10 free IB Biology practice questions in the real exam format, covering the official content areas, with an explanation for every answer.
IB Biology Practice Test 13Tutor mode
Question 1 of 10
Interaction and interdependence
Students placed 100 quadrats (1 m × 1 m) at random coordinates in a mixed woodland in late spring. In each quadrat they recorded whether bluebell (Hyacinthoides non-scripta) and bracken (Pteridium aquilinum) were present or absent. They used a chi-squared test to find out whether the two species are associated.
Observed number of quadrats
Bluebell present
Bluebell absent
Total
Bracken present
12
28
40
Bracken absent
33
27
60
Total
45
55
100
Expected frequency = (row total × column total) ÷ grand total. χ² = Σ (O − E)² ÷ E. Degrees of freedom = 1; critical value at p = 0.05 is 3.84.