Respiration

This is the oxidation of organic substance to liberate energy in the body. Aerobic respiration requires oxygen whereas anaerobic respiration does not require oxygen.

Organic molecules (usually carbohydrate or fat) are broken down bond by bond, by a series of enzyme – controlled reactions.  Each bond broken releases a small amount of energy converted to adenosine triphosphate (ATP). ATP is the immediate source of energy for cellular reactions. 

Uses of ATP

1. Provide energy to build up macromolecules such as proteins from amino acids, polysaccharides form monosaccharides and DNA synthesis.
2. Provide energy for movement of materials such as active transport.
3. Provides energy for secretion of materials.
4. Provide energy for muscle contraction, spindle formation in cell division and ciliary action
5. Provide energy for activation of molecules before they are used in the body.

Cell respiration.

Cell respiration involves oxidation of a substrate to yield chemical energy (ATP).  Organic compounds which are used as substrates in respiration are carbohydrates, fats and proteins.

Carbohydrates:  

These are usually the first choice of most cells.  In fact, brain cells of mammals cannot use anything but glucose. Polysaccharides are hydrolyzed to monosaccharides before they enter the respiratory pathway i.e. starch in plant and glycogen in animals are first converted to glucose.

Fats/lipids.

They form the “first” reserve and are mainly used when carbohydrate reserves have been exhausted.  However, in skeleton muscle cells, if glucose and fatly acids are available, these cells respire the acids in preference to glucose.

Lipids are better energy source than carbohydrates because they have a higher proportion of hydrogen and an almost insignificant proportion of oxygen compared with carbohydrates. Thus a given mass of lipids yields more energy on oxidation than an equal mass of carbohydrate.

Proteins.

Since proteins have other essential functions they are only used when all carbohydrate and fat reserves have been used up, as during prolonged starvation. 

Function

Production of cellular energy, ATP

Adaptations

• Has an extensive inner membrane to create a high surface area for enzymes that produce.
• have a small amount of mitochondrial DNA, allowing them to create mitochondrial proteins quicker than from nucleic genes.
• Have necessary enzymes for the production of energy

Anaerobic respiration

A variety of microorganism (anaerobes) employ anaerobic respiration as their major ATP yielding process.  An organism that survives only in the absence of oxygen is termed obligate anaerobe e.g. C. Brotulium and C. tetani). Obligate anaerobes find oxygen poisonous.

Other organisms such as yeast and alimentary canal parasites (such as tapeworms), can exist whether oxygen is available or not.  These are called facultative anaerobe.   Also, some cells that are temporarily deprived of with no oxygen available to accept the hydrogen  (such as muscle cells) are able to respire anaerobically.

Pyruvate serves as an electron/hydrogen acceptor in absence of oxygen to accept the hydrogen atoms released during glycolysis; and depending on the metabolic pathways within the organisms’ cells, the end-product of anaerobic respiration will either be ethanol and carbon dioxide (e.g. fermentation as in yeast) or lactate, for example, lactate fermentation in muscle cells:

In Alcoholic fermentation, the glucose is converted to ethanol and carbon dioxide

Alcoholic fermentation is the basis of brewing in which ethanol is an important product and baking industry in which carbon dioxide expands the dough.

Lactic fermentation occurs occasionally in animal cells during strenuous exercise and oxygen is insufficient. It allows animals to survive periods of insufficient oxygen. When oxygen is latter availed, lactic acid is oxidized to carbon dioxide and water or can be turned into carbohydrates. The amount of oxygen required to oxidize lactic acid accumulated in muscles is called the oxygen debt.

Differences in aerobic and anaerobic respiration

Aerobic Respiration	Anaerobic Respiration
Aerobic respiration uses oxygen.	Does not require oxygen
Aerobic respiration occurs in most cells.	Anaerobic respiration occurs mostly in prokaryotes
Produces a lot of energy	Produces little energy
Occurs in mitochondria	Occurs in cytoplasm
Does not produce ethanol	Produces ethanol

Importance of anaerobic respiration

1. Cause decay and recycling of matter
2. Food production: cheese, yoghurt and vinegar, beers, etc.
3. Manufacturing process. E.g. making soap powder, tanning leather.

Differences between respiration and photosynthesis

	Cellular Respiration	Photosynthesis
1.	Produces energy	Uses energy
2	Produces carbon dioxide	Uses carbon dioxide
3	Does not require light	Can occur only in presence of sunlight
4	Aerobic respiration occurs in mitochondria	Occurs in chloroplasts
5	Does not release oxygen	Releases oxygen
6	Glucose is broken down	Glucose is synthesizes

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Compiled bY Dr. Bbosa David