cell: Unit of life (Class 11 CBSE)

Till prokaryotes

Anton Von Leeuwenhoek

first saw and described a live cell.

Robert Brown

Discovered nucleus of a cell.

Matthias Schleiden

Examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant.

Theodore Schwann

studied different types of animal cells and reported that cells had a thin outer layer which is today known as the ‘plasma membrane’.

Cell wall

is a unique character of the plant cells

Schwann

proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells

cell theory

all living organisms are composed of cells and products of cells. all cells arise from pre-existing cells.

Rudolf Virchow

cells divided and new cells are formed from pre-existing cells

nucleus

contains the chromosomes which in turn contain the genetic material, DNA

cytoplasm

semi-fluid matrix that occupies the volume of the cell, main arena of cellular activities

centrosome

animal cell. help in cell division

Mycoplasma

the smallest cell. 0.3 micron in length

human red blood cells

7.0 micron in diameter

All prokaryotes have a cell wall surrounding the cell membrane except

mycoplasma

plasmid

small circular DNA outside the genomic DNA.

plasmid DNA confers certain unique phenotypic characters like

resistance to antibiotics. Monitor bacterial transformation with foreign DNA.

Mesosome

specialised differentiated form of cell membrane. infoldings of cell membrane

cell envelope

glycocalyx followed by the cell wall and then the plasma membrane.

Bacteria can be classified into two groups on the basis of the differences in the cell envelopes and the manner in which they respond to the staining procedure

Gram positive, Gram negative

cell wall

shape of the cell and provides a strong structural support to prevent the bacterium from bursting or collapsing.

membranous structure mesosome

in the form of vesicles, tubules and lamellae. help in cell wall formation, DNA replication and distribution to daughter cells, respiration, secretion processes, to increase the surface area of the plasma membrane and enzymatic content.

motile bacterial cells

filamentous extensions from cell wall, flagella

Bacterial flagellum

filament, hook, basal body

pili

surface structure. elongated tubular structures made of a special protein

fimbriae

bristle like fibres sprouting out of the cell, help attach the bacteria to rocks in streams and also to the host tissues.

polyribosomes or polysome

ribosomes of a polysome translate the mRNA into proteins.

Inclusion bodies

Reserve material in prokaryotic cells stored in the cytoplasm

Inclusion bodies examples

phosphate granules, cyanophycean granules and glycogen granules

Gas vacuoles

found in blue green and purple and green photosynthetic bacteria.