Photosynthesis: From Light Energy to Chemical Energy

Vocabulary flashcards focusing on key terminology, locations, chemical pathways, enzymes, and plant adaptations related to photosynthesis.

Photosynthesis

The process by which plants, algae, and some bacteria convert light energy into chemical energy stored in organic molecules.

Oxygenic Photosynthesis Equation

The overall simplified chemical equation: $6 CO_2 + 6 H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6 O_2$.

Chloroplasts

Organelles in plant cells where photosynthesis primarily occurs.

Thylakoid Membrane

Membrane inside chloroplasts containing chlorophyll and protein complexes that captures light, transfers electrons, builds a proton gradient, and produces ATP and NADPH.

Thylakoid Lumen

The interior compartment of the thylakoid that accumulates $H^+$ ions during the light reactions.

Stroma

The fluid-filled region surrounding the thylakoids; site of the Calvin cycle and carbohydrate synthesis.

Chlorophyll

Pigment located in thylakoid membranes that absorbs mainly blue and red wavelengths of light.

Light-Dependent Reactions

The stage of photosynthesis occurring in the thylakoid membrane that converts light energy into ATP and NADPH while releasing $O_2$ as a by-product.

Photosystem II

Protein complex where light excites electrons in chlorophyll and water is split to replace the lost electrons.

Photolysis

The light-driven splitting of water molecules that releases electrons, hydrogen ions ($H^+$), and molecular oxygen ($O_2$).

Chemiosmosis

The mechanism where hydrogen ions flow back into the stroma through ATP synthase to phosphorylate ADP into ATP.

Photosystem I

Protein complex where electrons are re-excited by light and ultimately transferred to $NADP^+$ to form NADPH.

Calvin Cycle

Stage of photosynthesis occurring in the stroma that uses ATP and NADPH from the light reactions for carbon fixation.

Carbon Fixation

The first phase of the Calvin cycle where $CO_2$ combines with RuBP in a reaction catalyzed by Rubisco to produce 3-PGA.

Rubisco

An abundant enzyme that catalyzes the fixation of $CO_2$ to RuBP, but can also react with oxygen to initiate photorespiration.

3-PGA

3-phosphoglycerate; the molecule produced when $CO_2$ combines with RuBP during carbon fixation.

G3P

Glyceraldehyde 3-phosphate; the carbohydrate molecule formed in the Calvin cycle using ATP and NADPH, two of which can combine to form one glucose molecule.

Photorespiration

A competing metabolic reaction occurring when Rubisco reacts with oxygen instead of carbon dioxide, reducing photosynthetic efficiency.

Limiting Factor

The required environmental or chemical factor that currently restricts the overall rate of photosynthesis.

C3 Plants

Plants that utilize the standard C3 pathway for initial carbon fixation.

C4 Plants

Plants, such as maize and sugarcane, that spatially separate initial $CO_2$ capture from the Calvin cycle to reduce photorespiration in hot, bright conditions.

CAM Plants

Plants, such as many succulents, that open stomata mainly at night and temporarily store carbon to conserve water in arid conditions.