Biology Chapter 4: Energy & Life

Chemical Energy

Energy stored in the chemical bonds of molecules; a form of potential energy.

Energy

The capacity to cause change, or to move matter in a direction it would not move if left alone.

Entropy

A measure of disorder, or randomness. One form of disorder is heat, which is random molecular motion.

Heat

The amount of kinetic energy contained in the movement of the atoms and molecules in a body of matter. Heat is energy in its most random form.

Kinetic Energy

Energy of motion. Moving matter performs work by transferring its motion to other matter, such as leg muscles pushing bicycle pedals.

Potential Energy

Stored energy; the energy that an object has due to its location and/or arrangement. Water behind a dam and chemical bonds both possess potential energy.

Work

The movement of an object against an opposing force through the expenditure of energy.

Consumers

An organism that obtains its food by eating plants or by eating animals that have eaten plants.

Producers

An organism that makes organic food molecules from carbon dioxide, water, and other inorganic raw materials: a plant, alga, or autotrophic bacterium; the trophic level that supports all others in a food chain or food web.

Chlorophyll

A light-absorbing pigment in chloroplasts that plays a central role in converting solar energy to chemical energy.

Grana

A stack of hollow disks formed of thylakoid membrane in a chloroplast. Grana are the sites where light energy is trapped by chlorophyll and converted to chemical energy during the light reactions of photosynthesis.

Thylakoid

One of a number of disk-shaped membranous sacs inside a chloroplast. Thylakoid membranes contain chlorophyll and the enzymes of the light reactions of photosynthesis. A stack of thylakoids is called a granum.

Calvin Cycle

The second of two stages of photosynthesis; a cyclic series of chemical reactions that occur in the stroma of a chloroplast, using the carbon in CO2 and the ATP and NADPH produced by the light reactions to make the energy-rich sugar molecule G3P, which is later used to produce glucose.

Light Reactions

The first of two stages in photosynthesis, the steps in which solar energy is absorbed and converted to chemical energy in the form of ATP and NADPH. The light reactions power the sugar-producing Calvin cycle but produce no sugar themselves.

NADPH

An electron carrier (a molecule that carries electrons) involved in photosynthesis. Light drives electrons from chlorophyll to NADP+, forming NADPH, which provides the high-energy electrons for the reduction of carbon dioxide to sugar in the Calvin cycle.

Electron Transport Chain

A series of electron carrier molecules that shuttle electrons during the redox reactions that release energy used to make ATP; located in the inner membrane of mitochondria, the thylakoid membrane of chloroplasts, and the plasma membrane of prokaryotes.

Photosystems

A light-harvesting unit of a chloroplast’s thylakoid membrane; consists of several hundred molecules, a reaction-center chlorophyll, and a primary electron acceptor.

ADP

A molecule composed of adenosine and two phosphate groups. The molecule ATP is made by combining a molecule of ADP with a third phosphate in an energy-consuming reaction.

Aerobic Respiration

A series of chemical reactions controlled by enzymes in which organic molecules (often the sugar glucose) are broken down through the use of oxygen (O2) to produce energy in the form of molecules of ATP.

Citric Acid Cycle

The metabolic cycle that occurs after glycolysis in cellular respiration. Chemical reactions in the cycle complete the metabolic breakdown of glucose molecules to carbon dioxide. The cycle occurs in the matrix of mitochondria and supplies most of the NADH molecules that carry energy to the electron transport chains. Also referred to as the Krebs cycle.

Fermentation

The anaerobic harvest of food by some cells.

Glycolysis

The multistep chemical breakdown of a molecule of glucose into two molecules of pyruvic acid; the first stage of cellular respiration in all organisms; occurs in the cytoplasmic fluid.