Mitosis Lab
All new cells come from previously existing cells. New cells come from
the process of cell division, which involves both the division of the cells
nucleus and division of its cytoplasm. There are two types of nuclear
division; mitosis and meiosis. Today we will focus on mitosis, which is
a process that typically results in the production of new body (somatic)
cells. Development of an adult organism from a fertilized egg, asexual
reproduction, regeneration, and maintenance and repair of body parts
are accomplished through mitotic cell division. Meiosis is a similar
process that is used to produce gametes (sperm or egg cells) and
results in cells with half the chromosome number of the parent cell.
Where does one find cells undergoing mitosis? Plants and animals
differ in this respect. In higher plants the process of forming new cells
is restricted to special growth regions called meristems. These regions
usually occur near the tips of the roots or stems. In animals, cell
division is dispersed over the entire organism and occurs anywhere
new cells are replacing damaged or worn out cells.
To study the stages of mitosis we will look at tissues where there are
many cells in the process of mitosis. Thus we will look at the tips of
growing plants, such as the root tips of an onion, and in the case of
animals, we will look at developing embryos such as the blastula (an
early embryonic stage) of whitefish.
Roots consist of different regions. At the very tip of the root is the root cap,
which functions in protection. Just past the root cap is the apical meristem.
This is the region that contains the highest percentage of cells undergoing
mitosis and this is the region you should focus on today while viewing the
onion root tip.
The whitefish blastula is often used for the study of cell division. As soon
as the egg is fertilized it begins to divide, nuclear division after nuclear
division follows as the embryo develops from a single cell into a blastula, a
ball of rapidly dividing cells early on in embryonic development. Thus the
whitefish blastula provides a high concentration of cells in the process of
mitosis.
Pre-Lab Questions
1. What is the difference between chromatin, chromosomes, and
sister chromatids.
2. Mitosis only occurs in eukaryotic cells. What process is
similar, and serves the same purpose, but takes place
exclusively in prokaryotic cells?
Figure 1: Onion Root Tip
Figure 2: Apical Meristem
400x
Figure 3: Whitefish Blastula
