Energy Sources and Generation - Online Tutor, Practice Problems & Exam Prep

Cells require energy to maintain order and perform essential functions, derived from energy sources like phototrophs, which convert light into chemical energy, and chemotrophs, which utilize organic nutrients. Metabolism encompasses catabolism (breaking down molecules) and anabolism (synthesizing molecules), facilitated by enzymes. Energy transfer involves oxidation (electron removal, releasing energy) and reduction (electron addition, requiring energy). Understanding these processes is crucial for grasping cellular functions and energy dynamics.

Energy Sources

Hi, in this video we're going to be talking about energy sources and consumption. So, first let's talk about energy sources, where do cells get their energy, and what terms do we use to describe energy in cells? The first thing is that in order to survive, cells need a constant source of energy. Energy allows them to live and undergo all the chemical reactions required for life, so in order to be constantly doing those chemical reactions that allow cells to survive, they need the energy for those chemical reactions. Now before we get into energy in terms of cells, your book and your professor are probably going to describe energy just in terms of science. So a lot of these, especially this first section here, is going to be talking about energy and typically from a chemistry perspective. But, I'm going to introduce it here because your textbook does and your professor probably will, but then I'll get more into what energy means in terms of cells and cell biology.

The first thing is let's talk about the second law of thermodynamics, which says that the disorder in the universe only increases. What does that mean? That means that things happen that destroy the perfect order of the universe. For instance, an example I'm going to use later is this card tower. Cards don't spontaneously form into these nice towers. The order of the universe includes these cards most likely falling down and becoming disarrayed. Now, we can use the example of a card tower, but pretty much everything in the universe is like this nice form of a card tower, but that's not usually what happens. Usually, the card tower gets knocked over, the cards go everywhere. The same thing happens with chemical reactions and cells, or anything else outside of cell biology as well. Disorder, or the mess of everything, is always increasing. To measure that increase of disorder, we use entropy, a measure of the system's disorder. Now, entropy is a term here that your book is going to describe, your professor is going to mention, but we are not going to talk about it any other time in cell biology. They just need you to know this now because it's an important concept in science. So, make sure you understand the definition.

Now, in chemistry, you're going to focus on physics. Potentially, you're going to focus on this a lot more. But, for cell biology, I'm just going to introduce the term because that's how it's supposed to be, and then I'm not ever going to mention it again. So, in terms of how we relate entropy to anything else, we say that systems, so that can be anything, like a card tower, a chemical reaction, a cell, spontaneously change towards more entropy, which equals more disorder. So, like the card tower, it is going to spontaneously fall, possibly because someone knocks it or the wind knocks it over, and so systems are always going toward more disorder, and that means more entropy. Now, because the disorder in the universe is only increasing, we're getting more and more diso

Energy Consumption

So now we're going to talk about energy consumption, which plays a big role in the functions of cells and organisms. Cells must be able to transfer energy from one form to another, and the reason they have to do this is due to the first law of thermodynamics, which states that energy cannot be created or destroyed. However, it can be changed, and that's what cells and organisms do. There are a few classifications that we use to determine how cells get their energy and how they transfer it. One of them is phototrophs. Phototrophs use photosynthesis, which is a term you should be familiar with, to change light energy into chemical energy. Another one is chemotrophs, and they change organic nutrients into freely usable energy. This energy can be carbon dioxide; it can be water, and we see this a lot with ourselves. We are technically chemotrophs because we take in food, eat organic nutrients, and then release things like carbon dioxide and water, which can then be used by our cells or by other organisms as energy sources. There is this continual exchange of energy and heat between organisms and the universe in the forms of these atoms and molecules. These are carbon, oxygen, nitrogen, commonly found in the universe. So, there is this constant uptake and release by all of these different organisms.

Now, when we talk about chemical reactions and energies in cells, we use the term metabolism. Metabolism is the sum of chemical reactions in a cell, and it's really made up of two components. These components are catabolism, which is the breakdown of food into smaller molecules, and anabolism, which is the synthesis of molecules. So, catabolism is breakdown, and anabolism is synthesis. Enzymes are proteins that really assist with these breakdowns and syntheses in these chemical reactions that make up cellular metabolism.

This is going to be a really big overview, but you can see here you have phototrophs. These are things like plants, algae, some bacteria, and you have chemotrophs over here with animals, fungi, some other bacteria. And you can see that these arrows are constantly moving around, going around in circles because they're exchanging organic compounds, oxygen, carbon dioxide, water, with each other, and also with the environment. So there's this constant energy source. There are all of these different reactions and metabolisms happening that allow this cyclic energy transfer between organisms and also between the universe.

One really important energy transfer that we're going to talk about is actually the movement of electrons. And they have fancy names, which you may remember from your chemistry class, and these are oxidation and reduction. So oxidation is the removal of electrons from an atom or molecule, and it releases energy. One example of this is the fact that cellular respiration, which we're going to talk about a lot more in future topics, depends on the oxidation of organic molecules. We're moving the electrons from organic molecules in order to consume and use the energy from food. So oxygen is the removal of electrons, which means that reduction is going to be the addition of electrons to an atom or a molecule, and typically, this requires some type of energy input. Here we have this molecule, NAD, and it becomes NADH through the addition of electrons. Going to be the removal of electrons and oxidation in the reverse. And this is going to be a really important molecule that we're going to talk about a lot more in the future, but it's just a general overview of oxidation and reduction so that we understand these principles moving forward. So now, let's move on.

Which of the following is a measure of the energy needed to move a sodium ion from a high concentration to a low concentration?

• A. Kinetic Energy
• B. Entropy
• C. Potential Energy
• D. Work

Reduction is the process of adding electrons to an atom or molecule?

• A. True
• B. False

Metabolism, which is the sum of chemical reactions, consists of all but which of the following components?

• A. Catabolism
• B. Melabolism
• C. Anabolism

Here’s what students ask on this topic:

What is the second law of thermodynamics and how does it relate to cell biology?

The second law of thermodynamics states that the disorder, or entropy, in the universe always increases. In cell biology, this means that cells must constantly expend energy to maintain order and perform essential functions. Without this energy input, cells would succumb to disorder and cease to function properly. This principle underscores the importance of energy in maintaining cellular structure and facilitating biochemical reactions necessary for life.

What are the differences between potential and kinetic energy in cells?

Potential energy in cells is stored energy, such as the energy found in chemical bonds or membrane concentration gradients. For example, molecules in a high concentration on one side of a membrane represent stored energy. Kinetic energy, on the other hand, is the energy of motion. Examples include heat, light, and the movement of electrons. When molecules move across a membrane or when electrons are transferred during chemical reactions, potential energy is converted into kinetic energy, facilitating cellular processes.

How do phototrophs and chemotrophs differ in their energy acquisition?

Phototrophs, such as plants and some bacteria, acquire energy through photosynthesis, converting light energy into chemical energy. Chemotrophs, including animals and fungi, obtain energy by metabolizing organic nutrients. They break down these nutrients into smaller molecules, releasing energy in the process. This energy is then used for various cellular activities. Both types of organisms play crucial roles in the energy exchange within ecosystems, contributing to the overall energy balance.

What roles do oxidation and reduction play in cellular energy transfer?

Oxidation and reduction are key processes in cellular energy transfer. Oxidation involves the removal of electrons from a molecule, releasing energy. This is crucial in cellular respiration, where organic molecules are oxidized to produce energy. Reduction, on the other hand, involves the addition of electrons to a molecule, which typically requires energy input. These processes are often coupled, with electrons transferred from one molecule to another, facilitating the flow of energy within cells.

What is metabolism and what are its two main components?

Metabolism is the sum of all chemical reactions occurring within a cell. It consists of two main components: catabolism and anabolism. Catabolism involves the breakdown of complex molecules into simpler ones, releasing energy that the cell can use. Anabolism, in contrast, involves the synthesis of complex molecules from simpler ones, which requires energy input. Together, these processes enable cells to grow, reproduce, and maintain their structures.