SS1 Biology Lesson Note on Cellular Respiration

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TOPIC: SOME PROPERTIES AND FUNCTIONS OF CELLS (continued)

CONTENT:

• Cellular Respiration
• Excretion
• Growth

SUB-TOPIC 1: CELLULAR RESPIRATION

Respiration is the enzymatic breakdown of organic food substances, like glucose, through a series of chemical reactions in the cell to release energy and produce carbon (iv) oxide and water as by-products. Respiration occurs in all living cells.

Now, the energy released during respiration is used by the organism for such activities as synthesis of proteins, lipids and protoplasm; germination; cell division and enlargement leading to growth; movement; transmission of nerve impulses; active transport and maintenance of body temperature. There is variation in the amount of energy used by different organisms depending on their activities. A very active organism like Tiger uses much more energy than a sluggish one, like Chameleon.

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

C₆H₁₂O₆  +  6O₂             →           6CO₂   +  6H₂O  + Energy

Glucose     Oxygen            Carbon iv oxide Water

The equation represents only a summary of the raw materials and the end products of tissue respiration. The complex pathway of cellular respiration is shown below:

Tissue respiration is divided into two main parts. The first is glycolysis, the stepwise series of reactions which leads to the breakdown of glucose into pyruvic acid. The process occurs in the cytoplasm in the cells. It consists of step-wise reactions, each brought about by specific enzymes. Glycolysis is common to, and occurs in the same general manner in all organisms. In animal cells,

TYPES OF RESPIRATION

You already know that we have external and internal respiration, while external deals with breathing in and out i.e. inhalation and exhalation, the internal which takes place in the cell hence, cellular respiration is divided into two basic parts:

1. Anaerobic Respiration and
2. Aerobic Respiration

Anaerobic respiration is that type which involve the use of very little or no Oxygen, while Aerobic Respiration is that type which involves the use of large amount of Oxygen.

 Anaerobic respiration

In anaerobic respiration, pyruvic acid is converted alcohol in plants and lactic acid in animals

Equation for lactic acid formation:         C₆H₁₂O₆     →   2C₃H₆O₃ + Energy

In plant cell, the products of anaerobic respiration are ethanol and carbon iv oxide. Formation of alcohol is represented by the equation: C₆H₁₂O₆   → 2C₂H₅OH   +  2CO₂ + Energy

As for glycolysis, or anaerobic glycolysis or fermentation, Oxygen is not required because the process is anaerobic. This series of reaction convert glycogen in animal and starch in plant to glucose. The glucose is then converted by ten steps to pyruvic acid as below:

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