ATP (adenosine triphosphate), commonly known as the cell's energy currency, is crucial for many biological processes like muscle contraction, DNA replication and movement, and active transport of molecules across the membrane. We need the energy to do work. Running a marathon or even a 1-meter race is impossible without power. Do you know where this energy comes from? The obvious answer would be food which acts as fuel for our bodies (which is theoretically correct). However, the exact mechanism is more complex and needs further explanation.
The food we eat is broken down into glucose which goes through a series of oxidation-reduction reactions to yield ATP. This catabolic energy-yielding process occurs inside cells hence known as cellular respiration. It comprises three main steps: glycolysis, Krebs (or citric acid), and electron transport chain (ETC). Many enzymes, reactions, and mechanisms are found within these processes. Students might feel overwhelmed by learning about the complexities involved in yielding ATPs.
Cellular respiration is one of the most fundamental topics in biology. Teachers often find it challenging to keep students hooked and interested in the process because things get complicated as the process progresses. This article will identify three points that make this topic tricky to teach at the college/university level, followed by five practical strategies to help educators efficiently deliver related lectures.
Figure: Interactive GIF from Labster's Cellular Respiration: Measuring energy consumption during exercise simulation.
Many reasons contribute to making cellular respiration a tricky topic. Our top three picks experienced by most educators are discussed below.
The "glycolysis" breaks down in the cytoplasm resulting in two pyruvate molecules. These pyruvate molecules make their way into the mitochondrial matrix, where pyruvate is oxidized into two-carbon acetyl-CoA. Then the "TCA (tricarboxylic acid) cycle begins," in which oxaloacetate reacts with acetyl-CoA to produce citrate. The last stage of cellular respiration, the "electron transport chain, " occurs in the inner mitochondrial matrix. A series of redox reactions in ETC pumps protons across the membrane with the help of high-energy electrons creating an electrochemical gradient. At the end of the process, water and ATP is produced through O2 (final electron acceptor) and ATP synthase, respectively.
The paragraph above is only a short description of the entire process, which gets much more complicated in depth. Moreover, cellular respiration occurs at the molecular level, making it abstract and challenging for educators to paint a correct picture and depict the process in the best and easiest way possible. Students won't be able to correctly imagine how pyruvate moves into mitochondria from the cytoplasm or how ATP synthase generates ATPs. Students need background knowledge about cytoplasm, mitochondrial matrix, reduction, oxidation, phosphorylation, etc. Teaching this topic to students who lack an understanding of basic concepts is especially tricky.
We've discussed how pyruvic acid is oxidized to citrate in normal circumstances but what happens when pyruvic acid is decarboxylated and reduced in the absence of oxygen? This twist of events in cellular respiration makes students feel overwhelmed and make the topic a tricky one to teach. Educators often find it challenging to teach students such hidden concepts in cellular respiration.
The process discussed is fermentation, which could be any of the two types, i.e., alcoholic or lactic acid fermentation. Students would also have to understand and memorize the difference between each type of fermentation. For instance, in lactic acid fermentation, the mechanism follows hydrolysis, glycolysis, and reduction. The process could be intra-cellular or extra-cellular and usually occurs in the muscles of higher organisms. Contrary to this, in alcoholic fermentation, the mechanism follows glycolysis, decarboxylation, and reduction. The process is intra-cellular and occurs in some bacteria and fungi.
Educators are challenged by chemical reactions involved in this process, enzymes, and various end-products. Luckily cells can quickly revive to the usual method of cellular respiration yielding maximum energy as the oxygen supply returns to normal.
The process of glycolysis, TCA/Krebs cycle, ETC, depends on the bunch of enzymes. Each enzyme with a specific function is responsible for running the process smoothly. The absence of a single enzyme would lead to the development of disease, as the process of cellular respiration is vital for the body to function correctly. For instance, Glucose-6-phosphate isomerase (GPI) is responsible for converting glucose-6-phosphate to fructose-6-phosphate in glycolysis. This enzyme regulates the level of glucose-6-phosphate in the body, which otherwise causes the development or proliferation of cancer cells.
Students at the college/university level memorize the names of all the enzymes, molecules, and their chemical structures. Such a content-heavy topic is bound to make students feel anxious and pose a challenge to educators. The series of oxidation and reduction reactions in the electron transport chain, which releases protons and drives the process, would be another tricky aspect of this topic. Educators would first need to explain the concepts of oxidation and reduction before delving into the complexities of this process.
We've discussed how cellular respiration could be a tricky topic yet a crucial aspect of biology. Here we'll discuss five effective strategies educators could use to make it a more relatable and exciting topic for college/university students.
One way to make this topic more approachable for students is to share fun and interesting facts. Educators would notice promising changes in students' attitudes with these facts in the classroom. Some of the top most exciting facts about cellular respiration are as follows:
One molecule of glucose produces 28-30 molecules of ATP. Students often see these figures in their textbooks, but researchers are still unsure about the net ATP production in cellular respiration. There is a chance that we'll soon have to rethink the number of ATP generated by each glucose item.
In the limited or no oxygen availability, pyruvate converts into lactic acid, accumulating in the muscles and causing muscular cramps. This shows that cellular respiration could be replaced by fermentation.
Anaerobic respiration (fermentation) only yields 2 molecules of glucose which is negligible compared to aerobic respiration. Do you know that ETC is responsible for most ATP production in cellular respiration? Aerobic respiration limits the process of respiration to the initial step only, i.e., glycolysis hence limited energy generation.
The mitochondria in the cells of the leg muscles of athletes have modifications (higher rate of cristae), helping them to adapt to extensive training.
Teaching and learning cellular respiration include introducing many terms that students are already familiar with at the college/university level. However, it is a good idea to help students freshen up their memory by revising some core concepts as discussed below:
Cellular respiration is a catabolic process in which glucose is broken down in the presence of oxygen to produce carbon dioxide, water, ATPs (28-30), and heat.
Respirometry measures metabolism and energy expenditure by calculating the oxygen uptake rate and CO2 production rate in metabolic processes like cellular respiration.
Reduction is the process in which an atom or ion is reduced by adding electrons/protons (H+) and removing oxygen.
Oxidation is when an atom or ion is oxidized by removing electrons/protons and adding oxygen.
Phosphorylation is a reversible process in which the phosphate group from a molecule/compound is removed and added to another molecule, like ADP (adenosine diphosphate), to produce ATP (adenosine triphosphate).
The cytoplasm is the matrix surrounded by the cell membrane. All cellular organelles, like mitochondria, float in the cytoplasm.
Mitochondria, also known as the cell's energy house, is a double membrane-bounded organelle essential for many biochemical processes like respiration. Many mitochondria are found in healthy cells to perform their duties well.
An electron is a small particle with a negative charge in all atoms. The flow of electrons through the electron transport chain generates energy for protons to do their job.
Proton is a positively charged particle present inside the nucleus of the cell. In cellular respiration, the electrons move down a chain of molecules, releasing energy that pumps protons (H+) out of the matrix. At the end of the electron transport chain, these protons move back into the matrix through ATP synthase, making ATP. Here oxygen is responsible for accepting electrons and taking up protons to produce the end product, i.e., water.
Biological processes like cellular respiration occur inside the cell; organelles make the entire topic abstract. Students are more likely to enjoy reading and learning about things they can see and feel. The visual representations, like the snippet from Labster shown below, make the learning/ teaching process fun and rewarding.
The image below shows the mitochondrial structure, which would intrigue students to know the journey of pyruvate to ATP inside this organelle.
The image below depicts a snippet taken from Labster's Cellular Respiration: The Electron Transport Chain Virtual Lab showing the electron transport chain in the intramitochondrial matrix. Students could understand the proton gradient across the membrane and various agents involved in ATP production.
The terms used in cellular respiration are complicated for students to remember. Since the process is extensive with many molecules and enzymes, word-play would help students in exams.
Glycolysis itself suggests its mechanism as the word "glycol" means "glucose" and "lysis" means break down. The Krebs or citric acid cycle is named after the scientist who discovered it, "Hanks Kreb," and its end-product, "citric acid." The electron transport chain highlights a chain of molecules through which electrons move to generate energy.
The enzyme involved in each step is named after its function; for instance, the first enzyme in glycolysis, "hexokinase" (Hexa means 6), shows that this enzyme would phosphorylate six-carbon compounds like glucose.
Help students learn the sequence of molecules involved in the Krebs cycle by a mnemonic like "Citrate Is Krebs Special Substrate For Making Oxaloacetate." “Citrate, Isocitrate, α Ketoglutarate, Succinyl CoA, Succinate, Fumarate, Malate and Oxaloacetate.”
To remember the difference between oxidation and reduction in chemical mechanisms, use the phrase LEO; the lion says GER, which stands for Loss of Electrons, is Oxidation. The gain of Electrons is Reduction.
A virtual laboratory simulation is a great way to teach about cellular respiration. At Labster, we're dedicated to delivering fully interactive advanced laboratory simulations that utilize gamification elements like storytelling and scoring systems inside an immersive and engaging 3D universe.
Check out simulations of cellular respiration, including glycolysis, Krebs cycle,ETC, and Respirometry at Labster. After learning all about the first stage of aerobic respiration and carrying out your investigation, you can pass on your knowledge to the basketball players, giving them advice on how they can keep energized during their game and improve how they train in the future!
Please take a look at the following GIF from Labster's Cellular Respiration: The Krebs Cycle Virtual Lab or get in touch to find out how you can start using virtual labs with your students.
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