The Effect of Temperature on the Rate of Respiration in Yeast

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The Effect of Temperature on the Rate of Respiration in Yeast

There are two types of respiration in yeast:

Aerobic: [IMAGE]

Anaerobic: Glucose [IMAGE] Carbon dioxide + ethanol + energy

Respiration is controlled by enzymes, which are proteins which speed

up one or more biological reactions. Within any cell many chemical

reactions are going on at any one time. Yeast has many different types

of enzymes that speed up respiration.


I predict that as temperature increases, the rate will also increase,

until a certain optimum temperature, after which, the rate will

decrease until the rate is zero as respiration has stopped completely.


As temperature increases, rate of respiration increases, because

particles move faster and with more energy, which in turn means more

particles collide with enough energy to react. However, as temperature

increases, enzyme stability decreases, so at temperatures above the

optimum temperature, the rate will decrease, until all the enzymes

have been fully denatured and all the active sites have been lost.

Enzymes speed up reactions in organisms. Each enzyme works on a

specific substance, called its substrate.

The diagram below shows an “E” (an enzyme) catalysing the breakdown of

“S” (the substrate) into two different products (“P”). Catalysis

occurs because substance S fits precisely into surface of the enzyme

E, so this reaction and no others are speeded up.

Diagram showing an enzyme catalsying the breakdown of its substrate into two product molecules.

As can be seen from the diagram, if the enzyme changes shape, the

active site (the area where the substrate reacts) would no longer be

able to fit the substrate. This would mean the enzyme would lose its

effect; the substrate would not break down.

This happens when the temperature is too high; the process is called

“denaturing”. When an enzyme reaches a certain temperature, it will

have so much energy that it is de-shaped; it is “denatured”. This

diagram shows how a denatured enzyme will not work:


The enzymes will hardly work at very low temperatures (they wont be
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