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Fluorescence-stained cell undergoing mitosis

In this image, a fluorescently stained cell is shown undergoing mitosis. The cell membrane is stained red and the green stains show the mitotic spindles inside the cell. The chromosomes are shown in blue.
A lung cell from a newt, commonly studied for its similarity to human lung cells, is stained with fluorescent dyes. The green stain reveals mitotic spindles, red is the cell membrane and part of the cytoplasm, and the structures that appear light blue are chromosomes. This cell is in anaphase of mitosis. (credit: “Mortadelo2005”/Wikimedia Commons)

Chapter objectives

After studying this chapter, you will be able to:

  • Describe the structure and function of the cell membrane, including its regulation of materials into and out of the cell
  • Describe the functions of the various cytoplasmic organelles
  • Explain the structure and contents of the nucleus, as well as the process of DNA replication
  • Explain the process by which a cell builds proteins using the DNA code
  • List the stages of the cell cycle in order, including the steps of cell division in somatic cells
  • Discuss how a cell differentiates and becomes more specialized
  • List the morphological and physiological characteristics of some representative cell types in the human body

You developed from a single fertilized egg cell into the complex organism containing trillions of cells that you see when you look in a mirror. During this developmental process, early, undifferentiated cells differentiate and become specialized in their structure and function. These different cell types form specialized tissues that work in concert to perform all of the functions necessary for the living organism. Cellular and developmental biologists study how the continued division of a single cell leads to such complexity and differentiation.

Consider the difference between a structural cell in the skin and a nerve cell. A structural skin cell may be shaped like a flat plate (squamous) and live only for a short time before it is shed and replaced. Packed tightly into rows and sheets, the squamous skin cells provide a protective barrier for the cells and tissues that lie beneath. A nerve cell, on the other hand, may be shaped something like a star, sending out long processes up to a meter in length and may live for the entire lifetime of the organism. With their long winding appendages, nerve cells can communicate with one another and with other types of body cells and send rapid signals that inform the organism about its environment and allow it to interact with that environment. These differences illustrate one very important theme that is consistent at all organizational levels of biology: the form of a structure is optimally suited to perform particular functions assigned to that structure. Keep this theme in mind as you tour the inside of a cell and are introduced to the various types of cells in the body.

A primary responsibility of each cell is to contribute to homeostasis. Homeostasis is a term used in biology that refers to a dynamic state of balance within parameters that are compatible with life. For example, living cells require a water-based environment to survive in, and there are various physical (anatomical) and physiological mechanisms that keep all of the trillions of living cells in the human body moist. This is one aspect of homeostasis. When a particular parameter, such as blood pressure or blood oxygen content, moves far enough out of homeostasis (generally becoming too high or too low), illness or disease—and sometimes death—inevitably results.

The concept of a cell started with microscopic observations of dead cork tissue by scientist Robert Hooke in 1665. Without realizing their function or importance, Hook coined the term “cell” based on the resemblance of the small subdivisions in the cork to the rooms that monks inhabited, called cells. About ten years later, Antonie van Leeuwenhoek became the first person to observe living and moving cells under a microscope. In the century that followed, the theory that cells represented the basic unit of life would develop. These tiny fluid-filled sacs house components responsible for the thousands of biochemical reactions necessary for an organism to grow and survive. In this chapter, you will learn about the major components and functions of a prototypical, generalized cell and discover some of the different types of cells in the human body.

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Anatomy & Physiology 03 Cellular Organization
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Educational Materials

Sample Questions from the Anatomy & Physiology 03 Cellular Organization Flashcards

Question: Explain in your own words why DNA replication is said to be "semiconservative"?


DNA replication is said to be semiconservative because, after replication is complete, one of the two parent DNA strands makes up half of each new DNA molecule. The other half is a newly synthesized strand. Therefore, half ("semi") of each daughter DNA molecule is from the parent molecule and half is a new molecule.

Question: Visit this link ( to see diffusion and how it is propelled by the kinetic energy of molecules in solution. How does temperature affect diffusion rate, and why?


Higher temperatures speed up diffusion because molecules have more kinetic energy at higher temperatures.

Question: Compare and contrast lysosomes with peroxisomes: name at least two similarities and one difference.


Peroxisomes and lysosomes are both cellular organelles bound by lipid bilayer membranes, and they both contain many enzymes. However, peroxisomes contain enzymes that detoxify substances by transferring hydrogen atoms and producing H2O2, whereas the enzymes in lysosomes function to break down and digest various unwanted materials.

Question: Watch this video ( to learn about the endomembrane system, which includes the rough and smooth ER and the Golgi body as well as lysosomes and vesicles. What is the primary role of the endomembrane system?


Processing, packaging, and moving materials manufactured by the cell.

Question: Watch this video ( to learn about ribosomes. The ribosome binds to the mRNA molecule to start translation of its code into a protein. What happens to the small and large ribosomal subunits at the end of translation?


They separate and move and are free to join translation of other segments of mRNA.

Question: Visit this link ( to learn about mitosis. Mitosis results in two identical diploid cells. What structures form during prophase?


the spindle

Question: Explain why the structure of the ER, mitochondria, and Golgi apparatus assist their respective functions.


The structure of the Golgi apparatus is suited to its function because it is a series of flattened membranous discs; substances are modified and packaged in sequential steps as they travel from one disc to the next. The structure of Golgi apparatus also involves a receiving face and a sending face, which organize cellular products as they enter and leave the Golgi apparatus. The ER and the mitochondria both have structural specializations that increase their surface area. In the mitochondria, the inner membrane is extensively folded, which increases surface area for ATP production. Likewise, the ER is elaborately wound throughout the cell, increasing its surface area for functions like lipid synthesis, Ca++ storage, and protein synthesis.

Question: What materials can easily diffuse through the lipid bilayer, and why?


Only materials that are relatively small and nonpolar can easily diffuse through the lipid bilayer. Large particles cannot fit in between the individual phospholipids that are packed together, and polar molecules are repelled by the hydrophobic/nonpolar lipids that line the inside of the bilayer.

Question: Watch this video ( to learn about DNA replication. DNA replication proceeds simultaneously at several sites on the same molecule. What separates the base pair at the start of DNA replication?


an enzyme

Question: What do osmosis, diffusion, filtration, and the movement of ions away from like charge all have in common? In what way do they differ?


These four phenomena are similar in the sense that they describe the movement of substances down a particular type of gradient. Osmosis and diffusion involve the movement of water and other substances down their concentration gradients, respectively. Filtration describes the movement of particles down a pressure gradient, and the movement of ions away from like charge describes their movement down their electrical gradient.

Question: Why is receptor-mediated endocytosis said to be more selective than phagocytosis or pinocytosis?


Receptor-mediated endocytosis is more selective because the substances that are brought into the cell are the specific ligands that could bind to the receptors being endocytosed. Phagocytosis or pinocytosis, on the other hand, have no such receptor-ligand specificity, and bring in whatever materials happen to be close to the membrane when it is enveloped.

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Disclaimer:  This course does NOT provide the education or experience needed for the diagnosing or treating any medical condition, all site contents are provided as general information only and should not be taken as a medical advice.
Source:  OpenStax College. Anatomy & Physiology, OpenStax-CNX Web site., Jun 11, 2014
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