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
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