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 9Tutor mode
Question 1 of 10
Interaction and interdependence
The net rate of photosynthesis of shoots of the aquatic plant Cabomba caroliniana was measured with a dissolved-oxygen sensor. Shoots of equal fresh mass were placed in 0.1% or 0.5% sodium hydrogencarbonate solution (the source of carbon dioxide). Light intensity was varied by moving an LED lamp and measured with a light meter; the water bath was kept at 25 °C. Each mean is from three shoots. A negative value shows net oxygen uptake.
Net rate of photosynthesis / µmol O₂ g⁻¹ h⁻¹ (mean ± SD, n = 3)
Light intensity / µmol photons m⁻² s⁻¹
0.1% sodium hydrogencarbonate
0.5% sodium hydrogencarbonate
0
−4 ± 1
−4 ± 1
100
10 ± 2
11 ± 2
200
22 ± 2
24 ± 3
400
30 ± 3
45 ± 4
600
31 ± 3
58 ± 4
800
31 ± 4
60 ± 5
Which factor limits the net rate of photosynthesis between 600 and 800 µmol photons m⁻² s⁻¹ in 0.1% sodium hydrogencarbonate?