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Chapter 1
The Science of Life
Biology- the study of life

Biologists study questions about
o How living things work
o How they interact with their environment
o How they change over time

Biologists actively work to solve real world problems such as
o Improving our food supply
o Curing disease
o Preserving our environment
Characteristics of Life

Biologists have established that living things share seven characteristics of life
1. Organization and cells- all living things, whether made up of one cell or many
cells have some degree of organization
 Cells- smallest unit that can perform life’s functions
 Unicellular-organisms composed of one cell
 Multicellular-organisms that are made up of more than one cell
 Organisms at the highest level of organization are made up of organ
systems. An example of an organ system would be the digestive system.
Organ systems are composed of smaller parts:
 Organs- structures that carry out specialized jobs within the organ system
 Example: Kidneys
 Tissues- are groups of cells that have similar abilities and allow the organ
to function
 Example: nervous tissue in the ear allows the organism to hear
 Cells- the smallest unit that can perform life’s functions
 Organelles- tiny structures inside a cell that perform a specific function
 Biological molecules- chemical compounds found in cells
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2. Response to Stimuli
 Organisms can respond to a stimulus- a physical or chemical change in
the internal or external environment
 Organisms must be able to respond and react to changes in the
environment to stay alive
 Example: An owl’s eyes dilate when it gets dark to help them see
better
3. Homeostasis- the maintenance of a stable level of internal conditions even
though environmental conditions are constantly changing
 Example: Owl’s feathers fluff up in the cold to trap a layer of
insulating air next to their bodies
4. Metabolism- the sum of all the chemical reactions in the body
 Example: An owl’s metabolism allows the owl to extract and
modify the chemicals trapped in its nightly prey and use them as
energy to fuel activities and growth
5. Growth and Development
 The growth of living things results from the division and enlargement of
cells
 Development is the process by which an organism becomes a mature
adult
 A human body is composed of trillions of specialized cells which
originated from a single fertilized egg
6. Reproduction
 Reproduction, unlike the other characteristics, is not essential to the
survival of an individual organism
 Reproduction is essential for the continuation of the species
 Organisms transmit hereditary information, DNA, to their offspring
 Gene- is a short segment of DNA that contains the instructions for
one trait
 During sexual reproduction, hereditary information recombines from
two organisms from the same species
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
In asexual reproduction one organism is able to make an identical copy
of itself
7. Change through Time – Evolution
 Organisms change slowly over time as their environment changes
 This factor helps us explain the diversity of life forms we see today
Themes in Biology

Diversity and Unity of Life
o Diversity, or variety
 There are single celled and multi-cellular organisms
 There are organisms that live in ice and ones that live in hot springs
 We have identified more than 1.5 million species on Earth, with many
more still to be identified
o Unity – features that all living things have in common
 Genetic code
 Organelles that carry out all cellular activities
 All living things share certain genes, but no two types of organisms have
the same full set of genes
o Three Domains of Life
 Bacteria- prokaryotes (simplistic organism) found in more common
environments
 Archae- prokaryotes (simplistic organisms) that live in extreme
environments such as hot springs, high salinity ecosystems
 Eukarya- consists of protists, fungi, plants, and animals

Interdependence of Organisms
o Ecology is the branch of biology that studies organisms interacting with each
other and with the environment
o Ecosystems are communities of living species and their physical environment
o Studies have shown that organisms depend on each other as well as on minerals,
nutrients, water, gases, heat, and other aspects of the physical world
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
Example: a panther eats a bird, which eats nuts from a tree. The tree
needs carbon dioxide and water. Carbon dioxide is a main byproduct of
all animals
o Humans have had a huge impact on the world’s environment
 Example: We have cleared vast areas of the rain forests for the rare
wood that grows only there. The rain forests are the biggest filters of
greenhouse gases on our planet

Evolution of Life
o Also referred to as descent with modification, is the process in which the
inherited characteristics within a population change over generations
o Natural selection- organisms that have certain favorable traits are better able to
survive and reproduce successfully than organisms that lack these traits
o Adaptations are traits that improve an individual’s ability to survive and
reproduce
 Example: Rabbits with white fur and short ears living in a snowy place as
opposed to somewhere that gets no snow
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The Study of Biology


Scientific Method is an organized approach to learn how the natural world works
The methods of science are based on two important principles
1. Events in the natural world have natural causes
Example: Lightning and thunder result from electric charges in the
atmosphere
2. Uniformity is the idea that the fundamental laws of nature operate the same way at
all places and at all times
Example: Scientists assume that the law of gravity works the same way on
Mars as it does on Earth
Steps of the Scientific Method
1. Observation
a. Identify there is a problem
b. Gather as much information as you can about the problem
2. Hypothesis- a proposed solution to the problem
a. It is a prediction of what would happen in a test situation if the hypothesis were
true
b. Good hypotheses answer a question and are testable in the natural world
3. Design and Perform an Experiment
a. A controlled experiment is used to test the hypotheses
i. A controlled experiment compares an experimental group and a
controlled group
1. Control group provides a normal standard against which the
biologist can compare results of the experimental group
2. Experimental group is identical to the control group except one
factor, the independent variable, is manipulated or change
a. Independent variable, sometimes called the manipulated
variable, is a factor that can be altered to see how it could
change the outcome of the experiment.
i. It is not affected by the experiment but it could
change the results of the experiment
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ii. Only one variable is manipulated at a time so the
experimenter knows which variable is bringing
about the change
b. Dependent variable, sometimes called the responding
variable, is affected by, or depends on the independent
variable.
i. It is the result of the experiment
c. The experiment is usually completed many times to assure
the results were accurate
b. Example:
i. Problem: Sara believes her cake does not taste good
ii. Hypothesis: Sara believes adding more milk to her cake recipe will make
the cake taste better
iii. Experiment: Sara bakes 2 cakes, one using the old recipe, and one using
the new recipe
iv. Collecting and Analyzing Data: Sara asks several friends and family
members to try her cake using the old recipe and the new recipe and
records their comments
4. Collecting and Analyzing Data
a. The dependent variable is measured, which provides quantitative data, data
that can be measured
b. In analyzing data, the goal is to determine whether the data are reliable, and
whether they support or fail to support the hypothesis
c. Scientists can now compare their data to other experiments done testing the
same thing
d. Data is usually displayed in graphs and tables
5. Drawing Conclusions
a. Scientists analyze their data to see if the hypothesis is supported
b. An experiment can only disprove not prove an experiment
c. When a hypothesis is confirmed to be true many times it is reclassified as a
theory
i. A theory in science is classified as a highly tested and proven idea
ii. A theory in everyday language is more like a hypothesis
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