And how we try to figure it out

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 - Organization2. Reproduction3. Based on DNA4. Growth and Development5. Need for Energy6. Response to Environmental Stimuli7. Homeostasis8. 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!