Answers to STUDY BREAK Questions
Essentials 5th
Chapter 12
LIFE IN THE OCEAN
1. What do I mean when I write “all life in Earth is fundamentally the same?” A shark and a
seaweed don’t seem similar.
A shark and a seaweed are certainly superficially dissimilar, but the physical and
biochemical organization of the cells that comprise both is startling in its similarity. On the
molecular level, there are few differences.
2. How does an atom of iron in steel differ from an atom of iron in your blood?
An atom of iron is an atom of iron wherever it is found. There are no differences in
the structure of an iron atom incorporated into a hemoglobin molecule and an atom or iron
holding up a bridge. The definition of life depends on the manipulation of energy, not the
physical composition of the objects themselves.
3. What are the starting products for photosynthesis? The end products?
Photosynthesis requires carbon dioxide, water, and light energy. The carbohydrate
glucose and oxygen are end products.
4. How is chemosynthesis different from photosynthesis?
Chemosyntheis does not require light, but instead releases the energy held in
chemical bonds in molecules of simple hydrogen- and sulfur-containing compounds to
construct glucose from carbon dioxide.
5. What do primary producers produce? How is productivity expressed?
The immediate organic material produced is the carbohydrate glucose. Primary
productivity is expressed in grams of carbon bound into organic material per square meter of
ocean surface area per year (gC/m2/yr).
6. What is a trophic pyramid? What is the relationship of organisms in a trophic pyramid?
A trophic pyramid is a representation of mass flow through a system of producers and
consumers . A food web a more accurate representation of what actually happens: a group
of organisms interlinked by complex feeding relationships in which the flow of energy can be
followed from primary producers through consumers.
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7. Does this have anything to do with food webs? How?
A trophic pyramid implies an oversimplistic view of a marine community. Real
communities are more accurately described as food webs, an example of which is provided
as Figure 12.9. A food web is a group of organisms linked by complex feeding relationships
in which the flow of energy can be followed from primary producers through consumers.
Organisms in a food web almost always have some choices of food species.
8. What is an extremophile?
Extremophiles are capable of life under extreme conditions of temperature, salinity,
pressure, or chemical stress.
9. What is an autotroph? A heterotroph? How are they similar? How are they different?
Autotrophs make their own food. The bodies of autotrophs are rich sources of
chemical energy for any organisms capable of consuming them. Heterotrophs are organisms
(such as animals) that must consume food from other organisms because they are unable to
synthesize their own food molecules.
10. What’s a limiting factor? Can you provide an example?
Often too much or too little of a single physical factor can adversely affect the
function of an organism. Lack of light would be limiting to a photosynthetic organism.
11. How characterizes the photic, euphotic, and disphotic zones?
Light illuminates the entire photic zone (during the day). The euphotic zone is the
upper segment of the photic zone in which illumination is sufficient for photosynthesis to
occur. The disphotic zone, while still lit, is too dark to support photosynthesis.
12. How does metabolic rate vary with temperature?
An organism's metabolic rate increases with temperature. Clearly there is an upper
limit – too much heat and the organism cooks.
13. How do dissolved gas concentrations vary with temperature? Now look at your answer
to the last question. Do you see a problem for marine organisms?
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Colder water contains more gas at saturation. Metabolic rates rise with rising
temperature. As temperature rises, metabolic demand for oxygen will exceed supply which
may lead to the death of the plants and animals in the area.
14. Does the great hydrostatic pressure of the seabed crush organisms?
Land animals live in air pressurized by the weight of the atmosphere above them.
Pressures inside and outside an organism are virtually the same, both in the ocean and at the
bottom of the atmosphere. Nobody gets mashed.
15. How is diffusion different from osmosis?
Liquids and gases diffuse through water from zones of high concentration to zones of
low concentration. Osmosis is more specialized -- it is diffusion of water through a
membrane.
16. Distinguish between the pelagic and neritic zones.
The pelagic zone consists of ocean water. If the water is over the continental shelf, it
is considered neritic. (Water over the deep seabed is in the oceanic zone.)
17. Where would you look for a benthic organism?
Benthic organisms are found on or in the seabed.
18. Is evolution by natural selection a random process?
Although mutations occur randomly, evolution by natural selection is anything but
random. The natural environment winnows favorable mutations from unfavorable ones—
hence the origin of the term natural selection.
19. How is evolution by natural selection thought to operate?
Write a summary of the steps, and then check the list in the chapter.
20. How are new species thought to originate?
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Species can arise by physical isolation. Because the number of breeding animals
within an isolated species may be small, evolutionary change may be rapid. Generation after
generation, the species will change relatively rapidly to suit its new habitat.
21. What’s convergent evolution?
Since physical conditions in the open ocean are relatively uniform, large marine
animals with similar life-styles but different evolutionary heritages eventually tend to look
much the same. That is, similar conditions may result in coincidentally similar organisms.
22. How is a natural system of classification different from an artificial system?
A natural system of classification for living organisms relies on organism's
evolutionary history and developmental characteristics. Any system dependent on other
schemes is artificial – that is, it does not reflect the underlying biological relationships
between categorized organisms.
23. What are the three domains of living things?
Bacteria, Archaea, and Eukarya
24. How are organisms named?
Linnaeus's system of classification was decidedly natural. Though Darwin's insights
into evolutionary relationships were nearly a century in the future, Linnaeus's understanding
of the relationships between organisms, and his ability to arrange organisms into like
categories, was remarkable. His was a system of classification based on hierarchy, a
grouping of objects by degrees of complexity, grade, or class. In this boxes-within-boxes
approach, sets of small categories are nested within larger categories. Linnaeus devised
names for the categories, starting with kingdom (the largest category) and passing down
through phylum, class, order, family, and genus, to species (the smallest category).
25. How is a community different than a population?
A community is comprised of the many populations of organisms that interact with
one another at a particular location. A population is a group of organisms of the same
species occupying a specific area. The location of a community, and the populations that
comprise it, depend on the physical and biological characteristics of that living space.
26. How are benthic communities different from pelagic communities?
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Benthic organisms live on or in the bottom; pelagic organisms live suspended in the
water column.
27. How is a niche different from a habitat?
There are many different places to live and many different "jobs" for organisms
within even a simple community. Those “jobs” are called niches. A habitat is an organism's
"address" within its community, its physical location. Each habitat has a degree of
environmental uniformity. An organism's niche is its "occupation" within that habitat, its
relationship to food and enemies, an expression of what the organism is doing. For example,
the small fishes living among the coral heads in a coral reef community share the same
habitat, but each species has a slightly different niche. Each population in the community
has a different "job" for which its shape, size, color, behavior, feeding habits, and other
characteristics particularly suit it.
28. How would you describe the species diversity of an “easy” habitat – perhaps an
estuary?
Generally, the “easier” the habitat (that is, the milder the environmental extremes and
the larger the quantity of food and energy available), the more organisms will attend the
party. Species diversity in these places is relatively high.
29. What’s a climax community? What process terminates in a climax community?
A stable, long-established community is known as a climax community. This selfperpetuating aggregation of species tends not to change unless disrupted by severe external
forces such as violent storms, significant changes in current patterns, epidemic diseases, or
influx of great amounts of fresh water or pollutants.
30. Can you think of any way to prevent a cataclysmic asteroid or comet impact once the
object’s path has been shown to be on a certain collision course?
The near-space environment is being scanned for Earth-crossing comets and asteroids
(bodies whose orbits intersect that of the Earth). The resources dedicated to this task are
meager, however, and it will be decades before most of the potential threats are catalogued.
Congress has not supported a significant increase in funds for this purpose, and the attention
of the public waxes and wanes with Hollywood’s interest in the topic.
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Some indication of public response can be gleaned from the same Hollywood movies.
Among the earliest and best of these is a 1950s George Pal production titled “When Worlds
Collide” that greatly influenced me to study science when I was a small and impressionable
boy. In that memorable film, a select few folks left Earth in large transport ships moments
before the collision to settle on another world. A better solution (or so it seems to me) would
be to identify and then deflect any incoming asteroids. How might that deflection be
accomplished? Hmmmm.
31. Do you think all life on Earth would be wiped out by a huge impactor?
Life is tenacious. Unless surface temperatures rose everywhere to high temperatures,
some extremophiles might survive. Given another billion years or so, evolutionary processes
would again produce some interesting organisms.
32. Why do we see relatively few impact craters on Earth?
Because, unlike the Moon or Mars, our active atmosphere supplies erosive water to
scour the surface, erasing the images of impacts more than a few million years old.
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