Create an account
Highly organized, tiny structures with thin coverings called membranes. The smallest unit capable of life functions.
The process by which organisms make more of their own kind from one generations to the next.
The sum of all chemical reactions carried out in an organism. Almost all energy used by living organisms is captured from sunlight.
The maintenance of stable internal conditions despite changes in the external environment.
Sets of inherited instructions for making proteins. Control when proteins are made and what proteins are made.
The process in which organisms with favorable genes are more likely to survive and reproduce.
The science that studies the interactions of living organisms with one another and with the nonliving part of their environment.
A fatal disorder in which abnormally thick mucus builds up in many organs, including the lungs. Caused by a defective gene.
An explanation that might be true-a statement that can be tested by additional observations or experimentation.
A description of how acidic a solution is. Measured on a scale of 0-14 with 7 being neutral. Solutions measuring below 7 are more acidic and those measuring above 7 are more basic.
A set of related hypotheses that have been tested and confirmed many times by many scientists.
Organic compounds made of carbon, hydrogen, and oxygen atoms in the proportion of 1:2:1.
Nonpolar molecules that are not soluble in water including fats, phospholipids, steroids, and waxes.
Has three parts: a sugar, a base, and a phosphate group, which contains phosphorous and oxygen atoms.
Deoxyribonucleic acid. Consists of two strands of nucleotides that spiral around each other. The two strands are held together by hydrogen bonds between bases across from one another. Make up chromosomes.
Ribonucleic acid. Consists of a single strand of nucleotides. Plays several roles in cell function, including the manufacture of proteins.
Adeonsine triphosphate. A single nucleotide with two extra energy-storing phosphate groups. The main energy currency of cells.
A microscope in which light passes through one or more lenses to produce an enlarged image of a specimen.
scanning tunneling microscope
Uses a needle-like probe to measure differences in voltage caused by electrons that leak, or tunnel, from the surface of the object being viewed.
1. All living things are made of one or more cells.
2. Cells are the basic units of structure and function in organisms.
3. All cells arise from existing cells.
The outer boundary of a cell. Encloses the cell and separates the cell interior, called the cytoplasm, from its surroundings. Regulates what enters and leaves a cell-including gases, nutrients, and waste.
A single-celled organism that lacks a nucleus and other internal compartments. The modern version would be a bacterium.
In bacteria, fungi, and plants, surrounds the cell membrane providing structure and support.
An extensive system of internal membranes that move proteins and other substances through the cell. It is made of a lipid bilayer with embedded proteins.
A set of flattened, membrane-bound sacs that serves as the packaging and distribution center of the cell.
A large, membrane-bound space taking up much of the space of a plant cell. When full it presses the cytoplasm against the cell wall, making the cell rigid, which enables plants to stand upright.
The movement of a substance from an area of high concentration to an area of lower concentration caused by the random motion of particles of the substance.
A transport protein that can bind to a specific substance on one side of the cell membrane, carry the substance across the cell membrane, and release it on the other side.
Transport of substances through a cell membrane down a concentration gradient aided by carrier proteins.
The transport of a substance across the cell membrane against its concentration gradient.
In a complete cycle transports three sodium ions, Na+, out of a cell and two potassium ions, K+, into the cell.
A protein that binds to a specific signal molecule, enabling the cell to respond to the signal molecule.
Organisms that use energy from sunlight or inorganic substances to make organic compounds.
Organisms that must get energy from food instead of directly from sunlight or inorganic substances.
A metabolic process similar to burning fuel. Releases much of the energy in food to make ATP.
The primary pigment involved in photosynthesis. Absorbs mostly blue and red light and reflects green and yellow light.
Pigments that produce yellow and orange fall leaf colors, as well as the colors of many fruits, vegetables and flowers. Absorbs wavelengths of light different from those absorbed by chlorophyll.
electron transport chains
The series of molecules through which excited electrons are passed along a thylakoid membrane.
An electron carrier that provides the high energy electrons needed to make carbon-hydrogen bonds in the third stage of photosynthesis.
A process in which glucose is broken down in the cytoplasm. An enzyme-assisted anaerobic process that breaks down one six-carbon molecule of glucose to two three-carbon pyruvates.
An electron carrier formed when a glucose is broken down, transferring some of its hydrogen atoms to an electron receptor called NAD+.
A series of enzyme-assisted reactions involving Acetyl-CoA that produces electron carriers that temporarily store energy.
One of the 23 pairs of chromosomes in humans containing genes that will determine the sex of the individual.
A photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size.
Cell structures made up of both centrioles and individual microtubule fibers that are involved in moving chromosomes during cell division.
A form of cell division that halves the number of chromosomes when forming specialized reproductive cells, such as gametes or spores.
Occurs when portions of a chromatid on one homologous chromosome broken and exchanged with the corresponding portions on one of the chromotids of the other homologous chromosome.
Reproduction in which a single parent passes copies of all of its genes to each of its offspring.
A process in which the gametes (sperm and egg cells) join during the diploid life cycle.
A haploid reproductive cell produced by meiosis that is capable of developing into an adult without fusing with another cell.
law of independent assortment
The alleles of different genes separate independently of one another during gamete formation.
A diagram that predicts the expected outcome of a genetic cross by considering all possible combinations of gametes in the cross.
A cross in which an individual whose phenotype is dominant, but whose genotype is not known, is crossed with a homozygous recessive individual.
When an individual displays a trait that is intermediate between the two parents.
When two dominant alleles are expressed at the same time and both forms of the trait are displayed.
A substance that is prepared from killed or weakened microorganisms and is introduced into the body to protect the body against future infections by the microorganisms.
The pairing arrangement of the nitrogen bases between the two strands of a DNA molecule.
The state of two bases in DNA which must be paired. The sequence of bases on one strand determines the sequence of bases on the other strand.
Enzymes that move along each of the DNA strands during replication, adding nucleotides to the exposed nitrogen bases, according to the base-pairing rules.
A process in which instructions for making a protein are transferred from a gene to an RNA molecule.
A process in which cells use two different types of RNA to read the instructions on an RNA molecule and put together the amino acids that make up a protein.
The process by which proteins are made based on the information encoded in DNA - also known as protein synthesis.
A form of RNA that carries the instructions for making a protein from a gene and delivers it to the site of translation.
A series of three-nucleotide sequences on an mRNA molecule on which RNA instructions are written.
The amino acids and "start" and "stop" signals that are coded for by each of the possible 64 mRNA codons.
A group of genes that code for enzymes involved in the same function, their promoter site, and the operator that controls them all functioning together in a bacterium.
A protein that binds to an operator and physically blocks RNA polymerase from binding to a promoter site.
Bacterial enzymes that recognize and bind to specific short sequences of DNA, and then cut the DNA between specific nucleotides within the sequences.
Circular DNA molecules that can replicate independently of the main chromosomes of bacteria.
A process in which many copies of a gene of interest are made each time the host cell reproduces.
A technique that uses an electrical field within a gel to separate molecules by their size and charge.
Radioactive or fluorescent-labeled RNA or single-stranded DNA pieces that are complementary to the gene of interest.
A solution containing all or part of a harmless version of a pathogen (disease-causing microorganism).
A technique that involves putting a healthy copy of a gene into the cells of a person whose copy of the gene is defective.
A pattern of dark bands on a photographic film that is made when an individual's DNA fragments (RFLPs) are separated by gel electrophoresis, probed, and then exposed to an X-ray film.
human genome project
A project to determine the nucleotide sequence of the entire human genome and to map the location of every gene on each chromosome.
The calculation of the age of an object by measuring the proportions of the radioactive isotopes of certain elements.
Unstable elements (parent) that break up and give off energy in the form of charged particles (radiation).
The process through which life is thought to have developed when molecules of nonliving matter reacted chemically during the first billion years of Earth's history.
The preserved or mineralized remains (bone, tooth, or shell) or imprint of an organism that lived long ago.
Prokaryotes that contain a chemical called peptidoglycan in their cell walls and have the same type of lipids in their cell membranes as eukaryotes.
Prokaryotes that lack peptidoglycan in their cell walls and have unique lipids in their cell membranes.
The theory proposing that mitochondria are the descendants of symbiotic, aerobic eubacteria.
Members of the kingdom Protista, a large, varied group that includes both multicellular and unicellular organisms.
The death of all members of many different species, usually caused by a large ecological disaster.
The process by which populations change in response to their environment. By surviving long enough to reproduce, individuals have the opportunity to pass on their favorable characteristics to offspring. In time, the favorable characteristics will increase in a population, and the nature of the population will gradually change.
Bones or other structures present in an organism that are reduced in size and either have no use or have a less important function.
The model of evolution in which gradual changes over a long period of time lead to species formation.
The model of evolution in which periods of rapid change in species are separated by periods of little or no change.
The darkening of populations of organisms over time in response to industrial pollution.
Populations of the same species that differ genetically because of adaptations to different living conditions.
The inability of formerly interbreeding groups to mate or produce fertile offspring.
A member of a group of mostly night-active primates that live in trees. Includes lorises, lemurs, and tarsiers.
A thumb that stands out at an angle from the other fingers and can be bent inward toward them to hold an object.
A two-word system for naming organisms. Consists of the genus followed by the species names.
A group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.
Evolution in which organisms evolve similar features independently, often because they live in similar habitats.
A system of taxonomy that reconstructs phylogenies by inferring relationships based on similarities.
A hypothetical population that attempts to exhibit the key characteristics of a real population.
exponential growth curve
A curve in which the rate of population growth stays the same, as result the population size increases steadily.
Resources such as food and water for which a population model can be adjusted. The rate at which they become depleted depends upon the the population density of the population that uses them.
A population model in which exponential growth is limited by a density-dependent factor.
Environmental conditions such as weather and climate which limit growth but are not dependent on population density.
Species that grow exponentially when environmental conditions allow them to reproduce.
Populations that grow slowly and have small population sizes. Their population density is usually near the carrying capacity (K) of their environment.
States that the frequency of alleles in a population do not change unless evolutionary forces act on the population.
The movement of alleles into or out of a population due to the movement of individuals to or from a population, called migration.
A situation in which individuals mate with others that live nearby or are of their own phenotype.
A form of selection that causes the frequency of a particular trait to move in one direction.
A form a selection eliminating extremes at both ends of a range of phenotypes.
The study of the interactions of living organisms with one another and with their physical environment (soil, water, climate, and so on).
Consists of a community and all the physical aspects of its habitat, such as the soil, water, and weather. Also called an ecological system.
Succession that occurs in areas where there has been previous growth, such as in abandoned fields or forest clearings.
The rate at which organic material is produced by photosynthetic organisms in an ecosystem.
Organisms that first capture energy. Include plants, some kinds of bacteria, and algae. They make energy-storing molecules.
Those organisms that consume plants or other organisms to obtain the energy necessary to build their molecules.
Organisms that obtain their energy from the organic waste and dead bodies that are produced at all trophic levels.
A diagram in which each trophic level is represented by a block, and the blocks are stacked on top of one another, with the lowest trophic level on the bottom.
cycle in which a substance, such as carbon or water, enters into an environment's living reservoir where it remains for a certain period of time and is returned to a nonliving reservoir.
The process by which water evaporates from the leaves of plants after having passed through the plant.
A special case of predation in which one organism feeds on and usually lives on or in another, typically larger, organism.
A symbiotic relationship in which one species benefits and the other is neither harmed nor helped.
Ecological interaction between two or more species that use the same scare resource such as food, light and water.
The entire range of conditions an organism is potentially able to occupy within an ecosystem.
The elimination of a competing species. If two species are competing, the species that uses the resource more efficiently will eliminate the other.
In a pond or lake, the area that is farther away from the shore but close to the surface.
In a pond or lake, a deep-water zone that is below the limits of effective light penetration.
Bacteria, algae, fish larvae, and certain species of small animals drifting freely in the upper waters of the ocean.
Rain and snow carrying sulfuric acid to Earth's surface. Coal burning power plants send smoke into the atmosphere. The smoke contains sulfur which combines with water vapor to create the sulfuric acid.
Chemicals once used as a heat exchanger but found to be destroying the ozone layer.
Process by which molecules passing upward through the trophic levels of a food chain become increasingly concentrated.
A group of cells that are permanently associated but that do not communicate with one another.
A temporary collection of cells that come together for a period of time and then seperate.
An organism composed of many cells that are permanently associated with one another, such as green algae.
Members of the kingdom Protista. Defined on the basis that they are eukaryotes that are not fungi, plants, or animals.
In fungi, a wall-like division between cells within a hypha; wall that internally divides body segments in annelids.
Proteins with attached carbohydrate molecules that are derived from the host cell of a virus. Along with proteins and lipids they compose the envelope in a virus.
Cycle in which a viral genome replicates as a provirus without destoring the host cell.
a short, thick outgrowth on bactera which enables them to attach to surfaces or other surfaces.
dormant bacterial cell enclosed by a tough coating that is highly resistant to environmental stress.
alternation of generations
A reproductive cycle characterized by two distinct multicellular phases: a diploid, spore-producing phase, called the sporophyte generation, and a haploid, gamete-producing phase, called the gametophyte generation.
Members of the phylum Rhizopoda; protists that move by using flexible, cytoplasmic extensions.
Members of the phylum Bacillariophyta; photosynthetic, unicellular protists with unique double shells.
Members of the phylum Zoomastigina; unicellular heterotrophs that have at least one flagellum.
One of three stages of Plasmodium that lives in mosquitoes and is injected into humans. Infects the lliver where they divide rapidly producing millions of cells.
A form of asexual reproduction in which a small cell forms from a large cell and pinches itself off from the large cell.
The club-shaped sexual reproductive structure for which the basidiomycetes are named. Spores are produced on this structure.
A symbiosis between a fungus and a photosynthetic partner such as a green alga, a cyanobacterium, or both.
A waxy layer that covers the nonwoody aboveground parts of most plants. Does not let oxygen or carbon dioxide pass through it. Reduces water loss.
A system of well-developed vascular tissues that distributes water and other materials in plants.
Type of vascular tissue in plants that contains soft-walled conducting cells through which organic compounds are transported throughout the body of a plant.
Type of vascular tissue in plants that contains hard-walled conducting cells that transport water and dissolved minerals upward from the roots to the leaves.
Hairlike projections in nonvascular plants that anchor gametophytes to the surfaces on which they grow.
Flowering plants which produce seeds that develop while they are enclosed within a specialized structure.
The supple of stored food used by the seeds of angiosperms at some time during their development.
Structure consisting of a few haploid cells surrounded by a thick protective wall that contains a male gametophyte of a seed plant.
Structure of a seed plant sporophyte in which a female spore forms and then develops into a female gametophyte that contains an egg; structure in the ovary of a pistil that develops into a seed.
Transportation of pollen grains from a male reproductive structure of a flower to a female reproductive structure of a flower.
Structure that grows from a pollen grain to an ovule, enabling a sperm to pass directly to an egg.
Leaflike structures of a plant embryo functions in the transfer of stored nutrients to the embryo, in which food is stored.
Reproductive structure that produces eggs; in flowering plants, the lower part of a pistil that produces eggs in ovules.
Process by which two sperm fuse with cells of the female gametophyte, producing both a diploid (2n) zygote and a triploid (3n) endosperm.
A technique in which pieces of plant tissue are placed on a sterile medium and used to grow new plants.
Tissue that makes up much of the inside of the nonwoody parts of a plant, including roots, stems, and leaves.
A plant that completes its life cycle (grows, flowers, and produces fruits and seeds) and then dies within one growing season.
Structures located at the tips of stems and roots and produce primary primary growth through cell division.
Elements absorbed mainly as inorganic ions. Plants require small amounts of 13 of these.
A chemical that is produced in one part of an organism and transported to another part, where it causes a response.
Inhibition of lateral bud growth on the stem of a plant by auxin produced in the terminal bud.
The condition in which a plant or a seed remains inactive, even when conditions are suitable for growth.
In animals, the outer layer of embryonic tissue from which the skin and nervous system develop.
Arrangement of body parts so there are distinct left and right halves that mirror each other
In bilaterally symmetric animals, the development of a head end with a concentration of nerves and sensory structures.
Extremely thin projections of tissue that are rich in blood vessels, providing a large surface for gas exchange.
open circulatory system
System in which blood leaves the blood vessels and bathes the body's tissues.
closed circulatory system
System in which the blood does not leave the blood vessels and materials diffuse across the walls of the vessels.
A framework for supporting a body consisting of water that is contained under pressure in a closed cavity, such as a gastrovascular cavity or a coelom.
Fertilization that occurs when animals release the male and female gametes near one another in the water.
Fertilization in which the union of the sperm and egg occurs within the female's body.
A layer of flagellated cells lining the internal cavity of a sponge. Also called collar cells.
Clusters of amoebocytes encased in protective coats formed by sponges during harsh living conditions to ensure their survival.
An area of the body on animals of the genus Hydra which produces a sticky secretion used to attach to rocks or water plants.
A thick protective covering of cells found on endoparasites and used to avoid being digested by their host.
Two thick muscles connecting the valves of bivalves. These muscles contract they cause the valves to close tightly.
A process in which an arthropod sheds and discards its exoskeleton periodically so that it may grow.
Slender, fingerlike extensions from the arthropod's gut that are bathed by the blood that surrounds them.
Mouthparts in members of the subphylum Chelicerata that are modified into fangs or pincers.
Appendages on members of the subphylum Chelicerata that are modified to catch and handle prey.
Dramatic physical change through which an immature organism passes as it grows to adulthood.
An animal whose mouth develops from or near the blastospore. the opening in the gastrula.
Water-filled system of interconnected canals and tube feet that aids echinoderms in movement.
Deuterostome with a completely internal endoskeleton, notochord, pharyngeal slits, and post anal tail.
Spiny fishes. Appeared about 430 million years ago. Had strong jaws with jagged bony edges that served as teeth.
A single giant supercontinent in which all the continents were joined during the time of dinosaurs.
Animals whose metabolism is too slow to produce enough heat to warm their bodies. Such animals must absorb heat from their environment, and their body temperature changes as the temperature of their environment changes.
Animals that maintain a high, constant body temperature by producing heat internally through a faster metabolism.
An extinct order of reptiles that were probably endotherms and from which mammals evolved.
Arrangement in fish respiratory system where water going over the gills and blood in the gill filaments flows in opposite directions.
Tubelike structure in the kidneys that filters wastes from the body and retains useful molecules; also regulates the body's salt and water balance.
Group of bony fishes with highly mobile fins, thin scales, a swim bladder, and symmetrical tails; largest group of living fishes.
Internal, baglike respiratory organ of a vertebrate that enables gas exchange between the air and the blood.
Term that describes organisms that produce eggs that are retained in the mother's body until hatching or just before hatching.
In birds, a special gland that secretes oil that birds spread over their feathers to clean and waterproof them.
Gland located in the chest or abdomen of female mammals that secretes milk to nourish her young.
Partly digested food that is regurgitated, rechewed, and reswallowed for further digestion by mammals with a rumen.
Learning that can occur only during a specific period early in an animal's life and cannot be changed once learned.
Evolutionary mechanism by which traits that increase the ability of individuals to attract or acquire mates appear with increasing frequency in a population.
Thin, flat tissue layer that lines most body surfaces and protects other tissues from dehydration and physical damage.
System of the body that collects and recycles fluids leaked from the cardiovascular system and is involved in fighting infections.
ABO blood group system
A system used to classify human blood by proteins found on the surface of red blood cells.
Artery that branches from the aorta and carries oxygenated blood to the heart muscle.
A small cluster of cardiac muscle cells in the upper wall of the right atrium that initiates and regulates contraction of the heart.
Series of pressure waves within an artery caused by a contraction of the left ventricle; indicator of heart rate.
A sudden attack of weakness of paralysis that occurs when an area of the brain dies after blood flow to the brain is interrupted.
Amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius. The Calorie used to indicate the energy content of food is a kilocalorie.
Naturally occurring inorganic substance used to make certain body structures and substances, for normal nerve and muscle function, to maintain osmotic balance, and for enzyme function.
Contraction of the smooth muscle in the wall of the gut that moves food through the digestive system.
Digestive enzyme that secreted by the stomach that cuts single protein strands into smaller chains of amino acids.
One of many fine, finger-like projections that cover the lining of the small intestine, increasing its absorptive surface.
Tubelike structure in the kidneys that filters wastes from the body and retains useful molecules; also regulates the body's salt and water balance.
Water and metabolic wastes left after filtering process of the kidneys; expelled from the body.
Layer of epithelial tissue covering internal surfaces of the body that secretes mucus and functions in nonspecific defense.
Series of events, initiated by an injury or local infection, that suppress infection and promote healing.
Substance prepared from weakened or killed pathogens and introduced into a body to produce immunity.
(Acquired immunodeficiency syndrome) disease caused by infection by HIV that results in a depressed immune system.
Neuron that sends motor responses from the central nervous system to muscles. glands, and other organs.
Largest portion of the brain; center of memory, learning, emotion, and other highly complex functions.
The part of the brain that connects to the spinal cord; contains nerves controlling breathing, swallowing, digestive processes, heartbeat, and blood vessel diameter.
Part of the brain that directs incoming sensory information to the proper region of the cerebral cortex.
Region of the brain located below the thalamus that coordinates that activities of the nervous and endocrine systems and that controls many body activities related to homeostasis.
Cable of nerve tissue extending from the base of the brain through the backbone, to level just below the ribs.
Fluid-filled chamber in the inner ear that contains hair cells involved in maintaining equilibrium.
Condition of drug addiction in which increasing amounts of the drug are needed to achieve the desired effect.
Ductless gland in the body that releases its product directly into the bloodstream of the fluid around the cells.
Signal molecule produced in response to the binding of a chemical signal; alters the chemical activity within the cell.
Mechanism used in homeostasis to keep a monitored variable within a certain range. A change in one direction stimulates two control mechanisms to counteract further change in the same direction.
Region of the brain located below the thalamus that coordinates the activities of the nervous and endocrine systems and that controls many body activities related to homeostasis.
Endocrine gland at the base of the brain that stores and releases hormones produced by the hypothalamus and hormones that control endocrine glands elsewhere in the body.
Amino-acid based hormone released by the adrenal medulla in times of stress; formerly called adrenaline.
Amino-acid based molecule released as a hormone by the adrenal medulla in times of stress and as a neurotransmitter in the nervous system; formerly called noradrenaline.
Amino-acid based hormone produced by the islets of Langerhans in the pancreas that lowers blood glucose levels by promoting the accumulation of glycogen in the liver.
A peptide hormone produced by the pancreas that causes liver cells to release glucose stored in glycogen.
Serious disorder in which cells are unable to obtain glucose from the blood; caused by a deficiency of insulin or lack of response to insulin.
Glands of male reproductive system that produce fluid rich in sugars to nourish sperm cells.
Gland in males that secretes an alkaline fluid necessary to neutralize the acids produced by the female reproductive tract.
Glands in male reproductive system that secrete a fluid that neutralizes traces of acidic urine in the urethra.
Hollow, muscular organ of the female reproductive system in which the embryo and fetus develop.
Series of hormone-induced changes in which the ovaries prepare and release a mature ovum each month.
Structure that forms from the ruptured follicle in the ovary after ovulation and releases hormones.
Series of hormone-induced changes that prepare the uterine lining for a possible pregnancy each month.
Early stage in the development of plants and animals; term for a developing human during the first 8 weeks of pregnancy.
Sexually transmitted disease caused by bacteria that results in inflammation of the mucous membranes in the urinary and reproductive tracts.
pelvic inflammatory disease
Severe inflammation of the uterus, ovaries, fallopian tubes, or pelvic cavity usually caused by bacterial STDs.
Please allow access to your computer’s microphone to use Voice Recording.
Having trouble? Click here for help.
We can’t access your microphone!
Click the icon above to update your browser permissions and try again
Reload the page to try again!Reload
Press Cmd-0 to reset your zoom
Press Ctrl-0 to reset your zoom
It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.
Please upgrade Flash or install Chrome
to use Voice Recording.
For more help, see our troubleshooting page.
Your microphone is muted
For help fixing this issue, see this FAQ.
Star this term
You can study starred terms together