Biology- How Concentration Effects the Rate of Reaction

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Biology Controlled Assessment.

Kenishia Pascal 10x3.

Investigating How Different Concentration Effects The Rate Of Reaction.

Strategy A

Possible Factors

* Source of catalase
* Concentration
* Surface Area of enzyme
* Concentration of enzyme
* pH
* Temperature

Chosen Factor
We chose to investigate the concentration of enzyme as we had previously investigated the optimum temperature for catalase in the preliminary investigation. Concentration of enzyme is also fairly easy to investigate, as you need to only increase the amount of potato that you want to investigate at a given time.


As the concentration of enzyme increases it will have an effect on the rate of reaction. The suggested optimum will be 10g as the higher the mass of catalase the more enzymes, meaning more space for reactions to occur. In the space given there will be more enzymes reacting with the substrate, which in this experiment is hydrogen peroxide (H2O2), until it has reached its optimum, where the volume of oxygen produced will not increase due to the fact that there will not be enough H2O2 left for the enzymes

Quantitative Hypothesis

By doubling the mass of potato, the rate of reaction will double also. 2n=2r

Scientific Explanation

Enzymes are made from amino acids, and which are proteins. When an enzyme is formed; it is made by stringing together between 100 and 1,000 amino acids in a very unique order, the chain of amino acids then folds into a unique shape. That shape allows the enzyme to carry out specific chemical reaction

“Enzymes are biological catalysts - catalysts are substances that increase the rate of chemical reactions without being used up”. The place where these substrate molecules fit is called the active site.

Enzymes are proteins produced by micro-organisms, in turn speeding up the chemical reactions. These can be found in the cell’s gene. The lock and key model is a key way to express the way in which the chemical reactions that will be taking place during our investigation on the concentration of enzymes.

Every enzyme molecule has an active site, the part of which the substrate joins on to. Enzymes are really specific as they only speed up one reaction. This is because, for an enzyme to work, a substrate has to be the correct shape to fit into the active site.

These actions are called the ‘lock and key’ hypothesis, because the substrate fits the enzyme just like a key fits into a lock.

Impacts of Temperature and pH

The activity of enzymes is strongly affected by changes in pH and temperature. Each enzyme has its pH and temperature optimum, its rate can only decrease at values below that point.

The ascending part of the temperature curve, in the graph below, reflects the general effect of increasing temperature on the rate of chemical reactions. The descending portion of the curve reflects the loss of catalytic activity as the enzyme molecules become denatured as the temperature increases

By changing the temperature, changes in the rate of an enzyme-controlled reaction occur. A higher temperature increases the rate at first; however if it gets too hot bonds that hold the enzyme (e.g. hydrogen bonds) break. This changes the shape of the enzyme’s active site and so the designated substrate will no longer fit and the enzyme will become inactive. This process is called denaturing.

All enzymes have an optimum pH that they work best at. If the pH is too high or too low, it interferes with the bonds holding the enzyme together. This again begins the process of denaturing, as the active site changes shape.

Our Catalase

Our enzyme can be found in raw cooking potatoes and will be reacting with the catalase, hydrogen peroxide. Hydrogen peroxide (H2O2) is a by-product of respiration and is made in all living cells. The optimum temperature for our enzyme, is about 37°C (36°C -39°C), this is the same body temperature of human. Its...
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