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 10Tutor mode
Question 1 of 10
Continuity and change
A student investigated how the proportion of dividing cells changes with distance from the tip of garlic (Allium sativum) roots (independent variable). Three roots, each 20 mm long and grown in water at 22 °C, were cut at 10:00, fixed, stained with toluidine blue and squashed. Cells were classified using a light microscope at ×400 in five fields of view from each 1 mm zone of each root, and the totals for the three roots are shown. Mitotic index = number of cells in mitosis ÷ total number of cells.
Table 1: Numbers of cells in each stage in four zones of the root (totals for three roots)
Distance from root tip / mm
Interphase
Prophase
Metaphase
Anaphase
Telophase
Mitotic index
0–1
312
48
18
9
13
0.22
1–2
341
29
11
6
8
to be calculated
2–3
384
9
3
1
3
0.04
3–4
397
2
0
0
1
0.01
Which observation would the student have used to classify a cell as being in anaphase?