1 Wht is the difference etween pssive trnsport nd ctive trnsport? Pssive trnsport is the movement of prticles not requiring energy. Movement of prticles in ctive trnsport uses energy. 2 A gs tp in the science lortory is ccidentlly opened. Explin why students closest to the tp re the first to notice the smell. Prticles of gs move from where they re in higher concentrtion, close to the gs tp to where they re in lower concentrtion, in the room. It tkes time to diffuse out so students further wy from the tp will smell the gs fter the students closer to the gs tp. 3 When coloured dye is dded to wter, diffusion cuses the dye to spred throughout the wter until there is n even colour. This is n exmple of liquid diffusing in liquid. Give n everydy exmple of solid diffusing in liquid. Cn you think of ny other everydy exmples of diffusion? Your nswer my vry to this ut some exmples re given here. Adding sugr to cup of te, dding wshing powder to wshing mchine full of wter, dding ground pepper/slt to soup. Mny more exmples cn e given. 4 Wht gses importnt for life diffuse esily through the plsm memrne of cell? Oxygen nd cron dioxide. 5 Explin wht is ment y the concentrtion grdient. If the concentrtion of sustnce in one re is different to its concentrtion in nother re, the difference in concentrtion is referred to s the concentrtion grdient. 6 Fill in the digrms in Figure B.3 to show diffusion of prticles in this closed system. Beginning Midwy End Figure B.3 Diffusion At which time is equilirium reched? Equilirium is reched t the end. c Do prticles cese to move t equilirium? Explin your nswer. Prticles will continue to move t equilirium in rndom fshion. They move t equl rtes in ll directions. Section B: Movement of sustnces 29
1 A sugr solution is mixture of sugr nd wter. c Which one is the solvent nd which is the solute? The solvent is wter nd the solute is sugr. Wht would you dd to this solution to mke it more dilute? You would dd wter to mke the solution more dilute. How would you mke the solution more concentrted? You would dd sugr to mke the solution more concentrted. 2 Osmosis is form of diffusion. In the Venn digrm in Figure B.6, provide detils of specil fetures of osmosis nd common fetures of oth processes. Diffusion Movement of prticles from region of high concentrtion to region of low concentrtion. No input of energy Osmosis Movement of wter through semi-permele memrne Figure B.6 3 Using red dots for solute nd lue dots for wter (solvent), fill in the oxes in Figure B.6 to illustrte the situtions required. cell isotonic solution cell hypertonic solution cell hypotonic solution Figure B.7 4 Cells re plced in three different solutions. After period of time, cells in solution X filled with wter. Cells in solution Y remined the sme s they were to strt with, nd cells in solution Z shrnk nd lost wter. Which solution ws hypertonic compred with the cells? c Z Which cells were isotonic compred with the surroundings? Y Which cells were hypotonic compred with the surroundings? X. Section B: Movement of sustnces 31
1 A red pigment, hemogloin, is found in the cytoplsm of humn red lood cells. Explin why soking lood soiled clothes in cold wter removes the red colour. Due to osmosis, when red lood cells re plced in fresh wter there is net movement of wter into the cells. This cuses them to fill with wter nd urst. When cells urst, the red pigment hemogloin is relesed into the surroundings, hence removing the colour from the clothes 2 Soking grss-stined clothes in cold wter, however, is not enough to remove the green colour. Explin. The sme conditions pply in this sitution. There is net movement of wter into plnt cells due to osmosis. But in this cse, even though the cells will fill with wter they will not urst due to the tough cell wll. Chlorophyll, the green pigment, remins trpped within the plnt cells resulting in the green stin remining. 3 Explin why plnts wilt when they lck wter. When wter loss is greter thn wter gin, plnt cells will lose volume. As the cytoplsm shrinks, the plsm memrne is pulled inwrds wy from the cell wll. This reduces the turgor of the plnts, cusing them to wilt. 4 A ptient in hospitl sometimes needs to hve his/her ody fluids incresed. A sline (slt solution) drip my e set up. The sline concentrtion is similr to the ptient s lood plsm (the liquid prt of the lood). Explin why it is importnt tht the sline is neither more nor less concentrted thn lood plsm. If the sline drip is the sme concentrtion s the norml lood plsm it is likely to e isotonic in reltion to the lood cells. In this cse, there will e no net movement of wter. If the drip ws more concentrted thn lood plsm, wter would leve the cells cusing them to shrink nd if the drip ws more dilute, wter would enter the lood cells cusing them to urst. In either of these cses, the ptient s helth would e compromised. 5 A cell ws plced in three different solutions. Some time lter the following oservtions were mde: Solution A cell shrinks Solution B cell ursts Solution C no chnge to cell. Ws the cell from plnt or niml? Explin your nswer. This ws n niml cell ecuse even though plnt cells will lose wter, the cell wll keeps them much the sme size nd shpe. This cell shrnk in solution A. Plnt cells ecome turgid when filled with wter, wheres niml cells urst (solution B). Section B: Movement of sustnces 33
1 Explin why there is limit to the size cells cn grow. As cells get lrger, their volume increses proportionlly more thn their surfce re. Becuse of this, the mount of diffusion nd hence removl of wstes nd supply of nutrients decreses. When cell gets igger it reches size where the mount of diffusion possile is no longer enough to sustin the cell. 2 A round cell with dimeter of 2 cm hs greter chnce of survivl thn round cell with 5 cm dimeter. Explin why this is so. A 2cm round cell hs greter surfce re to volume rtio compred to 5cm round cell, therefore diffusion through its plsm memrne is more efficient. This gives it greter chnce of survivl, s requirements re otined nd wstes re removed more quickly. How could the 5 cm cell increse its chnces of survivl y chnging its shpe? Explin the significnce of this. By ltering the shpe of the 5cm cell, efficiency of movement of sustnces cross the cell re is gretly incresed llowing for more efficient diffusion. 3 A plnt cell hs roughly cuic shpe. See Figure B.9. Cue size (length) 10 mm 20 mm 30 mm 40 mm Complete the following tle. Surfce re (SA) mm 2 l h no. of fces Figure B.10 Volume (V) mm 3 l w h height ( h) width ( w) length ( l ) Surfce re to Volume rtio (SA : V ) On grph pper, drw grph sed on dt from your tle, showing the reltionship etween the SA : V rtio nd the increse in size of the cues. Put the cue size on the horizontl xis nd the SA : V rtio on the verticl xis. c Wht hppens to the SA : V rtio s the cues get igger? The grph will show tht s the size of the cue increses, the SA:V decreses. 4 How does flttening cell improve the efficiency of moving sustnces cross its surfce? To help nswer this, clculte the SA : V rtio of three shpes of equl volume in Figure B.10. Figure B.11 surfce cn e ltered. For instnce, if cell is long nd thin or hs incresed folding its surfce Cell A h = 4 mm Cell B w = 4 mm w = 4 mm I = 4 mm I = 8 mm I = 16 mm Cell Surfce re Volume SA : V Cell Surfce re Volume SA : V C 2(l w + l h + w h) l w h 600 1000 0.6 : 1 2400 8000 0.3 : 1 5400 27000 0.2 : 1 9600 64000 0.15 : 1 h = 2 mm Cell C h = 1 mm w = 4 mm A l w no. of sides l w h B 2(l w + l h + w h) l w h 4 x 4 x 4 = 96 64 = 2(8 x 4 + 8 x 2 + 4 x 2) = 8 x 4 x 2 = 112 64 = 4 x 4 x 6 = 96mm 2 64mm 3 1.50 : 1 112mm 2 64mm 3 1.75 : 1 2(16 x 4 + 16 x 1 + 4 x 1) = 168mm 2 16 x 4 x 1 = 64mm 3 168 64 = 2.63 : 1 Flttening the cell increses its SA:V Section B: Movement of sustnces 35
1 List the four memrne proteins nd riefly descrie their functions. Memrne protein Trnsport proteins Function Spn the plsm memrne from one side to the other nd thus llow certin sustnces ut not others to pss through Receptor proteins Bind hormones nd other sustnces to the plsm memrne, nd therefore cuse chnges to the cell s ctivities Recognition proteins Attch to crohydrte molecules on the surfce of the plsm memrne nd ct s mrkers, clled ntigens which llow the immune system to distinguish etween the ody s self cells nd non-self cells Adhesion proteins Link cells together in multicellulr orgnisms 2 List exmples of sustnces tht pss through the plsm memrne esily. Wter, oxygen, cron dioxide nd other smll molecules s well s lipid-solule molecules pss through the plsm memrne esily. List exmples of sustnces tht do not pss through the plsm memrne esily. Wter-solule molecules, chrged molecules nd toms nd mny lrge molecules do not pss esily through the plsm memrne. 3 Explin why memrnes re permele to lipid-solule molecules, ut impermele to wtersolule molecules. Lipid-solule molecules pss esily through the plsm memrne ecuse it is composed of phospholipid ilyer. The lipids in the memrne form rrier to wter-solule molecules. Section B: Movement of sustnces 37
1 Compre nd contrst chnnel proteins nd crrier proteins. Both form pssgewys for movement of sustnces cross plsm memrnes. Both types of proteins re selective in the prticles they llow through. Crrier proteins ind to specific molecules or ions on one side of the memrne, chnge shpe nd relese them on the other side wheres chnnel proteins form nrrow pssgewys for smll ions to diffuse rpidly through. Some crrier proteins move prticles ginst concentrtion grdient, chnnel proteins do not. 2 List four fetures of fcilitted diffusion. No energy is required. Prticles move from high concentrtion to low concentrtion. Proteins spnning the plsm memrne re involved. Trnsport is selective. 3 Wht differences re there etween diffusion nd fcilitted diffusion? Prticles move through the phospholipid ilyer y diffusion wheres fcilitted diffusion relies on crrier nd chnnel proteins emedded throughout the memrne. 4 Give two resons why simple diffusion nd osmosis re different from the process of ctive trnsport. No energy is required for simple diffusion nd osmosis nd prticles move from region of high concentrtion to region of lower concentrtion. Active trnsport needs n input of energy nd prticles move from region of low concentrtion to region of higher concentrtion. 5 Show the similrities nd differences etween fcilitted diffusion nd ctive trnsport y completing the Venn digrm in Figure B.16. Fcilitted diffusion Active trnsport no energy required movement from high to low concentrtion trnsport proteins cross memrne energy required movement from low to high concentrtion Figure B.16 Section B: Movement of sustnces 39
1 Nme type of cell where: exocytosis tkes plce Secretory cells such s those lining the stomch, nd nerve cells. phgocytosis tkes plce c White lood cells clled mcrophges. pinocytosis tkes plce. Cells lining the smll intestine. 2 Explin how the plsm memrne is involved in the processes of endocytosis nd exocytosis. In exocytosis, for instnce in cell tht secretes enzymes, memrne-ound vesicles form round the enzymes nd move through the cytoplsm to the plsm memrne, fusing with it nd relesing the enzymes to the exterior of the cell. In endocytosis, the plsm memrne extends round sustnce, engulfing it nd forming n endocytic vesicle. This is then drwn into the cytoplsm. 3 Pinocytosis is sometimes clled cell drinking nd phgocytosis cn e referred to s cell eting. Considering these processes, explin why these re pproprite descriptions. Pinocytosis involves intke of fluid, similr to drinking. When food is eten solids re tken in, just like phgocytosis, which is when cell tkes in solids. 4 Fill in the pproprite links in the concept mp in Figure B.19 illustrting movement of sustnces in nd out of cells. Use the letters from the lels in the following list. Lrge molecules enter the cell Movement of wter molecules cross semi-permele memrne c Net movement of prticles from region of high concentrtion to n re of low concentrtion d Energy required e Trnsport of fluid into the cell f Lrge molecules within the cell re trnsported out g Proteins in cell memrnes help sustnces move through h No energy required i Trnsport of lrge, solid mterils into the cell movement in nd out of cells h d pssive trnsport ctive trnsport c f exocytosis endocytosis diffusion g i phgocytosis e pinocytosis Figure B.19 osmosis fcilitted diffusion Section B: Movement of sustnces 41