AP Biology Big Ideas and Science Practices Overview

Principles of Life
An Overview of AP Biology
1

About AP Biology
AP Biology is equivalent to a two-semester
college-level introductory biology course.
Passing the AP Biology Exam, you could
receive credit for those college courses.
See the course catalog for the college of your
choice for more information.

About the AP Biology Exam
Date: 2nd
Monday of May
Score is based on the number of correct
answers.
There is no penalty for incorrect or
unanswered questions.

About the AP Biology Exam
Two Sections, each worth 50% of the test
Section I: 90 minutes, 1.3 minutes per question
Two Parts
Part 1: Multiple Choice
Part 2: Grid In
Section 2: 90 minutes
2 Long Free Response Questions
` 20 minutes per question
6 Short Free Response Questions
8.3 minutes per question

The Big Ideas
and
Science Practices
of Biology

Big Ideas of Biology
Make a concept map about what you know about the
big ideas.
BIG IDEA 1: The process of evolution drives the
diversity and unity of life.
BIG IDEA 2: Biological systems utilize energy and
molecular building blocks to grow, to reproduce, and
to maintain homeostasis.
BIG IDEA 3: Living systems store, retrieve, transmit,
and respond to information essential to life processes.
BIG IDEA 4: Biological systems interact, and these
interactions possess complex properties.

Science Practices (follow the links to watch videos about the science practices)
Science Practice 1: The student can use representations and models to
communicate scientific phenomena and solve scientific problems.
Science Practice 2: The student can use mathematics appropriately.
Science Practice 3: The student can engage in scientific questioning to extend
thinking or to guide investigations within the context of the AP course.
Science Practice 4: The student can plan and implement data collection
strategies in relation to a particular scientific question. (Note: Data can be
collected from many different sources, e.g., investigations, scientific
observations, the findings of others, historic reconstruction and/or archived
data.)
Science Practice 5: The student can perform data analysis and evaluation of
evidence.
Science Practice 6: The student can work with scientific explanations and
theories.
Science Practice 7: The student is able to connect and relate knowledge across
various scales, concepts and representations in and across domains.

Chapter 1 Principles of Life
Key Concepts of Ch. 1 – An Overview of the Big Ideas
and the Science Practices
1.1 Living Organisms Share Common Aspects of Structure,
Function, and Energy Flow (Big Ideas 2 and 4)
1.2 Life Depends on Organization and Energy (Big Ideas 2
and 4)
1.3 Genetic Systems Control the Flow, Exchange, Storage,
and Use of Information (Big Idea 3)
1.4 Evolution Explains the Diversity as Well as the Unity of
Life (Big Idea 1)
1.5 Science Is Based on Quantitative Observations,
Experiments, and Reasoning (Science Practices)

Concept 1.1 Living Organisms Share Common Aspects of
Structure, Function, and Energy Flow
Biology: the scientific study of living things or
organisms.
Living things are all descended from a single-
celled ancestor (a single common ancestor).
The characteristics shared by all organisms
logically lead to the conclusion that all life has
a common ancestry.

Characteristics of life
Working in pairs or small groups, make a list of the major
characteristics of life. Then, evaluate whether the
following exhibit some or all of those characteristics:
-a flowering plant, a diamond, and a frog.
Take a few minutes to discuss, and then present your list
and evaluations to the class.

1. Has DNA that encodes proteins
2. Is composed of cells
3. Results from interactions between complex parts
4. Can synthesize molecules from precursors
5. Can use energy from the environment
6. Can replicate genetic information while reproducing
7. Shares genetic and physical similarities with other forms of
life
8. Can evolve by changes to genetic information
A flowering plant and a frog share these characteristics,
while a diamond does not.

Characteristics shared by all living organisms:
• Composed of a common set of chemical components and
similar structures (e.g., cells)
• Depend on interactions among structurally complex parts to
maintain the living state
• Contain genetic information that uses a nearly universal
code
• Convert molecules obtained from their environment into new
biological molecules
• Extract energy from the environment and use it for life
functions
• Replicate their genetic information in the same manner when
reproducing
• Share structural similarities among a fundamental set of
genes

Earth formed between 4.6
and 4.5 billion years ago.
The earliest life evolved
about 600 million years
later.
Homo sapiens arose around
500,000 years ago (in the
last five minutes of day
30)
Recorded history covers the
last 30 seconds.

Complex biological molecules possibly arose
from random associations of chemicals in the
early environment.
Experiments that simulate conditions on early
Earth show that this was possible.
Critical step for evolution of life:
Formation of nucleic acids that could
reproduce themselves and contain the
information to produce proteins.

The next step:
Biological molecules were enclosed in a
membranes, to form a cell.
Fatty acids, which form membrane-like films in
water, were important in forming membranes.
Membranes separate the cell from the
surrounding environment.

For 2 billion years, organisms were unicellular
prokaryotes.
Early prokaryotes were confined to oceans,
where they were protected from UV light.
There was little or no O2 in the atmosphere, and
hence no protective ozone (O3) layer.

Select the false statement about oxygen (O2):
a. There was little or no O2 in the atmosphere of early Earth.
b. Once photosynthetic prokaryotes became abundant on
Earth, O2 began to accumulate in the atmosphere.
c. The presence of O2 allowed aerobic metabolism.
d. The ozone layer served as the source of Earth’s O2.
e. O2 in the atmosphere made it possible for life to move
from water to land.

Figure 1.2 The Basic Unit of Life Is the Cell
Single-celled organisms such as this one remain the
most abundant living organisms (in absolute
numbers) on Earth.

Photosynthesis evolved about 2.7 billion years
ago.
The energy of sunlight is transformed into the
chemical-bond energy of biological molecules.
Earliest photosynthetic cells were probably
similar to cyanobacteria.
O2 was a by-product of photosynthesis, and it
began to accumulate in the atmosphere.

Figure 1.3 Photosynthetic Organisms Changed Earth’s Atmosphere
Figure 1.3
Photosynthetic
Organisms Changed
Earth’s Atmosphere -
Cyanobacteria were the
first photosynthetic
organisms on Earth.
(A)Colonies of
cyanobacteria called
stromatolites are known
from the ancient fossil
record.
(B)Living stromatolites
are still found in suitable
environments on Earth
today.

O2 was poisonous to many early prokaryotes.
Organisms that could tolerate O2 evolved aerobic
metabolism (energy production using O2), which is
more efficient than anaerobic metabolism.
Organisms were able to grow larger. Aerobic
metabolism is used by most living organisms today.

O2 also produced a layer of ozone (O3) in the upper
atmosphere.
This layer absorbs UV light, and its formation allowed
organisms to move from the ocean to land.

Some cells evolved membrane-enclosed
compartments called organelles, where
specialized functions can be performed.
The nucleus contains the genetic information.
These cells are called eukaryotes.
Prokaryotes lack nuclei and other internal
compartments.

Some organelles may have originated by
endosymbiosis, when larger cells engulfed
smaller ones.
Mitochondria (sites of energy generation)
probably evolved from engulfed prokaryotic
organisms.
Chloroplasts (sites of photosynthesis) probably
evolved from engulfed photosynthetic
prokaryotes.

Multicellular organisms arose about 1 billion
years ago. Groups of eukaryote cells probably
failed to separate after division.
Cellular specialization—cells became
specialized to perform certain functions.
This allowed multicellular eukaryotes to
become larger and adapt to specific
environments.

Evolution of species:
• Mutations (changes) are introduced when
a genome is replicated.
• Some mutations give rise to structural and
functional changes in organisms, and new
species arise.

Each species has a distinct scientific name, a
binomial:
• Genus name
• Species name
Example: Homo sapiens

Evolutionary relationships of species can be
determined by comparing genomes.
Genome sequencing and other molecular
techniques have added molecular evidence to
knowledge from the fossil record.
Phylogenetic trees document and diagram
evolutionary relationships.

Figure 1.4 page 5
Read figure 1.4 on page 5.
1. Predict four characteristics that the first cell would have had.
Hint: these characteristics are shared by ALL organisms.
2. Make connections between these four characteristics and
the list on page 2.

Figure 1.4 page 5
1.The first cell would have had a cell membrane, DNA,
cytoplasm, and ribosomes.
2...
1.The cell membrane functions to obtain molecules from the
environment.
2.DNA stores genetic information which is replicated during cellular
reproduction.
3.Cytoplasm facilitates the interactions between the complex parts of the
cell.
4.Ribosomes use the genetic information (DNA ) to produce proteins
which are assembled from amino acids.

Figure 1.4 The Tree of Life
-3 Domains
Bacteria,
Archaea, and
Eukarya
-time flows from
left to right
common
ancestor at the
left

Relationships in the tree of life are based on
fossil evidence, structures, metabolic
processes, behavior, and molecular analyses.
Three domains of life:
• Bacteria (prokaryotes)
• Archaea (prokaryotes)
• Eukarya (eukaryotes)

All organisms that are alive today descended
from common ancestors in the past.
Living species did not evolve from other species
living today.

Because all life is related, discoveries made
using one type of organism can be extended
to other types.
Biologists use model organisms for research,
such as the green alga Chlorella to study
photosynthesis.

Energy and Organization of
Life

Concept 1.2 Life Depends on Organization and Energy
The second law of thermodynamics states
that, left to themselves, organized entities tend
to become more random.
Energy is required for cells to combat the
tendency for their molecules, structures, and
systems to lose organization.
Energy is required by cells throughout their
lives.

Organization is apparent in a hierarchy of
levels from molecules to ecosystems.
Cells use energy to synthesize complex
molecules by assembling atoms into new,
highly organized configurations.
Organization is essential for cells to function in
a multicellular organism, which has many
levels of organization.

Figure 1.5 Life Consists of Organized Systems at a Hierarchy of Scales (1)
Internal Hierarchy

Organisms also interact with their physical
environment and with each other, resulting in
hierarchy in the larger biological world.

Figure 1.5 Life Consists of Organized Systems at a Hierarchy of Scales (2)
External Hierarchy

A system is a set of interacting parts
(components) in which neither the parts nor
the whole can be understood without taking
into account the interactions (processes).
Systems are found at every level of biological
organization.

Figure 1.7 Organized Systems Exist at Many Levels

Biological systems are dynamic:
Characterized by rapid flows of matter and energy.
They constantly exchange energy and matter with their
surroundings.
But even though there is constant turnover of atoms,
molecules, etc., the organization of the systems persist.

Feedback: the amount of one component in a system affects the
rate of an earlier process in the system.
Positive feedback occurs when a product of the system speeds
up an earlier process.
Negative feedback occurs when a product of the system slows
down an earlier process.

Positive feedback tends to destabilize a system
(sometimes advantageous, provided it is ultimately
brought under control).
Negative feedback tends to stabilize systems and is
very common in regulatory systems.

In bacteria, as the amino acid tryptophan is synthesized, it
inhibits the expression of genes for enzymes that are
responsible for its synthesis. This is an example of
a. a hierarchy.
b. negative feedback.
c. a computational model.
d. a destabilizing system.
e. positive feedback.

Systems analysis is used to understand how
biological systems function.
The system components are identified, and
processes by which the components interact
are determined.
Rates of interactions can be affected by
feedback.
Then we can analyze how the system will
change through time.

Mathematical equations express amounts of the
different components and include processes
and their rates, resulting in a computational
model.

If a computational model is well grounded in
factual knowledge of the biological system, it
will mimic the biological system.
Computational models can be used for
prediction, for instance, the future behavior of
a system in a warming world.
Parameters of the model are adjusted to take
into account the expected increases in
temperature.

Concept 1.3 Genetic Systems Control the Flow, Exchange,
Storage, and Use of Information
The genome is the sum total of all the
information encoded by an organism’s genes.
DNA consists of repeating subunits called
nucleotides.
A gene is a specific segment of DNA that
contains information for making one or more
proteins.
Proteins govern chemical reactions in cells and
form much of an organism’s structure.

Figure 1.9 DNA Is Life’s Blueprint
The instructions for life
are contained in the
sequences of
nucleotides in DNA
molecules. Specific
DNA nucleotide
sequences comprise
genes. The average
length of a single human
gene is 27,000
nucleotides. The
information in each
gene provides the cell
with the information it
needs to manufacture
molecules of a specific
protein.

All cells in a multicellular organism contain the
same genome, but different cells have
different functions.
The different types of cells must express
different parts of the genome.
How cells control genome expression is a major
focus of biological research.

Mutations alter nucleotide sequences of a gene,
and the protein is often altered as well.
Mutations may occur during replication or be
caused by chemicals and radiation.
Most are harmful or have no effect, but some
may improve the functioning of the organism.
Mutations are the raw material of evolution.

Complete genome sequences have been
determined for many organisms.
They are used to study the genetic basis of
everything from physical structure to inherited
diseases and evolutionary relationships.
Bioinformatics is the field of study that
developed to organize and process the
immense amount of data resulting from
genome sequencing.

Concept 1.4 Evolution Explains the Diversity as Well as the
Unity of Life
Evolution is a change in genetic makeup of
biological populations through time—a major
unifying principle of biology.
A common set of evolutionary mechanisms
applies to all organisms.
The constant change that occurs among
populations gives rise to all the diversity of life.

Unity of Life
Charles Darwin proposed that all living
organisms are descended from a common
ancestor by the mechanism of natural
selection.
Natural selection leads to adaptations—
structural, physiological, or behavioral traits
that enhance an organism’s chances of
survival and reproduction.

Figure 1.10 Adaptations to the Environment

Unity of Life
Two kinds of explanations for adaptations:
• Proximate explanations—immediate
genetic, physiological, neurological, and
developmental processes that explain how
an adaption works.
• Ultimate explanations—what processes
led to the evolution of an adaptation.

Concept 1.4 Evolution Explains the Diversity as Well as the Unity
of Life
Proximate and ultimate explanations
Working in pairs or small groups, suggest the factors
that should be included in proximate explanations for
1. the stripes of tigers, and
2. the reflex that causes you to jerk your hand away
from a hot flame.
Then suggest the factors that should be included in
ultimate explanations for these same phenomena.

Unity of Life
In science, a theory is a body of scientific work in
which rigorously tested and well-established facts
and principles are used to make predictions about
the natural world.
Evolutionary theory is:
1. A body of knowledge supported by facts
2. The resulting understanding of processes by
which populations have changed and diversified
over time, and continue to evolve

Concept 1.4 Evolution Explains the Diversity as Well as the Unity
of Life
A scientific theory is best described as
a. a hypothesis.
b. a body of tested and well-supported facts.
c. the understanding of the processes that are responsible for
the subject of the theory.
d. a guess.
e. Both b and c

Unity of Life
Evolution can be observed and measured by:
• Changes in genetic composition of
populations over short time frames
• The fossil record—population changes over
very long time frames

Concept 1.5 Science Is Based on Quantifiable Observations and
Experiments
Scientific investigations are based on
observation, experimentation, and reasoning.
Understanding the natural history of
organisms—how they get food, reproduce,
behave, regulate functions, and interact with
other organisms—facilitates observation and
leads to questions.

Experiments
Observation is enhanced by technology—
microscopes, imaging, genome sequencing,
satellites.
Observations must be quantified by
measurement and mathematical and statistical
calculations.

Experiments
The scientific method (hypothesis–prediction
method):
1. Observations
2. Questions
3. Hypotheses
4. Predictions
5. Testing

Figure 1.11 Scientific Methodology

Experiments
To answer questions, biologists look at what is
already known to form possible answers, or
hypotheses.
Predictions are made based on observations,
and experiments are designed to test these
predictions.

Experiments
Controlled experiments manipulate the factor,
or variable, that is predicted to be causing the
phenomenon being investigated.
A method is devised to manipulate only that
variable in an “experimental” group, which is
compared with an unmanipulated “control”
group.

Experiments
Independent variable—the variable being
manipulated
Dependent variable—the response that is
measured

Figure 1.12: Page 14
1. Explain the significance of putting 30 tadpoles in
each tank and of using three tanks for each
atrazine concentration.
2. Describe the morphological changes in the frogs.
3. Predict what the results would be for atrazine
treatments of 1 and 10 ppb.

Figure 1.12 Controlled Experiments Manipulate a Variable (Part 1)

Figure 1.12 Controlled Experiments Manipulate a Variable (Part 2)

Figure 1.13: Page 15
1. Describe how the sites might vary from one
another, besides in the concentration of atrazine.
2. Describe other environmental conditions that could
affect frog development.
3. Describe how atrazine can enter water sources.

Experiments
Comparative experiments look for differences
between samples or groups.
• The variables cannot be controlled; data
are gathered from different sample groups
and compared.

Figure 1.13 Comparative Experiments Look for Differences among Groups (Part 1)

Figure 1.13 Comparative Experiments Look for Differences among Groups (Part 2)

Concept 1.5 Science Is Based on Quantitative Observations, Experiments, and Reasoning
Experimental design (part 1)
Consider an experiment designed to test the hypothesis that
hormones produced by rat testes are responsible for aggressive
behavior. In an experimental group, rats’ testes were surgically
removed. In a control group, rats’ testes remain intact. After the
experimental group recovers from surgery in individual cages,
experimenters measure the latency of each rat to attack another
male rat that is introduced to its home cage.
Working in pairs, discuss the following:
1. What are the dependent and independent variables?
2. Does the control group consist of unmanipulated males?
Why or why not? Would you include an additional group (or
groups) in your study? If so, describe the groups.

Concept 1.5 Science Is Based on Quantitative Observations, Experiments, and Reasoning
Experimental design (part 2)
The makers of a hypothetical energy drink, Smartz, claim that
the combination of nutrients in the drink will boost intelligence if
the drink is consumed regularly.
Working in pairs, design an experiment to test this claim.
1. What is the question?
2. What is the hypothesis?
3. Describe the control and experimental groups.
4. What is the dependent variable, and how would you measure
it?
5. What observations would lead you to conclude that your
hypothesis is supported? Unsupported?

Experiments
Statistical methods help scientists determine if
differences between groups are significant.
Statistical tests start with a null hypothesis—that no
differences exists.
Statistical methods eliminate the possibility that results
are due to random variation.

Experiments
Not all forms of inquiry into nature are scientific.
Scientific hypotheses must be testable and
have the potential of being rejected.
Science depends on evidence that comes from
reproducible and quantifiable observations.

Experiments
Religious or spiritual explanations of natural
phenomena are not testable and therefore are
not science.
Science does not say that untestable religious
beliefs are necessarily wrong, just that they
cannot be addressed using scientific methods.
Many advances in science raise ethical
concerns. Science can not tell us how we
should address these concerns.

Concept 1.5 Science Is Based on Quantitative Observations,
Experiments, and Reasoning
Which of the following terms is incorrectly matched with a
definition?
a. Data: Quantified observations
b. Controlled experiment: An experiment that manipulates
one or more of the factors under investigation
c. Null hypothesis: A prediction about what will happen to a
control group
d. Comparative experiment: An experiment that compares
unmanipulated data from different sources
e. Variable: The critical factor that has an effect on the
phenomenon being investigated

Mini Lab
Do beans soaked in water expand?
1. Make a prediction
2. Design an experiment
3. Describe the type of quantitative observations you
could make

Mini Lab
• Soak a group of beans in water overnight. For a
control group, leave the same number and strain of
beans untreated.
• Record the length, width, volume, and mass of all
the beans before soaking them. You may also record
qualitative measurements such as texture, bean
color…
• Record the same measurements the next day.
• Represent the data and describe them using tables,
graphs, mean, median, mode, standard deviation,
error bars.

AP Biology Big Ideas and Science Practices Overview

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