Question

Make a labeled sketch of the stages of mitosis. (P158 - p159) In your own words describe what happens in each stage of mitosis. Look at a prepared slide of allium (onion) root tip. Make a labeled sketch of 5 cells in different stages of mitosis. Look at a prepared slide of whitefish egg. Make a label sketch of 3 cells in different stages of mitosis. I. V. Refer to the drawings below to answer #'s List the letters of the cells shown above, in the order in which one cell divides to form two. Which cell is in anaphase? _ Which cell is in metaphase? _ What is #22 pointing to? _ Which cell is in prophase? _

Answer 1

Mitosis is also called as somatic cell division which takes place in the somatic cells or the body cells of an organism (Greek soma= body).The daughter cells so formed are identical to parental cells in all aspects including the number of chromosomes , which means if in the parent 2n =46 the daughter cell will also have 2n = 46.As a result of mitosis two daughter cells are produced.

The cells of the body need to be constantly replaced due to aging and various other factors it is here where the mitotic cell division plays an important role also the actively growing parts of the plant like the apical meristems exhibit mitosis.

he cell after undergoing the stages of cell division under goes cytokinesis to give rise to the daughter cells.

Before the cell undergoes cell division it undergoes a growth phase known as the Interphase where the cell prepares itself for cell division.This is followed by mitosis which is sub divided into Prophase, Metaphase, Anaphase ,Telophase and cytokinesis.

Interphase : Is also known as the preparatory phase and is one of the longest phase of cell divison. It is further subdivided into the G1 phase , s phase , G2and G0 phase.The chromosomes are distinct thread like , the nucleus and the nucleolus are distinct.

G1 phase : The cell increases in its size ,the cell synthesizes the proteins that are required for the cell division.

s phase : follows the G1 phase and is known as the synthesis phase , the chromosomes or the DNA undergoes replication,

G2 phase:the cell increase in its size further and continues to synthesize the proteins required for the cell division and indicates the second gap phase.

in animal cells the centrioles are formed during the interphase.At the end of interphase the nucleus and the nuclear membrane are intact and the er is a network of chromatin.

In some cells there is another phase called the Go phase this is the dormant phase or the quiscent phase where the cell does not under go any changes.

Prophase:During prophase the condensation of the chromatin to form chromosomes takes place.It is further subdivided into early and late phase

The nuclear envelope breaks down and the nucleolus also disappears.

Spindle fibres are formed at the poles of the cell.(In animal cells the spindle appears as asters surrounding the centrioles.

The centrioles in animal cells start moving away from each other in opposite direction.

Late prophase:

polar fibers reach the poles of the cells i.e the movement of the polar fibers is complete.

The nuclear membrane completly vanishes

The chromosomes are easily recognised with distinct arms or the chromatids

Each chromosome has two chromatids held by a centromere.

The movement of the centrioles, and asters is complete and are now at opposite ends of the cell and the thin protein spindle fibers are reaching out and attaching to the centromeres of each chromosome from opposite directions.

Metaphase :

the spindle formation is complete

chromatids align themselves at the center of the cell forming a metaphase plate.

The centromeres of the chromatid pairs align along the microtubules at the centre of the mitotic spindle.

Anaphase:

the centromeres split and seperating the two members of each chromatid pair(sister chromatids) - which then move to the opposite poles of the cell and are now called as the chromosomes.

they appear as "V" shaped structures and pulled by the the microtubules towards the opposite poles.

By the end of anaphase the movement of chromosomes is complete and are seen as clusters at each pole.

Telophase : The last stage of cell division The chromosomes which are at the poles now start uncoiling and form chromatin network once again .

the nucleolus and the nuclear membrane reappear.

Mitotic spindle breaks up.

Cytokinesis: It is initiated during the last phase of the cell division , the cytoplasm of the cell divides equally among the daughter cells and the daughter cells are formed.

The stages can be represented as follows .

  

Review questions 1

1.List of the order

F- Interphase As the chromosomes are seen in the form of network of chromatin,   

C--Prophase,the chromatids are clearly seen , spindle fibers are seen.

E- Metaphase ,The chromatids are organized on the metaphase plate.

D -late metaphase ,the chromosomesare being pulled apart, can be called as early anaphase also.

A.Late anaphase .The chromosomes are seen at the poles.

B.cytokinesis.The cell plate formation is complete the cell is divided into two.

2. Cell A is in anaphase as the movement of chromosomes is complete and they are seen as distinct clusters at the poles.

3.Cell E shows metaphase plate.

4. 22. points at the centromeres aligned at the metaphase plate.

5. Cell F is in prophase.