1. An Introduction to Life on Earth
Chapter 1
An Introduction to Life on Earth

2. 1.1 Why Study Biology?
Biology helps you understand your body.
Biology helps you become an informed citizen.
Biology can open career opportunities.
Biology can enrich your appreciation of the world.

3. 1.2 How Do Biologists Study Life?
The scientific method is the basis for scientific inquiry.
Life can be studied at different levels of organization.
Science is a human endeavor.
Scientific theories have been thoroughly tested.

4. 1.2 How Do Biologists Study Life?
The scientific method
Observation
Question
Hypothesis (proposed explanation)
Prediction
Experiment or observation
Conclusion
Communication to others

5. 1.2 How Do Biologists Study Life?
The scientific method
Observation
Question
Hypothesis
Prediction
Experiment or
Observation
Hypothesis
not supported:
pose new
hypothesis
Hypothesis
supported:
make more
predictions
Conclusion
Fig. 1-2

6. 1.2 How Do Biologists Study Life?
PLAY
Animation—Experimental Design

7. 1.2 How Do Biologists Study Life?
What is a well-designed experiment?
Each experiment has a control.
Each experiment has a single variable.
Example: spoiled meat experiment of Francesco Redi (1621–1697)

8. Fig. E1-1 Observation: Question: Hypothesis: Prediction: Experiment
Flies swarm around meat left in the open; maggots appear on the meat.
Question:
Why do maggots appear on the meat?
Hypothesis:
Flies produce the maggots.
Prediction:
If flies are kept away from the meat, then no maggots will appear.
Experiment
Obtain identical pieces of
meat and two identical jars
Place meat
in each jar
Experimental variable:
gauze prevents
entry of flies
Leave jar
uncovered
Cover jar
with gauze
Leave exposed
for several days
Controlled variables:
time, temperature,
place
Leave covered
for several days
Flies swarm around
and maggots appear
Results
Flies kept from meat;
no maggots appear
Control situation
Experimental situation
Conclusion:
Spontaneous generation of maggots from meat does not occur; flies
are probably the source of maggots.
Fig. E1-1

9. 1.2 How Do Biologists Study Life?
The scientific method in everyday life
Observation
Car won’t start.
Why won’t the
car start?
Question
The car won’t start
because the battery
is dead.
Hypothesis
IF the hypothesis is
correct, THEN the
car will start if the
battery is replaced.
Prediction
Experiment or
Observation
Replace the battery.
The car starts.
The dead battery
hypothesis is
supported.
Conclusion
Fig. 1-3

10. 1.2 How Do Biologists Study Life?
Question: Have all other variables been eliminated?
Example: loose battery cables
Example: broken electrical wires
Solution: Control for other variables
Make sure cables are tight.
Make sure electrical wires are in good condition.

11. 1.2 How Do Biologists Study Life?
Life can be studied at different levels of organization.
cell
nerve cell
tissue
nervous tissue
organ
brain
organism
pronghorn antelope
population
herd of pronghorn antelope
community
snakes, antelope, hawks, bushes, grass
Fig. 1-5

12. 1.2 How Do Biologists Study Life?
Science is a human endeavor.
Scientists are real people and sometimes make mistakes.
One of the greatest medical advances in history was made by mistake, by Alexander Fleming.
The mold Penicillium, which kills bacteria, was discovered by chance by Fleming.
This led to the discovery of penicillin, an important antibiotic that has saved millions of lives.

13. 1.2 How Do Biologists Study Life?
Penicillin kills bacteria.
A petri dish
contains solid
growth medium
Bacteria grow in
a pattern created
by streaking
A substance from
the mold diffuses
outward and inhibits
the growth of
nearby bacteria
A colony of the
mold Penicillium
Fig. 1-7

14. 1.3 What Is Life? Characteristics of living things
Living things are organized.
Fig. 1-8

15. 1.3 What Is Life? Characteristics of living things
Living things are complex
Fig. 1-8

16. 1.3 What Is Life? Characteristics of living things
Living things are organized and complex.
Fig. 1-8

17. 1.3 What Is Life? Characteristics of living things
Living things grow and reproduce.
Fig. 1-9

18. Characteristics of living things
1.3 What Is Life?
Characteristics of living things
Living things respond to stimuli
Light
Sound
Chemicals
Hunger
Pain
Touch
Heat
Cold
Motion
Gravity

19. Characteristics of living things
1.3 What Is Life?
Characteristics of living things
Living things acquire and use material and energy.
Fig. 1-10

20. Animation: What is Life?
PLAY
What is Life?

21. Characteristics of living things
1.3 What Is Life?
Characteristics of living things
Living things use DNA to store information.
Fig. 1-11

22. DNA: The universal molecule of life
1.4 Why Is Life So Diverse?
DNA: The universal molecule of life
DNA is found in the bodies of all organisms, from bacteria to whales.
Its universal presence suggests that all organisms have descended from a common ancestor having the same molecule.

23. DNA: The universal molecule of life (continued)
1.4 Why Is Life So Diverse?
DNA: The universal molecule of life (continued)
DNA is passed from generation to generation during periods of reproduction.
Organism diversity results from small changes in DNA accumulating over billions of years of evolution.

24. Life’s unity and diversity is a result of evolution.
1.4 Why Is Life So Diverse?
Life’s unity and diversity is a result of evolution.
Life changes over long periods of time.
Groups of organisms change from generation to generation.
The changes that accumulate in populations of organisms over time is called evolution.

25. Life’s unity and diversity is a result of evolution (continued).
1.4 Why Is Life So Diverse?
Life’s unity and diversity is a result of evolution (continued).
Life’s unity arises from the fact that diverse descendents arise from single ancestors.
The unifying principle of biology is that all of life’s features in today’s organisms arose through evolution.

26. Natural selection is the basis of evolutionary change.
1.4 Why Is Life So Diverse?
Natural selection is the basis of evolutionary change.
Characteristics of individuals in a group vary.
Some characteristics help individuals survive and reproduce.
Those that reproduce pass on these traits to future generations.

27. Natural selection is the basis of evolutionary change (continued).
1.4 Why Is Life So Diverse?
Natural selection is the basis of evolutionary change (continued).
The favored traits are accumulated in populations over time, changing the individuals within the group.
Example: Big teeth in beavers favor survival and are passed on to future generations.

28. Biodiversity is threatened by human activities.
1.4 Why Is Life So Diverse?
Biodiversity is threatened by human activities.
Biodiversity is the wealth of species in the world and the interrelationships that sustain them.
Human expansion in the world has severely reduced habitats for these interrelationships to flourish.
Extinction of many organisms have followed from the growth of human populations on all the world’s continents.
Pollution and chemical wastes kill aquatic organisms.

29. Logging activities remove trees and destroy the soil.
1.4 Why Is Life So Diverse?
Logging activities remove trees and destroy the soil.
Fig. E1- 4