1. INTRODUCTION TO BIOLOGY
Spontaneous Generation, Biogenesis and the Principles of Biology

2. How does life begin? There were 2 theories: Spontaneous generation
Biogenesis

3. Spontaneous Generation
Process by which life begins when ethers enter nonliving things
Francesco Redi conducted an experiment to disprove this theory

4. Redi’s Experiment
During Redi’s time maggots were thought to come from rotting meat
Experiment 1: Redi placed meat in an open jar and maggots appeared on the meat

5. Redi’s Experiment
Experiment 2: Redi placed meat in a closed jar and no maggots appeared
Critics stated that the ethers could not enter the jar; that is why no maggots appeared.

6. Redi’s Revised Experiment
Experiment 3: Redi placed meat in a jar covered with a mesh cloth to allow ethers to enter but nothing else
Maggots did not appear on the meat

7. Biogenesis Principle that life comes only from life
After Francesco Redi disproved the theory of spontaneous generation, Louis Pasteur conducted an experiment to prove biogenesis

8. Pasteur’s Experiment
Broth is placed in a flask with a curved neck to prevent dust from entering the broth
The broth is heated and after one year, the broth was still free of bacteria
The curved neck is broken off so that dust can now enter the flask
After one day, the broth was cloudy and filled with bacteria

9. Principles of Biology
Cell Theory
Gene Theory
Homeostasis
Evolution

10. Cell Theory All living things are made up of cells
Cells are the structural units of living organisms
Living cells always come from other living cells

11. Gene Theory
The idea that the characteristics of living organisms are controlled by genes, which are passed from parents to their offspring

12. Homeostasis
Maintaining a stable internal environment or keeping things constant

13. Evolution
Change in the characteristics of living things over time