Unit test scheduled for 14 November.
Cell Membranes Tutorial from the Biology Project
The last few units dealt with biology at the molecular level (and they won't be the last). Now we move up to the next level, that of the cell. In this unit we focus on the basic organization of cells, their internal structure, and some basic elements of cellular function. A following unit will explore the details of complex membranes that make up the outer boarder of cells and the structure of many of the internal cellular components. One of the challenges of this unit is the vocabulary; you need to learn and use a large number of new and sometimes strange sounding terms associated with the study of cells (i.e. cytology) and tissues (i.e. histology).
Learning Objectives: the successful student will be able to ...
- state the tenets of the Cell Theory as well as some of its exceptions.
- list several individuals who played a significant role in the development of the Cell Theory and briefly describe their contributions.
- explain why the "surface area to volume" problem limits the size of cells, perform simple calculations of surface area and volume of cells, and describe various strategies cells use to overcome this problem.
- name and describe the functions of the parts of a compound microscope and briefly describe other types of microscopes such as the transmission and scanning electron microscopes.
- distinguish between prokaryotic cells and eukaryotic cells and give examples and recognize examples of each.
- describe in some detail the structure of a "typical" prokaryote, name the two domains of prokaryotes, and give examples of beneficial, harmful, and extremophile prokaryotes
- name the important organelles of a eukaryotic cell, describe their structure, function, and their structural and functional relationship to other organelles.
- write a brief essay describing the "endosymbiotic" theory of eukaryote evolution and its supporting evidence.
- define and give examples of tissues, organs, and organ systems.
Lesson One: The Cell Theory, Module 14 pages 69-70.
Cells play such an import role in biology they have their own theory. This is not a theory that sprang up suddenly from the work of one or even a few scientists. It took years to emerge as a concept that brought together the contributions of many people working independently of one another. The Cell Theory is usually stated as two to four basic tenets:
- Cells are the basic, fundamental unit of life.
- All living organisms are composed of one or more cells.
- Living cells originate from other living cells.
Your text combines 1 and 2 of this list; what's important are the important concepts about the fundamental role of cells and where they come from.
Appreciate the role that Robert Hooke played in the development of the cell theory, but keep in mind that many scientists made important contributions. Read the article from the Complete Microscope Guide which provides an excellent overview of the long development of the Cell Theory. As you read this article pay attention to the following points:
- The long time line it took for the Cell Theory to develop.
- The international effort this took; from the beginning Biology has been, like most sciences, a world wide effort.
- The role (and limitations) of technology in the development of the Cell Theory.
- The contributions of individual scientists; particularly those who made early contributions that led to the tenets of the Cell Theory listed above and those that helped develop the first effective microscopes.
Homework U03-1, Due 24 October. Select three scientists other than Hooke and write a brief summary of their contribution to the developent of the Cell Theory. Submit your work via your FBA email account.
Lesson Two: The surface area to volume problem, Module 14 page 70.
Most cells are small, quite small, and there is a reason for this; geometry. Cells must obtain nutrients, water, and oxygen from their environment. To do this they must move these materials across a membrane that forms the boarder between the cell's environment and its interior.Try the animation on page 70 to get an appreciation for the range of cell sizes and a perspective of how small they actually are compared to organisms such as humans. Be sure you understand the relationship between surface area and volume of a solid (e.g. a cell) as it gets larger and a cells ability to aquire nutrients from its environment.
Homework U03-2, Due 28 November. On a piece of graph paper plot the change in surface area and the change in volume of a cubic cell with linear demensions growing from 1 to 2 to 4 to 8 to 10 to 20 micrometers. It will be much more instructive if you put both curves on the same graph.
Lesson Three: Prokaryotes and Eukaryotes, Module 14 page 71.
There are two types of cells, prokaryotic and eukaryotic. Although very different from one another in most respects, they also share much in common. You need to understand these differences and similarities and their implications for the evolution of cells.This page introduces you to a much longer study will make of the structure, function, and diversity of cells. Be aware that the distinction between Prokaryote and Eukaryote organisms is a bit out dated, but it is still a useful way to organize our study of cells. Appreciate the important differences between prokaryotes and eukaryotes, but also appreciate the many similarities. These similarities are the foundation for the evolutionary concept that all living organisms are ultimately related to one another. Finally, have a general understanding of the techiques of cell culture, fractionation, and centrifugation. We will study several experiments that use these basic laboratory techniques.
Homework U03-3a, Due 29 November. Take the self test on page 73 and submit your answers online.
Read the following page by Lynn Fancher from the College of DuPage. Not only should you understand the differences and similarities between prokaryotes and eukaryotes, you should also appreciate the evidence that eukaryotic cells evolved from assemblages of symbiotic prokaryotes.
It turns out that not all prokaryotes are the same. Go to the tree of life at the University of California Museum of Paleontology and read their introduction to the classification of organisms into the three domains. On the diagram of the three domains, click on the Bacteria and then the Archaea. In both cases, then click on the Systematics link and explore the cyanobacteria and the various types of Archaea bacteria.
Homework U03-3b, Due 4 November.
Read the article by Carl Zimmer on eukaryote evolution. Summarize this article using the posted guidelines. Be sure you use your own words to avoid plagiarism. Post your summary to the class blog. Instructions to follow in class. Once you have done that, you must also submit comments on the summaries of two of your classmates.
Image of sea anemone with symbiotic green algae in its cells from the Smithsonian National Zoological Park.
Lesson Four: Eukaryote cell structure and function, Module 15 pages 74-77.
This lesson will briefly survey the structure of a "typical" eukaryotic cell. Keep in mind that there is really no such thing as a typical cell. The diversity of cell types within and among species of eukaryote species is enormous. We will only touch upon the structures (or organelles) that make up a eukaryotic cell. As we progress through other units, we come back to these organelles and fill in the details. Your objective in this lesson is to learn the names, basic structure, location, and function of these organelles. In addition, you should appreciate the common features these organelles have in their construction and their functional interrelationships.This unit has several excellent diagrams of animal and plant cells that show the various organelles in relationship to one another. Use the interactive diagrams to clarify the functions of these organelles and there functional connections with other organelles in the cell. In particular pay attention to the following organelles in both animal and plant cells.
- Nucleus: understand the arrangement of the membranes of the nuclear envelope and what "chromatin" is. Understand the primary function of the genes located on the chromosomes located in the nucleus.
- Rough and smooth endoplasmic reticulum and the ribosomes: Again, appreciate the membrane structure of these structures and their association with the ribosomes. Understand the different function of the smooth vs rough ER. Know the structural and functional relationship between these structures and the nucleus.
- Golgi Apparatus: Understand the membrane structure of this organelle, its structural similarities to the endoplasmic reticulum, and its function. Be able to describe how material manufactured on the endoplasmic reticulum is transported to the Golgi Apparatus and the role of the membranes in this process.
- Vacuoles, Peroxisomes, Lysosomes, and Pinocytotic vesicles: Appreciate the similarities in the structure of these organelles and the differences in their function. Where applicable understand their functional relationship to the Golgi Apparatus. Appreciate the role of these structures in the storage and transport of materials within the cell and across the cell membrane.
- Other organelles: For the remaining organelles, have a general understanding of their structure and function. For most of these, we spend a good deal of time with them in future units.
Homework U03-4, Due 6 November. Write a brief paragraph addressing the following questions and email your work to me using your Fontbonne Academy account.
- A number of textbooks have used the analogy of a factory to describe the functions and relationships among the cellular organelles you just studied with various cell structures playing roles similar to those that occur in the manufacture of complex products such as automobiles or buildings. Using the organelles listed above from nucleus to pinocytotic vesicles, describe their functions and their relationships to one another using this "factory" analogy.
- Using information from your readings describe two different situations where a medical condition is a consequence of the disruption of the normal functions of a cell organelle.
Lesson Five: Basic elements of the cytoskeleton. Module 16, pages 79-83
In the previous lessons you were introduced to some of the basic structural and functional organization of eukaryotic cells. This lesson expands that theme and concentrates on the complex network of fibers and other proteins that form the internal cytoskeleton of cells and the interconnections between cells. Most of the structures you have studied are constructed with the basic cell membrane composed of a phospholipid bilayer and its associated membrane proteins. The elements of the cytoskeleton are quite different and much more variable. They have a wide range of functions including support of the cell and its organelles, movement of material within the cell, movement of the cells themselves, and the regulation of cell processes.
Read Module 16. Be sure you can discuss the basic characteristics and functions of the three major types of cytoskeletal elements; the microtubules, intermediate filaments, and microfilaments. In particular understand how the cytoskeleton functions to move material such as vessicles and other organelles in the cell and how it is used in flagella and cilia for cell locomotion.A more extensive treatment can be found at the University of Arkansas for Medical Sciences. Note the arrangement of the microtubules in the cilia and their relationship to the dynein protein arms. These are the proteins involved in the movement mechanisms of the cilia and flagella. Here is a short animation reviewing this material. Another excellent animation.