IGCSE Biology Human Respiration

Summary:

Respiration transfers energy from glucose to produce Adenosine triphosphate (ATP) in every cell. Aerobic respiration, which requires oxygen, occurs in mitochondria and produces carbon dioxide and water from glucose and oxygen. On the other hand, anaerobic respiration occurs in the cytoplasm of cells and produces lactic acid or ethanol and carbon dioxide without needing oxygen.

Glucose, the energy source, is obtained from food and broken down from starch by amylase enzymes. It is then absorbed into the blood and transported to cells. Oxygen is obtained from the air we breathe, diffusing into the blood through the alveoli and carried by red blood cells. Carbon dioxide, an excretory product of respiration, is released when we breathe out, diffusing out of the blood through the alveoli.

Anaerobic respiration is not ideal because it produces lactic acid, decreasing cell pH, denaturing enzymes, and potentially causing cell death.

Practical experiments can be conducted to investigate aspects of respiration. For instance, the carbon dioxide production by small living organisms can be observed using a hydrogen carbonate indicator. Breathing rate can be measured during exercise to understand how it increases to supply muscles with more oxygen and remove carbon dioxide.

Another practical experiment can demonstrate that heat is produced during respiration. The heat produced during respiration can be observed by measuring the temperature change in germinating peas compared to boiled ones in a vacuum flask.

The process of respiration involves the contraction and relaxation of the diaphragm and intercostal muscles, leading to changes in thorax volume and pressure, which in turn control inhalation and exhalation of air in the lungs.

Excerpt:

IGCSE Biology Human Respiration

RESPIRATION

Respiration is the transfer of energy from glucose. It happens in every cell. Energy transferred by respiration is used to make Adenosine triphosphate (ATP). ATP stores the energy. When needed, it is broken down to Adenosine diphosphate (ADP), and energy is released.

Aerobic respiration happens in mitochondria:
Glucose + Oxygen → Carbon dioxide + water
C6H12O6 + 6O2→ 6CO2 + 6H2O