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H FINAL EXAM (ESSAY-practice)
Problem
1. Nitrogen fertilizer is added to soils in virtually all agricultural areas of the world. The use of nitrogen
fertilizer greatly increases the amount of food produced. However, it can also affect the ecology of areas
near agricultural areas. The data presented in the table below were obtained in an experiment conducted
to evaluate the effects of nitrogen fertilizer on grass species diversity. Nitrogen fertilizer was applied
yearly to an experimental plot, beginning in 1856.
Year
1856
1872
1949
Total number of grass species
49
15
3
Number of species producing more than 10% of the total
dry weight of all species combined
2
3
1
Number of species producing more than 50% of the total
dry weight of all species combined
0
1
1
Number of species producing more than 99% of the total
dry weight of all species combined
0
0
1
a. Write three conclusions that you can draw from these data.
b. How could this experiment have been designed differently to make it a better experiment?
2. The diagram above depicts a typical energy pyramid. It shows how energy is lost as it is transferred from
one level to another in the food chain of the pyramid.
The next diagram, shown below, depicts the concentration of DDT, a pesticide, in water and in a number
of organisms comprising a food chain.
Explain how DDT and other toxic substances can become concentrated in organisms as it is transferred up
through a food chain. Write your answer in the space below.
Essay
3. Name five characteristics that are considered distinct properties of all living things.
4. Evaluate the role biologists play in saving our tropical forests.
5. The results of an experiment do not support the hypothesis that the experiment was designed to test. Was
the experiment a waste of time? Explain.
6. Small cells function more efficiently than large cells. Briefly explain why this is true using the concept of
surface-area-to-volume ratio.
7. The DNA molecule is described as a double helix. Describe the meaning of this expression and the
general structure of a DNA molecule.
8. Why did Darwin believe that the finches he observed and collected in the Galapagos Islands shared a
common ancestor?
9. You are a biologist accompanying some other scientists on an expedition in a region that has not been
studied intensively. In your explorations, you come across a colony of small vertebrates that do not look
familiar to you. After conducting electronic searches of world wide data bases, you arrive at the tentative
conclusion that this organism has never been observed before. Now your job is to determine what kind of
vertebrate it is by identifying its closest relatives. Identify three types of data that you would collect and
describe how you would use these data to draw your conclusions.
10. Why is competition among individuals of the same species generally so intense?
11. Suppose that you are a zoologist studying birds on a group of islands. You have just discovered four
species of birds that have never before been seen. Each species is on a separate island. The birds are
identical to each other except for the shape of their beaks. How can you explain their similarities and
differences?
12. Clover plants, rabbits, and coyotes are some of the organisms that occupy a particular ecosystem. Assign
the roles of primary producers, primary consumers, and secondary consumers to these three groups of
organisms and explain your answer.
13. Name the six kingdoms recognized by most biologists.
H03 FINAL EXAM (ESSAY)
Answer Section
PROBLEM
1. a. The following are some possible conclusions:
1. The total number of grass species decreased over time and with exposure to nitrogen fertilizer.
2. At the beginning of the experiment, there was no one dominant species of grass. Over time and
with exposure to nitrogen fertilizer, a few species became dominant.
3. Prolonged use of nitrogen fertilizer encourages the growth of one or a few dominant species.
b. It should have been designed to have a control plot that did not receive nitrogen fertilizer. As the
experiment was designed, the effects of nitrogen fertilizer cannot be distinguished from the effects of
time.
2. As energy is passed from one level of a food chain to another, only a small amount of it is retained by the
next organism up in the food chain. This occurs in part because all energy conversions involve a loss of
energy in the form of heat. It is also partly due to the fact that each successive organism in a food chain
requires more energy to maintain its body’s activities. If there are toxic substances, such as DDT, in an
organism’s food, it will pass through the organism’s body. These substances can be taken up and stored in
body tissues. When another organism ingests food containing stored toxins, it can also take up and store
the toxins. The toxic substances become increasingly concentrated as they move up through the food
chain because each successive organism requires more food energy than the one below it in order to
survive.
ESSAY
3. Each organism is composed of one or more cells. All living things carry out metabolic reactions that
involve the use of energy. Reproduction is characteristic of all living things, as is homeostasis, the
maintenance of a constant internal environment. All organisms pass on genetic information to offspring.
All living organisms respond and adjust to their environment, as well as grow and develop.
4. Biologists study the plants and animals in the rain forests in order to better understand how we can
maintain a balance between people’s growing need for land and the need to protect these plants and
animals.
5. No, the experiment was not a waste of time. A scientist works by systematically showing that certain
hypotheses are not valid when they are not consistent with the results of experiments. The results of
experiments are used to evaluate alternative hypotheses. An experiment can be successful if it shows that
one or more of the alternative hypotheses are inconsistent with observations.
6. All substances must cross the cell surface. A small cell has a high surface-area-to-volume ratio. This
allows materials to pass readily into or out of the cell. As cells increase in size, the surface-area-to-ratio
volume decreases. Large cells cannot take in, or get rid of, materials in numbers large enough to meet
their needs. Also, materials have further to travel in large cells than in small cells.
7. DNA molecules are composed of two complementary strands of nucleotides arranged in a pattern
resembling a spiral staircase. Each nucleotide consists of a sugar molecule, a phosphate group, and one of
four possible bases. The double helix arrangement is maintained by the formation of hydrogen bonds
between complementary bases. Within the base pair adenine and thymine, as well as within the base pair
guanine and cytosine, equal numbers of molecules are present.
8. Although there were differences among these finch species, all the species also had many traits in
common. The main similarities among these species led Darwin to conclude that they had a common
ancestor.
9.
10.
11.
12.
13.
a. Analysis of anatomical structures and comparison of these to similar structures of other vertebrates is
one type of data that should be collected. For example, the bones composing the forelimb of the
organism could be compared to the forelimbs of other vertebrates. Those vertebrates having the
greatest number of similar (homologous) anatomical structures to those of your organism could be
presumed to be its closest relatives.
b. Analysis of the DNA and/or a protein and comparison of this material to that of other vertebrates
could also be studied. For example, DNA hybridization studies could be conducted with the organism
and other vertebrates. Or, an analysis of the cytochrome c of the organism in comparison to the
cytochrome c of other vertebrates could be done. Those vertebrates having the fewest differences in
sequences of DNA and/or proteins from the organism could be presumed to be its closest relatives.
c. Analysis of embryonic development and comparison of structures present at different stages and the
pattern of development with the structures and patterns of other vertebrates would be a third type of
data collected. For example, an analysis could be made of the persistence of a particular trait until late
in embryonic development. This analysis could be compared to the persistence of the same trait in the
embryos of other vertebrates. Those vertebrates having the greatest similarity in structures present
and pattern of development could be presumed to be its closest relatives.
Individuals of the same species require the same resources for survival. Since resources are generally
limited, only those individuals able to secure sufficient amounts of such resources will survive.
It is likely that the four species evolved from a common ancestor, with each species adapting to the
conditions on its island. The differences in beak shape may be the result of differences in available food
among the islands. Each bird species adapted to the food that was available on its island.
In this ecosystem, the clover plants are the primary producers. They help manufacture the organic
nutrients necessary to sustain the ecosystem. Rabbits are herbivores that consume the primary producers
(the clover plants), so they are classified as primary consumers. Coyotes eat the primary consumers (the
rabbits), so they are classified as secondary consumers.
The six kingdoms recognized by most biologists are Eubacteria, Archaebacteria, Protista, Fungi, Plantae,
and Animalia.