cell basics and microscopes

cells

• first observed using a microscope in 1665 by Robert Hooke

  • Schleiden and Schawnn proposed cell theory

cell theory

• proposed by Schleiden and Schwann

• all organisms are composed of cells

• cells are the smallest living things

• ONLY arise from PRE-EXISTING cells

  • all cells tdy represent a continuous line of descent from first living cells

cell size is limited

• most cells are relatively small due to reliance on diffusion of substances in and out of cells

  • rate of diffusion

rate of diffusion

impacted by:

• surface area available

• temperature

• concentration gradient

  • distance

surface area to volume ratio

• an organism made of many small cells has an advantage over an organism composed of fewer, larger cells

• as cell’s size increases, volume increases MUCH MORE rapidly than its surgace area

  • neurons overcome limitation by being long and narrow

microscopes

allow for cells to be visible that can’t be seen with the naked eye

resolution

minimum distance 2 pts can be apart and still be distinguished as 2 separate pts

• objects must be 100 micrometers apart for the naked eye to resolve them as 2 objects rather than one

light microscopes

• use magnifying lenses with visible light

• resolve structures that are 200 nanometers apart

  • limit to resolution using light

electron microscopes

• use beam of electrons

• resolve structures that are 0.2 nanometers apart

• transmission electron microscopes

• scanning electron microscopes

transmission electron miscroscope

transmit electrons THROUGH the material

scanning electron microscopes

beam electrons ONTO the specimen surface