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


  • LEAF (LEAVES): usually a green, flattened structure attached to a stem and functioning as a place where photosynthesis and transpiration occurs in most plants.
  • LEAF LITTER: decomposing but recognizable leaves and other plant debris forming a layer on top of the soil, especially in forests, but also in tree-lined streams, ponds, wetlands and other aquatic habitats.
  • LENS: a transparent (clear), flexible disc behind the iris. An eye lens is similar to a camera lens, that is, it refracts (redirects) light to focus it onto the retina.
  • LICHEN(s): a composite organism, which means that lichens are actually two organisms living together as one. Lichens form from algae (or cyanobacteria) living among filaments of fungi. The combined lichen has properties different from those of its component organisms. Lichens come in many colors, sizes, and forms. The properties are sometimes plant-like, but lichens are not plants.
  • LIGHT: in science, the word “light” usually refers to visible light, which is defined as electromagnetic radiation within a certain portion of the electromagnetic spectrum.
  • LITHOSPHERE: the rigid outer part of the earth, consisting of the crust and upper mantle.
  • LIQUID: a state of matter in which the particles (e.g., atoms and/or molecules) do not occupy fixed positions and can migrate to other positions in the substance. In the liquid state, the particles (atoms and/or molecules) conform to the shape of a container in which it is held. Although this is also a good definition for the gas (or gaseous) state of matter, in the liquid state the particles (atoms and/or molecules) acquire a defined surface in the presence of gravity. Gases do not typically acquire such defined surfaces in the presence of gravity.


  • MASS: a measure of how much matter (or how many atoms) is in an object or sample combined with the density of those atoms (or how tightly or loosely they are packed together). In our middle science classes we typically use ‘balances’–both electronic and non-electronic–to measure the mass of an object or sample in units such as “grams” or “kilograms.”
  • MATTER: a general term for the substance (or substances) which all physical objects consist.  Matter can also be defined as that which a) takes up space and b) has mass.  In our class, we will often talk about matter as something that contains atoms (and often molecules).
  • MICROBE: a term for incredibly tiny organisms that individually are almost always too small to be seen with the unaided eye. (Believe it or not, one species of bacteria has been discovered that is actually about the size of a typed period when using Times New Roman, 12 pt. font!). Microbes include organisms such as bacteria, archaea , fungi, and protists. However, some scientists think that viruses, which are non-living, can also be considered microbes.
  • MICROPYLE: a tiny opening in the ovule of a seed through which a sperm cell can enter. This opening also allows water to enter a mature seed during the process of germination.
  • MINERAL(s): minerals are naturally occurring (they are not made by humans), inorganic solids (they have never been alive and are not made up from plants or animals), with a definite chemical composition (each one is made of a particular mix of chemical elements), and an ordered atomic arrangement (the chemical elements that make up each mineral are arranged in a particular way – this is why minerals ‘grow’ as crystals). For more information go to The Oxford Museum of Natural History’s website.
  • MIXTURE: two or more substances mixed together.  The mixture may be two or more different types of molecules (e.g., sugar dissolved in water) OR it may be two or more different types of elements (e.g., steel = a mixture of iron (Fe) atoms and carbon (C) atoms). Either way, in a mixture each substance retains its own chemical identity.
  • MOLECULE(s): two or more atoms bonded together to form a ‘unit.’  The atoms may be of the same type (e.g., O2) or two or more different types (e.g., CO2).
  • MONOCOTYLEDON: a plant whose embryo has one cotyledon.  This word is often abbreviated as “monocot.”
  • MOTION (see also MOVEMENT): the state of changing something’s position—that is, changing where something is. A flying bird or a walking person are moving, because they change where they are from one place to another.
  • MOVEMENT (see also MOTION): the state of changing something’s position—that is, changing where something is. A flying bird or a walking person are moving, because they change where they are from one place to another.


  • NAUPLII: the name given to the first phase or stage of growth of young crustaceans such as crabs, lobster, and brine shrimp. In this growth stage, the young crustaceans usually have bodies that are not divided into parts (or sections) and possess a single eye.
  • NECTARY: a gland located in flowers (often near the base) that produces a sugary liquid which ‘pollinators’ (e.g., birds and insects) use as food.
  • NEUTRON: a subatomic particle of about the same mass as a proton, but without an electric charge. Neutrons are present in all atomic nuclei except those of ordinary hydrogen (H).
  • NODE: the part of a stem where one or more leaves are attached.
  • NORMAL FORCE: the force that the ground (or any surface) pushes back up with. If there was no normal force acting upon you at this moment, for example, you’d be slowly seeping into the ground.
  • NUCLEUS: an organelle found inside of the cell membrane, it controls the activities of and the cell and contains most of the cell’s genetic material (e.g., DNA).


  • OMNIVORE: an animal or person that eats food of both plant and animal origin.
  • OPTIC NERVE: a bundle (collection) of sensory neurons at the back of an eye. The optic nerve carries impulses from the eye to the brain.
  • ORAL GROOVE: a sort of cell ‘mouth,’ through which food particles can enter into a cell. Oral grooves are easy to see in paramecium.
  • ORGANIC COMPOUND: any substance that contains a chain of carbon (C) atoms, but also most likely hydrogen (H) and oxygen (O) atoms. In science class, we will use the term “CHO” to remind ourselves of substances that are organic.
  • ORGANIC MATTER: matter composed of organic compounds (see above) that have come from the remains of organisms such as plants and animals and their waste products. Organic matter provides nutrition to living organisms.
  • ORGAN(s): a group of tissues (specialized cells) that perform a specific function or group of functions. Examples of animal organs include heart, lungs, brain, eye, and stomach. Examples of plant organs include roots, stems, leaves, flowers, seeds, and fruit.
  • ORGANISM(s): highly organized, coordinated structures that consist of one or more cells. Even bacteria [singular: bacterium], each of which consists of only a single cell, are considered to be organisms.
  • ORGANELLE(s): a specialized unit within a cell that has a specific function (or functions). Individual organelles are usually separately enclosed within their own membranes. Contrary to popular opinion, the cytoplasm is not an organelle (the cytoplasm consists of the cytosol–the liquid in which organelles are suspended–and the organelles themselves).
  • ORGAN SYSTEM(s): a group of organs that work together to carry out a particular function (task, job). An example of an organ system found in humans is the digestive system.
  • OVARY: the enlarged base of the pistil in which the ovules are contained.  It is sometimes called the carpel.
  • OVULE(s): a structure in seed-producing plants that contains the egg cell.
  • OXYGEN: a chemical element with symbol O and atomic number 8. It is one of the 92 naturally occurring elements on Earth. A single oxygen atom typically contains 8 protons, 8 neutrons, and 8 electrons.
  • OXYGEN GAS: a molecule with the chemical formula O2. A single molecule of oxygen gas contains 2 oxygen atoms bonded together to form a ‘unit.’ It is expelled as waste by photosynthesizing organisms and taken in by other living things such as animals.


  • PALISADE CELLS: leaf cells located right below the top two layers of other types of leaf cells. They often have a distinctive shape (elongated) which is different from the leaf cells found above and below them. Their chloroplasts absorb a major portion of the light energy used by the leaf during photosynthesis.
  • PARAMYLON RINGS (or BODIES): cell organelles that store certain types of carbohydrates resulting from photosynthesis processes occurring in the chloroplasts.
  • PARTICLE(s): in our science classes, we will often use the word “particle” to refer to an extremely small portion of matter. At some point, however, we will start replacing the word “particle” with more precise words such as “atom” and “molecule.”
  • PATTERN: a natural or accidental arrangement or sequence; a regular and intelligible form or sequence discernible in the way in which something happens or is done.
  • PEDICLE (or PEDICEL): the stem-like structure just below the receptacle that connects a single flower (or flower bud) to stem or branch of stems leading to other flowers.
  • PELLICLE: a highly flexible (and elastic) structure of membranes that permits movement of the cell. Despite the fact that it is a membrane, it functions differently than the cell (or plasma) membrane.
  • PERENNIAL PLANT: a plant that lives year after year and usually produces reproductive structures in two or more years.
  • PETAL: a flower part that is usually colored to help attract ‘pollinators’ (e.g., birds and insects).
  • PETIOLE: the stem-like structure just below the base of the leaf that connects a leaf blade to a plant stem.
  • PHLOEM TISSUE (or TUBES): phloem tissue, or sometimes just “phloem,” is the specialized tissue of vascular plants that transports the products of photosynthesis (e.g., sugars) from the leaves to all other parts of the plant. When phloem tissue is arranged to form hollow tubes these structures are called “phloem tubes.”
  • PHOTOSYNTHESIS: you might consider two different definitions for this term. The second definition is the one we are likely to use in our middle school science class.

a process occurring in plants and plant-like organisms (e.g., some bacteria) in which light energy from the sun is converted into chemical energy and stored in the form of food (e.g., glucose, sugars, starch).


a process that uses light to put together carbon dioxide (CO2) and water (H2O) to make food (sugars = CHO).  The energy from the sun is used to split apart the water and carbon dioxide molecules. Pieces of the molecules–called atoms–are rearranged to make a new substance, sugars.

  • PHOTOTROPISM: the response of a shoot or root to light.
  • PHYSICAL: of or related to…the properties of matter and energy and the relationship between them.
  • PISTIL: the female organ of a flower which produces ovules.  It typically consists of three parts: the stigma, the style, and the ovary (or carpel).
  • POLLEN (or POLLEN GRAINS): a structure in seed-producing plants that contains the sperm cell.  Plants often make it in great quantities.
  • POLLINATION: the transfer of pollen from the anther (a special part of the male organ) to the stigma (a special part of the female organ).
  • POOL (in stream or river): a reach of a stream that is characterized by deep, low-velocity water and a smooth surface.’
  • PLANT: a living thing that grows in the ground, usually has leaves or flowers, and needs a source of light (e.g., from the sun), a source of water (e.g., from the rain), and a source of carbon dioxide (from the air) to survive.
  • PLUMULA: same as plumule (see below).
  • PLUMULE: the first ‘bud’ of an embryo.  It is the portion of a young ‘shoot’ above the cotyledons.  Some people like to refer to the plumule as the “future stem and leaves.”
  • PRESSURE: continuous physical force exerted on (or against) an object by something in contact with it.
  • PRIMARY CONSUMER: animals that are specially adapted to a diet consisting mainly or exclusively of plant materials.
  • PRODUCER: an organism capable of making their own food. In other words, they produce complex organic compounds (e.g., glucose) from simple inorganic molecules (e.g., CO2 and H2O) through the process of photosynthesis (using light energy) or chemosynthesis (using chemical energy).
  • PROTEIN(s): large molecules consisting of one or more long chains of amino acids. They perform an incredible number of diverse, important functions inside the body of living organisms. Proteins are one of the three main macronutrients, along with the other two: carbohydrates and fats.
  • PROTON: a stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron.
  • PSEUDOPOD: a temporary extension of the surface of a cell that is filled with cytoplasm. It is used by organisms such as amoeba for movement and feeding. Translated from its two Latin root words, pseudo– and pod (or poda), it means “false foot.”
  • PUPIL: a hole (not a substance!) in the middle of the (eye) iris. It allows light to pass through as it enters the eye.
  • PURE SUBSTANCE: a pure substance consists of only one type of molecule (e.g., pure water) OR only one type of element (pure gold).

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

Last updated: March 2021

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