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Living Mysteries: Meet Earth’s simplest animal

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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.

amoeba     A single-celled microbe that catches food and moves about by extending fingerlike projections of a colorless material called protoplasm. Amoebas are either free-living in damp environments or they are parasites.

animal ecology     A branch of biology that deals with the relations of animals to one another and to their physical surroundings. A scientist who works in this field is called an animal ecologist.

anus     The opening at the end of an animal’s digestive system through which solid waste leaves the body.

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

bilaterian         Any of the animals whose bodies generally exhibit two-sided (or bilateral) symmetry. That means they would have equal numbers of appendages (such as legs, fins or antennae) on the right and left sides, for instance. The best known animal phyla are bilaterians, including fish, birds, mammals (including humans), amphibians and reptiles. Not included in this group are sponges, placozoans (such as Trichoplax), jellyfish and other jellies.

biology     The study of living things. The scientists who study them are known as biologists.

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.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

cilia     (singular cilium) Small hairlike features that occur on the surface of some cells and larger tissue structures. They can move and their wavelike motion can propel liquids to move in a particular direction. Cilia play an important role in many biological functions throughout the body.

coral     Marine animals that often produce a hard and stony exoskeleton and tend to live on reefs (the exoskeletons of dead ancestor corals).

crystal     (adj. crystalline) A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals. Apatite, for example, forms six-sided crystals. The mineral crystals that make up rock are usually too small to be seen with the unaided eye.

digest     (noun: digestion) To break down food into simple compounds that the body can absorb and use for growth. Some sewage-treatment plants harness microbes to digest — or degrade — wastes so that the breakdown products can be recycled for use elsewhere in the environment.

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.

ecology      A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

egg     The unfertilized reproductive cell made by females.

evolution     (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed. 

evolutionary     An adjective that refers to changes that occur within a species over time as it adapts to its environment. Such evolutionary changes usually reflect genetic variation and natural selection, which leave a new type of organism better suited for its environment than its ancestors. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.

exotic     An adjective to describe something that is highly unusual, strange or foreign (such as exotic plants).

fat     A natural oily or greasy substance occurring in plants and in animal bodies, especially when deposited as a layer under the skin or around certain organs. Fat’s primary role is as an energy reserve. Fat also is a vital nutrient, though it can be harmful if consumed in excessive amounts.

fertilize     (in biology) The merging of a male and a female reproductive cell (egg and sperm) to set in create a new, independent organism.

fossil     Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

fruit     A seed-containing reproductive organ in a plant.

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.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

genome     The complete set of genes or genetic material in a cell or an organism. The study of this genetic inheritance housed within cells is known as genomics.

insect     A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.

larva     (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)

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.

microscope     An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

mineral     Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns). (in physiology) The same chemicals that are needed by the body to make and feed tissues to maintain health.

morph     Short for metamorphosis, it means to change from one form to another (such as from a caterpillar to a butterfly). Or it can mean to evolve or mutate, where one or more parts of the genome undergo some sort of change in their chemistry — and potentially in their function.

muscle     A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.

National Institutes of Health (or NIH)      This is the largest biomedical research organization in the world. A part of the U.S. government, it consists of 21 separate institutes — such as the National Cancer Institute and the National Human Genome Research Institute — and six additional centers. Most are located on a 300 acre facility in Bethesda, Md., a campus containing 75 buildings. The institutes employ nearly 6,000 scientists and provide research funding to more than 300,000 additional researchers working at more than 2,500 other institutions around the world.

nerve     A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

nervous system     The network of nerve cells and fibers that transmits signals between parts of the body.

neurobiologist     Scientist who studies cells and functions of the brain and other parts of the nervous system.

neuron     An impulse-conducting cell. Such cells are found in the brain, spinal column and nervous system.

neuropeptides      This is the most diverse group of signaling molecules in the brain. Each member of this group is a peptide — a molecule made of two or more amino acids (the building blocks of proteins). Neuropeptides ferry messages between nerve cells in the brain.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

Pacific     The largest of the world’s five oceans. It separates Asia and Australia to the west from North and South America to the east.

predator     (adjective: predatory) A creature that preys on other animals for most or all of its food.

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.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

sea anemone     An animal that usually lives on the seafloor and reefs. Although the young larvae disperse through the water, they eventually settle and permanently anchor themselves to a solid structure. They have a tube like structure and resemble a soft, flower. But what appear to be petals are actually stinging tentacles that ring their mouths.

sex     (in biology) An animal’s biological status, typically male or female. There are a number of indicators of biological sex, including sex chromosomes, gonads, internal reproductive organs, and external genitals. It can also be a term for some system of mating between male and female animals such that each parent organism contributes genes to the potential offspring, usually through the fertilization of an egg cell by a sperm cell.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

sperm     The reproductive cell produced by a male animal (or, in plants, produced by male organs). When one joins with an egg, the sperm cell initiates fertilization. This is the first step in creating a new organism.

sponge     A primitive aquatic animal with a soft, porous body.

synapse     The junction between neurons that transmits chemical and electrical signals.

taste     One of the basic properties the body uses to sense its environment, especially foods, using receptors (taste buds) on the tongue (and some other organs).

tissue     Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

tree of life     A diagram that uses a branched, treelike structure to show how organisms relate to one another. Outer, twiglike, branches represent species alive today. Ancestors of today’s species will lie on thicker limbs, ones closer to the trunk.

vein     Part of the body’s circulation system, these tubes usually carrying blood toward the heart.

venom     A poisonous secretion of an animal, such as a snake, spider or scorpion, usually transmitted by a bite or sting.

waste     Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.

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