Effect of Activity on Respiration in Humans
Introduction to Respiration
Breathing and respiration are two separate processes. Breathing is the process of moving air in and out of the lungs
(inhalation and exhalation). Respiration is the process in all living organisms where energy, ATP, is produced in cells.
ATP is adenosine triphosphate, which is a phosphorylated nucleotide with a similar structure to DNA and RNA. ATP is
unable to leave the cell it was produced in. It occurs in the mitochondria, which are found in all animal cells. The
mitochondria have two membranes, which are important as they allow the aerobic respiration reactions to be
separated from the rest of the cell. There are also enzymes which are important for the Link Reaction and Krebs
Cycle stages of respiration. These enzymes are housed in the matrix of the mitochondria. A large surface area is
provided by the cristae of the mitochondria, which is important as it allows for many Electron Transport Chains.
Why is respiration important? Respiration is required in cells to produce energy, which allows for other processes
within the body to function properly. Examples of bodily functions which require the energy produced in respiration
are active transport, muscle contraction, synthesising proteins and enzymes from larger molecules, cellulose from
glucose, starch from glucose, and amino acids from glucose and nitrates.
Aerobic Respiration – Aerobic respiration is respiration using oxygen. This occurs in animal cells and plant cells, as
well as a limited number of microbes. Aerobic respiration is more efficient than anaerobic respiration and releases a
higher amount of energy. Energy released from the glucose and oxygen is around 32 ATP molecules. Aerobic
respiration takes place in the mitochondria.
Equation: Glucose + Oxygen Carbon Dioxide + Water
Anaerobic Respiration – Respiration that takes place in animal, plants, and some microbial cells in condition of low
oxygen or absence of oxygen. Some examples of where anaerobic respiration occur include plant roots in
waterlogged soil, bacteria in puncture wounds and human cells during vigorous exercise. Anaerobic respiration in
microbes can be used to make useful products. Bacteria are used to break down waste to make biogas. Yeast is used
to make carbon dioxide in dough to make bread rise. Yeast can also be used to ferment sugars to make alcohol in
beer and winemaking. Less energy is released (2 ATP molecules) than that of aerobic respiration.
Equation: Glucose Lactic Acid (some energy released)
Or
Glucose Ethanol + Carbon Dioxide (some energy released)
In aerobic respiration, the heart is unable to get enough oxygen to the muscles during exercise, so the body
produces energy via anaerobic respiration in an attempt to combat the lack of oxygen that the body is receiving. It
releases energy from glucose, but the amount is lower. It happens when there is not enough oxygen for aerobic
respiration. Anaerobic respiration is a short-term fix as too much lactic acid produces after anaerobic respiration can
lead to a stitch or taste in mouth. Lactate builds up in the cells, causing fatigue, hence why you become tired after
lots of physical activity. It is a waste product. Our cells produce lactate to provide energy during exercise when
oxygen is not readily available to do so via aerobic respiration. Lactate fermentation is a way of producing ATP
without the need for oxygen as lactate allows for glucose to be broken down. It temporarily converts pyruvate into
lactate, which allows glucose breakdown.
Anaerobic respiration produces an oxygen debt. This is the amount of oxygen needed to oxidise lactic acid to carbon
dioxide and water. This is because glucose is not broken down completely to form carbon dioxide and water. Some
of it is broken down to form lactic acid. The lactic acid is metabolised by the liver, converting some it back to
pyruvate which then undergoes aerobic respiration, which requires O 2. The existence of an oxygen debt explains
why we continue to breathe deeply and quickly for a while after exercise.
, Stages of Respiration – P2
Glycolysis
Glycolysis is the first stage of respiration and occurs in both aerobic respiration and anaerobic respiration. The
purpose of this stage is to convert large molecules of glucose into small molecules called pyruvate. This can then be
transported to the mitochondria, which is the double-membraned organelle found in human cells.
It is important to start off the glycolysis stage with 2 ATP, as it will allow for more ATP to be produced later on in
glycolysis. Phosphorylated Glucose is extremely unstable, as it separates into two molecules of Triose Phosphate
almost instantly. Pyruvic Acid is formed when triose phosphate is oxidised (also known as Pyruvate). The coenzyme
NAD is responsible for this, and NADH (reduced NAD) is generated as a result of the process. This is known as a redox
reaction, in which one molecule is reduced while the other is oxidised. 2 ATP, 2 x NADH, and 2 x Pyruvate are the
results of glycolysis. There is now a total of four ATP. This ATP is an example of substrate-level phosphorylation.
Aerobic and anaerobic respiration differ after glycolysis. This is the only stage that is shared.
Energy is required for glycolysis to take place. Without glycolysis, the other stages of respiration would not be able to
take place. The energy that glycolysis uses to take place essentially ‘kick-starts’ the respiration process. It requires a
small amount ATP, which allows more ATP to be produced by the end of this phase. Where glycolysis requires energy
to take place, the subsequent phases complete the transformation of Pyruvate to produce ATP as well as NADH. The
energy produced here is for the cell to use.
Link Reaction
The Link Reaction is the shortest stage of respiration, whereby the Pyruvate created in the glycolysis stage passes
over to the membranes of the mitochondria and then into the matrix of the mitochondria.
As a result of the oxidation of pyruvate, NAD is reduced to NADH. Decarboxylation, which involves the elimination of
carbon dioxide, also happens. Keep count of your carbons; pyruvate was a 3C molecule before the carbon dioxide
was eliminated, thus the resultant molecule will be 2C. The conversion of Pyruvate to Acetyl CoA is completed by
adding a coenzyme termed Coenzyme A (CoA). Because glycolysis produces two molecules of Pyruvate for every
molecule of glucose, two link reactions occur. As a result, each molecule of glucose will create two molecules of
Acetyl CoA.
Two carbon dioxide, two acetyl CoA and two NADH are the products of the Link Reaction for one molecule of
glucose, and therefore two molecules of pyruvate.
No energy is produced in the form of ATP at this stage, however, acetyl CoA, which will be used in the Krebs Cycle
and NAD (which has been reduced as is used in oxidative phosphorylation) are produced. These are both vital
components required for the next stages of respiration to
take place.
Krebs Cycle
The Krebs Cycle stage of respiration occurs in the matrix
region of the mitochondria. It is also the phase that
produces the carbon dioxide that is exhaled after gaseous
exchange. This is so that enzymes can catalyse the
reactions that take place, as the enzymes are housed here.
Acetyl CoA from Link Reaction enters the Krebs' cycle,
where it reacts with a four-carbon molecule formed during
a prior cycle run.
6C Compound = Acetyl CoA (2C) + 4C Compound
The 6C chemical is subsequently subjected to two
decarboxylation processes, resulting in the removal of two
molecules of carbon dioxide. In addition, the 6C complex
