Lesson 1 : Cell Structure and Function
December 18, 2001
In Tiny Cells, Glimpses of Body's Master Plan
By: Nicholas Wade
New York Times
Lesson Plan Dealing with NYT Article:
What is shown in the picture on the left? What is shown in the picture on the right? The picture on the left is a picture of a school. What do you think a school would be like if there was no principal? It might be fun at first, but I think that would come to pass very quickly because you have to someone to control everything that goes on within the school. Just as the principal is in charge of a school, the nucleus is the control center of the cell. An analogy is a comparison between two things to show their similarities in some respect. A school is one example of an analogy for the cell.
SWBAT (Students Will Be Able To)
1. Identify the specialized structures and regions of the cell and the functions of each (PA Standard 3.3.10 B).
2. Explain how plant cells differ from animal cells.
3. Tell the main differences between prokaryotic and eukaryotic cells.
4. List and explain the three main ideas of the "Cell Theory."
5. Develop a cell analogy.
Does anyone know any other parts (parts of the cell are called organelles) of the cell besides the nucleus?
Plasma Membrane (or Cell Membrane):
The plasma membrane bounds the cell. It controls the movement of materials into and out of the cell. It's a complex double layer made up of phospholipids and proteins. Phosopholipids are a special class of lipids that contain two fatty acid "tails" and one negatively charged phosphate "head." The two fatty acid "tails" are hydrophobic (water hating) and the phosphate "head" is hydrophilic (water loving). The plasma membrane is made up of two layers of phospholipids. The hydrophobic fatty acid tails face inwards and the hydrophilic phosphate heads face outwards.
Analogy: The door and exterior of the school would represent the plasma membrane because they control who and what enters the school.
The shape of the cell is determined by a network of fibers called the cytoskeleton. The two main fibers involved are microtubules and microfilaments. Microtubules are made of the protein tubulin and participate in cell division and movement. Microfilaments are also important in cell movement. They are thin, rod-like structures composed of the protein actin.
Analogy: The cytoskeleton could be represented by steal or wooden beams that hold the structure of the school together.
Nonmembrane Bound Organelles
Ribosomes are sites of protein synthesis; their only function is to build proteins for the entire cell. They're round structures composed of RNA and proteins. They can be either free floating in the cell or attatched to another structure called the endoplasmic reticulum (ER).
Analogy: The classrooms of the school could represent the ribosomes of the cell. Just as the ribosomes are the sites where proteins are made (food for the cell), the classrooms are the sites where "brain food" or knowledge is made.
These are small, paired cylindrical structures that hang out near the nucleus. As animal cells prepare for cell division these two centrioles separate and go to opposite ends of the cell. They produce fibers called microtubules, which pull the chromosomes apart and move them to opposite ends of the cell. They are common in animal cells, but not found in plant cells. These will be discussed in more detail when we learn about cell reproduction.
Membrane Bound Organelles
Endoplasmic reticulum (ER):
Endoplasmic reticulum is a network of folded membranes that extend through the cytoplasm to the nuclear membrane. There are two kinds of ER: rough and smooth. Rough ER has ribosomes associated with it, while smooth has no ribosomes. The basic function of ER is transport, proteins produced by the ribosomes are transported to regions of the cell where they are need or they are transported to the Golgi body for export from the cell.
Analogy: The ER could be represented by a teacher. The ER is responsible for transporting proteins just as a teacher is in charge of transporting knowledge. The teacher is in control of the classroom (ribosome).
The function of Golgi apparatus is two-fold: modification of lipids and proteins and storage and packaging of materials that will be exported from the cell. The Golgi apparatus is often called the "shipping department" of the cell. The vesicles that pinch off from the Golgi apparatus move to the cell membrane and the material in the vesicle is released to the outside of the cell.
Analogy: In a way, parents or guardians could be used as a representative for the Golgi body since they pick up where the ER left off. The Golgi bodies modify, process, and sort the protein products. In a similar way, parents or guardians are responsible for their children once they leave the responsibility of their teacher (ER). Parents or guardians can also become involved in modifying the information the teacher tries to teach the students.
These are tiny sacs that carry digestive enzymes, which they use to break down old, worn out organelles, debris, or large ingested particles. They are the cleanup crew.
Analogy: The custodial crew of the school would represent the lysosomes. They are responsible for keeping the school clean.
Vacuoles store water and a number of other things, such as food, wastes, salts, or pigments. There are a wide variety of vacuoles, containing a wide variety of substances.
Analogy: Storage areas of the school, such as closets that hold books or other supplies, could represent vacuoles.
Double Membrane Bound Organelles
The nucleus is considered the control center of the cell. It is usually the largest organelle. It not only directs what goes on in the cell, it is also responsible for the cell's ability to reproduce. It's the home of the hereditary information, DNA, which is bunched into large structures called chromosomes. The nucleolus is visible in the nucleus, and it makes another cell organelle called the ribosomes. The nucleus is bound by the nuclear envelope, a phosopholipid bilayer similar to that of the plasma membrane.
Analogy: The principal of the school would represent the nucleus because he or she would be in control of what goes on throughout the entire school.
The mitochondria is the powerhouse of the cell. They're responsible for converting the energy from organic molecules into useful energy for the cell. The basis of energy in the cell is ATP. Mitochondria are usually shaped like stubby cigars sometimes they are round. They have a double membrane consisting of an outer membrane and a highly folded inner membrane. The inner mitochondrial membrane forms folds called cristae. Most of the production of ATP is done in the cristae.
Analogy: The school cafeteria could represent the mitochondria. The cafeteria would be where all of the employees and students of the school get energy to function through the day by eating food.
Do plants and animals function in the exact same way? How are they different? How are they alike? Do you think that plant cells and animal cells have the exact same structures?
As mentioned above, plant cells have no centrioles. Unlike animal cells, plant cells have a protective outer covering called the cell wall. The cell wall is made up of cellulose. In our school analogy, the cell wall could be represented by a fence around the school and its property. Plant cells also have chloroplasts, which contain chlorophyll. Chlorophyll is full of the light-capturing pigment which gives plants their characteristic green color. Chloroplasts could represent the windows that let sunlight into the school. Another difference between plant and animal cells is that most of the cytoplasm within a plant cell is usually taken up by a huge vacuole that crowds the other organelles.
We talked about plants and animals so far. Are there any other types of living forms that wouldn't fall into the plant or animal categories?
The plant and animal cells described so far are eukaryotic cells. Eukaryotic organisms include all living things except for bacteria and cyanobacteria (blue-green algae). Bacteria and cyanobacteria are known as prokaryotes. The major similarities between the two types of cells (prokaryote and eukaryote) are:
1. They both have DNA as their genetic material.
2. They are both membrane bound.
3. They both have ribosomes.
4. They have similar basic metabolism.
5. They are both amazingly diverse in forms.
The major and extremely significant difference between prokaryotes and eukaryotes is that eukaryotes have a nucleus and membrane-bound organelles, while prokaryotes do not. The DNA of prokaryotes floats freely around the cell; the DNA of eukaryotes is held within its nucleus. Also, on average, eukaryotic cells are ten times the size of prokaryotic cells.
Can you think of any living thing that doesn't have cells? Does like always beget like? (For example, can a dog and a cat ever mate?)
The Cell Theory:
1. All living things are made of cells.
2. Cells are the basic units of life.
3. Cells come only from other cells
When I discussed the parts of the eukaryotic cell I tried to compare them to a school. Come up with your own cell analogy. Start by saying, "The cell is like a __________ because _________." Then continue using that pattern for the various organelles.
This website may be helpful. However, you don't have to complete the activities listed on it.
Cells Alive! : Compare the plant, animal, and bacteria cell models
Interactive flashcards, matching, and concentration to help review organelle functions
Drag and drop cell organelle game
Review the organelles in the interactive cell
Check out the cell movie and quiz and explore other parts of this site: Choose "cell structures" under the lists of movies
Cell Webquest : Activity #1 from this site
Compare different types of cells in the cell gallery
Later on we will be discussing the cell cycle and mitosis. You may want to view the following animations and activities ahead of time.
Cells Alive! : Cell Cycle Animation
Cells Alive! : Mitosis Activity
Name and briefly describe the organelles of the animal cell. Briefly discuss the main differences between animal and plant cells and between prokaryotes and eukaryotes. Be sure that the student comprehend that the organization and specialization of the cell is what enables it to work so smoothly. Address any student questions.
Click here for references for this lesson.
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