AP Bio - Unit 2: Cell Size

Cell size

all organisms must be able to absorb, transport, and release materials into their environment to survive. (ex: gases - O2 and CO2 , water, nutrients, communication molecules, metabolic waste etc)

Why worry about size?

Cells must exchange substances with its environment at a rate that keeps up with its metabolism. The cell membrane can only handle so many exchanges at a time. The bigger a cells surface area is, the more substances can cross the membrane at any given interval.

Surface area to volume ratio

Efficient transport requires a surface area to volume ratio that is as high as possible. As organisms increase in volume, their surface area to volume ratio decreases. Basically, if a cell is getting bigger, its volume increases faster than its surface area

Cells are limited in size

Too large: cannot exchange matter efficiently (nutrients can’t travel inside the cell fast enough, or wastes can’t be transported out fast enough). Too small: not enough materials can fit inside, or heat and nutrients diffuse out too fast to keep the cell alive

Cell shape

cell shape determines function! larger surface area means cells need to absorb more nutrients, transport out more molecules, or communicate faster via messenger molecules. smaller surface area is great for storage (like adipose fat cells)

Organisms

You can see the same sort of principle when it comes to heat exchange with the environment. Large round organisms have less surface area and conserve more heat to adapt to colder climates. Animals with increased surface area can quickly get rid of excess heat to adapt to hotter climates.