Answers to Open-Ended Questions
Hoefnagels Concepts 3/e
Chapter 1
Mastering Concepts
1.1
1. Does any nonliving object possess all of the characteristics of life? Explain your
answer.
No. Although many nonliving objects have some characteristics of life, such as
organization or energy use, none has every characteristic.
2. List the levels of life’s organizational hierarchy from smallest to largest, starting with
atoms and ending with the biosphere.
Atom, molecule, organelle, cell, tissue, organ, organ system, organism, population,
community, ecosystem, biosphere
3. If evolution requires genetic variation, can populations of asexually reproducing
organisms evolve? Explain.
Yes. Mutations alone can generate the genetic variability that evolution requires.
1.2
1. What are the goals of taxonomy?
The goals of taxonomy are to name species and classify them based on evolutionary
relationships.
2. How are domains related to kingdoms?
Domains are larger, more encompassing taxonomic categories than kingdoms. Each
domain may contain multiple kingdoms.
3. List and describe the four main groups of eukaryotes.
Protists are eukaryotes that are not animals, fungi, or plants; they may be multicellular or
unicellular, and they may be autotrophs and heterotrophs. Animals are all multicellular,
and they are heterotrophs by ingestion. Fungi are mostly multicellular, and they are
heterotrophs by external digestion. Plants are multicellular, and they are autotrophs.
1.3
1. Identify the elements of the experiment summarized in the Apply It Now box.
Independent variable = presence or absence of saccharin; dependent variable = incidence
of cancer (number of tumors); standardized variable = brand of chow; control group =
rats that did not receive saccharin; sample size = 100 rats
2. Why is statistical analysis important?
Statistical analysis helps researchers to determine the probability that changes in an
independent variable (and not chance) caused the measured effects on a dependent
variable.
3. What is the difference between a hypothesis and a theory? What is the relationship
between theories and facts?
A hypothesis is not as widely accepted or as broad in scope as a theory. A theory is
supported by multiple lines of evidence, and no credible evidence has falsified it. Facts
are repeatable, undisputed observations; a theory is a comprehensive explanation that
incorporates a body of facts.
4. What are some limitations of scientific inquiry?
Scientific inquiry cannot answer subjective questions related to beauty, morality, ethics,
religion, or any other subject for which it is not possible to develop testable hypotheses.
Other limitations include multiple plausible interpretations of certain experimental
results, and the human tendency to disregard results that are contrary to our preexisting
beliefs.
5. Compare and contrast science and technology.
Scientific discoveries enable people to develop new technologies, and new technologies
can help advance scientific knowledge. The goal of science is to explain phenomena that
can be observed in the natural world, and the goal of technology is to discover practical
uses for scientific knowledge.
1.4
1. What observations led Darwin and Wallace to predict the existence of a long-tongued
moth in Madagascar?
They knew of orchids with long nectar tubes in Madagascar, and they knew of longtongued moths in England. They also understood the basic facts of plant reproduction,
including the fact that many insects eat nectar and pollinate flowers.
2. How does this story illustrate discovery science?
The moth was finally discovered by scientists examining insect collections from
Madagascar, not through experimentation.
Write It Out
1. Describe each of the five characteristics of life, and list several nonliving things that
possess at least two of these characteristics.
(1) Life is organized, following a hierarchical pattern from atoms to the biosphere. (2)
Organisms acquire and use energy to build cells, repair damage, and reproduce. (3)
Organisms maintain homeostasis, so the interiors of cells and living organisms remain
within a constant range even if environmental conditions change. (4) Organisms
reproduce, meaning they produce offspring that grow and develop into adult forms that
can also reproduce. (5) Life evolves, which means that the genetic makeup of every
population changes from generation to generation.
The following are examples of nonliving things that possess at least two of life’s
characteristics: a house is structurally organized and maintains a constant range of
temperature; automobiles are organized and require energy; crystal formations are
organized and grow; viruses are organized and evolve.
2. Explain how an atom relates to the biosphere by describing the levels of life’s
organization.
Multiple atoms make up a molecule, and molecules form structures (including organelles)
inside cells. Cells form tissues, which work together in organs. Many organs make up an
organ system inside an organism. (Note that an organism can also consist of a single
cell.) Multiple organisms make up a population, and many populations together form a
community. An ecosystem incorporates communities plus the nonliving parts of the
environment, and the biosphere includes all of Earth’s ecosystems.
3. Why is a cell, and not an atom or a molecule, considered the basic unit of life?
A cell is the basic unit of life because it is the first level of organization that displays all
of the characteristics of life. Atoms and molecules do not have all five of life’s properties.
Furthermore, both living and nonliving things are composed of atoms and molecules, but
only living things are composed of cells.
4. Think of an analogy that will help you remember the differences between populations,
communities, and ecosystems.
Many analogies are possible; this is just one. All of the pieces of a single puzzle are
analogous to individuals of the same species, which make up a population. A puzzle is
just one of many types of toys in a child’s room, just as a species represents just one of
many populations in a community. All of the objects in the child’s room, including the
toys, furniture, carpet, and air, are analogous to an ecosystem.
5. Other than the brownie example given in the text, name an example of emergent
properties from everyday life.
Examples could include anything that incorporates the interactions among multiple
simpler parts, such as bricks and mortar coming together to make a house, or a large tub
of water creating a swimming pool.
6. Draw and explain the relationship between producers and consumers (including
decomposers).
Answers will be visual and based on Figure 1.4.
7. How does a home’s air conditioning system illustrate homeostasis?
When the temperature gets too hot, the air conditioner turns on, and the house cools
down. When the temperature gets too cold, the air conditioner turns off, allowing the
temperature to rise.
8. Describe the main differences between asexual and sexual reproduction. Why are both
types of reproduction common?
In asexual reproduction, all the genetic information comes from one parent, so the
offspring are almost identical. In sexual reproduction, the genetic information comes
from two parents, generating variation. Asexual reproduction may be faster and does not
require finding a mate; it is typically adaptive in habitats that are unchanging. Sexual
reproduction generates much more variation, which promotes reproductive success in a
changing environment.
9. How are the members of the three domains similar? How are they different?
The members of all three domains are made of at least one cell and contain DNA.
Domains Bacteria and Archaea are superficially similar; both consist of prokaryotes and
are typically unicellular. However, DNA sequences differ between bacteria and archaea.
Domain Eukarya consists of organisms with eukaryotic cells, which have a nucleus.
10. List each step of the scientific method and explain why it is important.
First, a scientist must observe a phenomenon and question how it works. Without this
curiosity, much of what we know about the natural world would never have been
discovered. Next, a scientist must use what he or she already knows to form a hypothesis,
which is a tentative explanation. This is important because it is a testable statement that
should help answer the question. The prediction that follows from the hypothesis
specifies which results will support or refute the hypothesis. The scientist can then collect
data by further observation or experimentation. This step is crucial because it provides
the information required to test the hypothesis. The resulting data, when integrated with
prior knowledge, leads the scientist to conclude whether or not the hypothesis should be
rejected. Finally peer review ensures that other knowledgeable scientists have evaluated
the data before publication in a scientific journal.
11. Give two examples of questions that you cannot answer using the scientific method.
Explain your reason for choosing each example.
Science cannot answer questions regarding moral, ethical, aesthetic, and religious issues.
Two examples of questions that science cannot answer are “Is a rattlesnake or a peacock
more beautiful?” and “Is it wrong to use animals in cosmetics research?” The former is a
question of aesthetics and taste, and the latter is a question of ethics.
12. Design an experiment to test the following hypothesis: “Eating chocolate causes zits.”
Include sample size, independent variable, dependent variable, the most important
variables to standardize, and an experimental control.
Overall, the experiment would require dividing a population into two groups, only one of
which receives chocolate. Before, during, and after the experiment, the researchers
would measure the density of pimples in each group. The independent variable in this
experiment is presence or absence of chocolate, and the dependent variable is the density
of zits. The experiment should include a large sample size (hundreds of people at
minimum). Some variables to standardize include other components of the diet, the age
group of the subjects, and the subjects’ history of skin problems. The control group
would consist of individuals not consuming chocolate.
Pull It Together
1. What are the elements of a controlled experiment?
A controlled experiment consists of a control group and one or more experimental
groups. The simplest experiments have only one difference between the groups, and this
difference is the independent variable. The control group is one that is considered
“normal” for the variable being tested. It could be a healthy population compared to a
diseased population or it could be a population receiving no treatment compared to a
population receiving treatment. The dependent variable is the response that the
investigator measures. Standardized variables are factors that are the same for all
subjects, including the treatment and control groups.
2. What is the relationship between natural selection and evolution?
Natural selection is one of several mechanisms of evolution. For example, certain
members of a population might be more likely to reproduce than others because they are
stronger, better able to survive environmental stress, more efficient at finding resources,
or better at avoiding predation. Because they have greater reproductive success, their
adaptations become more common in the next generation of offspring.
3. Give an example of each of the five properties of life.
Organization: A deer dies after being hit by a car because the force of the accident has
disrupted the connections among its organ systems. Energy: A kitten extracts energy
from its mother’s milk. Homeostasis: A dog’s panting helps the animal get rid of excess
heat. Reproduction and development: An oak tree produces acorns, which germinate and
grow into mature oak trees. Evolution: Random mutations cause changes in the shape of
fins, enabling fish to exploit new resources in shallow water.