Lesson Video: Animal and Plant Cells Biology

In this video, we will learn how to recall the main sub-cellular structures of animal and plant cells, and describe their functions.

16:07

Video Transcript

In this video, we will learn about the subcellular structures called organelles found in plant and animal cells. We will describe their form and their functions. Then we’ll look at some practice questions. And finally, we’ll review what we’ve learned. Let’s begin by describing cells in general. Hopefully, some of this is information that you’re already familiar with.

Cells are the basic unit of life. That means that cells are the smallest thing that can be considered to be independently alive. All living things are made of one or more cells: plants, animals, fungi, protists and bacteria, everything that’s considered to be alive. There are certain things that all cells have in common. All cells have a way to define their boundaries and to control what enters and leaves the cell. This is called the cell membrane. All cells have a liquid substance that fills their internal space. This jellylike fluid is called cytoplasm.

All cells contain genetic material that directs the functions and activities of the cell. This genetic material is called DNA. If the DNA of the cell is floating in the cytoplasm, the cell is classified as prokaryotic. Bacteria are prokaryotic cells. If the DNA is contained and protected within a structure known as the nucleus, the cell is classified as eukaryotic. Plants, animals, fungi, and protists are all made of eukaryotic cells. Lastly, all cells contain tiny structures that interpret the information stored in DNA by translating it into proteins. These structures are called ribosomes.

These four structures, the cell membrane, the cytoplasm, DNA, and ribosomes, are found in all living cells. However, different types of cells have different structures within them in addition to these four. Next, let’s take a look at the structures within an animal cell. Animals like you, me, cats, fish, lizards, insects, birds, and more are made of cells that have certain features in common. This is a simplified drawing of an animal cell. This is the cell membrane, which we introduced a little bit earlier. The cell membrane defines the boundary of the cell and controls what can enter and what can leave.

The cell membrane is made of molecules called phospholipids. These phospholipids are arranged in two layers, so we refer to the cell membrane as a phospholipid bilayer, bi- meaning two. The phospholipids arranged in this way give the cell membrane lots of special properties, like being flexible and self-sealing and being permeable to some things but not to others. We’re also familiar with the cytoplasm that fills the inside of the cell. Cytoplasm is a word that means cell liquid. Cytoplasm is mostly water, but it also contains proteins, nutrients, and minerals.

We often draw cells as two-dimensional, but it’s important to remember that they are not flat. You can think of the cell as a water-filled balloon. The outer membrane is thin and flexible. The inner filling helps to give the cell its three-dimensional shape. The subcellular structures or parts that make up a cell are called organelles. Organelle is a term that means little organs. One example of an organelle is the nucleus, which we’ve learned stores and protects the genetic material or DNA inside of all eukaryotic cells. Each cell only contains one nucleus. Some students draw an analogy between the nucleus in your cell and the brain in your body because the nucleus stores information and controls the activities of the cell.

The nucleus can also be distinguished by some other special features. The membrane that surrounds the nucleus is like the membrane that surrounds the cell, but the nucleus has a double membrane. The nucleus also has pores. The pores allow certain things to easily move into and out of the nucleus but keeps the DNA safely protected inside. The ribosomes are tiny organelles that interpret the genetic code and make proteins. Proteins are important biological molecules that carry out the majority of a cell’s functions. The way this happens is called the central dogma of biology, or protein synthesis, which, put simply, states that DNA is transcribed into RNA, which is then translated into a protein.

In this drawing, we see one other important organelle. These bean-shaped structures are called mitochondria, the singular of which is mitochondrion. Mitochondria are often referred to as the powerhouse of the cell because they convert the chemical energy found in glucose, which animals get from their food, into stored cellular energy in a molecule called ATP. The process of turning glucose and oxygen into the stored energy in ATP, water, and carbon dioxide is called cellular respiration. This process is the reason that we breathe in oxygen and breathe out carbon dioxide, a cycle also known as respiration.

Mitochondria are bean shaped. They possess a smooth outer and a folded inner membrane. The folds in the inner membrane facilitate the complex chemical reactions involved in cellular respiration. Mitochondria, interestingly, contain their own ribosomes and DNA, a feature which lead scientists to believe that, long ago, these were separate prokaryotic organisms that formed a symbiotic relationship with eukaryotic cells. Most animal cells also contain a number of additional organelles. For now, let’s move on and take a look at the structures within a plant cell.

Here we see a simplified diagram of a plant cell. It’s different than an animal cell in several different ways. Sometimes students mistakenly get the idea that all plant cells are square and all animal cells are round. The truth is that plant cells and animal cells come in a variety of different shapes depending on their function. The correct way to distinguish between them is to look at the structures inside. Plant cells contain all of the structures that we’ve already labeled in animal cells. So we won’t read them again right now. Instead, we’ll just focus on the three structures that you find in plant cells and not an animal cells.

You’ll notice that this plant cell has a thick outer layer that the animal cell did not. The cell wall is a tough outer structure that gives the plant cell its shape. Under different conditions, the cell may fill with water and become turgid. Or fluid may leave the cell, making it flaccid. In all conditions, the cell wall remains unchanged. Plant cells contain a special organelle that they used to store water. The central vacuole looks like a big bubble and, in some cases, will take up the majority of the space in the plant cell. Other types of cells, including animal cells, also contain vacuoles. But the central vacuole is found only in plant cells. It’s especially large and helps to give the plant cell its structure.

The last organelle that we see here that’s present in plant cells and not in animal cells is the chloroplast. Chloroplasts are the part of the plant cell that give plants their green color. Since plants don’t eat food like animals do, they have to synthesize or make their own glucose using sunlight. This is a process known as photosynthesis, a word that means to make something using light. During photosynthesis, plants use water, the energy in sunlight, and carbon dioxide to make glucose and oxygen. Let’s take a closer look at a chloroplast.

The chloroplast is surrounded by a double membrane. It’s filled with series of stacked membranes that facilitate the complex chemical reactions involved in photosynthesis. Like the mitochondria, a chloroplast has its own DNA and ribosomes, leading scientists to believe that they, too, were once independent prokaryotic organisms that formed symbiotic relationships with eukaryotic cells. Now that we’ve learned about the subcellular structures found in plant cells and in animal cells, let’s try a few review questions.

The diagram provided shows the basic outline of an animal cell. Which component is represented by W? Which organelle is represented by Z?

Before we attempt to answer the question, we’ll go ahead and review the things that we know about animal cells. An animal cell is a type of eukaryotic cell. This means that this cell possesses a nucleus in which the DNA is stored. Also, since we know that this is an animal cell and not a plant cell, we know that this cell will not have a cell wall, will not possess a central vacuole, and will not contain any chloroplast to carry out photosynthesis. So what is in the animal cell that we see pictured here?

Well, first, this cell, like all living cells, possesses a cell membrane. The cell membrane defines the boundary of the cell and also controls what enters and leaves. The animal cell possesses cytoplasm, the jellylike substance that fills the cell and helps to give it its shape. In this cell, we also see several mitochondria. These organelles are responsible for carrying out cellular respiration, a process which stores cellular energy in the form of ATP. Mitochondria are bean shaped and possess a smooth outer and folded inner membrane.

Finally, we see the nucleus, which we mentioned just a little bit earlier. The nucleus is surrounded by a double membrane that has openings called nuclear pores. The nucleus is responsible for storing and protecting the genetic material, also called DNA. Now, we’re ready to answer our question. Which component is represented by W? W represents cytoplasm. Which organelle is represented by Z? Z represents the cell membrane.

Let’s try another practice question.

Which of the following organelles is found in the majority of both plant and animal cells? (A) Chloroplast, (B) cell wall, (C) large vacuole, or (D) cell membrane.

This question is asking us to select the organelle among the choices which we’re likely to find in both plant and animal cells. First, let’s recall that both plant and animal cells are types of eukaryotic cells, meaning that they have many things in common, most importantly, a nucleus that contains and protects the DNA. While these cells have much in common, they also have many differences. Let’s review what we know.

Here we have a simplified diagram of an animal cell and a plant cell. We can see that both the plant and animal cell possess a cell membrane, a thin and flexible outer layer that defines the cells boundaries and controls what enters and what leaves. Both the plant and animal cell possess mitochondria, bean-shaped organelles with double membranes that are the site of cellular respiration. Both the plant and animal cell possess ribosomes, tiny organelles that are the site of protein synthesis.

And finally, as we’ve mentioned before, both of these cells will possess a nucleus, an organelle found in all eukaryotic cells whose job it is to protect and store the genetic material or DNA. However, we see some additional structures in the plant cell that we did not see in the animal cell. The plant cell possesses a cell wall or a rigid outer layer. The plant cell also possesses a central vacuole that functions to provide cell storage as well as cell structure. The plant cell also contains chloroplasts, which are the site of photosynthesis.

Now, we’re ready to answer our question. Which organelle is found in both plant and animal cells? Well, chloroplasts are found in only plant cells, and so are cell walls. A large vacuole, also called a central vacuole, is another structure found in plant cells and not in animal cells. However, the cell membrane, which defines the boundary of the cell and controls what can enter and what can leave, is found in both plants and animal cells.

Let’s try one last practice question together.

State the organelle being described: Only found in plant cells, this is a layer made of cellulose that surrounds the cell to provide structure and support.

This question is asking us to identify the organelle or subcellular structure being described in the prompt. It must be exclusive to plant cells, found on the outside of the cell, and it must provide structure and support to the cell. In order to answer this question, first we’ll draw and label a plant cell. Then we’ll identify the parts that are only found in plant cells. And then we’ll be able to choose our answer.

Here’s a simplified diagram of a plant cell. Let’s label what we see. The plant cell has a cell membrane, which defines the boundary of the cell and controls what enters and what leaves. The plant cell contains cytoplasm, a jellylike fluid that fills the internal space of the cell. The plant cell contains ribosomes, tiny organelles that are the site of protein synthesis. We also see several mitochondria, bean-shaped organelles that are the site of cellular respiration. The plant cell also contains a nucleus, an organelle which stores and protects the genetic material or DNA.

In addition to the structures we listed, the plant cell possesses a cell wall, a rigid outer layer that provides structure and support. It possesses several chloroplasts, organelles that give the plant its green color and are the site of photosynthesis. The plant cell also possesses a large central vacuole, an organelle that provides both storage and structure to the plant cell. Well, we’ve labeled all the parts of our cell.

Let’s recall that our question is looking for an organelle that’s only found in plant cells. All of these organelles to the right are found in both plants and animal cells, while the ones on the left are only found in plant cells. So the correct response must be cell wall, chloroplast, or central vacuole. Of these three, the layer that surrounds the cell to provide structure and support is the cell wall.

Next, let’s take a moment to review what we’ve learned in this lesson. In this video, we learned that organelle is what we call specialized subcellular structures. We learned there are certain organelles that can be found in all living cells, some organelles that are found in both plant and animal cells, and some organelles that are found in plant cells but not animal cells. All cells possess a cell membrane, cytoplasm, and ribosomes. Also found in both plant cells and animal cells, are several mitochondria and a nucleus. And finally, organelles that we find in plant cells and not in animal cells include the cell wall, the central vacuole, and the chloroplasts.

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