botany

Viridiplantae

Clade including green algae and land plants; defined by chlorophyll a & b and green color.

Streptophytes

Clade including charophyte green algae and land plants; originated in freshwater; characterized by sporopollenin-coated spores and shared cell wall structure.

Embryophytes (land plants)

Land plants; characterized by protected embryos, stomata, waxy cuticle, UV-protective pigments, alternation of generations, meristems, and sporangia.

Tracheophytes (vascular plants)

Plants with vascular tissue (xylem and phloem) and true roots; sporophyte generation is dominant.

Spermatophytes (seed plants)

Seed-producing plants; gametophyte is reduced and protected inside the ovule; reproduce via pollen (no water needed for fertilization).

Angiosperms

Flowering plants; produce flowers and fruits; the most diverse group of land plants.

Alternation of generations

A life cycle alternating between a haploid gametophyte phase (produces gametes) and a diploid sporophyte phase (produces spores).

Sporophyte

The diploid phase of a plant's life cycle; undergoes meiosis to produce haploid spores.

Gametophyte

The haploid phase of a plant's life cycle; undergoes mitosis to produce gametes (sperm/egg).

Spore

A haploid, unicellular reproductive cell with high resistance; allows non-flowering plants to reproduce and disperse asexually.

Sporangium

A structure that produces and stores spores.

Archegonium

The female reproductive structure in non-vascular and some vascular plants; site of fertilization that produces and protects the egg.

Antheridium

The male reproductive structure in mosses and liverworts; stores and releases sperm into water to swim to eggs.

Mycorrhizae (incl. Arbuscular mycorrhizae)

A symbiotic relationship between fungi and plant roots; the fungus acts as an extended root system, increasing nutrient and water uptake and improving soil structure.

Mycoheterotrophy

A condition in which a plant obtains carbon and nutrients from fungi rather than through photosynthesis.

Haustorium

A specialized root-like structure of a parasitic plant that attaches to and penetrates the host's vascular system to extract nutrients.

Epiphyte

A plant that grows on another plant for physical support but is non-parasitic; absorbs water and nutrients from the air (e.g., orchids growing on trees).

Photosynthesis

The process by which plants convert light energy into chemical energy (sugars), using CO₂ and water.

Light reactions vs. dark reactions

Light reactions: occur in thylakoids, generate energy (ATP/NADPH). Dark reactions (Calvin cycle): occur in stroma, consume energy to fix carbon into sugar.

Photosystem

A protein complex containing chlorophyll that captures light energy for photosynthesis.

Chloroplast

Specialized organelle that is the site of photosynthesis; converts solar energy to chemical energy.

Thylakoid

Membrane structures inside the chloroplast that contain photosystems and help absorb light energy.

ATP / NADPH

Energy carriers in cells; ATP stores and transfers energy; NADPH carries electrons used in the Calvin cycle.

Chlorophyll

The green pigment in plants that absorbs light energy and drives photosynthesis.

Calvin Cycle

The "dark reactions" of photosynthesis; uses ATP and NADPH to convert CO₂ into sugar.

Rubisco

The enzyme in the Calvin cycle that fixes CO₂ into sugar; notoriously slow and inefficient, and can react with O₂ instead of CO₂ (causing photorespiration).

Photorespiration

A wasteful process in which Rubisco reacts with O₂ instead of CO₂; absorbs oxygen but produces no useful sugar, wasting energy.

CAM & C4 photosynthesis

Alternative photosynthetic pathways that reduce photorespiration and minimize water loss; adaptations to hot, dry, or low-CO₂ environments.

Auxin

A plant hormone that promotes cell elongation and controls directional growth (phototropism, gravitropism).

Gibberellic Acid

A plant hormone that stimulates stem elongation, seed germination, and flowering.

Abscisic Acid

A plant hormone that promotes dormancy, seed maturation, and stomatal closure in response to stress.

Cytokinins

Plant hormones that promote cell division and delay senescence.

Ethylene

A gaseous plant hormone that promotes fruit ripening and leaf/flower abscission.

Photoperiodism

A plant's ability to respond to the relative lengths of day and night (seasonal changes); regulates flowering and other developmental processes.

Senescence

The aging process in plant cells; can halt cell division in response to stressors or damage while the cell remains metabolically active.

Tannins

Defensive compounds in plants that reduce the digestibility of proteins, making plant tissue less palatable and slowing herbivore growth.

Latex

A defensive sap produced by some plants (e.g., dandelions, milkweed); often toxic to herbivores and seals plant wounds.

Escape & radiation (coevolution)

An escalating evolutionary "arms race" between plants and herbivores/pathogens, where new plant defenses drive new counter-adaptations, accelerating diversification in both.