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Lynn Margulis

Lynn Margulis. Endosymbiont Hypothesis. A. This hypothesis was proposed by Lynn Margulis in the 1960’s. B. Define symbiosis and introduce common types of symbiotic relationships.

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Lynn Margulis

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  1. Lynn Margulis

  2. Endosymbiont Hypothesis • A. This hypothesis was proposed by Lynn Margulis in the 1960’s. • B. Define symbiosis and introduce common types of symbiotic relationships.

  3. C. It basically hypothesized that Prokaryotes came to live together in a symbiotic relationship, the smaller living inside the larger, to gain a survival advantage over other prokaryotes and eventually they evolved into Eukaryotic cells over many generations that spanned hundreds of thousands of years. • 1. Smaller organism gained protection. • 2. Larger organism gained energy production or faster motility

  4. Endosymbiont Hypothesis

  5. Surface Area to Volume Ratio • The surface area to volume ratio refers to the ratio of the cell’s total surface area in relation to its volume. • Maximizing surface area to volume ratios is important so that the transport systems in cells can run efficiently

  6. Surface- to- Volume Ratio Importance • A. Cells can only be so small. (There has to be enough room (volume) to hold things and to perform work inside a cell.) • B. Cells can only be so large. (Larger means more traffic going in both directions across the cell membrane) • C. A cell must be large enough to contain DNA, Ribosomes, and some cytoplasm. They can only be so big because we have to be able to move enough “Food” into and “waste” out of a cell efficiently. If it is too large the cell becomes inefficient at moving these things so it divides to get back to a smaller state.

  7. Surface Area to Volume Ratio • Reasons for keeping cell sizes small • Decreases distances that substances have to travel … increasing the rate of diffusion.

  8. Human Systems • Maximizing surface area is also important for the efficiency of several systems in the body

  9. Human Systems • Cardiovascular system (alveoli in the lungs and capillaries that surround them aid in the diffusion of O2 and CO2 in and out of the blood)

  10. Human Systems • Digestive system • villi and microvilli are structures in the small intestine that aid in the absorption of nutrients into the body)

  11. Plant Systems • Structures in plants are also designed to maximize surface area to volume ratios for their specific functions. • Examples: • Leaf thickness and shape

  12. Plant Systems • Root structures

  13. Surface Area to Volume relationship

  14. Surface Area to Volume Ratio • If we were to watch nutrients being absorbed at a constant rate in 3 different size cubes, the nutrients could reach the entire cytoplasm of smaller cells because, for their volume, they had a much larger surface area. The smaller the cell, the larger the SA / V ratio, and the easier it is for diffusion to reach all parts of the cell 2 cm3 4cm3 1 cm3 Dead: nutrients can’t get to all parts of the cell. Better, but still dead. Alive! Nutrients make it to all parts of the cell. Surface Area = (base) (height)added upfor all sides S.A.= (4cm)(4cm)(6 sides) = 96 cm2 x 1 cube = 96 cm2 S.A.= (2cm)(2cm)(6 sides) = 24 cm2 x 8 cubes = 192 cm2 S.A.= (1 cm)(1cm)(6sides) = 6 cm2 x 64 cubes = 384 cm2 Volume = (base) (width) (height) V = (4cm)(4cm)(4cm) = 64cm3 x 1 cube = 64cm3 V = (2cm)(2cm)(2cm) = 8cm3 x 8 cubes = 64 cm3 V = (1cm)(1cm)(1cm) = 1cm3 x 64 cubes = 64 cm3

  15. 16 7.11 • Shape also affects surface area to volume ratio. • Skinnier, flatter cells large SA / V ratios. • Cells with projections, like microvilli, have large SA / V ratios.

  16. In order for an organism to be large, it must be multi cellular. • Which of the equal volumes below has the greatest SA / V Ratio and is therefore most likely to survive?

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