Life!

And how we try to figure it out

Figure 1.2 The hierarchy of biological organization

Biology

• Define life (good luck!).

• How do we know a living thing when we see one?– list characteristics common to

ALL living things.

Characteristics of all living things:

1. Made Up of Cells - Organization

2. Reproduction

3. Based on DNA

4. Growth and Development

5. Need for Energy

6. Response to Environmental Stimuli

7. Homeostasis

8. Evolution

What makes Biology a science?

• How do you know science when you see it?– list some characteristics of

science and describe how scientists work.

Science is…

• Objective

• Data driven

• Experimental

• Attempt to find the best possible naturally occurring explanation for a phenomenon.

Observations are objective

• Observe the familiar actions and describe them. No talking!

• Compare notes with others – how objective were your observations?

• What happens when new observations don’t fit with the old?

• How did observations lead to hypotheses on life?

Where does life come from?

• At least by Aristotle’s time, people were concerned with this.

• Prevailing theory: Spontaneous generation or Abiogenesis– Life comes from non-living things.– Based on everyday observations– Aristotle described an “active principle”

that was responsible.

Abiogenesis examples

• Salamanders and frogs come from river mud.

• Mice come from wheat that has been exposed to sweat.

• Humans??? – pregnancy and birth were understood,

sexual intercourse was important, but sperm and eggs didn’t play a role!

Really small life?

• Microscopes allowed observation of micro-organisms, but these were thought to come from plants or mud mixed with water (van Leeuwenhoek, mid 1600’s).

• Bacteria in meat broth were formed from the meat (Needham, 1745).

An alternative view: Biogenesis

• By the mid 17th century some individuals questioned abiogenesis.

• Their observations suggested all living things were produced by other living things

– Biogenesis

• A test of biogenesis/abiogenesis was needed!

Francisco Redi

• 1668: An Italian physician decided to test the “common knowledge” that maggots came from rotting meat.– Without refrigeration or concern about

covering food, maggots tended to appear on meat within a few days. Therefore, the meat produced the maggots.

• OBSERVATION: Flies land on meat that is left uncovered. Later, maggots appear on the meat.

• HYPOTHESIS: Flies produce maggots.

Redi’s Alternative:

Redi’s Experimental Design

• If flies are kept away from meat by a covering, no maggots should appear.

• Compare to meat stored in the usual way (uncovered) which should develop maggots.

• Keep every other factor the same!

The variables:• Independent variable:

–covering over jar or not• Controls fly access to meat

• Controlled Variables:

–jars, type of meat, location, temperature, time

• Dependent variable:

–maggots?

Uncovered jars Covered jars

Several days pass

?

Procedure

?

Results

Uncovered jars Covered jars

Several days pass

Maggots appear No maggots appear

CONCLUSION:

• Maggots form only when flies come in contact with meat. – Spontaneous generation of

maggots did not occur.

Spallanzani’s Experiment: 1765

Gravy is boiled. Flask isopen.

Gravy is teeming with microorganisms.

Figure 1-10 Spallanzani’s Experiment

Gravy is boiled. Flask issealed.

Gravy is free of microorganisms.

Pasteur’s Experiment: 1860

Broth is boiled.

Pasteur

Broth is boiled. Broth is free ofmicroorganismsfor a year.

Pasteur

Broth is boiled. Broth is free ofmicroorganismsfor a year.

Curved neckis removed.

Pasteur

Broth is boiled. Broth is free ofmicroorganismsfor a year.

Curved neckis removed.

Broth is teeming with microorganisms.

Biogenesis wins!

• Pasteur’s experiments finally won general support for the biological origins of living things.

• Pasteur also introduced methods of food preservation (Pasteurization!) that dramatically increased the shelf life of foods.

But wait! There’s more!

• Where did the FIRST living thing come from???

• Where did the universe come from???

• Let’s start with nonliving things and how they affect living things.

• Abiotic vs Biotic factors!