-
Abiotic factors
Nonliving things in the environment such as climate, light, temperature, water, soil and territory.
-
Absolute dating
A method used to determine the approximate age of a fossil by relying on the radioactivity of certain elements and their half-lives.
-
Acetylcholine
A neurotransmitter produced by the terminal branches of a nerve cell.
-
Acid
A compound that forms hydrogen H+ ions when dissolved in water and has a pH less than 7.
-
Addition
One type of addition is a gene mutation, where a nitrogen base is inserted into an mRNA molecule. Another type of addition is a chromosome mutation, where a segment of one chromosome breaks off and is added to its homologous chromosome.
-
Aerobic respiration
Cellular respiration that requires oxygen and takes place inside the mitochondria.
-
Allele
One of the two different kinds of genes for a trait. Alleles occupy the same location on a pair of homologous chromosomes.
-
Alveoli
Tiny air sacs, located at the end of bronchioles, where the exchange of oxygen for carbon dioxide in the blood takes place.
-
Amino acid
An organic compound that is the building block of proteins. Amino acids have an amino group (NH2) on one end and a carboxyl group (COOH) on the other.
-
Anaerobic respiration
Cellular respiration that does not require oxygen and takes place in the cytoplasm outside the mitochondria.
-
Analogous structures
Structures that are similar in function but dissimilar in construction and evolutionary development.
-
Anther
Part of the stamen of a flower and the producer of pollen grains.
-
Anthophyta
A phylum in kingdom Plantae that includes flowering plants that usually reproduce by seeds hidden inside fruits.
-
Antibiotic
A substance produced by some bacteria or fungi that can destroy bacteria but not viruses.
-
Antibody
A protein in the blood that can help fight disease by destroying harmful substances such as antigens, bacteria and viruses.
-
Anticodon
The side of tRNA that is complementary to the codon on an mRNA molecule. Antigen A protein that stimulates the production of antibodies.
-
Archaea
A domain that includes prokaryotic unicellular organisms with cell walls lacking peptidoglycan. In a six-kingdom system of classification, organisms in the domain Archaea are classified in the kingdom Archaebacteria.
-
Artery
A blood vessel with thick muscular walls that has a pulse and carries blood away from the heart to the organs.
-
Asexual reproduction
The formation of a new individual from one parent.
-
ATP (adenosine triphosphate)
The energy molecule produced during cellular respiration.
-
Autosomes
The chromosomes in the nucleus of a cell that do not determine the sex of an individual.
-
Autotroph
An organism that makes its own food by the process of photosynthesis.
-
Axon
The part of a neuron that carries nerve impulses from the cyton to the terminal branches.
-
Bacteria
A domain that includes prokaryotic unicellular organisms with cell walls containing peptidoglycan. In a six-kingdom system of classification, organisms in the domain Bacteria are classified in the kingdom Eubacteria.
-
Bilateral symmetry
The right and left sides of an organism are similar.
-
Binary fission
A kind of asexual reproduction that results in the formation of two identical daughter cells, each with the same amount of cytoplasm and nuclear material (chromosomes).
-
Binomial nomenclature
A two-name naming system for organisms composed of their genus and specific epithet names.
-
Biological pest control
The control of a pest population by nonchemical methods (as opposed to pesticides and insecticides), such as the use of predators, parasites, animal-like protists, bacteria and diseases.
-
Biology
The science that studies living things, their structure and function.
-
Biome
A large area of the earth defined by a climax community of plants and specific abioticfactors such as light, precipitation, temperature and soil type.
-
Biosphere
The interaction between all the ecosystems on earth.
-
Biotic factors
Living things in the environment such as organisms, populations, communities, food chains, symbiotic relationships, competition between organisms and succession.
-
Blastocyst (blastula)
A stage of embryological development that takes place about five days after fertilization, characterized by a hollow ball of cells with fluid and an inner mass of cells at one end.
-
Bowman’s capsule
The part of the nephron that receives wastes from blood in the glomerulus.
-
Bryophyta
A phylum in the kingdom Plantae characterized by the lack of vascular tissue. Bryophytes do not have true roots, stems or leaves.
-
Budding
A type of asexual reproduction that results in two unequal-sized cells. The larger cell is called the parent, and the smaller one is called the bud.
-
Cambium
The cells of a vascular bundle (vein) located between the phloem and the xylem. Cambium cells are meristematic cells and are capable of reproduction.
-
Capillary
Connects arteries to veins and is the smallest blood vessel (one cell in diameter).
-
Capsid
A protein coat that surrounds a virus.
-
Carcinogen
A chemical that causes mutations that result in cancer.
-
Carnivore
An animal that eats other animals.
-
Carpel
The part of a flower that contains the stigma, style and ovary.
-
Carrier
A female that has an allele for a sex-linked disease but does not have the disease.
-
Carrying capacity
The ability of a land area to supply enough food to feed a population.
-
Cartilage
A connective tissue that is flexible and softer than bone.
-
Cell
The basic unit of structure and function in all living things.
-
Cell membrane
The outer boundary of a cell that protects the cell, controls what goes in and out of the cell (selective permeability) and holds the cell together. This structure is composed of two layers of lipid with protein molecules suspended inside.
-
Cell wall
Found only in plant cells surrounding the cell membrane. The cell wall is made of cellulose, is rigid and is nonliving. This organelle gives the plant cell support and shape.
-
Cellular respiration
The process by which a cell converts food into energy (ATP).
-
Characteristic
A version of a trait.
-
Chemistry
The science that studies matter and changes in matter.
-
Chlorophyll
A green pigment found inside the chloroplasts of cells located in the palisade and spongy mesophyll layers of a leaf. This pigment traps light energy that is used to split water during the process of photosynthesis.
-
Chloroplast
A small, oval-shaped structure containing the green pigment chlorophyll that functions in photosynthesis.
-
Chordata
A phylum in the animal kingdom characterized by a dorsal notochord, which is a flexible, rod-like structure found at some point during embryonic development.
-
Classification
A system for organizing diverse living things into logical groupings that make it easier for biologists to study them.
-
Cleavage
A special series of mitotic cell divisions where each time the cells divide they get smaller and smaller. This process results in embryological development.
-
Climate
The weather in an area over a period of a year.
-
Climax community
The last community to occupy an area. A climax community is a stable and self-perpetuating community of plant and animal life.
-
Clone
DNA, genes, cells, tissues or organisms that are genetically identical to the ancestor they are derived from.
-
Codominance
Both alleles for a trait are dominant, and organisms produced from these crosses have both characteristics of the trait.
-
Codon
A set of three nitrogen bases on mRNA.
-
Coenzyme
A molecule that transfers hydrogen and electrons from one reaction to another.
-
Coevolution
The process by which species adapt to changes in one another.
-
Commensalism
A symbiotic relationship where one organism benefits from the association, and the other is neither helped nor harmed.
-
Common ancestor
An individual from which two or more related species could have evolved.
-
Community
Different populations living together in a specific location.
-
Coniferophyta
A phylum in kingdom Plantae, which includes nonflowering plants that reproduce by seeds found in cones. These trees have needlelike leaves that in most species usually stay on the plant all year long.
-
Conservation
The protection and maintenance of an ecosystem and its biological communities.
-
Control
The comparison group in a scientific experiment.
-
Cotyledons
These are the seed leaves that contain endosperm, which is food for a germinating plant. Monocots have one cotyledon, and dicots have two.
-
Cuticle
A thin, waxy layer that covers the upper epidermis of a leaf and prevents the loss of water.
-
Cyton
The cell body of a neuron, consisting of the nucleus, cytoplasm and dendrites.
-
Cytoplasm
The liquid part of a cell found within the cell membrane.
-
Dark reactions
A series of reactions in photosynthesis that takes place in the absence of light.
-
Deamination
A process that takes place in the liver, where excess amino acids have their amino group (NH2) removed, converted into ammonia and then into urea.
-
Dehydration synthesis
The formation of a large molecule from two smaller molecules by the removal of water.
-
Deletion
One type of deletion is a gene mutation, where a nitrogen base is lost from an mRNA molecule. Another type of deletion is a chromosome mutation, where a segment of a chromosome is lost, resulting in lost genes.
-
Deoxyribonucleic acid (DNA)
A nucleoprotein found in chromosomes that contains genes.
-
Deoxyribose
A five-carbon sugar that is part of the DNA molecule.
-
Dependent variable
In a scientific experiment, the variable that changes in response to changes in the independent variable.
-
Dicot (dicotyledon)
A plant that produces seeds that have two seed parts (cotyledons) and two seed leaves with netted veins.
-
Differentiation
A process that occurs at some point between the blastocyst stage and the gas- trula stage and results in the cells of the developing embryo becoming different from each other.
-
Diffusion
The movement of any molecule (except water) from areas of high concentration to areas of low concentration.
-
Diploid number (2n)
The number of chromosomes found in a somatic cell.
-
Disjunction
The separation of homologous chromosomes during meiosis.
-
Domain
A taxon higher than a kingdom.
-
Dominant
In a hybrid, the characteristic of the trait that shows up.
-
Dormancy
In a seed, a period of inactivity where life functions have significantly slowed down or have been temporarily suspended.
-
Ecological pyramid
A pyramid that shows the flow of energy from one trophic level to the next and the relative numbers of organisms at each level.
-
Ecosystem
The interaction between a community and the abiotic factors in the environment.
-
Ectoderm
The outer cell layer of a hydra or the outer germ layer in the gastrula stage of embryological development.
-
Effector
A muscle or gland that can carry out a response to a stimulus.
-
Embryo
An organism during the early stages of development.
-
Emulsification
The breakdown of large fat molecules into small fat molecules by the action of bile.
-
Endocrine gland
A ductless gland that secretes hormones, which are chemical messengers that travel through the blood to regulate the activity of a target organ.
-
Endoderm
The inner cell layer of a hydra or the inner germ layer in the gastrula stage of embryological development.
-
Endoplasmic reticulum (ER)
A canal-like network within a cell that functions in the transport of materials.
-
Endoskeleton
A skeleton composed of bones and cartilage found inside the body.
-
Endosperm
The part of the cotyledon that provides food for a germinating seed.
-
Environment
The surroundings of an organism: its abiotic and biotic factors.
-
Enzyme
An organic catalyst that speeds up the rate of chemical reactions.
-
Epicotyl
The two leaves of a plant embryo that become the upper part of the stem and the leaves of the plant.
-
Erosion
The loss of topsoil and other soil components from one area and their movement to another.
-
Eubacteria
A kingdom that includes prokaryotic unicellular organisms with cell walls contain- ing peptidoglycan.
-
Eukarya
A domain that includes eukaryotic organisms in the kingdoms Protista, Fungi, Plantae and Animalia.
-
Eukaryotic
A cell with a nuclear membrane surrounding its chromosomes.
-
Evaporation
The change of a liquid into a gas.
-
Evolution
The change that occurs in a species with the passage of time.
-
Excretion
The removal of cellular wastes such as water, carbon dioxide and urea.
-
Exocrine gland
A gland that has a duct.
-
Experiment
The procedures and materials used by a scientist to support or reject a hypothesis.
-
Exponential growth
The doubling of a population every few years.
-
Extracellular digestion
The breakdown of food outside the cells of an organism.
-
Fallopian tube
A narrow tube lined with cilia that connects the ovaries to the uterus.
-
Fermentation
A type of anaerobic respiration performed by yeast. Glucose is broken down to yield ethanol, carbon dioxide and ATP (energy).
-
Fibrinogen
A protein found in plasma that interacts with platelets and helps the blood to clot.
-
Flexor
A skeletal muscle that moves a bone toward the body.
-
Follicle
A cavity in an ovary where an egg cell matures.
-
Food chain
The transfer of energy from one organism to another in an ecosystem.
-
Food web
Several interconnecting food chains in an ecosystem.
-
Fossil
The remains of an organism that lived in the distant past.
-
Fossil fuel
Oil, natural gas or coal that formed millions of years ago from organisms that died and decayed.
-
Frameshift mutation
A type of mutation where one nitrogen base is deleted from or added to a codon on an mRNA molecule.
-
Free radical
An atom with unpaired electrons that can cause breaks in a DNA molecule.
-
Fungi
A kingdom of organisms with cells that do not have chloroplasts. Fungi are heterotrophicand obtain their food by absorption from decaying vegetation.
-
Gamete
A sperm or egg cell with the haploid number of chromosomes.
-
Gameteophyte
In organisms that reproduce by alternation of generations, this generation is characterized by the production of male and female haploid (n) gametes.
-
Gametogenesis
The production of gametes during meiosis.
-
Ganglion
A group of nerve cells and cytons combined.
-
Gastrula
A stage of embryological development characterized by the presence of three cell layers (ectoderm, mesoderm and endoderm).
-
Genetic engineering
A process by which genes from the chromosomes of one species are inserted into the chromosomes of another species.
-
Genomics
The study of genes in the chromosomes of an organism, their structure and function.
-
Genotype
The gene combination for a trait (homozygous or heterozygous).
-
Genus
The classification category that includes similar species.
-
Germination
The development of a seed into a new plant.
-
Global warming
An increase in the earth’s temperature caused by the greenhouse effect.
-
Glucose
A simple sugar (monosaccharide) produced by green plants during the process ofphotosynthesis.
-
Glycogen
A large polysaccharide used to store glucose in animals.
-
Glycolysis
The breakdown of glucose during anaerobic respiration into two molecules of pyruvate with a gain of 2ATP.
-
Golgi apparatus
Flattened membranes in a cell that look like plates stacked one on top of the other. This organelle packages proteins.
-
Gonad
A sex gland; the ovary in a female or testis in a male.
-
Gradualism
The belief that evolution is a slow, continual and gradual process that proceeds in numerous small steps taking many years and generations to produce new species.
-
Guard cells
Cells containing chloroplasts found in the lower epidermis of a leaf that are responsible for forming the stomates.
-
Habitat
Where an organism lives in its environment.
-
Half-life
The time that it takes for an element to decay into half of its original amount.
-
Haploid number (n)
Half the diploid number, or the number of chromosomes in a gamete.
-
Hemoglobin
An iron-containing pigment that gives red blood cells their color and aids in the transport of oxygen to the cells of an organism.
-
Herbivore
An animal that eats plants, a primary consumer.
-
Heterotroph
An organism that eats to obtain food.
-
Heterozygous (hybrid)
Two different alleles for a trait.
-
Hilum
A scar on a seed that shows the point of attachment of the seed to the inside of the ovary.
-
Homologous chromosomes
Pairs of similar chromosomes found in diploid cells.
-
Homologous structures
Are similar in construction and evolutionary development but dissimilar in function.
-
Homozygous (pure)
Two identical alleles for a trait.
-
Hormone
A chemical messenger produced by an endocrine gland that travels through the blood and functions in regulation.
-
Humus
Soil that is rich, fertile and formed by the decay of dead plants and animals.
-
Hydrolysis
The breakdown of a large molecule into two or more smaller molecules by the addition of water.
-
Hydrophytes
Plants adapted for growth in water or in areas that have a great deal of precipitation.
-
Hypocotyl
The part of a seed embryo that develops into the roots and lower part of a stem.
-
Hypothesis
An educated guess that provides a possible answer to a scientific problem.
-
Igneous rock
A rock formed by volcanic activity.
-
Incomplete dominance
In genetics, the presence of two different alleles for a trait where neither one is dominant or recessive.
-
Independent assortment
In genetics,when two dihybrids are crossed, alleles for the different traits separate and are inherited independently.
-
Independent variable
In a science experiment, the experimenter controls the independent variable (the factor that is being tested). As the independent variable is changed, the dependent variable changes.
-
Index fossil
A fossil of a species of organism that is found all over the world but lived for a short period of time.
-
Interspecific competition
Competition between members of different species.
-
Intracellular digestion
The breakdown of food inside the vacuoles of a cell.
-
Intraspecific competition
Competition between members of the same species.
-
Invertebrate
An animal without a backbone.
-
Islets of Langerhans
Cells located in the pancreas that produce the hormones insulin and glucogon.
-
Karyotype
Chromosomes that are removed from the nucleus of a cell and arranged in decreas- ing size order.
-
Kingdom
A category in classification, including phylum, class, order, family, genus and species.
-
Latitude
The distance north or south of the equator measured in degrees.
-
Life functions
Various life processes that are performed by living things (for example, nutrition, transport, respiration, excretion and reproduction).
-
Ligament
A tissue that connects one bone to another.
-
Light reactions
A series of reactions that begins the process of photosynthesis. Light energy trapped by chlorophyll is used to split water molecules (photolysis).
-
Limiting factors
Any abiotic or biotic factors that determine the distribution and kinds of organisms that can survive in an area.
-
Lipids
Organic molecules composed of one molecule of glycerol combined with three molecules of fatty acid. Examples are fats, oils and waxes.
-
Loop of Henle
The U-shaped part of a nephron that reabsorbs food materials (glucose, amino acids) and water into the blood of the surrounding capillaries.
-
Lysosomes
Small, irregularly shaped structures in a cell that have their own membrane and contain digestive enzymes for the breakdown of food.
-
Malpighian tubules
A network of tubes in insects that functions in the excretion of nitrogen waste (uric acid).
-
Mechanical digestion
The physical breakdown of food into small particles.
-
Menstrual cycle
A hormonal cycle in women where an egg cell is matured and released, accompanied by the preparation of the uterine lining to receive a fertilized egg.
-
Menstruation
A stage in the menstrual cycle characterized by the shedding of the uterine lining.
-
Mesoderm
The middle germ layer found in the gastrula stage of embryological development.
-
Mesophytes
Land plants that require average amounts of rainfall during the course of a year.
-
Metamorphic rock
A rock formed from igneous or sedimentary rock by tremendous heat and pressure.
-
Metamorphosis
A change in body form from young to adult (for example, a caterpillar becoming a butterfly).
-
Micrometer
The unit used for cellular measurement. One micrometer (μm) equals one thou- sandth of a millimeter (mm).
-
Mitochondrion
This organelle is the energy factory of cells and is associated with cellular res- piration. It has an elliptical shape with outer and inner membranes. Mitochondria contain their own DNA and reproduce independently of cells.
-
Mitosis
A type of cell division that results in the formation of daughter cells, which have the diploid number of chromosomes.
-
Molecular transport
The movement of molecules across a membrane by passive or active transport.
-
Monocot (monocotyledon)
A plant that produces seeds that have one seed part (cotyledon), which cannot be split, and one seed leaf with parallel veins.
-
Morula
The stage in embryological development characterized by a solid ball of cells.
-
Motile
Capable of movement.
-
Mutagenic agent
An environmental or man-made factor that increases the frequency of mutation.
-
Mutation
A change or error in a gene or chromosome.
-
Mutualism
A symbiotic relationship where both organisms benefit from living together.
-
Natural selection
Darwin’s theory that nature selects those variations in a population that are the most fit. These variations are passed on to the next generation.
-
Negative feedback - A homeostatic control mechanism, where one action or change inhibits another. For example, increasing levels of thyroxin in the blood inhibit the pituitary gland from producing a thyroid-stimulating hormone (which in turn results in the thyroid gland producing less thyroxin).
-
Nephridia
A pair of tubes in an earthworm segment that is surrounded by capillaries and func- tions in excretion.
-
Nephron
A tiny tube found in the human kidney that filters waste products out of the blood.
-
Nerve
A bundle of axons held together by connective tissue.
-
-
Neurotransmitter
A chemical secreted by the terminal branches of a neuron that carries a nerve impulse across a synapse to the dendrites of the next neuron.
-
Niche
The role or job of an organism in its environment.
-
Nondisjunction
The failure of homologous chromosomes to separate during meiosis.
-
Nonrenewable resources
Resources such as fossil fuels that cannot be replaced.
-
Nucleolus
A part of a cell found inside the nucleus that is associated with the production of ribosomes and RNA.
-
Nucleotide
A part of a DNA molecule that contains deoxyribose, a phosphate group and one of four possible nitrogen bases (adenine, guanine, cytosine or thymine).
-
Nucleus
The part of an atom that contains protons and neutrons. In a cell, this structure controls metabolism and reproduction. The nucleus contains chromosomes, which have genes that govern the heredity of the cell.
-
Omnivore
An animal that eats plants or other animals.
-
Oogenesis
The production of egg cells during meiosis.
-
Osmosis
The movement of water molecules from areas of high concentration to areas of low concentration.
-
Ovary
In an animal, the female gonad, which produces egg cells and the hormones estrogen and progesterone. In a flower, the part of the pistil that produces ovules and becomes the fruit.
-
Palisade layer
A leaf layer composed of long columnar cells that are packed tightly together. These cells contain chloroplasts for photosynthesis.
-
Pancreas
An exocrine gland that secretes pancreatic fluid, which aids in the chemical diges- tion of food, and an endocrine gland (the Islets of Langerhans), which produces the hormones insulin and glucogon.
-
Parasitism
A symbiotic relationship, where one organism benefits from the association, and the other is harmed.
-
Parthenogenesis
The development of an unfertilized egg into an embryo that eventually becomes a new individual.
-
Passive transport
The movement of molecules from areas of high concentration to areas of low concentration, without the use of energy. Diffusion and osmosis are two kinds of passive transport.
-
Pedigree chart
A chart used in genetics to track the inheritance of a trait in a family through several generations.
-
Peristalsis
A series of involuntary muscle contractions that forces food through the digestive system.
-
pH scale
A logarithmic scale (from 0 to 14) that is used to indicate the relative strength of acids and bases.
-
Phenotype
The characteristic (version) of a trait that is determined by observation.
-
Phloem
Cells in a vascular bundle (vein) that carry food downward in a stem.
-
Photolysis
The splitting of water molecules into hydrogen and oxygen during the light reac- tions of photosynthesis.
-
Photosynthesis
A process by which green plants take in carbon dioxide and water from their environment and produce glucose and oxygen.
-
Phylum
A classification category that includes similar classes.
-
Pioneer organism
In succession, the first organism to occupy an area.
-
Pistil
The female part of a flower.
-
Pituitary gland
An endocrine gland called the master gland because it produces hormones that regulate the other endocrine glands.
-
Placenta
In mammals, this structure is formed from a combination of tissues from the mother’s uterine wall and the developing fetus.
-
Plantae
A kingdom of multicellular, autotrophic organisms that includes green plants.
-
Plasma
The straw-colored liquid part of blood that consists mostly of water and proteins.
-
Plasmid
The circular DNA found in bacteria.
-
Platelet
A cell fragment that interacts with fibrinogen and helps the blood to clot.
- Point mutation
- A type of mutation where one nitrogen base is replaced by another nitrogen base in an mRNA molecule.
-
Point-source pollution
Pollution that can be traced back to its point of origin.
-
Pollination
The transfer of pollen from an anther to a stigma.
-
Pollution
The addition of chemical or biological substances to land, water or air that changes the natural composition of these abiotic factors.
-
Population
Organisms in the same species that live together in a specific location.
-
Primary succession
Succession that begins from an area that never had life.
-
Prokaryotic
Cells that lack a nuclear membrane around their chromosomes.
-
Proteins
Organic molecules that contain nitrogen and are composed of 40 or more amino acids combined.
-
Protista
A kingdom of eukaryotic, unicellular organisms with animal-like, plant-like or fungus- like characteristics.
-
Pseudopod
A cellular extension in some animal-like protists that can change shape, capture food and help the organism move.
-
Punctuated equilibrium
The belief that evolutionary change occurs in sudden spurts during which many species are formed and followed by long periods of stability and no speciation.
-
Radial symmetry
A cut through the axis of an organism produces halves that are mirror images of each other.
-
Recessive
In a hybrid, the characteristic of the trait that we don’t see.
-
Recombinant DNA
- DNA produced when a gene from one chromosome is spliced into the
- chromosome of another species.
-
Red blood cell (RBC)
A blood cell that contains hemoglobin and transports oxygen to the cells and carbon dioxide from the cells.
-
Reflex
An automatic, involuntary, unlearned response to a stimulus.
-
Regeneration
The replacement or repair of a lost or damaged part of an organism.
-
Regulation
The ability of an organism to respond to a stimulus (a change in environment); the reaction of the organism is the response.
-
Relative dating
A method used to determine the age of a fossil by comparing its location relative to fossils in nearby rock layers.
-
Renewable resources
Resources that are replaceable.
-
Reproduction
The life function by which organisms produce new individuals of the same kind(species) or new cells necessary for growth and repair.
-
Respiration
The life function that provides an organism with energy (ATP) needed to carry out all the other life processes.
-
Response
The reaction of an organism to a stimulus.
-
Ribonucleic acid (RNA)
A nucleoprotein involved in the process of protein synthesis.
-
Ribose
A five-carbon sugar that is part of an RNA molecule. Ribosome A cell organelle that is the site for protein synthesis.
-
Root hair cells
Specialized root cells that have a large surface area adapted for the increased absorption of water.
-
Saprobe
An organism of decay that eats dead plants and animals.
-
Scavenger
A carnivore that eats food left over by a predator.
-
Scientific method
An organized series of steps used by biologists to solve problems. The steps of the scientific method include problem, hypothesis, experiment, results and conclusion.
-
Secondary succession
Succession that takes place in an area where life has already existed.
-
Sedimentary rock
A rock formed by the deposition of very small particles of rock, clay or silt.
-
Segregation
In genetics, when two hybrids are crossed, each gene segregates (separates) during gamete formation so that new gene combinations can be formed at fertilization.
-
Self-pollination
The transfer of pollen from anther to stigma within the same flower.
-
Semiconservative replication
The duplication of DNA where two molecules are formed, each composed of one original and one new strand.
-
Seminiferous tubules
Coiled tubes inside the testes that produce sperm cells.
-
Sensory neuron
A neuron that detects a stimulus and transmits a nerve impulse from a receptor to an interneuron in the spinal cord.
-
Sessile
Not capable of independent movement.
-
Setae
Small bristles on the segments of an earthworm that are used for locomotion.
-
Sex chromosomes
A pair of chromosomes that determines the sex of an individual.
-
Sex-linked trait
A trait that has an allele located on the X chromosome.
-
Sexual reproduction
The formation of a new individual from two parents (by the fertilization of gametes).
-
Somatic cell
A body cell with the diploid (2n) number of chromosomes.
-
Speciation
New species formation.
-
Species
Organisms that can mate with each other and produce fertile offspring.
-
Specific epithet
The second name in the scientific name of an organism that often describes a distinguishing characteristic of the organism.
-
Spermatogenesis
The production of sperm cells during meiosis.
-
Spinal cord
A nerve that begins at the base of the medulla and extends down through the vertebrae in the back.
-
Spiracles
Openings in the abdomen of an insect that function in respiration.
-
Spongy mesophyll layer
A leaf layer composed of cells that have chloroplasts.
-
Sporophyte
In organisms that reproduce by alternation of generations, this generation is characterized by the fertilization of gametes and the formation of a diploid (2n) organism.
-
Stamen
The male part of a flower.
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Starch
A large polysaccharide used to store glucose in plants.
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Stem cells
Undifferentiated cells inside the blastocyst stage of embryological development.
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Stigma
Part of a flower’s pistil (carpel) that is sticky and holds pollen grains.
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Stimulus
A change in the environment of an organism.
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Stomate
An opening in the lower epidermis of a leaf that allows carbon dioxide in and water and oxygen out.
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Structural formula
Indicates the kinds of elements, number of atoms and arrangement of atoms in a compound.
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Substrate
The substance that an enzyme acts on.
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Succession
An ecological process by which one biotic community is replaced by another until a climax community develops.
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Symbiosis
A relationship between two organisms that live together where at least one of the organisms benefits from the association.
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Synapse
A space between two nerve cells.
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Synapsis
A process in meiosis where two pairs of homologous chromosomes come together to form a tetrad.
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Synthesis
A process by which two or more small molecules are combined to form a larger molecule.
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Taxon
A classification group.
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Taxonomy
The branch of biology that is concerned with the classification and naming of organisms.
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Tendon
A connective tissue that attaches skeletal muscles to bones.
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Terminal branches
The parts of a neuron that produce neurotransmitters.
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Testes
The male gonads, which produce sperm cells and the hormone testosterone.
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Tetrad
Two pairs of homologous chromosomes that have joined together by synapsis.
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Tracheal tubes
Tiny tubes found in insects that carry oxygen to the cells and carbon dioxide from the cells.
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Trait
A distinguishing feature or property of an organism.
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Transcription
A process that produces ribonucleic acid (RNA) nucleoproteins.
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Translation
A process by which ribosomes combine amino acids to produce proteins.
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Translocation
The movement of food throughout a plant.
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Transpiration
The loss of water through the stomates of a leaf.
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Transport
The life function that distributes food, water and oxygen from the environment to all cells of an organism.
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Umbilical cord
A structure that connects a fetus to the placenta.
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Urea
A poisonous, nitrogenous waste produced from the breakdown of proteins.
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Uterus (womb)
The muscular organ in the female reproductive system where an embryo develops into a fetus.
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Vacuoles
Organelles of a cell that are storage sites for food or water.
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Vas deferens (sperm duct)
A tube that carries sperm cells from the epididymis to the ejacula- tory duct and into the urethra.
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Vegetative propagation
Asexual reproduction in plants that results in the production of a new plant from the root, stem or leaf of an existing plant.
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Vein
In animals, a blood vessel with a thin, muscular wall that has valves and carries blood back to the heart. In plants, vascular tissue specialized for the transport of materials.
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Vertebrates
Animals with backbones.
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Vestigial structure
A structure that at one time had a function in the evolutionary history of an organism but no longer has a function.
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Weather
The day-to-day change in the atmosphere.
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White blood cell (WBC)
A cell that helps the body fight disease. Some white blood cells engulf and kill bacteria, others produce antibodies, which are proteins that can destroy antigens (foreign substances in the body).
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Xerophytes
Plants adapted to growing in a dry environment, such as a desert.
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Xylem
Cells in a vascular bundle (vein) that carry food upward in a stem.
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Zygote
A fertilized egg cell.
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