1.2 Development of the Cell Theory

Biology

• Biology is the study of life and living organisms

• 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:1. They need energy (usually in some sort of food)2. They produce waste material3. They respond and adapt to the environment4. They reproduce5. They grow

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.

Spontaneous Generation

• The theory that life came from nonlife• Also known as abiogenesis• 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.

• Redi's Experiment

• http://www.youtube.com/watch?v=WzbHOY5fGqc

Needham

• Read page 247 about John Needham

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

Scientific Method

• Before 1800’s scientists used little proof to back up their discoveries and beliefs

• General public would believe them based on hearsay and assumptions

• Because of the lack of scientific data, there was great difficulty in introducing new ideas that did not follow the norm of the day

Scientific Method

• The steps that you will use and are used in laboratories are ones that are used by all modern scientists

• Each step is important and plays a large role in verifying data and theories

Scientific Method – Steps:• Problem• Hypothesis• Experimental Design – Manipulated Variable, Responding

Variable, Controlled Variables• Observations• Conclusion• Open-ended – new questions that arise from the

investigation

Experimental Design - Variables

• Manipulated Variable (independent) – the variable that is directly manipulated, or changed, by the experimenter

• Responding Variable (dependent) – variable that responds to the manipulated variable (what we observe)

• Controlled Variables – factors that remain exactly the same in each part of the experiment

Experimental Design - Variables

• For each of the following statements, identify the MV and RV.• The number of pigs in a litter is determined by the weight of the mother

pig.• Will the number of foxes in Kananaskis Country have any effect on the

rabbit population?• The score on the final test depends on the number of skills attained.• More bushels of potatoes will be produced if the soil is fertilized more.

Experimental Design - Variables• Students pointed a flashlight at a screen in an investigation to

determine if the distance from the light to the screen had any effect on the size of the illuminated area.

• A study was done with rats to determine if the number of offspring born dead was affected by the number of minutes of exposure to X-rays on mother rats.

• Five groups of rats are fed identical diets except for the amount of Vit A that they receive. Each group gets a different amount. After 3 weeks on the diet, the rats are weighed to see if the amount of Vit A affected their weight.

Experimental Design - Variables

• Will the number of nails picked up by an electromagnet be increased if more batteries are put in the circuit?

• The amount of algae growth in lakes seems to be directly related to the number of sacks of phosphate fertilizer sold by local merchants.

• Six groups of children were used to see if the scores on their weekly spelling tests were affected by the number of minutes of spelling practice they had each day.

Experimental Design - Graphing

Experimental Design

Example:• Problem: Which variety of peanut butter cookies do

people like best?• Variables:

• Manipulated: type of extra ingredient added to basic recipe• Controlled: basic recipe as well as …

• Responding:

Pasteur's Scientific Experimental Variables

• Controlled Variable- held constant throughout• Broth type, flask type, light and temperature

• Manipulated Variable- conditions changed• Access of dust to the flask

• Responding Variable- condition that changes in response• Abillity to grow mould

• Control- not changed from its normal condition• Flask where dust had normal access to the broth

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 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 preexisting cell.”

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

To Do

• Answer questions 3 and 4 on page 252• Fill in Development of Cell Theory Chart up to Virchow in

your workbook