The effects of temperature, PH and enzyme concentration on enzyme activity.

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Title: Enzymes


To study the effects of temperature on enzyme activity.

To investigate the effect of pH on enzyme activity.

To study the effect of enzyme concentration on enzyme activity.

To investigate the catalase activity in different tissues.


Refer to page 25 to page 28

Materials/ apparatus:

Test tubesLiver puree 3% (v/v) H2O2

PipetteChicken puree 01. M sodium citrate buffer solution

Deionized waterApple puree

ThermometerPotato puree

Carrot puree


  1. Control

Enzyme Activity (1-5)


Positive Control


No bubbles produced

Negative Control


Bubbles produced overflow

  1. Did the reaction give off heat? Yes
  1. Effect Of Temperature On Enzyme Activity

Temperature ( ÌŠ C)

Enzyme Activity (1-5)

Tube 1 (ice bath)



Tube 2 (room temperature)



Tube 3 (37 ÌŠ C)



Tube 4 ( 100 ÌŠ C)



  1. Is there a temperature at which the catalase activity was the most effective? Was it the temperature you were expecting? IF it was not, how can you explain the results?

The temperature at which the catalase activity was the most effective is 37 ÌŠ C. Yes, it was the temperature that I was expecting.

  1. Why put the tubes of H2O2 (and not just the liver tubes) into the water baths?

To obtain the respective temperature which is the same with the temperature of the liver puree so that the results obtained is more accurate.

  1. Effect Of pH On Enzyme Activity

Enzyme Activity (1-5)

pH 3


pH 7


pH 11


  1. At what pH does catalase exhibit the greatest activity?

pH 7 exhibit the greatest activity.

  1. Plot a graph (enzyme activity vs pH) that correspond with the results of your test.
  1. Effect Of Enzyme Concentration On Enzyme Activity


Enzyme Activity (1-5)




Bubbles overflow



More bubbles are produced



Less bubbles are produced

  1. Were the results of this experiment as you expected? If they were not, can you explain why they were not?

Yes, the result of the experiment was as I expected.

  1. How effective is catalase? In this experiment setup, do you think you would detect a difference in reaction rates between a 100% and a 50% liver solution?

The catalase is very effective. 50% enzyme produce less bubbles and react slower with hydrogen peroxide compared to 100% enzyme concentration.

  1. Catalase Activity In Different Tissues


Enzyme Activity (1-5)




Bubbles overflow



Less bubbles produced



No bubbles produced



More bubbles produced



Less bubbles produced

  1. What do your results tell you about the functions of the different types of tissues?

Different types of tissues have different concentration of catalyst, thus producing different results.

  1. Why is it important that the puree of each substance is obtained by blending the same amount of substance in a similar volume of water?

It is important in order to achieve the same concentration of substance.


 aA + bB \rightleftharpoons cC + dD aA + bB \rightleftharpoons cC + dDEnzymes are proteins that function as biological catalysts. They can help to alter or speed up chemical reactions. At the end of each reactions, they will remain chemically unchanged. Enzymes speed up chemical reactions by lowering the activation energy which is required to start a reaction. They provides an alternative pathway with lower activation energy for reaction to take place. Since enzymes are very efficient molecules and remain unchanged during chemical reactions, the same enzymes molecules can be used again and again. Thus, only a small amount of enzymes is required to catalyse a large number of chemical reactions. Enzymes are specific, undergoing ‘Lock-and-key’ hypothesis. According to this hypothesis, enzyme reaction depends on the presence of active sites. The enzyme is the lock and the substrate is the key. The mode of action of an enzyme is as below. An enzyme has a specific three-dimensional (3-D) shape, with a depression, active site. Only the substrate with a 3-D shape complementary to that of the active site can only fit into the enzyme. This is the formation of enzyme-substrate complex. The substrate will binds to the active site of the enzyme. Chemical reaction occurs while substrate is attached to the enzyme. During this process, the substrate is then converted to products. The general equation is : Enzyme + Substrate Enzyme-substrate Enzyme +Product. At the end of the reaction, the products will leave the active sites, leaving the enzyme chemically unchanged.

However, enzymes are affected by a few factors such as temperature, pH value and also concentration of enzyme- substrate. Enzymes are most active at optimum temperature about 36 – 37.5 ÌŠ C. They are usually inactive, but not destroyed at low temperature as the kinetic energy will be low. This causes the chances for the substrate molecules to collide with the enzyme is very low. With an increase in temperature (not over the optimum temperature), the rate of enzyme reaction and formation of enzyme-substrate complex will increase. For every rise in 10 ÌŠ C in temperature, the rate of enzyme reaction is doubled, until the optimum temperature is reached. If the increase of temperature is over the optimum temperature, the bonds that keep the enzyme in shape will be broken, causing the active site of the enzyme to lose shape. The substrate can no longer fit into the active site and the enzyme is said to be denatured. It no longer can acts as a catalyst. Most enzymes are completely denatured at a temperature of 60 ÌŠ C.

Moreover, enzymes are affected by the pH of solution. Some enzymes work best in different pH, some work best in acidic solution while some in alkaline solution. For example, the optimum pH for amylase in saliva is pH 7, pepsin in stomach is pH 2 and trypsin in small intestine is pH 8. Extreme changes in the pH of the solutions denatures the enzymes. Lastly, enzymes are affected by enzyme and substrate concentration. As the concentration of enzyme and substrate increase, the rate of reaction also increases. For a given concentration, the rate of reaction increases with an increasing concentration of substrate up to a certain point. There will be no significant change in the rate of reaction as the substrate concentration increases more than that particular certain point. This happens as the active sites of the enzyme molecule at that time will be saturated with substrate. Active sites are able to accommodate more substrate after the enzyme-substrate complex has dissociated. However, the rate of reaction will be proportional to the enzyme concentration if the substrate concentration is high enough and the temperature and pH value is kept constant.


The optimum temperature for enzyme activity is 37 ÌŠ C.

The pH 7 allows catalase to exhibit the greatest activity.

The enzyme activity is the most effective when enzyme concentration is 100%.

Liver puree has the highest enzyme activity.


  1. List the conditions you tested to determine which catalase exhibited the greatest activity. How do these conditions compare to those of a cell in the body?

The conditions tested are temperature, pH value and enzyme concentration. Since our body temperature differs from time to time, the conditions required also varies every time. Each body part requires different pH value, so pH value varies in different parts of the body. The enzyme concentration is also dependent on our state of body and the amount of enzyme secreted by our organs.

  1. H2O2 is commonly used as a disinfectant for scrapes and cuts. What exactly are you trying to do when you apply H2O2 to your scraped knee? What on your knee causes the H2O2 to bubble up when you apply it?

H2O2 acts as a wound sanitizer. Scrapes and cuts open up skin wound to blood and damages cells, which contain an enzyme called catalase. H2O2 bubbles up when applied as the catalase in blood comes in contact with H2O2, turning H2O2 into H2O (water) and O2 (oxygen).

  1. The browning that occurs when fresh potatoes and apples are cut is a result of this reaction:

Catechol + O2 Benzoquinone

Why do mashed potatoes stay white?

Raw potatoes contain enzyme polyphenol oxidase that will oxidized and turn potatoes brown in contact with air. However, mashed potatoes are cooked potatoes, causing the enzymes to denature and will not oxidize the mashed potatoes. Hence, mashed potatoes stay white instead of brown.

  1. Some people put fresh lemon juice on fruit salad to keep it from browning – what might the chemical explanation be for this practice?

Lemon juice contains citric acid of pH 3. The high concentration of acidic citric acid stops chemical reaction to occur. This will keep fruit salad fresh from browning.

  1. (a) The U.S. Food & Drug administration recommends that cooked beef be refrigerated for no more than 3-5 days before it is eaten; for cooked fish they recommend only 1-2 days. Why do you think fish might not keep as long in the refrigerator?

Fish decays faster than beef. Fish filters water, where bacteria are presence.

The bacteria presence in the fish are active even though being refrigerated at low temperature or cooked.

(b) It is recommended that uncooked ground beef is refrigerated for only 1- 2 day’s as well. Why might this be?

After 2 days, fresh cuts of meat containing spoilage bacteria on the surface will grow rapidly and produce slime. Oxidation of iron in the muscle’s myoglobin of the meat will occur, causing the meat to turn brown. Any potential microbial action will happen, causing a shorter shelf life of the meat, which is unsafe to consume.

  1. Fever is a common symptom of a viral or bacterial infection. What are two different functions of a rise in body temperature in this case? What would the danger be if the temperature got too high (above about 42 ÌŠ C, in humans)?

Fever is important in the component of immune respond. The increase in body temperature helps to inhibit the growth of bacteria but at the same time increasing the rate of chemical reactions that help body’s cell to repair themselves. Besides that, the rise in body temperature aids in increasing the heart beating rate that will speed up the circulation of blood in the body so that white blood cells are able to arrive more quickly to the infected body parts.

However, a high temperature will be a danger to human body, especially young children. High fever will more likely to trigger seizures in children or the fever might be accompanied with serious infection that should be brought to immediate attentions of doctors for emergency treatment.

  1. Lizards and snakes may often be found sitting in sunny spots (on exposed rocks, in the middle of a road) in the morning. They do not use the heat generated by their bodies to heat themselves: they obtain heat from the environment. After a cold night, they are sluggish and must heat up before they can be active.
  1. What do they need heat for?

They required heat for metabolic process as their body losses heat easily across their skin as they do not have any insulating layers of feathers or fur. Besides that, they are hardly protected by layers of subcutaneous fat to keep them warm at night.

  1. From where does the body heat from mammals and birds come? (The Second Law of Thermodynamics might help you answer this one)

The second law of thermodynamics states that energy cannot completely transformed in a chemical reaction, some energy is lost to a lower energy state, while heat is the only part that is used metabolically. However, this heat is considered as waste and is harnessed by terrestrial animals in a new niche - the endotherm. To remain active (with optimal temperature) despite the variations in temperature, both mammals and birds have adapted to retain and regulate their body heat. Their body size are large in order to retain heat that cannot diffuse or conduct away from the body faster than being produce. They also has a body function of insulation, non-conducting layer to trapped air in fur or feathers. Some mammals like penguins have layers of adipose for thermal insulation which is controlled with vasodilation or constriction coupled with sweating or shivering.

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LIVESTRONG.COM, (2014).What Do You Put on Freshly Cut Fruit to Keep It From Turning Brown? | LIVESTRONG.COM. [Accessed 16 Feb. 2015].

M, H. (2015).Why Do Mashed Potatoes Stay White? | Why. [Accessed 16 Feb. 2015].,. (2015).PROVET HEALTHCARE INFORMATION - Reptiles - Environmental Temperatures. Retrieved 16 February 2015, from, (2015).Chemistry for Biologists: Enzymes. [Accessed 16 Feb. 2015].