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8.3 Cell Size and Function

(pages 308 – 314). 8.3 Cell Size and Function. Diffusion is a slow p rocess. Once a particle has crossed the cell membrane it must diffuse through the liquid cytoplasm to reach other areas of the cell. Diffusion occurs without any input of energy. Diffusion takes a lot of time!

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8.3 Cell Size and Function

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  1. (pages 308 – 314) 8.3 Cell Size and Function

  2. Diffusion is a slow process • Once a particle has crossed the cell membrane it must diffuse through the liquid cytoplasm to reach other areas of the cell. • Diffusion occurs without any input of energy. • Diffusion takes a lot of time! • Particles take 1 week to diffuse 1 meter in cytoplasm.

  3. Cells must minimize the distance over which substances must diffuse. • There is an upper limit on cell size. • The relative magnitude of a cell’s surface area to its volume is called its surface area-to-volume ratio.

  4. Can a “human-sized” amoeba survive? Substances diffuse very slowly throughout the cell’s cytoplasm, it would take more than a week to 1.65 m reach the centre! 1.65 m

  5. The Importance of Surface Area-to-Volume Ratio • As a cell grows, its volume increases much faster than its surface area. • A very large cell with a very low surface area-to-volume ratio could either: • starve to death • be poisoned from the buildup of its own wastes

  6. Area and Volume • As things get bigger their volumes increase rapidly, but their surface areas don't increase as quickly. Since a cell is mostly composed of water, as a cell's volume increases, so does it's mass. A simple example of the relationship of length, area and volume is a cube.

  7. SAVR Applet

  8. Cell Shape and Surface Area • Certain cell shapes boost surface area-to-volume ratio. • In-folding of the membrane and flattened cell shapes produce cells with large surface areas and relatively low volumes. • The higher the surface area-to-volume ratio, the more transport is possible across the cell membrane

  9. Cells specialized for transporting nutrients have shapes that result in high surface area-to-volume ratios

  10. Plant root hairs have a high surface area-to-volume ratio for maximizing water and nutrient transport.

  11. From One Cell to Many Cells • Multicellular organisms, such as human and trees, have millions of cells of many different types. • Multicellular organisms grow larger by adding more cells instead of just growing larger.

  12. Because the sizes of their individual cells are small, rapid diffusion within the cells of multicellular organisms is possible. • In single-celled organisms, one cell must perform all the functions of a living organism.

  13. Having many cells makes it possible for different groups of cells to become specialized. • Cells are organized into tissues that do specific jobs.

  14. Question 1. How is each of the cells below specialized to perform its role in the human body?

  15. Question 2.To keep warm on a cold day, dogs often lie dawn curled up in a round ball. To cool off on a hot day, they starch flat on the floor, bellies exposed. Why would this behavior help dogs to regulate their body temperature?

  16. Question 3. Explain why cells the size of basketballs do not exist.

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