Cellular Respiration
Definition and meaning of Cellular Respiration in chemistry.
Cellular respiration is a series of chemical reactions that happen inside cells to make energy. The process converts chemical energy from glucose into a usable energy molecule called adenosine triphosphate, or ATP. Aerobic respiration requires oxygen to completely break down food molecules into carbon dioxide and water.
In more detail
This complex process has three main stages: glycolysis, the citric acid cycle, and oxidative phosphorylation. First, glycolysis occurs in the cytoplasm, which is the watery fluid inside the cell. This stage breaks one glucose molecule into two smaller molecules of pyruvate.
Glycolysis does not need oxygen and only makes a small amount of ATP. Next, the pyruvate molecules enter the mitochondria, which are the powerhouses of the cell. Here, the citric acid cycle breaks down the pyruvate completely.
This cycle releases carbon dioxide gas as waste and transfers energy to carrier molecules. These carriers are nicotinamide adenine dinucleotide, or NADH, and flavin adenine dinucleotide, or FADH2. In the final stage, these carriers deliver high-energy electrons to the electron transport chain.
The chain is a series of proteins embedded in the inner mitochondrial membrane. As electrons flow, they pump protons across the membrane to build a strong gradient. This gradient acts like a dam to power a protein machine called ATP synthase.
The machine spins to make a large amount of ATP. A common student mistake is thinking that plants only do photosynthesis and not respiration. In reality, plants must also perform cellular respiration to use their stored sugars.
Oxygen is the final electron acceptor at the end of the transport chain. It joins with protons to form water molecules.
Key facts
| Field | Biochemistry |
|---|---|
| Formula | C6H12O6 |
| Molar mass | 180.16 g/mol |
| Maximum ATP yield | 30 to 32 ATP per glucose |
| Primary location | Mitochondria |
| Final electron acceptor | Oxygen |
During a long running race, human muscle cells perform aerobic cellular respiration at a very high rate. The cells need to produce massive amounts of ATP to keep the muscles contracting. When oxygen runs low during intense exercise, the cells must switch to lactic acid fermentation. This backup process keeps making a tiny amount of ATP but leads to muscle fatigue.
Frequently asked questions
What happens when cells do not have enough oxygen for respiration?
Without oxygen, cells must switch to anaerobic pathway options like fermentation. These pathways produce much less ATP and create waste products like lactic acid or alcohol.
Is cellular respiration the exact reverse of photosynthesis?
The chemical equations are opposites, but the pathways and enzymes are completely different. Photosynthesis stores energy in glucose, while respiration releases that energy to make ATP.
Do plants perform cellular respiration or only photosynthesis?
Plants perform both processes. Photosynthesis makes glucose using sunlight, but plants must still use respiration to break down that glucose for energy.