1. 1.5 Origin of Cells
Understanding:
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
Nature of science:
Testing the general principles that underlie the natural world: the principle that cells only come from pre-existing cells needs to be verified
Applications:
Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth

2. 1880s
Theory cells only produced by division of pre-existing cells
Cells in body formed this way
Trace our cells back to sperm and egg
Sperm and egg made by division in parents
Trace back through the whole of history to earliest cells on earth
Origin of cells
Understanding:
Cells can only be formed by division of pre-existing cells

3. Origin of cells Must reach the first ever cell – what was before that?
Unless cells arrived from somewhere else they must have arisen from non-living material
How could this have happened?
Complete the sheet to describe a possible sequence
Understanding:
The first cells must have arisen from non-living material

4. Endosymbiotic Theory Formation of eukaryotes from prokaryotes
Mitochondria were once free-living prokaryotes
Developed aerobic respiration
Larger prokaryotes that could not respire aerobically took them in by endocytosis
Continued to live in their cytoplasm
Persisted to become the mitochondria in eukaryotes today
Understanding:
The origin of eukaryotic cells can be explained by the endosymbiotic theory

6. Endosymbiotic Theory Symbiotic relationship (both benefit)
Smaller cell provided with food
Larger cell provided with energy
Natural selection favored cells that had developed this relationship
Can also be applied to chloroplasts
Understanding:
The origin of eukaryotic cells can be explained by the endosymbiotic theory

7. Chloroplasts and Mitochondria
Although unable to live independently now
Evidence they once were:
Own genes on a circular DNA molecule like that of prokaryotes
Ribosomes same size and shape of those in prokaryotes
Synthesize their own proteins
Only produced by division of pre-existing mitochondria or chloroplasts
Understanding:
The origin of eukaryotic cells can be explained by the endosymbiotic theory

8. Endosymbiotic Theory Spontaneous generation of life Louis Pasteur
Who is he?
What did he believe?
What were his experiments?
When did he publish his results?
What were his conclusions?
Louis Pasteur: French scientist
Designed a broth to test whether sterile nutrient broth could spontaneously generate microbial life
No spontaneous generation of life
Applications:
Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth