Life Science Curriculum K-7
Submitted by: Annie Kelly
Institution: Azusa Pacific University
Title of Experiment: Comparing Plant and Animal Cells
Green play dough (or modeling clay), M & Ms, sprinkles, large marshmallows, yarn, macaroni noodles, Styrofoam bases (for example the tray from a quarter pound of beef), toothpicks, sandwich bags, and plastic wrap.
Scientific Background of Experiment:
The cell is the basic unit of life, and therefore merits study. By comparing plant and animal cells the relationship between structure and function within each cell becomes evident. The concept that structure and function are related constitutes a reoccurring theme throughout science. Because hands-on learning is an important component of scientific study this exercise is designed to incorporate kinesthetic and visual learning. In order to recall information the neurons within the brain must make specific connections, the hands-on component of this lab facilitates the making of those connections.
The cell is the basic unit of life in that, all living things are composed of cells. Some living organisms are composed of only one cell, such as the animal like Amoeba and the plant like Euglena. The majority of living organisms that we are familiar with, including ourselves, are multicellular. All cells possess some basic characteristics. Cells have at least one membrane. Cells have structures called organelles, which function, as the name implies, like intercellular organs, carrying out specific tasks vital to the life of the cell. Cells have cytoplasm, which holds all the organelles of the cell. The cytoplasm is bound by the outer membrane of the cell, and is the site of the cytoskeleton, the internal support and transport system of the cell. All cells possess a level of organization, which allows them to carry out the processes needed to survive.
Plant and animal cells share one very important feature, the presence of a nucleus. The nuclei of both types of cell consist of four components, the nuclear membrane (or envelope), nucleoplasm, nucleolus, and chromatin. The nucleus functions as the control center for the cell, because it houses the genetic material or DNA (deoxyribonucleic acid). The nucleus gives the instructions and facilitates the processes necessary for cell survival. The nuclear membrane surrounds the nucleus, binding the nucleoplasm, and allowing transport into and out of the nucleus. The nuclear membrane is semi-permeable; meaning that it can select what materials can pass through it, into and out of the nucleus. The nucleoplasm functions like the cytoplasm of the cell. The nucleolus, which is important in the formation of ribosomes, appears as a dense mass of RNA (ribonucleic acid), chromatin, and proteins. Chromatin are coiled strands of DNA that are found spread throughout the nucleus, that come together and coil tightly during cell replication.
There are several organelles that are unique to plant cells. The presence of the cell wall and chloroplasts are defining features of plant cells. The cell wall is a thick outer layer surrounding the cell membrane, which is made up of cellulose fibrils. The cell wall provides both rigid support and protection for the plan cell. The chloroplasts are sac-like structures, filled with stacks of very thin, green sacs called grana. It is the pigment chlorophyll that gives the chloroplast its green color. It is the chloroplasts within plant cells that give the plant its overall green color. Chloroplasts function in photosynthesis. Next to the nucleus they are the most important organelle a plant cell possess, because they facilitate the production of food (in the form of glucose) from nutrients, water, and sunlight. The ability of plant cells to produce their own food sets them apart from animal cells.
Photosynthesis is the defining process of plant cells, whereas cellular respiration is the defining process of animal cells. Cellular respiration is the process by which the cell converts food (in the form of glucose) into energy that can be used to do work. The animal cell needs a unique organelle, called mitochondria to facilitate this process. Mitochondria have been nicknamed the powerhouse of the cell due to the process of respiration, which produces energy in the form of ATP (Adenosine triphosphate). Cellular respiration actually begins in the cytoplasm of the cell and then moves into the inner membranes of the mitochondria called the cristae. The cristae appear as being folded over several times within the mitochondria.
The Golgi apparatus (or Golgi body), and the centrioles are organelles unique to animal cells. The Golgi apparatus is a fairly large organelle that is made of flattened, membranous sacs. The Golgi apparatus is the packaging center of the cell, facilitating the production of other organelles such as lysosomes and vacuoles. Lysosomes are nicknamed suicide sacs because they contain enzymes capable of breaking down the cell. They function in digestion and when the cell dies they split open and digest the dead material. Vacuoles are membrane sacs that function in the storage and transport of food, water and wastes. Plant cells have one very large, central vacuole that takes up the majority of the volume of the cell and also functions is the storage of food, water and wastes. The centrioles are two structures found at the base of the nucleus, that are made up of nine microtubules each. They are important in the process of cell replication.
Finally both plant and animal cells have the capability to produce proteins. Ribosomes are the organelle in which proteins are synthesized. As mentioned earlier, the nucleolus found in the nucleus functions in the production of ribosomes. Ribosomes are found in two places within the cell, free floating and on rough endoplasmic reticulum (ER). There are two types of endoplasmic reticulum found in plant and animal cells, rough and smooth. The smooth ER do not have ribosomes, but function in the production of fats and lipids, which are used throughout the cell, especially in its membranes. Rough and smooth ER are flattened membranous sacs that are located in close proximity to the nucleus. Rough ER transports proteins through its membranes while smooth ER transports lipids and fats.
Gather all needed materials, giving each student an equal number of cell building components. Have each student prepare a chart with three large columns. Label the first column PLANT CELLS, label the second column, BOTH, and label the third column, ANIMAL CELLS. Now subdivide these three major columns into two columns each. Label the first sub-columns in each of the three main columns, STRUCTURE, label the second sub-column in each of the three main columns, FUNCTION. Using the scientific background and the diagrams have each student fill out the chart, writing the structure name in the structure column and its purpose or task in the function column. Once this chart is completed have the students pair up. Now each pair of students should have enough materials to make two cells. Instruct the students to use the materials to create one plant and one animal cell being sure to include every structure from their charts. Allow twenty to twenty five minutes for each group to complete this part of the exercise. At the conclusion of this time examine the models made by the students having them explain why they chose certain materials for certain structures.
One model of each cell should be made according to the key provided. At the conclusion of the exercise the instructor should go over the models, contrasting the plant and animal structures. Review the function of each structure as it is pointed out.
PLANT CELL MODEL
Cytoplasm small Styrofoam tray
Cell Membrane plastic wrap
Cell Wall modeling clay, or play dough
Nucleus half of one large marshmallow
Nuclear Envelope plastic wrap
Nucleolus one M & M
Central Vacuole plastic sandwich bag
Rough ER clay and sprinkles
Smooth ER clay
Chloroplasts green clay or play dough
Grana green M&Ms
Begin by gathering all the needed materials. Use toothpicks to stick structures into the styrofoam base. Line the outside of the styrofoam base with the plastic wrap, next add a thick layer of clay or play dough around the outside of the stay. Cut one large marshmallow in half and wrap it in plastic also. Now stick one M & M and several sprinkles into the goo. Use a toothpick to secure the marshmallow in the styrofoam. Take one sandwich bag, close and secure it in the styrofoam. Place left over materials into the plastic bag to demonstrate the storage capabilities of the vacuole. Make a long, thin roll of clay and fold it over several times, and place this structure close to the marshmallow. Now press several sprinkles into the clay to show the ribosomes on the rough ER. Fold over another thin clay roll several times and place structure close to nucleus also to demonstrate the smooth ER. Finally, make two or three flat circles with the clay. The circles should be of medium thickness. Press green M & Ms into the circles for grana.
ANIMAL CELL MODEL
Same as plant model without the cell wall, central vacuole, chloroplasts, or grana. Use yarn folded over several times for the Golgi apparatus. Use M & Ms scattered throughout the styrofoam base to represent vacuoles. Use maccaroni noodles scattered throughout the styrofoam base to represent mitochondria. Stick the scattered organelles to the styrofoam using small bits of clay or play dough. At the base of the nucleus place two groups of two maccaroni noodles at right angles to each other to represent the centrioles.
Misc. Helpful Information/ Hints/ Suggestions:
It is fun to use several different types of materials to create the models, however it is just as useful to use all clay or play dough. Also using a combination of completely edible materials would make for a great treat at the end of the exercise!