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Teeny, tiny cells
- 1. Structure and Function of Cells:Structure and Function of Cells: Teeny, Tiny CellsTeeny, Tiny Cells All About You Science Teacher Education Course Summer 2013
- 2. Teeny, Tiny Cells Key Take-Away • We will write it at the end of the lesson Objectives • Visualize how the scale of a cell affects its metabolism • Calculate surface area to volume ratios to determine efficient cell size
- 3. Warm Up Place the following items in order from largest to smallest in your science journals coffee bean E. coli egg cell flu virus glucose red blood cell grain of rice grain of salt water molecule skin cell sesame seed NOTE: items are not to scale
- 4. Warm Up Place the following items in order from largest to smallest in your science journals coffee bean E. coli egg cell flu virus glucosered blood cell grain of rice grain of salt water molecule skin cell sesame seed
- 5. Teeny, Tiny Cells Think about a typical cell and compare it to the size of your body Why do our cells have to be so small?
- 6. Teeny, Tiny Cells All cells have organelles, each of which has a specific job to fulfill to ensure that the cell is properly functioning One of the jobs of organelles is to undergo cellular transport - the constant flow of materials into and out of cells through the cell membrane. Substances go in and out of cells. What would happen if they didn’t? BA C
- 7. Why are cells small? Cells undergo metabolism in order to sustain life Many of the substances that are necessary for metabolism are microscopic - so small that they cannot be seen with the unaided eye That’s 8 millionths of a meter That’s 8 millionths of a meter That’s 275 trillionths of a meter That’s 275 trillionths of a meter
- 8. Teeny, Tiny Cells Our cells need to be microscopic - specifically the need to have a large surface area compared to its volume (how much it holds) Surface Area: the number of units that cover the outside of an object. On a cell, the area of its cell membrane or wall. Volume: the amount of three-dimensional space enclosed by a boundary. In a cell, the volume is the space within the cell membrane or wall
- 9. Teeny, Tiny Cells Let’s explore surface area: Your task is to dry off quickly. Which would you rather use: a towel or a bed sheet? Why? Let’s explore volume: Your task is to drain water quickly. Which would you rather drain: a bath tub or a sink? Why? versus versus
- 10. Calculating Surface Area Surface Area: the number of units that cover the outside of an object. Calculating surface area of a cube Surface area = height x width x number of sides 4” 4” 6 sides
- 11. Calculating Volume Volume: the amount of three-dimensional space enclosed by a boundary. Calculating volume of a cube Volume = height x width x length 4” 4” 4”
- 12. Teeny, Tiny Cells Part 1: Surface Area to Volume Ratios of Individual Cubes 1” 2” 3”
- 13. Teeny, Tiny Cells Part 2: Surface Area to Volume Ratios of an Individual Cube Compared to a Group of Cubes 3” 3” 3” 6 sides 1” 1” 1”
- 14. Teeny, Tiny Cells If our cells were too big compared to these necessary substances, it would take a long time, and possibly use more energy, for the cells and organelles to undergo metabolism Thus our cells need to be small—microscopic—in order to be an efficient system for metabolism
- 15. Teeny, Tiny Cells What is the lesson’s key take-away? How does this lesson specifically relate to: • The Characteristics of Life • Homeostasis • Form Fits Function
Notes de l'éditeur
- Cell Size: - Minimum size is that needed for all the molecules required for cellular activity - Maximum is limited by the need for sufficient surface area to carry out functions
- After students have a chance to place the items in order from largest to smallest in their science journals, ask for a few volunteers to share their lists and their reasoning. Afterward, pull up the online interactive: http://learn.genetics.utah.edu/content/begin/cells/scale/ and zoom in so students can compare and contrast their lists. Why a microscopic size for most cells? ensures a sufficient surface area for nutrients/wastes to move across the membrane a small cell has a greater ratio of surface area to volume than a large cell
- Why a microscopic size for most cells? ensures a sufficient surface area for nutrients/wastes to move across the membrane a small cell has a greater ratio of surface area to volume than a large cell
- Ask students to volunteer answers to the question: Why do our cells have to be so small? Answers will vary. Why a microscopic size for most cells? ensures a sufficient surface area for nutrients/wastes to move across the membrane a small cell has a greater ratio of surface area to volume than a large cell
- What are some substances that need to go into and out of cells? Cells need to take in oxygen gas and glucose. Cells need to release carbon dioxide and lactic acid. Water has to be able to move in and out of cells. If the flow of substances is blocked, the cell will not be able to efficiently carry out life processes and will eventually die. Refer to the figure. A - A normal red blood cell looks like a disk with a pinched-in center. If water can move into and out of the cells, the cells will be able to have just enough water to carry out life processes and retain its normal shape. B - If water is only allowed to flow out of cells, the cells will shrivel and ultimately die. C - If water is only allowed into cells, the cells will burst and ultimately die.
- Metabolism: set of life-sustaining chemical processes within the cells of living organisms that allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Cellular transport thus affects the cell size
- Let’s explore surface area … Which would you rather dry off with after a shower: a towel or a bed sheet? Why? Answers will vary. Let’s explore volume … Which will take longer to drain: a bath tub or a sink? Why? Answers will vary.
- Let’s explore surface area … Your task is to dry off quickly. Which would you rather use: a towel or a bed sheet? Why? You would want to use a towel because it can soak up more water in a shorter amount of time. If we look closely, we see that a towel has many fibers extending from its surface. This increases the surface area of the towel. A bed sheet does not have fibers extending from its surface, thus has a lower surface area. More surface area means there is more “space” to soak up water in a short amount of time. The task is to dry off quickly, so the towel is the most efficient means. Let’s explore volume … Your task is to drain water quickly. Which would you rather drain: a bath tub or a sink? Why? The sink would drain quickly compared to the bath tub because the sink holds less water. This means the sink has less volume than the bath tub. The task is to drain the water quickly, so the sink is the most efficient means.
- An aquarium’s surface area is represented by its glass plates, base, and lid. Surface area of 4 inch cube = 4 in x 4 in x 6 = 96 in2 Volume of the 4 inch cube = 4 in x 4 in x 4 in = 64 in3 Surface Area/Volume of 4 inch cube: 1.5
- An aquarium’s volume is the amount of space inside the glass sides and lid - the amount of water it can hold. Surface area of 4 inch cube = 4 in x 4 in x 6 = 96 in2 Volume of the 4 inch cube = 4 in x 4 in x 4 in = 64 in3 Surface Area/Volume of 4 inch cube: 1.5
- Divide students into groups of three to four. Distribute the ruler and acrylic cubes to each group: a 1” cube, a 2” cube, and a 3” cube. Instruct the students to measure the dimensions of the cubes and label the diagram in their student worksheets (cubes are to scale). Since they are cubes, they only need to measure one side. Ask students to share their measurements as a class so you can ensure that all student groups measured correctly before proceeding with calculations. Inform students that we are using inches in this activity because it is easier to manipulate and measure a 1 inch cube compared to a 1 centimeter cube (it is also easier to purchase 1 inch cubes). Discuss with the students that the surface area is the number of units that cover the outside of an object. For example, an aquarium’s surface area is represented by its glass plates, base, and lid. The volume is the amount of space something occupies or how much it can hold. For example, an aquarium’s volume is how much water it can hold. Next, review the formulas for surface area and volume. Surface area is height multiplied by width, or SA = h x w. Volume is height multiplied by width multiplied by length, or V = h x w x l. 8. Using the formulas, help the students calculate the surface area and volume of the 1” cube: To find the surface area of a cube, we have to multiply the height by the width by the number of sides: SA = 1 in x 1 in x 6 = 6 in2. Note that surface area is expressed as a square because inches was multiplied two times. To find the volume of a cube, we have to multiply the height by the width by the length: V = 1 in x 1 in x 1 in = 1 in3. Note that volume is expressed as a cube because inches was multiplied three times. To find the surface area to volume ratio, we divide the surface area by the volume. S.A.:V = 6:1 = 1. 9. Ask the students to complete the two remaining cubes on their own. 10. Walk around the room to ensure that students are on the right track. 11. Reconvene as a class after student groups are finished and ask volunteers to share their work. 12. Discuss with the class: which type of cell is would be most efficient at metabolism? Why?
- Set up a 3” cube next to a “group of cubes” (a 3” cube made up of 27 1” cubes). Ask students to compare and contrast the two models using the Venn diagram in their student worksheet. Facilitate the discussion to include the terms surface area and volume. Instruct the students to label the dimensions of the two models (to scale) in their student worksheet. Instruct them to return to their desks and complete the calculations and questions. Walk around the room to ensure that students are on the right track. Discuss the answers when all student groups are finished with their calculations. The 3” cube’s calculations are as follows: S.A. = 3 in x 3 in x 6 = 54 in3, V = 3 in x 3 in x 3 in = 27 in3 S.A.:V = 54:27 = 2:1 The 3”x3” cube’s calculations are as follows: S.A. = 1 in x 1 in x 6 x 27 = 162 in2 V = 1 in x 1 in x 1 in x 27 = 27in3 S.A.:V = 162:27 = 6:1 = 6 Ask the students to discuss whether they think our cells grow bigger as we grow, or if they increase in numbers as we grow. Facilitate the discussion to include terms such as metabolism, cellular transport, surface area, and volume.
- Emphasize TIME and ENERGY – use large square and small square grid to compare and contrast the time and energy componets when dealing with objects of different scales.
- The characteristics of life: When organisms grow, their cells grow a little, but then divide to produce more cells: this allows the SA/V ratio to remain high and for metabolism to occur efficiently. All living things are made of cells Homeostasis: Cells, such as RBC, can achieve homeostasis by efficient exchange of essential materials Form Fits Function: The shape and size of cells allows for a high Sf.Area/Vol., and thus it allows cells to perform its main function (metabolism) efficiently.