Midterm Exam 1 Notes

Since there are no answer keys posted for the exams, here is a space to create our own pool of key points for each question so we can learn from each other. Hopefully this will be a useful study tool for the final. Please fill in as appropriate!

1. Describe Biological and Morphological Species Concept with strengths and shortcomings:

a) Biological Species Concept
-distinct species are reproductively isolated or produce infertile offspring
-Strengths: viable offspring as indicator allows for more accuracy, less subjectivity
-Shortcomings: not applicable to fossils or museum specimens

b) Morphological Species Concept
-uses physical appearances of species to differentiate between different species
-Strengths: wide applicability - can be used for extinct or inaccessible species
-Shortcomings: only using physical appearance can be prone to error (mimicry, male vs. female appearances, pre-zygotic and post-zygotic barriers)

2. Prokaryotic vs. Eukaryotic cells – key characteristics. Give overview of evolution theories of eukaryotic cell from an earlier and simpler cell type.

Prokaryotic cells are primitive cells; they have a cell wall and free-floating DNA within. They make up the branches of bacteria and archaea. Eukaryotic cells are highly organized cells with specialized organelles and a nucleus to house their genetic material. Eukaryotes evolved from prokaryotes (archaea) about a billion years ago. Current theory states that they evolved from prokaryotes that assumed other prokaryotes as symbionts. Mitochondrial DNA, for example, is actually closer to bacterial DNA than to eukaryotic DNA.

3. Define a) autotroph, b) heterotroph, and c) trophic level. Describe “trophic pyramid” concept.

a. autotroph: an organism able to produce its own food by assimilating inorganic carbon with use of sunlight (photosynthesis) or energy contained in other inorganic molecules (chemoautotrophy, such as bacteria in hydrothermal vents that use sulfur)

b. heterotroph: organisms that must consume (eat, decompose, parasitize) other organisms for energy and nutrients.

c. trophic level: energetic position of an organism in an ecosystem relative to other organisms (primary producers, primary consumers, secondary consumers, etc.)

The trophic pyramid concept is the hierarchy of trophic levels in an ecosystem. For example, the first level are the primary producers (ex. plants) which are eaten by primary consumers at the second level (herbivores), which are in turn eaten by secondary consumers (carnivores), and so on. All are decomposed eventually by decomposers/detritivores. The transfer of energy through the pyramid, between trophic levels, is very inefficient - only 5 to 20 percent is transferred from one level to the next. This also explains why there are far greater numbers of individuals at lower trophic levels than at higher trophic levels.

4. List and explain 5 environmental controls on primary productivity in terrestrial ecosystems. Refer to specific biomes or differences among biomes to describe 2 of the controls.

5. Describe how GPP, NPP, autotrophic respiration (RA), and heterotrophic respiration (RH) enter into concept of net ecosystem production (NEP).

-GPP = total amount of production, usually measured by photosynthesis
-NPP takes into account RA, since carbon is released in respiration: NPP = GPP – RA
-RH can be thought of as decomposition – eventually NPP goes to heterotrophs and detritovores and ends up being respired or decomposed.
-NEP takes RH into account, and yields the overall net productivity of an ecosystem: NEP = NPP-RH (however, it ignores inorganic fluxes and lateral movements – we need net ecosystem exchange for that)


6. Explain the idea of a tipping point with the example of ice sheet albedo. Positive or negative feedback?

-Tipping point: where any small perturbation in system will push it away from equilibrium with a potential of conditions never returning back to original state
-Ice sheet albedo: temperature increase → ice sheets will melt → change albedo (since ice is a very reflective surface) →more absorption of heat energy from the sun → temperature increase → more ice sheets will melt…
-Positive feedback: no equilibrium reached: melting ice sheets leads to more melting ice sheets

7. Briefly describe 4 of the 5 factors in Jenny’s formula that determine soil formation.

Climate, Organisms, Relief, Parent material, Time

Climate: temperature and precipitation influence rates of formation and leaching
Organisms: different organisms in the soil will shred and process soil differently
Relief: slope influences drainage
Parent material: different materials yield different nutrients and weathering rates
Time: time since glaciation, soils develop over time (from entisol to ultisol)

8. Describe nitrification and denitrification and how they relate to oxygen availability in standing water and sediment.

Nitrification: immobile nitrogen to mobile nitrogen (ammonium [+] to nitrate [-])
Denitrification: nitrate to nitrogen gas (by bacteria)
Standing water and sediment: in areas with high oxygen availability (aerobic conditions), nitrification occurs. In areas without oxygen (anaerobic conditions), denitrification occurs.

9. Describe a “dead zone” and the processes that cause it.

Dead zone: where oxygen is lacking, organisms suffer from hypoxia
Upstream processes: excess nutrient runoff
Estuarial/Coastal ocean processes: excess nutrient increases productivity/phytoplankton activity, when phytoplankton die they sink to bottom and are decomposed. Decomposition requires oxygen; with much more to decompose due to higher productivity, this quickly depletes oxygen and leaves little oxygen to sustain other aquatic life.

10. Name and describe 5 movements within terrestrial nitrogen cycling – both nitrogen transformations and if they are aerobic, anaerobic, or both).

I got all of this from Wikipedia (God bless Wikipedia!):

1. Fixation (both) - refers to the biological process by which nitrogen in the atmosphere is converted into ammonia. This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g. nucleotides for DNA and amino acids for proteins.
a. aerobic: blue-green algae
b. anaerobic: Rhizobium in association with plant roots.

2. Assimilation (aerobic) - nitrogen assimilation is a fundamental biological process that occurs in plants and algae that are incapable of independent nitrogen fixation. The assimilation of nitrogen has marked effects on plant productivity, biomass, and crop yield, and nitrogen deficiency leads to a decrease in structural components.

3. Ammonification (both) - When a plant dies, an animal dies, or an animal expels waste, the initial form of nitrogen is organic. Bacteria, or in some cases, fungi, convert the organic nitrogen within the remains back into ammonium (NH4+), a process called ammonification.

4. Nitrification (aerobic) - Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates. Degradation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil.

5. Mineralization (both, then aerobic) - the release of organic compounds during decomposition.

6. Denitrification (anaerobic) - a microbially facilitated process of dissimilatory nitrate reduction that may ultimately produce molecular nitrogen through a series of intermediate gaseous nitrogen oxide products. This respiratory process reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License