Key Idea: All organisms, both land-based and aquatic, are connected to other organisms by their need for food. This results in a global network of interconnections, which is referred to as a food web.
Students are expected to know that:
- When organisms eat or are eaten by other organisms, there is an effect on the two organisms involved and on the populations to which they belong.
- When organisms eat or are eaten by other organisms, there may be an effect on other populations that are not eating or being eaten by those organisms. This is because once an individual organism (or part of an organism) is eaten, it is no longer available as food for other populations of organisms and/or will no longer eat other organisms from other populations.
- Changes in the size of a population may result from changes in the size of the populations of organisms that it consumes, that consume it, or both. Specifically, if the size of a population increases (or is introduced), the size of a population of organisms that consumes it may increase because there will be more food available to that population, and if the size of a population increases (or is introduced), the size of a population of organisms that it consumes may decrease because more of them may be consumed. If the size of a population decreases (or the population disappears), the size of a population of organisms that consume it may decrease because less food is available to that population, and if the size of a population decreases (or the population disappears), the size of a population of organisms that it consumes may increase because there are fewer organisms to consume them.
- Changes to the size of populations of organisms due to changes in the size of populations it consumes or that consume it take time, and the relative sizes of the starting populations involved may affect the outcome.
- The network of populations of organisms being eaten by other populations can be thought of as a single global food web encompassing all populations, but food webs can also be described for populations in particular environments.
- Feeding interactions among selected populations of organisms in food webs can be represented by diagrams with arrows from populations being eaten to populations doing the eating. If an arrow is not present in a diagram, there is no feeding interaction between two populations, and if an arrow is present, there is a significant feeding interaction between the two populations.
Boundaries:
- Students are not expected to know that microorganisms are part of food webs. This is addressed in a later idea.
- Students are not expected to know the terms producer, consumer, or trophic level.
- Students are not expected to know what any particular organism eats apart from what can be determined from food web diagrams they are given.
- Students are not expected to know that although a population may be connected by arrows to more than one population, organisms may rely on some organisms more than others for food.
| Item ID Number |
Knowledge Being Assessed | Grades 6–8 |
Grades 9–12 |
Select This Item for My Item Bank |
|---|---|---|---|---|
84% |
80% |
|
||
73% |
79% |
|
||
70% |
81% |
|
||
66% |
78% |
|
||
72% |
74% |
|
||
69% |
77% |
|
||
Changes in a population in a food web (robins) can affect the population of its prey (caterpillars). | 66% |
74% |
|
|
63% |
74% |
|
||
63% |
72% |
|
||
Changes in a population in a food web (large fish) can affect the population of its prey (tadpoles). | 61% |
69% |
|
|
59% |
68% |
|
||
56% |
68% |
|
||
55% |
66% |
|
||
55% |
58% |
|
||
51% |
62% |
|
||
53% |
57% |
|
||
52% |
57% |
|
||
50% |
53% |
|
||
44% |
53% |
|
||
34% |
45% |
|
||
37% |
46% |
|
||
35% |
42% |
|
||
35% |
40% |
|
||
29% |
38% |
|
||
20% |
28% |
|
||
20% |
27% |
|
Misconception |
Student Misconception |
Grades |
Grades |
|---|---|---|---|
31% |
30% | ||
20% |
19% | ||
18% |
15% | ||
15% |
12% | ||
12% |
8% | ||
10% |
8% | ||
10% |
8% | ||
9% |
7% |
Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.