Analyzing Enzyme Activity in IBDP Biology (Practical 3) Tips & Tricks!
The third of the seven required practicals is all about factors affecting enzyme activity! In case you're new to the IBDP Biology course there are six required practicals for Standard Level (SL) as well as one additional required practical for Higher Level (HL) Biology students. This is my third blog post about these required practicals, you can find the post about the Practical 1 or Microscopy practical here and my post about Practical 2 or the Potato Core Practical here. This post is all about Practical 3, or as I call it the Enzyme Activity practical. This lab is an excellent one for students who are learning about working with biological molecules, experimental design and collecting reliable and valid data. Like all seven of the practicals they can, and do show up in the IBDP Biology exams; I have seen questions about the skills in this practical in Papers 1, 2 and 3 over the years. It is worth including some of those past paper questions on your unit tests and mock exams to help prepare students for the variety of ways in which the required practicals can be assessed.
Here is the description of Practical 3 which you will find on page 42 of the IBDP Biology Subject Guide: Skill: Experimental investigation of a factor affecting enzyme activity. (Practical 3). The previous skill in the guide (also on page 42) is Skill: Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes, so I give my students the choice of those three factors (as their independent variable) in planning their investigation. After many years of teaching this lab I have broken it down into the following skills:
Identifying a Control Group (room temperature, neutral pH & a researched standard substrate concentration)
Determining different iterations for the Experimental Group (four different temperatures, pHs and substrate concentrations, ideally two above & two below the control group)
Planning a methodology with clear controlled variables/constants, in this case temperature should be constant if it is not the IV, the same with pH and substrate concentration, the quantity and format of the enzyme should also be kept constant
Identifying how to measure reaction rate (using substrate consumption or product production)
Using sensors or tools like oxygen probes, glucose test strips etc.
As this is often the third or fourth required practical we tackle in the course I ask the students to plan their own methodology and give guidance in the form of individual check-ins rather than a structured lab sheet. It is important that students build up to the IA later in the course and this is a good lab to begin that process with. Here is the slide I use to introduce this lab during our lesson on enzymes, I make sure to schedule the lab day at least two classes after the lesson so students have time to apply their knowledge.
I do require that my students all use the same enzyme, and since enzymes are tricky to ship into Morocco we use Lactase enzyme pills. This is also handy since lactose in milk is a readily available substrate in a variety of forms (think different forms of milk). The role of lactase as it breaks down lactose into galactose and glucose is an application in Subtopic 2.5 which students need to know anyway and I love to help my students by double-dipping content whenever possible. You can see the slide I use to check in on student progress below, this is usually the day after we have our lesson on enzymes. I want to make sure they understand the reaction they are analyzing and they think about how to measure reaction rate as well as thinking about their constants (controlled variables).
On lab day I gather the following materials and let the students get to it! I make sure they have:
As many hot water baths as I can get my hands on (large beakers full of water on hot plates work well too)
Thermometers or temperature probes
pH paper or pH probes/sensors
Lactase enzyme in pill form
Mortar & pestle to grind up the pills
Mass balance (ideally up to 0.01 g precision)
Weigh boats or small scraps of paper
Graduated cylinders
Pipettes
Test tubes & matching test tube racks
Glucose test strips (be careful, students can go through these very quickly)
Benedict's solution instead of glucose test strips (less precise, but more affordable)
Whole & skim milk (I use UHT milk since it doesn't need to be refrigerated so starts at room temperature)
I also make sure to ask students to send me their materials list and procedure ahead of time to help them develop their planning skills, make sure they are on the right track and that I have everything they need for the lab. I recommend having students write a full formal lab report for this practical as part of your lead-up to the IA, I have included the rubric and checklist I use for formal lab reports below.
Enjoy the chaos of an open inquiry lab with your students, it's a great learning opportunity for them and I always find it really fun to watch them learn!
As always, thanks for reading teachers, travelers and curious souls of all kinds!
The Roaming Scientist
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