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## AP®︎/College Biology

### Course: AP®︎/College Biology>Unit 2

Lesson 2: Cell size

# Cell size

Thinking about the limiting factors of cell size. Focus on volume to surface area ratio.

## Want to join the conversation?

• I have a problem to understand how volume can get bigger while sphere area stays the same?
• It doesn't stay the same, it's just that the volume increases faster tan the surface area, because the S.A. contains the term (r^2), while the volume formula includes (r^3), so as the radius increases, the volume increases faster than the surface area.
• At , what does the concept of ratio of volume to surface area mean? I don't really understand it. Why will it break down?
• It is in practical terms a ratio of demand to supply of nutrients. The demand will be proportional to volume, because the larger a cell is, the more nutrients, energy and organic materials it will need. The supply will depend on the surface area as it is through the membrane that the cell exchanges materials with the environment.

If the ratio volume to surface area is too big, that means that the cell needs more materials than it can obtain through membrane transport, and will eventually die.
• Why are human egg cells so large relative to other cells?

I read/remember hearing that the nucleus takes up ~10% of the cell volume at most. Is the size of the nucleus influenced by how unravelled the DNA is/is this a reason for the human egg cell being so large in relation?
• Since a sperm essentially only contributes DNA and there is no source of nutrition in the fallopian tube, the egg needs to contain all the resources needed for the zygote to undergo the initial stages of development until the blastocyst reaches the uterine cavity.

To begin learning more:
http://sitn.hms.harvard.edu/flash/2009/issue57/

Does that help?
• why don't we tend to see eggs much larger than a human egg cell?
(1 vote)
• We do... I'm assuming you've seen a chicken egg? The largest current egg cell is the ostrich egg.
• Volonia Ventricosa: Allow me to introduce myself I am the largest singular celled organism in the world
• he said that the largest cells are on the order of a 100 micrometer, but what about egg also cells. so shouldn't the cell be the ostrich's egg ?
• While eggs are a single cells they are not the typical cell, they are a specialized case.
• how big is a paramecium?
• The length of a paramecium cell can vary between 50 to about 350 micrometers.
• What kind of adaptations does a chicken egg (or other bird egg) have in order to be as large as it is?