Section 11.1Cell Growth, Division, and

Reproduction

I Can…

• LS 1.7 I can explain the significance of the surface area-to-volume ratio of cells.

• LS 3.1 I can compare and contrast sexual and asexual reproduction, identifying advantages and disadvantages of each.

• LS 3.1 I can argue that the process of sexual reproduction leads to both genetic similarities and variation in diploid organisms.

Key Questions

1. What are some of the difficulties a cell faces as it increases in size?

2. How do asexual and sexual reproduction compare?

Limits to Cell Size

• Living things grow by producing more cells.

• The average human body contains nearly 40 trillion cells.

• Cells can grow by increasing in size, but most cells divide after growing to a certain point.

Limits to Cell Size

• Two main reasons why cells divide:

• Traffic Problems- The larger a cell becomes, the less efficient it is at moving nutrients and wastes across its cell membrane.

• Information Crisis- As a cell grows, it places increasing demands on its own DNA.

A Problem of Size

• Surface Area• = cell membrane

• The rate at which materials enter and leave a cell depends on the surface area

• Volume • = inside the cell

• The rate at which food is used and wastes are produced depends on the volume

A Problem of Size

• As a cell increases in size, its volume increases faster than its surface area.

• This is not good…

• Most cells function best with a large surface area and a small volume.

• Cells must eventually divide instead of growing without limit.

Caulerpa taxifolia- a type of algae

• Largest known living cells of any organism

• One cell can grow up to 30 cm (12 inches)

Cell Division

• The process by which a cell divides into two new daughter cells is called cell division.

• Before cell division can occur, DNA must be copied.

• Each new daughter cell gets one complete copy of DNA.

• Dividing keeps the surface area-to-volume ratio high.

Asexual Reproduction in Unicellular Organisms • Cell division (binary fission)

• Ex. Bacteria

• A single parent produces genetically identical offspring

• Simple, efficient, and effective

• Enables populations to increase in number very quickly

Asexual Reproduction in Multicellular Organisms • Animal example- hydra

• Budding- small bud will eventually break off and become an independent organism

• Plant example- kalanchoe

• Vegetative propagation- the plantlets at the end of the leaf can eventually drop and grow into new plants

Sexual Reproduction

• Involves the fusion of two separate parent cells

• Offspring inherit some of their genetic information from each parent

Comparing Reproduction

Asexual

• Produce many offspring in short period

• Don’t need to find a mate

• In stable environments, genetically identical offspring thrive.

• If conditions change, offspring not well adapted.

Sexual

• Relatively fewer offspring; growth takes more time

• Need to find a mate

• In changing environments, genetic diversity can be beneficial.

• Offspring may be less well adapted to current conditions.

Section 11.1 Exit Ticket

1. How can you calculate the surface area and volume of a cell?

2. How can you use that data to calculate the surface area-to-volume ratio?

3. Why do small cells have a higher surface area-to-volume ratio?

4. Why are small cells more efficient than large cells?

The End