What is Life?

Think of an example of a living thing… What is it? How do you know it is living?

Examine the items provided Which one is living? Which is dead? Which is non-living?

HOW CAN YOU TELL? What are the characteristics that allow you to make that conclusion?

Class share

Characteristics of Living Things1. Highly organized and contain many

complex chemical substances2. Composed of one or more cells3. Use energy4. Grow5. Possess a definite form and limited size6. Limited lifespan7. Reproduce8. Respond to changes in their environment9. Groups of living things evolve over time

Place the following items Toenail Sun Hair Nerve cell Leaf

Fire Tree Bark Water Algae Seaweed

Where does life come from?

Something from nothing?? Sometimes living things seem to appear

out of “nowhere”!

Think of an example

Observation 1: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t there previously.

What was happening?

Conclusion: People thought that muddy soil gave rise to the frogs.

What do you think was really happening?

What was happening?

Observation 2: In many parts of Europe, medieval farmers stored grain in barns with thatched roofs. As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and then there were lots of mice around.

What was happening?

Conclusion: They thought the mice came from the moldy grain.

What do you think was really happening

What was happening?

Artistotle reasoned that they must be created by reactions between nonliving substances.

For almost 2000 years people believed Aristotle’s theory of ABIOGENESIS

AristotleGreek philosopher (384-322 BC)

ABIOGENESIS: the theory that non-living things can be transformed into living things.

BIOGENESIS: living organisms come from other living organisms.

ABIOGENESIS vs BIOGENESIS

Over 300 years ago, a Belgian doctor, van Helmont set up an experiment to test abiogenesis

He concluded that mice could be created from grains of wheat and a dirty shirt!

van Helmont1580 - 1644

What is wrong with this experiment?

Development of the Scientific Method… Up to this point, science was based on observation and analysis

people began to see that this was inadequate and that controlled experiments were needed to test hypotheses

In 1668, Italian physician, Redi, conducted an experiment to test abiogenesis

Showed that flies were not produced by rotting meat.

Francesco Redi1626 - 1697

What is better about this experiment?

Redi’s experiment Answer the following questions…

1. What was the experimental variable?2. What were the controlled variables?3. What was the “active ingredient” that

people believed was needed for spontaneous generation?

4. What were his results? What could he conclude from these results?

In 1748, John Needham performed an experiment to study the spontaneous generation of microorganisms instead of maggots.

Micro-organisms grew in all flasks. He saw this as proof of spontaneous generation.

John Needham1713 - 1781

What is wrong with this experiment?

In 1768, Spallanzani performed an experiment to disprove Needham

Micro-organisms did not grow in the sealed flask. He felt this “disproved” abiogenesis.

Lazzaro Spallanzani1729 - 1799

What is better with this experiment? What is still wrong?

What is still wrong? Critics said that, by sealing his flasks, he had cut

off access to a key ingredient for abiogenesis – fresh air. That was why no micro-organisms grew.

Spallanzani could not think of a way of letting air but not airborne micro-organisms into his flasks.

So the theory of abiogeneisis survived Spallanzani’s challenge and lived on

Spallanzani’s findings were used as a new way to preserve food – canning!

In 1864, Louis Pasteur “definitively” disproves abiogenesis

The swan-necked flask developed by Pasteur enabled him to definitely disprove abiogenesis for micro-organisms by showing that these creatures arise in food from airborne spores.

Louis Pasteur1822 - 1895

What is better with this experiment?

Where did the FIRST cells come from? And why can’t they form now?

Summary Questions 1. What are some problems that

scientists have with observations? 2. What is a hypothesis? 3. Why did early scientists believe that

frogs came from mud? 4. Define abiogenesis and biogenesis,

give your own example for each.