WARM UP

With the person next to you complete the table on “Why are cell’s so small?”

When finished with the table complete the questions on the back.

Mr. E. will be checking Passive Transport and Plant Cell Coloring.

Tomorrow: Study Guide Due (w/ Vocab) & Active Transport

Thursday: Exam

LECTURE 13: CELL SHAPE, SIZE & PARTS

Cells come in many different shapes and sizes. With over 200 types they range from flat to branching to round to rectangular.

CELL SIZE: SIZE VARIES WITH FUNCTION Cells vary in size from microscopic to visible

to the naked eye. Ex/ A giraffe’s spinal nerve running to its foot can be up

to 6.5 ft long

WHY IS A CELL SMALL?

Difficulty exchanging materials (such as nutrients, oxygen, and waste products) across the cell

Why is this important to the cell? Small cells can exchange things faster than larger

cells due to surface-to-volume ratio. The higher the ratio the faster the exchange. As the volume of a cell grows there needs to be enough

plasma membrane surface to complete all the necessary transport.

FigureTotal number

of Cubes

Surface area of figure

(=6 x length x width)

Volume of figure

(= length x width x height)

Surface area to Volume

RatioSA / V

Total surface of individual

cubes(6 x # of cubes)

 A  

 1 6 1 6 6

  

B 

8 24 8 3 48

 C 

 27 54 27  2 162

D 64  96 641.5

 384

CELL SIZE

Cell size is limited by its surface area-to-volume ratio Larger the cell, the volume increases faster than its

surface area. Surface area to volume ratio decreases with increasing

cell size (EX. 6:1 vs 3:1)

WHAT DOES THIS MEAN FOR THE CELL? The bigger the volume the less surface

area not enough surface area to meet the

needs of the increasing volume distance to center increases as cell

increases Difficulty exchanging materials (such

as nutrients, oxygen, and waste products) across the cell