NCERT XTRACT ON CELL UNIT OF LIFE PART 2
Cell quick revision
Cell unit of life notes part 2 , Ncert xtract, Short notes on cells unit of life part 2 , IMPORTANT point of cell unit of life 2
PART 1 OF SHORT NOTES ON CELL UNIT OF LIFE
37. Ribosomes in Prokaryotes ----> 70s Type
Associated with the plasma membrane
About 15 nm by 20 nm in size
Made of two subunits - 50S and 30S units
Site of protein synthesis.
Cell quick revision
Cell unit of life notes part 2 , Ncert xtract, Short notes on cells unit of life part 2 , IMPORTANT point of cell unit of life 2
Several ribosomes may attach to a single
mRNA ------>
Polyribosomes or polysome.
The ribosomes of a Polysome translate
the mRNA into proteins.
38. Inclusion bodies in Prokaryotic cells ----->
Reserve material in the cytoplasm ; Not bound
by any membrane
Phosphate granules, Cyanophycean granules
and Glycogen granules.
39. Gas vacuoles are found in blue green and
purple and green photosynthetic bacteria.
40. The Eukaryotes includes ----->
All the Protists, Plants, Animals and Fungi (4
Kingdom out of 5 are eukaryotic)
41. Eukaryotic cells characteristics ----->
Extensive compartmentalisation of cytoplasm
(Membrane bound organelles)
An organised nucleus with a nuclear envelope,
Variety of complex locomotory and cytoskeletal
structures.
Their genetic material is organised into
chromosomes.
42. Cell walls, plastids and a large central vacuole
-----> Absent in animal cells.
43. Centrioles ------> Absent in almost all plant cells.
44. Most studies on the cell membrane ----->
Human red blood cells (RBCs)
45. Cell membrane features ------>
Lipid bilayer. (Polar head outer sides &
hydrophobic tails inner part)
The lipid component ----->
Mainly phosphoglycerides.
Also possess protein and carbohydrate.
Membrane of the erythrocyte ------>
52 % protein and 40 % lipids.
Peripheral proteins ----->
On surface of membrane
Integral proteins ------>
partially or totally buried in the membrane.
46. Most accepted model of cell membrane
Proposed by Singer & Nicolson in 1972
(fluid mosaic model)
47. Advantage of quasi-fluid nature of lipid
in membrane:
Enables lateral movement of proteins within
the overall bilayer. This ability to move within
the membrane is measured as its fluidity
The fluid nature of the membrane------>
important for cell growth, formation of
intercellular junctions, secretion, endocytosis,
cell division etc.
48. Most important functions of the plasma
membrane ----->
Transport of the molecules across it.
The membrane is selectively permeable.
49. Transport across Membrane
Without any requirement of energy ----->
PASSIVE TRANSPORT
Neutral solutes -------> Simple diffusion along
the concentration gradient,
Movement of water by diffusion is called
osmosis.
Polar molecules cannot pass through the
nonpolar lipid bilayer so they require a carrier
protein of the membrane to facilitate their
transport across the membrane.
A few ions or molecules are transported
against their concentration gradient & energy
dependent process ------> Active transport,
e.g., Na+/K+ Pump.
50. Cell wall features ------>
Non-living rigid structure ; Outer covering
for the plasma membrane of fungi and
plants. ---------->
Gives shape, protects the cell ,
helps in cell-to-cell interaction and provides
barrier to undesirable macromolecules.
Algae cell wall ---------->
Cellulose, Galactans,
Mannans and Minerals like calcium carbonate,
Other
plants wall --------> cellulose, hemicellulose,
pectins and proteins.
Primary wall is capable of growth
Secondary wall is formed on the inner side
of the cell.
51. The middle lamella is a layer mainly of
calcium pectate which holds or glues the
different neighbouring cells together.
52. Plasmodesmata ------->
Connect the cytoplasm of neighbouring Plant
cells
