A Level Biology RP 2

1) Aim: Investigating the stages of cell division in root tip cells in garlic

You are looking specifically at mitosis (prophase, metaphase, anaphase, telophase) during the cell cycle in the actively dividing root tip cells in garlic (Cells further up the tip are in the process of cell elongation). Concentrated hydrochloric acid halts cell division - allows it to be visible under the microscope, Toluidine blue stains chromosomes blue - makes chromosomes visible, Single layer of cells - individual cells visible - do not move coverslip sideways as it could break chromosomes - Transmission of light.

You should be able to identify the cell cycle at each stage (specify magnification in lab book - and calibrate eyepiece graticule for each magnification) and analyse and explain the appearance of the cells. It is also important to remember that before cell division, interphase takes place which is the unravelling of the cell's DNA, which allows DNA replication to take place (double genetic content) so that when chromosomes split apart, both cells are able to be diploid - hence all cells in our body apart from gametes are diploid.

Prophase - chromosomes condense. Centrioles (protein) at opposite poles of cell form network of spindle fibres. The nuclear membrane breaks down and chromosomes are free in cytoplasm
Metaphase - chromosomes line up in the middle of cell and held in place by centromeres attaching to spindle fibres.
Anaphase - spindle fibres contract so v-shaped sister chromatids pulled apart at centromere to opposite pole ends of the cell.
Telophase - at opposite poles, chromatids uncoil (long+thin) so are chromosomes - 2 nuclei formed by nuclear envelopes
- Cytokinesis - cytoplasm divides into 2 genetically identical daughter cells
- Cell cycle restarts

2) Analyse recorded results by calculating mitotic index = no.cells mitosis/total no. cells

If you require something more specific, please comment - I am not quite sure what you can speculate for your hypothesis w/o your results or requirements from your teacher.

This was really helpful thank you so much!!!!! I think the hypothesis is meant to be like what I think is going to happen but how am I supposed to make a hypothesis for a practical on mitosis?

I am not quite sure either. Perhaps you could make a hypothesis on how you will be able to investigate mitosis on garlic root tip cells?

The hydrochloric acid breaks down the hydrogen bonds that join the nucleotide bases and hold the 2 DNA strands together - doing so prevents cell division as the doubled genetic content is not produced during DNA replication. This causes the cells to remain in their stages of the cell cycle, and allows us to investigate the mitotic index on garlic root tip cells. Heating the hydrochloric acid increases the rate of breakdown - so that the bonds between some nucleotide bases are broken down at a faster rate. The bond between some of the bases has to be broken to ensure that the blue pigmented toluidine blue can bind with the bases and highlight the chromosomes against the rest of the cell. This will allow the chromosome to be visible under the microscope.

Hopefully you can summarise this into a conclusion. Some of the information is not included in the textbook and is extra knowledge, but maybe it would help to show why you are able to investigate the mitotic index of garlic root tip cells through what happens when these chemical molecules are added to the investigation.

Hope it helps!