4.1 Cell Biology Lesson 12

Baseline (flightpath D): Know that as the size of the organism increases the SA:Vol ratio decreases which reduces the efficiency of diffusion and active transport. Further (flightpath C): Describe several examples of cellular adaptations which larger organisms use to increase diffusion and active transport. Challenge (flightpath B&A): Explain why there are limits to the size individual cells and how larger organisms overcome this barrier.

Limitations of diffusion and active transport Diffusion only works efficiently if the distance over which the substances have to diffuse is small. Diffusion is a slow process and the larger the distance the longer it takes. And an organism must have a large surface area to volume ratio for diffusion to be efficient. This is only the case for small organisms Larger more complex organisms have a bigger distance from the surface to the cells inside the body

Cellular adaptations – inside the small intestine

Cellular adaptations – inside the lungs

Cellular adaptations – inside the gills

Cellular adaptations – inside the roots

Cellular adaptations – inside the leaves

Sailors’ eyeballs Valonia ventricosa, also known as bubble algae or sailors' eyeballs. They are one of the largest single-celled organisms and can grow up to 5 cm in diameter.  Discuss why there is a limit to how big they can grow.