AS Biology- Core Practicals

Independent veriable: Caffein concentrashon 

Dependant variable: Hear rate of Daphnia 

Other variables:

• Temperature,
• volume of solution,
• stress of Daphnia,
• time of acclimatation 

Equipment:

• Microscope  test tubes
• counter  stop clock
• cavity slide
• dropping pipettes
• stop clock
• distiled water 

Method:

Place 1 Daphnia on cavity slide that contains distild water. leave for 5 minits to acclimatise then abserve and count heart rateunder microscope for 1 minit, calculate beets per mint (bpm). repet 2 more times and take an average.

Repeat agin, but with a small concentrashon of caffeine solution in place of distiled water.

Carrie out for 5 concentrations of caffeine=3 repets for all concentrashons 

Out come: As caffeine concentration increaces, heart rate also increases.

Issues: 

• Ensuring Daphnia were same size, age, sex
• Tempricer increace because of light bulb in microscope=increace heartrate
• To high caffeine concentrashon kills Daphnia
• Counting can be inacurate due to speed of heart

Independent Variable: Fruit Juice 

Dependent Variable: Volume of juice required to decolourise 1cm^3 of DCPIP

Other Variables: 

• Temperature
• Concentration of DCPIP 
• Shake each tube the same number of times
• Same end point colour

Equipment: 

• 1% DCPIP solution       1% vit-C solution 
• Range of fruit juices       Test tubes 
• Pipet accurate to 1cm^3     Burette
• Safety goggles

Method: 

Pipette 1cm^3 DCPIP in to a test tube. Using burette add the 1% vitamin C solution drop by drop. Shake after each drop. Continue till blue colour disappears. Record volume of solution needed to decolourise the DCPIP. Repeat further 2 times and calculate mean result. Repeat for different juices.

Calculation:  1cm^3 of 1% vitamin C solution contains 10mg Vitamin C, therefore mass in 1cm^3=10mg times volume of 1% vitamin C to decolourise 1cm^3 of DCPIP

Mass in sample=mass of vitamin C to decolourise 1cm^3 DCPIP divided by volume of sample required to decolourise 1cm^3 DCPIP.

Independent Variable: Temperature of water

Dependent Variable: % transmission of light through resulting solution 

Other Variables: 

• Volume of distilled water
• Time left in water
• Size of beetroot pice

Equipment:

• Raw beetroot           water baths
• cork borer boiling tubes
• white tile  thermometer
• knife colorimeter & cuvettes
• ruler stop clock
• beaker distilled water
• forceps syringe

Method: Cut pieces of beetroot in to 1cm length cylinders. Put in to distilled water over night to remove resin. Blot dry. Place 8 boiling tubes of distilled water in to 8 water baths of different temperature. Once they have reached temperature, place a pice or beetroot in to each for 30 mins. Remove beetroot and shake tubes to disperse dye. Set colour meter to % absorbance on blue green filter. calibrate using distilled water in a cuvette first then add 2cm^3 of beetroot solution form the first temperature in to a new curvet. Place into colorimeter to read % absobance. Repeat for all other pieces.

calculations: to calculate % transmission= 100% absorbance. As temperature increased, % transmission slightly increased to a point at witch it greatly increased due to membrane molecules gaining more heat energy, to a point were the membrane ruptures and a large amount of colour leeks out. 

Issues: Some beetroot may have skin on affecting surface area, difficulty maintaing temperature, accurate reading of colour meter, accurare size of beetroot, from different parts of root, ensuring same amount of time at the different temperatures. 

Independent Variable: Concentration of enzyme

Dependent Variable: Time taken for enzyme to brake down substrate

Other Variables:

• Temperature
• Volume of enzyme
• Volume of substrate 
• Concentration of substrate 
• PH

Equipment: 

• Protease e.g. 1% trypsin Syringes
• Casein solution Stopclock
• Small beakers Large beaker
• thermometer
• distilled water 

Method: Make up different concentrations of enzyme using distilled water. Use different syringes for each chemical. Set up water baths. Place 1 test tube of 5cm^3 casein solution into water bath alongside 1 test tube of 2cm^3 of 0.2% trypsin. Allow to acclimatise for 3 mins. Add trypsin to casein, time how long it takes to become transparent.

Calculation and out come: As concentrations of enzymes increase, rate of reactions increases, until a plateau point where all enzyme has metabolised all substrate immediately. 

Issues: 

• Maintaining constant temperature
• Accurately making up the different concentrations 
• Identifying end point consistently 
• Difficult to see cross through solution