W ARM U P With the person next to you complete the table on “Why are cell’s so small?” When finished with the table complete the questions on the back. Mr. E. will be checking Passive Transport and Plant Cell Coloring. Tomorrow: Study Guide Due (w/ Vocab) & Active Transport Thursday: Exam

L ECTURE 13: C ELL S HAPE, S IZE & P ARTS Cell Diversity: Shape Cells come in many different shapes and sizes. With over 200 types they range from flat to branching to round to rectangular. A cell’s shape reflects its function.

C ELL S IZE : S IZE VARIES WITH F UNCTION Cells vary in size from microscopic to visible to the naked eye. Ex/ A giraffe’s spinal nerve running to its foot can be up to 6.5 ft long

W HY IS A CELL SMALL ?  Difficulty exchanging materials (such as nutrients, oxygen, and waste products) across the cell

Why is this important to the cell? Small cells can exchange things faster than larger cells due to surface-to-volume ratio. The higher the ratio the faster the exchange. As the volume of a cell grows there needs to be enough plasma membrane surface to complete all the necessary transport.

Figure Total number of Cubes Surface area of figure (=6 x length x width) Volume of figure (= length x width x height) Surface area to Volume Ratio SA / V Total surface of individual cubes (6 x # of cubes) A B C D

C ELL SIZE Cell size is limited by its surface area-to-volume ratio Larger the cell, the volume increases faster than its surface area. Surface area to volume ratio decreases with increasing cell size (EX. 6:1 vs 3:1)

W HAT DOES THIS MEAN FOR THE CELL ? The bigger the volume the less surface area not enough surface area to meet the needs of the increasing volume distance to center increases as cell increases Difficulty exchanging materials (such as nutrients, oxygen, and waste products) across the cell