Overview of Tissue Structures - Online Tutor, Practice Problems & Exam Prep

The evolution of multicellular organisms began with single cells forming tissues through cell-to-cell interactions and the extracellular matrix (ECM). In animals, cell adhesion proteins (CAM) and in plants, plasmodesmata connect cells. Tissues are categorized into plant types: ground, dermal, and vascular, and animal types: epithelial, connective, blood, nervous, and muscle. Early development involves a zygote differentiating into specialized cells, influenced by patterning genes that regulate tissue formation and symmetry, crucial for complex organism structures.

Cells to Tissues

Hi. In this video, we're going to be talking about the evolution of tissue structure. So first, let's talk about how cells became tissues. Before they were multicellular organisms, there were all of these single cells just sort of floating around, but eventually, they started interacting with each other and found that that was beneficial. To increase these interactions, cell-to-cell interactions led to the formation of an extracellular matrix in the first multicellular organisms. The extracellular matrix is really just composed of these proteins that connect cells together. Metazoans, which is another term for multicellular organisms, evolved from these very small cellular colonies of cells around 1,000,000,000 years ago. When they did this, they needed to be able to attach together, so one of the proteins that did this is called the cell adhesion protein or molecules, which you can use CAM for short, and they attach animal cells together. These proteins are obviously still present today and they still attach animal cells, within our bodies and with other animals' bodies. Now for plant cells, this term is a little different, and it's called plasmodesmata which is actually just the cytoplasmic bridges that connect plants at walls.

Referring back to the extracellular matrix, we're talking about all of these things that connect cells together. The extracellular matrix is composed of multiple proteins, some of them called basal lamina, which forms the basal lamina that provides support and structure for groups of epithelial cells. So there are a lot of connected words, but all of them are responsible for attaching cells together. Basal lamina does it through proteins, plasmodesmata through cytoplasmic bridges, but all of these are connecting cells together. You can see animal cells in this image, which is actually animal skin and plant cells. Down here, you can see the extracellular matrix, which you can shorten to ECM, and then you have the basal lamina, which is this black structure here. Both are composed of all these different proteins that help attach all the cells above together, helping them act as one force as skin instead of as individual cells. For plant cells, as mentioned, there is plasmodesmata, which is here at the bottom, and you can actually see them here in green, connecting all of these plant cell walls together.

This is how cells eventually started evolving into tissues because they were acting as one unit connected by all of these proteins instead of as individual cells. Today we have tissues, so organized groups of cells form tissues. I've divided this into two sections: different types of plant tissues and different types of animal tissues, and I've bolded some of these terms that you're probably familiar with from your intro bio class, which went over some of the basics of tissues. This is mainly just a refresher of what the tissue terms are for plants and animals. For plant cells, you have ground tissue, which is the area of metabolism, you have dermal tissue, which forms the protective coat, and is also a place for nutrient absorption, and then you have vascular tissue which transports water and nutrients throughout the plant. For animal cells, you have five main tissue groups: epithelial which forms sheets that cover the body for protection, connective tissue that provides mechanical support for the body (this also includes bone tissue), blood, which is responsible for transporting oxygen throughout the body, the nervous system, which is responsible for transporting signals throughout the body, and muscle tissue, which helps your body move.

These bolded terms are familiar to you already from your intro bio class, but I just wanted to refresh them here so we can understand these are the tissues that groups of cells make. If we look at the plant tissue here, you can see the vascular tissue, which transports water. You don't need to know exactly where these tissues are, just that they exist on this plant cross-section of the three tissue types. Then you also have the dermal tissue, which provides support and structure and protection for the plant, and the ground tissue, which is responsible for absorbing nutrients and helping things flow between all the different tissues.

Now let's move on to the next concept.

Multicellular Development

So we've talked about cells and tissues, but now let's talk about the formation of multicellular organisms. First, the formation of tissues must occur early in the development of an organism. This is because in the human body, a single cell, which is called a zygote—the first single cell—eventually results in 100 trillion cells. That's a huge amount of diversity, complexity, and number of cells. In order for that to happen, the cells have to decide very early on what they are going to become. They have to say, "Okay, you're going to become this." So you need to focus on becoming blood or you're going to become the head, so you need to focus on doing that. By separating those divisions and those responsibilities out early, we're actually able to form this functional organism instead of a jumbled mass of cells. One of the earliest patterns actually depends on the placement of where your mouth and the anus go. In protostomes, which are a type of organism, it's a sort of division of organisms, the mouth develops near this thing called a transient opening, and they have a ventral nerve cord. Now you should have gone over this in your bio 101 class. This is just really a refresher for you. But in early development, there's this kind of hole that opens, which I'll actually just show you down here.

So you have some of these very early cells, before the opening, but eventually this opening starts forming. This transient opening right here. And then depending on whether the mouth forms near this or the anus forms near this, that's how you're classified. So for protostomes, the mouth develops near this transient opening. So eventually the mouth will form down here. Whereas in deuterostomes, the anus forms near the transient opening. So you can see this down here. And this really starts to divide how organisms eventually develop. So for protostomes, they have a ventral nerve cord, and for deuterostomes, they have a dorsal central nervous system. You don't necessarily need to remember, you know, what's a dorsal central nervous system. Just know that these different classifications affect how the multicellular organism is developed. Now, a second large type of patterning occurs, and this is actually for patterning genes. Master regulatory pattern genes control the timing and formation of specific tissues.

So before we were just talking about the mouth and anus, now we're talking about specific tissues. The type of symmetry that's controlled by patterning genes includes anterior-posterior, dorsal-ventral, so which side of the body you're talking about. And then it also controls where the head, the chest, the abdomen, and tails are going to develop. What are patterning genes? What do they do? Well, actually, they are pretty conserved. They are found in almost every pretty much every organism, things called transcription factors. And what transcription factors do is that they control gene expression, which makes sense. You need to control the development of cells and tissues, so then you have to control the genes that are expressed in them. Patterning genes are transcription factors that control gene expression. And so they can be, I mean, like really specific. For instance, the gene that controls the development of eyes is actually the exact same gene in flies and in humans.

Now this might seem a little weird because the fly eye is very different than the human eye, but it's true because they're both eyes. Very early in development, they are controlled by the same patterning gene. So this is actually an image. It has a lot of colors to it, a lot of aspects to it. So let me walk you through it. This is actually a fruit fly zygote, very early in the development of the fruit fly. And you can see that there are all of these different colors. The different colors have names, you don't need to know the names, just sort of know that these are genes. These are patterning genes. So this is gene 1, or gene red, gene blue, gene purple, and so on and so forth.

Now, this is kind of a graph. You have the anterior and posterior moving across here. And then you also have the time, so this is earlier in development and later in development. You can see that this very early organism expresses this blue gene on the anterior side and the red gene on the posterior side very early in development, and this stimulates the formation of tissues in this area. As it progresses on in time, it stops expressing this blue and starts expressing these purple and green genes, but it only does it in these very specific locations. You can see that they actually, over time, become extremely specific, where you can see that right here and here, there are these blue genes expressed, but in this area between them, there's not. And so these patterning genes over time lead to complex structures found in organisms. They can lead to various organs or symmetry, and that's what allows these patterning genes to really control the early development of specific structures in an organism. So now let's move on.

Choose which of the following is true:

• A. Protostomes and Deuterostomes describe the formation of eyes during development
• B. Patterning genes are transcription factors that control the expression of important developmental genes
• C. Ground tissue is found in animal cells
• D. Plat cell walls prevent communication and connection between adjacent plant cells

Which of the following is not a tissue type in plants?

• A. Ground Tissue
• B. Dermal Tissue
• C. Mesodermal Tissue
• D. Vascular Tissue

Which of the following is the name for the group of genes that control development of different body regions (ex:anterior/posterior, dorsal/ventral)?

• A. Segmental genes
• B. HOX genes
• C. Patterning genes
• D. Dividing genes

Here’s what students ask on this topic:

What is the extracellular matrix (ECM) and what role does it play in tissue structure?

The extracellular matrix (ECM) is a complex network of proteins and other molecules that provide structural and biochemical support to surrounding cells. In animals, the ECM includes proteins like collagen, elastin, and fibronectin, which help in cell adhesion, communication, and differentiation. The ECM is crucial for maintaining the physical structure of tissues, enabling cells to form organized layers and structures. In plants, the ECM is referred to as the cell wall, which includes cellulose and other polysaccharides, providing rigidity and protection. Overall, the ECM plays a vital role in tissue integrity, repair, and cellular signaling.

How do cell adhesion molecules (CAMs) function in multicellular organisms?

Cell adhesion molecules (CAMs) are proteins located on the cell surface involved in binding with other cells or the extracellular matrix. In multicellular organisms, CAMs facilitate cell-to-cell adhesion, which is essential for the formation and maintenance of tissues. They help cells stick together, communicate, and coordinate their functions. CAMs are crucial during embryonic development, wound healing, and immune responses. They include cadherins, integrins, selectins, and immunoglobulin superfamily members, each playing specific roles in cellular interactions and signaling pathways.

What are the main types of tissues in plants and their functions?

Plants have three main types of tissues: ground, dermal, and vascular. Ground tissue is involved in metabolism, storage, and support. It includes parenchyma, collenchyma, and sclerenchyma cells. Dermal tissue forms the outer protective layer, consisting of the epidermis and periderm, which protect against water loss and pathogens. Vascular tissue is responsible for the transport of water, nutrients, and sugars throughout the plant. It includes xylem, which transports water and minerals from roots to leaves, and phloem, which distributes sugars produced by photosynthesis.

What are patterning genes and how do they influence tissue development?

Patterning genes are master regulatory genes that control the spatial and temporal expression of other genes during development. They are crucial for establishing the body plan and organizing tissues and organs in multicellular organisms. Patterning genes include transcription factors that regulate gene expression, ensuring that specific genes are activated or repressed at the right time and place. They influence the development of structures such as the head, thorax, and abdomen, and are responsible for the symmetry and organization of tissues. Examples include Hox genes, which determine the identity of body segments in animals.

How do protostomes and deuterostomes differ in their early development?

Protostomes and deuterostomes are two major groups of animals that differ in their embryonic development. In protostomes, the mouth develops from the first opening (blastopore) formed during early embryogenesis, and they typically have a ventral nerve cord. Examples include arthropods and mollusks. In deuterostomes, the blastopore becomes the anus, and the mouth forms secondarily; they usually have a dorsal central nervous system. Examples include chordates and echinoderms. These differences in early development lead to distinct body plans and organ systems in the two groups.