1.2 Development of the Cell Theory

1. 1.2 Development of the Cell Theory

2. Biology • Biology is the study of life and living organisms

3. The scientific definition of what constitutes life has changed over time, but today it is agreed upon by scientists that all living organisms must have five characteristics in order to be considered alive: • They need energy (usually in some sort of food) • They produce waste material • They respond and adapt to the environment • They reproduce • They grow

4. Aristotle • Aristotle (384322 B.C.) devised a theory of the origin of life based on observations. • He observed the sexual and asexual reproduction of some organisms and noted that life often comes from other living organisms • Some living organisms, particularly organisms that were very small, seemed • to reproduce from nonliving material • (e.g. maggots appearing in meat, mould on food, etc.). • This led Aristotle and others to hypothesize that under certain conditions, life can come from nonliving matter.

5. Spontaneous Generation • The theory that life came from nonlife • It was once believed that to produce mice, one simply had to put sweaty underwear and husks of wheat in an open jar. • It was also believed that maggots appeared spontaneously from raw meat • Later it was determined that flies laid their eggs on the meat. • Eels came from the slime in river mud • Rats came from garbage or dirty laundry • Frogs came from mud

6. Q: Choose one of the previous examples and describe how to refute the idea using scientific experimentation.

7. Redi'sExperiment • http://www.youtube.com/watch?v=WzbHOY5fGqc • http://www.youtube.com/watch?v=WNByRghR6sw Francesco Redi (1626 – 1697) – Italian physician who used controlled scientific experiments to refute the theory of spontaneous generation

8. Needham • Read page 247 about John Needham

9. Pasteur • Before boiling meat broth in a flask, Louis Pasteur heated the neck of the bottle and bent it into an s-shape. • Air could reach the broth, but micro-organisms and other particles would get caught in the s-bend • Nothing would grow in the broth, but if the flask was tipped so the broth reached the s-bend mould would later appear • Read page 249 • http://www.youtube.com/watch?v=63IoOLXmzKg

10. Experiments • Controlled Variable • Broth type, flask type, light and temperature • Manipulated Variable • Access of dust to the flask • Responding Variable • Abillity to grow mould • Control • Flask where dust had normal access to the broth

11. Results • Pasteur provided strong evidence that spontaneous generation did not occur, but also that micro-organisms are found in the air • Lead to the study of microbiology, immunology and biochemistry • Showed the importance of conducted controlled experiments. The accepted theory became biogenesis – living things could only arise from other living organisms (suggested by Vichow in 1858)

12. The Cell Theory • It wasn’t until the 1830’s that the importance of the cell as the functional unit of life was recognized • Robert Brown identified the nucleus • Schleiden and Schwann: Two German scientists in the 1800s who concluded that all plants and animals were made up of cells • Rudolf Virchow: German physicist who concluded that cells divide to produce more cells. This corrected the misconception of Schleiden and Schwann that cells formed from nonliving materials “Where a cell exists, there must have been a preexistingcell.”

13. The Cell Theory • States: • All living things are made up of one or more cells and the materials produced by these cells • All life functions take place in cells, making them the smallest unit of life • All cells are produced from pre-existing cells through the process of cell division • http://www.youtube.com/watch?v=4OpBylwH9DU • http://www.youtube.com/watch?v=KuJqqiATlqw