Glossary

The binomial system of plant names (based on Carl Linnaeus’ work) assigns a specific name to each species of plant and consists of genus (pl. genera) and species.

Example: Rosa rugosa (a type of rose). Genus: Rosa, species: rugosa. Another species: Rosa californica.

Abbreviation of species: sp. (pl. spp.). Sp. is sometimes used when a species is not defined.

Genera are grouped into families. Example: The Rose family (Rosaceae) includes numerous other plants aside from roses, all with certain common characteristics.

Plant families are grouped into orders.

Accessory pigments

Light-absorbing pigments that work in conjunction with chlorophyll.

Aerobic respiration

Respiration in the presence of plenty of oxygen, leading to the complete breakdown of sugars and other organic compounds into carbon dioxide and water.

Aglycon

The nonsugar portion of a glycoside.

Alkaloids

A large family of nitrogen-containing organic natural products with basic properties.

Allele

One of the two or more alternative forms of a gene.

Anaerobic respiration

Respiration in the absence of oxygen.

Anions

Negatively charged ions.

Anthocyanins

A large group of water-soluble phenolic plant pigments. A subgroup of flavonoids.

Antinutrients

Compounds that interfere with the absorption of nutrients.

Antioxidants

Molecules that inhibit the oxidation of other molecules by trapping radicals.

Aqueous

Dissolved in water.

Atomic number

The unique number of protons in the nucleus of each atom of an element (equal to the number of electrons in the neutral atom). Determines the position of an element in the periodic table.

Atoms

The smallest particle of an element that retains the chemical nature of the element.

Bases

Substances that produce an increase in the concentration of OH⁻ ions when dissolved in water. Opposite of acids.

Basic or alkaline

Producing hydroxide ions (OH⁻) when dissolved in water. Having a pH above 7.

Betalains

A family of nitrogen-containing plant pigments that are found only in specific plant families.

Biosynthesis

The biological synthesis of natural products.

C₃ plants

Plants that follow only the Calvin cycle, or C₃ pathway, in the fixation of CO₂; the first stable compound is a three-carbon compound. It is the most common pathway of CO₂ fixation.

C₄ plants

Plants in which the first product of CO₂ fixation is a four-carbon compound. It is a pathway common in plants originating from hot climates.

Calvin cycle

The series of light-independent photosynthetic reactions during which CO₂ from air is reduced to produce organic molecules in the form of simple sugars.

CAM plants (crassulacean acid metabolism)

A variant of the C₄ pathway, characteristic of most succulent plants, such as cacti.

Carbon skeleton

The carbon–carbon backbone of an organic molecule.

Cardenolides or cardiac glycosides

A group of steroid glycosides from plants that affect the activity of the heart muscle.

Carotenoids

A group of C₄₀ isoprenoid pigments.

Catalyst

A substance that increases the rate of a reaction without being used up in the process.

Cations

Positively charged ions.

Chiral

Asymmetric or “handed”.

Cis/trans isomers

Stereoisomers that differ in the positioning of atoms attached to a carbon–carbon double bond (or a ring).

Coagulate

To change to a solid or semisolid state, to form clots.

Coevolution

Close interaction between two or more organisms, like a plant and an insect, resulting in strong selective forces on each other and leading to evolutionary adaptations.

Cofactor

A nonprotein component that is required by enzymes in order to function.

Compound

A substance composed of two or more elements that are chemically combined in fixed proportions.

Condensed tannins

Large, complex phenolic molecules, providing dark pigments.

Conjugated double bonds

Alternating single bond–double bond sequences.

Coordinate covalent bond

A covalent bond formed when one atom donates both electrons for a bond. Common in metal–organic bonds.

Covalent bonds

Bonds formed by sharing of electrons between two atoms.

Cuticle

Waxy or fatty layer on outer wall of epidermal cells of leaves and stems.

Cyanogenic glycosides

A group of plant glycosides that release HCN when reacting with enzymes from neighboring plant cells.

Denaturation

Destruction of the original shape of a protein which makes it nonfunctioning.

Disaccharides

Carbohydrates consisting of two sugar units. An example is sucrose.

Dissociation

Separation into ions.

Diterpenes

Terpenes consisting of four isoprene units and thus having 20 carbon atoms.

Dye

A colorant, like a plant pigment, that can form bonds with a fiber like wool or cotton.

Electron configuration

The arrangement of electrons in defined energy levels around an atom's nucleus.

Electronegative

Having a tendency to attract electrons.

Electrons

Negatively charged particles, arranged in specific energy levels, occupying the space around an atom's nucleus.

Element

A substance composed of only one kind of atoms.

Enantiomers

Compounds that are mirror images of each other.

Endergonic

Describing a chemical reaction that requires energy to proceed.

Endothermic

Describing a chemical reaction that requires energy in the form of heat to proceed.

Enzyme

A biological catalyst.

Essential amino acid

An amino acid that is not produced by an organism and that has to be ingested through nutrition.

Essential oils

Volatile, fat-soluble plant oils (from the word “essence”).

Exergonic

Energy-yielding (as in chemical reactions).

Exothermic

Giving off energy in the form of heat.

Exudate

A fluid or sap that is formed as a response to injury.

Fermentation

The extraction of energy from organic compounds in the absence of oxygen.

Flavonoids

A large family of plant pigments with a common phenolic three-ring structure.

Functional groups

Attachments to the carbon skeleton that provide characteristic chemical properties to compounds.

Gene

A sequence of DNA nucleotides that codes for a protein, tRNA, or rRNA molecule, or regulates the transcription of such a sequence; a unit of heredity.

Genetic code

The system of triplets of nucleotides in DNA or RNA that determine the amino acid sequence in proteins.

Glucosinolates

A family of sulfur-containing, defensive plant glycosides.

Glycolysis

The breakdown of sugars during respiration.

Glycoside

A noncarbohydrate molecule that is bonded to a sugar.

Gum

Water-soluble plant exudates that consist of large carbohydrate structures, usually formed as a response to injury.

Herbivores

Organisms that feed on plants.

Hydrated

Surrounded by water molecules. Abbreviated as aq.

Hydrocarbons

Organic compounds consisting of hydrogen and carbon.

Hydrogen bonds

A chemical bond formed through the attraction between the partial positive charge on a hydrogen atom and the partial negative charge on a nearby oxygen or nitrogen atom.

Hydrolysis

Cleaving a molecule by reaction with water.

Hydrolyzable tannins

Water-soluble, phenolic plant compounds derived from gallic acid.

Hydrophilic

Having an affinity for water. (Opposite of hydrophobic.)

Hydrophobic

Water-repelling, fat-soluble.

Inorganic compounds

Compounds that do not contain carbon, as well as carbonic acid, carbon dioxide, carbon monoxide, carbonates, cyanides, and a few others.

Ion

A charged atom.

Ion-exchange

Exchange of one type of ion with another one.

Ionic bonds

Bonds between positively and negatively charged ions, formed due to electrostatic attraction.

Ionic compounds or salts

Compounds with ionic bonds.

Isomers

Molecules with the same molecular formula but with different structures.

Isoprene unit

Characteristic C₅ building block of terpenes.

Isoprenoids

Another name for terpenes.

Isotopes

Atoms of the same element, but with different numbers of neutrons.

Latex

A milky plant sap that contains rubber particles.

LD₅₀

Lethal dose that kills 50% of a population of test animals, like mice or rats; a measure of toxicity of a compound.

Light reactions

The reactions of photosynthesis that require light.

Lipid

Any nonpolar substance, found in biological systems, that is fat-soluble but insoluble in water.

Macronutrients

Inorganic chemical elements required in large amounts for plant growth, like nitrogen, potassium, and phosphorus.

Meso compounds

Compounds composed of molecules with several chiral centers, but have a symmetry in their molecules. Meso forms are not optically active.

Metabolism

The sum of all chemical reactions occurring in living organisms.

Metabolites

Compounds formed by living systems.

Metals

Elements that conduct heat and electricity well. Tend to form positive ions. Metals are found on the left-hand side of the solid dividing line in the periodic table.

Micronutrients

Essential inorganic chemical elements required only in trace amounts, such as iron, manganese, and zinc.

Mineral

An inorganic substance other than water. Usually an inorganic salt or its ions.

Molecular formula

A formula that shows the total number of atoms of each element in a molecule. Example: C₆H₁₂O₆.

Molecule

A particle consisting of two or more atoms joined by a chemical bond.

Monomers

The subunits that serve as building blocks in polymers.

Monosaccharides

The simplest carbohydrates or sugars, consisting of one sugar unit. Example: glucose.

Monoterpenes

Terpenes consisting of two isoprene units, and thus having 10 carbon atoms.

Mordant

A solution, usually of a metal salt, used to pretreat fibers before the dye process. Metal ions bond to the fiber and then also to the dye molecules.

Neurotransmitters

Natural chemical compounds that act as chemical messengers within the nervous system.

Neutrons

Neutral particles in the nucleus of an atom.

Nonmetal element

Element that lacks metallic properties. Found on the right-hand side of the solid dividing line in the Periodic Chart. Tends to form negative ions.

Nucleotides

The monomers of nucleic acids (DNA or RNA).

Orbitals

The three-dimensional spaces where electrons can be found about 90% of the time.

Organelle

Specialized subunit within a plant cell with a specific function. Examples: cell nucleus, chloroplast.

Organic compounds

Compounds that contain carbon in their structure. (For exceptions see “inorganic compounds”.)

Organo-metallic compounds

Compounds that have bonds between a metal ion and an organic portion of the molecule.

Osmosis

The diffusion of water across a selectively permeable membrane.

Oxidation

Reaction in which a compound or ion loses electrons. An oxidation has taken place if a compound has gained oxygen atoms or has lost hydrogen atoms.

Oxygenic (as in oxygenic photosynthesis)

Generating oxygen.

Peptide

A molecule that is made up of two to a couple of hundred amino acid monomers. Not as large as proteins.

pH

A measure that indicates how large the surplus of H⁺-ions or OH⁻-ions is in an aqueous solution. The pH-value is defined as the negative logarithm of the hydrogen ion concentration. The pH range extends from 0 to 14, with 7 being neutral.

Phenolics

Organic molecules that have phenolic rings, i.e. hydroxyl groups (OH) attached to an aromatic ring.

Phloem

The part of vascular tissues that transport sugars and other organic compounds in a plant.

Phospholipid

Phosphorylated lipid. Similar in structure to a fat, but with only two fatty acids attached to the glycerol backbone, and the third space occupied by a phosphorus-containing molecule. Phospholipids are important components of cellular membranes.

Phosphorylation

A reaction in which phosphate is added to a compound.

Pigment

A compound that absorbs a section of sunlight and traps this way energy for further reactions.

Polar compound

Compound consisting of molecules with an unequal distribution of charge.

Polymers

Giant molecules that consist of a large number of repeating subunits (monomers).

Polysaccharides

Polymeric carbohydrates. Examples: starch, cellulose.

Primary metabolites

Molecules that are found in all plant cells and that are necessary for plant life.

Products

Substances formed as the result of a chemical reaction.

Proteins

Polymers that consist of amino-acid monomers linked up by peptide bonds.

Protons

Subatomic particles in the atomic nucleus, each with one positive charge.

Racemic mixture

A mixture of equal amounts of two enantiomers.

Radicals

Atoms or molecules that have unpaired valence shell electrons.

Radioactivity

Emissions resulting from the spontaneous decay of unstable atomic nuclei.

Reactants

Starting substances in a chemical reaction.

Reduction

Reaction in which an ion or molecule gains electrons. This may also involve the loss of oxygen atoms and/or the gain of hydrogen atoms.

Resin

A water-insoluble, elastic plant exudate.

Respiration

The intracellular process in which larger organic molecules are broken down to smaller ones, usually in the presence of oxygen, with the help of enzymes.

Salt

Generally, the same as ionic compound. Specifically, often refers to sodium chloride (NaCl).

Saponins

A group of soapy, surface-active defensive plant compounds.

Secondary metabolites

Metabolites derived from the primary metabolites, restricted in their distribution in plants and often specific to certain types of plants.

Serpentine (serpentinite)

Rocks and soils with low content of macronutrients like calcium, and high in magnesium content and heavy metals (a property referred to as “ultramafic”).

Sesquiterpenes

Terpenes consisting of three isoprene units, thus having 15 carbon atoms.

Stereoisomers

Molecules with the same connections of atoms but with different orientation of groups in space. Examples: Enantiomers, cis/trans isomers.

Steroids

A large family of organic natural products with a characteristic four-ring pattern.

Stigma

Part of a flower that receives pollen from pollinators.

Stoma, pl. stomata

Small opening in the epidermis of leaves and stems through which gases can pass.

Strong acid/strong base

Acid or base that is fully dissociated into ions in water.

Tannins

Acidic, phenolic plant pigments with astringent properties.

Terpenes

Secondary metabolites composed of isoprene units.

Total synthesis

Synthesis of a complex compound from simple, easily available organic compounds.

Transition elements

Metallic elements listed in the short vertical groups in the center of the periodic table.

Unsaturated

Having double (or triple) bonds.

Vacuole

A space or cavity bounded by membranes within the cytoplasm of a cell, filled with a watery fluid.

Valence electrons

Electrons in the outermost electron shells of an atom.

Vascular system

The system of conducting tissues in plants, including the xylem and the phloem.

Volatile

Evaporating easily.

Weak acid/weak base

An acid or base that is only partially dissociated into ions in water.

Xanthophyll

A yellow plant pigment related to carotenoids.

Xylem

Vascular tissue through which most of the water and minerals of a plant are conducted.