10. Respiration (10.1, 10.2, & 10.3)

Table of Contents

10.1 Respiration

The contraction of muscle cells – to move from the organism, for peristalsis to move food along the alimentary canal, or the contraction of the uterus wall during childbirth
Building up proteins from amino acids
The process of cell division produces more cells, replaces damaged or worn-out cells, or makes reproductive cells.
The process of active transport involves the movement of molecules across a cell membrane against a concentration gradient
Growth of an organism through the formation of new cells or a permanent increase in cell size
The conduction of electrical impulses by nerve cells
Maintaining a constant body temperature in warm-blooded animals

Optimal Temperature: Yeast, like most organisms, has an optimal temperature range at which its metabolic processes, including respiration, occur most efficiently. For many strains of yeast commonly used in baking or fermentation, this optimal temperature range is typically between 25°C and 35°C.
Increased Respiration Rate: As temperature increases within the optimal range, the rate of respiration in yeast generally increases. This is because higher temperatures lead to greater kinetic energy among yeast cells, which accelerates metabolic reactions, including respiration. As a result, more glucose is broken down into carbon dioxide and water, releasing more energy for yeast growth and fermentation.
Denaturation: However, beyond the optimal temperature range, the rate of respiration begins to decline. This is because enzymes involved in the respiration process start to denature as temperatures rise too high, typically above 45 °C to 50°C. Denaturation refers to the alteration of a protein's structure, rendering it non-functional. Once enzymes are denatured, they can no longer catalyse metabolic reactions effectively, leading to a decrease in respiration rate.
Cold Temperatures: Similarly, at very low temperatures, yeast metabolism slows down significantly, including respiration. While cold temperatures do not typically denature enzymes like high temperatures do, they decrease the kinetic energy of yeast cells, leading to a reduction in metabolic activity

Muscles normally respire aerobically, but they may respire anaerobically for a short period when there are vigorous muscle contractions. When a person is vigorously exercising, they start to rapidly breathe to increase the amount of oxygen taken in and remove carbon dioxide quickly. The heart also starts pumping faster to supply the muscles rapidly with oxygen. But the heart rate and the breathing rate cannot keep increasing. Hence, to produce extra energy, the muscles start respiring anaerobically. This produces very little energy, but together with the energy produced by aerobic respiration, it is sufficient to keep the muscles going. Since there is insufficient oxygen to meet the demands of the vigorous muscle contractions, lactic acid slowly builds up in the body, causing fatigue. The muscles are said to incur “oxygen debt”. Lactic acid may build up to such toxic proportions that the body needs to stop and rest because the person experiences muscle fatigue

This is the reason we continue to breathe heavily and our heart rate remains high even after finishing exercise – we need to transport the lactic acid from our muscles to the liver to produce energy

This energy is further used to oxidise the remaining lactic acid and convert it into glucose, which is then transported back to the muscles

Credits: Notes compiled by Manahil Naeem of Karachi Grammar School

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