Energy, Cellular Respiration, and Photosynthesis

Vocabulary practice flashcards covering Energy and Metabolism (Chapter 3), Cellular Respiration (Chapter 4), and Photosynthesis (Chapter 5).

Metabolism

The sum of all chemical reactions that occur in an organism, including reactions that break down molecules and reactions that build new molecules (e.g., cellular respiration breaking down glucose).

Kinetic Energy

The energy of movement; an object possesses more kinetic energy when it is moving (e.g., a diver moving toward the water).

Potential Energy

Stored energy that can be converted into another form of energy (e.g., a diver standing on a diving board possesses gravitational potential energy).

First Law of Thermodynamics

The principle stating that energy cannot be created or destroyed, but can only be transferred or transformed from one form to another.

Bond Energy

The energy required to break a chemical bond. Energy must be added to break bonds, whereas forming new bonds releases energy.

Activation Energy

The minimum amount of energy needed to start a chemical reaction, which reactant molecules must reach for the reaction to proceed.

Transition State

The temporary, unstable, high-energy state reached during a chemical reaction as bonds break and new bonds form after reactants gain sufficient activation energy.

Exothermic Reaction

A chemical reaction that releases energy into the surroundings, usually in the form of heat (e.g., burning wood).

Endothermic Reaction

A chemical reaction that absorbs energy from the surroundings (e.g., an instant cold pack).

Second Law of Thermodynamics

The principle stating that every energy transfer or transformation increases the total entropy of the universe, with some energy becoming dispersed and less available to do useful work.

Entropy

A measure of how dispersed energy and matter are, which generally increases during spontaneous processes (e.g., heat spreading from a hot drink into cooler surroundings).

Spontaneous Change

A change that can continue without a continuous input of energy once it has started, though it is not necessarily immediate or fast.

Free Energy

Energy available to perform useful work, which cells utilize to power essential cellular processes such as $ATP$-driven reactions.

Catabolic Pathway

A metabolic pathway that breaks down larger molecules into smaller molecules, generally releasing energy (e.g., cellular respiration breaking down glucose).

Anabolic Pathway

A metabolic pathway that synthesizes larger molecules from smaller molecules, requiring an input of energy (e.g., building a protein from amino acids).

Phosphorylation

The addition of a phosphate group to a molecule, which can alter a molecule's activity or transfer energy (e.g., adding inorganic phosphate to $ADP$ to produce $ATP$).

ATP Cycle

The cyclic process in which $ATP$ is broken down into $ADP$ and inorganic phosphate to release free energy, and energy from cellular processes is used to regenerate $ATP$ from $ADP$ and phosphate.

Enzymes

Biological catalysts that speed up chemical reactions by lowering the activation energy required, without being consumed or used up by the reactions they catalyze.

Oxidation

The loss of electrons from a substance during a chemical reaction.

Reduction

The gain of electrons by a substance during a chemical reaction.

Aerobic Cellular Respiration

The process of breaking down glucose using oxygen to produce $ATP$, carbon dioxide, and water through glycolysis, pyruvate oxidation, the citric acid cycle, and the electron transport chain with chemiosmosis.

Glycolysis

A metabolic pathway in the cytoplasm that splits one glucose molecule into two pyruvate molecules, producing a net gain of $2$ $ATP$ (produced $4$, used $2$) and $2$ $NADH$.

Pyruvate Oxidation

The process in the mitochondrial matrix that converts each pyruvate into acetyl-CoA, yielding two acetyl-CoA, two $CO_2$, and two $NADH$ per glucose to prepare for the citric acid cycle.

Citric Acid Cycle

A series of reactions in the mitochondrial matrix that breaks down acetyl-CoA, producing $CO_2$, $NADH$, $FADH_2$, and $ATP$ (or GTP) to deliver high-energy electrons to the electron transport chain.

Electron Transport Chain (Cellular Respiration)

A series of proteins in the inner mitochondrial membrane that uses energy from electrons delivered by $NADH$ and $FADH_2$ to pump hydrogen ions, with oxygen serving as the final electron acceptor to form water.

Chemiosmosis

The process in which hydrogen ions flow down their concentration gradient through $ATP$ synthase, powering the synthesis of $ATP$ from $ADP$ and phosphate.

Alcohol Fermentation

An anaerobic process in which pyruvate is converted into ethanol and carbon dioxide, regenerating $NAD^+$ so glycolysis can continue producing a net $2$ $ATP$ per glucose (e.g., in yeast).

Lactate Fermentation

An anaerobic process in which pyruvate is converted into lactate, regenerating $NAD^+$ so glycolysis can continue producing $ATP$ (e.g., in human muscle cells during intense exercise).

Anaerobic Respiration

A form of cellular respiration that uses an electron transport chain with an inorganic final electron acceptor other than oxygen.

Substrate-Level Phosphorylation

The direct transfer of a phosphate group from an organic donor molecule to $ADP$ by an enzyme to form $ATP$ (e.g., in glycolysis).

Oxidative Phosphorylation

The production of $ATP$ using energy derived from the electron transport chain and chemiosmosis across a membrane gradient.

Obligate Aerobes

Organisms that strictly require oxygen for their energy-producing metabolic processes.

Obligate Anaerobes

Organisms that cannot survive or grow under normal oxygen conditions because oxygen is toxic to them.

Facultative Anaerobes

Organisms that can use oxygen when it is present but can switch to anaerobic metabolism or fermentation when oxygen is absent (e.g., yeast).

Chloroplast

The plant and algal organelle containing thylakoid membranes (the site of light-dependent reactions) and stroma (the fluid-filled site of the Calvin cycle).

Chlorophyll a

The primary photosynthetic pigment located in photosystem reaction centres; it absorbs blue-violet and red light, reflects green light, and is directly involved in light-driven electron transfer.

Chlorophyll b

An accessory pigment that absorbs light wavelengths not absorbed as well by chlorophyll a and transfers the captured energy to chlorophyll a.

Carotenoids

Accessory pigments that absorb additional wavelengths of light, dissipate excess light energy to protect the photosynthetic apparatus, and produce yellow and orange colours in autumn leaves.

Xanthophylls

A group of carotenoid accessory pigments that aid in light absorption and help protect chloroplasts from excessive light energy.

Antenna Complex

A light-harvesting complex containing chlorophyll b and accessory pigments that captures light energy and channels it toward the reaction centre.

Reaction Centre

The core of a photosystem containing specialized chlorophyll a molecules that absorb channeled energy and release high-energy electrons into the electron transport pathway.

P680

The specialized reaction-centre chlorophyll a molecule of Photosystem II that absorbs light most effectively at a wavelength of $680\,nm$.

P700

The specialized reaction-centre chlorophyll a molecule of Photosystem I that absorbs light most effectively at a wavelength of $700\,nm$.

Light-Dependent Reactions

Reactions occurring in the thylakoid membranes that utilize light and water to produce $ATP$, $NADPH$, and oxygen.

Photosystem II (PSII)

The first photosystem in linear electron transport; it absorbs light via P680 and splits water molecules to replenish lost electrons, releasing oxygen and hydrogen ions.

Photosystem I (PSI)

The photosystem containing P700 that absorbs light to re-energize electrons from the electron transport chain, which are subsequently used to reduce $NADP^+$ to $NADPH$.

Linear (Non-Cyclic) Electron Transport

The unidirectional pathway of electrons from water through PSII, an electron transport chain, and PSI to $NADP^+$, yielding $ATP$, $NADPH$, and oxygen.

Cyclic Electron Transport

An electron pathway using only PSI that returns electrons to the electron transport chain to generate additional $ATP$, without generating $NADPH$ or releasing oxygen.

Calvin Cycle

The light-independent metabolic pathway occurring in the chloroplast stroma that consumes $CO_2$, $ATP$, and $NADPH$ to produce G3P.

Rubisco

The enzyme responsible for attaching inorganic $CO_2$ to RuBP during the carbon fixation phase of the Calvin cycle.

Carbon Fixation (Phase One)

The initial stage of the Calvin cycle where $CO_2$ combines with the five-carbon molecule RuBP via Rubisco, splitting into molecules of 3-PGA.

Reduction (Phase Two)

The stage of the Calvin cycle where $ATP$ and $NADPH$ provide energy and reducing power to convert 3-PGA into the three-carbon carbohydrate G3P.

Regeneration (Phase Three)

The final stage of the Calvin cycle where $ATP$ is used to rearrange remaining molecules to regenerate RuBP so the cycle can continue.

G3P (Glyceraldehyde 3-phosphate)

The three-carbon sugar output of the Calvin cycle; two net G3P molecules provide the six carbon atoms needed to synthesize one glucose molecule.

Photorespiration

A wasteful process occurring when Rubisco binds oxygen instead of $CO_2$, reducing photosynthetic efficiency; it is more prevalent in hot, dry conditions when stomata close.

C3 Plants

Plants that fix $CO_2$ directly via the Calvin cycle into a three-carbon compound without special cell-type or temporal separation, making them vulnerable to photorespiration (e.g., wheat, rice).

C4 Plants

Plants that fix $CO_2$ initially into a four-carbon compound and separate carbon fixation from the Calvin cycle across different cell types to reduce photorespiration (e.g., corn, sugarcane).

CAM Plants

Arid-adapted plants that open stomata at night to fix and store $CO_2$, and close stomata during the day to run the Calvin cycle, separating processes by different times of day (e.g., cacti, pineapple).

C3 vs. C4 vs. CAM Adaptations

Comparison of photosynthetic adaptations showing initial carbon fixation compounds, separation of processes (none, different cell types, or different times of day), photorespiration levels, and representative plant examples.