In this explainer, we will learn how to recall different specialized cells, describe their adaptations, and relate these adaptations to their functions.
When you imagine a cell, you probably picture something like Figure 1. This common image is of what we call a “generalized” cell. This means that it generally represents the common structure of a typical cell. However, the actual cells in our bodies are “specialized.” This means that they possess adaptations that allow them to carry out their specific job.
Key Term: Structure
The structure is the shape and organization of related elements of an object or biological component.
Key Term: Function
The function is the job of an object or biological component, or what it does.
One of the core concepts of biology is that structure is always directly related to function. The structure of an object is its shape and its parts. Function refers to what a thing does or what its job is. When we say that a cell is specialized, we mean that it has a specific structure that allows it to carry out a particular function.
Key Term: Specialized
An object or biological component is specialized when it possesses specific structures that make it adapted to its particular function.
Let’s look at some examples of human cell types including the egg cell, the sperm cell, muscle cells, red blood cells, nerve cells, and ciliated cells and examine how their structure is adapted to their function.
An egg cell is also called an ovum, or an oocyte. The suffix “-cyte” means “cell.” Egg cells are reproductive cells. Reproductive cells are cells that play a role in producing offspring and are also referred to as gametes. In humans, the egg cell is the female reproductive cell. The egg cell is produced by the ovaries, which are organs in the female reproductive system. If an egg cell is fertilized by the male reproductive cell or the sperm cell, it will develop into an embryo in the uterus and will eventually grow into a baby human.
The egg cell, as shown in Figure 2, has several adaptations that allow it to carry out its function as the female reproductive cell. It is larger than a normal cell and has the basic cell organelles, structures, and extra nutrients necessary to begin embryonic development if fertilized by a sperm cell. It also has a special jellylike coating, which hardens immediately after fertilization. This prevents more than one sperm cell from fertilizing the same egg cell. Perhaps most importantly, the egg cell has half of the genetic material that will be inherited by the offspring. This is called a haploid cell. The other half of the genetic material is delivered to the egg cell by the sperm cell. Reproductive cells, like egg cells and sperm cells, are made through a special process that ensures they possess exactly half of the parent’s DNA.
Key Term: Egg Cell
An egg cell is the female reproductive cell, or gamete.
Key Term: Haploid
A cell is referred to as haploid when it contains half of the typical amount of genetic information for an organism. Haploid cells are typically reproductive cells, or gametes.
A sperm cell, as shown in Figure 3, is also called a spermatocyte. Sperm cells are reproductive cells, like egg cells, so they play a role in producing offspring. In humans, the sperm cell is the male reproductive cell.
Key Term: Sperm (Sperm Cell)
Sperm are the male reproductive cells, or gametes.
A sperm cell has special adaptations that are complementary to those of the egg cell. It has a streamlined shape with a long tail, called a flagellum. The sperm cell has this particular shape because it needs to swim through the uterus in order to fertilize an egg cell. Typically, many sperm cells are produced, which are much smaller than the egg. At the base of the flagella, the sperm cell possesses many mitochondria. This ensures that the sperm cell has enough cellular energy for its journey. In addition, the tip of the sperm cell holds an enzyme-filled organelle called an acrosome. This structure helps the sperm cell to penetrate the protective covering of the egg cell in order to fertilize it. You can see this in Figure 4.
Like the egg cell, the sperm cell is haploid, and it carries half of the genetic material, or DNA, that the cells of the offspring will inherit. The other half comes from the mother and is already present within the egg cell.
Example 1: Recalling Adaptations Regarding Genetic Material Found in Sperm Cells and Egg Cells
Which of the following is correct about the genetic material contained in sperm and egg cells?
- Sperm cells contain half the amount of DNA that egg cells do.
- Egg cells contain half the amount of DNA that sperm cells do.
- Sperm and egg cells are haploid, so they contain half the genetic material of a normal body cell.
- Sperm and egg cells contain double the normal number of chromosomes of a normal body cell.
Answer
Each of the cells in our bodies possesses a nucleus that contains and protects our genetic material, or DNA, in structures called chromosomes. DNA tells us who we are and tells our cells what to do. One inherits half of their genetic material from their mother and half from their father. This is accomplished through the female reproductive cells, called egg cells, and the male reproductive cells, called sperm cells. These specialized cells are specifically adapted for reproduction. They join together in a process called fertilization, which is the first step in creating offspring through sexual reproduction. These two cells combine to provide the offspring with the genetic material their cells need to develop normally. And we know that half that DNA comes from the mother’s egg cell and half from the father’s sperm cell.
This leads to the conclusion that the correct answer must be that sperm and egg cells are haploid, so they contain half the genetic material of a normal body cell.
Muscle cells, as shown in Figure 5, are also referred to as myocytes. A muscle cell is specialized to contract, or shorten, which produces the forces that cause movement in the body.
Key Term: Muscle Cell
A muscle cell is a cell adapted to cause movement. Muscle cells possess special contractile proteins (protein filaments) that can shorten the cell, generating force.
There are different types of muscle cells that are adapted to their specific functions, but they all have certain features in common. Muscle cells possess specialized protein filaments (contractile proteins) that slide past each other when activated, shortening the cell. These cells possess many mitochondria that provide the additional cellular energy necessary for contraction. They are able to store additional glucose in the form of a poorly soluble molecule called glycogen. This stored form of glucose can later be released to be used in cellular respiration by the mitochondria.
Example 2: Recalling the Adaptations of Muscle Cells
Muscle cells have many adaptations to help them function.
- Which parts of the muscle cells slide over each other to contract the fibers?
- Which part of the muscle cell allows respiration to take place?
- In the muscle cell, glucose is stored when it is not needed for respiration. Which compound is glucose stored as?
Answer
Part 1
Muscle cells are specialized cells. This means that they possess specific adaptations that allow them to carry out a particular function. The function of muscle cells is movement. Muscle cells are the primary component of muscle tissue. And muscle tissue is the tissue responsible for movement throughout the body. Muscle tissue contracts, causing our hearts to beat, our stomachs to churn, and our bodies to move. The muscle cells that make up muscle tissue are responsible for this contraction. They possess many strands of proteins that slide past each other, shortening the cell that exerts the force we know as muscle contraction.
Therefore, the parts of the muscle cells that slide over each other to contract are protein filaments.
Part 2
The type of motion explained above requires a large amount of energy. You may recall that cells use glucose and oxygen in a process called cellular respiration to transfer energy into a form that they can use to perform life processes. This cellular respiration primarily occurs in the mitochondria. For this reason, muscle cells each possess many mitochondria.
Therefore, the part of the muscle cell that allows respiration to take place is the mitochondria.
Part 3
Glucose is stored in muscle cells in a special carbohydrate molecule called glycogen. The glucose can be released when needed and used in cellular respiration.
Therefore, the compound glucose is stored as glycogen.
Red blood cells, as shown in Figure 6, are also called erythrocytes. Red blood cells function to carry oxygen from our lungs to the cells throughout our bodies and then return carbon dioxide from the body to the lungs, so it can be exhaled. Body cells use the oxygen during cellular respiration, which is a process that generates cellular energy. This job is so big and important that over of the cells in the human body are red blood cells.
Key Term: Red Blood Cell
Red blood cells, or erythrocytes, are cells adapted to carry oxygen from the lungs to the tissues of the human body. They have a biconcave shape and possess hemoglobin.
Red blood cells have a special, biconcave shape. This means that they are flattened disks with indents on both sides. This shape allows oxygen to efficiently diffuse into all of the cytoplasm within the cell and also allows the red blood cell to pass through narrow blood vessels. In order to accommodate this special shape, mature, human red blood cells do not possess a nucleus. They also lack mitochondria and most other organelles usually found in human body cells. The cytoplasm of red blood cells is rich in a molecule called hemoglobin. Hemoglobin helps the cells to carry oxygen and also gives the red blood cells their characteristic color.
The typical nerve cell, as shown in Figure 7, is also called a neuron. Neurons are cells that are specialized for communication. These cells are a part of the nervous system, and they communicate by transmitting electrical impulses from place to place. This communication network is responsible for monitoring and controlling almost all of our life functions.
Key Term: Neuron (Nerve Cell)
A neuron is a specialized cell that transmits nerve impulses.
Nerve cells possess dendrites that receive signals from other cells. They also have a cell body that carries out the life functions of the cell. Among other things, the cell body contains the nucleus, which directs the cell’s activities, as well as the mitochondria, which carry out cellular respiration.
Nerve cells typically possess an axon that carries the signal from the cell body and toward the target cells. The axon may possess a special coating called a myelin sheath that serves as electrical insulation and speeds up the transmission of electrical signals. At the end of the axon, or the axon terminals, special chemicals called neurotransmitters pass the signal on to the target cell, which may be a nerve cell, a muscle cell, or a gland cell.
The structure of nerve cells is highly specialized. They may possess some or all of these structures depending on their specific function.
Example 3: Recalling the Cells Adapted to Allow Rapid Responses in the Body
Which specialized cells are described as cells that carry electrical impulses to allow rapid responses in the body?
Answer
The system within the body that communicates through electrical impulses and carries out rapid responses to stimuli is called the nervous system. You may recall that organ systems are made of organs, which are made of tissues, which are made of cells. The nervous system contains organs like the brain and spinal cord. These organs are characterized by a specialized type of tissue called “nervous tissue.” And nervous tissue contains many nerve cells, also called neurons. Nerve cells are adapted to function within the nervous system. They have special parts to receive and transmit electrical impulses that allow them to communicate with each other, as well as trigger responses in muscular tissue and glandular tissue.
This means that the cells that carry electrical impulses to allow rapid responses in the body are nerve cells.
Ciliated cells, as shown in Figure 8, are typically a kind of lining cells, or epithelial cells. An epithelial cell is a type of cell that lines the surfaces of your body. These cells are found on your skin, blood vessels, urinary tract, and organs and are present in the layers of cells that coat the insides of many moist surfaces.
Key Term: Ciliated Cells
Ciliated cells are epithelial cells that possess long, thin, hairlike projections called cilia. Cilia move in a sweeping motion, pushing fluids from place to place.
Cilia are hairlike extensions of the cell body that move in a coordinated sweeping motion.
You find ciliated cells in the lining of the lungs and nasal cavities and in the Fallopian tubes where they move the egg cell toward the uterus; they can even be found circulating the fluid that surrounds the spinal cord. Ciliated cells are usually elongated, or columnar, in shape and packed closely together. These cells are characterized by the cilia they have on one end.
Table 1: A table summarizing the structure and function of some specialized cells.
| Specialized Cell | Special Structure | Function |
|---|---|---|
| Egg cell | Haploid nucleus, extra nutrients | Female reproductive cell |
| Sperm cell | Haploid nucleus, flagellum, acrosome | Male reproductive cell |
| Muscle cell | Contractile proteins | Contraction and movement |
| Red blood cell | Biconcave shape, hemoglobin | Carries oxygen and carbon dioxide |
| Nerve cell | Special cell membrane extensions (i.e., dendrite) | Transmits signals |
| Ciliated cell | Hairlike cilia | Moves and circulates fluids |
Specialized cells have specific adaptations that allow them to carry out a particular function. This also means that the function a cell performs is determined by its structure.
Let’s review what we have learned in this explainer.
Key Points
- Examples of specialized animal cells include nerve cells, sperm cells, egg cells, muscle cells, ciliated cells, and red blood cells.
- Specialized cells possess adaptations, special structures and features, which make them adapted to a particular function.
- The structures cells possess are directly related to the function they are able to carry out. For example, red blood cells have a special shape and are full of hemoglobin that helps them to efficiently carry oxygen and carbon dioxide.
