14.1: Lab Practicals - Biology

14.1: Lab Practicals - Biology

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During the course of the semester, there will be two lab practical exams: the Midterm Practical and the Final Practical. The final practical will occur on the last day of class.

The practical exams are each worth 20% of your lab grade. Each practical exam has a different format.

The Midterm Practical is an open book exam in which you will use Gram staining and metabolic tests to determine the identity of two bacterial unknowns, and write a lab report based on your results. A more complete description of what is required for the midterm and lab report can be found below.

The Final Practical is a cumulative exam that is not open book. Twenty five stations will be set up around the lab, and you will be expected to answer questions about the material at these stations. You may be asked to identify microorganisms, analyze the results of a metabolic test or interpret the results of an experiment. Since the exam is cumulative, it can cover material from the first lab through the last lab of the class. The Microbiology Review site on Blackboard contains material that will help you review the material that you have covered throughout the semester.

Midterm Practical

This first lab practical involves the identification of two unknown bacteria using both Gram staining and metabolic assays. There are 3 parts to this lab practical—Part I: Gram staining (Lab 5); Part II: Preparation of dichotomous key (Lab 6) and metabolic testing (Lab 7); Part III: a written lab report (due on Lab 10). Each part of the lab practical is graded separately (see below). This first lab practical is an open book exam. You are being tested on your ability to correctly perform procedures and interpret results. Although you can use your books and your notes, you cannot seek the advice or assistance of other students or the instructor!

Schedule for Midterm Practical

Lab 5: You will be given two unknown bacteria and asked to Gram stain them following the procedures you have learned in previous labs. After Gram staining, you will observe the cells under the microscope, and determine their morphology and Gram reaction. At the end of the lab period you will submit your results (see sample sheet below) to your instructor for grading. Your slide will be saved and may also be photographed for use in your lab report.


You will be required to show the results of your Gram staining procedure to your instructor. Make sure you don’t wait until the last minute to call the instructor over to view your slides!

Lab 6: You will learn how to construct a dichotomous key for bacterial identification. Using what you know about the Gram reactions of your unknown bacteria as well as information about the metabolic reactions of bacterial species obtained in Lab 5, you will construct a dichotomous key that can be used to identify your 2 unknown bacteria. You will also choose the media that you will need to use for the inoculations you will do in the next lab. You will turn in the dichotomous key for grading and the instructor will return it to you on Lab 7 (corrected if necessary).

Lab 7: You will inoculate your unknown bacteria in the media that you chose in Lab 6.

Lab 8: You will analyze the results of your metabolic tests. Using these results and your dichotomous key, you will identify your two unknown bacteria.

Lab 10: You will turn in the Lab Report for the Midterm Practical.

Midterm Practical Grading

Point Distribution—out of 100%:

Gram reactions: 25%

Metabolic assays: 25%

Written lab report: 50% (see Lab Report Rubric)

Grading Breakdown:

Part I: Gram Reactions (25/100)

Morphology for unknown A correct – 5 points

Morphology for unknown B correct- 5 points

Gram reaction for unknown B: color and interpretation is correct -5 points

Gram reaction for unknown B: color and interpretation is correct- 5 points

Unknown A slide shown to professor -2.5 points

Unknown B slide shown to professor - 2.5 points

Part II: Metabolic Assays (25/100)

Dichotomous key- complete and correct - 5 points

Media required based on student’s key complete and correct - 5 points

Metabolic test results recorded and interpreted correctly - 15 points

Part III: Lab Report (50/100)

GCSE Biology: Practicals

Biology is clearly a practical science, students confirm understanding and apply knowledge through practical activity.

Practicals are by their very nature active, they stimulate interest and motivate students.

In GCSE Biology from September 2016 there are required practical activities that students must complete and whilst these will not contribute marks to a final grade, schools will be required to confirm that they have provided opportunities for students to undertake these practical activities. Teachers should consult their Awarding Body specifications to confirm the exact practicals that are required.

Ideas for protocols and investigations that will meet the requirements of some of these specified practicals are provided in the following resouce list, along with other investigations that will support the development of practical skills.

AS and A Level Biology practicals – student and teacher tips

Do your students find practical activities a challenge? We spoke to the author of our new practical workbook* for Cambridge International AS & A Level Biology to get their advice for practical lesson ideas. We asked what practical skills are required, and why you need them, what the main challenges are for students and teachers, and what are their top five tips.

What are the practical skills required for biology and why do you need them?

Before they can embark on AS & A Level practical work with confidence, students should be familiar with the use of a typical school laboratory. This includes things such as balances, measuring cylinders, beakers, pipettes (or syringes), heating apparatus and thermometers. It is also important that students know how to work safely when carrying out practical work.

A knowledge of basic biochemical tests such as the tests for starch, glucose, protein and lipids is useful as these are often revisited at AS & A Level. There is also an assumption that students are aware of simple tests from Cambridge IGCSE™ chemistry, such as using universal indicator paper and testing for using limewater to test for carbon dioxide gas. These chemical tests are often used when carrying out practicals at AS and A Level biology.

Students should also understand how to plan valid experiments with standardised variables and repeats. They should also know how to draw results tables that display data effectively. Evaluating the design of simple experiments, such as recognising the level of accuracy of equipment is also a useful skill to reinforce before AS & A Level. All these skills help to provide a good foundation upon which to build.

What can be the main challenges for students carrying out practical work?

For biology experiments, results can often be unpredictable! Living organisms often do not respond in the ways that we expect. For example, a piece of pond weed in an investigation into the effect of light intensity, may not photosynthesise due to several reasons. Students need to be patient, accept that all results are valid and explore the reasons for results not being as expected. Many students think that getting unexpected results is essentially the mark of a bad experiment – in reality, getting the ‘wrong results’ can be a learning experience in itself. Students should also not be scared to ‘have a go’ and be encouraged to try again if something did not seem to work first time.

What can be the main challenge for teachers?

It can be difficult to get enough laboratory equipment or the correct reagents, although it may be possible to improvise or use alternative methods. Getting some practicals to work can be a challenge and it is certainly worthwhile for the teacher to try things before the class does. This means that concentrations of reagents, such as enzymes, can be adjusted to give the best outcome. As teachers, we can sometimes find it difficult not to do the practicals for students, especially when they seem to be struggling.

Sometimes we need to let them explore and find solutions – for example, letting them decide on the appropriate length of time to collect carbon dioxide gas from respiring yeast. We need to encourage and help but still allow them independence. Health and safety should also be the top priority for all teachers. We need to risk assess everything – it is our job to ensure the safety of our students.

What are your 5 top tips for students?

  1. 1) Be confident and keep trying even if a technique is difficult
  2. 2) Don’t expect results to always go the way you planned – remember that living organisms can be very different to one another
  3. 3) Work safely – always wear eye protection and risk assess everything
  4. 4) Be organised – keep all your equipment tidy on your bench
  5. 5) Enjoy practical work – it is your opportunity to apply your knowledge to the real thing

What are your 5 top tips for teachers?

  1. 1) Be safe – you need to watch the whole room while talking to individual students. Walk round the room so that you can see every group. Risk assess everything carefully.
  2. 2) Encourage independence and exploration, but help when needed
  3. 3) Demonstrate things clearly before letting your students try
  4. 4) Trial experiments, especially those that involve enzymes
  5. 5) Don’t shy away from practical work – it really does bring the subject to life and although it can be difficult to organise, it will help students see theory put into practice

By Matthew Parkin

*Our new series, updated for the new syllabuses for Biology is available in 2020! The series includes coursebooks, teacher’s resources, workbooks and practical workbooks.

Watch the video: How to Stock a BiologyGenetics Lab (February 2023).