Photosynthesis: Light Reactions, Calvin Cycle, and Alternative Pathways

Comprehensive vocabulary flashcards covering the components of photosynthesis, chloroplast anatomy, the light-dependent reactions, the Calvin cycle, and alternative photosynthetic pathways (C4 and CAM).

Carbohydrate

An organic compound containing only carbon, hydrogen, and oxygen, usually in a $1:2:1$ ratio.

Photosynthesis

The process by which autotrophs convert light energy into chemical energy, represented by the overall chemical reaction $6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.

Chloroplasts

Pigmented organelles that capture light energy and serve as the site where photosynthesis occurs.

Thylakoids

Flattened saclike internal membranes of the chloroplast where the light-dependent reactions take place.

Grana

Stacks of thylakoids found inside chloroplasts (singular: granum).

Stroma

The fluid-filled space outside the grana within the chloroplast, serving as the location for phase two of photosynthesis.

Oxygen

A waste product of photosynthesis that is released into the environment as a result of water molecules splitting.

Pigments

Light-absorbing colored molecules found in thylakoid membranes that absorb specific wavelengths of light.

Carotenoids

Photosynthetic pigments that absorb the greatest percentage of light at a wavelength of $500\,\text{nm}$.

Photosystems

Two types of protein complexes embedded in the thylakoid membrane that contain light-capturing pigments and proteins essential to the light reactions.

Photosystem II

A protein complex where light energy excites electrons and causes a water molecule to split, initiating the electron transport process.

Photosystem I

A protein complex that receives electrons carried along a series of electron carriers from an electron acceptor molecule and transfers them to ferredoxin.

Ferredoxin

A protein that receives electrons from photosystem I and transfers them to the electron carrier $\text{NADP}^+$, forming the energy-storage molecule NADPH.

Chemiosmosis

The mechanism by which ATP is produced as a result of the flow of electrons down a concentration gradient, requiring the breakdown of water.

Light-Dependent Phase

The first phase of photosynthesis where light energy is captured and converted into the chemical energy storage molecules ATP and NADPH.

Calvin Cycle

The second phase of photosynthesis (light-independent phase) where chemical energy stored in ATP and NADPH is used to store energy in organic molecules such as glucose.

Carbon Fixation

The first step of the Calvin cycle, where $\text{CO}_2$ molecules combine with 5-carbon molecules to form 3-phosphoglycerate (3-PGA).

3-Phosphoglycerate (3-PGA)

Three-carbon molecules formed during carbon fixation that receive chemical energy transferred from ATP and NADPH to form G3P.

Glyceraldehyde 3-Phosphate (G3P)

Three-carbon molecules formed in the Calvin cycle; some exit to synthesize glucose and other organic compounds, while the remaining molecules are recycled.

Rubisco

An enzyme that converts inorganic carbon dioxide into organic molecules used by the cell and regenerates remaining G3P molecules into 5-carbon ribulose 1,5-bisphosphate molecules.

Ribulose 1,5-Bisphosphate (RuBP)

Five-carbon molecules regenerated by rubisco from G3P that combine with new $\text{CO}_2$ to continue the Calvin cycle.

C4 Plants

Plants with significant structural modifications in leaf cell arrangement that utilize an alternative pathway to maintain photosynthesis while reducing water loss.

CAM Plants

Desert plants utilizing Crassulacean acid metabolism that collect $\text{CO}_2$ at night to store in organic compounds and release it during the day for photosynthesis.