Cell Size Limitatio

ns

• Why are living organisms the sizes that they are?

• Are there advantages to being large or small?

• What are the advantages to being a certain size?

1 – limits cell size:

• Diffusion is ______ and efficient over _______ distances and becomes ______ and inefficient as distances become larger

2– limits cell size:

• The nucleus has DNA which contains instructions for making _________. Proteins are used by all organelles in the cell.

Imagine a 20cm cell with a speck of DNA inside the nucleus.

The cell won’t survive if there isn’t enough DNA to build all the protein cell needs.

3– limits cell size:

Surface Area to Volume Ratio

First, calculate Surface Area

of this box

• Area of one square = Length x Width = __ in2

3– limits cell size:

Surface Area to Volume Ratio

• A cube has 6 sides (multiply the area of one side by six)

• Total Surface Area = ____ in2

Volume

Second, calculate Volume for this box

• Volume = Length x Width x Height =

__ inches3

3– limits cell size:

• We now have _____ in2 of surface area and ____ in3 of volume.

• Reduce the ratio. ___ to ___

Is the surface always a larger number?

No. Let's look at some more cubes.

Side of cube

Area of 1 Side

Area x 6Surface area of Cube

Length x height x width

Volume

Ratio of Surface Area to Volume

2 4 4 x 6 24 2 x 2 x 2 8 3 to 1

4 16 16 x 6 96 4 x 4 x 4 64 3 to 2

6 36 36 x 6 216 6 x 6 x 6 216 3 to 3

8 64 64 x 6 384 8 x 8 x 8 512 3 to 4

12 144 144 x 6 86412 x12 x 12

1728 3 to 6

20 400 400 x 6 240020 x 20 x 20

8000 3 to 10

What does this mean?

What does this mean?

• It means that small animals, like mice, have a lot of skin on the outside compared to a small volume of bones, blood, and internal organs on the inside. So a mouse or a baby bird loses ______ rapidly.

• When an animal has a large volume (big bones, muscles, lungs, digestive system) the skin on the outside (the surface area) gets progressively smaller when it is compared to the volume inside. This means that large animals tend to maintain their temperatures and to get cooler or warmer _______.  It is also difficult for them to get rid of excess body heat, for example, if they have been running.

What is Surface Area to Volume ratio? Why is it Important?

• Surface area to volume ratio is just the surface area of a cell divided by its volume.

What is Surface Area to Volume ratio? Why is it Important?

• In biology, the larger this number the better for cells because that would mean that the cell has a relatively large surface area compared with its volume.

• This is important because it is one of the factors that determines how _________ substances can diffuse into and out of the cell.

• Generally the smaller the cell, the larger the SA to V ratio and the ______ the rate of diffusion.

• This is also why larger organisms need more specialized transport systems to carry substances to certain parts- diffusion would be too slow.

• In the end, cell size can have dramatic

and negative effects on a cell. If it is too large, it might not function properly.

Since everything wants to reach equilibrium, there is some ________ size where a cell (or an organism) performs best.