Biology : Cellular Or Tissue Respiratory System

Our today’s topic on biology is “What Is Respiration”

What is Respiration

Previous Topic : Anabolism And Feeding In Living Organisms


Respiration : is the process by which complex food substances are broken down in a stepwise series of reactions, in cells, to produce energy with carbon dioxide and water as waste products. Respiration occurs in all Living things.

The energy produce during respiration is used by the organism to carry out its activities, such as synthesis of lipids, proteins, protoplasm, cell division and enlargement(growth and development), transmission of nerve impulses, maintenance of body temperature and active transport.

The amounts of energy use in each organisms vary. A very active organism such as horse or man tends to use much more energy than a sluggish organism e.g↑

Types Of Respiration

There are two types of respiration. anaerobic and aerobic respiration.
Respiration occurs in cells and for that reason, it is called cellular or tissue respiration.

Chemical Process In Cellular Or Tissue Respiration

The reactions that occur in cellular or tissue respiration are usually represented by the following equation.

C6H12O2 + 6O2 → 6CO2 + 6H2O + Energy
This equation represents only a summary of the raw materials and the end products of tissue respiration. Respiration equation is far more complicated than the equation above.

Tissue respiration is divided into two main parts. The first part of tissue respiration is glycolysis.


glycolysis pathway

Glycolysis : is the breaking down of glucose to pyruvic acid (C3), which is represented CH3COCOOH (Aliphatic hydrocarbon) in chemistry.

Below Is The Pathway Of Glucose Breakdown In Tissue Respiration

pathway of glucose breakdown in tissue respiration

This process occurs in the cytoplasm inside the cells. It consists of stepwise reactions, as you can see above, each reaction is brought about by a specific enzyme.
Glycolysis is common to, and occur in this manner in all organism. Oxygen is not required In glycolysis, that is, glycolysis is an anaerobic respiration.
In this series of reactions, glycogen (in animals) or starch ( in plants) is converted to glucose, then converted through ten series of steps to form pyruvic acid as shown above.


Examples Of Specific Enzymes In Respiration

a] The conversion of glucose to glucose-6-phosphate is catalyzed by the enzyme hexokinase

Glucose + ATP → Glucose + -6- phosphate + ADP
b] Glucose-6-phosphate is converted to fructose -6- phosphate by the action of the enzyme glucose phosphate isomerase.


In this series of reactions, 2 molecules of ATP are used to convert glucose into glucose -6- phosphate and fructose -6- phosphate into fructose -1-6-diphosphate.
In some other reactions of glycolysis, 4 molecules of ATP are formed, as a result of a net gain of 2 molecules of ATP.

After the formation of pyruvic acid, the path of further reaction depends on whether the respiration reaction is aerobic or anaerobic


Aerobic Tissue Or Cellular Respiration

Aerobic respiration : is the respiration reaction that occurs in the presence of oxygen. In aerobic respiration, pyruvic acid is converted into acetyl-coenzyme A, which is fed into a cyclic series of enzyme controlled oxidation reactions known as the Kreb’s cycle.

Kreb's cycle

Kreb’s cycle reaction occur after the discoverer or the Tricarboxylic Acid Cycle (TCA) and take place in the mitochondria within the cells

In Kreb,s cycle, oxygen is not actually involved. The oxidation reactions that occur in the Kreb,s cycle involve the removal of hydrogen ions, similar to chemistry definition of oxidation.
These hydrogen ions are accepted by compounds known as hydrogen ion acceptors such as Nicotinamide Adenine Dinucleotide (NAD) to form reduced Nicotinamide Adenine Dinucleotide (NADH2).top↑

The hydrogen ions are passed through a series of reactions in what is called the electron transport chain. In these reactions, hydrogen is oxidized to water and energy is released in form of ATP.

Anaerobic Respiration

Anaerobic respiration : is the type of respiration that occurs in absence of oxygen.
When oxygen is not present in a reaction, the path of reaction depends on whether respiration is in plants or in an animal cell.

In an animal cell or bacterium, lactic acid is formed by anaerobic respiration. top↑
For example, in the skeletal muscles of athletes, the formation of lactic acid occurs when the rate of use of oxygen, during a race, exceeds the rate of oxygen supply. The vigorous exercise creates an anaerobic condition in which lactates accumulates. The athlete may experience muscle pain, at this time of period, the body is said to have an oxygen debt. At the end of the exercise, the athlete continues to breathe rapidly for some time, supplying much oxygen to the muscles until the lactic acid is oxidized to carbon dioxide and water.
The formation of lactic acid at this point is represented by the equation below;


C6H12O6 → 2C3H6O3 + Energy
C6H12O6 → Glucose
C3H6O3 → Latic acid
Energy → ATP

In plant cells, the end products of anaerobic respiration are ethanol and carbon dioxide.. The equation for the reaction is written below;

C6H12O6 → 2C2H5OH + 2CO2 + Energy
C6H12O6 → Glucose
C2H5OH → Ethanol
CO2 → Carbon dioxide or Carbon (iv) oxide
Energy → ATP
The above equation also represents formation of alcohol. Below is the pathway of anaerobic respiration in plant↑

Fermentation In Anaerobic Respiration

Fermentation is the breaking down of glucose to form ethanol and carbon dioxide by the aid of enzymes.
Fermentation is a special case of anaerobic respiration by micro-organisms such as yeast. Yeast fermentation results in the formation of ethanol with production of bubbles of carbon dioxide.

brief : Lactic acid is formed by fermentation of glucose and lactose by latic acid bacteria.

pathway of anaerobic respiration in animal and plant cell

Energy Release During Respiration

During aerobic respiration, one molecules of glucose yields 38 molecules of ATP which represents a large amount of↑
In a alcoholic fermentation, only 2 molecules of ATP are formed per molecules of glucose fermented.
Hence aerobic respiration produces more energy (ATP) than anaerobic respiration.

Experiment To Demonstrate That Energy Is Produced During Respiration

Materials needed (Specimen) : soaked cowpea seeds, cotton wool, two clamps, two retort stands, two vacuum and two thermometers. top↑


a] Set up the apparatus as shown above. The cowpea seeds in flask A were soaked in water for 2 hours beforehand. Equal number of cowpea seeds in flask B were boiled, cooled and sterilized in dilute formalin solution beforehand, to prevent decay or growth of↑

Brief : formalin is a solution of formaldehyde in water which is normally use for preserving and sterilizing specimens or as a disinfectant.

b] Leave the experiment in a to stand for 24 hours (a day).
The vacuum flasks should be turn upside down, so as for the thermometer to records the temperature of the seeds, not the temperature of the air in the flask and also to diffuses carbon dioxide out through the cotton wool. Carbon dioxide is heavier(denser) than air, so when the flask is turn upside down, it easily diffuses out of the flask through the cotton wool but if the flask is placed upright, carbon dioxide will accumulates around the seeds and reduces availability of oxygen to the seeds.
c] Read the temperature shown by the thermometer in each flask.

Conclusions And Observations

It will be observed that, the thermometer in flask A gives a higher reading than in flask B. This concluded that live, respiring seeds, in flask A produce heat energy, while the boiled, non-respiring seeds in flask B do not.

Experiment To Demonstrate Fermentation By Yeast


Materials needed (Specimen) : Two test tubes, cork carrying bent delivery tube, active yeast, lime water and 5% of sucrose↑
a] Put 5cm³ of 5% sucrose solution in a test tube and add half a tea spoonful of active baker’s yeast.
b] Quickly place the tube in the apparatus as shown above and set up control without yeast in the test tube.
c] Observe for 30 minutes.

Observations And Conclusions

It will be observed that the lime water in the apparatus with active yeast turns milky and the residual in flask A has a smell of ethanol but the lime water in control does not turn milky. This concluded that yeast breaks down sucrose solution to produce carbon dioxide and↑

Let stop here for today, till next class. Our next topic is on Excretion

Next Topic : Excretory System

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