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Glossary Terms

abdomen the bottom part of an insect or arachnid that contains the reproductive organs (Lesson 21)
abiotic non-living (referring to non-living factors of an organism's environment) (Lessons 1, 2, 4)
abscisic acid a hormone that keeps plants from germinating or budding too early by stimulating a period of dormancy (Lesson 15)
accessory pigment a pigment other than chlorophyll in a plant cell (Lesson 15)
acid rain a type of precipitation (snow, sleet, hail, fog, or rain) with higher than normal amounts of gases called nitric and sulfur oxides (Lesson 6)
active immunity long-term immunity that is given through vaccines (Lesson 29)
active virus a virus that immediately takes over cell operations and begins making new viruses (Lesson 12)
adaptation any characteristic of an organism that makes it better suited to live in its environment (Lessons 2, 10, 15, 19, Lab 2)
adrenal gland the gland that secretes hormones that help deal with stress (Lesson 30)
aerobe an organism that needs oxygen to carry out respiration (Lesson 12)
aerobic a process or organism that needs oxygen to carry out respiration (Lesson 15)
aggression threatening or forceful behavior used by one animal to establish dominance over another (Lesson 5)
alga (plural: algae) a plant-like protist (Lesson 13)
algal bloom the rapid growth of a population of algae (Lesson 13)
allele an alternate form of a gene (Lesson 9)
allergen a substance that triggers allergies (Lesson 29)
allergy a disorder of the immune system that recognizes harmless substances as harmful (Lesson 29)
alveolus (plural: alveoli) a tiny air sac in the lungs that absorbs oxygen (Lesson 27)
amino acid a small molecule that joins with other amino acids to make up a protein (Lessons 7, 28)
amniotic egg a self sufficient environment with a protective coating that provides a developing organism with nutrition, waste removal, and gas exchange (Lessons 22, 23)
amniotic sac a sac filled with fluid used to protect and cushion the embryo or fetus (Lesson 30)
amphibian a group of organisms represented by frogs, salamanders, and caecilians (Lesson 2)
anaerobe an organism that does not need oxygen to carry out respiration (Lesson 12)
anaerobic a process or organism that does not need oxygen (Lesson 15)
angiosperm a vascular seed plant that produces seeds encased in fruit (Lessons 17, 18)
Animalia all organisms in the animal kingdom that are multicellular, eukaryotic, and heterotrophs (Lesson 19)
antenna (plural: antennae) a sensory organ that extends from an animal's head (Lesson 21)
anther structure in a flower where pollen is produced; located at the top of the filament (Lesson 18)
antibiotic a chemical produced by some bacteria or fungi that helps limit the growth of harmful bacteria (Lessons 12, 29)
antibody a protein in the body that is produced to attach to specific germs and kill them (Lessons 24, 29)
anus an opening in the body where waste is excreted (Lesson 28)
apoptosis a type of cell death (Lesson 8)
artery a muscular, elastic tube that carries blood away from the heart to the cells, tissues, and organs of the body (Lesson 26)
arthritis a disease that causes inflammation in the joints (Lesson 25)
arthroscopy a minor surgery used to diagnose a joint injury (Lesson 25)
asexual reproduction reproductive process that only requires only one parent to produce offspring that are identical to the parent (Lessons 8, 12, 14, 19, 20)
asymmetrical not identical on both sides of a middle line (Lessons 19, 20)
atherosclerosis the process in which deposits of fatty materials build-up in an artery (Lesson 26)
atrium (plural: atria) one of the upper two chambers of the heart that receives blood and forces it into the lower chambers (Lesson 26)
auditory nerve a nerve that carries impulses from the ear to the brain (Lesson 31)
auricle the outer portion of the ear in which sound waves are gathered (Lesson 31)
autotroph an organism that makes its own food (Lessons 4, 11, 12, 13, 15, 19, Lab 1)
auxin a type of plant hormone that stimulates growth (Lesson 15)
axon the part of the cell body that transmits the signal to the dendrites of another cell body (Lesson 31)
B cell a cell that produces specific antibodies for each specific germ (Lessons 24, 29)
backbone a protective covering over the spinal cord that also provides support to the animal
bacterium (plural: bacteria) a single-celled organism that lacks a nucleus; lives off nutrients of other organisms (Lesson 12, 29, Lab 3)
bacteriophage a virus that attacks bacteria (Lesson 12)
ball-and-socket joint the joint that gives the greatest range of motion; found in the shoulder and hips (Lesson 25)
bark protects the plant and provides extra support (Lesson 17)
barnacle a marine crustacean that lives its adult life attached to substrates such as rocks (Lesson 2)
behavior what an organism does and how it goes about doing it (Lesson 5)
bilateral symmetry the quality of having similar characteristics on each side of a middle line (Lessons 19, 21)
binary fission simplest form of asexual reproduction in which one cell divides to form two identical cells (Lessons 12, 13)
binomial nomenclature the system of naming organisms in which the organism is given a two-part name to indicate species; e.g., Canis lupus (Lessons 11, 12, 15)
biochemical reaction a reaction that takes place in an organism (e.g. metabolism of nutrients) (Lesson 1)
biodiversity the number of different species in a particular area (Lesson 2)
biogeochemical cycling the cycling of matter between organisms and the environment (Lesson 4)
biogeography the study of where organisms live (Lesson 1)
bioluminescence an organism's ability to produce its own light caused by a chemical reaction in an organism's body (Lesson 5)
biomagnification increasing concentrations of a chemical in higher levels of a food chain (Lesson 4)
biome a major ecosystem that is defined by its vegetation and characterized by adaptations to that environment (Lessons 1, 2)
bioremediation the process by which other bacteria are used to break down harmful substances into less harmful substances (Lesson 12)
biosphere the entire portion of Earth inhabited by life (Lessons 2, 21)
biotic living (referring to the living components of an organism's environment) (Lessons 1, 4)
birth rate the number of births in a population over a certain period of time (Lesson 3)
bladder the muscle that stretches to hold urine until it is released (Lesson 28)
blood clot platelets that stick together and trap blood cells (Lesson 26)
blood pressure pressure of the blood against the wall of the arteries (Lesson 26)
blood transfusion when blood is taken from one person and given to another (Lesson 26)
blood vessel a tube that circulates blood throughout the body (Lesson 24)
body cells all cells other than sex cells (Lesson 8)
body plan the basic shape or structure an organism takes on as it develops (Lesson 19)
bog made up of acidic and still water (Lesson 16)
bone marrow a gel substance found inside bones; produce red blood cells which are important to the functioning of the human body (Lesson 25)
bony fish fish that have skeletons made of bone instead of cartilage, scales, and jaws (Lesson 22)
brackish an aquatic environment with a mix of fresh and saltwater; used to describe the water in an estuary (Lesson 2)
brain the body's control system (Lesson 31)
brain stem the part of the brain that connects the spinal cord to the brain; controls involuntary functions (Lesson 31)
bronchi two tubes that connect the trachea to the lungs (Lesson 27)
bronchiole one of several tiny tubes located in the lungs that help spread the air over the lungs as quickly as possible (Lesson 27)
brown alga (plural: brown algae) a plant-like multicellular protist that grows in cool, rocky water (Lesson 13)
budding the process of asexual reproduction by which a small cell grows from a parent organism and breaks off a new, complete, genetically identical organism (Lessons 8, 14, 20)
calorie the amount of energy in a certain food (Lessons 24, 28)
cambium a third vascular tissue present in some plants that is located in between xylem and phloem; it produces new xylem and phloem cells (Lesson 17)
Cambrian Explosion the relatively short time over which many of the animals on the fossil record appeared; about 525 million years ago (Lessons 19, 20)
camouflage the way an organism conceals itself in order to blend in with the environment to hide from predators (Lessons 1, 2, 21)
cancellous bone a network of tiny bones located in compact bones; they are meant to withstand stress from different directions (Lesson 25)
canopy the leafy roof that is comprised of the tallest trees in the forest (Lesson 2)
capillary a small blood vessel that links the end of an artery to the beginnings of a vein (Lesson 26, 27)
carbohydrate an organic compound that is made of carbon, hydrogen and oxygen that provides energy for the cell (Lesson 7)
carbon monoxide an odorless gas that is formed when certain fuels are burned; Large quantities can be toxic to humans. (Lesson 6)
carcinogen a substance that causes cancer (Lesson 29)
cardiac muscle a specialized type of muscle found in the walls of the heart (Lesson 25)
carnivore an animal that eats other animals (Lessons 4, 19, 22, Lab 1)
cartilage strong tissue that holds joints together (Lessons 22, 25)
cartilaginous fish a type of fish with a flexible endoskeleton, scales, and a bony jaw (Lesson 22)
catastrophism the concept which states that changes in the earth's geological and biological history were due to widespread disasters like flooding or drought (Lesson 10)
cell the basic unit of structure and function in an organism; requires a microscope to see (Lessons 1, 19, Lab 4)
cell body the largest part of a neuron that receives signals from other neurons (Lesson 31)
cell division when a cell divides from one cell into two cells (Lesson 8)
cell theory the theory devised by three scientists that states that: (1) all organisms are made up of one of more cells; (2) a cell is the basic unit of structure and function in an organism; and (3) All cells come from previously existing cells (Lesson 7)
cellulose a carbohydrate that makes up the cell wall and gives support to the cell (Lessons 7, 15)
cell wall a protective covering around the plasma membrane that protects the cell and gives it shape and support; located only in bacteria, some protists, fungi, and plant cells (Lessons 12, 14, 15, 16)
central nervous system the system that sends and processes messages; includes the brain and spinal cord (Lesson 31)
centriole an oblong structure in an animal cell that associates with spindle fibers during cell division (Lesson 8)
centromere the location of the chromosome where the chromatids are held together (Lesson 8)
cephalothorax the first section of an arachnid and some insects that contains the head and the chest (Lesson 21)
cerebellum the part of the brain that controls muscle movement, balance, and coordination (Lesson 31)
cerebrum the biggest part of the brain; controls voluntary movements (Lesson 31)
cervix the narrow part of the uterus where it joins the vagina (Lesson 30)
cheliped the first set of a crustacean's legs that contain claws or pincers (Lesson 21)
chemical digestion breaking down food through chemical reactions (Lesson 28)
chemical sense a sense that functions when it comes into contact with chemicals (Lesson 31)
chest cavity the cavity in the body containing the heart and lungs (Lessons 24, 27)
chlorophyll a light-absorbing green pigment found in plant cells, some algae, and bacteria cells that allows them to make food using the sun's energy and other substances in their environment (Lessons 7, 15)
chloroplast portion of a plant cell that holds chlorophyll and in which photosynthesis occurs (Lesson 15, 16, 17)
chromatid a strand of DNA that makes up one half of a duplicated chromosome (Lesson 8)
chromosome a structure in the cell's nucleus that contains genetic material (Lessons 8, 30)
cilium (plural: cilia) one of many short, hair-like structures that are attached to cells and used to propel the organism, obtain food, and to sense the environment; tiny hairs in the nose that help clean the air that is inhaled  (Lessons 13, 20, 21, 27, 29)
circulatory system the body system that consist of the heart, blood, and blood vessels (Lessons 24, 26, 27)
classical conditioning a new stimulus is placed with an old stimulus-response relationship until this new stimulus elicits the old response (Lesson 5)
classification a grouping of organisms, or other things, based on similar characteristics (Lesson 11)
closed circulatory system system in which blood travels through vessels to the rest of the body (Lessons 20, 21, 22, 23)
club fungus classification of fungus that contains a type of spore shaped like a club (Lesson 14)
cochlea a fluid-filled bone inside the ear that change sound waves to nerve impulses (Lesson 31)
codominance when two different alleles for a trait are expressed in the phenotype of a heterozygote (Lesson 9)
colony a collection of individual organisms of the same species that live in the same place (Lesson 20)
commensalism a symbiotic relationship in which one species benefits and the other is neither harmed nor benefited (Lesson 3)
community all of the populations that live and interact in the same area (Lessons 1, 3)
community ecologist a scientist who studies the effects of interactions such as disease, competition, or predation on community structure (Lesson 1)
compact bone a bone that is dense and hard on the outside (Lesson 25)
competition a struggle between individuals for a common resource (Lesson 3)
complete metamorphosis insect life cycle in which egg, larval, pupal, and adult stages occur (Lesson 21)
complex carbohydrate a carbohydrate made of hundreds or even thousands of sugar molecules linked together; found in foods like potatoes and wheat (Lesson 28)
compound fracture a broken bone that sticks out through the skin (Lesson 25)
compound a substance that is made up of two or more elements (Lesson 7)
condensation the process of water vapor turning into a liquid (Lesson 4)
conditioning learning that a certain stimulus will lead to a specific outcome (Lesson 5)
cone the reproductive structure of a gymnosperm (Lesson 18)
coniferous tree a tree with leaves shaped like needles and cones instead of seeds (Lessons 2, 18)
conjugation the process by which a unicellular organism transfers some of its genetic material to another unicellular organism (Lessons 12, 13)
connective tissue materials that hold body tissues and organs in place (Lesson 24)
consumer an organism that obtains nutrients by feeding upon other organisms (Lesson 4)
continental shelf the gently seaword sloping surface that extends between the shoreline and the continental slope (Lesson 2)
contour feather one of the several outer feathers that give birds a smooth, aerodynamic shape for flight (Lesson 23)
contraction when muscles in the wall of the uterus begin to contract (Lesson 30)
control in an experiment, the standard or comparison (Intro, Lesson 1)
cornea the clear part of the eye that covers the iris and pupil (Lesson 31)
cotyledon a first seed leaf that sometimes stores food for the developing plant (Lessons 17, 18)
courtship display a signal made by animals aimed at the opposite sex that is meant to attract mates (Lesson 5)
crop the section of bird anatomy where the first stage of digestion takes place, softening the food in preparation for the stomach (Lesson 23)
crossing over the event that takes place during meiosis I whereby homologous chromosomes exchange segments of genetic material (Lesson 8)
cross pollinate pollen from one flower is placed on a pistil of a different flower (Lesson 9)
cuticle a waxy layer secreted by cells on the surface of a plant (Lessons 15, 16, 17)
cycad a gymnosperm found in the tropics that is similar to palm trees and ferns but produces cones (Lesson 18)
cyclic behavior any behavioral pattern that occurs regularly over a certain period of time; e.g., migration and hibernation (Lesson 5)
cytokinesis the splitting of the cytoplasm of one cell so it becomes two; takes place right after telophase in mitosis (Lesson 8)
cytoplasm the contents of the region inside the plasma membrane that contains all of the vital parts of the cell (Lessons 7, 8, 12, 13)
dam a barrier built across a waterway that controls the flow of water (Lesson 6)
daughter cell a cell that results from the process of cellular division (Lesson 8)
death rate the number of deaths in a population over a certain period of time (Lesson 3)
deciduous describes trees whose leaves fall at the end of the growing season (Lesson 2)
decomposer an organism that breaks down the chemicals in dead organisms and waste and returns material to the soil and water (Lessons 2, 4, 12, 14, 16, Lab 3)
deep zone the area of the ocean located beneath the surface zone; it is much darker and cooler than the surface zone (Lesson 2)
deforestation the removal of trees in an area, usually to make room for farming or construction on that piece of land (Lesson 2)
demography the statistical study of populations (Lesson 3)
dendrite a tiny branch extending from the cell body that transmits impulses to the cell body (Lesson 31)
dermis the inner layer of skin beneath the epidermis (Lesson 25, 26)
detritivore an organism that feeds on organisms that are dead, decaying, or breaking down (Lesson 19)
development the act of an organisms becoming more complex (Lesson 1)
dialysis a life support treatment used on patients with renal failure; a machine replaces the kidney when filtering the blood (Lesson 28)
diaphragm the muscle located at the bottom of the chest cavity; helps air move in and out the lungs (Lesson 27)
diatom unicellular plant-like protist that lives in fresh or saltwater environments (Lesson 13)
dichotomous key a series of questions scientists use to identify an organism (Lesson 11)
dicot an angiosperm that has two seed leaves (Lesson 18)
diffusion the movement of substances from an area of higher concentration to an area of lower concentration (Lesson 7)
digestion the breaking down of food; converts the food into energy the body can use (Lesson 28)
digestive system the system that breaks down food and absorbs nutrients the body needs (Lessons 24, 28)
dinoflagellate unicellular plant-like protist with two flagellum that spin to propel the protist forward (Lesson 13) 
diploid a cell's chromosomes that are in pairs (Lesson 8)
dislocation when a bone is moved out of its joint (Lesson 25)
dispersion the pattern by which individuals arrange themselves within a certain area (Lesson 3)
division the term for phylum in the plant kingdom (Lessons 15, 18)
DNA the main component of chromosomes and the genetic information of life (Lessons 7, 8, 10)
DNA replication when a DNA molecule makes a duplicate copy of itself (Lesson 8)
dominant allele an allele whose trait shows up in an organism when the allele is present (Lesson 9)
down feather one of several soft, short, fluffy feathers that keep heat from escaping a bird's body (Lesson 23)
duodenum the first part of the small intestine that breaks down the food (Lesson 28)
ear the organ used for hearing (Lesson 31)
ear canal the narrow passage where sound waves travel through the ear (Lesson 31)
eardrum a thin flap of skin that vibrates sound waves off of it (Lesson 31)
echolocation a sensory system using high-pitched sounds; used by animals such as dolphins to determine direction and the distance of objects (Lesson 5)
ecological time a matter of minutes, months, or years; a short period of time (Lesson 1)
ecologist a scientist who studies the interactions between organisms and the environment (Lesson 1)
ecology the study of the interactions between organisms and the environment (Lesson 1)
ecosystem all the organisms in an area (a community) in addition to the abiotic factors in which they interact (Lessons 1, 2)
ecosystem ecology the study of a community and its physical environment (Lesson 1)
ectotherm an animal whose body temperature is regulated by its surroundings; formerly referred to as "cold blooded" (Lesson 22)
egg the female sex cell (Lesson 30)
electron a subatomic particle with a negative charge (Lesson 7)
element a substance that cannot be broken down into simpler forms (Lesson 7)
embryo the young of any animal in the early stage of development; in plants: a young plant usually contained in a seed (Lessons 8, 17, 18, 30)
embryonic stem cell a cell in an embryo that gives rise to other stem cells and becomes specialized (Lesson 8)
emigration leaving a population (Lesson 3)
endocrine gland glands that secrete hormones into the blood stream (Lesson 30)
endocrine system the system that is run by hormones and glands (Lessons 24, 30)
endoskeleton a skeleton that is located inside the body (Lessons 21, 22)
endospore a small, round, thick-walled structure that forms inside a bacterial cell (Lesson 12)
endotherm an animal that generates internal heat to maintain body temperature; formerly referred to as "warm blooded" (Lessons 22, 23)
energy pyramid a diagram that shows the amount of energy at each level of a food chain (Lesson 4)
enzyme a protein that speeds up chemical reactions in organisms and breaks apart the chemical in foods (Lessons 7, 28)
epidermis the top and bottom covering of a leaf; the outer layer of skin (Lessons 17, 25, 26, Lab 4)
epiglottis the flap of tissue that covers the opening to the trachea (Lesson 27)
epiphyte a plant with aerial roots that grows on or attaches to another plant for support (Lesson 3)
epithelial tissue a layer of cells that protects the body (Lesson 24)
erosion the process by which the surface of the earth is worn away by wind, water, etc. (Lesson 10)
esophagus the muscular passage that connects the mouth and the stomach (Lesson 28)
estrogen the female sex hormone that produces eggs (Lesson 30)
estuary an ecosystem located where the fresh water of a river meets with the salt water of an ocean (Lesson 2)
ethologist a scientist who studies the behavior of animals (Lesson 5)
ethylene a hormone produced as gas and released into the air; stimulates the ripening of fruit and the falling of leaves from trees (Lesson 15)
euglenoid unicellular plant-like protist found in fresh water; has the ability to become heterotrophic when conditions are not right to make their own food (Lesson 13) 
eukaryote an organism whose cells contain nuclei and other membrane-bound organelles (Lessons 7, 8, 13, 14, 15, 19)
eutrophication the buildup of nutrients in lakes and ponds that causes an overgrowth of algae (Lesson 13)
evaporation the process of water changing from a liquid to a gas (Lesson 4, Lab 4)
evolution change in organisms that occurs over time (Intro, Lessons 1, 10, 11)
evolutionary time a matter of decades, centuries, millennia, and longer (Lesson 1)
excretory system the system that removes waste from the body (Lesson 24)
exoskeleton a skeleton that is located on the outside of the body (Lesson 21)
experimental group the group of organisms, other than the controls, being observed in an experiment (Intro)
expiratory reserve the amount of oxygen that can be forced out of the lungs after exhalation (Lab 6)
extinction the process of a species dying out (Lesson 10, 16)
eye the organ used for seeing (Lesson 31)
F1 generation offspring that result from crossing the parental generation (Lesson 9)
F2 generation offspring that result when two F1 organisms are crossed (Lesson 9)
fallopian tube a tube that carries the egg from the ovaries to the uterus (Lesson 30)
family the fifth broadest level of classification below kingdoms, phyla, order, and class
fat soluble able to be absorbed by fat (Lesson 28)
fertile the ability to mate with another organism of the same species to produce offspring (Lessons 11, 18)
fertilization the combination of a sperm cell and an egg cell (Lessons 8, 15, 18, 19, 30)
fetus an unborn baby after the eighth week of pregnancy (Lesson 30)
fibrin a protein that helps form blood clots (Lesson 26)
fibrous a root system in which several main roots branch many times (Lesson 17)
filament the structure in a flower that connects the stamen to the base of the flower (Lesson 18)
filter feeder an organism that eats microorganisms by filtering them out of water that passes through their body (Lessons 19, 21)
flagellum (plural: flagella) a long, whip-like structure that assist in movement (Lessons 12, 13, 15, 20)
food chain a single path of feeding and energy flow in an ecosystem (Lesson 4)
food web a series of interlocking food chains (Lesson 4)
foot a muscular appendage that helps mollusks move (Lesson 21)
fossil any remains or trace of a living thing that is preserved from another geological era (Lessons 1, 10)
fossil fuel an energy source, in the form of coal, oil, or natural gas, which has formed in the Earth's crust over hundreds of millions of years (Lessons 4, 6)
fossil record the information scientists can gain by looking at the fossils in a certain area (Lessons 1, 10, 15, 18)
fracture when a bone is cracked or broken (Lesson 25)
frond the leaf of a fern (Lesson 16)
fruit the ripened ovary of an angiosperm that protects the seeds (Lesson 18)
fruiting body reproductive structure of a fungus made up of hyphae (Lesson 14)
Fungi the kingdom in which all of the organisms are eukaryotic and heterotrophic; e.g., mold and yeast (Lessons 7, 14, 29)
gametangium structure that forms when two fungal hyphae meet and house the exchange of genetic information (Lesson 14)
gametophyte the stage in a plant's life cycle in which the plant produces sex cells (Lesson 15)
gas exchange the process in which oxygen is inhaled into the body and carbon dioxide is exhaled out (Lesson 27)
gemma (plural: gemmae) small, cup-shaped structures in liverworts used for asexual reproduction (Lesson 16)
gene a unit of hereditary information; contains DNA (Lessons 8, 10)
gene therapy a technique that uses genes to treat diseases instead of using drugs (Lesson 9)
genetic disorder an abnormality in genes that is passed down from the parents to the offspring (Lesson 9)
genetic engineering methods used to change the arrangement of DNA in an organism (Intro)
genetics the study of how genes are involved in the inheritance of traits (Lesson 9)
genome the entire set of genes, or inheritable traits, in an organism (Intro)
genotype an organism's genetic makeup, or combination of alleles (Lesson 9)
genus a group, or taxon, that contains similar organisms that are closely related; the seventh broadest level of classification below domain, kingdom, phyla, class, order, and family (Lesson 11)
germination the sprouting of an embryo out of its seed; usually occurs after the dormant stage when the embryo begins growing again (Lessons 17, 18, 23)
gestation period the amount of time from fertilization to birth (Lesson 23)
gill a organ that removes oxygen from water (Lesson 22)
ginkgo a type of ancient gymnosperm with few surviving species (Lesson 18)
gizzard the muscular organ in a bird that squeezes and grinds up tough food (Lesson 23)
gliding joint a joint where one bone slides over the other; found in wrists and ankles (Lesson 25)
global warming an average increase in the Earth's temperature, which can cause climate change (Lessons 4, 6)
gnetophyte a woody gymnosperm that lives in hot climates (Lesson 18)
golgi body sends out cells received from the ER and delivers them to other parts of the cell or releases them outside of the cell
gradualism the concept that Earth evolved slowly and continuously over time, and came to mean that species also evolved slowly over time (Lesson 10)
gravitropism the tendency for a plant to grow in response to gravity; also known as geotropism (Lesson 15)
green alga (plural: green algae) multicellular protists that closely resemble plants (Lesson 13)
greenhouse effect the trapping of heat by greenhouse gases near Earth's surface  (Lesson 6)
greenhouse gas gases that trap heat in the atmosphere, and are the main contributors of global warming (Lessons 4, 6)
growth energy used by organisms to become larger (Lesson 1)
guard cell a cell that surrounds and protects stomata by expanding and contracting to allow substances to enter and exit the plant; this is the act of opening and closing the stomata (Lesson 17)
gymnosperm a vascular seed plants that produces "naked seeds," meaning that the seeds are not protected by fruit (Lessons 17, 18)
habitat physical place where an organism lives (Lesson 3)
habituation the simplest form of learning for an organism; An organism stops responding to a particular stimulus after repeated exposure to it. (Lesson 5)
haploid a cell that has half the number of chromosomes as body cells (Lesson 8)
heart attack when blood stops flowing to any part of the heart (Lesson 26)
hemoglobin a protein that helps red blood cells carry oxygen through the body; it gives red blood cells its color (Lesson 26)
herbaceous stem a type of stem that is generally soft and green (Lesson 17)
herbivore an organism that only eats plants (Lessons 2, 3, 4, 19, 22, Lab 1)
heredity the passing of traits from parents to their children (Lesson 9)
hermaphrodite an animal or organism that has both male and female reproductive organs (Lesson 20)
heterotroph an organism that cannot make its own food and so must feed off of other organisms to obtain energy (Intro, Lessons 1, 11, 12, 13, 14, 19, 20, Lab 1)
heterozygous having two different alleles for the same trait (Lesson 9)
hibernate to slow down metabolism during long periods of cold temperatures (Lessons 2, 5, 22)
hibernation when an organism goes into a deep sleep;body temperatures drop and heart and breathing rate decrease (Lessons 2, 5, 22)
hinge joint a joint which allows forward and backward movement; found in the knees and elbows (Lesson 25)
homeostasis an organism's ability to maintain certain conditions within the body (Lessons 1, 24, 28)
homologous pair a pair of chromosomes that have the same sequence of genes (Lesson 8)
homozygous having two of the same alleles for a given trait (Lesson 9)
host the organism that provides the energy source and suitable environment necessary in order for an organism to survive (Lessons 3, 12, 20)
hormone a substance produced in one part of an organism that affects another part of that same organism; sends messages from one cell to another (Lessons 15, 30)
hornwort another seedless nonvascular plant; similar to liverworts (Lesson 16)
hybrid an organism that has two different alleles for a given trait (Lesson 9)
hydroelectric power electricity that is made using the energy of water (Lesson 6)
hypertonic a solution that has a higher solute concentration than the one to which it is being compared (Lesson 7)
hypha (plural: hyphae) a thin, thread-like tube that makes up the body of multicellular fungus (Lesson 14)
hypothalamus the gland that secretes hormones that control the pituitary gland (Lesson 30)
hypothesis a testable prediction about a specific phenomena (Intro, Lesson 19)
hypotonic a solution that has a lower solute concentration than the one to which it is being compared (Lesson 7)
immigration movement into a population (Lesson 3)
immune response how the body recognizes and defends itself against bacteria, viruses, and other foreign substances (Lesson 29)
immune system the body's defense system that protects it from pathogens (Lessons 24, 29)
immunity when the body has the ability to kill pathogens before they cause illness (Lesson 29)
imperfect fungus (plural: imperfect fungi) classification of fungus that does not reproduce sexually or have never been observed to reproduce sexually (Lesson 14)
imprinting when an animal forms a social attachment with another organism during a short period of time after the animal is born or is hatched; usually takes place with no reinforcement (Lesson 5)
incomplete dominance a type of inheritance whereby a heterozygote has a phenotype that is intermediate to that of its parents' phenotypes (Lesson 9)
incomplete metamorphosis a life cycle of certain insects that does not include a larval or pupal stage (Lesson 21)
infectious disease disease that is passed from one infected person to another (Lesson 29)
inflammatory response the second line of defense when the body's cells are damaged; blood circulation increases around the affected area (Lesson 29)
inhale to breathe in (Lesson 27)
innate behavior a behavior that an organism is born with, which is passed down from one generation to the next (Lesson 5)
insecticide a chemicals that is used to kill insects (Lesson 4)
insight using prior knowledge and experience to solve new problems (Lesson 5)
instinct an inborn response to stimuli that depends on sending and processing messages in the brain (Lessons 20, 31)
integumentary system a body system that consists of the skin, along with hair and nails; used for protection (Lessons 24, 25)
interphase the longest stage of the cell cycle; The cell grows and DNA replicates during this stage. (Lesson 8)
interspecific between two different species (Lesson 3)
intertidal the area between the lowest and highest tide lines on the shore (Lesson 2)
intraspecific among the same species (Lesson 3)
introduced species organisms that are placed (usually by people) in a new location different from where they normally live; also called exotic or non-native species (Lesson 1)
invertebrate an animal without backbones (Lesson 22)
involuntary muscle a muscle that a person cannot control (Lesson 25)
iris the colored part of the eye (Lesson 31)
isotonic two solutions with equal solute concentrations (Lesson 7)
jawless fish primitive fish with flexible endoskeletons, no scales, and no jaws (Lesson 22)
joint the place where two bones meet (Lesson 25)
keystone species a species that influences the survival of other organisms in an ecosystem (Lesson 4)
kidney an organ in the ribcage that forms and excretes urine (Lesson 28)
large intestine the intestine where waste is collected and processed for excretion (Lesson 28)
larva the immature form of an organism (Lessons 20, 21)
larynx a structure located at the upper part of the trachea, in which the vocal cords are located; the voice box (Lesson 27)
latent virus a virus that does not immediately take over a cell's operations upon entering the cell (Lesson 12)
lateral line a canal that runs the length of a fish's or amphibian's body and serves as a sensory organ (Lesson 22)
law a statement about how things work in nature that is accepted and believed to be true all the time (Intro)
learned behavior behavior that is acquired through experience (Lesson 5)
lens a piece of shaped glass used to focus the light from the microscope; the part of the eye that focuses light to form an image on the retina (Lesson 31)
lichen an organism that is composed of a fungus and a green alga or bacteria (Lessons 14, 16)
ligament strong tissue that connect the joints (Lesson 25)
limiting factor an environmental factor that can limit growth of a population; they also cause population numbers to decrease (Lesson 3)
lipid an organic compound that contains carbon, oxygen, hydrogen, and phosphorous; these compounds are energy-rich (Lesson 7)
liverwort a type of seedless nonvascular plant that grows flat and has a leaf-like body (Lesson 16)
lung capacity the amount of oxygen that lungs can inhale (Lab 6)
lymph the fluid that leaks out when blood is circulating in the body (Lesson 26)
lymph node part of the system that removes germs from lymph before it returns to the blood plasma (Lesson 29)
lymphatic system a network of vessels that are connected to large veins in the chest (Lessons 24, 26)
lymphocyte a white blood cell that attacks and kills germs (Lesson 29)
mammary gland the mammalian gland responsible for milk production (Lesson 23)
manatee a herbivorous marine mammal commonly found in estuaries (Lesson 2)
mantle the outer fold of skin that is responsible for forming the shell of a mollusk (Lesson 21)
marker molecule a protein that determines blood type (Lesson 26)
mechanical digestion breaking down food through chewing (Lesson 28)
meiosis a cellular process that produces sex cells for reproduction (Lessons 8, 13, 16, 18)
melanin pigment that determines the color of a person's skin (Lessons 24, 25, 26)
membrane the outer protective barrier found in some cells (Lesson 19)
membrane-bound organelle a specialized structure that carries out specific functions and is covered by membrane; found in eukaryotic cells (Lesson 19)
menstrual cycle a month long cycle in which menstruation and ovulation occur (Lesson 30)
menstruation the process in which extra tissue, blood, and the dried up egg breaks down and exits the body through the vagina (Lesson 30)
metabolism a chemical process that converts food into energy (Lesson 30)
metamorphosis the process of changes in form throughout an organism's life cycle (Lessons 21, 22)
metastasize to spread throughout the body (Lesson 8)
microscope an instruments that makes small objects look larger (Lesson 7)
migrate to move from one region or climate to another (Lesson 2)
migration a movement from one region or climate to another; It is an example of a cyclic behavior. (Lesson 5)
mimicry a technique used by animals in order to avoid becoming prey (Lesson 19)
mitochondrion (plural: mitochondria) an organelle within a cell that releases energy from stored food molecules (Lesson 15)
mitosis a type of cellular division in which one cell divides to form two cells that are identical to each other and the parent cell (Lesson 8)
molting the process of shedding an outer covering such as a shell, feathers, or skin, to make room for new growth (Lessons 21, 22)
monocot an angiosperm that has one seed leaf (Lesson 18)
moss a tiny, leafy, and flowerless plant that grows predominantly in moist areas (Lessons 2, 16)
motor nerve a nerve that transmits commands from the central nervous system (Lesson 31)
multicellular organisms that have more than one cell, such as humans (Lessons 1, 7, 13, 15, 20)
multiple alleles when a single gene is affected by three or more alleles (Lesson 9)
muscle tissue tissue that provides movement to the body (Lesson 24)
muscular system the body system that works with the skeletal system to produce movement, move blood, and push food through the body (Lessons 24, 27)
muscular tail a growth that extends past the anus during development that helps propel the animal when swimming; also known as an "post-anal tail" (Lesson 22)
mutate to change; in biology, a change in genetic material that creates diversity (Lessons 10, 12)
mutualism a relationship between two organisms in which both benefit from living together; a type of symbiosis (Lessons 3, 13, 14)
mycelium the thick, underground mass of tangled hyphae that forms the body of a fungus (Lesson 14)
mycorrhiza (plural: mycorrhizae) the symbiotic relationship of plant roots and fungi (Lessons 14, 15)
nasal cavity the large air-filled space above and behind the nose (Lessons 24, 27, 31)
natural resource a resource that occurs in a natural state and is valuable to humans (Lesson 6)
natural selection the process by which life forms have traits that better suit them to a certain environment (Lesson 10)
nematocyst a specialized cell for stinging found in cnidarians (Lesson 20)
neritic the area just beyond the intertidal zone, from the lowest tide mark to the continental shelf (Lesson 2)
nerve cord a tract of tissue located above the notochord that, in vertebrates, will develop into the spinal cord (Lesson 22)
nerve impulse a message that is carried through the body (Lesson 31)
nerve a bundle of fibers that send signals to the spinal cord and the brain (Lesson 31)
nervous system the system of nerves in a living organism (Lessons 20, 23, 24, 31)
nervous tissue tissue that is made up of cells that send messages through the body (Lesson 24)
neuron a cell that processes and passes on information (Lesson 24)
neurotransmitter a chemical that transmits impulses from a neuron to another cell (Lesson 31)
niche the role of a species and all the resources it uses to survive (Lesson 3)
nitrogenous base a compound that contains nitrogen; there are four major types in DNA: adenine, thymine, guanine, and cytosine (Lesson 8)
nocturnal of, or pertaining to, the night; in biology, refers to organisms that are awake by night and sleep by day (Lesson 22)
noninfectious disease a disease that cannot be spread by contact with another infected animal (Lesson 29)
nonrenewable resource a resource that are easily depleted because they are not replaced in a useful time frame (Lesson 6)
non-vascular plant plants that do not have tube-like structures to transport nutrients and must use other ways to transport water and other materials (Lessons 15, 16)
notochord a firm, flexible cord that runs along the back of a chordate (Lesson 22)
nuclear envelope the membrane that surrounds the nucleus (Lesson 7)
nucleic acid an organic molecule made of carbon, oxygen, hydrogen, nitrogen, and phosphorous; DNA and RNA are nucleic acids. (Lesson 7)
nucleus the area inside a eukaryotic cell that directs the cell's activities (Lessons 13, 19)
nutrient a chemical found in food that is needed to survive (Lesson 24)
oceanic zone the marine biome that is located just beyond the neritic zone; also called the open-ocean (Lesson 2)
offspring the result of organism reproduction (Lessons 1, 8)
omnivore an animal that eats plants and animals (Lesson 19, Lab 1)
open circulatory system circulatory system in which the heart pumps blood into an open space in the body, instead of through a closed network of vessels (Lessons 20, 21)
operant conditioning a stimulus comes after a behavior; When a behavior takes place many times, it has been reinforced in the past, when a behavior stops taking place as often, it has been punished in the past. (Lesson 5)
optic nerve a large nerve that connects the eye to the brain (Lesson 31)
organ a structure made up of two or more tissues that work together to carry out a life function (Lesson 19)
organelle a structure found in cells that have a specialized function (Lesson 7, 15)
organic compound a compound that contains carbon (Lesson 7)
organism a living thing (Intro, Lessons 1, 7)
organismal ecology the study of the effects of abiotic and biotic forces on an individual organism (Lesson 1)
organ system a group of organs that work together to perform a like function (Lesson 19)
osteoporosis a condition in which the bones become soft and brittle, which is caused by the loss of minerals (Lesson 25)
ovary a reproductive structure; in flowers, the female part of the flower or part of the carpel (which contains all female parts of flower); the gland that secretes estrogen; found only in females (Lessons 18, 30)
ovulation when an egg is released from the ovaries (Lesson 30)
ovule a plant structure that contains the egg cell that, when fertilized, will become a seed (Lesson 18)
ozone ground-level, or "bad ozone" is formed when sunlight and gases mix in the troposphere; the "good ozone" that is located in the stratosphere: absorbs UV light so it cannot get back to the Earth's surface (Lesson 6)
pain receptor a nerve ending that detects pain (Lesson 31)
palisade layer the layer below the upper epidermis layer that contains most of the plant's chlorophyll (Lesson 17)
pancreas the gland that makes hormones that regulates sugar in the blood (Lesson 30)
parasite an organism that lives on or in a host, causing harm to the host (Lessons 3, 11, 13, 14, 19, 20, 21)
parasitism a symbiotic relationship in which a parasite obtains nourishment from a host (Lesson 3)
paramecium a complex freshwater protist with two nuclei (Lesson 13)
parent cell the cell that is divided during cell division (Lesson 8)
passive immunity short-term immunity in which antibodies are given to the body, usually while babies are still in the womb (Lesson 29) 
pathogen a disease-causing agent such as bacteria or virus (Lessons 12, 24, 29)
peat layers upon layers of moss (Lesson 16)
pedigree a chart that shows relationships between relatives, and which relatives have a particular trait (Lesson 9)
penicillin an antibiotic produced naturally from a type of imperfect fungi (Lesson 14)
penis the male sex organ used to carry semen and urine out the body (Lesson 30)
permafrost permanently frozen subsoil (Lesson 2)
peripheral nerve a nerve that starts at both the brain and the spinal cord (Lesson 31)
peripheral nervous system the nerves that extend from the brain and run throughout the body (Lesson 31)
peristalsis muscular motion in the esophagus that pushes the food to the stomach (Lesson 28)
pesticide a chemical that is used to kill organisms that destroy crops (Lesson 4)
petal a colorful, leaf-like structure in some flowering plants (Lesson 18)
pharyngeal pouch one of the pouches located in the throat area; In fish, they will develop into gills. In vertebrates they are only present during development; also known as "gill slits." (Lesson 22)
pharynx upper part of the throat that connects the mouth and nasal passages with the esophagus (Lesson 27)
phenotype an organism's physical appearance (Lesson 9)
pheromone a chemical signal given off by an animal that is meant to influence the behavior of another animal of the same species (Lesson 5)
phospholipid a type of lipid that is found in large quantities in cell membranes (Lesson 7)
photoperiodism a plant's response to periods of light and darkness (Lesson 15)
photosynthesis the process by which plants use water, carbon dioxide, and sunlight to make their own food (Lessons 1, 2, 3, 13, 15, 17)
phototropism a plant's tendency to grow toward a light source (Lesson 15)
phylum (plural: phyla) the third broadest level of the classification system; phylum is below kingdom (Lessons 18, 19)
phloem vascular tissue that carries food (Lesson 17)
phylogeny the evolutionary history of a species or group of related species (Lessons 11, 13, 15)
phytoplankton microscopic photosynthetic organisms found in water (Lesson 4)
pigment a chemical that produces color (Lesson 13)
pioneer species a type of species who make the environment more hospitable for different species to move in (Lesson 16)
pistil the female reproductive part of a flower (Lessons 9, 18)
pituitary gland the gland that makes hormones that affect and control other endocrine glands (Lesson 30)
pivot joint a joint in which one bone rotates around another; found in the neck (Lesson 25)
placenta the organ that forms in a pregnant female mammal that nourishes the developing embryo (Lessons 23, 30)
Plantae the plant kingdom, in which all organisms can make their own food using the sun's energy
plasma the liquid part of blood (Lesson 26)
plasma membrane present in both plant and animal cells; the boundary around a cell that determines which materials flow in and out of the cell (Lessons 12, 13)
plasmid a small, circular piece of DNA in bacteria that carries additional genetic information (Lesson 12)
platelet a blood cell that uses its sticky surface to form blood clots (Lesson 26)
pollen male part of a flower that contains male sex cells, or sperm (Lesson 9)
pollen tube a structure that forms when a flower is pollinated, allowing the sperm cells to travel down the tube and fertilize the egg (Lesson 18)
pollination the transfer of pollen from male to female reproductive structures (Lesson 18)
pollutant a substance that causes pollution (Lessons 4, 6)
pollution a change to the environment that negatively affects living things (Lesson 6)
polygenic inheritance many genes affecting one trait (Lesson 9)
population a group of organisms of the same species that live in the same area (Lessons 1, 3)
population ecologist a scientist who studies factors, that affect the number of individuals of a population that live in a given area, such as disease, predation by other organisms, and temperature of the environment (Lesson 1)
precipitation includes rain, snow, hail, or sleet that fall to the Earth's surface from the atmosphere (Lesson 4)
predation an interaction whereby one organism consumes the other organism (Intro, Lessons 3, 19)
preening bird behavior during which the bird uses oil from a gland near the tail to comb through its feathers in order to prevent them from wearing out (Lesson 23)
premenstrual syndrome symptoms that come from menstruation (Lesson 30)
primary producer an organism that makes its own food and ultimately supports all other life in an ecosystem (Lessons 2, 4, Lab 1)
prokaryote an organism whose cells lack a nucleus and membrane-bound organelles (Lesson 7, 12)
protective coloration camouflage that allows an animal to blend in with its surroundings (Lesson 21)
protein organic compounds made of nitrogen, hydrogen, oxygen, carbon, and sulfur; made by amino acids (Lesson 7)
Protista one of the six kingdoms, in which these organisms are similar to bacteria except that they are eukaryotic; also referred to as protists (Lessons 7, 10, 13)
protist an organism that has a nucleus but is not a plant, animal, or fungus (Lessons 7, 10, 29)
protozoan unicellular, heterotrophic, animal-like protist (Lessons 3, 13)
pseudopod a bulge that extends from the cytoplasm and is used for movement or feeding in some protozoans (Lesson 13)
puberty sexual changes that both boys and girls go through (Lesson 30)
Punnett square a chart that shows the possible combination of alleles that result from a mating or a cross (Lesson 9)
pupil the black dot located in the center of the eye, which controls the amount of light that enters the eye (Lesson 31)
purebred an organism that produces the same traits generation after generation (Lesson 9)
pyramid of numbers a graphical representation of the number of individuals at each trophic level of a food chain (Lesson 4)
radial symmetry the quality of having many lines of symmetry that pass through a common central point (Lessons 19, 20, 21)
radon an odorless radioactive gas that is given off by certain rocks and soil (Lesson 6)
radula the extension of a mollusk's mouth that contains sharp teeth for scraping food (Lesson 21)
recessive allele an allele whose trait does not show up in an organism if it is paired with a dominant allele; there must be two recessive alleles present for a recessive trait to show up in the organism (Lesson 9)
red alga (plural: red algae) multicellular plant-like protist, usually a type of seaweed, that is capable of living deep below the surface of the ocean (Lesson 13) 
red blood cell a blood cell that carries oxygen through the body (Lesson 26)
red bone marrow a type of marrow that produces some of the body's blood cells (Lesson 25)
red tide an algae bloom that occurs in salt water (Lessons 13, 31)
reflex an innate and  involuntary response to a stimulus (Lessons 5, 31)
regeneration the process by which parts of an organism break off and grow into brand new organisms (Lessons 13, 20)
renal failure when the kidneys stop functioning properly due to waste build-up (Lessons 28)
renewable resource a resource that is either always available or recycled in nature over a short period of time (Lesson 6)
reproduce living organisms makes more of its own kind (Lessons 1, 8)
reptile a group of organisms that is represented by lizards, snakes, tortoises, alligators, and crocodiles (Lesson 2)
reproductive system the system organs that produce sex cells (Lesson 24)
respiration plants: the process of breaking down food to use energy (Lessons 12, 15)
human systems: the intake of oxygen and release of carbon dioxide (Lessons 19, 27)
respiratory system the system that supplies the blood with oxygen (Lessons 24, 27)
response the reaction of living things to changes in their environment (Lesson 1)
retina the back part of the eye that responds to light (Lesson 31)
rhizoid root-like structures that anchors plants whenever they are growing (Lesson 16)
ribosome a small structure in the cytoplasm that makes the proteins in a cell (Lessons 12, 15)
river a freshwater aquatic ecosystem with running water that is larger than a stream (Lesson 2)
RNA ribonucleic acid; a nucleic acid that makes proteins (Lesson 7)
root anchors the plant in place and absorbs necessary water and nutrients from the soil in which they grow (Lesson 17)
root cap contains dead roots that are used to protect the root (Lesson 17)
root hair absorbs water and other substances needed for the plant, also increase the amount of surface area in the soil that the roots are in contact with (Lesson 17)
sac fungus a classification of fungus that produce asci and can be unicellular or multicellular (Lesson 14)
saliva liquid that helps break down the food and carries enzymes (Lesson 28)
saprophyte an organism that feeds on dead or decaying organisms (Lesson 14)
saturated fat a fat that is solid at room temperature; tends to cause high cholesterol (Lesson 28)
scale the pointy part of a cone that closes after a female cone is pollinated (Lesson 18)
scavenger an organism that feeds on dead organisms (Lesson 2)
scientific method a set of guidelines used to answer scientific questions in a systematic manner (Intro)
scoliosis a condition in which the spine is curved in the shape of an "S" (Lesson 25)
scrotum a sac outside of the body that holds the testes (Lesson 30)
second-hand smoke the pollutants that people inhale from others who smoke cigarettes (Lesson 6)
seed reproductive part that has a complete young plant inside of it (Lesson 17)
seed coat the outer covering of the seed (Lesson 17)
self-pollinate when pollen from a flower lands on a pistil of that same flower (Lesson 9)
semen a mixture of sperm and other fluids found in glands (Lesson 30)
semicircular canal a tiny fluid-filled tube inside the ear that helps keep balance (Lesson 31)
semipermeable allowing some substances, but not others, to cross a cell membrane (Lesson 7)
sensory nerve a nerve that gathers information about the environment (Lesson 31)
sensory receptor a special neuron that responds to stimulation (Lesson 31)
sepal a leaf-like structure in flowering plants that encloses the bud (Lesson 18)
septum a wall that separates the oxygen-depleted blood from the oxygen-rich blood in the heart (Lesson 26)
sessile permanently attached; not able to move freely (Lesson 20)
seta (plural: setae) one of several tiny bristles that a worm uses to move and hold onto soil (Lesson 20)
sex cell sperm, in males; eggs, in females (Lesson 8)
sex chromosome one of a pair of chromosomes that determine gender (Lesson 9)
sex-linked trait a trait that is located on sex chromosomes (Lesson 9)
sexual reproduction reproductive process that involves two parents who combine their genetic material to produce at least one new organism (Lessons 8, 12, 14)
silica a coarse substance that is used to scour objects present in horsetails stem (Lesson 16)
simple carbohydrate also known as sugar or glucose; made from only one or two sugar molecules bonded together (Lesson 28)
simple fracture a broken bone that remains under the skin (Lesson 25)
skeletal muscle a voluntary muscle that allows movement in the body (Lesson 25)
skeletal system the bodily system that consists of bones, joints, and cartilages that supports and protects the body (Lessons 24, 25, 27)
small intestine the intestine that absorbs nutrients from food partially digested in the stomach (Lesson 28)
smell to inhale an odor through the nose (Lesson 31)
smog a type of air pollution that is formed when sunlight reacts with gases in the air (Lesson 6)
smooth muscle involuntary muscle tissue that assists in digestion (Lessons 25, 28)
solute a chemical that is dissolved in a solvent (Lesson 7)
solution one or more solutes dissolved in a solvent (Lesson 7)
solvent a chemical in which other chemicals dissolve in  (Lesson 7)
species a group of similar organisms that can produce fertile offspring (Lessons 1, 11, 18)
sperm the male sex cell (Lesson 30)
sphygmomanometer a device used to measure blood pressure (Lesson 26)
spinal cord a bundle of nerves that links the brain to the nervous system (Lesson 31)
spiracle a structure similar to a hole, usually on the abdomen, that allows oxygen into an organism's blood (Lesson 21)
spongy layer a loose layer of cells that contains air pockets where vascular tissue is located (Lesson 17)
sporangium (plural: sporangia) a structure in fungi that contains spores (Lesson 14)
spore a small, single cell that is capable of growing into a new organism (Lessons 13, 14, 16, 17)
sporophyte stage the stage in a plants life cycle in which it produces spores (Lesson 15)
sprain an injury in the ligament; a tear is formed by too much stress on the ligament. (Lessons 25)
stamen the male reproductive part of a flower that contains the anther and filament (Lessons 9, 18)
stigma the sticky part of the pistil on which pollen grains land and get stuck (Lesson 18)
stimulus (plural: stimuli) anything that causes a response in a living thing (Lessons 5, 15, 19, 29)
stomach the muscle where food is transported and processed (Lesson 28)
stoma (plural: stomata) a hole in the epidermis that regulates the entry and exit of water, carbon dioxide, and oxygen (Lesson 17)
stratum (plural: strata) one of several layers of parallel rock that forms one on top of another (Lesson 10)
stratosphere located above the troposphere, the part of the atmosphere that contains "good" ozone (Lesson 6)
stream a freshwater aquatic ecosystem with running water that is smaller than a river (Lesson 2)
striated muscle muscles that have a repeated pattern of parallel lines (Lesson 25)
style the structure in flowers that connects the stigma to the ovary (Lesson 18)
surface zone the area of the ocean located from the surface of the water down to a depth of a few hundred meters (Lesson 2)
swim bladder a pouch that fishes can inflate or deflate with gas at will to allow them to swim to different depths without extra effort (Lesson 22)
symbiosis (plural: symbioses) an interaction between two individuals that form a close relationship (Lessons 3, 13, 16)
symmetry the quality of having similar characteristics on two or more sides (Lesson 19)
system a group of organs or tissues that carry out the same function (Lesson 19)
T cell a cell that kills the cells that germs have attached to (Lessons 24, 29)
taproot one long, main, wide root (Lesson 17)
taste the ability to detect flavor in substances (Lesson 31)
taxon a level of organization into which organisms are classified (Lesson 11)
taxonomy the branch of biology concerned with naming and organizing different forms of life (Lesson 11)
technology applying scientific knowledge to practical means
tendon strong tissues that connect skeletal muscle with bone (Lessons 24, 25)
terrestrial living on land (Lesson 2)
territory an area that an animal defends, mainly because of the resources, such as food and mates, that exist in these areas (Lesson 5)
tertiary third in order (Lesson 4)
testis (plural: testes) a gland that secretes testosterone; found only in males (Lesson 30)
testosterone the male sex organ that produces sperm (Lesson 30)
theory a verified or established explanation that supports facts or explains phenomena (Intro, Lessons 19, 20)
thigmotropism the tendency of a plant to respond to touch such as a vine curling around a fence (Lesson 15)
thymus the gland that makes hormones that support the immune system (Lesson 30)
thyroid gland the gland that produces hormones that control metabolism (Lesson 30)
tidal volume the amount of air that is inhaled and exhaled during each breath (Lab 6)
tide the periodic rise and fall of waters in the ocean and its inlets (Lesson 2)
tissue a group of similar cells that perform a similar function in an organism (Lessons 15, 19, Lab 4)
touch when the skin has physical contact with an object (Lesson 31)
toxin a poison that can harm an organism (Lessons 12, 13, 29)
trachea the tube that carries air down the lungs; extends from the larynx to the bronchi (Lessons 24, 25, 27)
trait a characteristic of a living thing; e.g., height, eye color, hair color (Lesson 9, Lab 2)
trial and error learning by doing something many times until it is done correctly; This type of learning involves a behavior that is changed by experience. (Lesson 5)
trisomy 21 a condition where three chromosome 21s are present; this is seen in patients with Down syndrome (Lesson 9)
trophic level the position of an organism on a food chain (Lesson 4)
trophic structure the organization of organisms feeding in an ecosystem (Lesson 4)
tropism a plant's response to stimuli in its environment (Lesson 15)
troposphere part of the atmosphere that is closest to the Earth's surface; contains ground-level ozone (Lesson 6)
tumor an abnormal growth of cells (Lesson 29)
umbilical cord the reproductive structure that connects the placenta to the mother and embryo (Lessons 23, 30)
understory the layer of plants under the tallest trees in the forest; includes shrubs, vines, and shorter trees (Lesson 2)
unicellular one celled organisms such as bacteria (Lessons 1, 13)
unsaturated fat a fat that is liquid at room temperature; healthier than saturated fat (Lesson 28)
ureter a tube that transports urine from a kidney to the bladder (Lesson 28)
urethra a tube that releases the urine from the bladder and semen from the penis (Lessons 28, 30)
urine liquid waste that is excreted by the kidneys (Lesson 28)
uterus an organ in the female that houses a fertilized egg (Lesson 30)
vaccine a substance introduced into the body that causes the production of chemicals that will destroy disease-causing organisms and viruses (Lessons 12, 29)
vacuole a bubble-like storage area within a cell (Lessons 13, 15)
vagina the female sex organ used to carry urine and blood from menstruation out the body (Lesson 30)
valve a flap of tissues that lets blood flow in the right direction (Lesson 26)
venom a chemical produced by some organisms that, when injected, injures or kills prey (Lesson 21)
variable anything that changes in an experiment (Intro)
vas deferens a tube that carries semen from the testes to the urethra (Lesson 30)
vascular plant a plant that contains vascular tissue (Lessons 15, 16)
vascular tissue tissue that consists of a series of tube-like structures that transport nutrients throughout the body of a plant (Lessons 15, 16, 17, 18, Lab 4)
vein a blood vessels that carry the blood back to the heart (Lesson 26)
ventricle one of the lower chambers of the heart that push the blood into the arteries (Lesson 26)
vertebra (plural: vertebrae) a bone segment that makes up part of the backbone of an animal (Lessons 22, 25)
vertebrate an animal that has a backbone (Lessons 22, 23)
vestigial organ a structure that is left over from the organism's ancestors and is of little or no use to the organism (Lesson 10)
villus (plural: villi) a finger-like extension in the small intestine that helps with absorption (Lesson 28)
virus a tiny non-living particle that invades a host cell and multiplies (Lessons 12, 29)
visible spectrum the range of light that humans are able to see; the colors of the rainbow (Lesson 15)
voluntary muscle a muscle that is controlled by the person (Lesson 25)
water-soluble able to be dissolved in water (Lessons 12, 28)
water vascular system a system of fluid-filled tubes in an echinoderm's body (Lesson 21)
white blood cell a blood cell that defends the body from infections (Lesson 26)
white light light made up of all the colors on the visible spectrum; sunlight (Lesson 15)
woody stem a type of stem that is hard and difficult to bend (Lesson 17)
x-ray a picture of bones taken by sending an invisible beam through the body (Lesson 25)
xylem vascular tissue made up of tube-like cells stacked up on top of each other; also used to transport water and other substances to the roots (Lessons 16, 17)
yellow marrow bone marrow that contains fat (Lesson 25)
zygote a fertilized egg (Lessons 8, 15, 17, 18, 30)
zygote fungus (plural: zygote fungi) a classification of fungus that includes molds and produces round spores on top of upright hyphae (Lesson 14)