How do plants recycle carbon during photosynthesis?
The carbon in oxygen molecules
The carbon in carbon dioxide
The carbon in water is recycled
The carbon in glucose is recycled
During photosynthesis, plants recycle carbon in multiple ways:
1. The carbon in carbon dioxide (CO2) is recycled: Plants take in carbon dioxide from the atmosphere through tiny pores called stomata on their leaves. Inside the chloroplasts of plant cells, the enzyme ribulose bisphosphate carboxylase/oxygenase (Rubisco) combines carbon dioxide with a 5-carbon molecule called ribulose bisphosphate (RuBP) in a process called carbon fixation. This results in the formation of two 3-carbon molecules called phosphoglycerate (PGA).
2. The carbon in water is indirectly recycled: During photosynthesis, plants require water as a reactant. Although the carbon in water (H2O) is not directly recycled in the form of carbon atoms, it plays a crucial role in the photosynthetic process. Water is split by light energy in a process called photolysis, releasing oxygen and hydrogen ions. These hydrogen ions combine with carbon dioxide during the Calvin Cycle (a series of enzymatic reactions) to produce glucose.
3. The carbon in glucose is recycled: Glucose is a sugar molecule that contains carbon atoms. The carbon from glucose is recycled in various ways within the plant. Some glucose molecules are used for immediate energy production through cellular respiration, releasing carbon dioxide back into the atmosphere. Other glucose molecules are converted into starches or stored as complex carbohydrates for later use or growth. When plants are consumed by animals or decomposed, the carbon in glucose is further recycled through different food chains and ecosystems.
But which one is the answer
The specific answer to your question is: "The carbon in carbon dioxide is recycled." During photosynthesis, plants take in carbon dioxide (CO2) from the atmosphere and convert it into glucose, a sugar molecule that contains carbon. This process allows plants to effectively recycle the carbon from carbon dioxide and incorporate it into organic compounds.
During photosynthesis, plants recycle carbon from two main sources: carbon dioxide (CO2) and water (H2O). Here's how it happens:
1. Carbon in carbon dioxide: Plants take in carbon dioxide from the atmosphere through tiny openings called stomata, primarily located in their leaves. Inside the leaves, cells called mesophyll cells contain chloroplasts, which are key to photosynthesis. Carbon dioxide enters the chloroplasts and combines with other molecules to form a five-carbon compound called ribulose bisphosphate (RuBP), through a process known as carbon fixation. This enzyme-mediated reaction leads to the formation of two three-carbon compounds called phosphoglycerate (PGA).
2. Carbon in water: Plants absorb water from the soil through their root system. Inside the chloroplasts, water molecules undergo a process called photolysis, where they are split into hydrogen (H+) ions, electrons, and oxygen (O2). The water molecules' oxygen atoms are released as oxygen gas into the atmosphere, while the hydrogen ions and electrons are used in other reactions of photosynthesis.
3. Carbon in glucose: The PGA molecules produced from carbon fixation combine with energy-rich molecules called ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), both of which are products of other reactions in photosynthesis. These reactions collectively form a process called the Calvin cycle, also known as the dark reactions or the light-independent reactions. Within the Calvin cycle, the PGA molecules are transformed into a three-carbon sugar molecule called glyceraldehyde-3-phosphate (G3P). Some of the G3P molecules continue along the cycle to regenerate RuBP, while others combine to form glucose and other carbohydrates, which serve as energy storage and building blocks for the plant.
So, in summary, plants recycle carbon during photosynthesis by incorporating carbon from carbon dioxide into organic molecules through carbon fixation, and by splitting water molecules to release oxygen and utilize the hydrogen ions and electrons in other reactions. The resulting glucose and other carbohydrates store the recycled carbon and serve as essential resources for the plant's growth and metabolism.