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PLANNING Aim My aim is to plan, design and conduct an experiment in which I will investigate the effect of temperature on the rate of respiration in yeast. Background Scientific Knowledge and Understanding In this investigation I will be dealing with yeast, respiration of yeast, respiratory enzymes, the way enzymes work and factors that effect a rate of an enzyme-controlled reaction. Yeast Yeast are a number of microscopic, one-celled fungi, which are generally widespread in nature, occurring in the soil and on plants. They are made up mostly of protein, which is especially important for their ability to ferment carbohydrates in various substances. After activation yeast create the ferments carbon dioxide and ethanol. The alcohol produced has been used in making wines and beers and the carbon dioxide produced has been used in baking as it gets trapped in the dough and causes it to rise. (3) Respiration of Yeast Yeast can respire aerobically and anaerobically, I will be discussing the aerobic respiration process which yeast carries out. Aerobic respiration is a form of cellular respiration in which oxygen is required. The generalised equation for aerobic respiration is given below: 6O2 + C6H12O6 à 6CO2 + 6H2O + 38ATP oxygen + glucose à carbon dioxide + water + energy (2) For every single molecule of glucose, up to 36 molecules of ATP (adenosine triphosphate – the universal intermediary molecule between energy requiring and energy yielding cells) can be produced. The complete breakdown of glucose can be divided into four stages (11): 1. Glycolysis 2. The ‘Link’ Reaction 3. Krebs Cycle 4. The Electron Transport System Glycolysis occurs in the cytoplasm of the yeast cell, The Link Reaction and The Krebs Cycle both take place in the matrix of the yeast’s mitochondria, and finally The Electron Transport System carries out it’s process within the inner mitochondrial membrane. (10) As it can be seen from the equation, oxygen is needed for yeast to respire, the glucose is already inside the yeast. Yeast acquires its oxygen by breaking down water into hydrogen and oxygen. The equation also shows us that carbon dioxide is released from the yeast cells, this is released during The Link Reaction and the Krebs Cycle as shown in figure 1. As it can be seen carbon dioxide is released at 3 different points, once in The Link Reaction and twice in the Krebs Cycle. As water is broken down, it must mean that hydrogen is released. This is released at al four stages of aerobic respiration with the help of two molecules. These are nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD). NAD and FAD are reduced (i.e. gain hydrogen) to form reduced NAD and reduced FAD, this is shown in the below equations: (6) (3) NAD+ + 2H à NADH + H+ FAD+ + 2H à FADH + H+ NAD and FAD are known to be redox carriers.
Approximate Word count = 1896
Approximate Pages = 7.6
(250 words per page double spaced)
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