• Cells undergoing different stages of the cell cycle can be identified using photomicrographs taken from microscope slides
• Cells undergoing certain stages of the cell cycle have distinctive appearances

Interphase

• As cells spend the majority of the cell cycle in this stage then most cells will be in this stage
• The?chromatin?is?visible?so the nuclei have a dark appearance

Prophase

• Chromosomes are?visible
• The nuclear envelope is breaking down

Metaphase

• Chromosomes?are lined up along the?middle?of the cell

Anaphase

• Chromosomes are moving away?from the middle of the cell, towards opposite poles

Telophase

• Chromosomes have arrived at?opposite poles?of the cell
• Chromosomes begin to?uncoil?(are no longer condensed)
• The nuclear envelope is reforming

Cytokinesis

• Animal cells: a?cleavage furrow?forms and separates the daughter cells
• Plant cells: a?cell plate?forms at the site of the metaphase plate and expands towards the cell wall of the parent cell, separating the daughter cells

Identification of phases

Micrograph showing a cell undergoing prophase (P)

Micrograph showing cells undergoing metaphase (M) and anaphase (A)

Micrograph showing cells undergoing metaphase (M) and anaphase (A)

Micrograph showing a cell undergoing anaphase (A)

Investigating mitosis in root tissue

• Growth in plants occurs in specific regions called?meristems
• The root tip meristem can be used to study?mitosis
• The root tip meristem can be found?just behind the protective root cap
• In the root tip meristem, there is a?zone of cell division?that contains cells undergoing?mitosis
• Pre-prepared slides of root tips can be studied or temporary slides can be prepared using the?squash technique?(root tips are?stained?and then?gently squashed, spreading the cells out into a thin sheet and allowing individual cells undergoing mitosis to be clearly seen)

Micrograph showing a stained root tip

Analysis

• Cells undergoing mitosis (similar to those in the images below) can be seen and drawn
• Annotations can then be added to these drawings to show the?different stages of mitosis
• The?mitotic index?can be calculated

The mitotic index

• The mitotic index is the?proportion?of cells (in a group of cells or a sample of tissue) that are?undergoing mitosis
• The mitotic index can be calculated using the formula below:

• You can multiply the answer by?100?if you need to give the mitotic index as a?percentage

mitotic index =?0.76

mitotic index =?0.44

Step 1: Identify the cells undergoing mitosis

Number of cells with visible chromosomes (green) = 20

Step 2: Count the total number of cells

Total number of cells (green + red) = 20 + 55 = 75

Step 3: Substitute numbers into the equation

mitotic index =?0.27