Vacuoles and Cell Division

1.0Vacuoles

Vacuoles are membrane bound storage sacs that contain non living liquid or solid contents.

Contractile vacuole in unicellular fresh water organisms take part in osmoregulation and excretion.

In animal and young plant cells, vacuoles are small. In mature plant cells, there is a large central vacuole occupying 50–90% of cell volume and contain cell sap. The covering membrane of the vacuole is called tonoplast. 

Functions

(i) In plant cell, vacuoles are full of cell sap and provide turgidity and rigidity to the cell.

(ii) Vacuoles store amino acid, sugars, various organic acids and some proteins.

(iii) They act as dump house for excretory products in plant cells. 

(iv) In single celled organisms like amoeba, the food vacuole contains the food items that the amoeba has consumed.

In some unicellular organisms, specialised vacuoles also play important roles in expelling excess water and some wastes from the cell.

Comparison between Animal cell and Plant cell

Prokaryotes

Organisms whose cells lack a nuclear membrane and the genetic material (DNA, RNA) lies freely in the form of nucleoid, are known as prokaryotes. The Nucleoid (meaning nucleus-like) is an irregularly shaped region within the cell of a prokaryote that contains all or most of the genetic material. e.g. Bacteria, blue green algae.

Prokaryotic cells also lack most of the other cytoplasmic organelles present in eukaryotic cells. Many of the functions of such organelles are also performed by poorly organized parts of the cytoplasm. The chlorophyll in photosynthetic prokaryotic bacteria is associated with membranous vesicles (bag like structures) but not with plastids as in eukaryotic cells.

Eukaryotes

Organisms whose cells have a well-organized nucleus with nuclear membrane are known as eukaryotes. e.g. All plant and animal cells.

Comparison between Prokaryotes & Eukaryotes

2.0Cell Division

New cells are formed in organisms in order to grow, to replace old, dead and injured cells and to form gametes required for reproduction. The process by which new cells are made is called cell division. There are two main types of cell division: mitosis and meiosis.

The process of cell division by which most of the cells divide for growth is called mitosis. In this process, each cell called mother cell divides to form two identical daughter cells. The daughter cells have the same number of chromosomes as mother cell. It helps in growth and repair of tissues in organisms. 

Specific cells of reproductive organs or tissues in animals and plants divide to form gametes, which after fertilization give rise to offspring. They divide by a different process called meiosis which involves two consecutive divisions. When a cell divides by meiosis it produces four new cells instead of just two. The new cells only have half the number of chromosomes than that of the mother cells.

Note: Centrosome: Centrioles and centrosphere are collectively called centrosome. Two centrioles are located just outside the nucleus and lie at right angle (90°). It initiates cell division by arranging spindle fibers between 2 poles of cell.

3.0Also Read