6. Classification of Living Organisms

These are the key vocabulary words that we will learn as we study this topic. 
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active virus A virus that, when it enters a cell, begins to the host cell to make new viruses. This process eventually destroys the cell and releases more viruses. 
amphibian A cold-blooded vertebrate animal that lives in water and breathes with gills when it is young. As an adult, it moves onto land and breathes air with lungs. 
angiosperm A plant that has flowers and produces seeds enclosed in fruit. 
Animalia Kingdom Animalia includes multicellular organisms, from humans to insects and microbes that rely on food for energy. All animals are eukaryotes. 
annelid An invertebrate worm with a segmented body and developed gut. 
antibiotic A medicine that can block the growth and reproduction of bacteria. 
arachnid An arthropod with two body sections, four airs of legs, and no antennae. Spiders are in this class. 
arthropod An invertebrate animal with an exoskeleton, segmente4d body, and jointed legs.  
asexual reproduction The process of reproduction by which a single organism produces offspring with the same genetic material as the parent. 
bacteria (singular: bacterium) A large group of one-celled prokaryotic organisms.  
bilateral symmetry A body plan with two halves that are mirror images of each other. 
binomial nomenclature The two-part naming system used to identify species. The first part of the name is the genus, and the second part of the name is the species. 
bird An endothermic vertebrate that has feathers and a four-chambered heart and lays eggs. 
bivalve A mollusk that has two shells held together by hinges and strong muscles. Examples are clams, mussels, oysters, and scallops. 
branching tree A diagram that shows how scientists think different groups of organisms are related. 
chordate The phylum whose members have a notochord (a nerve cord) and had slits in their throat area at some points in their lives. 
class In taxonomy, the level below phylum. Chordate classes include fish, amphibians, reptiles, birds and mammals. 
classification The systematic grouping of different types of organisms by their shared characteristics. 
cnidarian An invertebrate animal such as a jellyfish that has a body with radial symmetry, tentacles with stinging cells, and a central internal cavity. 
crustacean An arthropod that has two or three body sections, five or more pairs of les, and two pairs of antennae. 
dichotomous key A series of questions, each with only two answers that can be used to help identify and organism’s genus and species. 
domain One of three divisions in a classification system based on different types of cells. The six kingdoms of living things are divided into three domains Archaea, Bacteria, and Eukarya. 
echinoderm An invertebrate sea animal with a spiny skeleton, a water vascular system, and tube feet. 
ectotherm  An animal whose body temperature changes with environmental conditions (“cold-blooded’). 
endospore A small, rounded, thick-walled, resting cell that forms inside a bacterial cell; a dormant stage for a bacterium. 
endotherm  An animal that maintains a constant body temperature (“warm-blooded”). 
Eukarya A domain of organisms whose genetic material is enclosed within a nucleus. Includes Kingdoms Protista, Fungi, Plantae and Animalia, 
eukaryote An organism that has a nucleus in its cell(s). 
family A taxonomic rank in the classification of organisms between genus and order. Organisms in the same family would have evolved from the same ancestors and share relatively common characteristics. 
fish An ectothermic vertebrate that lives in water and has fins. 
fungi Kingdom Fungi includes multicellular mushrooms, molds and single-celled yeasts. 
gastropod A class in the Mollusca phylum that includes snails 
genus The first part of a binomial name that groups together closely related species. For example, the genus Felis includes all species of small cats, while the genus Canis includes all dogs and wolves. 
gills A respiratory organ that filters oxygen dissolved in water. 
gymnosperm A plant that produces seeds that are not enclosed in flowers or fruit. This group includes conifers, cycads and ginkgoes. 
hidden virus A hidden virus is one that, when it enters a cell, does not immediately become active. Hidden viruses can remain dormant for many years before becoming active. 
insect An arthropod with three body segments, six legs, two antennae, and compound eyes. 
invertebrate An animal that has no backbone. There are ten phyla of invertebrates. 
kingdom A kingdom is one of the major classification levels in biology. 
mammal A warm-blooded vertebrate animal whose young feed feed on milk produced by the mother’s mammary glands. 
mollusk An invertebrate animal with a soft body, muscular foot, and a mantle. Many mollusks have a hard outer shell. 
nematode An invertebrate phylum that includes round worms. 
notochord A flexible rod that supports a chordate’s back. All chordates have a notochord. 
order A taxonomic level between class and family. 
parasite An organism that absorbs nutrients from the body of another organism, often harming it in the process. 
pasteurization A process of heating food to a temperature that is high enough to kill most harmful bacteria without changing the taste of the food. 
phylum (phyla) One of the major groups into which biologists classify members of a kingdom.  
Plantae Kingdom Plantae includes multicellular organisms, such as trees, grass, and moss that are capable of photosynthesis, capturing energy from the sun. 
Platyhelminthes  The invertebrate phylum that includes flatworms. 
Porifera The invertebrate phylum that includes sponges. 
prokaryote An organism that does not have cells with a nucleus and other organelles and whose DNA is not organized into chromosomes. 
Protista Kingdom Protista includes mostly single celled organisms with cells similar to those of plants, animals and fungi kingdoms. 
radial symmetry The quality of having many lines of symmetry that all pass through a central point. 
reptile A cold-blooded vertebrate tat has skin covered with scales or horny plates and has lungs. 
scientific name The scientific name for any organism is its genus and species. 
seed A plant embryo that is enclosed in a protective coating and has its own source of nutrients. 
species A group of living things that are so closely related that they can breed with each other and produce offspring that can breed as well. 
spore A single reproductive cell that can grow into a multicellular organism. 
taxonomy The science of classifying and naming organisms. 
vaccine A small amount of a weakened pathogen that is introduced into the body to stimulate the production of antibodies. Vaccines are used to prevent viral diseases. 
vascular tissue Long tube-like tissues in plants through which water and nutrients move from one part of the plant to another. 
vertebrate An animal with an internal backbone. 
viral disease A disease that is caused by a virus. 
virus A non-living particle that uses the materials inside cells to make copies of itself. A virus consists of genetic material enclosed in a protein coat. Most viruses cause diseases in the organisms they infect.  
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