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SL biology unit 2.8- cell respiration

Terms in this set (22)

Cell respiration is the controlled release of energy from organic compounds to produce ATP. The main organic compound used for this process is carbohydrates (glucose), although lipids and proteins can also be digested. There are two main types of cell respiration, anaerobic respiration involves the partial breakdown of glucose in the cytosol for a small yield of ATP, aerobic respiration utilises oxygen to completely break down glucose in the mitochondria for a larger ATP yield
Define cell respiration
ATP (adenosine triphosphate) is a high energy molecule that functions as an immediate source of power for cell processes. One molecule of ATP contains three covalently linked phosphate groups - which store potential energy in their bonds. When ATP is hydrolysed (to form ADP + Pi) the energy stored in the phosphate bond is released to be used by the cell. Cell respiration uses energy stored in organic molecules to regenerate ATP from ADP + Pi (via oxidation)
Describe ATP
Both anaerobic and aerobic respiration pathways begin with the anaerobic breakdown of glucose in the cytosol by glycolysis. Glycolysis breaks down glucose (6-C) into two molecules of pyruvate (3C), and also produces hydrogen carriers (NADH) from an oxidised precursor (NAD+) and a small yield of ATP (net gain of 2 molecules)
Describe glycolysis
Anaerobic respiration proceeds in the absence of oxygen and does not result in the production of any further ATP molecules. In animals, the pyruvate is converted into lactic acid (or lactate). In plants and yeasts, the pyruvate is converted into ethanol and carbon dioxide
Describe the process of anaerobic respiration
The purpose of anaerobic respiration is to restore stocks of NAD+ - as this molecule is needed for glycolysis. By restoring stocks of NAD+ via anaerobic pathways, the organism can continue to produce ATP via glycolysis
Outline the purpose of anaerobic respiration
Muscle contractions require the expenditure of high amounts of energy and thus require high levels of ATP. When exercising at high intensity, the cells' energy demands will exceed what the available levels of O2 can supply aerobically. Hence the body will begin breaking down glucose anaerobically to maximise ATP production. This will result in an increase in the production of lactic acid, which leads to muscle fatigue. When the individual stops exercising, oxygen levels will increase and lactate will be converted back to pyruvate. Although carbohydrates, lipids and proteins can all be consumed as energy sources, only carbohydrates will typically undergo anaerobic respiration
Describe oxygen debt
At high intensities, the aerobic consumption of fats is decreased while the anaerobic consumption of sugars increases. Consequently, lactate levels will increase at higher levels of exercise intensity
Describe how the conditions of cell respiration change with increasing energy demand
Aerobic cell respiration requires the presence of oxygen and takes place within the mitochondrion. Pyruvate is broken down into carbon dioxide and water, and a large amount of ATP is produced (~34 - 36 molecules). Although aerobic respiration typically begins with glycolysis in carbohydrates, glycolysis itself is an anaerobic process. Aerobic respiration consists of the link reaction, citric acid cycle (or Krebs cycle) and the electron transport chain
Describe aerobic respiration
Anaerobic respiration (fermentation) involves the breakdown of carbohydrates in the absence of oxygen. In yeasts, fermentation results in the production of ethanol and carbon dioxide which can be used in food processing.
Outline the uses of fermentation
Bread - Carbon dioxide causes dough to rise (leavening), the ethanol evaporates during baking. Alcohol - Ethanol is the intoxicating agent in alcoholic beverages (concentrations above ~14% damage the yeast)
Outline two uses of fermentation of food processing
Yogurt/Cheese - Bacteria produce lactic acid anaerobically, which modifies milk proteins to generate yogurts and cheeses
Outline the use of fermentation of bacterial cultures in food processing
A respirometer is a device that determines an organism's respiration rate by measuring the rate of exchange of O2 and CO2
State the purpose of a respirometer
The living specimen (e.g. germinating seeds or invertebrate organism) is enclosed in a sealed container. Carbon dioxide production can be measured with a data logger or by pH changes if the specimen is immersed in water. When an alkali is included to absorb CO2, oxygen consumption can be measured as a change in pressure within the system. The pressure change can be detected with a data logger or via use of a U-tube manometer
Outline a method in which a respirometer can be used
temperature, hydration, light (plants), age and activity levels
State 5 factors which may affect respiration rates
An increase in carbon dioxide levels will indicate an increase in respiration (CO2 is a product of aerobic respiration). A decrease in oxygen levels will indicate an increase in respiration (O2 is a requirement for aerobic respiration)
Outline two ways an increase in respiration may be indicated
They are easier to transport and digest (unlike lipids), They don't produce nitrogenous wastes (unlike proteins)
Outline why carbohydrates are preferable as a ready-made energy source
Carbohydrates can be broken down into monosaccharides (e.g. glucose), which are able to be used in glycolysis
State how carbohydrates may be used as an energy source
Lipids (i.e. triglycerides) can be broken down into glycerol and fatty acids, which are able to be used in aerobic respiration. Lipids produce roughly twice as much energy (~4000 kJ per 100 g) as proteins and carbohydrates
State how lipids may be used as an energy source
Proteins can be broken down into amino acids, which are also capable of being used in aerobic respiration
State how proteins may be used as an energy source
ATP is the energy currency of the cell and is used to power a variety of cellular reactions
Describe ATP
Biosynthesis of macromolecules (e.g. polymer assembly), Active transport (e.g. endocytosis / exocytosis), Nerve transmission (e.g. propagation of action potentials), Growth and repair (e.g. mitotic division), Movement (e.g. muscle contraction), Emission of light (e.g. bioluminescence)
Outline six key uses of ATP (mnemonic: BANG ME)
In terms of reactants, anaerobic uses glucose and aerobic uses glucose and oxygen. Anaerobic undergoes incomplete combustion with a low energy yield (2 ATP) whereas aerobic undergoes complete complete combustion with a high energy yield (36-38 ATP). Anaerobic reactions have two stages (glycolysis and fermentation) and takes place in the cytoplasm, aerobic reactions have four stages (glycolysis, link reaction, krebs cycle, electron transport chain) and takes place in the cytoplasm and mitochondrion. The products of anaerobic respiration are lactic acid in animals and yeast in ethanol and co2, the products of aerobic respiration are co2 and h2o.
Compare aerobic and anaerobic reactions.
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