Form 4 Chapter 3

Paper 1

1.  C 2. C 3. A 4. B 5. B  6. C 7. A 8. C 9. A 10. B

11. D 12. D 13. D 14. C 15. B 16. D 17. D 18. C 19. B 20. B

21. D 22. C 23. D 24. A 25. A

Paper 2

1 (a) (i) Fluid mosaic model

        (ii) Fluid refers to the free movement of proteins and phospholipids within the

              membrane.

             Mosaic refers to the array of different protein embedded in the phospholipid bilayer.

(b) (i) A : Carrier protein     B : Phospholipid    C : Cholesterol   D : Channel protein

 (ii) A à involved in active transport and facilitated diffusion.

      D à allows small uncharged molecules pass through the phospholipid bilayer.

(c) (i) This is because it is composed of two layers of lipids with phosphate heads.

      (ii) – Acts as a barrier between the internal and external environment of the cell.

            – It is selectively permeable and does not allow most molecules to pass through

               freely.

(d) (i) by facilitated diffusion

      (ii) by active transport

      (iii) by simple diffusion

2 (a) – Water enter the cell vacuole when placed in a hypotonic solution (lower solute

            concentration)

        – The vacuole gains water, expands and the protoplast pushes up against the cell wall.

        – Cellulose cell walls become turgid, resist further expansion and prevents it from

           bursting.

    (b) Osmosis

            (ii) Smaller vacuole, shrinks and its size become smaller.

      (d) Solution X : Lower solute concentration

            – hypotonic solution

           Solution Y : Higher solute concentration

            – hypertonic solution

Section B

3 (a) (i) • The process shown is osmosis.

             • The membrane is partially permeable, so there is a movement of water molecules,

                from high water concentration towards   

               the lower water concentration.

            • X contains a less concentrated solution, less solutes.

            • Y contains more concentrated solution, having higher solutes. Thus, water move

              from X to Y.

            • The movement of water molecules down the concentration gradient is continued

               until a dynamic equilibrium is achieved.

(ii)                                                            Passive                                      Active

            Concentration gradient  -     Down concentration gradient        Against concn gradient

      

             Energy                             Does not expend energy                    Need to expend energy

            Transport                            Substances move freely                  Substances move across

                                                     through phospholipid bilayer  with the help of carrier protein                                                                                                                                                                                                                       protein

               Substances                     Oxygen, carbon dioxide, water             Dissolved substances in          

            transported                  molecules, glucose, amino                the form of ions and                                                                                 

                                                  acids                                                    molecules

   

(b) (i) Movement of potassium ions from the villus into the cell membrane:    

          – The movement is through facilitated diffusion. 

          – The K+ ions move down the concentration gradient without expending energy.

          – The K+ ion are transported across the cell membrane by transport protein.

          – The pore in the protein molecules only allow small dissolved particles to pass

             through membrane.

          – Pore proteins have specifi c internal characteristics that only allow specifi c ions such

             as potassium ions to diffuse across the membrane.

(ii) Movement of potassium ions from the cell to the blood.

     – The movement of substances is by active transport.

     – The K+ ions move against the concentration gradient.

     – This transport requires energy, the cell must expend its own energy.

     – The transport is performed by a specifi c protein, which is the carrier protein.

     – The energy required is adenosine triphosphate (ATP). ATP splits into ADP (adenosine

         diphosphate) and P (phosphate).  With the ATP, the shape of carrier protein will change

         to help pumping out potassium ions.