Natural Sciences CLEP

Evolution

the gradual change of characteristics within a population, producing a change in a species over time.

Natural Selection

a feature of population genetics that is the driving force behind evolution.

Gene Pool

the entire collection of genes within a given population.

Differential Reproduction

individuals within a population that are most adapted to the environment and are also the most likely individuals to reproduce successfully; tends to strengthen the frequency of expression of desirable traits across the population.

Mutation

a change of the DNA sequence of a gene, resulting in a change of the trait.

Genotype

the combination of alleles that make a particular trait.

Phenotype

the trait expressed.

Genetic Drift

over time, a gene pool (particularly in a small population) may experience a change in frequency of particular genes simply due to change fluctuations.

Gene Migration

the introduction of new genes from an immigrant, which results in a change of the gene pool.

Hardy-Weinberg Law of Equilibrium

in situations where random mating is occurring within a population (which is in equilibrium with its environment), gene frequencies and genotype ratios will remain constant from generation to generation.

Allopatric Speciation

occurs when two populations are geographically isolated from each other.

Sympatric Speciation

genetically different members reproduce with each other, producing a population, which is separate from the original species.

Adaptive Radiation

a single species can develop into several diverse species over time; over time a species will specially adapt to live more effectively in a new environment.

Punctuated Equilibrium

scientific model that proposes that adaptations of species arise suddenly and rapidly; specific species undergo a long period of equilibrium, which at some point is upset by environmental forces causing a short period of quick mutation and change.

Homologous

structures that exist in two different species because they share a common ancestry.

Analogous

structures that are similar because of their common function, although they do not share a common ancestry.

Extinction

when the entire population of a particular species is eliminated.

Taxonomy

study that organizes living things into groups based on morphology or, more recently, genetics.

Organism Classification System

Domains

classification category even more general than kingdoms.

Cell

the smallest and most basic unit of most living things.

Prokaryotic Cells

cells with no nucleus or any other membrane-bound organelles.

Eukaryotic Cells

cells the contain membrane-bound intracellular organelles, including a nucleus.

Organelles

cells components that perform particular functions.

Viruses

smaller than even the smallest cells; survive and replicate by invading a living cell.

Cell Membrane

structure that encloses the cell and separates it from the environment; also known as the plasma membrane.

Microvilli

projections of the cell extending from the cell membrane; increase the surface area of the cell membrane, increasing the area available to absorb nutrients.

Cytoskeleton

provides structural support to a cell.

Cytoplasm

region between the nucleus and cell membrane.

Ribosomes

the site of protein synthesis within cells.

Endoplasmic Reticulum

large organization of folded membranes; responsible for the delivery of lipids and proteins to certain areas within the cytoplasm (a sort of cellular highway).

Rough Endoplasmic Reticulum

has attached ribosomes; instrumental to protein synthesis.

Smooth Endoplasmic Reticulum

network of membranous channels; does not have attached ribosomes.

Golgi Apparatus

instrumental in the storing, packaging, and shipping of proteins; also known as Golgi bodies or the Golgi complex.

Secretory Vesicles

carry substances produced within the cell to the cell membrane; packets of material packaged by the Golgi apparatus or endoplasmic reticulum.

Exocytosis

the export of substances from the cell.

Lysosomes

membrane-bound organelles containing digestive enzymes; digest unused material within the cell, damaged organelles, or materials absorbed by the cell for use.

Mitochondria

center of cellular respiration

Nucleus

an organelle surrounded by two lipid bilayer membranes that is located near the center of the cell and contains chromosomes, nuclear pores, nucleoplasm, and nucleoli.

Nucleolus

a rounded area within the nucleus of the cell where ribosomal RNA is synthesized.

Nuclear Membrane

the boundary between the nucleus and the cytoplasm.

Cell Walls

made of cellulose and lignin, they enclose the cell membrane providing strength and protection for the cell.

Chloroplasts

the site of photosynthesis within plant cells.

Chlorophyll

pigment molecules that give the chloroplast their green color.

Stroma

the body of the chloroplast.

Passive Transport

substances freely pass across the membrane without the cell expending any energy.

Active Transport

uses energy to move molecules across a cell membrane against a concentration gradient.

Diffusion

the process whereby molecules and ions flow through the cell membrane from an area of higher concentration to an area of lower concentration; mixing of particles in a gas or liquid.

Osmosis

a special process of diffusion that occurs when the water concentration inside the cell differs from the the concentration outside the cell; the water on the side of the membrane with the highest water concentration will move though the membrane until the concentration is equalized on both sides.

Facilitated Diffusion

allows for the transfer of substances across the cell membrane with the help of specialized proteins.

Endocytosis

the process whereby large molecules are taken up into a pocket of membrane; the pocket pinches off, delivering the molecules, still inside a membrane sack into the cytoplasm.

Anabolism

the process whereby cells build molecules and store energy.

Catabolsim

process of breaking down molecules and releasing stored energy.

ATP (adenosine triphosphate)

energy currency of cellular activity; consists of a nitrogenous base (adenine), a simple sugar (ribose), and three phosphate groups.

Photosynthesis

a crucial set of reactions that convert the light energy of the sun into chemical energy usable by living things.

CO(little)2 Fixation

the second phase of photosynthesis in which six CO(little)2 molecules are linked with hydrogen (produced in photolysis), forming glucose (a six-carbon sugar); also known as the dark reaction.

Aerobic

steps in the cellular respiration process that require oxygen.

Anaerobic

steps in the cellular respiration process that do not require oxygen.

Krebs Cycle

the first step in aerobic respiration that occurs in the matrix of a cell's mitochondria and breaks down pyruvic acid molecules (three carbons each) into CO(little)2 molecules, H+ (protons), and 2 ATP molecules; also liberates electrons.

Glycolysis

the breaking down of the six-carbon sugar (glucose) into smaller carbon-containing molecules yielding ATP.

Electron Transport

the second step of aerobic respiration that captures the energy created by the release of electrons from the Krebs cycle.

Fermentation

another name for anaerobic respiration, which breaks down the two pyruvic acid molecules (three carbons each) into end products (such as ethyl alcohol, or lactic acid), plus carbon dioxide.

Gene

length of DNA that encodes a particular protein.

Genomes

sum total of genetic information.

Transcription

the formation of an RNA molecule, which corresponds to a gene.

mRNA

RNA strand that migrates form the nucleus to the cytoplasm; also known as messenger RNA.

Translation

phase of photosynthesis that requires a second type of RNA.

tRNA

a chain of about 80 nucleotides that provide the link between the "language" of nucleotides (codon and anticodon) and the "language" of amino acids; also known as transfer RNA.

Structural Genes

code proteins that form organs and structural characteristics.

Regulatory Genes

code proteins that determine fictional or physiological events.

Transduction

the transfer or genetic material (portions of a bacterial chromosome) from one bacteria cell to another.

Transformation

a process in which bacteria absorb and incorporate pieces of DNA from their environment (usually from dead bacterial cells).

Cell Division

the process of cell reproduction that centers on the replication and separation of strands of DNA.

Histones

short length of DNA wrapped around a core of small proteins.

Chromatin

the combination of DNA with histones.

Chromatids

the two identical strands of duplicated chromatin in a cell that is getting ready to divide.

Cell Cycle

a particular sequence of events ending in cell division, which produces two daughter cells.

Interphase

the period when the cell is active in carrying on its functions.

G1 Phase

first phase of interphase; metabolism and protein synthesis are occurring at a high rate, and most of the growth f the cell occurs at this time.

S Phase

second phase of interphase where cell begins to prepare for cell division by replicating the DNA and proteins necessary to form a new set of chromosomes.

G2 Phase

final phase of interphase; more proteins are produced, which will be necessary for cell division, and the centrioles are replicated as well.

Mitosis

the process by which a cell distributes its duplicated chromosomes so that each daughter cell has a full set of chromosomes.

Prophase

step one in mitosis; chromatin condenses into chromosomes within the nucleus, the centrioles move to opposite ends of the cell, and spindle fibers begin to extend from the centromeres of each chromosome toward the center of the cell.

Metaphase

step two of mitosis; occurs when the spindle fibers pull the chromosomes into alignment along the equatorial plane of the cell, creating the metaphase plate.

Anaphase

step three in mitosis; when the centromere divides, chromatids are separated from each others and become a chromosome; the two identical chromosomes move along the spindle fibers to opposite ends of the cell.

Telophase

step four in mitosis; occurs as nuclear membranes form around the chromosomes and disperse through the new nucleoplasm; spindle fibers also disappear.

Meiosis

the process of producing four daughter cells, each with single unduplicated chromosomes.

Haploid

single unduplicated chromosomes.

Diploid

the parent cell that has a normal set of paired chromosomes.

Gametes

the four haploid cells (egg and sperm) that are found in reproductive organs as a result of meiosis.

Division

distributes the remaining set of chromosomes in a mitosis-like process.

Synapse

point at which homologous chromosomes pair up during meiosis.

Enzymes

protein molecules that act as catalysts for organic reactions.

Catalyst

a substance that changes the speed of a reaction without being affected itself.

Substrate

particular substance of an enzyme that fits within the active site.

Regulation

enzyme control that may occur when the product of the reaction is also an inhibitor to the reaction.

Vascular

plants that have tissue organized in such a way as to conduct food and water throughout their structure; also known as tracheophytes.

Agiosperms

plants that produce flowers as reproductive organs.

Gymnosperms

plants that produce seeds without flowers.

Flower

the primary reproductive organ for a plant.