Dimensions of a Cell and its Organelles

Background

(Includes information extracted from: https://www.ck12.org/book/ck-12-biology-advanced-concepts/section/3.5/)

Cells are extremely small and can only be seen with a microscope. If cells are the main structural and functional unit of life, why are they so small? This is because the need to be able to pass nutrients and gases into and out of the cell sets a limit on how big cells can be. As a cell grows, its volume increases more quickly than its surface area. If a cell was to get very large, the small surface area would not allow enough nutrients to enter the cell quickly enough for the cell's needs. This idea is explained in the figure below. Larger metabolically active cells often have cell protrusions, increasing the surface area available for transport of materials into and out of the cell. Such cell types are found lining your small intestine, where they absorb nutrients from your food through protrusions called microvilli.

A small cell (left), has a larger surface-area to volume ratio than a bigger cell (center). The greater the surface-area to volume ratio of a cell, the easier it is for the cell to get rid of wastes and take in essential materials such as oxygen and nutrients. In this example, the large cell has the same volume as 27 small cells, but much less surface area.

In cell studies, we use certain units of measurement of length when describing a cell. 

Scale of Measurements

• • 1 centimeter (cm) = 10 millimeters (mm) = 10-2 meters (m)

  • 1 mm = 1000 micrometers (µm) = 10-3 m

  • 1 µm = 1000 nanometers (nm) = 10-6 m

  • 1 nm = 10-3 µm

Task

Your task is to find out more on the Dimensions of a Cell and its Organelles by accessing the resources below:

A) Given the scale of measurements above, complete the segment on the conversions between the units of length in your Pre-Tutorial Handout (page 3).

B) Cell Size and Scale : explore this animation on relative cell size and scale 

C) Have a better sense of the size of cells and their organelles by referring to the table provided in the Pre-Tutorial Handout (page 3)

Once you have gone through the resources on this page, click on Eukaryotic Cells (Animal, Plant Cells) and Prokaryotic Cells found on the navigation sidebar to move onto the next segment.