Photosynthesis is a set of chemical reactions that plants and other organisms use to make chemical energy in the form of sugar. Like any chemical reaction, photosynthesis has reactants and products. Overall, the reactants of photosynthesis are carbon dioxide and water, while the products of photosynthesis are oxygen and glucose (a sugar).
Here’s a closer look at the products of photosynthesis and the balanced equation for the reaction.
The reactants for photosynthesis are carbon dioxide and water, while the products are the sugar glucose and oxygen.
Balanced Chemical Equation for Photosynthesis
Photosynthesis actually involves many chemical reactions, but the net balanced equation is that six moles of carbon dioxide react with six moles of water to produce one mole of glucose and six moles of oxygen. Light from the Sun provides the activation energy for the reaction. Sometimes light is listed in the balanced equation as a reactant, but it’s usually omitted.
6 CO2 + 6 H2O → C6H12O6 + 6 O2
Carbon Dioxide + Water + Light → Glucose + Oxygen
Closer Look at the Products of Photosynthesis
Photosynthesis occurs in a series of steps that are classified as light-dependent reactions and light-independent reactions. Adding up the reactants and products of these reactions gives the overall equation for photosynthesis, but it’s good to know the inputs and outputs for each stage.
Light-Dependent Reactions
The light-dependent reactions or light reactions absorb certain wavelengths of light to make adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH). The light reactions occur in the chloroplast thylakoid membrane. The overall balanced equation for the light-dependent reactions is:
2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2
Light-Independent Reactions
While the light reactions use water, the light-independent reactions use carbon dioxide. The light-independent reactions are also called the dark reactions. These reactions do not require darkness, but they don’t depend on light to proceed. In plants, algae, and cyanobacteria, the dark reactions are called the Calvin cycle. Bacteria use different reactions, including the reverse Krebs cycle.
The overall balanced equation for the light-independent reactions (Calvin cycle) in plants is:
3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O
Finally, the three-carbon product from the Calvin cycle becomes glucose during the process of carbon fixation.
Other Products of Photosynthesis
Glucose is the direct product of photosynthesis, but plants turn most of the sugar into other compounds. These are indirect products. Linking glucose units forms starch and cellulose. Cellulose is a structural material. Plants store starch or link it to fructose (another sugar) to form sucrose (table sugar).
What Is Not a Product of Photosynthesis?
On an exam, you may need to identify which chemical is not a product of photosynthesis. For the overall process, choose any answer except “glucose” or “oxygen.” It’s good to know the overall reactants and products of the light reactions and dark reactions, in case you’re asked about them. The products of the light reactions are ATP, NADPH, protons, and oxygen. The products of the dark reactions are C3H6O3-phosphate, ADP, inorganic phosphate, NADP+, and water.
Where Does Photosynthesis Occur?
In addition to knowing the reactants and products of photosynthesis, you may need to know where photosynthesis occurs in different organisms.
- In plants, photosynthesis occurs in organelles called chloroplasts. Photosynthetic protists also contain chloroplasts. Leaves contain the highest concentration of chloroplasts in plants. Plants obtain carbon dioxide via diffusion through leaf stomata. Water comes from the roots and travels to the leaves via the xylem. Chlorophyll in chloroplasts absorbs solar energy. Oxygen from photosynthesis exits the plant via leaf stomata.
- Photosynthesis occurs in photosynthetic bacteria in the plasma membrane. Chlorophyll or related pigments are embedded in this membrane.
References
- Bidlack, J.E.; Stern, K.R.; Jansky, S. (2003). Introductory Plant Biology. New York: McGraw-Hill. ISBN 978-0-07-290941-8.
- Blankenship, R.E. (2014). Molecular Mechanisms of Photosynthesis (2nd ed.). John Wiley & Sons. ISBN 978-1-4051-8975-0.
- Reece J.B., et al. (2013). Campbell Biology. Benjamin Cummings. ISBN 978-0-321-77565-8.