In the mutualistic relationship between mycorrhizae and Orchidaceae, what role do mycorrhizae play?
Correct Answer: \( \boxed{\mathbf{A}} \)
Mycorrhizae are fungi that increase the plant’s absorption of water and mineral nutrients, especially phosphorus, from the soil. In return, the plant supplies the fungi with carbohydrates, making the relationship mutually beneficial.
A capture–mark–release–recapture study was conducted to estimate the population size of common periwinkles (Littorina littorea) on a rocky shore. Researchers used the Lincoln index formula, given by Population size estimate = (M × N) / R. The following data were collected:
| Description | Number |
|---|---|
| Individuals captured and marked initially | 100 |
| Individuals recaptured | 50 |
| Marked individuals recaptured | 10 |
What is the estimated total population size of Littorina littorea based on these results?
A. 160
B. 500
C. 1000
D. 5000
What is an example of a population control mechanism within a community?
Correct Answer: \( \boxed{\mathbf{B}} \)
Top-down control occurs when consumers or predators regulate the populations of organisms at lower trophic levels. Grazing by consumers controls the population of grasses, making this a top-down population control mechanism.
The other options misuse the terms: bottom-up control is driven by resource availability (not predators), soil nutrients are an abiotic factor rather than top-down control, and dissolved oxygen is not a population within a community.
