Cells and The Cell Theory

Cells were unknown until the invention of microscopes in the 1650’s two scientists working independently built the first microscopes Anton von Leeuwenhoek in Holland Robert Hooke in England

Robert Hooke in 1665 - First to coin term – “Cell” Looked at Cork Looked really at a dead plant cell Only saw the cell wall

Anton Van Leeuwenhoek 1600’s Made lenses that could magnify more. Observed many living organisms Looking at Protists called them “Wee Beasties” or “animalcules” (small animals)

Anton Van Leeuwenhoek Leeuwenhoek’s drawings of “animalcules” set off a flurry of amateur and sometimes ridiculous claims, such as: - pondwater animalcules causing madness!

Anton Van Leeuwenhoek -- looked at pond scum -- looked at blood from different animals -- looked at tartar from teeth -- first person to see bacteria --discovered yeast is a unicellular organism (yes….yeast found is bread is a living thing!)

Birth of the cell theory… 1838 Matthias Schleiden – concludes all plants made up of cells 1839 – Theodore Schwann concludes all animals are composed of cells Wrote 1st two parts of cell theory.

Birth of the cell theory… 1858 Rudolph Virchow – discovered that cells could not develop from anything except other cells Wrote the third part of the Cell Theory.

The Cell Theory The cell theory has three parts: All living things contain at least one cell (Schwann) The cell is the basic unit of life (Schwann) Cells can only come from pre-existing cells. (Virchow)

All living things contain at least one cell The Cell Theory 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.

Cells are the smallest living units of matter The Cell Theory 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

Cells can only come from pre-existing cells The Cell Theory 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

All cells have the following in common: Cell Similarities All cells have the following in common: 1. Cell Membranes -surrounds the cell -barrier between inside of cell and environment -controls the passage of materials through the cell 2. Hereditary Material -DNA -controls activities of the cell -contains the info needed to make new cells

All cells have the following in common: Cell Similarities All cells have the following in common: 3. Cytoplasm and Organelles -organelles = structures that allow the cell to live, grow, and reproduce. -cytoplasm = the fluid inside a cell that surrounds the structures. 4. Small Size

Benefits of Being Multicellular Grow by producing more small cells, not larger cells. Can perform more functions than unicellular. Many kinds of cells A single cell cannot do all the things that many different things that cells can do.

1. Prokaryotic Cells Two Types of Cells AKA = Bacteria World’s smallest cells NO NUCLEUS! DNA is on long, circular molecule (rubber band) Organelles do not have membranes Have ribosomes (to make protein) Most have a hard cell wall Probably the first type of cells on Earth. Oldest fossils ever found (3.5 billion yrs ago)

2. Eukaryotic More complex than prokaryotic 10 times larger Fossil evidence (2 billion yrs ago) All living things (except bacteria) have eukaryotic cells Have a nucleus All have cell membrane Some have cell wall Organelles have membranes Have more DNA than prokaryotic DNA stored in nucleus DNA molecules are linear (not circular)

Prokaryotic vs. Eukaryotic No nucleus Nucleus Organelles = no membranes Organelles = have membranes DNA = circular DNA = linear (line) Bacteria All other cells

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

Redi’s Experiment Independent variable = cover Dependent variable = 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 Redi Many 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 bringing it to life” “Scientists seek only to challenge belief systems and stir things up”

Lazzaro Spallanzani 1729. Italian Believed microbes that spoil food come from the air and can be killed by boiling Independent variable = air Dependent variable = food spoilage Hypothesis: If air is allowed to reach food, then microbes will get in and cause it to spoil

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 1859. 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 Independent variable = bacteria Dependent variable = 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= 0 Biogenesis = 3 Experimental method wins out over superstition the cell theory takes hold among ordinary people

Pasteur is the father of modern microbiology supported 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 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