NLN NEX Science key terms

The movement of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.

The net movement of particles from a region where they are more concentrated to a region where they are less concentrated, driven by random molecular motion.

A thin, flexible barrier of lipids and proteins around a cell that controls which substances enter and leave and separates the cell's interior from its surroundings.

A protein that speeds up a specific chemical reaction in living things by lowering the energy needed to start it, without being used up itself.

The set of reactions in cells that release energy from glucose and other fuel molecules, mostly using oxygen, and store that energy in ATP.

The process by which plants, algae, and some bacteria use light energy to turn carbon dioxide and water into glucose, releasing oxygen as a byproduct.

A type of cell division that produces two daughter cells with the same number of chromosomes as the parent cell, used for growth and repair.

The long, double-stranded molecule in cells that carries genetic instructions using four bases and is copied before a cell divides.

The smallest unit of an element that keeps that element's properties, made of protons and neutrons in a nucleus with electrons around it.

A chemical bond formed when one atom transfers electrons to another, creating oppositely charged ions that are attracted to each other.

A scale from 0 to 14 that measures how acidic or basic a solution is, based on the concentration of hydrogen ions.

The energy that an object has because of its motion; for a moving object it increases as the object's mass or speed increases.

The tendency of an object to resist a change in its motion; an object at rest stays at rest, and a moving object keeps moving, unless a force acts on it.

The body's ability to keep its internal conditions, such as temperature and blood sugar, within a stable range despite changes in the environment.

A nerve cell that receives, processes, and transmits electrical signals, consisting of a cell body, branching dendrites, and a long axon.

The small gap between two neurons, or between a neuron and a muscle or gland, across which a signal is carried by a chemical messenger.

One of the tiny air sacs in the lungs where oxygen passes into the blood and carbon dioxide passes out, surrounded by capillaries.

The microscopic filtering unit of the kidney that removes wastes and excess water from the blood and forms urine.

A blood vessel that carries blood away from the heart under high pressure; most arteries carry oxygen-rich blood.

A very thin blood vessel where the exchange of gases, nutrients, and wastes takes place between the blood and body tissues.

One of the two lower chambers of the heart; the right ventricle pumps blood to the lungs and the left pumps blood to the body.

A chemical made by a gland or cell that travels in the blood and changes the activity of a target organ or tissue.

A small cell fragment in blood that clumps at the site of a vessel injury and helps form a clot to stop bleeding.

A microorganism, such as a bacterium, virus, fungus, or parasite, that can invade a host and cause disease.

Single-celled organisms without a nucleus; many are harmless or helpful, while others cause infections that are treated with antibiotics.

A tiny infectious agent made of genetic material inside a protein coat; it can only reproduce inside a living host cell.

A medicine that kills bacteria or stops them from multiplying, used to treat bacterial infections; it has no effect on viruses.

A preparation that exposes the immune system to a weakened or inactive germ or its proteins so the body can build protection before a real infection.

A Y-shaped protein made by the immune system that binds to a specific antigen, such as a virus or bacterium, and helps destroy it.

The microorganisms that normally live on and inside the human body, such as in the gut, without causing disease and often helping health.

Practices that keep equipment and surfaces free of all microorganisms, used in surgery, wound care, and laboratory work to prevent infection.

A testable statement or prediction about how two or more variables are related, which an experiment is designed to support or reject.

The factor that a researcher deliberately changes in an experiment so that its effect on another factor can be observed.

The factor that is measured in an experiment; it is expected to respond to changes in the independent variable.

The group in an experiment that does not receive the treatment being tested, used as a baseline for comparison with the experimental group.

A statistical relationship in which two variables change together; it does not by itself show that one variable causes the other.

The average of a set of numbers, found by adding all the values and dividing by the number of values.

How close a measured or calculated value is to the true value; it differs from precision, which is how close repeated measurements are to each other.

The number of observations or subjects included in a study; larger samples generally give more reliable estimates of the population.