Cell Theory: Discovery of the Cells and its Theory Chapter 7.1

History Cells were not discovered until the development of the microscope in the 1650s Two scientists working separately of each other built the first microscopes: Anton von Leeuwenhoek in Holland Robert Hooke in England

Leeuwenhoek Studied pond water, sour milk, and semen The first person to see cells under the microscope Names moving organisms “animacules” (there was no other name for cells at this time!) Scared people and caused a sensation

Leuuwenhoek’s Drawings of “animacules” These drawings led to ridiculous claims “Pond water causes madness!!”

And…. They thought human sperm cells contained tiny human beings and reproduction worked like planting a seed. The human grew out of the cell! We look back and think this is “crazy” but at the time, people took these ideas very seriously!

Hooke Studied Cork- kind of tree bark (plant cells) The first person to coin the term “Cell” Named them cells because they reminded him of the small rooms (cells) that monks slept in

The Cell Theory Many men contributed to the discovery of the cell theory and what we know about cells now Theodore Schwann (all animals made of cells) Mathias Scheiden (all plants made of cells) The cell theory states that cells: are the basic unit of life can only come from prior cells all living things are made of at least one cell

How did they determine this? When cells were dissected or broken open, they died This meant that whatever “life” is, it is something that happens inside cells Observations of many living things were made and if it was alive, it had cells

Cells come from pre-existing cells Does not answer the question where the first cell came from or how it came to be The idea is now disproved that life can come from non- life No scientist has ever built a living cell from non-living organic molecules

Spontaneous Generation Idea that was believed to be true up until about 1850 Spontaneous generation says that life could arise from non-living things Life can be “spontaneously” created, also called abiogenesis (life not from life) Today we believe in biogenesis (life from life)

Spontaneous Creation in mice idea People in the Middle Ages believed that mice could be spontaneously created by putting grain in a dark, quiet place and leaving it for a few weeks. They thought the bag of grain would produce the mice!

Disproving Spontaneous Generation The following scientists attempted to disprove the idea of spontaneous generation; they believed life came from life: Francesco Redi Lazzaro Spallazani Louis Pasteur

Redi Italian scientist, 1600s First person to challenge the idea of spontaneous generation Disbelieved the idea that flies would magically be created from rotting meat Designed a simple experiment to disprove this

Redi’s Experiment Hypothesis: If a jar containing rotting meat is covered, it will produce no flies. The jar left uncovered will produce flies. Experiment: IV-cover DV-presence of flies

Redi’s Conclusions Flies are produced from rotting meat only because the flies lay eggs, they grow into maggots, and metamorphose into flies (If flies can’t get to meat to lay eggs, no new flies will be created) Meat doesn’t produce flies

Objections to Redi’s Experiment Redi’s claim that flies don’t spontaneously re-generate was REJECTED!!! Why? “Sealing the jar closed prevented a magical essence from entering the rotting meat and bringing it to life”

Lazzaro Spallanzani Italian scientist, 1700s Believed microbes in the air cause food spoilage and they can be killed by boiling Designed an experiment to disprove that food produced living microbes to cause spoilage

Spallanzani’s Experiment Hypothesis: If air is allowed to reach food, then microbes will get in it and cause food spoilage Both flasks were boiled to kill any prior microbes Flask 1-uncovered (Spoiled) Flask 2-covered (didn’t Spoil)

Objections to Spallanzani’s Experiment Spallanzani’s Experiment was REJECTED!!! Why? “Sealing the flask shut blocked the entrance of a magical life force in the air from getting to the broth (Few people had seen microbes, so few believed in them)

Disproving a Magical Life Force A special experiment needed to be designed to disprove the idea of a magical life force How? Louis Pasteur is going to improve Spallanzani’s experiment

Pasteur French Scientist, 1800s (nearly 200 years later!!!) Invented pasteurization: sterilization by heat Pasteur’s Experiment: Hypothesis: If boiled broth is kept free of bacteria, then it will not spoil even if air can reach it. Designed a special flask that would allow air to flow it, but not allow microbes to fall/settle into flask

Swan-Necked Flask (S-Flask) Curved neck allows air in, but prevents microbes in air from settling into jar

Spontaneous Generation is Disproved Pasteur concluded that the food didn’t spoil because microbes in air didn’t get to food, even though air was allowed to flow in Pasteur is considered the “Father of Modern Microbiology” Pasteurization (sterilization by heat) lead to preserving foods with the canning process and eventually canned goods at stores

How have discovery of cells impacted humans? Hygiene: In the late 1870s, doctors start to wash hands and utensils before surgery, some start to wear gloves! Joseph Lister invented Listerine because bacteria in mouth cause bad breath Medicine: Understanding of medical diseases such as cancer Development of antibiotics and preventative disease measures Food: Use of refrigerators to keep foods longer Cover food dishes to keep microbes out