Course Learning Outcomes for Unit III. Reading Assignment. Unit Lesson. UNIT III STUDY GUIDE Essential Parts: Cells

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1 UNIT III STUDY GUIDE Essential Parts: Cells Course Learning Outcomes for Unit III Upon completion of this unit, students should be able to: 1. Evaluate concepts and theories of basic biological sciences including: the scientific method, cellular processes, heredity, and biodiversity. 1.1 Discuss cell theory. 1.2 Discuss how substances are moved in and out of the cellular membrane. 5. Analyze the fundamental structure and function of the cell. 5.1 Describe the structure and function of cell parts including the plasma membrane, organelles and cytoplasm. 5.2 Identify prokaryotic and eukaryotic cells. 5.3 Identify plant and animal cells. Reading Assignment Chapter 4: Life s Home: The Cell Chapter 5: Life s Border: The Plasma Membrane Click here to access the Chapter 4 PowerPoint Presentation. Click here to access a PDF version of the presentation. Click here to access the Chapter 5 PowerPoint Presentation. Click here to access a PDF version of the presentation. Unit Lesson What came first: the chicken or the egg? Where do babies come from? Do flies come from rotting meat? You probably know the answers to these questions already. Living organisms come from other living organisms; however, that still does not really answer the questions. To be more specific, cells come from other cells, and all living organisms are composed of at least one cell. This is part of the cell theory. Eggs and sperm are cells; both are living yet neither can survive very long without the other. Once they combine and form a zygote, that cell divides into two cells those cells divide into four cells and so forth. Eventually, you end up with trillions. Your cells are not all the same, and they do not have the same function. You have about 200 different types of cells; however, all cells on Earth fit into one of two main categories. At one time, we thought all organisms were either plant or animal; therefore, all cells were either a plant cell or an animal cell. Now we categorize cells as either prokaryotic or eukaryotic. Prokaryotic cells are divided into bacteria and archaea while eukaryotic cells include plants, animals, fungi, and protists. We will not spend a lot of time discussing the specifics of those cells because your textbook includes detailed information concerning how cell types differ and what organelles (tiny organs) make them up (Krogh, 2014). If you are having problems imagining what a cell looks like, you can picture a chicken egg. A chicken egg contains a shell made up of calcium carbonate. That shell is not the plasma membrane of the egg. The membrane is under the shell. You have probably peeled a boiled egg. When you removed the shell, you may have noticed a smooth, thin membrane around the white part of the egg under the shell. That was the plasma membrane. The white part of the egg is made up primarily of protein and is actually the cytoplasm of the cell. BIO 1030, General Biology I 1

2 What is the yolk or the yellow part? That is the nucleus the control center that UNIT contains x STUDY the genetic GUIDE material. Most eukaryotic cells contain those three things: the plasma membrane, cytoplasm, and the nucleus. The membrane helps to protect the cell. The membrane acts as a boundary to keep things in or keep things out of the cell. Should the membrane keep everything in or keep everything out? No! If that were the case, the cell could not acquire nutrients, it could not produce products, it could not perform functions, and it could not get rid of waste. The membranes of cells must be able to allow some things in; therefore, cell membranes are said to be semipermeable. What does this mean? What determines what goes in or out? Think about this concept by thinking about your house. The walls, ceiling, and floor would be the membrane. Those act as a barrier to keep things in our out. You do not want birds, snakes, thieves, etc. coming in; however, you do need to allow guests, furniture, groceries, etc. into your house. Yes, you can consciously decide what comes in and out of your house through the door; however, this can only be regulated to a certain point. You do not want dirt or microbes coming in; however, they can still squeeze through cracks and spaces. You cannot bring a car through your door because it cannot squeeze through. Do you see a trend here? If something is small enough to fit through an opening, it can move through an opening. Cells do not have doors; however, they do have pores. The primary component of a plasma membrane is the phospholipid bilayer. That may sound like a foreign term so break it down. Phospholipid means that it is a special lipid with a phosphate attached to it, and bilayer means there are two layers of the phospholipids. The phospholipids look like a lollipop on two sticks. The lollipops are the hydrophilic (water loving) heads, and the sticks are the hydrophobic (water fearing) tails. Again, we will not go into detail about the construction here because Krogh (2014) explains this in full in Chapter 5. The main purpose of our discussion here is to point out that there are pores between the phospholipids, and particles can fit through the pores if they are small enough. Examine the images below: Title BIO 1030, General Biology I 2

3 Iodine is an indicator for starch. That means UNIT if you x STUDY put iodine GUIDE on something that contains starch, the iodine, and starch Title react, and a color change occurs. Iodine is originally a rusty orange color; however, it turns a dark bluish/black color if it reacts with starch. Notice the original color in the dropper in Figure 1. In Figure 2, when the iodine was dropped on the potato and cornstarch solution, the color changed to bluish/black. What do iodine and starch have to do with the plasma membrane of a cell? Nothing really unless one of them can cross the membrane. Figure 3 contains a mug of plain tap water. Figure 4 contains a plastic sandwich bag with a solution of starch. The bag is representing the plasma membrane of a cell and the solution is intracellular fluid (fluid inside the cell). The solution is made up of tap water and cornstarch. The sandwich bag is just an ordinary sandwich bag purchased from the grocery store. You put stuff in bags so nothing gets in the bag and to ensure what is in the bag does not get out. If you put water in a sandwich bag and close it, assuming it did not contain any holes, the water will stay inside the bag. If you place the bag on the counter, the water will still stay inside the bag. Things change when you put a bag in a solution. Living organisms are made up of water; therefore, cells are in solutions that constantly change. Again, the bag or plasma membrane is separating the solution inside the bag and outside the bag or inside the cell and outside the cell. Molecules will move across a membrane if there is a concentration gradient and if the molecules are small enough to fit through the pore size. Figure 5 contains the same mug from Figure 2; however, 30 drops of iodine have been added. If iodine or starch is small enough to fit through the pores of the sandwich bag, we would know because the contents would turn a bluish/black color. What do you think will happen? Are there pores in a sandwich bag? You do put items in a bag to protect them. Observe Figures 6, 7, and 8 below. The inside of the bag turned from a white color to a bluish/black color. What does that tell you? Did the iodine diffuse across the membrane or did the starch diffuse across the membrane? Think about what you have learned. The mug contained iodine. If the starch diffused across the membrane into the mug, the contents of the mug would turn a bluish/black color. In Figure 7, you can see that the inside of the bag turned bluish/black, meaning that the starch stayed inside the bag and the iodine diffused across the membrane. What can we determine about the size of the starch molecules and the size of the iodine molecules? Which is smaller? The iodine has to be smaller since it was the molecule that diffused across the membrane. BIO 1030, General Biology I 3

4 What does this matter besides being a pretty cool experiment that you could UNIT conduct x STUDY at home? GUIDE It matters because all living organisms are made up of at least one cell. Bacteria are prokaryotic Title organisms and are single celled. Often, when we hear the word bacteria, we think of an infectious pathogen. Most bacteria are actually helpful or harmless. Still, there are some that are pathogenic they cause illness. How can we stop them? How can bad bacteria be destroyed? In order to destroy a bacterium, a scientist has to understand the cell membrane. Some snakes inject venom that contains phospholipase. The -ase ending tells us that this is an enzyme. This particular enzyme breaks down phospholipids. Therefore, when a snake bites you, your cell membranes deteriorate. What happens to a cell with no membrane? The same thing that happens to a balloon that has a hole in it its contents leak out and the cell dies! In order to understand living organisms and how they relate, we must first understand how individual cells operate. Chemical processes occur on the cellular level; in order for those processes and reactions to occur, molecules must move into the cell. In order for you to have enough energy to function, nutrients must enter the cell. In the next unit, we will discover what cells need for energy and how they use it to keep you and millions of other species alive! Reference Krogh, D. (2014). Biology: A guide to the natural world (5th ed., Technology update). Upper Saddle River, NJ: Pearson. Suggested Reading This is an interesting article that discusses porosity and the influence of structure. In order to access the article below, you must first log into the mycsu Student Portal and access the Academic Search Complete database within the CSU Online Library. Oikonomopoulou, V., Krokida, M., & Karathanos, V. (2013). Influence of structure on saltiness and sweetness of dehydrated food products. Drying Technology, 31(7), The video below depicts an interesting experiment that demonstrates how osmosis works. The Sci Guys. (2013). Science at home - SE1 - EP14: The naked egg and osmosis [Video file]. Retrieved from Learning Activities (Non-Graded) Osmosis Egg Lab If you have time, you can conduct the actual Osmosis Egg Lab; however, it takes 5 days. If you do not have time, you can view it on YouTube; the link is provided in the Suggested Reading section of the study guide. Materials Needed: Egg (you may want to use 2 just in case it breaks) Vinegar Corn syrup Food coloring (it does not matter the color) Clear glass Old spoon BIO 1030, General Biology I 4

5 Directions: UNIT x STUDY GUIDE 1. Carefully place the egg in the bottom of the empty glass, and pour enough vinegar over the egg to cover it. 2. Let the egg sit for 24 hours in the vinegar. 3. Carefully drain the vinegar. Make sure you catch the egg with your hand. Be gentle! 4. Return the egg to the glass and add more vinegar. 5. Allow the egg to sit for another 24 hours in the vinegar. 6. Pour out the vinegar, and gently rinse the egg and the glass. 7. Examine the size of your egg, and compare it to a normal fresh egg. 8. Notice the egg shell has been dissolved by the acidic vinegar. What you see and touch on the outside is the plasma membrane of the egg. 9. Put the naked egg back into the empty glass, and pour corn syrup over the top. 10. The egg may float towards the top. This will cause the membrane to dry out. Use the spoon to keep the egg under the corn syrup. You may have to bend the handle. 11. Let the egg sit for hours. 12. Pour out the syrup, and gently rinse egg. 13. Examine the size of the egg again. 14. What happened? Why do you think that happened? 15. Rinse the glass, and fill it with tap water. 16. Add a few drops of food coloring and stir. 17. Gently place the shriveled egg in the water. 18. Let the egg sit for 24 hours. 19. Pour out the water and catch the egg. 20. Examine your egg again. What happened? Why? Non-graded Learning Activities are provided to aid students in their course of study. You do not have to submit them. If you have questions, contact your instructor for further guidance and information. Title BIO 1030, General Biology I 5