Chapter 10 Cell Growth and Division

10-1 Cell GrowthDoes an animal get larger because its

cells increase in size or because it produces more of them?

Most living things grow by producing more cells, the cells of a small animal are almost the same size as an adult animal.

They both have the same size cells!

2 reasons cell divides: (don’t write anything yet)-The larger the cell becomes the more demands the cell places on its DNA (DNA overload)

-The more trouble the cell has moving enough nutrients and wastes across the cell membrane. (Membrane traffic jams)

1. DNA “Overload”

DNA stores the info that controls cells fxn.

As the cell size increases it does not make more DNA for the cell. If the cell were to grow without limit, an information crisis would occur. Compare this to a small town with a library…

1000 books 1000 books

2. Exchanging Materials

Food, oxygen and water enter through a cell membrane and wastes leave the cell in the same way.

The rate of exchange depends on the surface area of the cell.

Surface area = total area of its cell membraneThe rate at which food and O2 are used up and

waste products are produced depends on the cell’s volume.

Ratio of Surface Area to Volume

To obtain the ratio: divide the surface area by the volume

Surface area/volume= ratio

Volume = length x width x heightSo a 1 cm cell would be: 1 x 1 x 1 = 1cm3

S.A. = length x width x # of sidesSo a 1 cm cell would be: 1 x 1 x 6 = 6 cm2

In this case, the S.A. to vol. ratio would be 6:1

Ratio of Surface Area to VolumeThe volume increases much more rapidly than

the surface area, causing the ratio to decreaseThink of the town:

The small town has one, two-lane main street. As the number of people increase the size of the street remains the same. The people encounter more traffic and traffic jams occur. The cell experiences the same thing . As it grows it is harder to move materials into and out of the cell. That is why cells do not grow very big.

Why do we need more cells?

1. To grow/get bigger

2. To repair/heal a wound

3. To replace dead cells (G.I. tract, skin)

Cell DivisionBefore it gets too large to cause “traffic”

problems the cell divides into 2 daughter cells.

Before division the cell replicates its DNA so that each cell receives its own identical “library”

Chromotin

Chromotin is the form that DNA is in most of the time in a cell. It is loose and unorganized.

Chromosomes

A chromosome is the form that DNA is in before a cell divides. It is X shaped and organized.

If the DNA is not organized it cannot be equally divided between the two new cells.

ChromatidsChromatids are half of the chromosome X.Each pair of chromatids contains identical

DNA.They are known as “sister chromatids”

Chromatids

The sister chromatids are identical so that each new “daughter cell” gets a copy of the same DNA.

Centromere

A centromere holds the two sister chromatids together like a belt.

Histones

Histones

Histones are disk shaped proteins that help to organize the DNA within the chromosome.

Let’s review!

1. What are two reasons why a cell would divide?

2. What is a chromosome? What does it contain and where can it be found?

3. What is the difference between a chromosome and chromotin?