xylem and phloem, that is characteristic of tracheophytes.

Vascular Tissue - A conductive component (either xylem or phloem) of the system that transports food and nutrients throughout the plant body.

Xylem - Vascular tissue composed of cells (tracheids or vessel elements) that are dead at maturity; transports water and dissolved minerals upwards from the roots to the shoot.

Zygote - The diploid product of fertilization that develops into an embryo.

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