Name: Period: Date: 1. Cell Size Lab / 30

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1 Name: Period: Date: 1 Cell Size Lab / 30 Pre-Lab Introduction: Cells come in a variety of sizes. Some red blood cells are only 8 µm in diameter. Nerve cells can reach lengths up to 1 meter. Most living cells, however, are between 2 and 200 µm in diameter. Why can t organisms be just one giant cell? 1. Diffusion limits cell size: cells require a constant supply of glucose and oxygen to carry out photosynthesis and to produce large amounts of ATP (cell energy). These substances, and waste products such as carbon dioxide, move through the cytoplasm by diffusion. It has been estimated that it takes a molecule of oxygen only a fraction of a second to diffuse through the cytoplasm from the plasma membrane to the center of a typical cell that is 20 µm. What would happen if the cell got bigger? Explain. Although diffusion is efficient over short distances, it becomes slow and inefficient as the distance becomes larger. Hypothetically, a cell with a diameter of 20 cm would have to wait months before receiving molecules that enter the cell. Because of this time restriction the cell/organisms would die if they were one large cell. 2. A cells DNA limits size: The second reason why cells are small is because they usually only contain one nucleus. If a cell doesn t have enough DNA to program its metabolism, it cannot live. When a cell is larger it requires more enzymes and parts to function correctly, therefore it needs more instruction. In many large cells there are more than one nuclei to ensure that all cell activities will be carried out quickly. Is that considered an adaptation or an inefficient redundancy? Explain.

Name: Period: Date: 2 3. Surface area-to-volume ratio: The third reason why cells are limited in size is that as a cell s size increases, its volume increases much faster than its surface area.

2 Name: Period: Date: 2 3. Surface area-to-volume ratio: The third reason why cells are limited in size is that as a cell s size increases, its volume increases much faster than its surface area. Note: Surface area = length of a side X width of a side X number of sides Volume = length X width X height Surface area to volume ratio = surface area / volume The smallest cell has a volume of 1mm 3 and a surface area of 6mm 2. If the side of the cell is doubled to 2 mm, the surface area will increase fourfold. Calculate what happens when the cell side is 4mm. (Include unit) Volume. Surface area. If cell size is doubled, the cell would require eight times more nutrients and would have eight times more waste to excrete. The surface area would only increase by a factor of 4. Therefore, the plasma membrane would not to have enough surface area through which oxygen, nutrients, and waste could diffuse. The cell would either starve to death or be poisoned by the build up of waste products. How would cell size hinder early cell reproductive growth? Explain.

3 Name: Period: Date: 3 Objective: In this lab, you will make illustrations of cube shaped models to represent cells. The dimension along one side will be doubled with each model. You will then calculate the surface area, volume, and the ratio between the two. Materials: Protractor/Ruler Calculator Procedure: 1. Illustrate three cell models like the pattern shown. The dimensions of a side will double each time, with the sides being 2 cm, 4 cm, and 8 cm. Label the units of length, width, and depth of your cube. Record the dimensions in the DATA TABLE (the first one is done for you in the table). 2. Calculate the total surface area for each cell model by the following formula: surface area = (Length X Width) X 6 sides Record the surface areas in the DATA TABLE. 3. Calculate the volumes for each cell model by the following formula: volume = length X width X height Record the volumes in the DATA TABLE Calculate the surface area-to-volume ratio for each cell model by the following formula: ratio = surface area volume Record the ratio values in the DATA TABLE. Data Table: Cube A Side length (cm) Surface area (cm 2 ) Volume (cm 3 ) Surface area to volume ratio (surface area : volume) B C

4 Name: Period: Date: 4 Data Illustrations: Label your models and label the unit lengths. Place a nucleus in your illustration and Identify the plasma membrane.

5 Name: Period: Date: 5 Conclusion Questions: (Use complete sentences when required to explain to receive full credit) 1. Rank the cubes from the largest surface area to volume ratio to the smallest surface area to volume ratio. 2. Why are cells relatively small in size? List three reasons. 3. All of the cells below have approximately the same volume. Calculate the surface area for all cubes. Then, circle the letter of the one with the largest surface area. A. B. C. 4. To maintain life, and carrying-out cellular functions, materials must be able to move into and out of the cell. Also, materials need to be able to move within the cell. What might be the advantage of having large surface area? Explain. 5. What might be the disadvantage of having a large volume? Explain.

6 Name: Period: Date: 6 6. Infer, what is the connection between small cell size and rapid cell growth (reproduction/ cell division)? Explain. 7. Reviewing the location of the nucleus, why would DNA limit the size of the cell? Consider how prokaryotes and eukaryotes divide. Explain. 8. Making the larger connection. Why would an elephant and a rodent have different metabolic needs (food) and developmental growth (develops longer over time/matures). Explain.

Test 2: Cell Structure and Function

Name Test 2: Cell Structure and Function Date 1. Our bodies are made of, which are made up of many different parts and are the basic units of life. 1. a. cells b. organelles c. molecules d. proteins 2.