biology ch3

What is the cell theory?

1. All organisms are made up of one or more cells.

2. Cell is the basic unit of life

3. Cells arise from pre existing cells(Extension by Virchow)

Light vs electron microscope

Working principle:

• uses lenses to refract and focus light

• SEM: scan surface of 3D specimen with electron beam

• TEM: pass electron beam through thinly sliced specimen and focus with magnetic field

Differences:

• living cells/ biological processes/ preserved cells vs completely dehydrated and chemically treated cells

• colored vs black and white with false color added by computer software

• 1000 times (not high enough magnification to see all cell structures) vs 10,000,000 for TEM (internal structure)and 500,000 for SEM (external structure)

Magnifications of microscope

• Eyepiece: 5,10,15

• Objective: 4,10,40

Structure of light microscope