A student examines 160 cells from a growing garlic root tip. The observations are recorded in the table.
| Observation | Number of cells |
|---|---|
| Visible chromosomes | 24 |
| Evenly stained nucleus | 136 |
Mitotic index = number of cells in mitosis ÷ total number of cells × 100.
The table below shows the stages of the cell cycle in order. The events for positions 1 to 3 have been filled in.
| Position | Stage | Event |
|---|---|---|
| 1 | Cell growth | Cell grows |
| 2 | DNA replication | DNA is copied |
| 3 | Further cell growth | Cell grows again |
| 4 | Mitosis | |
| 5 | Cytokinesis |
Describe the event at each of positions 4 and 5.
Calculate the mitotic index of the cells examined.
Explain why separate chromosomes cannot be seen in the cells recorded as having an evenly stained nucleus.
194 exam-style questions on OCR GCSE Biology 2.1 Supplying the cell, covering 2.1.1 Transport across cell membranes, 2.1.2 Mitosis and the cell cycle, 2.1.3 Importance of cell differentiation, and 2.1.4 Stem cells. Each one has a worked solution and a mark scheme showing where the marks go.