2. CELL WALL
• IN ADDITION TO PLASMA MEMBRANE, HAVE ANOTHER RIGID OUTER COVERING
CALLED CELL WALL.. THE CELL WALL LIES OUTSIDE THE PLASMA MEMBRANE. THE
PLANT CELL WALL IS MAINLY COMPOSED OF CELLULOSE . CELLULOSE IS A COMPLEX
SUBSTANCE AND PROVIDES STRUCTURAL STRENGTH TO PLANTS. CELL WALL
POSSESSES SMALL PORES THROUGH WHICH ADJACENT CELL REMAIN CONNECTED
CALLED PLASMOLYSIS.
• CELL WALL PERMIT THE CELLS OF PLANTS, FUNGI AND BACTERIA TO WHICH STAND
VERY DILUTE (HYPOTONIC) EXTERNAL MEDIA WITHOUT BURSTING . IN SUCH MEDIA
THE CELL SWELLS, BUILDING UP PRESSURE AGAINST THE CELL WALL. BECAUSE OF
THEIR WALLS, SUCH CELLS CAN WITHSTAND MUCH GREATER CHANGES IN THIS
SURROUNDING MEDIUM THAN ANIMAL CELL.
3. WHAT IS THE ROLE OF CELL WALL?
• IT PROVIDES SHAPE TO CELLS.
• IT PROVIDES MECHANICAL STRENGTH TO PLANTS.
• PROTECTS AGAINST MECHANICAL INJURY.
• CELL WALL PREVENTS BURSTING OF CELL ON ENDOSMOSIS.
• ABILITY TO WITHSTAND A LOT OF VARIATION IN NATURE.
4. NUCLEUS
• THE NUCLEUS HAS A DOUBLE LAYERED COVERING CALLED NUCLEAR MEMBRANE
. THE NUCLEAR MEMBRANE HAS PORES WHICH ALLOWED THE TRANSFER OF
MATERIAL FROM INSIDE THE NUCLEUS TO ITS OUTSIDE THAT IS TO THE
CYTOPLASM .
• NUCLEOPLASM-IT IS COLORLESS DENSE SAP FOUND INSIDE NUCLEUS IN WHICH
CHROMATIN A NUCLEOLUS ARE SUSPENDED.
• IN PROKARYOTES NUCLEAR MEMBRANE IS ABSENT.
• IT IS CALLED NUCLEOID
• CELLS LIKE RBC SIEVE ELEMENTS LACK NUCLEUS.
