Lab 4: Passive Transport & Graphing Data

Transcription

1 CWI Cncepts f Bilgy LAB Manual 42 Lab 4: Passive Transprt & Graphing Data The internal envirnment f all cells is a slutin. A slutin is a mixture f tw r mre substances that are evenly distributed thrughut. Typically, a slutin is frmed by disslving a slid (the slute) in a liquid (the slvent). Fr example, in a sugar slutin, sugar is the slute and water is the slvent. The mvement f water and disslved substances invlves varius physical prcesses. The energy necessary fr this mvement is derived frm mlecular mtin. Mlecular mtin within and between cells can be explained by the laws f physics and chemistry. One f these laws, the law f diffusin, is f particular imprtance t ur understanding f the mvement f mlecules int and ut f cells. Diffusin ccurs withut requiring the expenditure f cellular energy. In a given quantity f matter, the amunt f energy available fr wrk (the mvement f matter) is defined as free energy. The energy available t mve matter is defined as the chemical energy f the matter. Chemical energy is prprtinal t cncentratin--a relatinship that allws us t mre accurately state the law f diffusin. The law f diffusin states that mlecules tend t mve frm areas f higher chemical ptential (and higher cncentratin) t areas f lwer chemical ptential (and lwer cncentratin). Osmsis, a special type f diffusin, is the mvement f WATER mlecules frm areas f higher water ptential (lwer slute cncentratin) t regins f lwer water ptential (higher slute cncentratin) acrss a SELECTIVELY PERMEABLE MEMBRANE. A selectively permeable membrane is a membrane that allws water and small slute mlecules t pass thrugh it (i.e., permeable) but is impermeable t large slute mlecules. In all living cells, the membrane that keeps the utside wrld ut and the inside wrld in is selectively permeable Slvent (water) mving thrugh selectively permeable membrane always mves frm the slutin that cntains a lwer slute cncentratin t the slutin cntaining a higher slute cncentratin. The slutin cntaining the lwer slute cncentratin is said t be hyptnic (hyp = less than) and the slutin with the higher slute cncentratin is hypertnic (hyper = mre than) t the slutin with the lwer slute cncentratin. If the tw slutins acrss a selectively permeable membrane cntain equal slute cncentratins, they are said t be istnic and there will be n net mvement f water acrss the membrane. The difference in cncentratin f like mlecules in tw regins is called a cncentratin gradient. Diffusin and smsis take place DOWN cncentratin gradients. With time, the cncentratin f slvent and slute mlecules becmes equally distributed, the gradient ceases t exist. If the gradient ceases t exist, the system is said t be at equilibrium. Hwever, yu shuld keep in mind, even at equilibrium, mlecules are always in mtin. Thus slvent and slute mlecules cntinue t mve because f randmly clliding mlecules. At equilibrium there is n net change in the cncentratin. Surely yu have smelled fresh bread r garlic and nins wafting frm sme lcal merchant as yu walked dwn the street. This is an example f diffusin at wrk; the mvement f mlecules frm areas f higher chemical ptential (and higher cncentratin) t areas f lwer chemical ptential (and lwer cncentratin). During this prcess, mlecules f ne substance pass thrugh and freely intermingle

2 CWI Cncepts f Bilgy LAB Manual 43 with thse f anther. Remember, diffusin is based upn the fundamental principle that all mlecules- -slids, liquids, and gases--are in cnstant mtin. WEB ACTIVITY! The link belw will take yu t a demnstratin f mlecular mtin; the phenmenn knwn as Brwnian Mvement. Investigatin 1: Diffusin (This Applicatin will be dne as a demnstratin) Intrductin The mvement f water and disslved substances invlves varius physical prcesses. The energy necessary fr this mvement is derived frm mlecular mtin. Mlecular mtin within and between cells can be explained by the laws f physics and chemistry. One f these laws, the law f diffusin, is f particular imprtance t ur understanding f the mvement f mlecules int and ut f cells. Diffusin ccurs withut requiring the expenditure f cellular energy. Als, we see diffusin happening in semi-slids, liquids, and gases making it a near universal phenmenn in nature. Our bjectives in the investigatin are t 1) understand the prcess f diffusin and 2) bserve this example f diffusin; the mvement f tw liquids thrugh a semi-slid substance. Null Hypthesis (i.e., the n difference hypthesis): ptassium ferricyanide and ferrus sulfate will nt diffuse thrugh a semi-slid material (i.e., the chemicals will nt leave the wells that we put them in). Materials and Methds Materials: 1. Petri dishes cntaining 2% agar (5mm deep). 2. Crk brer. 3. Drpper bttle with a dilute aqueus slutin f ptassium ferricyanide. 4. Drpper bttle with a dilute aqueus slutin f ferrus sulfate. 5. Clred pencils Prcedure: Fr this demnstratin, yur instructr will: 1. Cut tw wells in a Petri dish cntaining agar. 2. Fill ne well with a dilute aqueus slutin f ptassium ferricyanide. 3. Fill the ther well with a dilute aqueus slutin f ferrus sulfate.

3 CWI Cncepts f Bilgy LAB Manual When slutins f ptassium ferricyanide and ferrus sulfate meet, an intense blue precipitate (Prussian blue) frms. Observe the plate at 15-minute intervals fr the frmatin f a thin blue line midway between the wells. Prussian blue will frm as the slutins diffuse t meet each ther. Draw yur bservatins. 15 minutes 30 minutes 45 minutes 60 minutes Results and Questins Is this investigatin an example f discvery science r hypthesis-driven science? Was yur null hypthesis supprted by this investigatin? What evidence allws yu t make this cnclusin? What cnclusin can yu make abut the relative rates f diffusin f ptassium ferricyanide and ferrus sulfate? If plates have been left ut frm previus investigatins (i.e., earlier labs), cmpare yur results with theirs. Des the previus wrk supprt r refute yur findings? What des this mean fr the validity f yur hypthesis?

4 CWI Cncepts f Bilgy LAB Manual 45 Investigatin 2: Osmsis in a Nnliving System Intrductin Osmsis is the mvement (diffusin) f water mlecules frm areas f higher water ptential t regins f lwer water ptential acrss a selectively permeable membrane. In this exercise dialysis tubing will serve as the selectively permeable membrane. Like cell membranes, dialysis tubing has pres which select fr mlecular size. Small mlecules such as water can freely pass thrugh the membrane while larger mlecules such as starch are unable t pass thrugh the membrane. In effect, the dialysis tubing will simulate the plasma membrane f a living cell, the cntents represent the cell cntents, and the surrunding slutin represents the envirnment utside the cell. Null Hypthesis (i.e., the n difference hypthesis): The mvement f water acrss a semi-permeable membrane is nt affected by the slute cncentratin f the slutin Objectives: Understand the prcess f smsis and distinguish between smsis and diffusin. Observe the net mvement f water fr the experimental systems in this exercise. Fllw a scientific prtcl precisely, recrd accurate data, wrk tgether as a team. Understand the difference between hypertnic, hyptnic, and istnic slutins (refer t the sectins abve if yu ve frgtten what they mean!). Materials: Materials and Methds 1. Apprximately 30 presaked 15-cm lengths f 44-mm flat diameter dialysis tubing per lab. 2. Dental flss r dialysis tubing clips. 3. Scissrs. 4. Varius cncentratins f sucrse (clred red). 5. Pure water. 6. Pure water (clred red). 7. Pipettes. 8. Tp-lading balances. 9. Wax pencils ml beakers.

5 CWI Cncepts f Bilgy LAB Manual 46 Prcedure: 1. Wrk in grups as assigned by yur instructr. 2. Each grup shuld btain fur 15-cm lengths f wet dialysis tubing. 3. Rll the tubing briskly between yur fingers and thumb t separate the tw layers. Run water thrugh t pen the tube full length. 4. Seal ff ne end f the dialysis tubing by flding it ver itself and tying the tube clsed with dental flss, making a bag with ne pen end. It will be easier t d if ne persn hlds the tube and ne persn ties. 5. Fill the dialysis tubing abut tw-thirds full with the apprpriate experimental slutin. Clse the free end f the tube with dental flss as described abve. Remve as many air bubbles as pssible befre the final tying. 6. Wrk quickly, s that the dialysis tubing des nt dry ut. After the dialysis bag has been prepared, rinse the utside f the bag with distilled water t wash away any spilled slutin. Cut ff excess dental flss and blt dry the bag with a paper twel. 7. Repeat this prcedure until yu have fur dialysis bags that cntain the slutins indicated in Table Weigh each bag by placing a clean, empty weighing bat n the scale and pressing the tare/zer buttn, wait until the scale display reads zer t the nearest tenth f a gram (0.0g). Place yur filled dialysis bag in the weighing bat and recrd the weight in the table prvided. 9. Place each filled dialysis bag in a small empty beaker and pur just enugh f the slutin indicated by the chart int the beaker t cver the bag. Number the beaker and Table 1 (1 thrugh 4) s yu dn t mix them up. 10. After apprximately ne hur, remved the bags frm the beakers and blt them dry. Examine and weigh all bags and recrd the weights in the table. In the last clumn, nte what type f slutin was cntained in the beaker (i.e., hyptnic, istnic, hypertnic). Dispse f the dialysis tubing in the trash bin at the frnt f the rm. Wash all equipment and place n the drying rack lcated next t the sink.

6 CWI Cncepts f Bilgy LAB Manual 47 Results and Questins Table 1. Recrd yur data fr Investigatin 1 here! Number Bag Cntents The Bag's immersed in? Type f Slutin in the Beaker? the start the end Ttal weight change (+/-) 1 Red Water Water 2 10% Sucrse Water 3 25% Sucrse Water 4 Water Sucrse Is this investigatin an example f discvery science r hypthesis-driven science? Which f the bag(s) served as a cntrl in this experiment? (Indicate by the beaker number the bag was in) Which bag(s) gained weight? a. Why? (think in terms f water mvement) b. Which bag(s) lst weight? c. Why? (think in terms f water mvement) Which bag(s) had neither an appreciable weight gain nr lss? d. Why? (think in terms f water mvement) Did yu bserve anything else that either supprted r refuted yur riginal hypthesis?

7 CWI Cncepts f Bilgy LAB Manual 48 Did yur results supprt r reject the null hypthesis? e. Why? Dispse f yur sausage bags and any pieces f flss lying arund in the regular trash bins Use a paper twel and wipe up any spills f water r sucrse slutin frm yur wrk statin and/r the staging areas. Rinse ut yur beakers with tap water and place these, inverted, in the drying racks next t ne f the sinks. Return the scissrs, grease pencils, and ther supplies t where yu fund them. Investivatin 3: Intrductin t Graphing Prcedure: Visit Mastering Bilgy student cmpanin website Click n Student Study Area Click n Chapter 1 Click n chapter guide in the left hand bar Scrll dwn t Sectin 4, Extend Yur Knwledge Click Graph It! Intrductin t Graphing Cnversely, yu may be able t use the link belw and g directly t this activity after signing in