Cell Size Limitations：细胞大小的限制

Cell Size Limitations：细胞大小的限制 Why are living organisms the sizes that they are? Are there advantages to being large or small? What are the advantages to being a certain size? 1 – limits cell size: , Diffusion is _____________ and efficient over ______________ distances, but it becomes _______________ and inefficient as distances become larger. Imagine a 20cm cell! It would take months before organelles in the center would receive needed items (oxygen, water, etc…) 2– limits cell size: , The nucleus has DNA which contains instructions for making __________________. Proteins are used by all organelles in the cell. Imagine a 20cm cell with a speck of DNA inside the nucleus. The cell won’t survive if there isn’t enough DNA to build all the protein cell needs. 3– limits cell size: Surface Area to Volume Ratio First, calculate Surface Area of this box Area of one square = Length x Width = ________ square inches A cube has 6 sides (multiply the area of one side by six) Total Surface Area = _________ Second, calculate Volume for this box 3Volume = Length x Width x Height = _______ inches 23 We now have _____ in of surface area and ____ inof volume. Reduce the ratio. _____ to _____ Is the surface No. Let's look always a larger at some more number? cubes. Length x Side of Area of Area Surface area Ratio of Surface height x Volume cube 1 Side x 6 of Cube Area to Volume width 2 4 4 x 6 24 2 x 2 x 2 8 3 to 1 4 16 16 x 6 96 4 x 4 x 4 64 3 to 2 6 36 36 x 6 216 6 x 6 x 6 216 3 to 3 8 64 64 x 6 384 8 x 8 x 8 512 3 to 4 144 x 12 144 864 12 x12 x 12 1728 3 to 6 6 400 x 20 400 2400 20 x 20 x 20 8000 3 to 10 6 What does this mean? It means that small animals (like mice) have a lot of skin on the outside compared to a small volume of bones, blood, and internal organs on the inside… So a mouse or a baby bird loses ___________ rapidly. When an animal has a large volume (big bones, muscles, lungs, digestive system) the skin on the outside (the surface area) gets progressively smaller when it is compared to the volume inside… This means that large animals tend to maintain their temperatures and to get cooler or warmer ________________. It is also difficult for them to get rid of excess body heat, for example, if they have been running. What is Surface Area to Volume ratio? Why is it Important? Surface area to volume ratio = surface area of a cell Volume of a cell In biology, the larger this number the better for cells because that would mean that the cell has a relatively large surface area compared with its volume. This is important because it is one of the factors that determines how ______________ substances can diffuse into and out of the cell. Generally the smaller the cell, the larger the SA to V ratio and the _______________ the rate of diffusion. This is also why larger organisms need more specialized transport systems to carry substances to certain parts- diffusion would be too slow. In the end, cell size can have dramatic and negative effects on a cell. If it is too large, it might not function properly. Since everything wants to reach equilibrium, there is some ______________ size where a cell (or an organism) performs best.