1. An Introduction to Life on Earth1
An Introduction to Life on Earth 1

2. Chapter 1 At a Glance 1.1 What Is Life? 1.2 What Is Evolution?
1.3 How Do Scientists Study Life?
1.4 What Is Science?

3. 1.1 What Is Life?
Biology comes from the Greek words “bio” meaning “life” and “logy” meaning “the study of.” Organisms share common characteristics that, taken together, define life. Organisms:
Acquire and use materials and energy
Actively maintain organized complexity
Perceive and respond to stimuli
Grow
Reproduce
Have the capacity to evolve, collectively

4. 1.1 What Is Life? The cell is the basic unit of life
It is separated from its surroundings by a membrane
It encloses a variety of structures and chemicals in a fluid environment

5. Figure 1-1 The cell is the smallest unit of life
nucleus
cell wall
plasma
membrane
organelles
Plant Cell 5

7. 1.1 What Is Life? Organisms: Acquire and use materials and energy
Actively maintain organized complexity
Perceive and respond to stimuli
Grow
Reproduce
Have the capacity to evolve, collectively

8. 1.1 What Is Life? Organisms acquire and use materials and energy
Materials and energy are required for organisms to maintain organization, to grow, and to reproduce
Important materials (minerals, water, & other simple chemical building blocks) are acquired from the air, water, soil, and bodies of other living things
Organisms use energy continuously to sustain themselves

9. Figure 1-2 Properties of life
Antennae and
eyes: living
things respond
to stimuli
Gut: living
things acquire
nutrients
Eggs: living
things
reproduce 9

10. 1.1 What Is Life?
Organisms acquire and use materials and energy (continued)
Organisms obtain energy in two ways, coming directly or indirectly from the sun
Photosynthesis is the process by which plants and some single-celled organisms capture sunlight
Other organisms consume energy-rich molecules in the bodies of other organisms

11. Figure 1-3 The flow of energy and the recycling of nutrients11

12. 1.1 What Is Life? Organisms actively maintain organized complexity
Living things use energy on a continuous basis to self-sustain
Cells pump chemicals in and out for appropriate chemical reactions to occur
Organisms maintain relatively constant internal conditions or homeostasis

13. Figure 1-4 Organisms maintain relatively constant internal conditions13

14. 1.1 What Is Life? Organisms perceive and respond to stimuli
Organisms sense and respond to internal and external environmental stimuli
Sensory organs in animals can detect and respond to external stimuli such as light, sound, chemicals, etc.
Internal stimuli in animals are perceived by stretch, temperature, pain, and chemical receptors
Plants and bacteria respond to stimuli as well (e.g., plants grow toward the light, and bacteria move toward available nutrients in a medium)

15. 1.1 What Is Life? Organisms grow
Every organism becomes larger over time
Plants, birds, and mammals grow by producing more cells to increase their mass
Bacteria grow by enlarging their cells; they divide in half to reproduce after genetic material is copied
Growth involves the conversion of acquired materials to molecules of the organism’s body

17. 1.1 What Is Life? Organisms reproduce
Organisms reproduce by dividing in half, producing seeds, bearing live young, and laying eggs
Organisms give rise to offspring of the same type
The parent’s genetic material (DNA) is passed on to the offspring, creating continuity of life

18. Figure 1-6 Organisms reproduce
Dividing Streptococcus
bacterium
Dandelion producing
seeds
Panda with its baby 18

19. Figure 1-7 DNA 19

20. 1.1 What Is Life? Organisms, collectively, have the capacity to evolve
Evolution is the process by which modern organisms descended, with modifications, from preexisting forms of life
Changes in DNA within populations occur over the course of generations, which results in evolution
Populations are groups of the same type of organism living in the same area

21. 1.2 What Is Evolution?
Evolution explains the diversity of life on Earth
Evolution provides an explanation for the similarities found among different types of organisms
Chimpanzees and people have various physical features in common
DNA of humans differs from that of chimpanzees by less than 5%

22. Figure 1-8 Chimps and people are closely related
Dr. Jane Goodall 22

23. 1.2 What Is Evolution? Three natural processes underlie evolution
Genetic variation among members of a population due to differences in their DNA
Inheritance of those variations by offspring of parents carrying the variation
Natural selection of individuals whose survival and enhanced reproduction are due to the favorable variations they carry

24. 1.2 What Is Evolution?
Mutations are the original source of differences in DNA
Variations are due to the differences in genes, which are components of DNA and the basic units of heredity
Mutations occur when changes in genes are mistakenly copied
Mutations can also result from DNA damaged by
UV rays from sunlight and toxic chemicals from cigarette smoke

25. 1.2 What Is Evolution? Some mutations are inherited
Occur in sperm or egg cells
Effects of mutation
No effect (harmless)
A decrease in the organism’s ability to function
Death of the organism
An increase in an organism’s ability to survive and reproduce (rare)

26. 1.2 What Is Evolution?
Some inherited mutations help individuals survive and reproduce
Natural selection is the process by which organisms with certain inherited traits survive and reproduce better than others in a particular environment
Organisms that best meet environmental challenges leave the most offspring
Natural selection preserves genes that help organisms flourish

27. 1.2 What Is Evolution?
Some inherited mutations help individuals survive and reproduce (continued)
Adaptations are structures, physiological processes, or behaviors that aid in survival and reproduction
Adaptations that are good for one environment may be poor in another
Species that cannot adapt to environmental change become extinct, as for example, the dinosaurs
Extinction is the complete elimination of a particular species

28. Figure 1-9 A fossil Tyrannosaurus rex28

29. 1.2 What Is Evolution?
Some inherited mutations help individuals survive and reproduce (continued)
The many different habitats (environments) in an area coupled with evolutionary adaptive processes produce species variety, or biodiversity
Humans are responsible for accelerating the rate of environmental change (and therefore, the rate of extinction of species)

30. 1.2 What Is Evolution?
Some inherited mutations help individuals survive and reproduce (continued)
Darwin and Wallace formulated the basis of our modern understanding of evolution when they devised the theory of evolution in the mid-1800s
Abundant evidence has been found to support evolutionary theory since the 1800s

33. Evolutionary relationships among various biological species
Phylogenetic Tree
Evolutionary relationships among various biological species
Based upon similarities and differences in their physical or genetic characteristics.
Descended from a common ancestor.

35. Biological taxonomy classification:
Biologists classify organisms based on their evolutionary relationships
Biological taxonomy classification:

38. 1.3 How Do Scientists Study Life?
Life can be studied at different levels
All matter is formed of elements
An atom is the smallest particle of an element retaining the properties of an element
Atoms combine to form molecules
Molecules provide the building blocks for cells, the smallest unit of life

39. 1.3 How Do Scientists Study Life?
Life can be studied at different levels (continued)
Some forms of life consist of single cells
In multicellular forms, cells combine to form tissues
Tissues combine to form organs, which can be united as organ systems
Multicellular organisms are composed of multiple organ systems

40. 1.3 How Do Scientists Study Life?
Life can be studied at different levels (continued)
Organisms of the same type that are capable of interacting and interbreeding are called a species
A group of organisms of the same species living in a given area is a population
Interacting populations make up a community
A community and its nonliving environment is an ecosystem
The entire surface of Earth, including living and nonliving components, is the biosphere

41. Levels of biological organization
Fig. 1-10

42. 1.3 How Do Scientists Study Life?
Biologists classify organisms based on their evolutionary relationships
Scientists generally categorize organisms into three major groups, or domains
Bacteria
Archaea
Eukarya
The fundamental differences among cell types in organisms are reflected in classifications

43. 1.3 How Do Scientists Study Life?
Biologists classify organisms based on their evolutionary relationships (continued)
Bacteria and Archaea are single, simple cells
Eukaryotic organisms have one or more extremely complex cells
The domain Eukarya contains four subdivisions or kingdoms
Fungi
Plantae
Animalia
Protists

44. 1.3 How Do Scientists Study Life?
Biologists classify organisms based on their evolutionary relationships (continued)
Three characteristics underlie the classification of an organism into a domain and kingdom
There are exceptions to any simple set of rules used to distinguish the domains and kingdoms, but three characteristics are particularly useful
Cell type—simple or complex
The number of cells in each organism—unicellular or multicellular
Energy acquisition

45. Figure 1-11 The domains and kingdoms of life
DOMAIN BACTERIA
FIRST CELLS
DOMAIN ARCHAEA
Protists
Plants
DOMAIN EUKARYA
Fungi
Animals 45

46. 1.3 How Do Scientists Study Life?
Cell type distinguishes the Bacteria and Archaea from the Eukarya
All cells share common features
Plasma membrane is a thin sheet of molecules surrounding the cell
Organelles are specialized structures that carry out specific functions
All cells contain DNA, the hereditary material

47. 1.3 How Do Scientists Study Life?
Cell type distinguishes the Bacteria and Archaea from the Eukarya (continued)
The domains Bacteria and Archaea consist of prokaryotic cells
The domain Eukarya is composed of eukaryotic cells

48. 1.3 How Do Scientists Study Life?
Cell type distinguishes the Bacteria and Archaea from the Eukarya (continued)
Two cell types are seen among all living things: prokaryotic and eukaryotic cells
Cell types are named after presence or absence of a nucleus
The nucleus is a membrane-enclosed sac containing the cell’s genetic material

49. 1.3 How Do Scientists Study Life?
Cell type distinguishes the Bacteria and Archaea from the Eukarya (continued)
Eukaryotic (“true nucleus” in Greek)
They are larger than prokaryotic cells
They contain a variety of organelles, including a nucleus
This cell type is found only among members of the domain Eukarya
They are extremely complex

50. 1.3 How Do Scientists Study Life?
Cell type distinguishes the Bacteria and Archaea from the Eukarya (continued)
Prokaryotic (“before nucleus” in Greek)
They are only 1–2 micrometers in diameter
They lack organelles enclosed by membranes
They lack a nucleus
This cell type is found in the domains Bacteria and Archaea
They are smaller and much simpler than the eukaryotic cell

51. 1.3 How Do Scientists Study Life?
Multicellularity occurs only among the Eukarya
Unicellular (single-celled) organisms are found in
Bacteria
Archaea
Multicellular (many-celled) organisms are found in Eukarya, within the kingdoms
Fungi
Plantae
Animalia

52. 1.3 How Do Scientists Study Life?
The Eukarya acquire energy in different ways
Autotrophs (“self-feeding”)
Photosynthetic organisms that capture sunlight and store it in sugar and fats
Includes plants, some bacteria, and some protists
Heterotrophs (“other-feeding”)
Organisms that acquire energy through ingesting molecules in the bodies of other organisms
Includes many archaeans, bacteria, protists, fungi, and animals
The size of the food eaten varies from individual food molecules to ingestion and digestion of whole chunks

53. 1.3 How Do Scientists Study Life?
Biologists use the binomial system to name organisms
Organisms are placed in a hierarchy of categories
Genus and species are the two smallest categories
Genus includes many different species with similar characteristics
Species includes organisms that can interbreed and are nearly identical

54. 1.3 How Do Scientists Study Life?
Biologists use the binomial system to name organisms (continued)
Binomial system based on Latin words two (bi) and names (nomial), and consisting of the genus and species
Genus name is capitalized
Both genus and species names are italicized
People are Homo sapiens

55. 1.4 What Is Science?
Science is the systematic inquiry – through observation and experiment – into the origins, structure, and behavior of living and nonliving environments

56. 1.4 What Is Science?
Science is based on the principle that all events have natural causes
The belief that some events happen through supernatural forces (e.g., the actions of Greek gods)
The belief that all events can be traced to natural causes that we can comprehend (natural causality)
Corollary: Evidence gathered from nature has not been deliberately distorted to fool us

57. 1.4 What Is Science?
The scientific method is an important tool of scientific inquiry
The scientific method consists of six interrelated elements
Observation
Question
Hypothesis
Prediction
Experiment
Conclusion

58. 1.4 What Is Science?
The scientific method is an important tool of scientific inquiry (continued)
Scientific inquiry is a rigorous method for making observations
The scientific method for inquiry follows six steps

59. 1.4 What Is Science? The six steps of scientific inquiry
1. Observation of a specific phenomenon
2. The observation, in turn, leads to a question
3. The question leads to formulation of a hypothesis, based on previous observations, which is offered as an answer to the question

60. 1.4 What Is Science? The six steps of scientific inquiry (continued)
The hypothesis leads to a prediction, which is the expected outcome of testing if the hypothesis is correct
The prediction is tested by carefully designed additional observations or carefully controlled manipulations called experiments
The experiments produce results that either support or refute the hypothesis, allowing the development of a conclusion

61. 1.4 What Is Science?
Biologists test hypotheses using controlled experiments
Two types of situations are established
A baseline or control situation in which all possible variables are held at a constant
An experimental situation in which one factor, variable, is manipulated to test the hypothesis to determine that this variable is the cause of an observation
Science is useless unless communicated
The scientific method is illustrated by experiments by Francesco Redi and Malte Andersson

62. Obtain identical pieces of meat and two identical jars
Figure E1-1 The experiment of Francesco Redi illustrates the scientific method
Observation:
Flies swarm around meat left in the open; maggots appear on the meat.
Question:
Where do maggots on the meat come from?
Hypothesis:
Flies produce the maggots.
Prediction:
IF the hypothesis is correct, THEN keeping the flies away from the meat
will prevent the appearance of maggots.
Experiment:
Obtain identical pieces of
meat and two identical jars
Place meat
in each jar
Experimental variable:
Leave the jar
uncovered
Cover the jar
with gauze
gauze prevents the
entry of flies
Leave exposed
for several days
Controlled variables:
Leave covered
for several days
time, temperature,
place
Flies swarm around
and maggots appear
Results
Flies are kept from
the meat;
no maggots appear
Control situation
Experimental situation
Conclusion:
The experiment supports the hypothesis that flies are the source of
maggots and that spontaneous generation of maggots does not occur. 62

63. Figure E1-2 The experiment of Malte Andersson
Observation:
Male widowbirds have extremely long tails.
Question:
Why do males, but not females, have such long tails?
Figure E1-2 The experiment of Malte Andersson
Hypothesis:
Males have long tails because females prefer to mate with long-tailed males.
Prediction:
IF females prefer long-tailed males, THEN males with artificially lengthened tails will attract more mates.
Experiment:
Divide male birds
into four groups
Manipulate the
tails of the males
Do not
change the tail
Cut the tail and
re-glue in place
Experimental
variable:
Cut the tail to half of
the original length
Add feathers to
double the tail length
length of tail
Release the males,
wait a week,
count the nests
Release the males,
wait a week,
count the nests
Controlled
variables:
Release the males,
wait a week,
count the nests
Release the males,
wait a week,
count the nests
location, season,
time, weather
Average of
about one nest
per male
Average of
about one nest
per male
Results
Average of less
than half a nest
per male
Average of
About two nests
per male
Control groups
Experimental groups
Conclusion:
The hypothesis that female widowbirds prefer to mate with long-tailed males (and are less likely to mate
with short-tailed males) is supported. 63

64. 1.4 What Is Science? Scientific theories have been thoroughly tested
A scientific theory is a general and reliable explanation of important natural phenomena that has been developed through extensive and reproducible observations and experiments
A scientific theory is best described as a natural law, a basic principle derived from the study of nature, which has never been disproven by scientific inquiry

65. 1.4 What Is Science?
Scientific theories have been thoroughly tested (continued)
The cell theory (that all living organisms are composed of cells) and the theory of evolution are fundamental to the study of biology
Natural causality is the principle that all events can be traced to natural causes
Natural laws apply to every time and place
Scientific inquiry is based on the assumption that people perceive natural events in similar ways

66. 1.4 What Is Science?
Scientific theories have been thoroughly tested (continued)
New scientific evidence may prompt radical revision of existing theory
For example, the discovery of prions

67. 1.4 What Is Science?
Scientific theories have been thoroughly tested (continued)
Before 1980, all known infectious diseases contained DNA or RNA
In 1982, Stanley Prusiner showed that the infectious sheep disease scrapie is caused by a protein (a “protein infectious particle,” or prion)
Prions have since been shown to cause “mad cow disease” and diseases in humans
The willingness of scientists to revise accepted belief in light of new data was critical to understanding and expanding the study of prions

68. 1.4 What Is Science?
Scientific theories involve both inductive and deductive reasoning
Inductive reasoning is used in the development of scientific theories
A generalization is created from many observations that support it and none that contradict it
For example, the theory that Earth exerts gravitational forces on objects began from repeated observations of objects falling downward toward Earth and from no observations of objects falling upward away from Earth

69. 1.4 What Is Science?
Scientific theories involve both inductive and deductive reasoning (continued)
Deductive reasoning is the process of generating hypotheses based on a well-supported generalization (such as a theory)
For example, based on the cell theory, any newly discovered organism would be expected to be composed of cells

70. 1.4 What Is Science?
Scientific theories are formulated in ways that can potentially be disproved
Basic principles of science are referred to as theories because theories can be disproved or falsified
Falsifying theories is distinctly different between scientific theories and faith-based beliefs
“Each creature on Earth was separately created” cannot be subjected to scientific inquiry because it is a belief rooted in faith

71. 1.4 What Is Science? Science is a human endeavor
Human personality traits are part of “real science”
Scientists, like other people, may be driven by pride, ambition, or fear
Scientists sometimes make mistakes
Accidents, lucky guesses, intellectual powers, and controversies with others contribute strongly to scientific advances

72. 1.4 What Is Science? Science is a human endeavor (continued)
In the 1920s, bacteriologist Alexander Fleming grew bacteria in cultures
One of the bacterial cultures became contaminated with a mold
Fleming was about to destroy the culture when he noticed the mold (Penicillium) inhibited bacterial growth in the culture

73. 1.4 What Is Science? Science is a human endeavor (continued)
Fleming hypothesized that the mold produced an antibacterial substance
Further tests using broth from pure Penicillium cultures lead to the discovery of the first antibiotic, penicillin

74. Figure 1-12 Penicillin kills bacteria
A Petri dish
contains solid
growth medium
Bacteria grow in
dense red colonies
on the growth medium
A substance diffuses
from the mold and
kills the bacterial
colonies, which lose
their color as they die
A colony of the
mold Penicillium 74

75. 1.4 What Is Science? Science is a human endeavor (continued)
Fleming continued beyond a lucky “accident” with further scientific investigation to a great discovery
“Chance favors the prepared mind” Louis Pasteur