Glossary
ATP
Adenosine triphosphate; the primary energy currency of the cell, used to power most cellular activities like muscle contraction and active transport.
Example:
Muscle cells rapidly hydrolyze ATP to fuel contraction during a strenuous workout.
Cellular respiration
The metabolic process that breaks down glucose and other organic molecules in the presence of oxygen to produce ATP, carbon dioxide, and water.
Example:
Your muscle cells perform cellular respiration to generate the ATP needed for running a marathon.
Citric acid cycle
Also known as the Krebs cycle, a central metabolic pathway in aerobic respiration that completes the breakdown of glucose derivatives, producing ATP, NADH, and FADH2.
Example:
In the mitochondrial matrix, the citric acid cycle efficiently extracts energy from acetyl-CoA.
Death
The irreversible cessation of all vital functions in an organism, often occurring when energy input no longer exceeds energy loss.
Example:
Without sufficient energy intake, a plant will eventually experience death as it cannot maintain its cellular processes.
Electron transport chain
A series of protein complexes embedded in the inner mitochondrial membrane that transfer electrons, creating a proton gradient used to synthesize ATP.
Example:
The final stage of aerobic respiration, the electron transport chain, generates the vast majority of ATP.
Energy
The capacity to do work or cause change, essential for all life processes within an organism.
Example:
A cheetah uses stored chemical energy from its prey to sprint after a gazelle.
Entropy
A measure of the disorder or randomness in a system, which tends to increase in closed systems according to the second law of thermodynamics.
Example:
As a sugar cube dissolves in water, its molecules spread out, increasing the entropy of the solution.
Glycolysis
The first stage of cellular respiration, occurring in the cytoplasm, where glucose is split into two molecules of pyruvate.
Example:
During intense exercise, glycolysis can proceed anaerobically to quickly produce a small amount of ATP.
Internal environment
The stable conditions within an organism's body that are maintained despite external changes, crucial for survival.
Example:
Your body shivers to maintain a stable internal environment (body temperature) when it's cold outside.
Light-dependent reactions
The first stage of photosynthesis, occurring in the thylakoid membranes, where light energy is captured and converted into ATP and NADPH.
Example:
During the light-dependent reactions, water molecules are split, releasing oxygen as a byproduct.
Light-independent reactions (Calvin cycle)
The second stage of photosynthesis, occurring in the stroma, where ATP and NADPH from the light reactions are used to fix carbon dioxide into glucose.
Example:
The light-independent reactions are responsible for synthesizing the sugar molecules that serve as food for the plant.
Metabolic pathways
A series of interconnected biochemical reactions that convert a starting molecule into a final product, often catalyzed by enzymes.
Example:
The process of breaking down glucose into ATP involves several interconnected metabolic pathways.
Open systems
Systems that can exchange both matter and energy with their surroundings, allowing living organisms to maintain their highly ordered state.
Example:
A plant is an open system because it takes in sunlight, water, and CO2, and releases oxygen and water vapor.
Oxidative phosphorylation
The process by which ATP is synthesized as electrons are transferred through the electron transport chain, coupled with the pumping of protons and their subsequent flow back across the membrane.
Example:
Most of the ATP produced during aerobic respiration is generated through oxidative phosphorylation.
Photosynthesis
The process used by plants, algae, and some bacteria to convert light energy into chemical energy, stored in glucose.
Example:
Trees perform photosynthesis to produce the sugars they need for growth and to release oxygen into the atmosphere.
Principle of energy balance
The concept that for an organism to maintain its ordered state and function, the energy it takes in must be greater than the energy it expends or loses.
Example:
A hibernating bear reduces its metabolic rate to ensure its principle of energy balance remains positive during winter.
Second law of thermodynamics
A fundamental principle stating that the total entropy (disorder) of an isolated system can only increase over time, or remain constant in ideal cases.
Example:
A perfectly organized stack of papers will eventually become a messy pile, illustrating the second law of thermodynamics.