Cellular Respiration
Syllabus Objectives
State that respiration takes place at the level of the cell
Describe the process of aerobic respiration
State the function of ATP (adeosine triphosphate) in energy transfer
Distinguish between aerobic and anaerobic respiration
Carry out and interpret results from simple controlled investigations to demonstrate the products of respiration
Introduction
DefinitionProcess living organisms undergo to release energy from food (substrate)
The energy released is used to carry out all metabolic activities in living organisms
Respiration involves several steps controlled by enzymes
There are TWO main types of respiration:AEROBIC
ANAEROBIC
AEROBIC Respiration
Glucose is oxidized in many small steps to form carbon dioxide, water and energy.
The important energy releasing steps take place in the mitochondria
The energy is stored temporarily in ATP molecules
The energy is readily available for use when required in this form
AEROBIC Respiration Equation
The overall equation can be summarized as follows:
C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy
glucose + oxygen carbon + water + ATP
dioxide
AEROBIC Respiration
Summary:Glucose (or fat) is used as a substrate to provide energy
Energy is released in slow, controlled process
The energy released is temporarily stored in ATP
Oxygen is used in the process
Carbon dioxide and water are released
ANAEROBIC RespirationThe food (sugar) is only partly oxidized producing a little energy
In animals that respire anaerobically the sugar is broken down to form LACTIC ACID and energy
No CO2 is given off
In plants and yeast (a fungus) the sugar is converted into ETHANOL (alcohol), carbon dioxide and energy.
There are microscopic organisms that are AnaerobesThey can live without oxygen
Larger organisms can survive for short periods without oxygen
ANAEROBIC Respiration
During strenuous exercise, mammalian muscle cells can respire anaerobically for a short time
Lactic acid accumulates in the cells causing fatigue
Lactic acid is toxic in large quantities and must be broken down before the cells can function normally again
ANAEROBIC Respiration
The temporary shortage of oxygen results in an OXYGEN DEBT
Extra oxygen is required to break down the lactic acid to carbon dioxide and water.
Heavy breathing which continues after vigorous exercise is necessary to pay back the oxygen debt
ANAEROBIC Respiration Equation
The overall equation can be summarized as follows:
Plants and yeasts
carbon dioxide + ethyl alcohol + energy (ATP)
glucose
lactic acid + energy (ATP)
Animals
ANAEROBIC Respiration
Summary:
The events taking place in anaerobic respiration are the same as the first steps in aerobic respiration. During anaerobic respiration:
No oxygen is used
Little energy is produced
Alcohol and carbon dioxide are produced by plants and yeast
Only lactic acid is produced by animals
ATP
The adenosine triphosphate (ATP) molecule has three phosphate groups.
The 3rd phosphate in adenosine triphosphate (ATP) is easily removed to form adenosine diphosphate (ADP).
Energy is released during that reaction
The ATP molecule stores energy temporarily and transfers it to the other reactions when necessary
Energy Transfer Equation
ATP ADP + P + Energy
The ADP formed by that reaction is used to make more ATP
ADP + P + energy from respirationATP
The table below shows the amounts of lactic acid in the blood of a man who exercised vigorously for ten minutes.
Lactic Acid Concentration in the Blood of an Exercising Man
Time/minutes Lactic acid conc./mg per 100 cm3
0 20
10 80
14 97
19 90
30 70
57 40
(a) Draw a graph to show how the lactic acid concentration changed. 7
(b) By how much did the lactic acid increase during the period of exercise? 1
(c) How do you account for the rise in lactic acid concentration during the first ten minutes after the start of the exercise? 3
(d) Suggest why it continued to rise for a short time after the exercise ended. 2
(e) State TWO factors that should be kept constant if this method is to be used to compare results from several different persons. 2
15 marks
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