Biology 2 /SL RB Topic 5.1: Communities and Ecosystems
Name ___________________________
Review Book Topic 5: Ecology and ecosystems
Key facts - 5.1 Communities and Ecosystems
1. A species is a group of organisms that can interbreed and produce fertile offspring.
2. A population is a group of organisms of the same species who live in the same area at the same
time.
3. A community is a group of populations living and interacting with each other in an area.
4. Habitat refers to the environment in which a species normally lives or the location of a living
organism.
5. Ecosystems are very important to ecological studies. They are communities coupled with their
abiotic (non-living) environment.
6. Ecology is the study of relationships between living organisms and between organisms (biotic
component) and their environment (abiotic component).
7. Autotrophs are organisms that can synthesize their organic molecules form simple inorganic
substances. This would involve photosynthesis and/or chemosynthesis.
8. Heterotrophs are organisms that obtain their organic molecules from other organisms.
9. Consumers, detritivores and saprotrophs are all heterotrophs.
10. A consumer is an organism which ingests other organic matter that is living or recently killed.
11. A detritivore is an organism that ingests non-living organic matter. Dung beetles and earthworms
are examples.
12. Saprotrophs live on or in non-living organic matter, secreting digestive enzymes into it and
absorbing the products of digestion. Bread mold and mushrooms are common examples of
saprotrophs.
13. Two major components of ecology involve the study of energy and nutrients within biotic and
abiotic components of the environment.
14. Examples of autotrophs include plants, algae and even certain types of bacteria.
15. Common heterotrophs include animals, mushrooms and certain types of bacteria.
16. Light is the initial energy source for the vast majority of communities.
17. Whereas, photosynthesis and chemosynthesis allow the formation of molecules essential for energy
storage, respiration results in decomposition of these molecules so that the stored energy may be
released and utilized by the organism involved.
18. Energy flows through ecosystems in the following direction: light energy – producers – primary
consumers – secondary consumers. All biotic components of the ecosystem eventually become
utilized by decomposers.
19. Most of the energy flow in an ecosystem is lost as heat.
20. Food chains represent the flow of energy through a group of organisms.
21. Food webs are made up of multiple food chains interconnected by common organisms.
22. The various feeding levels of a food chain are referred to as trophic levels and include producers,
consumers, and decomposers.
23. Energy transformations between trophic levels are not 100% efficient. Usually, these
transformations are only 10% efficient. 90% of the original energy is usually lost. This energy loss
may be in the form of heat, it may be in the parts of organisms that are not eaten, or it may be lost
as indigestible material.
24. A pyramid of energy represents the flow of energy from one trophic level to the next in a
community. The units of these pyramids of energy are energy per unit area per unit time, for
example, kilojoules per square meter per year.
25. While energy enters and leaves ecosystems (flowing in one direction), nutrients are recycled or
reused.
Biology 2 /SL RB Topic 5.1: Communities and Ecosystems
Name ___________________________
26. Common examples of this nutrient recycling include the carbon cycle, the water cycle, the nitrogen
cycle and the carbon cycle.
Additional notes
Complete the following.
1. What does it mean when we say members of a species share a common gene pool?
2. Give an example of a population that exists in our school’s immediate vicinity.
3. Describe the community that exists in our school’s immediate vicinity.
4. Explain how an ecosystem differs from a habitat.
5. Why is a mule not considered to be part of its own species?
6. Describe briefly the following environments:
a. hydrosphere –
b. atmosphere –
c. lithosphere –
d. biosphere –
Biology 2 /SL RB Topic 5.1: Communities and Ecosystems
Name ___________________________
7. Differentiate between biotic and abiotic components of an ecosystem.
8. Why are autotrophs very important to heterotrophs?
9. Name two processes by which autotrophs may produce macromolecules.
10. Explain how a detritivore relates to a saprotroph.
11. What trophic level do all food chains and food webs begin with? ______________
12. What is the relationship between a food chain and a food web?
13. Construct a food chain involving four trophic levels.
14. From the above food chain which organisms are producers?___________________
Which organism are consumers?_________________________________________
Are there decomposers present?__________________________
Should all food chains and/or food webs include decomposers of some type?________
Why is this important?
15. How does a primary consumer differ from a secondary consumer?
16. Why is the number of trophic levels within a food chain limited to usually 4?
Biology 2 /SL RB Topic 5.1: Communities and Ecosystems
Name ___________________________
17. Why is it possible for the same organism to occupy different trophic levels within a food web?
18. What is the initial source of energy for all vegetation?___________________
19. How is it possible for some food chains to start without sunlight?
20. Typically, what percentage of energy is passed from one trophic level in a food chain to the next?
________________
21. What accounts for the energy that is not passed to the next trophic level?
22. When diagramming energy within a food chain, why is a pyramid shape obtained with the broadest
portion representing the energy of the first trophic level?
23. Why does each level of the energy pyramid decrease in size from the bottom up?
24. If one looks at a food chain, it would be seen that energy enters as light and exits as
_______________.
25. Energy is said to flow through a food chain, while nutrients are ___________________.
26. Why is the loss of energy at each trophic level as heat not a serious problem?
27. What organism types are especially involved in the recycling of nutrients within a food chain?