Bacteria comprise the simplest species of life on Earth. All bacteria are single-celled organisms, and they are capable of living and reproducing on their own in the right environments. Several bacterial cells form colonies, which have varied shapes, colors, and textures.
Because of their simplicity, bacteria are easy to cultivate in the lab. All they need is an appropriate culture medium and the appropriate temperature, and they will grow rapidly. The rates of growth vary per species of bacteria, but most of them can multiply from a few cells into millions overnight.
About 90% of all known bacteria have cell walls. The cell walls protect bacteria from environmental damage. They also give a definite form and shape to bacterial cells.
Most bacterial cell walls can be classified into two categories: either Gram-positive or Gram-negative. This is determined through Gram staining. Labster has a full simulation detailing the procedure.
Despite having only two major classifications, learning bacterial cell walls can still present a challenge to many students. Read on to discover why and how this topic can be made easier.
First off, let’s take a look at why students have a hard time studying bacterial cell walls. Here are the top three reasons students talk about and teachers encounter.
Bacteria are tiny organisms that cannot be seen with the naked eye. Students need a microscope to see bacterial cells. With that, it’s harder for them to comprehend the idea of cell walls, which are even smaller than the bacteria themselves.
The structure of cell walls cannot even be seen under the microscope. Students must rely on diagrams and illustrations to study the intricacies of bacterial cell walls. Not seeing the actual thing may have a negative impact on their learning ability.
Moreover, Gram staining can be a tedious process. Students who are not keen on doing lab work may find it intimidating to perform a Gram stain. That would make it even harder for them to fully understand the topic.
Gram-positive and Gram-negative cell walls have distinct components. However, these components are not exactly easy to remember. They have long-winded chemical names like peptidoglycan, teichoic acid, and lipopolysaccharides. These extra-long words may discourage students from studying the topic further.
However, these complicated-sounding components are essential bits of information for students to comprehend this topic fully. They will have to learn these chemical names sooner or later.
Bacterial cell walls are detail-heavy lessons. Distinguishing between Gram-positive and Gram-negative cell walls involves even more details. The differences between the compositions of the two types of bacterial cell walls can be quite challenging for students.
Diagrams are certainly useful, but even they can appear complicated. If the diagrams used to teach this topic contain lots of labels, students can easily get overwhelmed with the bulk of information.
Gram-positive vs. Gram-negative cell wall compositions (Image source: Wikimedia Commons)
Knowing the challenges that students face when studying bacterial cell walls, here are five tips for educators. Each tip addresses a specific challenge that students encounter with this particular topic. If teaching bacterial cell walls can be made more engaging to students, they will master this topic faster. They will also recall key concepts more easily when they take higher biology courses.
Gram staining of bacterial cell walls was a technique invented by Hans Christian Gram, a Danish bacteriologist. He pioneered the technique in 1882 when he used it to identify Streptococcus pneumoniae and Klebsiella pneumoniae, two species of bacteria that cause pneumonia.
At that time, these bacteria still had no species names. Gram identified them by dripping different chemical reagents on samples of lung tissue. He noticed that two distinctly colored microorganisms were present in the samples. Gram later concluded that the differences in color are because of differences in the chemical composition of bacterial cell walls.
Through the Gram staining technique, students can easily distinguish two major types of bacterial cells. Gram-positive bacteria stain purple, while Gram-negative ones stain red.
For students to identify Gram-positive and Gram-negative bacteria, they need to see the colors. Purple or violet is Gram-positive, while red is Gram-negative. The differences in structure and composition of the cell walls themselves are best explained using illustrations.
Gram-positive cell walls are composed of thick layers of peptidoglycan. Peptidoglycan is a combination of amino acids and sugars, and these are the main components of Gram-positive cell walls.
Gram-negative cell walls, on the other hand, have thinner layers of peptidoglycan. These thin layers are surrounded by an outer membrane composed of lipopolysaccharides, which are combinations of lipids and sugars. Only Gram-negative cell walls have outer membranes.
The structure and arrangement of these cell wall components can be introduced to students through illustrations. The engaging visuals make learning a lot more effective for students.
Interactive simulations, such as the one pictured below from Labster, work best because students can work at their own pace. They are free to make mistakes without costly consequences, too. They can play around with the simulation as they please until they master the concepts.
Before students can properly learn bacterial cell walls, they need to have the fundamentals ironed out. It pays to ensure that students have mastered these basic concepts regarding bacteria:
Bacteria are single-celled organisms
Nearly all bacteria have cell walls
There are two main types of bacterial cell wall: Gram-positive and Gram-negative
Gram-positive cell walls stain purple
Gram-negative cell walls stain red
Gram staining can help distinguish different species of bacteria under the microscope
It’s also a good idea to help students master the Gram staining technique and why each step is important. Here is a brief overview of the technique:
Primary stain (crystal violet or methylene blue) renders all bacteria violet or blue at first.
Addition of a mordant (Gram’s iodine) strengthens the binding of the primary stain to Gram-positive cell walls. The primary stain will not adhere strongly to Gram-negative cell walls.
Decolorization with ethanol or acetone removes the primary stain from Gram-negative bacteria. The primary stain remains bound to Gram-positive cell walls.
Counterstain (safranin) renders Gram-negative bacteria red. Gram-positive bacteria remain purple. Without a counterstain, Gram-negative bacteria will remain colorless.
Mnemonics can facilitate better recall when dealing with complex topics like bacterial cell walls. Here is an easy one for distinguishing the different components of Gram-positive and Gram-negative cell walls. Think of a long, boring PowerPoint lecture.
Another simple mnemonic relies on the fact that “Gram-positive” and “Purple” both have the letter P in them. This makes it easier to remember that Gram-positive bacteria stain purple, while Gram-negative ones stain red.
Virtual lab simulations are excellent tools for teaching bacterial cell walls. Labster is determined to deliver fully interactive advanced laboratory simulations that make use of gamification elements like storytelling and scoring systems while exposing students to an immersive, realistic, 3D environment.
Check out this simulation of Building Gram Positive and Gram Negative Cell Walls at Labster. This activity will let students build 3D models of Gram-positive and Gram-negative bacterial cell walls. After learning all about it, your students can be more confident when they will do it on their own in a real lab! The image below is an example of what students can explore in the simulation.
Please take a look at the GIF from Labster’s Virtual Lab called Building Gram Positive and Gram Negative Cell Walls or get in touch to find out how you can start using virtual labs with your students.
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