History of Cell Discovery

History of Cell Discovery

Daily Question:Brainstorm: What do you think of when you think of

the word cell?Use a circle map to brainstorm

History*Cells were unknown until the discovery of microscopes in the 1650’s

*two scientists working independently built the first microscopes

*Anton von Leeuwenhoek in Holland

*Robert Hooke in England

*Leeuwenhoek

*Studied pondwater, sour milk, and other fluids

*named moving organisms “animalcules”

scared people and caused a sensation

Leeuwenhoek’s drawings of “animalcules” set off a flurry of amateur and sometimes ridiculous claims, such as:

- pondwater animalcules causing madness!

*Hooke

*Studied cork - a kind of tree bark

*named the structures he saw “cells” because they reminded him of the small rooms monks slept in.

Pause

Take two minutes to summarize your notes into your own words.

*Spontaneous Generation

From pre-historic times to about 1850, most people believed that under the right conditions,

*living things could spontaneously appear from non-living material.

People throughout the Middle Ages

believed that mice could be “created” spontaneously by putting grain in dark, quiet place

and leaving it for a few weeks.

The discovery of cells only confused people more- If cells are alive, then where do they come from?

Can these almost invisible things appear spontaneously from the air?

*Francesco Redi*Born 1626 in Italy

*First to challenge the idea of spontaneous generation

Did not accept the common belief that flies magically appeared from rotting meat

Redi’s Experiment

IV=cover

DV=presence of flies

Hypothesis: If a jar containing rotting meat is covered, then it will produce no flies

Redi’s Conclusions

Flies lay eggs, which grow into maggots, which metamorphose into flies

If flies can’t lay eggs, then no new flies can grow

Fly eggs

Objections to RediMany people rejected Redi’s claim that flies do not spontaneously generate

Their reasoning:

“sealing the jar closed prevented a magical essence from entering the rotting meat and brining it to life”

“Scientists seek only to challenge belief systems and stir things up”

Pause

Take two minutes to summarize your notes into your own words.

*1729. Italian

*Believed microbes that spoil food come from the air and can be killed by boiling

IV= air, DV=food spoilage

Hypothesis: If air is allowed to reach food, then microbes will get in and cause it to spoil

*Lazzaro Spallanzani

Spallanzani’s Experiment

Flask 1: boiled broth, open

Flask 2: boiled broth, sealed shut

Results

Flask 1 spoiled

Flask 2 did not spoil

Objections to Spallanzani

Sealing the flask shut blocked the entrance of a magical life force in the air from getting to the broth.

Since few people had seen these microbes, few people believed him.

*Louis Pasteur*1822. France

Supported that spontaneous generation is a myth

*Invented pasteurization (sterilization by heat)

Pasteur’s Experiment

An improvement on Spallanzani’s work

Used special “swan-neck flasks” that allowed air in but kept bacteria out

IV= bacteria, DV=spoiling broth

Hypothesis; If boiled broth is kept free of bacteria, then it will not spoil even if air can reach it.

The curved neck allows air in but traps bacteria-carrying dust and dirt

particles

*Spontaneous generation is dead!

Redi didn’t believe in it, and did an experiment using flies

Spallanzani didn’t believe in it, and experimented with broth

*Pasteur disproved it conclusively with his open-air yet spoilage free flasks.

Life from dead stuff= 0Biogenesis = 3

Experimental method wins out over superstition

the cell theory takes hold among ordinary people

*Pasteur is the father of modern microbiologysupported the last part of the cell theory: cells only come from pre-existing cells

identified yeasts as the microbes that change grape juice into wine

showed that heat can be used to sterilize foods and preserve them in sealed glass containers, and later cans.

Finally...in the late 1870’s, doctors start to wash their hands and instruments before operating...some even start wearing gloves!

Joseph Lister’s wacky idea that antiseptics kill germs catches on...

The Cell TheoryThe cell theory has three parts:

All living things are composed of one or more cells

Cells are the basic unit of structure and organization of all living things

Cells can only come from pre-existing cells

*The cell theory

1. *All living things contain at least one cell

Many scientists working after Hooke and Leeuwenhoek observed different plants and animals

Each of them noted that no matter what they observed, if it was alive it had cells.

2. *Cells are the smallest living units of matter

scientists quickly realized that when cells were dissected or broken open they died

This meant that whatever “life” is, it is something that happens inside cells

*3. Cells can only come from pre-existing cells

does not answer the question of where the first cell came from or how it came to be.

has not been disproved yet- no scientist has ever built a living cell from nonliving organic molecules

*The cell theory is one of the most important theories in biology.

All living things contain at least one cell

Cells are the smallest living units of matter

Cells can only come from pre-existing cells

And now…Use Google images (select photos) to find photographs of cells.

Write a description of three cells that you see on your paper…

Complete the Study Guide for ch 7.1If you finish early you may work on credit Option A