A bigger cell has more cytoplasm to feed
- The idea
- Predict
- See it
- Why
- Check
The idea
“A bigger cell has more cytoplasm, so it can take in and handle more.”
In everyday life, bigger often means more room and more resources. In a cell, every bit of added cytoplasm is one more bit the membrane has to feed.
The short version
The mistake: A bigger cell has more cytoplasm, so it can take in and handle more.
What's actually true: Cytoplasm is the demand and the membrane is the supply. As a cell grows, its volume rises faster than its surface area.
- Oxygen, glucose and other materials enter across the plasma membrane, and wastes leave the same way. So surface area sets the supply.
- Every bit of cytoplasm uses those materials, so volume sets the demand.
- Volume grows faster than surface area. Double a cell's radius and its surface gets 4 times bigger, but its volume gets 8 times bigger.
- That's why cells stay small, or add surface without much volume, like the microvilli on cells lining the small intestine.
On the exam: Surface area is the supply and volume is the demand. Ask how much membrane each bit of cytoplasm gets.