• 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

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?decondense
• 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

Analysis

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)

• 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

Apparatus

• Scalpel
• Forceps
• Onion roots
• Gloves
• Ethanoic acid
• Dilute hydrochloric acid
• Water bath
• Spotting tile
• Microscope slides
• Coverslips
• Pipettes
• Acetic orcein stain
• Paper towels
• Optical microscope

Method

• Garlic?or?onion?(Allium cepa) root tips are most commonly used (the bulbs can be encouraged to grow roots by suspending them over water for a week or two)
• Remove the tips of the roots (about 1cm) and place them in?ethanoic alcohol
  • This helps to "fix" the tissue and prevent mitosis from continuing in the cells

   

• Place the root tips in warm (60oC)?dilute hydrochloric acid
  • This separates the cells

   

• Transfer the root tip to a?microscope slide
• Using a pipette, add a suitable?stain?(eg. acetic orcein, which stains chromosomes a deep purple)
• Place a?coverslip?on top of the root tip and press down firmly using a paper towel
  • This spreads out the cells so they are only one layer thick

   

• View the cells under a microscope

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

Limitations

• The preparation of tissue for microscope slides can damage cells and alter their appearance
  • During preparation, a sample is often?squashed?or?stained, which can generate artefacts
  • The occurrence of artefacts can be?decreased?by?more careful preparation?of samples

   

• The size of cells or structures of tissues may appear inconsistent in different specimen slides
  • Cell structures are 3D and the different tissue samples will have been?cut at different planes?resulting in inconsistencies when viewed on a 2D slide

   

• Optical microscopes do not have the same magnification power as other types of microscopes and so there are some structures that can not be seen