Cellular Energy: Photosynthesis and Cellular Respiration

Comprehensive vocabulary flashcards covering the biochemical mechanisms, structures, and pathways of cellular respiration, cellular energy sources (ATP and electron carriers), and photosynthesis.

Cellular Respiration

The energy-releasing chemical breakdown of glucose molecules ($C_6H_{12}O_6$) and the subsequent storage of released chemical energy into $ATP$.

Autotrophs

Organisms (producers at the base of the food chain) capable of synthesizing their own nutrients by converting inorganic compounds such as carbon dioxide ($CO_2$) into organic compounds like carbohydrates, lipids, and proteins.

Heterotrophs

Organisms (consumers further up the food chain, such as herbivores, carnivores, omnivores, parasites, and scavengers) that must acquire organic compounds from other living organisms to obtain nutrients and energy.

Chemosynthesis

An autotrophic nutritional process by which organisms (such as Archaebacteria and some Eubacteria) obtain energy from the breakdown of hydrogen sulfide, elemental sulfur, or iron-containing compounds.

Adenosine Triphosphate (ATP)

The primary energy currency for all cellular functions, composed of $1\text{ adenine}$, $1\text{ ribose}$, and $3\text{ phosphate groups}$; it releases energy when the high-energy bond between the second and third phosphate groups is broken by hydrolysis ($\text{ATP} + \text{water} \rightarrow \text{ADP} + \text{Phosphate} + \text{Energy}$) and is recycled approximately $1250\text{ times/day}$.

Phosphorylation

The energy-storing process in which a free phosphate group is bonded to an adenosine diphosphate ($ADP$) molecule through dehydration synthesis.

Electron Acceptors

Enzymes and coenzymes (such as $NAD^+$ and $FAD^+$) that accept high-energy electrons and hydrogen ions, temporarily storing energy that will later be converted into $ATP$.

Anaerobic Respiration

Cellular respiration occurring entirely in the cytoplasm in the absence of free oxygen, consisting of glycolysis and fermentation to generate a net output of $2\text{ ATP}$ and an organic byproduct.

Aerobic Respiration

Cellular respiration requiring oxygen that begins in the cytoplasm and continues in the mitochondria, yielding carbon dioxide, water, and $36\text{ ATP}$ according to the equation: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{ ATP}$.

Glycolysis

The initial metabolic pathway in the cytoplasm where $2\text{ ATP}$ are consumed to break down a 6-carbon glucose molecule ($C_6H_{12}O_6$) into two 3-carbon sugars ($PGAL$), producing a net yield of $2\text{ ATP}$, $2\text{ NADH}$, and $2\text{ pyruvic acids}$.

Fermentation

An anaerobic process in which two pyruvic acids accept hydrogens from $NADH$ to form an acid or alcohol and carbon dioxide, allowing $NAD^+$ to be regenerated and reused without producing any additional $ATP$.

Alcohol Fermentation

An anaerobic pathway occurring in yeast where pyruvic acid is converted into ethanol and carbon dioxide gas ($CO_2$) as byproducts.

Lactic Acid Fermentation

An anaerobic pathway occurring in some bacteria and mammalian muscle tissue where pyruvic acid accepts hydrogens from $NADH$ to produce lactic acid, which rapidly impairs muscle function and creates post-exertion soreness.

Oxygen Debt

The physiological recovery process required after heavy muscular exertion (such as sprinting or lifting weights) when the body cannot supply sufficient oxygen to meet the metabolic demands of large muscles.

Microbial Fermentation Byproducts

Distinct chemical end products resulting from microbial fermentation pathways, including $CO_2$ and propionic acid (Propionibacterium), lactic acid (Bacillus, Lactobacillus, Streptococcus), ethanol (Saccharomyces), acetone and isopropanol (Clostridium), and acetic acid (Escherichia, Acetobacter).

Kreb's Cycle

The second stage of aerobic respiration located in the mitochondria where 3-carbon pyruvic acid is converted into 2-carbon acetic acid (releasing $CO_2$) and bound to coenzyme A to form acetyl-CoA; two turns of the cycle per glucose yield $6\text{ NADH}$, $2\text{ FADH}_2$, $2\text{ ATP}$, and $4\text{ CO}_2$.

Electron Transport Chain (Respiration)

A process occurring along the inner membrane and matrix of the mitochondrion where $NADH$ and $FADH_2$ release electrons and $H^+$ ions, generating an electrical gradient that drives the synthesis of $32\text{ ATP}$ ($3\text{ ATP}$ per $NADH$ and $2\text{ ATP}$ per $FADH_2$) while bonding $H^+$ to oxygen to release $H_2O$.

ATP Synthase

A membrane-bound protein complex that functions like an overshot waterwheel, utilizing the potential energy of an $H^+$ ion proton channel gradient across the membrane to bond inorganic phosphate ($P_i$) to $ADP$, generating $ATP$.

Photosynthesis

The metabolic process in plants, cyanobacteria, and plant-like protists that converts solar radiant energy into chemical bond energy according to the equation: $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.

Chloroplast

The double-membraned plant cell organelle that contains photosynthetic membranes, internal compartments, and chlorophyll pigments responsible for absorbing light energy.

Thylakoid

A flattened sac of photosynthetic membrane situated inside a chloroplast where the light-dependent reactions take place.

Grana

Densely packed stacks of flattened thylakoid membranes located within the chloroplast.

Stroma

The fluid-filled aqueous region surrounding the grana inside the chloroplast where the light-independent reactions (Calvin Cycle) occur.

Chlorophyll A

The primary photosynthetic pigment that absorbs red and blue light while reflecting green wavelengths, functioning to convert absorbed light energy directly into chemical energy.

Chlorophyll B

An accessory photosynthetic pigment that absorbs blue and red light, reflects green light, and transfers its absorbed photon energy to Chlorophyll A.

Photosynthetic Pigment Absorption Spectrum

The distinctive pattern of light wavelengths absorbed by leaf pigments, demonstrating peak light absorption in the blue and red spectral regions for Chlorophyll a and b, and the blue-green region for carotenoids, while reflecting green light.

Photon

A packet of light energy that, upon striking a pigment molecule, excites its electrons to an elevated energy state.

Light Dependent Reactions

The light-requiring photosynthetic pathway occurring in the thylakoid membranes comprising Photosystem II, an electron transport chain, and Photosystem I to produce $O_2$, $ATP$, and $NADPH$.

Photosystem II

The initial light-dependent complex in the thylakoid membrane that absorbs sunlight, excites electrons, and photolyses water ($H_2O$) into oxygen gas ($O_2$), protons ($H^+$), and free electrons.

Photosystem I

The thylakoid membrane complex where excited electrons and $H^+$ ions from Photosystem II arrive, absorb additional sunlight, drive $ATP$ synthesis across a membrane protein channel, and transfer electrons to $NADP^+$ to form $NADPH$.

Calvin Cycle

The light-independent pathway occurring in the chloroplast stroma that consumes the $ATP$ and $NADPH$ produced by the light-dependent reactions to synthesize one glucose molecule ($C_6H_{12}O_6$) every two complete turns.

Carbon Fixation

The enzymatic phase of the Calvin cycle in which gaseous carbon dioxide ($CO_2$) is absorbed by the leaf one molecule at a time and bonded to a 5-carbon sugar to produce an unstable 6-carbon intermediate.

RuBisCO

The primary enzyme in the Calvin cycle responsible for catalyzing the split of the 6-carbon sugar into two 3-carbon PGA molecules using energy derived from $ATP$ and $NADPH$.