The Origin of Cells1.5

Understanding

Applications

Nature of Science

• Cells can only be formed by division of pre-existing cells

• The first cells must have arisen from non-living material

• The origin of eukaryotic cells can be explained by the endosymbiotic theory

• Evidence from Pasteur’s experiments that spontaneous generation of cells & organisms does not now occur on Earth

• Testing the general principles that underlie the natural world: the principle that cells only come from pre-existing cells needs to be verified.

Review the Cell Theory All living things are made of cells

Cells are the smallest unit of life

All cells come from pre-existing cells

Cell Theory Has been modified since the 1800’s Does not mention how the first cells

arose

Spontaneous Generation Life can be

created from non-living matter

Greek philosopher Theophrastus Plant Silphium

had sprung from soil where it had never been before

Spontaneus Generaton Aristotle

Wrote how insects formed from dew falling on leaves or from the hair, flesh or faeces of animals.

Maggots develop on meat only if they came in contact with it.

Boiled soup in 8 containers, sealed 4 & left 4 open.

Redi

Spallanzani

Was it something in the air? The containers that allowed growth were open to the air?

Pasteur

1. Nutrient broth boiled.2. Sterile broth placed in 3 flasks.3. A sample of each flask was transferred to a plate

containing solid medium & incubated.4. Only flask with bacteria was _____

So where did the first cells come from?

Endosymbiosis