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IB Biology HL internal assessment (scored 20/24)
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This is my IB Biology HL internal assessment. It scored 20/24 both as raw mark and after moderation, amounting to 7 in Biology HL.
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The International Baccalaureate Internal Assessment in biology.Title: The effect of ox bile solution on the activity of lingual bovine lipase
Research question: How does the increased volume of ox bile solution (50%) (0.0ml; 0.5ml; 1.0ml; 1.5ml;
2.0ml) affect the activity of lingual bovine lipase?
Personal code: gyz166 Session: May 2019
I declare that this work is my own work and is the final version. I have acknowledged each use of the
words or ideas of another person, whether written, oral or visual.
1. Introduction
The action of enzymes as taught in IB Biology shows some of the dependences between the structure of
these proteins and their working environment. The relationship between temperature, pH and amount of
substrate is stated (Solomon et al., 2007). However, it seems that there should be more to the action of
enzymes than that. The human physiology part of curriculum points onto relationship between the bile
salts and lipases as an important part of lipid digestion (Allot and Mindorff, 2014). Moreover, the study
by Casper et al. (2016) points on the vitality of the connection between bile salts and lipase in the infants.
The most important action carried out by bile salts is emulsification. It increases the surface area of
substrate thus allowing more enzymes to bind to it (Courses.washington.edu, n.d). This internal
assessment aims at more in-depth investigation of similar connection between ox bile and the ox lipase.
2. Research question
How does the increasing volume of ox bile solution (50%) (0.0ml; 0.5ml; 1.0ml; 1.5ml; 2.0ml) affect the
activity of lingual bovine lipase as measured indirectly by the rate of change of pH of the cream solution.
3. Outline of the experiment
In the experiment varying volumes (0.0ml; 0.5ml; 1.0ml; 1.5ml; 2.0ml) of ox bile solution (50%) were
added to 2 ml of lipase solution (5%) and the cream (30% fat) (5ml). There were 25 samples and 5 trials
involving different volumes of ox bile solution added. At first the cream with bile solution was put in the
water bath 45°C (optimum temperature for action of lipase) for bile to emulsify the fats and then lipase
, was added to break down the lipid droplets. The efficiency of this reaction was recorded as the rate of
decrease of pH, as the breakdown of fats to fatty acids and glycerol should cause pH to drop.
4. Background information
4.1 Lipases – a group of fat-splitting enzymes found in the gastric juices, pancreatic secretions and
intestinal juices (Encyclopedia Britannica, 1998). In mammals especially important in digestion
of triglycerides is pancreatic lipase (Aoubala et al., 1995) which hydrolyses triglycerides (fats)
into monoglycerides and free fatty acids (Winkler et al.,1990). The fatty acids consist of a methyl
group at one end and the carboxyl group at the other end of the hydrocarbon chain (Rustan and
Drevon, 2005). The carboxyl group is a weak acid so it dissociates into COO- and H+ in the pH
of 7 (Academic.brooklyn.cuny.edu, 2018). The protons released in turn lower the pH thus
preventing further dissociation (Ratusiński et al., 2014) .
4.2 Bile – it is an liver excretion product consisting of water, bile salts, bile dyes e.g. bilirubin,
cholesterol, mineral salts and lecithin. Bile is involved only in mechanical digestion of fats as it
doesn’t contain any enzymes, instead it emulsifies triglycerides (Solomon et al., 2007). According
to Frazer, Schulman and Stewart (1944) bile salts lower surface tension of lipids, however they
show low emulsification ability in pH range 6-8.5. On the other hand combination of
monostearate, bile salts and oleic acid showed spontaneous emulsification and greater dispersion
of fat droplets. These droplets are called micelles and are formed because of amphipathic
properties of bile salts. They have larger surface area than non-emulsified fats so the site of action
for lipase is enhanced (Courses.washington.edu, n.d.) . They also increase solubility of nonpolar
molecules, moreover they can render soluble certain insoluble substances like phospholipids and
monoglycerides (Carey and Small, 1972).
5. Variables
-independent: volume of ox bile solution (50%) (0.0ml; 0.5ml; 1.0ml; 1.5ml; 2.0ml) added to the solution
of cream (30% fat) and lipase
2
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