What happens to the energy stored in glucose during photosynthesis? How do living things make use of this stored energy? The answer is cellular respiration. This process releases the energy in glucose to make ATP (adenosine triphosphate), the molecule that powers all the work of cells.
Stages of Cellular Respiration
Cellular respiration involves many chemical reactions. The reactions can be summed up in this equation:
C6H12O6 + 6O2 $\rightarrow$ 6CO2 + 6H2O + Chemical Energy (in ATP)
The reactions of cellular respiration can be grouped into three stages: glycolysis (stage 1), the Krebs cycle, also called the citric acid cycle (stage 2), and electron transport (stage 3). the figure below gives an overview of these three stages, which are further discussed in the concepts that follow. Glycolysis occurs in the cytosol of the cell and does not require oxygen, whereas the Krebs cycle and electron transport occur in the mitochondria and do require oxygen.
Structure of the Mitochondrion: Key to Aerobic Respiration
The structure of the mitochondrion is key to the process of aerobic (in the presence of oxygen) cellular respiration, especially the Krebs cycle and electron transport. A diagram of a mitochondrion is shown in the figure below.
As you can see from the figure above, a mitochondrion has an inner and outer membrane. The space between the inner and outer membrane is called the intermembrane space. The space enclosed by the inner membrane is called the matrix. The second stage of cellular respiration, the Krebs cycle, takes place in the matrix. The third stage, electron transport, takes place on the inner membrane.
- Cellular respiration takes the energy stored in glucose and transfers it to ATP.
- Cellular respiration has three stages: glycolysis: the Krebs cycle and electron transport.
- The inner and outer membranes of the mitochondrion play an important roles in aerobic respiration.