Diversity of cell shape and size

DIVERSITY IN CELLS

1. Cell Diversity Cell size and shape

2. CELL DIVERSITY

3. DIVERSITY OF CELLS IN OUR BODY

4. TYPES OF CELL DIVERSITY Cell Diversity In Origin Cell Diversity In size Cell Diversity In Shape Some Other Types

5. Cell Diversity In Origin:- Based upon its origin it is basically divided into two types:- Prokaryotic Cell Diversity - Prokaryotic cells are primitive type of cells. These cells lacks true nucleus and other cell organelle like mitochondria, chloroplasts, endoplasmic reticulum, golgi complex, etc. The word prokaryotes is derived from Greek word ‘pro’ means primitive or old and ‘karyotes’ means nucleus or main. e.g. Cyanobacteria, Bacteria. Eukaryotic Cell Diversity - Eukaryotic cells have true nucleus and it also contains cell organelles. The word eukaryotes is derived from Greek word ‘eu’ means true and ‘karyotes’ means nucleus. e.g. General green plants, Starch containing amyloplasts, Typical Animal Cells, A live unicellular organism.

6. PROKARYOTIC & EUKARYOTIC CELL DIVERSITY

7. NUMBER, SIZE AND SHAPE OF CELL NUMBER OF CELLS Some organisms are unicellular i.e. bacteria, yeast, Chlamydomonas , diatoms, Cosmarium etc whereas most of organisms as plants and animals are multicellular. Human body is built of about one trillion cells. In case of unicellular forms single cell is capable of independent existence and to perform all the essential functions of life In green alga Pandorina , the coenobium is having a fixed number of cells (8/16/32 ) . Colonies like Volvox , Nostoc etc have many cells enclosed by mucilaginous sheath A multicellular organism is made of many cells Different cells become specialized for performing different functions. Cells are grouped into tissues, tissues into organs and organs into organ systems. Organ systems together form organism Cell Tissue Organ Organ system Organism

8. SIZE OF CELL Generally cell size ranges between 0.2µm-20 µm Smallest cell : PPLO : Mycoplasma gallisepticum :0.1 µm Bacteria : Unicellular : About 10 times smaller than Animal cell Escheritia coli : Rod shaped Bacteria : 1-2 micron long Protozoa : Amoeba proteus : 220–760 µm Generally plant cells are larger than animal cell Generally Animal cell range from 10µm to 30 µm & plant cell 10µm to 100µm Exceptions : Ostrich egg cell : 75 mm long Acetabularia a unicellular green alga is about 10 cms in length Bast fibre (phloem fibre ) of some plants (Ramie) are about 50-55 cm long A giraffe's nerve cell can reach about two meters Cell volume The volume of a cell is fairly constant for a particular cell type and is independent of the size of organism. The difference in the total mass of the organ or organism depends on the number ,not on the volume of the cells

9. Which Cell Type is Larger? 11 Plant cell Animal cell Ba c teria > > > Generally plant cells are larger than animal cell Animal cells are larger than bacterial cell

10. WHY ARE CELLS SO SMALL ? In order to survive, cells must constantly interact with their surrounding environment and can grow only to a certain size . If the cell grows beyond a certain limit , enough material will not be able to cross the membrane to accommodate with increased cellular volume. The reason cells can grow only to a certain size has to do with their surface area to volume ratio. Here, surface area is the area of the outside of the cell, called the plasma membrane. The volume is how much space is inside the cell. The ratio is the surface area divided by the volume. If the surface area to volume ratio is small, the cell is very big. When this happens, the cell must divide into smaller cells with favourable surface area/volume ratios. If the ratio is big, the surface area is greater than the volume then the cell is small

11. Cell Type Size(µm) Mycoplasma (PPLO) 0.10 Bacteria 0.20-2.50 Small Lymphocytes 4.0 Erythrocytes 7.0-8.0 Amoeba Proteus 1000 Liver Cells 20 Euglena 100-500 Human Oocyte 250 Ostrich Egg 75 × 10 3 Neurons (Length) 2 × 10 6

12. There is great variability in cell shape i.e. spherical, polygonal, disc like, cuboidal, columnar,spindle like or fibre like. Generally cells are spherical but in multicellular forms due to pressure become polyhedral . In plants as cells have cell wall appear hexagonal or polygonal . Cells some times change shape because of function as Amoeba and leucocytes . Whi l e a n i m a l ce l ls te n d t o h a ve ir r e g u l a r sh a pes, p l a n t c e l l s a r e t y p ic a l l y rectangular or cube shaped. CELL SHAPE

13. Cell shape Example 1. Variable cells Amoeba, Leucocytes, Myxomycetes. 2. Fixed cells (i) Spherical cells eggs of many animals. (ii) Flattened cells Squamous epithelium, endotheliums, and upper layer of epidermis. (iii) Cuboidal cells Thyroid gland follicles (iv) Columner cells The cells lining the intestine. (v) Discoidal cells Red Blood Cells Or Erythrocytes (vi) Spindle shaped cells Smooth muscle fibres (vii) Elongated cells Nerve cells or Neurons (viii) Branched cells Chromatophores Or Pigment cells of skin. (ix) Polyhedral (with 8,12 or14 sides) Squamous Epithelium

14. Dougherty (1957) classified cells into prokaryotic (Pro meaning primitive, karyon meaning nucleus) and eukaryotic ( Eu meaning true, Karyon meaning nucleus) types on the basis of structural organization of their nucleus. The cells which possess a primitive type of nucleus devoid of nuclear membrane are the prokaryotic cells. On the other hand, eukaryotic cells are those which possess a true, well organized nucleus having typical chromosomes and nuclear membrane . Dodge et al (1966) proposed a third type ( Mesokaryotic ) which can be placed in between prokaryotic and eukaryotic cells. TYPE OF CELLS

15. There is primitive type of nucleus which is not bounded by nuclear membrane as true nucleus and is termed as nucloid There are no membrane bound cell orgalleles , infolding of plasma membrane called mesosomes take their function The nuclear material lies diffused in central part of the cell, the ge n e tic m a ter ia l c on s i sts o f D N A , bu t i t i s n o t associated with proteins (Histones). Prok a r y otic c e l l s are g e n e r a l ly s m a l l er th a n e u ka r y o t ic cells. T h e c e l l s o f ba cter ia , Arc haea , b lue g r ee n a l gae , Mycoplasma, rickettsiae are included in this type P R OKA R YOTIC C E L LS

16. EU K A R YOT I C CELLS Eukaryotic: In this type of cell organization, there is definite or true nucleus surrounded by definite nuclear membrane. The genetic material consists of DNA complexed with histone proteins to form well developed chromatin/ chromosomes. Nucleus has nucleolous . There are different membrane bound cell organelles such as mitochondria, Endoplasmic Reticulum, Golgi body ,plastids etc for different functions. Plastids are presents in the plants cell only. This types of cells are in general larger and more organized than prokaryotic cells Most of the plants and animal cells fall under this category except Blue Green Algae(BGA).

17. MESOKA R YOTIC C ELLS In some organisms ( the Dinoflagellates ) the genetic material is surrounded by a nuclear membrane ( E u k a r y o tic c ha r a cter) bu t h ist o ne p r o te i n i s not associated with DNA ( prokaryotic character) The nucleus is larger in size and has been named as mesokaryon by Dodge (1966). These types of cells which are intermediate between prokaryotic and eukaryotic are called mesokaryotic cells. In these types of cells, the mitotic spindle is not formed. The cells of certain algae like Gymnodinium and Peridinium are the example of such type.

18. Some cells are even smaller than prokaryotic cell Sma l l e st k no w n cell i s o f Myco p l a s m a g a l l i s e pti c um (P P LO- P l e u ro Pneumonia like organism- a bacterium prokaryote ) Size – 0.1 µm -0.3 to 0.5 µm . The size of this cell may not be more than 1000 to 5000 times that of a hydrogen atom. W. V. Iterson (1969) placed PPLOs with bacteria in the group Mycoplasmata . N o vik o f f an d H o ltzman ( 197 ) h a ve e x c l u d ed t h em f r om b a cter i a and considered them as simplest prokaryotic cells. OTHER CELL TYPES Absence of cell wall and mesosomes Selectively permeable plasma membrane (75A⁰ in thickness ), composed of lipoproteins T he c y to p l a sm h a s ri b os o mes a n d e n z y mes required for protein synthesis and ATP metabolism Nucleus is absent and instead there occurs double stranded DNA molecule of circular or fibrillar type. It does not need a host cell (can live freely)