Question
Limpets are molluscs with conical shells that cling tightly to rocks on seashores. In a study of two species of limpets found on rocks along the Oregon coast, 30 randomly placed quadrats were used to determine how often the two species occurred together. The table shows the data that were collected.
Which statistical method will determine whether these two species occur together by chance or by some kind of interaction?
A. Chi-squared test
B. t-test
C. Standard deviation
D. Means and ranges
▶️Answer/Explanation
Answer: A. Chi-squared test
Explanation:
The Chi-squared (χ²) test is the appropriate statistical method when:
- You’re analyzing categorical data (e.g., presence/absence).
- You want to test whether two variables are independent or associated.
What the Table Shows:
- You are testing whether the presence of Lottia scutum is independent of the presence of Lottia pelta.
- This is categorical data (present/absent) across two species.
- A Chi-squared test for independence is ideal here.
Why the Other Options Are Incorrect:
| Option | Description | Why It’s Incorrect |
|---|---|---|
| B. t-test | Compares means of continuous data between 2 groups | Data here is categorical, not continuous |
| C. Standard deviation | Measures variability in numerical data | Doesn’t test relationships between variables |
| D. Means and ranges | Descriptive stats for continuous data | Can’t test statistical association or independence |
Question
Which organism can best be described as a saprotroph?
A. A fungus that digests its food externally and absorbs the products of digestion
B. A beetle that feeds by ingesting the dung of other animal species and digesting its food internally
C. A single-celled eukaryote that is able to photosynthesize and consumes smaller organisms by endocytosis
D. A giraffe that feeds by ingesting leaves from an acacia tree
▶️Answer/Explanation
Answer: A. A fungus that digests its food externally and absorbs the products of digestion
Explanation:
A saprotroph is an organism that feeds on dead or decaying organic matter by secreting digestive enzymes outside its body (external digestion) and then absorbing the broken-down nutrients. Fungi are classic examples of saprotrophs.
Answer Evaluation:
A. Correct – Fungi are saprotrophs. They release enzymes into the environment to break down complex organic materials (like dead plants), then absorb the simpler nutrients. This is the defining feature of saprotrophic nutrition.
B. Incorrect – The beetle ingests and digests food internally, which is typical of heterotrophic consumers, not saprotrophs.
C. Incorrect – This organism performs both photosynthesis and phagocytosis, making it a mixotroph, not a saprotroph.
D. Incorrect – A giraffe eats plants (autotrophs) and digests them internally. It is a herbivore, not a saprotroph.
Question
What is the ecological term for a group of different types of organisms that live together and interact with each other?
A. Community
B. Domain
C. Ecosystem
D. Population
▶️Answer/Explanation
Answer: A. Community
Explanation:
In ecology, a community is defined as all the different species (plants, animals, fungi, bacteria, etc.) that live together in the same area and interact with each other. These interactions can include feeding relationships, competition, and mutualism.
Answer Evaluation:
A. Correct – A community includes multiple species living in the same habitat, interacting through food webs, competition, and other relationships. This is the correct term for the group described.
B. Incorrect – A domain is a much broader taxonomic category (e.g., Bacteria, Archaea, Eukarya), not an ecological grouping of interacting species.
C. Incorrect – An ecosystem includes both the community (living organisms) and the non-living environment (like soil, water, and air). While related, the question asked about only the organisms and their interactions.
D. Incorrect – A population refers to individuals of the same species living in a particular area, not multiple species.