The Effect of Different Substrates on the Rate of Respiration on Yeast (Saccharomyces cerevisiae).

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The Effect of Different Substrates on the Rate of Respiration on Yeast (Saccharomyces cerevisiae)

What are the substrates being used?

Glucose

Glucose is a monosaccharide sugar, which is a ‘simple sugar’ that have between 3 and 10 carbon atoms per molecule. They are sweet and all soluble in H2O. It has the chemical composition C6H12O6. Glucose is a white crystalline solid but is less sweet then ordinary table sugar. Powdered dry glucose exists mainly in straight chain form. However, when glucose molecules are dissolved in water, two different ring structures are formed. See picture.

Fig 1

These ring structures are more stable in solution, so that, at equilibrium, almost all of the molecules are present as rings, with the straight chain form being a relatively short-lived intermediate. The structures of α-glucose and β-glucose differ only in the position of the ─OH and ─H groups attached to carbon atom number 1.

Lactose

It is formed by condensation reactions (where water is removed) between two monosaccarides, glucose and galactose. This allows an O2 bridge to form between the two molecules, holding them together forming a disaccharide. This is called a gycosidic bond. It consists of galactose and glucose molecules joined by a 1β-4 glycoside linkage

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Fig 2

Lactose is the only common sugar that is of animal origin.  Other sugars, such as sucrose and fructose, can be found only in plants.  In nature, the only place you can find lactose is in the milk of mammals.  Lactose is the principal carbohydrate found in milk, and composes about 2 to 8 percent of milk in all mammals

        Although milk and other dairy products are the only natural sources of lactose, this sugar can also be found in many prepared foods. Lactose is obtained commercially from evaporating whey, the watery part of milk that separates from the curd when milk sours and becomes coagulated, or when cheese is made.     

 It yields the simple  D-glucose and D-galactose on  (the reverse of glycolysis), which is catalysed by lactase, an enzyme found in gastric juice.

Galactose is one of the two simple sugars that make up each molecule of lactose, the compound sugar found in milk. The other simple sugar in lactose is glucose. Most birds cannot digest the lactose in milk products, because their bodies cannot make the enzyme that is necessary to break lactose down into the two simple sugars.

Sucrose

Consists of glucose and fructose joined by a 1α-2 glycoside linkage. This is a condensation reaction whereby the net result is to remove a molecule of water. The complementary process, whereby complex molecules can be split into their component parts, is called hydrolysis. Fructose is a monosaccharide that forms a five-sided ring. Together they make sucrose, which is a disaccharide made up of two monosaccharide units joined to form a single molecule

Fig 3

Yeast

What is it?

The type of yeast being used in this experiment belongs to the branch of living organisms called Saccharomyces cerevisiae (its binomial name), kingdom fungi, and phylum ascomycota, commonly known as Baker's yeast. Fungi are either unicellular or filamentous. All yeasts are unicellular and reproduce by budding and the parent cell buds off a daughter cell and this process is repeated indefinitely. The vast majority of fungi however are filamentous. Yeast feeds by heterotrophic nutrition because they lack chlorophyll and therefore are non-photosynthetic. They can be parasites, saprotrophs or mutulalists. Rigid cell walls contain chitin as the fibrillar material. 

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Yeast cells are microscopic, one-celled fungi made up mostly of protein which are more important for their ability to ferment carbohydrates in various substances. Yeasts are widespread in nature, found in the soil and on plants.

Uses of Yeast

Yeasts are well known for the making of bread and wine.

Respiration in Yeast

Yeast has to make energy, stored as ATP to carry out all cellular functions. To do this they can respire both aerobically when there is plenty of oxygen, but where oxygen is short, they respire anaerobically; they are therefore called partial anaerobes. ...

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