June 2010

How does pH affect cell membrane

The level of pH affects the pigment of the beetroot, the dye in the beetroot (betalain) diffuses out of the cell when the membrane proteins are damaged due to high acidic level of pH.

at extremes of acidity or alkalinity, the structure of the membranes will be destroyed. Membranes are necessary for osmosis, so all functions related to osmosis will be affected. Proteins become denatured (destroyed) at extremes of pH, so their activity will be completely changed and the proteins will become useless for their functions.Factors affecting Enzyme ActivityTemperature Increasing temperatureincreasestheKinetic Energythatmoleculespossess. In afluid, this means that there aremore random collisionsbetween molecules per unit time. Since enzymes catalyse reactions byrandomly collidingwithSubstrate molecules,increasing temperature increases the rate of reaction, forming more product. However,increasing temperaturealsoincreasestheVibrational Energythat molecules have, specifically in this caseenzyme molecules, which putsstrainon thebondsthatholdthem together. As temperature increases,more bonds, especially theweakerHydrogenandIonicbonds, willbreakas a result of this strain. Breaking bonds within theenzymewill cause theActive Sitetochange shape. This change inshapemeans that theActive Siteisless Complementaryto theshapeof theSubstrate, so that it isless likelytocatalysethe reaction. Eventually, the enzyme will becomeDenaturedand willno longer function. Astemperature increases,more enzymes' molecules' Active Sites' shapeswill beless Complementaryto theshapeof theirSubstrate, andmoreenzymes will beDenatured. This willdecreasetherate of reaction. In summary, astemperature increases,initiallytherateof reaction willincrease, because ofincreased Kinetic Energy. However, the effect ofbond breakingwill becomegreater and greater, and therateof reaction will begin todecrease.

The temperature at which themaximum rateof reaction occurs is called the enzyme'sOptimum Temperature. This is different fordifferent enzymes.Most enzymes in the human body have an Optimum Temperature of around 37.0 C.pH - Acidity and Basicity pHmeasures theAcidityandBasicityof a solution. It is a measure of theHydrogen Ion(H+)concentration, and therefore a good indicator of theHydroxide Ion(OH-) concentration. It ranges frompH1topH14.Lower pHvalues meanhigher H+concentrations andlower OH-concentrations. Acidsolutions have pH valuesbelow 7, andBasicsolutions (alkalis are bases) have pH valuesabove 7.Deionised waterispH7, which is termed 'neutral'. H+and OH-Ions arechargedand thereforeinterferewithHydrogenandIonicbonds thathold togetheran enzyme, since they will beattractedorrepelledby thechargescreated by the bonds. This interference causes achangeinshapeof theenzyme, and importantly, itsActive Site. Different enzymeshavedifferent Optimum pH values. This is the pH value at which the bonds within them are influenced by H+and OH-Ions in such a way that theshapeof theirActive Siteis themost Complementaryto theshapeof theirSubstrate. At the Optimum pH, therateof reaction is at an optimum. AnychangeinpHaboveorbelowtheOptimumwillquicklycause adecreasein therateof reaction, sincemoreof the enzyme molecules will haveActive Siteswhoseshapesare not (or at least are less)Complementaryto theshapeof theirSubstrate.

Smallchanges inpHabove or below theOptimumdonotcause apermanent changeto the enzyme, since thebondscan bereformed. However,extreme changesinpHcan cause enzymes toDenatureandpermanentlyloose their function. Enzymes in differentlocationshavedifferent Optimum pHvalues since theirenvironmental conditionsmay be different.For example, the enzyme Pepsin functions best at around pH2 and is found in the stomach, which contains Hydrochloric Acid (pH2).Concentration Changing theEnzymeandSubstrateconcentrationsaffect therateof reaction of an enzyme-catalysed reaction.Controllingthese factors in acellis one way that an organismregulatesitsenzyme activityand so itsMetabolism. Changing theconcentrationof asubstanceonlyaffects the rate of reaction if it is thelimiting factor: that is, it thefactorthat isstoppinga reaction from preceding at ahigher rate. If it isthe limiting factor,increasing concentrationwillincreasetherateof reaction up to apoint, after which anyincreasewillnot affectthe rate of reaction. This is because it willno longerbe thelimiting factorandanother factorwill belimitingthemaximum rateof reaction. As areaction proceeds, therate of reactionwilldecrease, since theSubstratewill getused up. Thehighest rateof reaction, known as theInitial Reaction Rateis themaximum reaction ratefor anenzymein anexperimental situation.Substrate Concentration Increasing Substrate Concentration increasestherateof reaction. This is becausemore substrate moleculeswill becollidingwithenzyme molecules, somore productwill be formed. However, after acertain concentration, anyincreasewill haveno effecton therateof reaction, since Substrate Concentration willno longerbe thelimiting factor. Theenzymeswill effectively becomesaturated, and will be working at theirmaximum possible rate.

Enzyme Concentration Increasing Enzyme Concentrationwillincreasetherateof reaction, asmore enzymeswill becollidingwithsubstratemolecules. However, this too will only have an effect up to acertain concentration, where the Enzyme Concentration isno longerthelimiting factor.

Bile salts

The main function of bile acids is to facilitate the formation ofmicelles, which promotes digestion and absorption of dietary fat, Bile acts to some extent as a detergent, helping to emulsify fats (increasing surface area to help enzyme action), and thus aid in their absorption in the small intestine. Bile salts combine with phospholipids to break down fat globules in the process of emulsification by associating its hydrophobic side with lipids and the hydrophilic side with water. Emulsified droplets then are organized into many micelles which increases absorption.

Detergent affects the phospholipid bilayer. It emulsifies the bilayer causing it to form misclles. As a results the membrane Is disrupted and therefore anything can leak out of cell.

As concentration of bile salts increases the absorbance also increases indicating increase in concentration of the coloured substance. Absorbance is an exponential scale from zero to infinity.

Reduce systematic errors when measuring colour by using a suitable reference solution and calibrate and use a suitable filter.

Practice method to see if it works and obtain measurable results. Check for most suitable conditions. Identify other variables that must be taken into account.

Sowing is planting seeds. A limitation would be that the timing of germination would be erratic. Measuring germination moreover does not correspond to yield of crop. Controlled condition may not represent natural growing conditions.

Remember that you need to clearly show that you have broken the axis between 0 and your next labelled data line if you are just plotting the top of the data range to magnify the differences between the two sets of data

January 2011

Variables to be controlled

. temperature ; 2. time incubated ; 3. concentration of antibiotic used ; 4. concentration / volume of bacteria solution used ; 5. nutrients in the agar / eq ; 6. type of bacteria used / eq ; 7. aerobic or anaerobic conditions / eq ; 8. {size / spacing / eq} of antibiotic discs

possible risk from indigenous animals / unidentified plants / insect bites / falling branches / slips and trips

If using quadrats check for most suitable size for quadrat, select suitable area for sampling and decide on total area on sampling.

Variables affecting growth of plants: gradient of slope, mineral content of grpwth, other surrounding vegetation, trampling, grazing. The variables can be controlled by selecting a proper site where for example there are minimum grazing animals. State number of measurements with reference to suitable statistical test.

Difficulty of sampling is a limitation

If the immune system is weakened doctor should not prescribe bacteriostatic antibiotics as it would stop the growth of bacteria but will not kill it.

It would be helpful if candidates used the same number of decimal points in any one column and limited these to 3 significant figures

Do we plot line of best fits or from point to point draw lines. At each quadrat record the light intensity using a light meter. The probe should be placed in the centre of the quadrat and as close to the ground as possible. The distance of light meter from the ground must be same in all quadrats.

The act of sampling should be done simultaneously such that the time of day does not interfere. The primrose count should be sampled according to light intensity eg: 10%-20%

Grouping results for different light intensities is reliable. A graph can be drawn by then using the midpoint of light intensity ranges and drawing a line graph.

Always use half the range of readings when calculating percentage uncertainties - unless this is smaller than the precision of the instrument.