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2. The major factor limiting cell size is the
a. concentration of water in the cytoplasm.
b. need for energy.
c. presence of membrane-enclosed organelles.
d. ratio of surface area to volume.
e. composition of the plasma membrane.
D. I would approach this by considering each one in order:
a - what does water concentration have to do with it? irrelevant
b - so if a cell has unlimited energy, will it grow to the size of a baseball? (obviously, no)
c - irrelevant, how could this impact cell size?
d - think about what you know about SA to volume: necessary molecules diffuse through the membrane (SA) and thus for enough to filter in so the cell can support all the organelles etc. Hence a big cell has low SA to volume and wouldn't survive.
e - this is more reasonable, but assume that the membrane is both strong and fluid and can support larger cells