Essential Idea
The continued survival of living organisms including humans depends on sustainable communities.
Understandings
Species are groups of organisms that can potentially interbreed to produce fertile offspring.
Members of a species may be reproductively isolated in separate populations.
Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods).
Consumers are heterotrophs that feed on living organisms by ingestion.
Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
A community is formed by populations of different species living together and interacting with each other.
A community forms an ecosystem by its interactions with the abiotic environment.
Autotrophs obtain inorganic nutrients from the abiotic environment.
The supply of inorganic nutrients is maintained by nutrient cycling.
Ecosystems have the potential to be sustainable over long periods of time.
Applications
None
Skills
Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.
Setting up sealed mesocosms to try to establish sustainability. (Practical 5)
Testing for association between two species using the chi-squared test with data obtained by quadrat sampling.
Recognizing and interpreting statistical significance.
Guidance
Mesocosms can be set up in open tanks, but sealed glass vessels are preferable because entry and exit of matter can be prevented but light can enter and heat can leave. Aquatic systems are likely to be more successful than terrestrial ones.
To obtain data for the chi-squared test, an ecosystem should be chosen in which one or more factors affecting the distribution of the chosen species varies. Sampling should be based on random numbers. In each quadrat the presence or absence of the chosen species should be recorded.
Key Vocabulary
Biotic
Organic
Abiotic
Inorganic
Species
Heterotroph (Consumer)
Detritivore
Saprotroph
Population
Community
Ecosystem
Autotrophic (Producer)
Nutrient cycling
Sustainability
Mesocosm
Chi-squared test
Statistical significance
Textbook Reading and/or Activities
Click HERE for a pdf of chapter 4.
Pages 166-179
Challenge Yourself (p.168)
Challenge Yourself (p.169)
TOK (p.169)
TOK (p.170)
TOK (p.171)
TOK (p.177)
Exercises (p.178)
Practice Questions (p.178-179)
Notes
4.1 Species, Communities and Ecosystems
A detailed set of notes, prepared by Bob Smullen, examining U1-U11 and S1-S4.
A detailed set of notes, created by Stephen Taylor, examining U1 - U9 and S1.
Another detailed set of notes, prepared by Stephen Taylor, that includes material on the whole of Topic 4. Worth checking out.
A detailed set of notes, created by Stephen Taylor, examining S3 and S4 (carrying out chi-squared tests).
A series of questions, prepared by Jacob Cedarbaum, to help you prepare for the relevant sections of the IB Exam. This is VERY GOOD practice.
A series of questions, prepared by Bob Smullen, to help check your understanding of both Topic 4 and Option C based on Ecology. This is VERY GOOD practice.
A series of questions, prepared by Jacob Cedarbaum, to help check your understanding of the IB learning expectations for all of Topic 4. Check your work when you're done HERE. This is VERY GOOD practice.
Learning Activities
This (children's) activity, prepared by PBS Learning, will help you better understand the different parts of an ecosystem.
This artistic activity challenges you to integrate the main concepts of this section.
This activity helps you understand the process of using quadrats to sample populations in order to make an estimate of total population.
Practical 5 - Virtual Ecosphere
This virtual lab will help you better understand how the variables within a system can be modified resulting in different states of balance.
This set of notes will help you prepare your mesocosm, an ecosystem in a jar.
Communities and Biomes - Virtual Lab
This virtual lab, prepared by McGraw-Hill, will help you better understand how different variables must maintain a balance in order for a system to be successful.
Practical 5 - Winogradsky Columns
This activity involves the preparation and monitoring of the micro-organisms that inhabit the photo and chemosynthetic layers of saturated systems.
This resource will help you understand how to carry out a Chi-Squared Test by clearly outlining the various stages of the process.
This activity, prepared for the American Statistical Association, will help you better understand how to determine whether or not a statistically significant difference exists between two data sets.
This activity, prepared by Biology Corner, will help you improve your statistical analysis skills.
Supplemental Reading
This reading (<15 mins), prepared by Diffen, clearly outlines the differences between abiotic and biotic components of the environment. It includes a relevant SlideShare and two videos to help clarify each concept.
This video outlines the mathematical process by which we can determine whether the difference between two (or more) things is due to chance or something else.
Must Watch Videos
Should Watch Videos
This video outlines the basics of ecosystem structure as well as many of the relationships between the organisms that inhabit the system.