Cell Growth and Division

10-1 Cell growth

Biology

Mr. Hines

A living thing will grow by making more cells.

Cells of an adult animal are about the same size as a young animal – there are just more of them

Limits to cell growth

Are there limits to the size in which cells can grow?

Yes

Cells are limited in size for 2 reasons

1. DNA overload

2. Exchanging materials

DNA overloadThe larger a cell gets, the more responsibility

is placed on the nucleus to control it. In other words, the nucleus can only effectively control a small cell.

Remember that DNA is located in the nucleus of Eukaryotic cells – which controls the cell.

This can be compared to a small town. If the

town grows too large, it will be harder to manage – garbage collection, police, mail, street cleaning, schools, jails, grocery store.

It is easier for a large town to divide into 2 smaller towns.

This is the same for cells – Cells will divide and each new cell will have its own nucleus.

Exchanging materials

Remember from earlier that all cells need to get nutrients into them; food, water, oxygen, etc.

Cells must also get rid of waste.

This happens through the cell membrane.

The area of the membrane that surrounds the cell is called ‘surface area’

The amount of materials that a cell can get inside of it will depend on the size of the surface area.

The amount of materials that a cell uses depends on its volume.

In order to understand this concept, you must understand the relationship between surface area and volume.

Ratio of Surface area to volume

To keep matters, simple, we will assume that a cell has the shape of a cube.

Calculating the surface area of a cube.

L x w x 6

Calculating the volume of a cube

L x w x h

Surface Area / Volume Ratio

All three have the same volume, but the group on the right has four times the surface area.

One 4-cm cube Eight 2-cm cubes Sixty-four 1-cm cubes

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Cell Size

Surface Area (length x width x 6)

Volume (length x width x height)

Ratio of Surface Area to Volume

Ratio of Surface Area to Volume in CellsSection 10-1

Notice that the volume increases more quickly than the surface area.

Since the surface area is responsible for getting nutrients in and out of the cell, a growing volume presents serious problems to a large cell.

In other words, a large cell can not get nutrients in and out fast enough.

This can be compared to a small town with one main road.

Once the town starts growing, the road becomes jammed up which causes difficulty getting supplies in and out of the town.

So what does this mean?

This means that as a cell grows too large, the surface area to volume ratio causes the cell to have difficulties getting nutrients in and out of the cell.

Division of the Cell

Before the cell becomes too large, it divides into 2 daughter cells.

Each daughter cell will have its own nucleus, DNA, as well a complete set of organelles

This process is called cell division.

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