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Biology Chapter 2 (STPM) Term 1 presentation :)

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#Oxaloacetate Etatecaolaxalo

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  • 1. Chapter 2:STRUCTURE OF CELLS AND ORGANELLES Presentation By: Faridah Hashim Rossharkina Gorisma Wong Hui Jin CELLULAR COMPONENTS OF TYPICAL PLANT AND ANIMAL CELLS

2. CELL MEMBRANE 3. WHAT IS CELL MEMBRANE ??? 4. A cell membrane is a general term that refers to any membrane found within a cell. The cell surface membrane which encloses the contents of the cell. Also called plasma membrane 5. Singer and Nicolsons fluid- mosaic model. 6. Characteristics : ~A thin , flexible layer which forms the outer boundary of a cell. ~Composed mainly of phospholipids and proteins. ~Semi-permeable ~The heads(hydrophilic). The tails(hydrophobic). ~The structure is dynamic where each lipid molecule can move within its own monolayer and so is each protein unit. ~The fluidity of the membrane depends on the length of the fatty acid chains . ~Cholesterol with its hydrophilic head and hydrophobic tail fits neatly within the phospholipid layer. ~The proteins are embedded in the phospholipid layer like mosaic,either in only one monolayer or span the bilayer. 7. WHAT THE FUNCTIONS OF CELL MEMBRANE ??? 8. Functions : ^_^ * Separates the contents of a cell from its external environment. *Regulates the movement of substance entering and leaving the cell. *Allows the exchange of nutrients respiratory gases and waste product between the cell and its environment. *Acts as receptor sites in recognising external stimuli such as hormone and antigen molecules. *Membranes allow compartmentalisation and division of labour especially within membrane-bound organelles. 9. CELL WALL *_* 10. CHARACTERISTICS ->The cell wall is carbohydrate layer of cellulose found outside the plasma membrane of plants cells. ->2 type of cell wall primary & secondary cell wall. 11. CELL WALL ^_^ 12. Primary Cell Wall =found in young cells and cells that not highly differentiated. =e.g:meristem,parenchyme & collenchyme. # thin layer found just outside the plasma membrane of most plant cells.Also found on the outer layer of cells with 2nd cell wall. #it consists randomly arranged microfibrils of cellulose in an amorphous matrix. #Each microfibril consists about 100 chains of cellulose molecule of 5-20 m and diameter of 1-2 m. #the matrix is made up of complex polysaccharides (pectins and hemicellulose with long and branched molecules) #a middle lamella layer consists of magnesium and calcium pectates for cementing adjacent cells. 13. #primary cell wall is porous. -enables water to be transported apoplastically along it. #Elastic and strong. -enables parenchyma cells to become turgid and support the whole plants especially in herbaceous plants. #the wall is usually perforated with plasmodesmata for the transport of substances between cells. 14. Secondary Cell Wall ->is a harder and usually thicker layer cell wall,formed between the plasma membrane and primary cell wall. 1.The wall is made up of regularly arranged microfibrils or bigger macrofibrils.The fibrils are arranged in layers parallel rows,which are perpendicular to those of upper lower layers. 2.The matrix in the 2nd wall is impregnated with lignin,forming a hard and impervious layer. 3.The deposition of lignin in xylem vessels is not uniform but in patterns like rings,helices or networks. 15. Fibrils arranged in layers of parallel rows. 16. Functions #Maintains the shape of plant cells. #Provide mechanical strength and support to plant cells. #Protects plants cells from bursting due to the movement of excess water into the cells. #cell wall of the xylem vessels forms empty tubes for water transport from the roots to the leaves. #provides food storage in the from hemicellulose in some seeds. #provides large surface area to volume ratio in root hair cells where absorption can take place. FUNCTIONS *_* 17. Any Question ?