Emergence of the Cell Theory

1
Emergence of the Cell Theory

• Objectives
• To understand the steps to the Research Method
• Critique the experiments done to challenge
  Abiogenesis
• Describe the Cell Theory

2
Research Method

• Observation (Ask a question)
• State a Hypothesis
• Test the Hypothesis with a controlled
  experiment
• Collect Data
• Make a Conclusion
• Report your Results

3
Controlled Experiments

• Independent variable (manipulated variable)
• The variable being tested.
• Dependent variable (responding variable)
• The effect of the variable being tested.
• Experimental Part has the variable being tested
• Control part lacks the variable being tested
• Variables
• Try this worksheet

4
Assignment

• Complete the assignment on the handout.
• Answers
• Observation/Question Does HGH increase speed?
• Hypothesis If mice receive HGH, then they will
  run faster
• Independent Variable HGH
• Variables kept constant Types of mice health of
  mice food environment amount of HGH, etc
• Dependent Variable Faster running
• Quantitative Data measurable data
• Qualitative Data observable data (senses)
• Conclusion Mice receiving HGH run faster

5
Controlled Experiment
6
Lets look at some experiments

• Francesco Redi conducted an experiment to prove
  that maggots could not mysteriously appear on
  decaying meat.
• Read about Redis first experiment on page 8 .
  In your notes, describe what Redi did in each of
  the 6 steps of the Research Method. ?
• Observation (Ask a question)
• Hypothesis
• Controlled Experiment
• Data Collection (Qualitative/Quantitative)-
• Conclusion
• Report Results
• Check next slide for answers..but not until you
  try first!

7
Redis Experiment

• 1. Flies landed on the meat before maggots
  appeared. (Why do maggots appear?)
• 2. If flies land on decaying meat, then maggots
  will appear.
• 3. Set up 2 jars, one covered and one open.
• 4. Open jar had maggots and the closed one
  didnt.
• 5. Flies lay eggs that develop into maggots.
• 6. Report his results.

8
Redis Experiment
9
Abiogenesis

• A theory that says living things can arise from
  non-living things
• First proposed by Aristotle - maggots appearing
  on decaying meat/recipe for mice/worms found
  after rain
• Anton vanLeeuwenhoek invented the first
  microscope. His discovery fuelled the debate
  about where life comes from.
• Read about John Needhams experiment described on
  p.11.
• In your notes, describe his experiment. ?
• From the next slide, answer the 2 questions.

10
Needhams Experiment

• What was his conclusion ?
• What mistake(s) did he make ?

11
Abiogenesis??

• Lazzaro Spallanzani recreated Needhams
  experiment, but made 2 changes in an attempt to
  disprove his conclusion. Check out his experiment
  on p. 11.
• What did he do ?
• Why were his findings not accepted ?
• What would a scientist have to do to satisfy the
  critics ?

12
Louis Pasteur

• Pasteur came up with a way to let air in , but
  keep microbes out.
• Read about his experiment on page 12 and describe
  what he did in your notes. ?

13
Pasteurs Experiment
14
Pasteurs Experiment
15
Pasteurs Experiment
16
Pasteurs Experiment

• Pasteur was able to reduce the variables
  affecting his experiment down to one..the
  microbes in the air!
• He disproved the Theory of Abiogenesis
• It was replaced with the Theory of Biogenesis
• Only life can produce life
• Biogenesis leaves one important question
  unanswered?
• Where did the first living thing come from???

17
Cell Theory

• Robert Hooke looked at slices of cork under a
  microscope and saw little compartments he called
  Cells
• German scientists Schleiden and Schwaan
  discovered that plant and animal tissue was
  composed of cells.
• The Cell Theory
• The cell is the basic structural component of all
  life
• The cell is the basic functional unit of all life
• Only cells can produce cells

18

• Answer the questions from the worksheet titled
  How Scientists Work. Use the page references
  from you textbook to find your answers.
• Ill be checking your results on