Redox Reactions - Online Tutor, Practice Problems & Exam Prep

Redox reactions, short for oxidation-reduction reactions, involve the transfer of electrons between molecules. Oxidation is the loss of electrons, while reduction is the gain of electrons. These processes occur simultaneously, as one molecule loses electrons while another gains them. Key electron carriers like NADH and FADH₂ transport electrons within cells, functioning like "electron taxi cabs." NADPH, differing by a phosphate group, is used specifically in biosynthetic reactions to build cellular structures. Understanding these concepts is crucial for grasping cellular respiration and metabolic pathways.

Redox Reactions

In this video, we're going to introduce redox reactions. Redox is really just short for oxidation-reduction. You can see that the "red" in redox is for the "red" in reduction, and the "ox" in redox is for the "ox" in oxidation. Oxidation-reduction and redox reactions refer to the same exact thing and they involve the transfer of electrons between molecules. This symbol here e− is the symbol for electrons, which is an e with a negative sign. Recall from our previous lesson videos that electrons are negatively charged.

Within oxidation-reduction, you can see the two words, oxidation, and reduction, of course. Oxidation is the process of losing one or more negatively charged electrons, whereas reduction is the process of gaining one or more negatively charged electrons. If something is gaining negatively charged electrons, then that means that its overall charge is going to be reduced because it's gaining negatives. That is why reduction is the process of gaining negatively charged electrons.

What's also really important to note is that oxidation and reduction reactions always occur simultaneously, which means that they always occur at the same exact time. If something is losing electrons, then something else must be gaining those electrons. This is why oxidation-reduction reactions always go hand in hand with each other.

So let's take a look at our example down below at these redox reactions or oxidation-reduction reactions. When it comes to redox reactions, all you need to remember is "Leo the lion says ger", and that's because if you can remember that Leo the lion says ger, then you'll be able to remember that anything that loses electrons is going to be oxidized, and oxidation just refers to anything that loses electrons, whereas the "ger" here refers to gaining electrons is reduction. Anything that gains electrons is going to be reduced. That means its charge is going to be reduced because it's gaining negatively charged electrons. Just by remembering "Leo the lion says ger", you'll be able to remember that oxidation is losing electrons and reduction is gaining electrons.

Down below, we have a little image of Leo here, and you can see that Leo the lion is going "grrr". By remembering this, you should be set on your problems for redox reactions. Over here on the right-hand side, we have an image to show you that oxidation and reduction reactions always go hand in hand. You can see here that we have a person that has some electrons in their hands right here, and this little blue circle with the negative charge in it is representing our electron. You can see that if this person is giving up the electron and giving it to this person over here, then this person will be gaining electrons, meaning that it will be reduced, that person will be reduced. Whereas the person that is giving up electrons, giving them away, they are losing electrons and because they are losing electrons, they are being oxidized.

The oxidation-reduction reactions will always go hand in hand because it's almost like a person giving a gift away. If someone's giving away a gift or losing a gift, that means that someone else is gaining the gift. Oxidation-reduction reactions will always go hand in hand just like what you could see here in this image. This concludes our introduction to redox reactions, and we'll be able to learn more and more about them as we move forward in our course. I'll see you all in our next video.

Redox Reactions Example 1

So here we have an example problem that's asking which of the following molecules is oxidized and which is reduced? And notice that we have molecule A over here and molecule B, and they are undergoing a chemical reaction. And so notice we have these 4 potential answer options over here. And so of course, what we need to recall from our last lesson video is that when it comes to oxidation-reduction reactions or redox reactions, really all we need to remember is 'Leo the lion goes ger'. And because if we remember 'Leo the lion goes ger', then we'll be able to remember that oxidation is when a substance loses electrons and reduction is when a substance gains electrons.

Looking at this reaction here between molecule A and molecule B, notice that molecule A is starting with an electron here in blue, and molecule B seems to not have those that electron. And so notice that after this reaction, molecule A is actually donating its electron to molecule B, and so molecule A is losing an electron by the end of the reaction whereas molecule B is gaining the electron. And so, because molecule B is gaining the electron that makes it reduced, and because molecule A is losing the electron by the end of the reaction that makes molecule A oxidized.

We need to choose the option that corresponds with that and notice option A says molecule A is oxidized whereas molecule B is reduced and that is going to be the correct answer to this example problem. So we can go ahead and mark A here as correct. And that concludes this example problem. So I'll see you all in our next video.

Oxidation is the _________________________, and reduction is the _________________________.

a) Gain of electrons; Loss of electrons.

b) Gain of protons; Loss of protons. 

c)  Loss of electrons; Gain of electrons.

d)  Gain of oxygen; Loss of oxygen.

• A. Gain of electrons; Loss of electrons.
• B. Gain of protons; Loss of protons.
• C. Loss of electrons; Gain of electrons.
• D. Gain of oxygen; Loss of oxygen.

When glucose donates electrons to NAD⁺ creating NADH, the glucose molecule becomes:

a) Hydrolyzed.

b) Oxidized.

c) Neutral.

d) Reduced.

• A. Hydrolyzed.
• B. Oxidized.
• C. Neutral.
• D. Reduced.

Electron Carriers:NADH & FADH2

In this video, we're going to introduce electron carriers, specifically NADH and FADH₂. It's important to note that many biological processes that we will discuss, including cellular respiration, conduct redox reactions using electron carriers. These electron carriers are helpful to perform redox reactions. Electron carriers such as NADH and FADH₂ each carry or transport a maximum of 2 electrons. NADH and FADH₂ can shuttle electrons to different locations within a cell, much like an electron taxi cab. You can think of NADH and FADH₂ as electron taxi cabs, and we'll be able to see that down below in our image.

It is also important to note that NAD⁺ and FAD are the oxidized forms of NADH and FADH₂ respectively. Recall that in oxidation (represented by LEO), the species losing electrons is oxidizing. This means that NAD⁺ and FAD will have fewer electrons; they have lost electrons compared to NADH and FADH₂. Let's take a look at our image down below to clarify some of this.

The electron carriers we are discussing, NADH and FADH₂, act like electron taxicabs. In the image, you can see an electron taxicab. On the left-hand side, you notice the empty form of the electron taxicab. However, when this electron taxicab picks up its 2 passengers, these 2 electrons, it becomes a full taxicab. Over here, we have the 2 electrons inside this electron taxicab, illustrating what NADH and FADH₂ act as these electron taxi cabs.

We observe that NADH forms when the oxidized form, NAD⁺ (the empty taxicab version), picks up its 2 passengers, these 2 electrons, along with a hydrogen ion, and it forms NADH. You can see that NADH is carrying these 2 electrons, the passengers of the taxicab, but it also picks up a hydrogen atom. When we look at FAD, this is the empty taxi cab version of the electron carrier. But when it picks up its 2 passengers, these 2 electrons, it also picks up 2 hydrogen ions and becomes FADH₂, the full taxicab version of this electron carrier.

One way to help you remember that NADH and FADH₂ are the full taxicab versions is just to think that they are a bit heavier because they're gaining electrons and hydrogen ions. Those labeled with 'H' are just a little bit heavier, and thus, they are the full taxicab versions. As we move forward in our course discussing cellular respiration, it's significant to note that during cellular respiration, these electrons carried by NADH and FADH₂ are going to go to what's known as the electron transport chain, which is the final stage of cellular respiration. We'll discuss this more as we progress in our course. For now, notice the full electron taxicab here, where one of the electrons is asking, "Where are we going?", and the other electron responds, "To the electron transport chain, duh." This memorable interaction highlights what we will learn about how NADH and FADH₂ take their electrons to the electron transport chain during cellular respiration.

This concludes our brief introduction to electron carriers, NADH and FADH₂, and we'll be able to get some practice applying the concepts we've learned here as we move forward in our course. I'll see you all in our next video.

An electron carrier before it harvests energy from glucose molecules in a series of gradual steps is:

a) Pyruvate.

b) AMP.

c) ATP.

d) NAD⁺.

e) NADH.

• A. Pyruvate.
• B. AMP.
• C. ATP.
• D. NAD⁺.
• E. NADH.

Electron Carrier NADPH

In this video, we're going to introduce yet another electron carrier, and that is the electron carrier, NADP. So NADPH only differs from NADH by this "P" that is present, and the "P" represents a phosphate group. Once again, NADPH is an electron carrier that is actually very similar to the electron carriers that we already talked about in our last lesson video, which recall are NADH and FADH₂. NADPH, like NADH and FADH₂, can carry 2 electrons and transport those electrons within the cell to different locations. They can be used for reduction reactions, or reactions that reduce other molecules and allow them to gain electrons.

However, unlike NADH and FADH₂, NADPH is specifically used in biosynthetic reactions for biosynthesis purposes, or in other words, it's used in reactions that are going to build molecules and cell structures. You can think of this electron carrier, NADPH, as a little construction truck. Here we have this construction truck that is going to be used for building, for biosynthetic reactions. Notice that the empty version of this construction truck corresponds with NADP⁺. This is the oxidized form of the electron carrier, and so it has no electrons. Notice that the electron spots are empty, but it can gain 2 electrons and become a full construction truck that's carrying 2 electrons, and this full construction truck corresponds with the electron carrier, NADPH.

Once again, NADPH can gain 2 electrons and a hydrogen ion to become NADPH, and it's going to carry electrons from one location within the cell to a different location within the cell, very similar to the other electron carriers that we already talked about. However, one of the main important differences is that NADPH is going to be used in biosynthetic reactions in order to build cell structures and build molecules. Here you can see a house that is under construction, and NADPH is going to be used to help build this house here or to build some kind of cell structure or molecule within the cell.

This here concludes our brief lesson on the electron carrier NADPH, and we'll be able to see this electron carrier as we move forward throughout our course. But for now, this here concludes this video, and I'll see you all in our next one.

NADH is commonly used as an electron carrier during the breaking down of complex molecules like glucose in cellular respiration. NADPH is also a common electron carrier. However, NADPH is used to build complex molecules like glucose in a process called:

• A. Biogenesis.
• B. Biocatalysis.
• C. Biosynthesis.
• D. Metabolism.

Which electron carrier is not matched with its correct function.

• A. NADH:Shuttles electrons to regions of the cell which need energy.
• B. FADH₂:Shuttles electrons to the electron transport chain during cellular respiration.
• C. NADPH:Shuttles electrons to photosynthesis where glucose molecules are being made.
• D. All of the above electron carriers are matched with their correct function.

Here’s what students ask on this topic:

What are redox reactions and why are they important in biological systems?

Redox reactions, short for oxidation-reduction reactions, involve the transfer of electrons between molecules. Oxidation is the loss of electrons, while reduction is the gain of electrons. These processes occur simultaneously, as one molecule loses electrons while another gains them. Redox reactions are crucial in biological systems because they are fundamental to processes like cellular respiration and photosynthesis. They help in the production of ATP, the energy currency of the cell, and are involved in various metabolic pathways. Understanding redox reactions is essential for grasping how cells generate energy and maintain homeostasis.

How do NADH and FADH₂ function as electron carriers in cellular respiration?

NADH and FADH₂ are key electron carriers in cellular respiration. They transport electrons within cells, functioning like 'electron taxi cabs.' NADH is formed when NAD⁺ picks up two electrons and a hydrogen ion, while FADH₂ is formed when FAD picks up two electrons and two hydrogen ions. These carriers shuttle electrons to the electron transport chain, the final stage of cellular respiration. Here, the electrons are used to generate a proton gradient that drives the production of ATP. This process is vital for the cell's energy production.

What is the difference between NADH and NADPH in terms of their roles in the cell?

NADH and NADPH are both electron carriers but serve different roles in the cell. NADH is primarily involved in cellular respiration, where it transports electrons to the electron transport chain to produce ATP. NADPH, on the other hand, is used in biosynthetic reactions, such as fatty acid and nucleotide synthesis. It acts as a reducing agent, donating electrons to build cellular structures and molecules. The key difference is that NADPH contains an additional phosphate group, which allows it to participate specifically in anabolic (biosynthetic) pathways.

Why do oxidation and reduction reactions always occur simultaneously?

Oxidation and reduction reactions always occur simultaneously because they involve the transfer of electrons from one molecule to another. When one molecule loses electrons (oxidation), another molecule must gain those electrons (reduction). This simultaneous occurrence ensures the conservation of charge and mass. For example, in cellular respiration, glucose is oxidized to carbon dioxide, and oxygen is reduced to water. This interdependence is fundamental to many biological processes, ensuring that energy transfer and chemical transformations occur efficiently within cells.

How can the mnemonic 'LEO the lion says GER' help in understanding redox reactions?

The mnemonic 'LEO the lion says GER' helps in understanding redox reactions by simplifying the concepts of oxidation and reduction. 'LEO' stands for 'Loss of Electrons is Oxidation,' and 'GER' stands for 'Gain of Electrons is Reduction.' This mnemonic aids in remembering that oxidation involves losing electrons, while reduction involves gaining electrons. By associating these processes with a simple phrase, students can more easily recall the definitions and apply them to various biochemical reactions, such as those in cellular respiration and photosynthesis.