Understanding Cell Specialization and Adaptations

Please report to your area and differentiate when instructed. Next! Hello, Mr. Chem Grade. Let me start off by saying I'm so excited to be here. I'm such a big fan and I am ready to differentiate. Is that so? Oh, I have been preparing, creating so much ATP, practicing turning genes on and off for the last three hours of my existence. My nucleus brain is truly unmatched. Well then, I think I have the perfect spot for you. Amazing! Red blood cell. Wait, what? Please report to your area and differentiate when instructed. But that would mean my brain would be... Next! No! We are going to continue our discussion on cell specialization by looking at a few examples that you need to know for the HL curriculum. The names of specific cells and concepts that we cover in this video will show up in other places throughout the curriculum, but we are talking about them here because they are examples of how cells are differentiated and specialized for performing specific functions. We mentioned in the SL video that cells need to maintain a threshold of surface area to volume in order to maintain homeostasis. which means that the ratio can't drop too low, meaning the cell becomes too large. Looking at different cells throughout the body, we can see that some cells contain specific adaptations to further increase their surface area to volume ratio to perform unique functions. And remember that a high or increased surface area to volume ratio means that there is a large amount of membrane area compared to a relatively smaller internal volume, which is totally fine for the cell to be maintained. The two examples you need to know are with red blood cells and the cells that line the proximal convoluted tubule of the kidney. Red blood cells are specially designed to carry and transport nutrients, and in order to do this efficiently, they need a larger area of the cell membrane so more nutrients can transfer at any given time. We see this adaptation within the shape of a red blood cell, which is a biconcave disc, meaning that the two sides pinch in to form concave curves, which make it look flattened. This membrane shape increases the total surface area to volume ratio of the cell, as it creates less room for cytoplasm and more area for the membrane compared to a spherical shape, allowing more space for nutrients to be passed and decreasing the distance they need to travel within the cytoplasm to reach the membrane. Proximal convoluted tubules are found within the kidneys. As blood is initially filtered when it enters the kidney, the filtrate gets pushed into the proximal convoluted tubule. But this filtrate contains specific nutrients that the body needs, and as it moves through the tubule those useful components, like glucose, vitamins, and electrolytes, are reabsorbed and put back into the blood, leaving any waste to continue to travel down to the next part of the nephron. The cells that line the proximal convoluted tubule contain adaptations that increase their surface area to volume ratio in order to reabsorb as many nutrients as possible. The layer is one cell thick, which supports quick material exchange and contains specialized structures on the apical and basal surfaces. The apical surface which the filtrate is in contact with contains microvilli, which are projections that increase the surface area for absorption, and the basal membrane contains infoldings called invaginations that do the same thing, increase the surface area. This ensures that a large number of nutrients can pass through from the filtrate and back into the bloodstream at a high rate. The next set of specialized cell adaptations you need to know about are found in the lungs. If you zoom in on lung tissue you will find small air sacs that inflate when you inhale to support gas exchange, which are called alveoli, which we will talk more about in section B3.1. But focusing here on cell specialization, there are two different types of cells that make up alveoli, which are drastically different in form and function. These cells are called pneumocytes, and they are split into two types which are simply labeled type 1 and type 2. Type 1 pneumocytes are wide and extremely extremely thin. These cells support the exchange of gases, such as oxygen and carbon dioxide, between the bloodstream and the atmosphere. The fact that they are very thin allows for a quick diffusion of these gases through a small amount of cell cytoplasm that travel along their concentration gradients. Type 2 pneumocytes are not thin, and instead take on more of a traditional cuboidal cell shape. The function of these cells is to create and secrete a substance called surfactant that gets pushed to the apical surface, lining the alveolus and holding in a film of moisture. The edge of the film is made up of phospholipids and proteins that are pushed out from secretory vessels of the type 2 pneumocytes, called lamellar bodies, which is their unique adaptation. This surfactant helps reduce surface tension as alveoli inflate and deflate, ensuring that each alveolus does not collapse in on itself and provides a means for alveoli of different sizes to distribute pressure accordingly. The overall structure of an alveolus is unique because it requires these two cell types, each with different adaptations, in order to function. Which is not the case for many other internal surfaces of the body, which generally only need one cell type to function. Moving on to muscle cells, both skeletal and cardiac muscle cells have unique adaptations that help them perform their function of contracting to generate movement. We will discuss the details of muscle contraction in section B3.3, but for now our focus here is on how these cells are specialized. Skeletal muscles are voluntary muscles that pull on bones to create movement. They are made up of very long cells that run parallel to each other and contain proteins called myofibrils that slide past each other which shortens the cell allowing it to contract. These myofibrils are arranged in a way that creates a striated dark and light pattern when viewing the muscle tissue. The interesting thing about these cells is their length and number of nuclei. The length of one of these cells is around 30 millimeters, where an average non-muscle cell in the body has a length of around 0.3 millimeters. Additionally, each one of these very long cells has multiple nuclei. They are developed this way through the fusion of embryonic cells that pull nuclei together to create one large structure. I have been referencing and calling these structures cells, but that classification is still debated because normally cells only have one nucleus, not many nuclei, and are usually not that long, which makes these muscle cells very unique. Cardiac muscle is similar to skeletal muscle in the sense that they contain contractile myofibrils. But cardiac muscle is found only in the heart and contains cells that are much shorter compared to skeletal muscle and generally contain only one nucleus. These specialized cells create a branching pattern that are connected end-to-end by structures called intercalated discs, which allows them to propagate electrical signals so groups of muscle can contract at the same time, making the heart beat properly. So for the exam make sure to know the specialization differences between skeletal and cardiac muscle. Lastly, there are unique adaptations seen in both sperm and egg cells. While both of these cells are haploid gametes, they play very different roles in the process of sexual reproduction and their ability to achieve fertilization. Egg cells are large and contain all of the necessary components to support and develop a fertilized zygote, which includes a large cytoplasm filled with macromolecules, mitochondria, and centrioles. Eggs are moved passively down the female reproductive tract and therefore do not contain any mechanisms for faster movement. The plasma membrane of an egg cell contains an adjacent glycoprotein outer layer that sperm cells can connect to, and when a sperm cell does connect and enter, the chemical composition of the membrane is changed to prevent any other sperm from entering. If we take a look at sperm cells, they are much smaller, with very little internal components in their cytoplasm, and have a tail packed with mitochondria, making them able to move up the reproductive tract of the female, and allow them to potentially find an egg to fertilize. The head of the sperm contains enzymes that allow it to break down the protective layer around the egg to reach the plasma membrane and fuse to release the genetic information. It goes without saying that these sperm and egg cells are the only cells in the body that can perform this role, showing just how important their specific pathway of specialization is.

Please report to your area and differentiate when instructed. Next! Hello, Mr. Chem Grade.

Let me start off by saying I'm so excited to be here. I'm such a big fan and I am ready to differentiate. Is that so? Oh, I have been preparing, creating so much ATP, practicing turning genes on and off for the last three hours of my existence. My nucleus brain is truly unmatched.

Well then, I think I have the perfect spot for you. Amazing! Red blood cell. Wait, what?

Please report to your area and differentiate when instructed. But that would mean my brain would be... Next!

No! We are going to continue our discussion on cell specialization by looking at a few examples that you need to know for the HL curriculum. The names of specific cells and concepts that we cover in this video will show up in other places throughout the curriculum, but we are talking about them here because they are examples of how cells are differentiated and specialized for performing specific functions. We mentioned in the SL video that cells need to maintain a threshold of surface area to volume in order to maintain homeostasis. which means that the ratio can't drop too low, meaning the cell becomes too large.

Looking at different cells throughout the body, we can see that some cells contain specific adaptations to further increase their surface area to volume ratio to perform unique functions. And remember that a high or increased surface area to volume ratio means that there is a large amount of membrane area compared to a relatively smaller internal volume, which is totally fine for the cell to be maintained. The two examples you need to know are with red blood cells and the cells that line the proximal convoluted tubule of the kidney. Red blood cells are specially designed to carry and transport nutrients, and in order to do this efficiently, they need a larger area of the cell membrane so more nutrients can transfer at any given time. We see this adaptation within the shape of a red blood cell, which is a biconcave disc, meaning that the two sides pinch in to form concave curves, which make it look flattened.

This membrane shape increases the total surface area to volume ratio of the cell, as it creates less room for cytoplasm and more area for the membrane compared to a spherical shape, allowing more space for nutrients to be passed and decreasing the distance they need to travel within the cytoplasm to reach the membrane. Proximal convoluted tubules are found within the kidneys. As blood is initially filtered when it enters the kidney, the filtrate gets pushed into the proximal convoluted tubule.

But this filtrate contains specific nutrients that the body needs, and as it moves through the tubule those useful components, like glucose, vitamins, and electrolytes, are reabsorbed and put back into the blood, leaving any waste to continue to travel down to the next part of the nephron. The cells that line the proximal convoluted tubule contain adaptations that increase their surface area to volume ratio in order to reabsorb as many nutrients as possible. The layer is one cell thick, which supports quick material exchange and contains specialized structures on the apical and basal surfaces.

The apical surface which the filtrate is in contact with contains microvilli, which are projections that increase the surface area for absorption, and the basal membrane contains infoldings called invaginations that do the same thing, increase the surface area. This ensures that a large number of nutrients can pass through from the filtrate and back into the bloodstream at a high rate. The next set of specialized cell adaptations you need to know about are found in the lungs. If you zoom in on lung tissue you will find small air sacs that inflate when you inhale to support gas exchange, which are called alveoli, which we will talk more about in section B3.1.

But focusing here on cell specialization, there are two different types of cells that make up alveoli, which are drastically different in form and function. These cells are called pneumocytes, and they are split into two types which are simply labeled type 1 and type 2. Type 1 pneumocytes are wide and extremely extremely thin. These cells support the exchange of gases, such as oxygen and carbon dioxide, between the bloodstream and the atmosphere.

The fact that they are very thin allows for a quick diffusion of these gases through a small amount of cell cytoplasm that travel along their concentration gradients. Type 2 pneumocytes are not thin, and instead take on more of a traditional cuboidal cell shape. The function of these cells is to create and secrete a substance called surfactant that gets pushed to the apical surface, lining the alveolus and holding in a film of moisture.

The edge of the film is made up of phospholipids and proteins that are pushed out from secretory vessels of the type 2 pneumocytes, called lamellar bodies, which is their unique adaptation. This surfactant helps reduce surface tension as alveoli inflate and deflate, ensuring that each alveolus does not collapse in on itself and provides a means for alveoli of different sizes to distribute pressure accordingly. The overall structure of an alveolus is unique because it requires these two cell types, each with different adaptations, in order to function. Which is not the case for many other internal surfaces of the body, which generally only need one cell type to function. Moving on to muscle cells, both skeletal and cardiac muscle cells have unique adaptations that help them perform their function of contracting to generate movement.

We will discuss the details of muscle contraction in section B3.3, but for now our focus here is on how these cells are specialized. Skeletal muscles are voluntary muscles that pull on bones to create movement. They are made up of very long cells that run parallel to each other and contain proteins called myofibrils that slide past each other which shortens the cell allowing it to contract.

These myofibrils are arranged in a way that creates a striated dark and light pattern when viewing the muscle tissue. The interesting thing about these cells is their length and number of nuclei. The length of one of these cells is around 30 millimeters, where an average non-muscle cell in the body has a length of around 0.3 millimeters. Additionally, each one of these very long cells has multiple nuclei.

They are developed this way through the fusion of embryonic cells that pull nuclei together to create one large structure. I have been referencing and calling these structures cells, but that classification is still debated because normally cells only have one nucleus, not many nuclei, and are usually not that long, which makes these muscle cells very unique. Cardiac muscle is similar to skeletal muscle in the sense that they contain contractile myofibrils.

But cardiac muscle is found only in the heart and contains cells that are much shorter compared to skeletal muscle and generally contain only one nucleus. These specialized cells create a branching pattern that are connected end-to-end by structures called intercalated discs, which allows them to propagate electrical signals so groups of muscle can contract at the same time, making the heart beat properly. So for the exam make sure to know the specialization differences between skeletal and cardiac muscle.

Lastly, there are unique adaptations seen in both sperm and egg cells. While both of these cells are haploid gametes, they play very different roles in the process of sexual reproduction and their ability to achieve fertilization. Egg cells are large and contain all of the necessary components to support and develop a fertilized zygote, which includes a large cytoplasm filled with macromolecules, mitochondria, and centrioles. Eggs are moved passively down the female reproductive tract and therefore do not contain any mechanisms for faster movement. The plasma membrane of an egg cell contains an adjacent glycoprotein outer layer that sperm cells can connect to, and when a sperm cell does connect and enter, the chemical composition of the membrane is changed to prevent any other sperm from entering.

If we take a look at sperm cells, they are much smaller, with very little internal components in their cytoplasm, and have a tail packed with mitochondria, making them able to move up the reproductive tract of the female, and allow them to potentially find an egg to fertilize. The head of the sperm contains enzymes that allow it to break down the protective layer around the egg to reach the plasma membrane and fuse to release the genetic information. It goes without saying that these sperm and egg cells are the only cells in the body that can perform this role, showing just how important their specific pathway of specialization is.

Transcript for:Understanding Cell Specialization and Adaptations

Transcript for:
Understanding Cell Specialization and Adaptations