THE UNIVERSITY OF NEW SOUTH WALES SCHOOL OF PHYSICS EXAMINATION NOVEMBER 2007

Transcription

1 THE UNIVERSITY OF NEW SOUTH WALES SCHOOL OF HYSICS EXAMINATION NOVEMBER 7 HYS 4 INTRODUCTORY BIOHYSICS Time Allwed hurs Ttal Number f Questins 8 Answer ANY FIVE questins The questins are f equal alue lease, write answers t questins - 4 and 5-8 in separate bks. This paper may be retained by the andidate Candidates may nt bring their wn alulatrs The fllwing materials will be prided by the Enrlments and Assessment Setin: Calulatrs All answers must be written in ink. Exept where they are expressly required, penils may be used nly fr drawing, skething r graphial wrk.

2 D z y x D t mgh zf V RTln N e N N e N A F 9 g r r 6 F d N 8 a Q A Q r a 4 d A F rdr r 4 dw V V V B U U V V V B rg s h r A E L F T RT j kt j D f T R 4 a i j j! " # $ % & ', µ µ /. /. - / / 3 l l!! " #! "! $ % & ' $ % & ' µ % & ' $, D D tan r d. sin R n n i n n R R n f i f I I Lg SL T m kt kt 3 m 4D x t 4Dt x exp Dt 4 x, t L s rms Cnstants: k.38x -3 J K -, ε 8.85x - F m -, q.6x -9 C R.8343 liter Ma ml - K - g 9.8 m.s - Agadr's number 6.x 3

3 3 Questin a Cnsider three water mleules in lse prximity. What are the imprtant fatrs that will determine their relatie psitins t eah ther? Illustrate yur answer with a sketh f a pssible nfiguratin and releant mleular data. List tw prperties f bulk water, resulting frm these mleular interatins. Hw are these prperties imprtant t life n Earth? b If yu shake a beaker f ery pure water, nt many bubbles will frm. When detergent is added, the liquid will beme frthy n shaking. Explain what is happening in terms f surfae tensin γ. Inlude definitin f surfae tensin and any releant equatins. A beetrt ell expsed t nentrated surse slutin, ttally detahed frm the ell wall and frmed a stable sphere with diameter f 4 µm. Desribe the presses that shrunk the ell away frm the wall int this new equilibrium state. Taking the membrane surfae tensin γ 5 mn.m -, alulate the supprting pressure. Hw is this pressure related t turgr pressure? hint: remember the definitin f turgr

4 4 Questin a The human windpipe is a tube abut 6 mm in diameter and m lng befre the branhing int eah lung. At the time f exhalatin r inhalatin the hange in lume f the hest aity prides the driing pressure differene Δ 34 a. i ii iii Calulate the lume flw Q in and ut f the lungs. What assumptins d yu hae t make? Calulate the aerage elity f air during inhalatin/exhalatin. Cmment n yur result. Calulate the Reynlds number fr the windpipe. Can yu nw explain yur result in part ii? What general nlusin an yu draw abut the air flw thrugh the windpipe? Data fr air: η 8 µa.s, ρ.3 kg.m -3 b Define issity η and explain the differene between newtnian and nn-newtnian fluid. Desribe the behaiur f the issity f the fluid shwn belw and speulate n the fluid nstituents. Shear stress F/A Velity gradient d/dx

5 5 Questin 3 a A 5 µm plant ell with internal nentratin f 6. mm KCl, is in equilibrium with the medium ntaining. mm KCl. The ell membrane is permeable t K, but nt t Cl -. Calulate: i ii The turgr pressure f the ell The eletrial ptential differene arss the membrane Shw all yur reasning and inlude the releant equatins, defining all the ariables. Assume that flws f water and ins are independent. Data: µ medium µ ell temperature 3 K, R.8343 L.Ma.ml -.K - t get pressure in Ma r J.ml -.K -, F 9.65 x 4 C/ml artial mlar lume f water 8 x -6 m 3 b If a slute diffuses thrugh water an aerage distane f - m in 6 hurs, what is its diffusin Ceffiient D?

6 6 Questin 4 a Desribe the physilgy f the inner ear and the transdutin f the mehanial signals at the al windw f the hlea t the pereptin f sund in the brain. What is meant by plae r rate thery f pith? Illustrate yur answer with releant diagrams. b Using the hrmatiity diagram belw, desribe prperties f light as pereied by human eye, suh as hue, saturatin and brightness. What are the mehanisms at the retina that allw us t see this wide range f lurs? Illustrate yur answer with releant diagrams.

7 7 Questin 5 i Researhers hae prdued a bilayer made frm a new type f lipid. The initial sample has an area f 9.3 mm and a thikness f 5.7 nm. a The measured apaitane f the lipid bilayer sample is 53 nf. Calulate the relatie dieletri nstant f the material that frms this lipid bilayer. b Calulate the expeted nentratin f K ins within this bilayer when bathed in a aqueus slutin f 6. mle m -3. Assume that the radius f a K in is.3 nm, the relatie dieletri nstant f water is 78.5 and the temperature is 5 C. Calulate the expeted ndutane f the abe bilayer t K ins. Yu may assume the diffusin nstant fr K ins is.5x -9 m s -. ii Explain why harged mleules r ins find it impssible t trael arss a lipid bilayer. Disuss the arius mehanisms that hae eled in bilgial systems t erme this prblem. Yu shuld inlude equatins where apprpriate. iii Explain what is meant by 'path-lamping' and hw it an nfirm the presene f hannels in bilgial membranes. Cnstants: k.38x -3 J K -, ε 8.85x - F m -, q.6x -9 C, Aagadr's number 6.x 3, temperature 98 K

8 8 Questin 6 i Biphysiists are trying t deide between tw pssible mdels respnsible fr prduing the ltage between the inside and utside f a ell. Mdel A: the ell has internal fixed harges. Mdel B: the ell has a fixed internal nentratin f K ins and is surrunded by a membrane that is permeable nly t K ins. The results f experiments whih measured V m the ltage f the ell interir with respet t the exterir as a funtin f K the external nentratin f K ins are: K mm V m mv a Deide whih Mdel A r B best explains the experimental data. Briefly explain yur reasning. b If yu think Mdel A is apprpriate, alulate the nentratin and sign f the fixed harges. If yu think Mdel B is apprpriate, alulate K i, the internal nentratin f K ins. ii The membrane f a nere ell has ini permeability ratis gien by α Na / K.8 and β Cl / K.. The external slutin ntains mles m -3 NaCl and 5 mles m -3 KCl, whereas the ell interir ntains 5 mles m -3 NaCl, mles m -3 KCl and 5 mles m -3 KA, where A represents the aspartate anin. The aspartate anins are t large t pass thrugh the ell membrane. N ther ins are present. Use the Gldmann-Hdgkin-Katz equatin t alulate the ptential f the interir f this nere ell with respet t the ptential f the external slutin.

9 9 Questin 7 i Desribe, with the aid f equatins and diagrams, the ini presses assiated with the nere impulse. ii Briefly desribe and distinguish between the terms spae-lamping and ltage-lamping. Briefly explain the rle eah played in determining the mehanism f the nere impulse. iii Desribe and explain any adantages affrded by the myelin sheath arund myelinated neres. ride at least ne diagram.

10 Questin 8 i Desribe and explain hw the eletrial signals f an eletrardigram are related t the presses that ur in the human ardia yle. Yur answer shuld inlude apprpriate skethes and perhaps explain hw sme arius abnrmal nditins might be deteted. ii Seeral animals hae deelped the ability t prdue and detet eletri fields. Desribe these abilities and then explain sme situatins in whih these abilities wuld be an adantage.