Photosynthesis in dry-climate plants Figure 3 has evolved with adaptations that conserve water. Some plants such as cacti can prepare materials for photosynthesis during the night by a temporary carbon fixation and storage process, because opening the stomata at this time conserves water due to cooler temperatures.
These two processes play an important role in the carbon cycle.
All organisms need energy to perform life functions, and energy that is released is reused in other ways. San Francisco, CA: Because the carbohydrate molecule has six carbon atoms, it takes six turns of the Calvin cycle to make one carbohydrate molecule one for each carbon dioxide molecule fixed. In the second stage Calvin cycle or dark reactions , carbon dioxide and water are converted into organic molecules, such as glucose.
Share Flipboard Email.
Living things access energy by breaking down carbohydrate molecules. In Organic chemistry with a biological emphasis section 13.
These variations increase efficiency and help conserve water and energy. The resulting 6-carbon molecule is unstable, however, and quickly splits into two molecules of a three-carbon compound called 3-phosphoglycerate 3-PGA. In addition, cacti have evolved the ability to carry out low levels of photosynthesis without opening stomata at all, a mechanism for surviving extremely dry periods.
Photosynthesis consumes carbon dioxide and produces oxygen. These variations increase the efficiency of water usage, helping to conserve water and energy. In nature, there is no such thing as waste.
This type of reaction is called a reduction reaction, because it involves the gain of electrons. This process occurs in two major steps:. In this way, the Calvin cycle becomes the way in which plants convert energy from sunlight into long-term storage molecules, such as sugars.
Reactions of the Calvin cycle.
The harsh conditions of the desert have led plants like these cacti to evolve variations of the light-independent reactions of photosynthesis. Search for: Only one carbon dioxide molecule is incorporated at a time, so the cycle must be completed three times to produce a single three-carbon GA3P molecule, and six times to produce a six-carbon glucose molecule.
This step makes a six-carbon compound that splits into two molecules of a three-carbon compound, 3-phosphoglyceric acid 3-PGA.