Cell Division SS2 Biology Lesson Note

Life begins as a single fertilized cell, continuous as the cell divides into two daughter cells then into four and so on. After cell division, the daughter cells increase in mass and size (enlargement). Eventually, each cell develops into a special type of cell (specialization) by changing its shape and structure to carry out a particular function. Most specialized cells, at maturity, lose their ability to divide.

 TYPES OF CELL DIVISION 

There are two types of cell division: 

(a) Mitosis     

(b) Meiosis 

 a) Mitosis

Mitosis is a cell division to produce two daughter cells with the same number of chromosomes and characteristics as those of the parent cell. This cell division takes place only in somatic cells (i.e. body cells that are not involved in the production of gametes) such as skin, bone marrow and meristematic tissues in plants.

Mitotic cell division involves five main stages:

i. Interphase: This is referred to as the resting stage where the chromosomes become elongated and form a network of fine threads called chromatids

ii. Prophase: in early prophase chromosomes become visible, nucleolus shrinks, centrioles start moving away from each other in opposite directions and the formation of spindle fibres begins. During the late prophase, chromosomes become shorter, thicker and visible. Each chromosome now forms two distinct chromatids joined by a centromere. The nucleolus and nuclear membrane disappear entirely.

iii. Metaphase: paired chromatids arrange themselves along the equator of the spindle and are attached to the spindle at the centromere.

iv. Anaphase: sister chromatids separate and start migrating to the opposite poles of the cell and eventually reach the poles.

v. Telophase: the cell starts dividing into two by constricting at the equator, nucleolus and nuclear membrane are reformed in each daughter cell, spindle fibres degenerate and chromosomes eventually regain their threadlike form.

Importance Of Mitosis

1. It brings about growth, development and specialization, especially in multicellular organisms.
2. Asexual reproduction binary and multiple fissions in protozoa, budding in yeasts are the result of mitosis.
3. It ensures the diploid condition of the cells is retained from generation to generation
4. It aids in the repair of damaged cells

 Life Processes Involved In Mitosis

1. Formation of new cells in the Malpighian layer of the skin
2. Production of red and white blood cells in the bone marrow
3. Healing of wounds
4. Growth in meristem
5. Binary fission