Unit 8 Essay Prompts
Sorry guys that this is so late... I just had to go to sleep. Anyways, this guide is to help
inspire you about the essay prompts and provide a little info, you'll have to do additional
research on your own. Also, I'll try to bring up better examples.
1) Explain and illustrate with one specific example of each of the following concepts:
a) competitive exclusion (Gause's principle)
1. definition = states that when two species with the same resource needs are put
into the same environment, the species that is able to use its resources better
and more efficiently will cause the other species to eventually become
extinct.
2. example = the experiment involving two species of protozoans (pg. 1115)
b) ecological succession
1. definition = transition in the species composition of a biological community,
often following ecological disturbances of the community
2. example = lichens and mosses are usually the pioneering species that
facilitate the land for later species during primary succession
3. example = a forest are that has been cleared may return to a forest if left
alone, that's secondary secession
4. R-selected populations usually are involved in the early processional stages
and later other better competitors slowly become established in the same
place.
5. page 1124
c) nutrient (biochemical cycles)
1. definition = the cycling of nutrients through biotic and abiotic components of
ecosystems
2. Water Cycle, Carbon Cycle, Nitrogen Cycle, Phosphorus Cycles
3. page 1139-1143
2) Many areas of N America that were once covered with many small lakes and
ponds have undergone succession and are now continuously covered with forests.
Give a detailed description of the events (biotic and abiotic factors) that lead to the
establishment of a climax forest.
a) try learning from prompt 5
b) things that might have dried up lake (thanks to Kevin Do and Julie Pham):
desertification, eutrophication, humans using up the water... etc.
3) Define, discuss, and give an example of each of the following close interactions of
species.
a) Predator-prey relationships
1. +/-, otherwise known as predation
2. example = lion eats zebra
3. page 1111
b) Commensalism
1. +/0, very rare
2. example = barnacles on wales
3. example = cowbirds and cattle egrets feed on insects flushed out of the grass
by grazing bison, cattle, horses, and other herbivores
4. example = algae growing on turtle's shell
5. page 1117
c) Mutualism
1. +/+, both partners benefited
2. example = nitrogen fixation by bacteria in plant's roots
3. example = ants and bull's horn acacias
4. page 1118
4) Describe the trophic levels in a typical ecosystem. Discuss the flow of energy
through the ecosystem, the relationship between the different trophic levels, and the
factors that limit the number of trophic levels.
a) sun -> primary producers -> secondary producers -> tetiary producers
b) factors that limits number of trophic levels = inefficiency in the transfer of
energy, only about 10%
c) look at chap 54 study guide for more details on each t. levels
5) Describe the process of ecological succession from a pioneer community to a
climax community. Include in your answer a discussion of species diversity and
interactions, accumulation of biomass, and energy flow.
a) definition = pioneer community = the first species to inhabit the land
primary – life in empty place
secondary – life in place with previous life that got cleaned out
climax – stable communities that have been there for a while
b) first pioneer communities such as lichen and moss facilitate a land to allow later
generations to grow. Usually, R-selected populations grow first since they have
higher fecundity. Later, K-selected species will become established and really settle
down... which is how climax forms.
c) species diversity and interaction = causes competition for the available resources
d) inhibition and facilitation
e) page 1124
6) Describe the biogeochemical cycles of carbon and nitrogen. Trace these elements
from the point of their release from a decaying animal to their incorporation into a
living animal.
a) check out chap 54 study guide for both cycles
b) carbon cycle = cellular respiration, photosynthesis
c) Nitrogen cycle = nitrification, denitrification, nitrogen fixation,
ammonification, atmospheric deposition
d) page 1140 – 41
7) Using an example for each, discuss the following ecological concepts:
a) Succession
1. um... look at prompt 5
b) Energy flow between trophic levels
1. look at chap 54 study guide....
2. primary productivity and secondary productvity
3. energy transfer only about 10% efficient
c) Limiting factors
1. density dependent and density independent
2. examples = water, oxygen, resources, fire, natural disasters, etc.
d) Carrying capacity
1. maximum number of organisms an environment can support over long
periods of time
2. as organisms reach this... their population growth slows
8) Living organisms play an important role in the recycling of many elements within
an ecosystem. Discuss how various types of organisms and their biochemical
reactions contribute to the recycling of either carbon or nitrogen in an ecosystem.
include in your answer one way in which human activity has an impact on the
nutrient cycle you have chosen.
a) carbon
1. cellular respiration and photosynthesis
2. humans with factories and cars add more carbon dioxide to the air
b) nitrogen
1. bacterias with the four processes
2. ammonification, nitrification, denitrification, nitrogen fixation
3. humans using too much nitrogen enriched fertilizer end up causing
eutrophication