AEPA Biology (NT305) key terms

A cyclical process of observing, asking questions, forming testable hypotheses, gathering data through controlled experiments or observation, and revising explanations based on evidence. Conclusions are always provisional and open to further testing.

A proposed, testable explanation for an observed phenomenon. It must generate predictions that could be shown false by data, distinguishing it from a guess or an unfalsifiable claim.

A study in which all variables except the one being tested are held constant. An experimental group receives the treatment while a control group does not, allowing researchers to attribute observed differences to the manipulated variable.

The factor deliberately changed or manipulated by the researcher in an experiment. Its effect on the measured outcome is what the study is designed to reveal.

The outcome that is measured or observed in an experiment. It responds to changes in the independent variable and provides the data used to evaluate the hypothesis.

Evaluation of a scientific manuscript by independent experts in the same field before publication. It screens for methodological flaws and unsupported claims, though it does not guarantee that findings are correct.

A broad, well-tested explanation supported by large bodies of evidence from many lines of research. In science, theory does not mean speculation; it is the strongest explanatory framework available.

The consistency of a measurement or study, meaning repeated trials under similar conditions yield similar results. A reliable measure is not necessarily accurate, but it is reproducible.

The number of individuals or observations included in a study. Larger samples generally reduce the influence of random variation and make results more trustworthy.

A large molecule built from smaller subunits, including carbohydrates, lipids, proteins, and nucleic acids. These four classes carry out most structural and functional roles in living cells.

A protein that speeds up a specific chemical reaction by lowering its activation energy. Enzymes are not consumed in the reaction and are sensitive to temperature and pH.

The minimum energy input required to start a chemical reaction. Enzymes reduce this barrier, allowing reactions to proceed rapidly at the moderate temperatures found in cells.

Loss of a protein's functional three-dimensional shape due to heat, extreme pH, or chemicals. Because structure determines function, a denatured enzyme typically can no longer catalyze its reaction.

A macromolecule made of amino acids linked in a chain that folds into a specific shape. Proteins serve as enzymes, structural components, transporters, and signaling molecules.

A macromolecule made of nucleotide subunits that stores and transmits genetic information. DNA and RNA are the two types found in cells.

A selectively permeable phospholipid bilayer surrounding the cell. It regulates which substances enter and exit and contains proteins involved in transport and signaling.

The net movement of particles from an area of higher concentration to an area of lower concentration. It requires no energy input and continues until concentrations are balanced.

The diffusion of water across a selectively permeable membrane from a region of higher water concentration to one of lower water concentration. It drives water balance in cells.

A membrane-bound organelle in eukaryotic cells where aerobic respiration produces most of the cell's ATP. It has folded inner membranes that increase the surface area for energy reactions.

A membrane-bound organelle found in plant cells and algae where photosynthesis occurs. It contains the green pigment chlorophyll, which captures light energy.

A single-celled organism lacking a membrane-bound nucleus and other membrane-bound organelles. Bacteria and archaea are prokaryotes, and their DNA lies in the cytoplasm.

An organism whose cells contain a nucleus and other membrane-bound organelles. Animals, plants, fungi, and protists are eukaryotes.

Deoxyribonucleic acid, a double-stranded molecule that stores hereditary information in the sequence of its nucleotide bases. It is copied before cell division and transcribed to make RNA.

A segment of DNA that carries the instructions for making a functional product, usually a protein. Genes are passed from parents to offspring and can exist in variant forms called alleles.

One of the alternative versions of a gene that can occupy the same position on a chromosome. Different alleles may produce different traits, and an organism inherits one from each parent.

The specific combination of alleles an organism carries for a given gene or set of genes. It is the genetic makeup that, together with environment, influences observable traits.

The observable traits of an organism, such as eye color or height. Phenotype results from the interaction between genotype and environmental factors.

A change in the nucleotide sequence of DNA. Mutations may be harmful, neutral, or beneficial and are the original source of new genetic variation in populations.

The process by which individuals with traits better suited to their environment tend to survive and reproduce more, passing those traits to offspring. Over generations this changes population characteristics.

A heritable trait that improves an organism's ability to survive and reproduce in its environment. Adaptations arise over generations through natural selection acting on variation.

The maintenance of stable internal conditions, such as temperature and blood pH, within a narrow range despite external changes. It relies on feedback mechanisms that detect and correct deviations.

A regulatory mechanism in which a change in a variable triggers a response that counteracts the change, returning the system toward its set point. It is the primary means of maintaining homeostasis.

The process by which plants, algae, and some bacteria use light energy to convert carbon dioxide and water into glucose and oxygen. It stores energy in organic molecules and releases oxygen.

The process by which cells break down glucose to release energy, producing ATP and carbon dioxide. Aerobic respiration uses oxygen; anaerobic respiration does not.

Specialized plant tissue that transports water, minerals, and sugars throughout the plant. Xylem carries water upward from roots, and phloem distributes sugars produced in leaves.

A group of individuals of the same species living in the same area at the same time. Populations are the unit on which natural selection and many ecological processes act.

The maximum population size an environment can sustain indefinitely given available resources. Populations may overshoot it temporarily, after which resource limits cause decline.

An environmental resource or condition that restricts population growth, such as food, water, or space. The scarcest limiting factor sets the ceiling on population size.

A network of interconnected food chains showing how energy and matter move among organisms in an ecosystem. It illustrates feeding relationships from producers through multiple consumer levels.

A position in a food chain defined by how an organism obtains energy, such as producer, primary consumer, or secondary consumer. Energy decreases at each higher level.

An organism, typically a photosynthetic plant or alga, that makes its own organic food from inorganic substances using an energy source such as sunlight. Producers form the base of food webs.