CHAPTER 4: A TOUR OF THE CELL

I. CELLS ARE THE SMALLEST UNITS OF LIFE

A. The study of cells began with the microscope. • Robert Hooke was the first to describe cells in 1665.

• Micrographs are photos taken with microscopes

• Light microscope (LM) has magnification up to 1000x

o For viewing living cells

• Electron microscope (EM) has magnification up to 1,000,000x

o Scanning EM (SEM) for viewing surface features

o Transmission EM (TEM) for viewing internal structures

[pic][pic][pic]

B. Why are cells small?

• A cell’s surface area-to-volume ratio limits its size

• Volume increases faster than Surface Area

• Larger cells do not have enough Surface Area to support their Volume

• Organisms get larger by becoming multicellular [pic] C. There are two major categories of cells.

[pic]

D. All cells are surrounded by a plasma membrane.

• Prokaryotic AND eukaryotic cells are surrounded by a plasma membrane

• Eukaryotic cells also have internal membranes

• All membranes act as selective barriers

• All membranes are built from proteins and phospholipids

• Form phospholipid bilayer when exposed to water

o Hydrophilic on outside, hydrophobic on inside

• Membranes are described by the fluid mosaic model

o Fluid because they have the consistency of salad oil

o Mosaics because of the diversity of proteins they contain

[pic] [pic]

II. PROKARYOTIC CELLS ARE SMALLER AND SIMPLER.

A. All prokaryotic cells are unicellular organisms. • All prokaryotes have a plasma membrane, nucleoid, and ribosomes.

o Plasma membrane