To investigate whether the concentration of substrate (starch) affects the time taken for color change.

Authors Avatar by yasir_subheyahoocom (student)

Strategy- Enzyme Concentration

Investigate what Factors affect enzyme activity

Enzymes are biological catalyst; they are responsible for chemical reactions in living organisms. Furthermore enzymes are proteins made of large molecules made up of long chains of amino acids, which speed up the chemical reaction in every living organism. The common model used to explain how food is broken down is called the lock and key model. The model consists of an active site, enzyme, and the product. An active site has a specific shape that whereby only another complimentary substrate can fit in. When the substrate has the matching shape it then fits into the active site. Then the enzyme speeds up the reaction, breaking down the substrate into 2 products. Now that the activation energy has been reduced to its minimum, the rate of reaction will escalate drastically.

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Factors that affect the rate of enzymes

  • Temperature- Enzymes have an optimum temperature of 37 degrees, the higher the temperature the faster the rate of reaction, but enzymes are proteins, and proteins at too high temperatures start to denature and therefore become inactive.

  • pH- Enzymes have an optimum pH (pH7), and if the pH is too high or too low the active site changes shape (denatures) and therefore the rate of reaction is much slower.

  • Concentration of enzyme- When the concentration of the enzyme increase, the number of active sites also increases allowing a faster reaction rate. However when the concentration of enzymes are low, the reaction is slow.

  • Concentration of Substrate- When the concentration of substrate is low, the active sites will be left unoccupied. But when the concentration of substrate is high there will be more active sites, therefore there is a faster reaction.


My investigation‘s aim is to find out, how different concentrations of enzymes affect reaction times. This will allow me to notice any difference in reaction times, also it will help me find the best concentration to work at. I chose to do concentrations as maintaining the temperature of a reaction is quite difficult, as you have to keep the experiment at a certain temperature, so it will be hard to keep the test fair. Furthermore, it is not easy to see if a reaction has taken place in a water bath, because of physical limitations such as the basin because it is high and therefore blocks the direct line of vision. I also did not choose to change the pH levels as they seem to have no effect on the experiment, therefore there is no point.

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First Preliminary experiment

Amylase and Starch

Whilst starting my first preliminary experiment, I decided to investigate whether the concentration of substrate (starch) affects the time taken for color change. I utilized starch and amylase, and constantly kept 5ml of the enzyme (amylase) in a boiling tube (this was our variable), but we changed the amount of the substrate in intervals of 5 (so we used 5ml, 10ml, 15ml) this was our independent variable. After putting 5ml of starch and amylase in a boiling tube, we then added 5 drop of iodine using a buffer. This then indicated if starch was ...

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