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

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

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

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

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.

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

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

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

Principles of Biology Cell Theory Gene Theory Homeostasis Evolution

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

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

Homeostasis Maintaining a stable internal environment or keeping things constant

Evolution Change in the characteristics of living things over time