Photosynthesis

Within the membranes of chloroplasts, electrons in pigments are energized by light and transferred across a series of molecules until they create the energetic NADPH molecule. This transfer also powers a hydrogen pump, which creates an ion imbalance that, when relieved, produces energetic ATP molecules. Outside the membranes, both NADPH and ATP are used to synthesize G3Ps, which are funneled into other metabolic pathways to produce sugars.

Each run of this second phase of photosynthesis begins with a five-carbon molecule called RuBP, which gains an additional carbon atom when carbon dioxide (CO₂) is attached. Across six cycles, the six six-carbon molecules—36 carbon atoms in total—are processed into 12 three-carbon sugars, which can be used to generate glucose, and six RuBP molecules, enough for each cycle to restart.

Using NASA satellite imagery, carbon absorption can be tracked and serves as a proxy for photosynthetic activity on land and in the oceans. Over the course of a year, seasonal changes can be observed as plants become dormant in the fall and active again in the spring.

Although light energy is captured to power the reactions that produce the building blocks of starch, cellulose, glucose, and other sugars, chlorophyll a and b are most sensitive to violet, blue, orange, and red light, leaving green light mostly unabsorbed. This green light is instead reflected, giving most plants this color appearance.

In the vast majority of plants, C3 photosynthesis produces three-carbon intermediate molecules in the Calvin cycle within the cells of leaves. Plants in hot, dry climates use C4 photosynthesis across two types of cells to produce four-carbon molecules before the Calvin cycle. Plants in drought conditions use CAM to store carbon dioxide as an acid at night, minimizing water loss.

Born in 1730, the Dutch scientist expanded on existing knowledge that plants produce and absorb gases in his 1779 paper, which detailed that light was necessary for the biochemical processes that produce oxygen in plant leaves. He also identified that all parts of plants produce carbon dioxide at night.

Between 3.2 and 2.8 billion years ago, threadlike microorganisms called cyanobacteria began consuming available water vapor, carbon dioxide, and sunlight to produce oxygen. However, molecules released from Earth's interior by volcanoes consumed this oxygen via chemical reactions, preventing it from accumulating until volcanism had sufficiently decreased about 2.4 billion years ago.

A major study found that pieces of plastic less than five millimeters long are causing an estimated 4% to 14% loss of the world's wheat, rice, and maize, potentially putting an additional 400 million people at risk of starvation within 20 years. The damage from microplastics to crops may already rival the impact of climate change on food supplies.

These systems link a molecular light absorber to a catalyst that can synthesize fuels—such as ethanol—and ethylene, a precursor to plastics, in a carbon-neutral manner. Because these byproducts have greater energy concentrations than the carbohydrates produced by photosynthetic organisms, research is ongoing to engineer the necessary catalysts.

In this simulation, users can track how the cellular concentrations of ATP, NADPH, glucose, and oxygen vary over time in response to changes in temperature, acidity, carbon dioxide concentration, and the properties of incoming light. Through multiple trials, users can identify the optimal conditions for photosynthetic reactions.