Cell Size

Surface Area

  • the amount of surface covering the outer part of the cell

  • allows for more things to be done at once 

Volume 

  • the amount of space that the entire cell takes up 

SA: V Ratio

  • larger ratio = more efficient at diffusion, transporting & exchanging materials 

  • smaller ratio = less efficent 

As the cell gets larger, the SA:V gets smaller.

larger cells have high SA & V 

smaller cells have lower

Smaller cells absorb better

Surface Area

membrane folding and projections increase surface area to increase the efficiency

Projections

  • roots hairs 

  • villi

  • microvilli

Plasma Membrane

SA must be large enough to exchange materials

To absorb things properly, you want larger SA

As cells increase in volume, the SA decreases, the demand for internal resources increases 

Surface Area and Volume Formulas

                                         Surface Area

SA: 4πr²

SA of a Sphere

SA: 2lh + 2lw + 2wh

SA of a Rectangular Solid 

SA: 2πrh + 2πr²

SA of a Cylinder 

SA: 6s²

SA of a Cube 

                                            Volume

4/3πr³

Volume of a Sphere

lwh

Volume of a Rectangular Solid

πr²h

Volume of a Cylinder

s³

Volume of a Cube 

Notes:

r= radius 

l = length

h = height 

w = width 

s = length of one side of a cube 

sa = surface area

v = volume 

Surface Area

Surface area refers to the amount of outer covering of a cell, which enables more functions to be performed simultaneously.

Volume

Volume represents the total space occupied by an entire cell.

SA: V Ratio

The Surface Area to Volume (SA:V) ratio is crucial for cellular efficiency. A larger SA:V ratio indicates greater efficiency in diffusion, transporting, and exchanging materials, while a smaller ratio implies less efficiency. As a cell grows larger, its SA:V ratio decreases. Larger cells possess both high surface area and volume, whereas smaller cells exhibit lower values for both. Consequently, smaller cells are better at absorption.

Surface Area

Cellular efficiency is significantly enhanced by increasing surface area through membrane folding and various projections. Examples of these projections include root hairs, villi, and microvilli. The plasma membrane's surface area must be sufficiently large to facilitate the exchange of necessary materials. For proper absorption, a larger surface area is desirable. As cells expand in volume, their surface area effectively decreases relative to volume, leading to an increased demand for internal resources.

Surface Area and Volume Formulas

Surface Area Formulas

  • SA: 4\pi r^2 for a Sphere

  • SA: 2lh + 2lw + 2wh for a Rectangular Solid

  • SA: 2\pi rh + 2\pi r^2 for a Cylinder

  • SA: 6s^2 for a Cube

Volume Formulas

  • 4/3\pi r^3 for a Sphere

  • lwh for a Rectangular Solid

  • \pi r^2h for a Cylinder

  • s^3 for a Cube

Notes:

  • r = radius

  • l = length

  • h = height

  • w = width

  • s = length of one side of a cube

  • sa = surface area

  • v = volume