Why do most cells have to be so small? NAME: DATE: PERIOD: As cells grow larger, they produce more parts inside this larger space or volume. This larger volume with more parts requires more food and materials and makes more waste. All the food and waste needs to enter the cell through the cell membrane. Only a certain amount of materials can pass through a unit of cell membrane, or surface area, at a time. This is because small materials slip in between phospholipid molecules. Larger materials go through special holes or are wrapped in a piece of membrane. There are a limited number of these openings in each unit of surface area. The problem is: as a cell gets larger, the volume inside needing materials increases more than the surface area of the membrane that materials pass through. Surface area to volume ratio compares the amount of membrane to the amount of space inside the cell: Calculate the surface area of one of the small buff cubes (model of a cell) Height * width = area of one side Area of one side * # sides = surface area Calculate the volume inside one of the small buff cubes Height * width * length = volume Calculate the surface to volume ratio for the small cube Surface area/ volume : volume / volume ______ : 1

Why do most cells have to be so small? NAME: DATE: PERIOD: Calculate the surface area of one of the large green cubes (model of a cell) Height * width = area of one side Area of one side * # sides = surface area Calculate the volume inside one of the large cubes Height * width * length = volume Calculate the surface to volume ratio for the large cube Surface area/ volume : volume / volume ______ : 1 Compare the surface to volume ratios of the small and large cubes (state both ratios and say which cube has a larger ratio) Calculate the surface area of several small cubes put together to make a larger cube (tissue made of several small cells) Height * width = area of one side of small cube Area of one side * # sides on small cube * # small cubes= surface area of tissue Calculate the total volume inside all of the cubes in this tissue Total Height * total width * total length = volume Calculate the surface to volume ratio for the tissue

Why do most cells have to be so small? NAME: DATE: PERIOD: Compare the surface to volume ratios of the large single and the tissue made of several small cubes (state both ratios and say which cube has a larger ratio) Explain whether the tissue made of smaller cells or the large cell would be better at getting materials in and waste out. Use the background information on page 1 and your comparison of surface are to volume ratios as evidence in your explanation. Sketch the small cube, the large cube and the tissue made of small cubes in the grid below, using one box for each unit: Write the surface area to volume ratios below the sketches