Chapter 7Respiration

What is respiration?

By :Azneezal Ar-Rashid

2009

Respiration in animal?

• In animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction. This is in contrast to the biochemical definition of respiration, which refers to cellular respiration: the metabolic process by which an organism obtains energy by reacting oxygen with glucose to give water, carbon dioxide and ATP (energy). Although physiologic respiration is necessary to sustain cellular respiration and thus life in animals, the processes are distinct: cellular respiration takes place in individual cells of the animal, while physiologic respiration concerns the bulk flow and transport of metabolites between the organism and the external environment.

Unicellular organisms?

• In unicellular organisms, simple diffusion is sufficient for gas exchange: every cell is constantly bathed in the external environment, with only a short distance for gases to flow across. In contrast, complex multicellular animals such as humans have a much greater distance between the environment and their innermost cells, thus, a respiratory system is needed for effective gas exchange. The respiratory system works in concert with a circulatory system to carry gases to and from the tissues.

Stages of respiration• In air-breathing vertebrates such as humans, respiration of oxygen

includes four stages:• Ventilation (pertukaran udara), moving of the ambient air into and

out of the alveoli of the lungs. • Pulmonary gas exchange, exchange of gases between the alveoli

and the pulmonary capillaries. • Gas transport, movement of gases within the pulmonary capillaries

through the circulation to the peripheral capillaries in the organs, and then a movement of gases back to the lungs along the same circulatory route.

• Peripheral gas exchange, exchange of gases between the tissue capillaries and the tissues or organs, impacting the cells composing these and mitochondria within the cells.

• Note that ventilation and gas transport require energy to power a mechanical pump (the heart) and the muscles of respitation, mainly the diaphragm. In heavy breathing, energy is also required to power additional respiatory muscles such as the intercostal muscles. The energy requirement for ventiliation and gas transport is in contrast to the passive diffusion taking place in the gas exchange steps.

• Respiratory behavior is correlated to the cardiovascular behavior to control the gaseous exchange between cells and blood. Both behaviors are intensified by exercise of the body. However, respiratory is highly voluntary compared to cardiovascular activity which is totally involuntary.

• Respiratory physiology is the branch of human physiology concerned with respiration.

Aerobic respiration

Introduction to Aerobic respiration

• Aerobic Respiration, biochemical process in living things whereby sugars and similar substances, resulting from the digestion of food, are broken down in the presence of oxygen to produce water, carbon dioxide, and energy. 'Aerobic' means 'with oxygen'. The reaction can be represented by the general chemical equation

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

• In words, sugars and oxygen react together to produce carbon dioxide and water with the release of chemical energy. In biology, the term “respiration” is also used for the physical process of breathing in animals, and for the general chemical process in animals, plants, and microbes of obtaining oxygen from the surrounding air or water. To distinguish from these, the biochemical processes of aerobic respiration and the closely related anaerobic respiration are sometimes termed “cellular respiration” (see Metabolism).

Chemical Respiration and Energy

• All living organisms require energy to carry out life processes such as bodily growth, repair, and reproduction. This energy is obtained by chemically breaking the energy-rich bonds in organic “fuel molecules”, usually sugars and similar carbohydrates, which are obtained from digested food. In cells, this energy is transferred to molecules of adenosine diphosphate (ADP), which are converted in the process to adenosine triphosphate (ATP). These high-energy ATP molecules are the main immediate source of useable energy for cell activities.

Two Stages of Aerobic Respiration

• The whole process of aerobic respiration contains more than 20 chemical steps or stages. The first series of stages is known as glycolysis. This occurs in the jelly-like cytoplasm of the cell, and it is anaerobic—that is, it does not require oxygen. It releases only a small proportion of the total energy available from a fuel molecule of glucose or a similar sugar. (The second series of stages is known as the citric acid cycle, tricarboxylic acid cycle, or Krebs cycle. It is aerobic—that is, it requires oxygen. It releases far more energy, compared to glycolysis, from the remainder of each sugar molecule. This series of stages happens inside the tiny organelles (parts inside the cell) called mitochondria. The food molecule is broken down in a step-by-step process that produces ATP molecules at almost every stage.

Products of Aerobic Respiration

• If one molecule of a sugar such as glucose is broken down completely during aerobic respiration, it yields 38 molecules of high-energy ATP. Up to eight of these come from the first, anaerobic stages (glycolysis). The other 30 are obtained from the second, aerobic or oxygen-requiring stages of the Krebs cycle.

• Almost all organisms, including plants, animals, fungi, and bacteria, use aerobic respiration. It is the reason that we and other animals breathe or respire, to obtain oxygen from air. However, some simpler organisms and cells can respire anaerobically when oxygen is absent. A few organisms, such as microbes at the bottom of the deep sea, are unable to respire aerobically at all. These are known as obligate anaerobes.

Anaerobic respiration

Introduction

• Anaerobic Respiration, also called anaerobiosis, biochemical process in living things whereby sugars and similar substances, resulting from the digestion of food, are broken down to release energy in the absence of oxygen. 'Anaerobic' means 'without oxygen'. It thus differs from the allied process of aerobic respiration, which requires the presence of oxygen. Life processes such as growth and repair of tissues require energy, and this is obtained by the chemical breaking of bonds in organic molecules such as sugars and other carbohydrates present in digested food. The chemical energy released by this process in cells is transferred to molecules of adenosine diphosphate (ADP), which become converted to adenosine triphosphate (ATP), forming the energy “bank” for the cell.

Products of Anaerobic Respiration

• The process of anaerobic respiration contains three main chemical steps or stages. The starting substance or 'fuel molecule' is usually the six-carbon sugar, glucose. The chemical process by which this is broken down is termed glycolysis. The results are usually substances such as lactic acid (lactate), pyruvic acid (pyruvate) or ethyl alcohol (ethanol). The reaction can be represented by the general chemical equation:

C6H12O6 → 2C3H4O3 + 2H2 + energy That is, sugar and oxygen react together to produce two smaller three-carbon molecules and hydrogen, with the release of chemical energy.

• Anaerobic respiration occurs in the cytoplasm of the cell and releases only a small proportion of the total energy contained in the fuel molecules such as glucose sugar, yielding up to 8 molecules of the high-energy ATP. If oxygen is available, the products of glycolysis can be used further in the oxygen-requiring breakdown process of the citric acid or Krebs cycle, to yield up to another 30 molecules of high-energy ATP. In this way, glycolysis becomes the first stage of aerobic respiration.

Variations of Anaerobic Respiration

• Yeasts, which are tiny fungi, can break down the pyruvic acid from glycolysis into ethyl alcohol (ethanol) and carbon dioxide. This process is called alcoholic fermentation. The alcohol is used in the brewing industry, and also in baking, where the carbon dioxide gas released by fermentation makes bread rise. Anaerobic respiration is far less efficient than aerobic respiration, but many organisms can use it when necessary, usually when oxygen is lacking. These are called facultative anaerobes and include yeasts and other fungi, bacteria, parts of plants such germinating seeds and waterlogged roots, certain worms and similar animals found in stagnant water or at the bottom of the sea, and mammalian muscle cells.

• A few bacteria and similar microbes are obligate anaerobes. They cannot use oxygen at all—indeed oxygen may be highly poisonous to them. In animal and human muscle cells that are working so hard that their blood circulation cannot bring in enough oxygen, aerobic respiration cannot occur. Anaerobic respiration then produces pyruvic acid that is converted to lactic acid. This situation is called oxygen debt, and the accumulating lactic acid may cause cramps. As the physical activity eases off and the oxygen level begins to rise again, the oxygen is used to break down the lactic acid aerobically.