Photosynthesis and Cellular Bioenergetics

Vocabulary flashcards covering the structural, light-dependent, and carbon-fixation processes of photosynthesis, including photophosphorylation, redox reactions, and environmental adaptations such as C3, C4, and CAM pathways.

Magnoliophytes

Flowering seed plants that produce flowers and fruits, making them suitable for residential landscaping due to their decorative appearance and nutrient production.

Photoautotrophs

Organisms, such as green plants, that utilize sunlight to synthesize organic carbon molecules from inorganic $\text{CO}_2$.

Thylakoid Membrane

The internal membrane system of a chloroplast where chlorophyll and other photosynthetic pigments are anchored in clusters called photosystems.

Grana

Stacks of flattened disc-shaped sacs of thylakoid membrane located inside the chloroplast.

Stroma

The semiliquid matrix surrounding the thylakoid membranes within the chloroplast, containing enzymes that catalyze the Calvin cycle reactions.

Chlorophyll

A photosynthetic pigment composed of a light-absorbing porphyrin head with a central magnesium ion and a hydrophobic lipid tail that anchors the molecule into the thylakoid membrane.

Photon

A particle of light acting as a discrete bundle of energy, whose energy content is inversely proportional to its wavelength.

Absorption Spectrum

The specific range and efficiency of wavelengths of light that a particular pigment molecule is capable of absorbing.

Chlorophyll a

The primary photosynthetic pigment present in plants, algae, and cyanobacteria; it is the only pigment directly capable of converting light energy into chemical energy in the reaction center.

Accessory Pigments

Light-absorbing pigments, including chlorophyll $b$ and carotenoids, that capture wavelengths not absorbed by chlorophyll $a$ and transfer that energy to the reaction center.

Carotenoids

Accessory photosynthetic pigments that absorb violet-blue and green wavelengths, reflect orange and yellow light, and protect plant cells from solar radiation damage.

Oxidation-Reduction (Redox) Reactions

Coupled chemical processes wherein oxidation involves the loss of electrons (producing a more positive ion), and reduction involves the gain of electrons (producing a higher-energy reduced species).

Charge Separation

A light-dependent stage in which excitation energy transferred to the reaction center causes an electron to be boosted to a higher energy level and transferred to an electron acceptor molecule.

Photosystem II ($\text{P}_{680}$)

A pigment-protein complex that absorbs photons with a peak wavelength of $680\,\text{nm}$, extracts electrons by oxidizing water (photolysis), and passes excited electrons to plastoquinone.

$$b_6\text{-}f\text{ Complex}$$

An electron transport protein complex that accepts electrons from plastoquinone (PQ), passes them to plastocyanin (PC), and uses the released energy to pump protons from the stroma into the thylakoid lumen.

Photosystem I ($\text{P}_{700}$)

A pigment-protein complex absorbing light optimally at $700\,\text{nm}$ that receives electrons from Photosystem II and passes photo-excited electrons via ferredoxin to $\text{NADP}^+$ reductase to form $\text{NADPH}$.

Chemiosmosis

The mechanism by which ATP is produced when protons accumulated in the thylakoid lumen move down their electrochemical gradient into the stroma through the channel formed by ATP synthase.

Non-Cyclic Photophosphorylation

The continuous, one-way Z-pathway flow of electrons from water through Photosystem II and Photosystem I that generates ATP, reduces $\text{NADP}^+$ to $\text{NADPH}$, and releases $\text{O}_2$.

Cyclic Photophosphorylation

An anoxygenic process involving only Photosystem I in which excited electrons return to the photosystem via an electron transport chain to generate a proton gradient for ATP production without generating $\text{NADPH}$ or $\text{O}_2$.

Rubisco

Ribulose 1,5-bisphosphate carboxylase/oxygenase; an enzyme that catalyzes the initial fixation of $\text{CO}_2$ to RuBP in the Calvin cycle, but can also bind $\text{O}_2$ during photorespiration.

Glyceraldehyde 3-phosphate (G3P)

A 3-carbon sugar synthesized during the Calvin cycle from reduced PGA; utilized to regenerate RuBP, construct transport sugars (sucrose), form storage polymers (starch), and function as a glycolytic intermediate.

Photorespiration

A wasteful process occurring when stomata close to prevent water loss under hot, arid conditions; resulting high $\text{O}_2$ and low $\text{CO}_2$ levels cause Rubisco to oxygenate RuBP instead of fixing carbon.

$$\text{C}_4\text{ Pathway}$$

A spatial photosynthetic adaptation where $\text{CO}_2$ is initially fixed into oxaloacetate by PEP carboxylase in mesophyll cells, converted to malate, and then transported to bundle-sheath cells for decarboxylation and entry into the Calvin cycle.

Crassulacean Acid Metabolism (CAM)

A temporal photosynthetic adaptation in succulents where stomata open at night to fix $\text{CO}_2$ into malate stored in vacuoles, and close during daylight to decarboxylate organic acids and drive the Calvin cycle with minimal water loss.

PEP Carboxylase

An enzyme present in $\text{C}_4$ and CAM plants that fixes inorganic $\text{CO}_2$ to phosphoenolpyruvate (PEP) to create oxaloacetate; it has high affinity for $\text{CO}_2$ and lacks oxygenase activity.