Starfish: External Characteristics

Introduction to Cell Biology

-         Cell was discovered by Robert hook

-         He has observed compartment like structure in section of cork

-         Cell Theory:  All organisms are made up of cells. This theory was proposed by Scheilden & Schwan

-          Modified version of Cell theory: All the organisms are made up of cell & cell products.

-         Types of Cells:  There are two types of cells viz.

1.     Prokaryotic cell

2.     Eukaryotic cell

1.     Characters of Prokaryotic Cell:

                               i.            The cells in which nuclear membrane and cell organelles are absent are called as prokaryotic cell.

                             ii.            The region in prokaryotic cell where DNA is present is called as nucleoid region/nuclear region.

                          iii.            DNA is in the form of circular DNA.

                          iv.            Different enzymes required for cellular functioning is present on foldings of cell membrane.

                             v.            Extra chromosomal DNA is present in the form of plasmid DNA.

                          vi.            Cell membrane contains amino sugars & muramic acid.

2    Characters of Eukaryotic cell:

                               i.            The cells in which nuclear membrane and cell organelles are present are called as eukaryotic cell.

                             ii.            DNA is present in nucleus.

                          iii.            DNA is in the form of chromosomes.

                          iv.            Different types of enzymes required for cellular functioning are present in various cell organelles.

                                                                     

Differences between Prokaryotic Cell & Eukaryotic Cell:

Prokaryotic Cell	Eukaryotic Cell
1.     Small in size (1-10µm)	1.     Large in size (10-100µm)
2.     Rod or sphere shaped	2.     Mostly spheroid
3.     Cell wall is non-celluloic (Cellulose absent) and contains amino sugars & muramic acid.	3.     Cell wall is celluloic (cellulose is present) in plant cell & absent is animal cell.
4.     Nuclear membrane is absent	4.     Nuclear membrane is present
5.     Nucleus is in the form of nucleoid region	5.     Nucleus is intact, single or occasionally more in number
6.     Endomembranes are absent	6.     Endomembranes are present.
7.     Cell division is of amitosis type i.e. takes place by budding or fission	7.     Cell division is by mitosis or meiosis
8.     Vacuoles are absent	8.     Vacuoles are present in plant cell
9.     Respiratory enzymes are present on plasma membrane	9.     Respiratory enzymes are present in mitochondria
10.            DNA is naked and without histone proteins	10.            DNA is in condensed form and is combined with histone proteins
11.            70s (50s+30s) ribosome is present	11.            80s (60s+0s)ribosome is present
12.            16s & 23s rRNA are present in ribosome	12.            18s, 28s & rRNA are present in ribosome
13.            Locomotion is by single fibril flagellum	13.            Locomotion is by cilia and flagella (9+2 fibrilar arrangement)

Differences between Plant Cell & Animal Cell:

Feature	Plant Cell	Animal Cell
1.     Size	Larger than animal cell	Smaller than plant cell
2.     Shape	Fixed generally rectangular	Irregular mainly round
3.     Cell wall	Present (contains cellulose)	Absent
4.     Delimiting factor	Cell wall	Cell membrane
5.     Vacuole	Prominent and permanent	Small & temporary
6.     Plastids (Chloroplast)	Present	Absent
7.     Mitochondria	Less in number than animal cell	More in number than plant cell
8.     Cilia	Very rare	Present (frequently)
9.     Golgi complex	Golgi complex is in form of dictyosome	Golgi complex are in normal form
10.            Lysosomes	Few in number	More in number
11.            Centrioles	Absent	Present
12.            Cytokinesis	Occurs by cell plate formation	Occurs by furrow formation