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RESPIRATION
7.1 THE RESPIRATORY PROCESS IN ENERGY PRODUCTION
CELL RESPIRATION
All organism require energy to carry out all living processes
Energy is required for various processes which occur in the cell such as: Cell division for growth Formation of gamete for reproduction Transmitting nerve impulses for response and
coordination Contraction of muscles for movement Synthesis of proteins, hormones, lipids and
enzymes
CELL RESPIRATION Respiration is the process in which nutrients
are converted into useful energy in a cell The main substrate for respiration is
glucose Glucose is obtained from:
Digestion of carbohydrates in humans and animals
The process of photosynthesis in plants Respiration at the cellular level is known as
cellular respiration The process occurs in the mitochondria and
cytoplasm of cells Respiration involves a series of reactions
controlled by enzymes
TYPE OF RESPIRATION
There are two types of respiration in the cell Aerobic respiration Anaerobic respiration
AEROBIC RESPIRATION
Aerobic respiration also known as 'oxidative metabolism‘
Aerobic respiration is the breaking down of glucose in the presence of oxygen to release chemical energy
Oxygen is required to oxidise the glucose to produce carbon dioxide, water and energy (ATP)
In aerobic respiration, the glucose is completely oxidised
AEROBIC RESPIRATION
Occurs in the mitochondria and cytoplasm of cells
The reactions occurs slowly and in stages controlled by enzymes
Some of the chemical energy released is changed to heat energy while the rest of the chemical energy is stored in the form of adenosine triphosphate (ATP), a carrier of chemical energy
ATP can be regenerated by combining inorganic phosphate (P) to adenosine diphosphate (ADP)
When body cells need energy, ATP molecules will be hydrolysed to yield energy, a molecule of ADP and an inorganic phosphate
During aerobic respiration, at least 38 molecules of ATP or 2898 kJ of energy is released
Aerobic respiration can be represented by the following equation:
The oxygen for aerobic respiration comes from inhaled air while the carbon dioxide released is removed during exhalation
ATP ADP + P + energy
Glucose + oxygen carbon dioxide + water + 38 ATP/ 2898 kJ
C6H12O6 + 6O2 6CO2 + 6H2O + 38 ATP/ 2898 kJ
ANAEROBIC RESPIRATION
Refers to the special type of respiration, which takes place without oxygen
Anaerobic respiration is the process of oxidation of molecules in the absence of oxygen
Anaerobic respiration is synonymous with fermentation
Glucose is not completely broken down. Not all the energy in glucose is released
Occurs in the cytoplasm of the cells
ANAEROBIC RESPIRATION IN HUMAN MUSCLES
Occurs in human muscles during vigorous activities
During vigorous activities, oxygen need to be transported fast enough to the muscles for rapid cell respiration
This will enable the release of sufficient energy for the vigorous muscle activity
The breathing rate and heart rate are increased to supply more oxygen quickly to the muscles for rapid muscular contraction
However, the supply of oxygen to the muscles is still insufficient and the muscles have to carry out anaerobic respiration to release energy
In the muscles cells, glucose is broken down in the absence of oxygen to form lactic acid and energy for muscle contraction
Lactic acid accumulates in the muscles causing muscular ache
An oxygen debt incurred because the maximum rate of oxygen used is less than the oxygen supplied
Oxygen is required to pay off the oxygen debt Rapid breathing continues after the vigorous
exercise obtain sufficient oxygen
Oxygen oxidises the lactic acid to carbon dioxide, water and energy When all lactic acid is oxidised, the oxygen debt is said to be paid
Oxidation of lactic acid mainly occurs in the liver Some of the lactic acid is oxidised to produce energy The remaining is converted to glucose and then glycogen which is then stored in the muscle cells
ANAEROBIC RESPIRATION IN YEAST Yeast carries out both aerobic respiration and
anaerobic respiration Anaerobic respiration in yeast cells is called
fermentation During fermentation, yeast secretes the enzyme
zymase which hydrolyses glucose in the absence of oxygen to form ethanol, carbon dioxide and 2 ATP
The enzyme zymase secreted by the yeast speed up the fermentation process
In the fermentation process, only a small amount of energy is released
A large amount of energy is still stored in the ethanol as chemical energy
This is because the glucose is not completely broken down
The products of fermentation such as carbon dioxide is used as raising agent in baking bread while ethanol is used to produce alcoholic drinks such as wine
COMPARISON BETWEEN AEROBIC AND ANAEROBIC RESPIRATION
Aerobic respiration Anaerobic respiration
Occurs in the _________ of oxygen
Occurs in the ____________ of oxygen
Releases _________ amount of energy (___ molecules of ATP or ______ kJ)
Releases ________ energy ( ____ molecules of ATP or ____ kJ (muscle cells) _____ kJ (yeast)
Produces ____________ and __________
Produces ____________ (human muscles) or ________________ (yeast)
Glucose is _______________ broken down
Glucose is ___________________ broken down
Occurs in the _________________ and _____________________
Occurs in the __________________ only