·     Organic compounds are broken down to release energy, which can then be used in the cell. 

·     In humans the source of the organic compounds broken down in cell respiration is in the food we eat. (Proteins, Carbohydrates, and lipids)

·     Cell respiration is carried out using enzymes, in a careful and controlled way, so that as much energy released is retained in a usable form. This form is ATP.

·      Cells require energy for three main types of activity:

·      Synthesizing large molecules like DNA, RNA, and proteins

·      Pumping molecules or ions across membranes by active transport.

·      Moving thing around inside the ell, such as chromosomes, vesicles, or in muscle cells the protein fibres that cause muscle contraction.

·     ATP is released by splitting ATP into ADP and phosphate. 

·     The ADP and phosphate can then be reconverted to ATP by cell respiration. 

·     When energy from ATP is used in cells, it is converted into heat. 

·     Heat energy cannot be reused for cell activities and is eventually lost to the environment. 

·     Glucose is broken without using any oxygen.

·     Anaerobic respiration is useful in three situations:

·     When a short rapid burst of ATP production is needed

·     When oxygen supplies run out in respiring cells

·     In environments that are deficient in oxygen, for example waterlogged soils

·      In humans glucose is converted to lactic acid, which is usually in a dissolved from known as lactate.

·      In yeast and plants glucose is converted to ethanol and carbon dioxide. 

·     Both lactate and ethanol are toxic in excess, so must be removed from the cells that produce them, or be produced in limited quantities.

·     It can respire either aerobically or anaerobically.

·     Yeast is added to bread to create bubbles of gas, so that the baked bread has a lighter texture. After kneading, the dough is kept warm to encourage the yeast to respire. Any oxygen in the dough is soon used up so the yeast carries out anaerobic respiration. The carbon dioxide produced by cell respiration cannot escape from the dough and forms bubbles. The swelling of the dough due to the production of bubbles of carbon dioxide is called rising. Ethanol is also produced by anaerobic cell respiration, but it evaporates during backing.

·     Bioethanol is ethanol produced by living organisms for use as a renewable energy source. Yeast converts sugars into ethanol in large fermenters by anaerobic respiration. Only sugars can be converted, so starch and cellulose must first be broken down into sugars. This is done using enzymes. The ethanol produced by the yeast is purified by distillation and other methods are then used to remove water from it to improve its combustion. 

·     Anaerobic respiration is likely to be sued during training or sport example; short distance runners in races up to 400m, long distance runners during a sprint finish

·     Anaerobic respiration involves the production of lactate, when it is being used to supply ATP, the concentration of lactate in a muscle increases. 

·     There is a limit to the concentration that the body can tolerate, and this limits the anaerobic respiration that can be done.

·     After vigorous muscle contractions, the lactate must be broken down. This involves the use of oxygen. 

·     It can take several minutes for enough oxygen to be absorbed for all lactate to be broken down= OXYGEN DEBT

·     Aerobic cell respiration involves a series of chemical reactions. 

·     Carbon dioxide and water are produced. 

·     In most organisms carbon dioxide (waste product) has to be excreted

·      glucose+oxygen  ---------->  carbon dioxide + water   

                                  ( ADP to ATP)

·     In eukaryotic cells most of the reactions of aerobic cell respiration, including all of the reactions that produce carbon dioxide, happen inside the mitochondria. 

·      Most involve these parts:

·      A sealed glass or plastic container in which the organism or tissue is placed.

·      An alkali, such as potassium hydroxide, to absorb carbon dioxide.

·      A capillary tube containing fluid, connected to the container.

·     If the respirometer is working correctly and organisms are carrying out aerobic respiration, the volume of air inside the respirometer will reduce and the fluid in the capillary tube will move towards the container with the organisms. 

·     This is because oxygen is used up and carbon dioxide produced by aerobic cell respiration is absorbed by the alkali.

·     If the rate of movement of the fluid is relatively even, the results are reliable. 

·     If the temperature inside the respirometer changes, the results will not be reliable because an increase in air temperature causes an increase in volume.

·     The temperature inside the respirometer should be controlled using a thermostatically controlled bath.

·      Respirometers can be used to perform various experiments:

·      The respiration rate of different organism could be compared

·      The effect of temperature on respiration rate could be investigated

·      Respiration rates could be compared in active and inactive organisms. 

·      Is it acceptable to remove animals from their natural habitat for use in an experiment and can they be safely returned to their habitat?

·      Will the animals suffer pain or any other harm during the experiment>

·      Can the risk of accidents that cause pain or suffering to the animals be minimized during the experiment? In particular, can contact with the alkali be prevented?

·      Is the use of animals in the experiment essential or is there an alternative method that avoids using animals?

·     It is very important to consider the ethics of animal use in respirometer experiments because the IBO has issued a directive that laboratory or field experiments and investigations need to be undertaken in an ethical. 

·     Also experiments should not be undertaken in schools that inflict pain or harm on humans or other living animals.