algae: Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.
archaea: (singular: archaeon) One of the three domains of life on Earth. This group consists of single-celled prokaryotes — organisms without a cell nucleus. Archaea are best known for living in extremely harsh environments, such as very salty water or highly acidic or hot places.
bacteria: (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals). Bacteria are one of the three domains of life on Earth.
behemoth: A term for anything that is amazingly big. The term comes from a monstrous animal described in the Bible’s book of Job.
cell: The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
COVID-19: A name given to the disease that caused a massive global outbreak. It first emerged in December 2019 and is caused by a new coronavirus known as SARS-CoV-2. Symptoms can include pneumonia, trouble breathing, feeling too tired to walk more than a few steps, fever, headaches, low blood-oxygen levels, blood clots and brain “fog.”
diatoms: Tiny, ocean- and lake-dwelling organisms made of no more than a few cells. Diatoms have cells made of silica, or glass. They live like plants, using sunlight to turn carbon dioxide into sugars.
DNA: (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.
environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).
enzymes: Molecules made by living things to speed up chemical reactions.
eukaryote: Any organism whose cells have a nucleus. Eukaryotes include all multicellular creatures (such as plants, animals and fungi) as well as certain types of single-celled microorganisms.
flagella: (sing. flagellum) A thread-like structure that comes out of certain types of cells. The term derives from the Latin word for whip. And that’s because the structures serve like oars to help these cells travel.
gene: (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
infect: To spread a disease from one organism to another. This usually involves introducing some sort of disease-causing germ to an individual.
influenza: (also known as flu) A highly contagious viral infection of the respiratory passages causing fever and severe aching. It often occurs as an epidemic.
malaria: A disease caused by a parasite that invades the red blood cells. The parasite is transmitted by mosquitoes, largely in tropical and subtropical regions.
marine: Having to do with the ocean world or environment.
microbe: Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.
multicellular: Having or consisting of many cells. This includes all animals and plants, and many types of fungus.
nucleus: Plural is nuclei. (in biology) A dense structure present in many cells. Typically a single rounded structure encased within a membrane, the nucleus contains the genetic information. (in astronomy) The rocky body of a comet, sometimes carrying a jacket of ice or frozen gases. (in physics) The central core of an atom, containing most of its mass.
organelle: Specialized structures, such as mitochondria, found within a cell.
organism: Any living thing, from elephants and plants to bacteria and other types of single-celled life.
plasmodium: A form within the life cycle of some simple organisms such as slime molds, typically consisting of a mass of naked protoplasm containing many nuclei. (in medicine) It also refers to a genus of protozoa that cause the disease malaria. The Plasmodium genus includes more than 100 species; just five are responsible for most malaria in humans.
prokaryote: Any single-celled organism that does not have a nucleus or membrane-bound organelles.
protein: A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.
protist: A broad group of mostly single-celled organisms that are neither plants nor animals. Some, like algae, may appear plant-like. Those known as protozoans may appear animal-like. And still others appear fungi-like.
slime mold: A simple organism that consists of a single cell of creeping, jellylike protoplasm containing nuclei. It is not a mold, despite its name; it isn’t even closely related to fungi.
species: A group of similar organisms capable of producing offspring that can survive and reproduce.
virus: Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.
yeast: One-celled fungi that can ferment carbohydrates (like sugars), producing carbon dioxide and alcohol. They also play a pivotal role in making many baked products rise.