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Unit 2A Ecology Study Guide
1. What is a biotic factor? Give some examples. Any living part of the environment; Animals, plants,
fungi, bacteria
2. What is an abiotic factor? Give some examples. Any nonliving (physical) part of the environment;
Sunlight, heat, precipitation (rain/snow), humidity, water etc.
3.
Classify the following as biotic or abiotic or both:
a. Rocks: Abiotic
b. Pine trees: Biotic
c. Waterfalls: Abiotic
d. Clouds: Abiotic
e. A mushroom in the soil: Both
f. A fish swimming in a lake: Both
4.
Define organism. An individual of a certain species
5.
What is a species? A group of organisms that can breed and produce fertile offspring
6.
What is a population? A Group of individuals of the same species living in the same area
7.
What is a community? Different populations living together in the same area
8.
Explain the difference between a population and a community? An example of a population would
be a school of fish in the sea (the fish are all of the same species) a community would be the school
of fish along with seals and sharks that are also living with in the same habitat
9. What is an ecosystem? Give an example. All the organisms in a certain place together with their
PHYSICAL environment
Materials and energy move between the living (biotic) and nonliving (abiotic) parts of ecosystems.
Materials (atoms, molecules) must be recycled, but energy is NOT! So, a constant supply of energy must
enter every ecosystem.
10. On Earth, what supplies our energy? The sun
11. Through what process does the sun enter an ecosystem? (hint: In this process, the plant uses
sunlight to make sugar molecules.) Through the process of photosynthesis
Organisms obtain their food in different ways. Some organisms are producers, while others are
consumers.
12. What is a producer? What is another term for producer? Give some examples of organisms that
are producers. An organism that uses energy from the sun to create its own food (sugars) through
photosynthesis. Autotroph; Trees, grass, algae
13. What is a consumer? What is another term for consumer? What are some examples of organism
that are consumers? Organisms that must consume other organisms as food. Heterotrophs; Dogs,
cows, fungi, bugs etc
14. What is a decomposer? Why are decomposers so important to ecosystems? Feed by chemically
breaking down organic matter (dead organisms); They help return organic materials back into the
soil- if we didn’t have them then dead matter would just pile up.
15. There are several different types of consumers in ecosystems: herbivores, carnivores, omnivores,
decomposers, detritivores and scavengers. Fill in the table below.
Type of consumer
Herbivore
Carnivore
Omnivore
Decomposer
Detritivore
Scavenger
Energy Source
Only eat plants
Kill and eat other animals
Eat both plant and animal
material
Feed by chemically breaking
down dead matter into detritus
Feed on detritus particles left
over by the decomposers
Feed on dead organic matter
Examples
Deer, rabbits
Lions, cheetahs
Bears, raccoon
Mushrooms, bacteria
Earthworms
Vultures, hyenas
Energy Transfer
Each time an organism eats another organism, a transfer of energy occurs. We can trace the transfer of
energy as it travels through an ecosystem by studying food chains, food webs, and trophic levels. These
tell us how and how much energy is transferred between organisms in an ecosystem.
16. What is a food chain? Food chain- a series of steps in which organisms transfer chemical energy by
eating and being eaten.
17. What is a food web? Why is a food web a more accurate way than a food chain to depict energy
transfer in an ecosystem? Food web- many food chains within an ecosystem Food webs are more
accurate because they depict ALL of the energy that is transferred through feeding within an
ecosystem where as a food chain only illustrates the passing of energy through a specific number of
organisms, not all.
18. What is a trophic level? A step in the food chain or web/energy level
19. What does an energy pyramid show us? How much energy is available at each trophic level
20. In an energy pyramid, which trophic level has the most energy available to it? What happens to the
amount of energy available to the organisms as the trophic levels go up? How much? Explain why
this happens. The most energy is within the first trophic level which consists of primary producers.
As you travel up the pyramid the amount of energy decreases- only 10% of the available energy is
passed up to the next trophic level because the other 90% is used by the organism to carry out
biological process and some is lost in the form of heat.
21. Draw an energy pyramid for a four step food chain. (make sure to show the producer and each
Bird- 0.1% energy
level of consumer)
Tertiary consumer4th TL
TL= Trophic Level
Bass- 1% energy
Secondary consumer3rd TL
Flag fish- 10% energy
Primary consumers- 2nd TL
Algae- 100% energy
Producers- 1st TL
22. If 100% of the energy is available at the first trophic level, what percentage of that energy is
available at each of the next trophic levels?
2nd tropic level- 10%
3rd trophic level- 1%
4th trophic level- 0.1%
23. If 8000 calories of energy are available at the first trophic level, how many calories are available at
each of the next trophic levels?
2nd tropic level- 800
3rd trophic level- 80
4th trophic level- 8
24. _____________always make up the first trophic level in a food web.
a. producers
b. primary consumers
c. secondary consumers
Use the following food chain to answer the questions below.
Algae  flag fish  largemouth bass  bird  alligator
Producer
Herbivore
Secondary consumer Tertiary consumer
25. Which organism is the producer? algae
26. Which organism is an herbivore? Flag fish
27. Which organism is a secondary consumer? Largemouth bass
28. Which organism is at the third trophic level? Largemouth bass
29. Which organism(s) is/are carnivores? Largemouth bass, bird, alligator
30. Which organism is a tertiary consumer? alligator
31. Which organism is at the second trophic level? Flag fish
32. What would happen to the population of largemouth bass if the population of alligators suddenly
decreased a great deal? If alligators decreased significantly, the population of largemouth bass
would decrease since the population of birds would increase because they would not have as many
predators (alligators) to eat them.
33. What type of pyramid is shown below? biomass
34. Producers have the ____most__________ biomass, while the top consumers have the least.
Pyramid of Numbers
35. Pyramids of numbers show the numbers of organisms at each trophic level. According to the
pyramid of numbers in the diagram above, which trophic level has the greatest number of
organisms? 4th trophic level, but the 1st trophic level has very few too!
36. What can you conclude about the size of the elder tree in the pyramid above? How do you know
this? It is a large tree. The bar is small so there are only a few of them, so they must be big enough
to provide food for the huge amount of aphids (bugs) that are in this ecosystem.
37. Arrange the following in order from least broad (smallest) to most broad (largest):
Biome, biosphere, organism, community, population, ecosystem
ORGANISM  POPULATION COMMUNITY ECOSYSTEM BIOME BIOSPHERE
38. The place where an organism lives is called its ___ habitat ________________.
39. What an organism does in its habitat, how it interacts with its environment, and how it contributes
to an ecosystem is known as the organism’s _____niche _______________.
40. Give an example of a biological (biotic)aspect of an organism’s niche, and give an example of a
physical (abiotic) aspect of an organism’s niche.
Biological- bear eats fish
Physical- bear creates a den out of the earth
41. Describe what happens if two different species try to occupy the same niche at the same time
According to the Competitive Exclusion Principle, two organisms cannot occupy the same niche,
when this does occur there are 3 possible outcomes:
1. One species will compete better for the niche and the other species will die out.
2. One species will compete better for the niche and the other will move away.
3. The two species will split or share the niche
42. In which biome do you live? Temperate forest
43. A lion eating a zebra is an example of
A. herbivory.
B. habitat destruction.
C. predation.
D. a keystone species.
44. A cow eating grass is an example of
A. herbivory.
B. predation.
C. habitat destruction.
D. a keystone species.
45. A keystone species is one that
A. eats a mixture of plants and animals.
B. is introduced into a community after a major disturbance.
C. causes the amount of diversity in a community to decrease.
D. helps to stabilize the populations of other species in the community.
Match the symbiotic relationship with the best description
a. parasitism
b. mutualism
c. commensalism
46. Symbiotic relationship between two organisms where both benefit B
47. Symbiotic relationship between organisms where one benefits and one is harmed A
48. Symbiotic relationship between organisms where one benefits and the other is not affected C
The Water Cycle
49. Using the words below, label the steps of the water cycle in the diagram above and describe each
step.






Evaporation- A process that helps introduces water into the atmosphere by changing its state of
matter from a liquid to a gas.
Condensation- When water change’s from a gas to a liquid we usually see this in the form of
clouds in the sky.
Precipitation- snow or rain- water is being released from the atmosphere on the land and water
bodies.
Transpiration- The process by which water is carried throughout plants and them turns into
vapor on their leaves.
Run off- Excess water that does not get absorbed by the ground that then “runs off” down hills
and into rivers, streams, and oceans.
Ground water- water that is stored underground
Answer “yes” or “no” for questions 13 and 14
50. Are materials recycled through an ecosystem? ____yes_________
51. Is energy recycled through an ecosystem?
____no________
52. For the following 3 steps in the carbon cycle, determine if the process increases or decreases the
amount of CO2 and O2 in the environment. Use up ↑ and down ↓ arrows to indicate an increase or
decrease.
Process
Cellular Respiration
Photosynthesis
Burning fossil fuels
CO2
↑
↓
↑
O2
↓
↑
↓
Burning fossil fuels:
For questions 16– 19, choose if each statement describes photosynthesis or cellular respiration.
a. photosynthesis
b. cellular respiration
53.
54.
55.
56.
Requires energy from the sun A
Converts CO2 from the atmosphere into food energy (glucose) A
Takes place in all organisms B
Converts glucose into ATP and releases CO2 B
Quick reminder – remember the equations for cellular respiration and photosynthesis!
Photosynthesis:
6CO2 + 6H20  C6H12O6 + 6O2
Cellular respiration:
C6H12O6 + 6O2  6CO2 + 6H20 + ATP
57. The nitrogen cycle is driven by what unicellular organisms? bacteria
58. Organisms need nitrogen so that they can produce which 2 important macromolecules? Proteins
and nucleic acids
59. The carbon in coal, oil, and natural gas came from
A. the combustion of fossil fuels.
B. the remains of dead organisms.
C. carbon-fixing bacteria in swamp soil.
D. carbon dioxide dissolved in ocean water.
60. How does most of the carbon in an organism’s body return to the environment after the organism
dies?
A. Decomposers break the body down into simpler compounds.
B. Heat from the sun causes the carbon in the body to evaporate.
C. Geological processes cause the body to turn into a fossil fuel.
D. Rainwater dissolves the carbon in the body and carries it to the ocean.
61. Human processes (such as burning fossil fuels) mainly contribute to the
A. release of large amounts carbon dioxide into the atmosphere.
B. decrease of the total amount of carbon found on Earth.
C. depletion of carbon dioxide reserves in the atmosphere.
D. increase in the amount of carbon contained in rock materials.
62. _______________ is the process in which certain bacteria convert nitrogen gas into usable forms of
nitrogen.
a. denitrification
b. nitrogen fixation
c. decompostion
63. ______________ is the process by which some soil bacteria convert nitrates back into nitrogen gas.
a. nitrogen fixation
b. denitrification
c. decomposition
64. Plants and animals can absorb nitrogen gas directly from the atmosphere.
a. true
b. false
65. What role do decomposers play in both the carbon and nitrogen cycles? Decomposers “recycle”
dead matter by helping return it to the environment.
66. How do humans affect the nitrogen cycle? Through the application of excess fertilizers that then
runoff into bodies of water.