Cellular waste product
Cellular waste products are formed as a by-product of
Each pathway generates different waste products.
Aerobic respiration
When in the presence of oxygen, cells use aerobic respiration to obtain energy from glucose molecules.[1][2]
Simplified Theoretical Reaction: C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) + ~ 30ATP
Cells undergoing aerobic respiration produce 6 molecules of carbon dioxide, 6 molecules of water, and up to 30 molecules of ATP (adenosine triphosphate), which is directly used to produce energy, from each molecule of glucose in the presence of surplus oxygen.
In aerobic respiration, oxygen serves as the recipient of electrons from the
Anaerobic respiration
Anaerobic respiration is done by aerobic organisms when there is not sufficient oxygen in a cell to undergo aerobic respiration as well as by cells called
Generally, in anaerobic respiration sugars are broken down into carbon dioxide and other waste products that are dictated by the oxidant the cell uses. Whereas in aerobic respiration the oxidant is always oxygen, in anaerobic respiration it varies. Each oxidant produces a different waste product, such as nitrite, succinate, sulfide, methane, and acetate. Anaerobic respiration is correspondingly less efficient than aerobic respiration. In the absence of oxygen, not all of the carbon-carbon bonds in glucose can be broken to release energy. A great deal of extractable energy is left in the waste products. Anaerobic respiration generally occurs in prokaryotes in environments that do not contain oxygen.
Fermentation
Fermentation is another process by which cells can extract energy from glucose. It is not a form of cellular respiration, but it does generate ATP, break down glucose, and produce waste products. Fermentation, like aerobic respiration, begins by breaking glucose into two
Lactic Acid Fermentation
Simplified Theoretical Reaction: C6H12O6 2C3H6O3 + 2 ATP (120 kJ)[6] Lactic Acid Fermentation is commonly known as the process by which mammalian muscle cells produce energy in anaerobic environments, as in instances of great physical exertion, and is the simplest type of fermentation. It starts along the same pathway as aerobic respiration, but once glucose is converted to
Generally, lactic acid fermentation occurs only when aerobic cells are lacking oxygen. However, some aerobic mammalian cells will preferentially use lactic acid fermentation over aerobic respiration. This phenomenon is called the Warburg effect and is found primarily in cancer cells.[9] Muscles cells under great exertion will also use lactic acid fermentation to supplement aerobic respiration. Lactic acid fermentation is somewhat faster, although less efficient, than aerobic respiration, so in activities like sprinting it can help quickly provide needed energy to muscles.[10]
Secretion and effects of waste products
Cellular respiration takes place in the
CO2 is excreted from the cell via diffusion into the blood stream, where it is transported in three ways:
- Up to 7% is dissolved in its molecular form in blood plasma.
- About 70-80% is converted into hydrocarbonate ions,
- The remainder binds with haemoglobin in red blood cells, is carried to the lungs, and exhaled.[11]
H2O also diffuses out of the cell into the bloodstream, from where it is excreted in the form of perspiration, water vapour in the breath, or
The products of fermentation can be processed in different ways, depending on the cellular conditions.
Lactic acid tends to accumulate in the muscles, which causes pain in the muscle and joint as well as fatigue.[13] It also creates a gradient which induces water to flow out of cells and increases blood pressure.[14] Research suggests that lactic acid may also play a role in lowering levels of potassium in the blood.[15] It can also be converted back to pyruvate or converted back to glucose in the liver and fully metabolized by aerobic respiration.[16]
See also
- Aerobic respiration
- Lactic acid fermentation
References
- ^ Aerobic Respiration
- ^ Aerobic Respiration Archived July 6, 2007, at the Wayback Machine
- ISBN 978-1-4292-3413-9.
- ISBN 978-1-4292-3413-9.
- ISBN 978-0-471-58651-7.
- ^ Lactic acid fermentation#cite ref-campbell 3-1
- ISBN 0-8053-7146-X.
- Fermentation (biochemistry)
- PMID 13298683.
- ^ Roth, Stephen. "Why does lactic acid build up in muscles? And why does it cause soreness?". Scientific American.
- ISBN 978-0-07-337809-1.
- ISBN 978-0-07-337809-1.
- ^ "Glycolysis: Anaerobic Respiration: Homolactic Fermentation".
- .
- S2CID 7196683. Retrieved 28 November 2012.
- ISBN 0-683-05731-6