Limits to Cell Growth

THINK ABOUT ITWhen a living thing grows, what happens to its cells?

Limits to Cell Size• Nearly all cells can grow by increasing in size, but

eventually, most cells divide after growing to a certain point.

Limits to Cell SizeWhy do cells divide rather than continuing to grow?

Limits to Cell Size• There are two main reasons why cells divide rather than

continuing to grow:1. Information “Overload”2. Problems Exchanging Materials

Information “Overload”• Living cells store critical information in DNA. • As a cell grows, that information is used to build the

molecules needed for cell growth. • A growing cell puts a greater demand on its DNA.• If the cell gets too big, the DNA would NOT be able to

serve the needs of the growing cell.

AnalogyTown: Library: BooksCell: Nucleus: DNA

Information “Overload”What would be a solution to the “overload” demand on the town’s library?

AnalogyTown: LibraryCell: DNA

Information “Overload”

• Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division.

• Before cell division, the cell copies all of its DNA.

• This replication of DNA solves the problem of information overload because each daughter cell gets one complete copy of genetic information (DNA).

Problems Exchanging Materials• Cells take in nutrients (ex. food, oxygen, and water)

through the cell membrane.

• Waste products created in the cell leave through the cell membrane.

• The rate at which this exchange of materials through the cell membrane takes place depends on the surface area of a cell.

Problems Exchanging Materials• As a cell grows, the more nutrients it needs to function

and the more waste it creates.

• The rate at which nutrients are used up and waste products created depends on the cell’s volume.

How could cell growth create a problem that is similar to a “traffic jam”?

Problems Exchanging Materials

• If a cell gets too large, the surface area of the cell is NOT large enough to get enough materials in and out across the cell membrane at the rate needed.

Problems Exchanging Materials

Problems Exchanging Materials• Imagine a cell shaped like a cube:✓ As the cell’s size increases, its volume increases

faster than its surface area, decreasing the ratio of surface area to volume.

• The ratio of surface area to volume is key to understanding the cell’s problems with exchanging materials.

Problems Exchanging MaterialsWhat would be a solution to the cell’s problems with exchanging materials (traffic jam)?

Problems Exchanging Materials• Cell division allows the cell to be more efficient at

exchanging materials.✓ Cell division reduces cell volume, resulting in an

increased surface area to volume ratio for each daughter cell.

✓ The increased surface to volume ratio solves the “traffic” problems.

Check for UnderstandingAll of the following are problems that growth causes for cells EXCEPT

Check for UnderstandingCompared to small cells, large cells have more trouble

Check for UnderstandingWhich of the following happens when a cell divides?

Check for UnderstandingThe process by which a cell divides into two daughter cells is called

Amoeba Sisters Video: Inside the Cell MembraneStart at 1:39 Stop at 3:16

Check for UnderstandingLooking at the structures (alveoli) inside the lungs, why do you think they are shaped as tiny sacs and only one-cell thick?

Check for UnderstandingLooking inside the small intestine, why do you think the cells have microvilli (small hair-like projections)?