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.

• 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

Endosymbiont Hypothesis

• 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

Surface Area to Volume Ratio

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.

Surface Area to Volume Ratio

• Reasons for keeping cell sizes small– Decreases distances that substances have to

travel … increasing the rate of diffusion.

Human Systems

• Maximizing surface area is also important for the efficiency of several systems in the body

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)

Human Systems

• Digestive system – villi and microvilli are structures in the small

intestine that aid in the absorption of nutrients into the body)

Plant Systems

• Structures in plants are also designed to maximize surface area to volume ratios for their specific functions.

• Examples:– Leaf thickness

and shape

Plant Systems

• Root structures

Surface Area to Volume relationship

• 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.

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.

4cm3 1 cm32 cm3

Surface Area = (base) (height) added up for 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

Surface Area to Volume Ratio

V = (1cm)(1cm)(1cm)

= 1cm3 x 64 cubes = 64 cm3

VolumeArea Surface

S.A.V

9664

1.5 364

192..

VAS 6

64384..

VAS

The smaller the cell,the larger the SA / V ratio, and theeasier it is for diffusion to reach

all parts of the cell

• Shape also affects surface area to volume ratio.

167.11

• Skinnier, flatter cells large SA / V ratios.

• Cells with projections, like microvilli, have large SA / V ratios.

• 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?