Spontaneous Generation

Where do cells come from?

Abiogenesis

Early scientists believed that living things formed from non-living things spontaneously.

These early scientists

believed that frogs and

fish fell from the sky with

the rain.

Aristotle proposed that fish and frogs came from the mud and that flies came from rotting meat.

He introduced his theory of ABIOGENESIS theory which states that nonliving things can be transformed into living things spontaneously.

This theory was accepted for more than 2000 years.

Jean van Helmont believed that mice came from grains of wheat and dirty shirts.

Redi

Redi, in 1668, did an experiment to prove that flies did not come from rotting meat.

- He had four jars each with a different kind of meat (eel, fish, veal, and snake). He put these meats in four other jars but put lids on the jars.

- After time maggots were all over the meat in the uncovered jars.

Redi

- Critics claimed that the difference was fresh air.

- Redi repeated his experiment but this time he put wire mesh over the jars. This time no maggots were found.

- Redi concluded that flies do not come from rotting meat.

Needham

In 1745 Needham boiled chicken broth then put it into a flaskHe wanted to see if microorganisms would

grow. He only boiled the broth for a short time, so the microorganisms grew.

He supported spontaneous generation

Spallanzani

SpallanzaniHe put the broth in a flask, sealed it, drew out

any air, he then boiled the broth.

Critics said that he only disproved that spontaneous generation cannot occur without air

Pasteur

1859 PasteurHe boiled a meat broth in a flask

Heated the flask’s neck until he could bend it into an S shape. (Therefore air could enter the flask but not airborne microorganisms, these organisms would settle in the neck of the flask).

He found no microorganisms to grow in the broth.

When he tilted the flask so that the airborne microorganisms could enter the flask, he found growth in the flask.

http://www.youtube.com/watch?v=WNByRg

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Brief Important Events in the Development of the

Cell Theory

Hooke (1635-1703): viewed pieces of cork through a microscope, and described ‘cells’ in 1665.

Leeuwenhoek (1632-1723): viewed small organisms, protozoa and single celled organisms, under a microscope, which he called ‘animalicules’. He was the first person to observe bacteria.

Lorenz Orken : He stated “all living organisms originate and consist of cells”.

Brown : first to coin the term nucleus, which he discovered in a plant cell.

Schwann and Schleiden : concluded that animals and plants are made up of cells

Modern Cell Theory

All Living things are composed of cells. The cell is the basic unit of life.All cells arise from pre-existing cells. Cells

do not spontaneously arise or come from non-living things.

Biogenesis

Is the idea that living things only arise from other living things of the same type.

What did the first cells ‘look’ like?

Prokaryotes

Characteristics of a Prokaryotic Cell

Simple cells

Smaller than Eukaryotic cells

Lack a cell nucleus

Organelles lack membranes

Majority are unicellular (one cell)

Two Domains: archaea and bacteria

Prokaryotic Cell

Reproduce asexually usually by budding or binary fission

Prokaryotic Cell

Structure:cell wall plasma membranenucleoid ( DNA (deoxyribonucleic acid) material)ribosomes (function in protein synthesis)plasmids (extra genetic material that is able to replicate

independently)PiliCytoplasmflagellumOne strand of DNA, usually circular

Eukaryotic Cells

Characteristics of a Eukaryotic Cell

Found in all 5 kingdoms EXCEPT monera (bacteria)

Membrane bound organellesHas a true nucleusUnicellular and multi-cellularContains many strands of DNALarger than prokaryotic cells; 10-100 µm (1

micrometer = 0.000 1 centimeter)

Structure of cell:Cytoplasm – gel like Mitochondria - energy sourceCell membraneNucleus ( the ‘control center’) – contains all the

cell’s genetic material.

Eukaryotic Cell

Vacuole (mostly in plant cells) - is a fluid filled sac that stores materials

Ribosomes (can be attached to the ER or are free) - are the site of protein synthesis

Eukaryotic Cell

Lysosomes (contain enzymes) - engulf molecules

Chloroplasts (mostly in plant cells) - site of photosynthesis

Eukaryotic Cells

Endoplasmic reticulum [ER] (made up of heavily folded membranes) - is important in protein and lipid synthesis

Golgi apparatus (is a stack of membranes) - involved in packaging of proteins

Eukaryotic Cell

Cytoskeleton - supports and shapes the cell

Centriole (made up of protein tubes) – aids in mitosis

May or may not have flagellum.

Similarities between Prokaryotic and Eukaryotic Cells

Which came first…..

Prokaryotic or Eukaryotic???

Endosymbiont Hypothesis

The idea that prokaryotic cells developed into eukaryotic cells.

Endosymbiont or Endosymbiosis Hypothesis

Endosymbiosis Hypothesisendo = “within” sym = together biosis = “way of life”

The idea that mitochondria and chloroplasts were at one time simple bacteria (prokaryotic cells) that were taken in by a larger prokaryotic cell about 1.5 billion years ago

These smaller bacteria gave the larger cell energy and sugars (via photosynthesis)

The larger cell gave the smaller cell a safe place to live.

Both cells benefitted.

Eventually the smaller cell became an organelle apart of the larger cell.

Evidence

Mitochondria and chloroplasts have their own DNA (deoxyribonucleic acids) and ribosomes. Their DNA is circular and similar to prokaryotes.

Mitochondria and chloroplasts are about the same size as prokaryotes.

Mitochondria and chloroplasts are able to copy themselves within the cell.