acid: a substance that produces hydrogen ions (H+) in water
actin filaments: threads that serve as structural support for the cell, as well as part of its transportation infrastructure and communication network
active transport: using energy to move a molecule against its concentration gradient
adenosine triphosphate (ATP): energy currency of life; this molecule has two phosphate-to-phosphate bonds that when broken provide energy
adhesion: tendency of dissimilar molecules to attach to each other, as with water and glass
amino acid: molecular building block of proteins
anion: negatively charged molecule
apoplast: extracellular pathway created by the connection of plant cell walls
aquaporin: membrane protein that allows water molecules to pass through
atom: smallest building block of an element; consists of a nucleus surrounded by a cloud of electrons
base: a substance that produces hydroxyl ions (OH−) in water
biofertilizer: fertilizer provided by living organisms carbohydrate: carbon-based molecules consisting of combinations of carbon, oxygen, and hydrogen, where there is usually one water (H2O) molecule for each carbon atom
Casparian strip: single layer of wax-clogged cells at the endodermis of a root
cation: positively charged molecule
cellulose: complex molecule made up of simpler glucose woven closely to form long strands
cell wall: strong, lattice-like structure that surrounds a plant cell; made up primarily of cellulose
channel proteins: tunnel-like, gated proteins that allow ions to move across membranes passively
chlorophyll: molecule that absorbs energy from light and is essential for photosynthesis; it gives plants their green color
chloroplasts: organelles that contain chlorophyll
chlorosis: inability of leaves to produce enough chlorophyll, resulting in yellow leaves surrounding greener veins
chromoplasts: cells that contain the red, yellow, and orange pigments found in flowers, fruits, and some roots
cohesion: tendency of the same type of molecules to stick to each other
collenchyma: thick-walled cells that provide support and flexibility to plants
compound: two or more molecules of different elements
cristae: compartments in mitochondria created by folding the inner membrane
cytoplasm: liquid and organelles (minus the nucleus) that make up a cell
cytosol: clear, jelly-like substance that is the major component of cytoplasm and literally holds the cell’s organelles
dermal tissue: cells that form the skin of plants, consisting of the epidermis and the periderm
desmotubule: small tubular structure found inside each plasmodesma
diazotrophs: soil microbes responsible for nitrogen fixation
diffusion: passive movement of molecules from regions of high concentration to those of low concentration
disaccharide: molecule that consists of two glucose molecules linked together
DNA: deoxyribonucleic acid, a molecule that contains the genetic code
electron: a negatively charged particle
element: a substance that cannot be separated into simpler ones
endoplasmic reticulum: organelle that serves as the major pathway for the transport of cellular material
enzyme: biological molecules that increase the rate of chemical reactions
food web: series of food chains linked together
Golgi apparatus: organelle responsible for protein transport
ground tissue: cells that provide most of the mass or bulk of a plant as well as its support
heavy metal: metal with a high specific gravity that is usually toxic
humus: extremely stable organic matter that is resistant to further decay
hyaloplasm: clear, fluid portion of the cytoplasm
hydrogen bond: a bond that forms between a hydrogen atom and a negatively charged atom that is itself part of a molecule or a group of atoms
hydroxyl ion (OH−): negatively charged molecule consisting of an oxygen atom and a hydrogen atom
hypha (pl. hyphae): thread-like filament formed by a fungus
integral membrane proteins: specialized proteins embedded in the plasmalemma that allow for transport through the membrane
ion: charged molecule
ionic bond: bond created by the mutual attraction of oppositely charged ions
ion pump: see protein pump
Law of Return: recycle all plant and animal waste to keep producing humus
Law of the Minimum: plant growth is limited by the least abundant mineral
leucoplasts: colorless cells located in parts of plants not exposed to light; used primarily for storage of lipids and proteins
lipids: organic molecule characterized by nonsolubility in water, making them hydrophobic; include fats, waxes, steroids, and triglycerides
lysosome: small organelles that contain hydrolytic enzymes that digest large molecules (mostly proteins) into their components; the cellular recycling centers
macronutrients: nutrients required in the largest quantities; includes carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur
meristematic tissue: undifferentiated plant cells that have the ability to become any type of cell
messenger RNA (mRNA): specialized RNA molecule that transcribes the DNA pattern in the nucleus and carries the pattern to the endoplasmic reticulum, where it is translated into protein molecules
micron: one millionth of a meter
micronutrients: nutrients needed in minute quantities; include iron, manganese, zinc, copper, molybdenum, boron, chlorine, and nickel
microtubule: specialized tubular structure for intracellular transport
mitochondria (sing. mitochondrion): organelles responsible for using the oxygen in sugar to produce energy
molecule: two or more atoms of different elements that are bonded together
monosaccharide: single glucose molecule
mycorrhizal fungus: fungus that forms symbiotic relationships with plants; brings nutrients and water to the roots in return for carbon-based exudates produced by the plant
nanometer: one billionth of a meter
neutron: subatomic particle found in the nucleus of the atom that does not have a charge
nitrogen fixation: breaking the strong bonds that hold nitrogen molecules together so that nitrogen becomes biologically available
nonpolar covalent bond: bond between atoms wherein electrons are shared equally
nucleic acid: a type of molecule that includes DNA and RNA
nucleotides: building blocks of nucleic acids
nucleus: organelle that contains the DNA of a cell
osmosis: diffusion of water across a semi-permeable membrane
oxidation: loss of electrons in a chemical reaction
parenchyma cell: specialized cells in which metabolic functions occur but that retain the ability to become further specialized
passive transport: movement of molecules without the input of energy
pericycle: outer boundary of the stele, consisting of a thin layer of cells that still have the ability to divide
peroxisome: digestive vessel that is involved in the conversion of fatty acids into sugars
pH: measure of hydrogen ions in solution; liquids with a high pH are basic or alkaline, and those with a low pH are acids
phloem: tissue responsible for the transport of nutrients throughout plants
phytoremediation: use of plants to remove or neutralize toxins
plasmalemma: double-layer phospholipid membrane that surrounds plant cells and is located just inside the cell wall
plasmodesmata (sing. plasmodesma): tunnels that connect individual plant cells
plastid: cellular mini-factories and storage facilities in plant cells that include chloroplasts, leucoplasts, and chromoplasts
polar covalent bond: a bond between atoms wherein electrons are not shared equally, thus forming a region in the molecule with a negative change and another with a positive charge
polysaccharide: chains of simple sugar molecules
protein: nitrogen-based molecules composed of amino acids, each of which has an amino group (NH2) and a carboxyl group (COOH), plus a side chain whose composition can vary
protein pump (or ion pump): proteins that pump ions across a membrane against their energy gradient
proton: positively charged particle within the nucleus of an atom
reduction: addition of electrons in a chemical reaction
rhizosphere: area immediately surrounding roots
ribosomes: organelles where mRNA is translated and proteins are made
RNA: ribonucleic acid, a molecule used to pass genetic information from the nucleus to the ribosome
root hair: specialized epidermal cells that increase the surface area of roots
salt: a molecule that is the end product of a neutralization reaction, in which two ions neutralize each other’s charge
schlerenchyma: cells that develop a lignified, secondary wall and can no longer elongate; these provide support and physical protection to plants
siderophore: chemicals produced by some rhizosphere microbes that free iron in the soil
statoliths: organelles in root cells that act like weights, sinking to the bottom in response to gravity
stele: central part of a root
stomata: openings in leaves that let in carbon dioxide and let out oxygen and water vapor
suberin: waxy substance that waterproofs cells
symplast: area encompassing the inside of all connected cells
thylakoid: flattened, hollow discs inside chloroplasts that contain the chlorophyll antennae that absorb energy from light
tonoplast: membrane that surrounds plant vacuoles
transfer RNA (tRNA): specialized RNA that carries amino acids to the ribosome during protein production
trichomes: hair-like structures that aid in the evaporation of water from leaves
vacuole: membrane-bound spaces inside plant cells
vascular tissue: combination of xylem and phloem
vesicle: membrane-bound structures that transport materials inside the cell
xylem: tissue responsible for the transport of water from the roots upward to the leaves