Microscopes

Cell theory

• Both plant and animal tissue is composed of cells

• Cells are the basic unit of all life

• Cells only develop from existing cells

What is the importance of microscopes in the study of living organisms

As microscopes w. higher magnification & resolution were developed, cells can be observed for the 1st time

• Helps theories be proposed, accepted, or debunked due to evidence

• Allows us to discover how details of their structures relate to their functions

Using a microscope

1. Light moves thru thin & transparent sample

2. Is magnified by objective lens (stain used to increase contrast)

3. Reflected in mirrors in turret

4. Magnified by eyepiece lens

Light microscope

• Objective lens: Produces magnified image

• Eyepiece lens: Thru which the specimen is viewed, further magnifies the image

Dry mount

Wet mount

Squash slides

Smear Slides

How do components in cell be visible?

Stains (cytosol of cells & cell structures often transparent)

• Increases contrast as diff. components within a cell takes up stains to diff degrees

• Increase in contrast allows components to be visible

Why do cells need to be stained?

Cells are transparent, so light passes thru them. Stain increases the contrast, making cells more visible

Positively charged dyes

Attracted to negatively charged organelles

• Crystal Violet

• Methylene blue

Negative stain technique

Using negatively charged dyes that are repelled by negatively charge cytosol 

These dyes stay outside cells, standing out against stained background 

E.g. nigrosin, Congo red

Differential Staining

Using specific stains to distinguish diff types of cell

Gram Stain Technique

To produce good scientific drawing