Listed below is a collection of some of the most important science vocabulary words used in our class. This page is updated periodically, so be sure to refresh your browser every now and then. If you don’t see a word you are looking for, try visiting Merriam-Webster’s Learner’s Dictionary (a dictionary for younger science students) or any of the online dictionaries recommended by Dr. Merritt.

 ABCD | EFG | HIJK | LMNOP | QRS | TUV | WXY&Z | 123s | Roots


  • ABSORB (ABSORPTION): to take in or soak up–usually energy (e.g., sunlight), a liquid (e.g., water), or other substance (e.g., oxygen gas)–by a chemical or physical action.
  • ACID: a chemical substance that donates or gives up protons (hydrogen ions) and/or accepts electrons.
  • ACIDIC: refers to an liquid (aqueous) solution having a pH less than 7.
  • AIR: a mixture of many different types of gases that surround the Earth and form the atmosphere. In our class, we will talk mostly about four of the gases found in air: nitrogen (N2), oxygen (O2), carbon dioxide (CO2), and water vapor (H2O).  However, always remember that air is a mixture of more than four gases.
  • ALKALINE: refers to an aqueous (liquid) solution having a pH greater than 7. Also known as “basic.”
  • AMYLOPLAST: also called “starch grains,” amyloplasts are organelles found in some plant cells. They are responsible for the making and storing starch granules, which are made from glucose (sugar). Large numbers of amyloplasts can be found in fruit, such as bananas, as well as in underground storage tissues of some plants, such as potatoes.
  • ANIMAL(s): a living organism that consumes substances that either are living or were once living. Animals typically have specialized sense organs (for example, eyes), a nervous system, and are able to respond to stimuli in their environment.
  • ANNUAL PLANT: a plant in which the entire life cycle is completed in a single growing season.
  • ANTHER: the tip of the stamen.  It produces and bears the pollen.
  • ARTHROPOD(s): an arthropod is an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda, and include the insects, arachnids, and crustaceans.
  • ATOM(s): the smallest unit of an element having all the characteristics of that element.  For example, in theory a single atom of gold still has all of the characteristics of a bar of solid gold, which probably consists of millions (or billions!) of atoms.
  • ATMOSPHERE: the envelope of gases surrounding the earth or another planet.


  • BACTERIA: are a type of biological cell. They constitute a large domain of prokaryotic (i.e., without a membrane-bound nucleus) microorganisms. Typically a few micrometers in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats.
  • BASE: in chemistry, a base is a chemical substance that donates electrons (or hydroxide ions) or accepts protons.
  • BASIC: in chemistry, basic refers to an aqueous solution having a pH greater than 7. Also known as “alkaline.”
  • BATTERY: like (non-living) cells, a battery is a sort of container that stores energy until it is needed. Chemicals inside the battery store the energy. When the battery is used, the chemical energy inside the battery is transformed into electric energy. Technically speaking, a battery consists of two or more cells joined together in a series. Battery power (or ‘push’) is typically measured in “Volts” (V).
  • BIENNIAL PLANT: a plant requiring two growing seasons to complete its life cycle. Vegetative growth occurs the first year and flowering and fruiting occur during the second year.
  • BIOLOGICAL: of or related to…life and living processes.
  • BIOLOGY: the study of life and living processes.
  • BIOMASS: the mass of material derived from the living (or recently living) organisms found in a defined area. Biomass can be measured by any instruments that typically measure the mass of objects. For example, a pile of cut grass (recently living organisms) sitting in a backyard (a defined area) would contain a certain amount of measurable biomass (which could be measured using an electronic balance in either grams or kilograms!).
  • BIOMES: the main ecological regions into which the land surface can be divided.  Each biome has its own characteristic seasons, day length, rainfall pattern and maximum and minimum temperatures.  Some of the major biomes include tundra, coniferous forest, deciduous forest, tropical forest, temperate grassland, savanna (tropical grassland), scrubland, mountains, desert, and ice.  Most are named after the dominant vegetation, since this is key in determining the presence of other living things.  Each biome is a giant habitat (or macrohabitat).
  • BIOSPHERE: the regions of the surface, atmosphere, and hydrosphere of the earth (or analogous parts of other planets) occupied by living organisms.
  • BLADE (leaf): The expanded part of a leaf (or petal). A blade is typically the broadest portion of a leaf (or petal) and distinct from the narrower petiole.


  • CARBOHYDRATE(s): a molecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen to oxygen atom ratio of 2:1. Carbohydrates perform numerous roles in living organisms. Carbohydrates are one of the three main macronutrients, along with the other two: proteins and fats.
  • CARBON (C): a chemical element with symbol “C” and atomic number 12. It is one of the 92 naturally occurring elements on Earth. A single carbon atom typically contains 6 protons, 6 neutrons, and 6 electrons.
  • CARBON DIOXIDE (CO2): a molecule consisting of three atoms made from two different elements, carbon (C) and oxygen (O). Carbon dioxide is most typically found in the Earth’s atmosphere in a gaseous form, where it is expelled by animals as a waste product and absorbed by photosynthesizing organisms.
  • CARBON MONOXIDE (CO): a molecule consisting of two atoms made from two different elements, carbon (C) and oxygen (O), it is considered toxic to many animals. Natural sources of carbon monoxide include volcanoes, forest fires, other forms of combustion.
  • CARNIVORE: an animal that feeds on flesh of another animal.
  • CAUDAL TUFT: a collection of cilia at the hind (or rear) end of a cell used for movement.
  • CELL (living): from the Latin word cella (meaning “small room”), cells are the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, which is why they are often called the “building blocks of life.”
  • CELL (non-living): a single power generating unit which stores chemical energy and then converts it into electrical energy. It has two electrodes: a positive (+) electrode also known as a “cathode” and a negative (-) one called the “anode.” The cell contains an electrolyte, a chemical substance that reacts with the electrodes and produces electric current.
  • CELL MEMBRANE: a thin layer that separates the interior of all cells from the outside environment. The cell membrane controls the movement of substances in and out of cells by allowing some substances to enter and exit the cell freely, while forbidding others. This selectivity of some substances and not others is why cell membranes are often referred to selectively-permeable or semi-permeable.
  • CELL WALL: a rigid layer of complex sugars (polysaccharides) lying outside of the plasma membrane of the cells of plants, fungi, and bacteria. In the algae and higher plants it consists mainly of cellulose.
  • CHEMICAL: of or related to…reactions involving changes in atoms or molecules.
  • CHEMOSYNTHESIS: a process occurring in bacteria and other living organisms (e.g., archaea) in which these organism convert molecules such as carbon dioxide (CO2) or methane (CH4) and other nutrients into organic matter (e.g., carbohydrates) by using raw materials such as hydrogen gas (H2), hydrogen sulfide (H2S), or methane (CH4) as a source of energy. Unlike photosynthesis, chemosynthesis does not depend on energy from sunlight.
  • CHLOROPHYLL: a molecule (or green-colored pigment) present in all green plants and in cyanobacteria, which is responsible for the absorption of light to provide energy for photosynthesis. A single molecule of chlorophyll has the general chemical formula, C55H72O5N4Mg.
  • CHLOROPLAST(s): an organelle within green plant cells containing chlorophyll and in which photosynthesis takes place.
  • CILIA: small, hairlike projections from the surface of a cell. Some cilia enable single-celled organisms to swim freely in liquid environments. Cilia is plural; one cilia is called a cilium.
  • CILIARY MUSCLE: a muscle connected to the (eye) lens by ligaments called “suspensory ligaments.” They adjust the shape of the lens by contracting or relaxing, which makes the lens more or less curved. Changing the curve of the lens increases or decreases the refraction (redirection) of light.
  • CLAY: a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of other elements such as silicon (e.g., in the form of SiO2), aluminum (e.g., in the form of Al2O3), magnesium (e.g., in the form of MgO), and organic matter.
  • COMPOUND: a substance that is composed of two or more separate elements found on the periodic table of elements. Sometimes, however, a compound is also defined simply as a “mixture” or “any substance that can be split up into simpler substances.”
  • CONSUMER: any organism that generally obtains food by feeding on other organisms because they lack of the ability to manufacture their own food.
  • CONTRACTILE VACUOLE: a specialized type of vacuole that helps regulate the quantity of water inside a cell. The contractile vacuole prevents the cell from absorbing too much water–and possibly lysing (rupturing) because of too much internal water pressure–by collecting water from inside the cell and expelling it out of the cell through the cell membrane.
  • COOL
  • CORNEA: a convex, tough, transparent (clear) window at the front of the eye. The cornea covers and protects the iris and the pupil. It refracts (redirects) light as it enters the eye. It plays an important role in focusing vision.
  • COTYLEDON (or SEED LEAF): the leaf of the embryo or seedling.  It contains food (e.g., starch) that the young plant can use as a source of energy.
  • CYST: a tough (strong) protective capsule.
  • CYTOPLASM: jellylike material that makes up much of a cell inside the cell membrane, and, in eukaryotic cells, surrounds the nucleus. The organelles of eukaryotic cells are contained in the cytoplasm.


  • DECOMPOSE: in our science classes, we usually use this word in reference to a dead body and/or to other material that was once considered living (i.e., organic). When such bodies or materials become rotten, we say they “decay” or “decompose.” This basically means to be broken down into smaller portions of matter.
  • DECOMPOSER: any living thing or organism–but especially a soil bacterium, fungus, or invertebrate–that decomposes organic material (see decompose above).
  • DECOMPOSITION: the process of decomposing (see decompose above).
  • DETRITUS: material consisting of dead leaves and other dead plant parts, animal remains, the waste products of living organisms, and other forms of organic debris. Detritus is typically colonized by communities of microorganisms (e.g., fungi and bacteria) which act to decompose the material.
  • DIGEST (DIGESTION): the breakdown of larger food molecules into smaller food molecules so that they can be more easily transported by tubes (e.g., capillaries, phloem tubes) found within an organism’s body.
  • DIGESTIVE SYSTEM: the system by which ingested food is acted upon by physical and chemical means to provide the body with absorbable nutrients and to excrete waste product.
  • DICOTYLEDON: a plant whose embryo has two cotyledons.  This word is often abbreviated as “dicot.”
  • DENSITY: a material’s density is often defined as its “mass per unit volume.” In simpler terms, density is a measurement of how tightly matter is crammed together into a finite (bounded) amount of space.
  • DIRT: to put it in the most simple terms, dirt is displaced soil. In other words, dirt consists of particles of soil that has been separated from the combination of minerals, air, water, animals and other living matter (and their wastes or decaying bodies) of which it was once an important part. Put differently, dirt is soil that has been separated from its history.
  • DISSOLVE: to cause a solute–whether solid, liquid, or gas–to ‘pass’ into solution. We might think of ‘passing into solution’ as the solute–again, whether solid, liquid, or gas–being distributed somewhat evenly throughout the solution.
  • DORMANT CYST: a tough (strong) protective capsule enclosing a resting organism, such as a brine shrimp.
    • DRY MASS: the mass of an object–or sample of an object–when it is completely dry. In other words, it is the mass of the object after the entire concentration of water has been effectively removed from it. Dry mass is sometimes known as dry weight or dry matter.
        • Compared to the measurement known as wet mass (or fresh mass)–which includes the mass of the water–dry mass is typically more reliable for comparisons because the concentration of water inside of living tissue can vary/change so much.
  • DUCT(S): in animal bodies, ducts are vessels (tubes) for carrying chemical substances such as tears, saliva, or bile. In plants bodies, ducts are also vessels (tubes) for carrying chemical substances such as water, sap, or air.

 ABCD | EFG | HIJK | LMNOP | QRS | TUV | WXY&Z | 123s | Roots

Last updated: October 2020

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