The unit of length is the meter. Other units are arranged in relation to the meter. For instance, 1m=100cm; centi-means 1/100, so a centimeter is 1/100 meter. That means there are 100 centimeters in 1 meter.



Mass is the amount of matter in an object. The units of mass are the gram and kilogram. 1 kg =1,000 g = 1,000,000 mg.



Volume is the amount of space an object occupies. Its unit is the liter.



The unit of time is the second. In a minute there are 60 seconds, and one hour is 60 minutes.


To measure temperature, there are three familiar scales: Celsius (C), Fahrenheit (F) and Kelvin (K).

The unit of temperature commonly used all over the world is the degree Celsius (C).





Besides the microscope, dissection kits, certain chemicals and dyes, and models and posters, the glassware above is commonly used for practical work in the biology laboratory.


Reagents (Indicators)

In biology laboratories, special solutions and dyes are used as indicators, to identify various substances. The most commonly used indicators are shown in the table.

As seen, if glucose reacts with Fehling or Benedict solution, the color of the solution changes to red.


Lab safety

The laboratory has the potential to be either a safe place or a dangerous place. The difference depends on your knowledge of and adherence to safe laboratory practices. As a result, it is very important that you read the information provided here. A few basic rules for working safely in the laboratory include the following:

General rules

1-Always keep your work area clean.

2-Wear proper safety clothing.

3-Wear proper eye protection.

4-Read all directions for an experiment several times.

5-Follow the direction exactly as they are written.

6-Be careful not to spill any material in the lab.

7-Always wash your hands before and after each experiment.

8-Do not eat or drink in the lab



First aid rules

Ø Report all accidents to your teacher immediately.

Ø Know where the first aid kits and fire extinguishers are located.

Ø Know where and how to report an accident or fire.

Heat and fire safety

Ø Never use a heat source without wearing safety goggles or glasses.

Ø Never heat a chemical that you have not been instructed to heat.

Ø Never reach across a flame.

Ø When working with a Bunsen burner, do not touch a hot burner.

Ø Never leave a lighted burner unattended.

Ø When heating a test tube or bottle, always point it away from yourself and others.

Ø Never heat a liquid in a closed container.

Ø Use tongs and clamps when handling hot containers.

Chemical safety

Ø Never taste, touch or smell a chemical unless you are instructed to do so by your teacher.

Ø Use only those chemicals needed in the activity.

Ø Dispose of all chemicals properly.

Ø Never mix chemicals for the fun of it.

Ø Always wear safety goggles.

Ø Handle chemicals carefully.


Glassware safety

Ø Never eat or drink from lab glassware.

Ø Do not handle glassware with your bare hands.

Ø Never use cracked or chipped glassware in the lab.

Ø Broken glassware should be swept up immediately.

Ø Never pick up broken glassware with your fingers.

Ø Use proper equipment when handling hot glassware.

Ø Make sure glassware is clean before you use it.

Ø Make sure glassware is clean before you put it away.

Sharp instrument safety

Ø Handle scalpels and razor blades with extreme care.

Ø Always cut materials with the sharp instruments going away from you.

Ø Immediately notify your teacher if you cut yourself.




absorption The process by which the products of digestion are transferred into the body's internal environment, enabling them to reach the cells.

acid A substance that increases the number of hydrogen ions in a solution.

acid rain The precipitation of sulfuric acid and other acids in rain. The acids form when sulfur dioxide and nitrogen oxides released during the combustion of fossil fuels combine with water and oxygen in the atmosphere.

acquired immunodeficiency syndrome (AIDS) A collection of disorders that develop as a result of infection by the human immunodeficiency virus (HIV), which attacks helper T cells, crippling the immune system and greatly reducing the body's ability to fight infection; results in premature death brought about by various diseases that overwhelm the compromised immune system.

activetransportTransport of molecules against a concentration gradient (from regions of low concentration to regions of high concentration) with the aid of proteins in the cell membrane and energy from ATR

adenosine triphosphate (ATP) A common form in which energy is stored in living systems; The energy coin of the cell.

alveoli Tiny, thin-walled, inflatable sacs in the lungs where oxygen and carbon dioxide are exchanged.

amino acids The subunits (monomers) from which proteins (polymers) are assembled. Each amino acid consists of an amino functional group, and a carboxyl acid group, and differs from other amino acids by the composition of an R group.

amphibians Class of terrestrial vertebrates which lay their eggs (and also mate) in water but live on land as adults following a juvenile stage where they live in water and breathe through gills. Amphibians were the first group of land vertebrates; today they are mostly restricted to moist habitats.

Animalia Animal Kingdom. Multicellular eukaryotic group characterized by heterotrophic nutritional mode, usually organ and tissue development, and motility sometime during the organism's life history.

antibiotics Substances produced by some microorganisms, plants, and vertebrates that kill or inhibit the growth of bacteria.

antibodies Proteins produced by immune system cells that bind to foreign molecules and microorganisms and inactivate them.

antigens Molecules carried or produced by microorganisms that initiate antibody production; mostly proteins or proteins combined with polysaccharides.

anus The posterior opening of the digestive tract.

aorta The artery that carries blood from the left ventricle for distribution throughout the tissues of the body. The largest diameter and thickest walled artery in the body.

appendicular skeleton The bones of the appendages (wings, legs, and arms or fins) and of the pelvic and pectoral girdles that join the appendages to the rest of the skeleton; one of the two components of the skeleton of vertebrates.

appendix Blind sac at the end of the large intestine that may rupture if inflamed.

arteries Thick-walled vessels that carry blood away from the heart. Singular=artery.

Asexual reproduction A method of reproduction in which genetically identical offspring are produced from a single parent; occurs by many mechanisms, including fission, budding, and fragmentation.

atmosphere The envelope of gases that surrounds the Earth; consists largely of nitrogen (78%) and oxygen (21%). atom The smallest indivisible particle of matter that can have an independent existence.

autonomic system The portion of the peripheral nervous system that stimulates smooth muscle, cardiac muscle, and glands; consists of the parasympathetic and sympathetic systems.

autotrophs Organisms that synthesize their own nutrients; include some bacteria that are able to synthesize organic molecules from simpler inorganic compounds.


bark The outer layer of the stems of woody plants; composed of an outer layer of dead cells (cork) and an inner layer of phloem.

binomial system of nomenclature A system of taxonomy developed by Linnaeus in the early eighteenth century. Each species of plant and animal receives a two-term name; the first term is the genus, and the second is the species.

biochemical cycle The flow of an element through the living tissue and physical environment of an ecosystem; e. g., the carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus cycles.

biochemistry Chemical processes associated with living things.

biodiversity Biological diversity; can be measured in terms of genetic, species, or ecosystem diversity.

biogeography The study of the distribution of plants and animals across the earth.

biosphere All ecosystems on Earth as well as Earth's crust, waters, and atmosphere on and in which organisms exist; also, the sum of all living matter on Earth.

bolus A mass of chewed food mixed with salivary secretions that is propelled into the esophagus during the swallowing phase of digestion.

brain The most anterior, most highly developed portion of the central nervous system.

bronchi Tubes that carry air from the trachea to the lungs (sing.: bronchus).

bronchioles Small tubes in the lungs that are formed by the branching of the bronchi; terminate in the alveoli.

bronchitis A respiratory disorder characterized by excess mucus production and swelling of the bronchioles; caused by long-term exposure to irritants such as cigarette smoke and air pollutants.


carbohydrates Organic molecules composed of carbon, hydrogen, and oxygen that serve as energy sources and structural materials for the cells of all organisms.

cardiovascular system The human circulatory system consisting of the heart and the vessels that transport blood to and from the heart.

capillaries Small, thin-walled blood vessels that allow oxygen to diffuse from the blood into the cells and carbon dioxide to diffuse from the cells into the blood.

carnivore Term applied to a heterotroph, usually an animal, that eats other animals. Carnivores function as secondary, tertiary, or top consumers in food chains and food webs.

cell cycle The sequence of events from one division of a cell to the next; consists of mitosis (or division) and interphase.

cells The smallest structural units of living matter capable of functioning independently.

cellular respiration The transfer of energy from various molecules to produce ATP; occurs in the mitochondria of eukaryotes, the cytoplasm of prokaryotes. In the process, oxygen is consumed and carbon dioxide is generated.

central nervous system (CNS) The section of the nervous system that includes the brain and spinal cord.

chlorophyll The pigment in green plants that absorbs solar energy.

chloroplasts Disk-like organelles with a double membrane found in eukaryotic plant cells; contain thylakoids and are the site of photosynthesis.

chromosomes Structures in the nucleus of a eukaryotic cell that consist of DNA molecules that contain the genes.

circadian rhythms Biorhythms that occur on a daily cycle.

circulatory system One of eleven major body organ systems in animals; transports oxygen, carbon dioxide, nutrients, and waste products between cells and the respiratory system and carries chemical signals from the endocrine system; consists of the blood, heart, and blood vessels.

classes Taxonomic subcategories of phyla.

clone An exact copy of a DNA segment; produced by recombinant DNA technology.

commensalism A symbiotic relationship in which one species benefits and the other is not affected.

community All species or populations living in the same area.

consumers The higher levels in a food pyramid; consist of primary consumers, which feed on the producers, and secondary consumers, which feed on the primary consumers.

coronaryarteriesArteries that supply the heart's muscle fibers with nutrients and oxygen.

cytology The branch of biology dealing with cell structure.

cytoplasm The viscous semiliquid inside the plasma membrane of a cell; contains various macromolecules and organelles in solution and suspension.


deoxyribonucleic acid (DNA) A nucleic acid composed of two polynucleotide strands wound around a central axis to form a double helix; the repository of genetic information. Nucleic acid that functions as the physical carrier of inheritance for 99% of all species.

dermis One of the two layers of skin; a connective tissue layer under the epidermis containing elastic and collagen fibers, capillary networks, and nerve endings.

diabetes mellitus Types I and II A disorder associated with defects in insulin action. Type I diabetes is characterized by inadequate insulin secretion; Type II diabetes is characterized by impaired insulin secretion in response to elevated blood glucose levels or by loss of sensitivity to insulin by target cells.

diaphragm A dome-shaped muscle that separates the thoracic and abdominal cavities.

diffusion The spontaneous movement of particles from an area of higher concentration to an area of lower concentration.

digestion The process of breaking down food into its molecular and chemical components so that these nutrient molecules can cross plasma membranes.

digestive system One of eleven major body organ systems in animals; converts food from the external environment into nutrient molecules that can be used and stored by the body and eliminates solid wastes; involves five functions: movement, secretion, digestion, absorption, and elimination.

diversity The different types of organisms that occur in a community.


ecology The study of how organisms interact with each other and their physical environment.

ecosystem The community living in an area and its physical environment.

element A substance composed of atoms with the same atomic number; cannot be broken down in ordinary chemical reactions.

embryo Term applied to the zygote after the beginning of mitosis that produces a multicellular structure.

endoplasmic reticulum (ER) A network of membranous tubules in the cytoplasm of a cell; involved in the production of phospholipids, proteins, and other functions. Rough ER is studded with ribosomes; smooth ER is not.

energy The ability to bring about changes or to do work.

enzymes Protein molecules that act as catalysts in biochemical reactions.

epidermis 1. The outermost layer of skin consisting of several layers of epithelial cells -notably, keratinocytes- and, in the inner layer of the epidermis, basal cells and melanocytes. 2. The outer layer of cells in the plant body, often covered by a waxy cuticle.

epiglottis A flap of tissue that closes off the trachea during swallowing.

erythrocytes Red blood cells; doubly concave, enucleated cells that transport oxygen in the blood.

esophagus The muscular tube extending between and connecting the pharynx to the stomach.

eukaryote A type of cell found in many organisms including single-celled protists and multicellular fungi, plants, and animals; characterized by a membrane-bounded nucleus and other membranous organelles; an organism composed of such cells.

evaporation The part of the hydrologic cycle in which liquid water is converted to vapor and enters the atmosphere.

excretion The process of removing the waste products of cellular metabolism from the body.

excretory system One of eleven major body systems in animals; regulates the volume and molecular and ionic constitution of internal body fluids and eliminates metabolic waste products from the internal environment.


families 1. In taxonomy, term applied to subcategories within orders. 2. Term applied to a group of similar things, such as languages, chromosomes, etc.

fats Triglycerides that are solid at room temperature.

fauna Term referring collectively to all animals in an area. The zoological counterpart of flora.

feces Semisolid material containing undigested foods, bacteria, bilirubin, and water that is produced in the large intestine and eliminated from the body.

fertilization The fusion of two gametes (sperm and ovum) to produce a zygote that develops into a new individual with a genetic heritage derived from both parents.

filter feeders Organisms such as sponges that feed by removing food from water that filters through their body.

flagella Long, whip-like locomotion organelles found in both prokaryotic and eukaryotic cells; sing.: flagellum.

flora Term collectively applied to all of the plants in an area. Thebotanicalcounterpartoffauna.

flowers The reproductive structures in angiosperm sporophytes where gametophytes are generated

food chain The simplest representation of energy flow in a community. At the base is energy stored in plants, which are eaten by small organisms, which in turn are eaten by progressively larger organisms; the food chain is an oversimplification in that most animals do not eat only one type of organism.

fruit A ripened ovary wall produced from a flower.


Gaia A hypothetical superorganism composed of the Earth's four spheres: the biosphere, hydrosphere, lithosphere, and atmosphere.

gametes Haploid reproductive cells (ovum and sperm).

genera Taxonomic subcategories within families (sing.: genus), composed of one or more species.

genes Specific segments of DNA that control cell structure and function; the functional units of inheritance. Sequence of DNA bases usually code for a polypeptide sequence of amino acids.

gene therapy The insertion of normal or genetically altered genes into cells through the use of recombinant DNA technology; usually done to replace defective genes as part of the treatment of genetic disorders.

genetics The study of the structure and function of genes and the transmission of genes from parents to offspring.

genome 1. The set of genes carried by an individual. 2. The set of genes shared by members of a reproductive unit such as a population or species.

gestation Period of time between fertilization and birth of an animal. Commonly called pregnancy.

Golgi complex Organelles in animal cells composed of a series of flattened sacs that sort, chemically modify, and package proteins produced on the rough endoplasmic reticulum.

greenhouse effect The heating that occurs when gases such as carbon dioxide trap heat escaping from the earth and radiate it back to the surface; so-called because the gases are transparent to sunlight but not to heat and thus act like the glass in a greenhouse.


habitat disruption A disturbance of the physical environment in which a population lives.

hardwoods Term applied to dicot trees, as opposed to softwoods, a term applied to gymnosperms.

heart Muscular structure that pumps blood through the circulatory system by contracting and relaxing.

hemoglobin A red pigment in red blood cells that can bind with oxygen and is largely responsible for the blood's oxygen-carrying capacity. Hemoglobin is composed of four polypeptide chains, two alpha (a) and two beta (b) chains.

herbaceous Term applied to a non-woody stem/plant with minimal secondary growth.

herbivores Term pertaining to a heterotroph, usually an animal, that eats plants or algae. Herbivores function in food chains and food webs as primary consumers.

heterotrophs Organisms that obtain their nutrition by breaking down organic molecules in foods; include animals and fungi.

homeostasis The ability to maintain a relatively constant internal environment.

Human Genome Project Federally funded project to determine the DNA base sequence of every gene in the human genome.

human immunodeficiency virus (HIV) The retrovirus that attacks T-cells in the human immune system, destroying the body's defenses and allowing the development of AIDS.

hypertension High blood pressure; blood pressure consistently above 140/90.


immune system One of the eleven major body organ systems in vertebrates; defends the internal environment against invading microorganisms and viruses and provides defense against the growth of cancer cells.

ingestive feeders Animals that ingest food through a mouth.

integumentary system The skin and its derivatives (hair, nails, feathers, horns, antlers, and glands), which, in multicellular animals, protect against invading foreign microorganisms and prevent the loss or exchange of internal fluids.


karyotype The chromosomal characteristics of a cell; also, a representation of the chromosomes aligned in pairs, kidney stones Crystallized deposits of excess wastes such as uric acid, calcium, and magnesium that may form in the kidney, kilocalorie The energy needed to heat 1000 grams of water from 14.5 to 15.5 degrees C.

kingdoms Five broad taxonomic categories (Monera, Protista, Plantae, Fungi, Animalia) into which organisms are grouped, based on common characteristics.


large intestine Consists of the cecum, appendix, colon, and rectum; absorbs some nutrients, but mainly prepares feces for elimination.

larynx A hollow structure at the beginning of the trachea. The vocal cords extend across the opening of the larynx.

leaves The site of photosynthesis; one of the three major organs in plants.

lipids One of the classes of organic macromolecules. Lipids function in the long-term storage of biochemical energy, insulation, structure and control. Examples of lipids include the fats, waxes, oils and steroids (e.g. testosterone, cholesterol).

leukocytes White blood cells; primarily engaged in fighting infection.

lymphatic system A network of glands and vessels that drain interstitial fluid from body tissues and return it to the circulatory system.

lysosomes Membrane-enclosed organelles containing digestive enzymes. The lysosomes fuse with food vacuoles and enzymes contained within the lysosome chemically breakdown and/or digest the food vacuole's contents.


macronutrients 1. Elements needed by plants in relatively large (primary) or smaller (secondary) quantities. 2. Foods needed by animals daily or on a fairly regular basis.

melanin A pigment that gives the skin color and protects the underlying layers against damage by ultraviolet light; produced by melanocytes in the inner layer of the epidermis.

metabolism The sum of all chemical reactions (energy exchanges) in cells.

migration Movement of organisms either permanently (as in the migration of humans to the Americas) or temporarily (migratory birds such as Canadian geese).

mitochondria Self-replicating, membrane-bound cytoplasmic organelles in most eukaryotic cells that complete the breakdown of glucose, producing NADH and ATP (singular term: mitochondrion). The powerhouse of the cell. Organelles within eukaryotes that generate (by chemiosmosis) most of the ATP the cell needs to function and stay alive.

Monera Prokaryotic kingdom that includes (in the most widely accepted classification system) archaebacteria, eubac- teria, and cyanobacteria. Members of this kingdom were among the first forms of life over 3.5 billion years ago.

multicellular organisms Composed of multiple cells and exhibiting some division of labor and specialization of cell structure and function.

mutualism A form of symbiosis in which both species benefit. The classic example is lichens, which are a symbiosis between an alga and a fungus. The alga provides food and the fungus provides water and nutrients.


nephron A tubular structure that is the filtering unit of the kidney; consists of a glomerulus and renal tubule.

nerves Bundles of neuronal processes enclosed in connective tissue that carry signals to and from the central nervous system.

nervous system One of eleven major body organ systems in animals; coordinates and controls actions of internal organs and body systems, receives and processes sensory information from the external environment, and coordinates short-term reactions to these stimuli.

niche The biological role played by a species.

orders Taxonomic subcategories of classes.

organelles Cell components that carry out individual functions; e.g., the cell nucleus and the endoplasmic reticulum. Subcellular structures (usually membrane-bound and unique to eukaryotes) that perform some function, e.g. chloroplast, mitochondrion, nucleus.

organism An individual, composed of organ systems (if multicellular). Multiple organisms make up a population.

organs Differentiated structures consisting of tissues and performing some specific function in an organism. Structures made of two or more tissues which function as an integrated unit. e.g. the heart, kidneys, liver, stomach.

organ systems Groups of organs that perform related functions.

osmosis Diffusion of water molecules across a membrane in response to differences in solute concentration. Water moves from areas of high-water/low-solute concentration to areas of low-water/high-solute concentration.

ozone A triatomic (03) form of oxygen that is formed in the stratosphere when sunlight strikes oxygen atoms. This atmospheric ozone helps filter radiation from the sun.


pancreas A gland in the abdominal cavity that secretes digestive enzymes into the small intestine and also secretes the hormones insulin and glucagon into the blood, where they regulate blood glucose levels. A digestive organ that produces trypsin, chymotrypsin and other enzymes as a pancreatic juice, but which also has endocrine functions in the production of the hormones somatostatin, insulin, and glucagon.

parasites Organisms that live in, with, or on another organism. The parasites benefit from the association without contributing to the host, usually they cause some harm to the host.

parasitism A form of symbiosis in which the population of one species benefits at the expense of the population of another species; similar to predation, but differs in that parasites act more slowly than predators and do not always kill the host. A type of symbiosis in which one organism benefits at the expense of the other, for example the influenza virus is a parasite on its human host.Viruses, are obligate intracellular parasites.

parasympathetic system The subdivision of the autonomic nervous system that reverses the effects of the sympathetic nervous system. Part of the autonomic nervous system that controls heartbeat, respiration and other vital functions.

penicillin The first of the so-called wonder drugs; an antibiotic discovered by Sir Alexander Fleming.

peripheral nervous system (PNS) The division of the nervous system that connects the central nervous system to other parts of the body. Components of the nervous system that transmit messages to the central nervous system.

pharynx The passageway between the mouth and the esophagus and trachea. Food passes from the pharynx to the esophagus, and air passes from the pharynx to the trachea.

phloem Tissue in the vascular system of plants that moves dissolved sugars and other products of photosynthesis from the leaves to other regions of the plant. Phloem tissue consists of cells called sieve tubes and companion cells. Cells of the vascular system in plants that transport food from leaves to other areas of the plant.

photosynthesis The process by which plant cells use solar energy to produce ATP The conversion of unusable solar energy into usable chemical energy, associated with the actions of chlorophyll.

phototrophs Organisms that use sunlight to synthesize organic nutrients as their energy source; e.g., cyanobacte- ria, algae, and plants.

Plantae The plant kingdom; nonmobile, autotrophic, multicellular eukaryotes. Kingdom of the plants, autotrophic eukaryotes with cellulose in their cell walls and starch as a carbohydrate storage product, with chlorophylls a and b as photosynthesis pigments.

pollen grains The containers for male gametophytes of seed plants produced in a microsporangium by meiosis. Microspores produced by seed plants that contain the male gametophyte.

pollination The transfer of pollen from the anthers to the stigma by a pollinating agent such as wind, insects, birds, bats, or in a few cases the opening of the flower itself.

population A group of individuals of the same species living in the same area at the same time and sharing a common gene pool. A group of potentially interbreeding organisms in a geographic area.

precipitation The part of the hydrologic cycle in which the water vapor in the atmosphere falls to Earth as rain or snow.

predation One of the biological interactions that can limit population growth; occurs when organisms kill and consume other living organisms.

producers The first level in a food pyramid; consist of organisms that generate the food used by all other organisms in the ecosystem; usually consist of plants making food by photosynthesis.

prokaryote Type of cell that lacks a membrane-bound nucleus and has no membrane organelles; a bacterium. Prokaryotes are more primitive than eukaryotes. Cells lacking membrane-bound organelles and having a single circular chromosome, and ribosomes surrounded by a cell membrane.

protists Single-celled organisms; a type of eukaryote. Protista


radiation Energy emitted from the unstable nuclei of radioactive isotopes.

recombinant DNA technology A series of techniques in which DNA fragments are linked to self-replicating forms 1 of DNA to create recombinant DNA molecules. These molecules in turn are replicated in a host cell to create clones of the inserted segments.

red blood cell Component of the blood that transports oxygen with the hemoglobin molecule. See also erythrocyte

reflex A response to a stimulus that occurs without conscious effort; one of the simplest forms of behavior.

reptiles Taxonomic class of vertebrates characterized by scales and amniotic eggs; the first truly terrestrial vertebrate group.

respiratory system One of eleven major body organ systems in animals; moves oxygen from the external environment into the internal environment and removes carbon dioxide from the body.

ribonucleic acid (RNA) Nucleic acid containing ribose sugar and the base Uracil; RNA functions in protein synthesis. The single-stranded molecule transcribed from one strand of the DNA. There are three types of RNA, each is involved in protein synthesis. RNA is made up nucleotides containing the sugar ribose, a phosphate group, and one of four nitrogenous bases (adenine, uracil, cytosine or guanine).

ribosomes Small organelles made of rRNA and protein in the cytoplasm of prokaryotic and eukaryotic cells; aid in i| the production of proteins on the rough endoplasmic reticulum and ribosome complexes. The site of protein synthesis. The ribosome is composed of two subunits that attach to the mRNA at the beginning of protein synthesis and detach when the polypeptide has been translated.


saprophytes Organisms that obtain their nutrients from decaying plants and animals. Saprophytes are important in recycling organic material.

seed Structure produced by some plants in which the next generation sporophyte is surrounded by gametophyte nutritive tissues. An immature sporophyte in an arrested state of development, surrounded by a protective seed coat.

sexual reproduction A system of reproduction in which two haploid sex cells (gametes) fuse to produce a diploid zygote.

smoothmuscleMuscle that lacks striations; found around circulatory system vessels and in the walls of such organs as the stomach, intestines, and bladder. Involuntary, non-striated cells that control autonomic functions such as digestion and artery contraction.

species One or more populations of interbreeding or potentially interbreeding organisms that are reproductively isolated in nature from all other organisms. Populations of individuals capable of interbreeding and producing viable, fertile offspring.The least inclusive taxonomic category commonly used.

sperm The male gamete.

spinal cord A cylinder of nerve tissue extending from the brain stem; receives sensory information and sends output motor signals; with the brain, forms the central nervous system. Nerve cell collections extending from the base of the * brain to just below the last rib vertebrae.

spleen An organ that produces lymphocytes and stores erythrocytes.

stamens The male reproductive structures of a flower; usually consist of slender, thread-like filaments topped by anthers. The male reproductive structures in the flower, composed of a filament and anther

sympathetic system The subdivision of the autonomic nervous system that dominates in stressful or emergency sit- uations and prepares the body for strenuous physical activity, e.g., causing the heart to beat faster.MM

systematics The classification of organisms based on information from observations and experiments; Currently, a system that divides organisms into five kingdoms (Monera, Protista, Plantae, Fungi, Animalia) is widely used.


taiga biome The region of coniferous forest extending across much of northern Europe, Asia, and North America; characterized by long, cold winters and short, cool summers and by acidic, thin soils.

tap root A primary root that grows vertically downward and gives off small lateral roots; occurs in dicots. Root system in plants characterized by one root longer than the other roots.Example: carrot.

taxon Term applied to a group of organisms comprising a given taxonomic category

taxonomy A systematic method of classifying plants and animals. Classification of organisms based on degrees of similarity purportedly representing evolutionary (phylogenetic) relatedness.

toxins Term applied to poisons in living systems


umbilical cord The structure that connects the placenta and the embryo; contains the umbilical arteries and the umbilical vein.

unicellular Single-celled.

ureter A muscular tube that transports urine by peristaltic contractions from the kidney to the bladder.

urethra A narrow tube that transports urine from the bladder to the outside of the body. In males, it also conducts sperm and semen to the outside.

urine Fluid containing various wastes that is produced in the kidney and excreted from the bladder.

uterus The organ that houses and nourishes the developing embryo and fetus. The womb.Female reproductive organ in which the fertilized egg implants.


vaccination The process of protecting against infectious disease by introducing into the body a vaccine that stimulates a primary immune response and the production of memory cells against the disease-causing agent.

vaccine A preparation containing dead or weakened pathogens that, when injected into the body, elicit an immune response.

veins Thin-walled vessels that carry blood to the heart. Units of the circulatory system that carry blood to the heart.

ventilation The mechanics of breathing in and out through the use of the diaphragm and muscles in the wall of the thoracic cavity.

virus Infectious chemical agent composed of a nucleic acid (DNA or RNA) inside a protein coat.

vitamins A diverse group of organic molecules that are required for metabolic reactions and generally cannot be synthesized in the body.

W-X- Y-Z

white blood cell Component of the blood that functions in the immune system. Also known as a leukocyte,

wood The inner layer of the stems of woody plants; composed of xylem. X-chromosomeOneofthesexchromosomes.

xylem Tissue in the vascular system of plants that moves water and dissolved nutrients from the roots to the leaves;

zygote A fertilized egg. A diploid cell resulting from fertilization of an egg by a sperm cell















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