Biology Practicals

Mineral Deficiencies

IV= minerals present               DV= characteristics of plant

CV= vol of mineral solution, species of plant, size of container, amount of light

Method:

  • Half fill tube with 'all nutrient'.
  • Cover top of tube with foil and create well in centre and push plant through (until in solution)
  • Repeat with solution lacking a nutrient e.g. nitrates, Mg, K, Ca, P or lacking all
  • Wrap all tubes with foil and place on windowsill in sun
  • Observe regularly

Stunted growth= lack of nitrates, Ca or P

Yellow leaves= lack of Mg or K (also can have brown discolouration)

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Tensile Strength of Plant Fibres

IV= source and type of fibre                DV= mass that can be held

CV= length of fibre, size of each individual mass, same aged fibres

Method:

  • Plant material left to soak for about a week can be extracted (retting)/ celery stalks left in coloured water so fibres can be seen and pulled out
  • Once removed, connect between 2 clamp stands
  • Gradually add mass in middle until fibre breaks
  • Try with individual fibres from different plants and different ways of combining fibres
  • Can also compare stem to individual fibres

More fibres combined the stronger it is

Eval- ensure consistency of twisting or plaiting fibres

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DNA Gel Electrophoresis

Method:

  • Mix DNA with desired restriction enzymes and loading dye.
  • Prepare agar and pour into electrophoresis mould. Once set fill wells with buffer solution
  • Use micropipette to load restriction ladder into first well and the samples with restiction enzymes into other wells
  • Connect to electrical supply and leave until dye has moved to opposite end of gel tank
  • Swithc off and disconnect supply
  • Carefully remove gel from tank and view under UV light

DNA will be seperated out through agar gel. Lightests strands at opposite end and heaviest strands near wells. The DNA resriction laddder can be used as a ruler to measure the different sizes of fragments.

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Ecological Sampling

CV= abiotic factors e.g. light, temp, soil, water, oxygen conc, pH, slope angle, aspect, humidity

Random Sampling or Systematic Sampling

Method:

  • Random= set up a grid using a tape measure, use random no. generator to generate place to quadrat and collect data
  • Systematic= line transect to study zonation, tape measure laid across several zones and quadrat are used to record data at regular interval
  • Measuring abundance= % cover, frequency, use pitfall trap (trap invertebrates) or sweepnet or pooter, tuliguen funnel (collect leaf litter) and baerman funnel (collect organisms from water)

Eval- constant changing abiotic factors hard to control, movement of organisms, can take large amount of time, limitations as only 1 study, ethics for organisms. disruption of habitat

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Natural Antibiotics (Garlic vs Mint)

IV=presence of mint or garlic            DV= zone on inhibition

CV= conc of plant material, lawn of bacteria on petri dish, contamination by other microbes, vol of plant material on each disc

Method:

  • Make plant extract by crushing 3g of plant material with 10cm3 denatured alcohol. Shake occassionally for 10 mins
  • Pipette 0.1cm3 of extract onto sterile paper disc and allow to dry
  • Label petri dish and split into 4 sections (for each type of extract and a control of distilled water)
  • Place a disc on each section of agar plate, close and tape
  • Leave incubated over night and observe any inhibition

Plant extract will create larger zones of inhibition and are more effective at lower conc (garlic better than mint)

Eval- use aseptic techniques, shake enough to ensure active ingredient

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Effect of Temp on Cell Membranes

IV= temp of water           DV=% transmission of light

CV= vol of distilled water, time left in water, size of beetroot piece

Method:

  • Use a cork borer to cut pieces of beetroot into 1cm3 length cylinders
  • Place in distilled water overnight to remove any dye from cutting. Wash and blot dry
  • Place 8 boiling tubes of distilled water into 8 differen temps
  • Add beetroot and leave for 30 mins
  • Remove beetroot and shake to disperse dye
  • Set colourimeter to % absorbed on blue/green filter
  • Calirate using a curvette of distlled water
  • Measure % absorbance at all different temps and record readings

Calculation- % transmitted= 100 - % absorbed

Eval- skin on beetroot affects SA, difficult to maintain temp, accurate of reading on colorimeter, different part of root

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Effect of Enzyme Conc on Rate

IV= conc of enzyme        DV= time for enzyme to breakdown substrate

CV= temp, vol of enzyme, vol of substrate, cocn of substrate, pH

Method:

  • Allow first conc of yeast solution and seperate tube of hydrogen peroxide to acclimatise to desired temp
  • Set up gas syringe and set to 0
  • Quickly add peroxide to yeast and attach gas syringe
  • Read vol of oxygen produced every 10 mins until 3 readings are the same
  • Repeat 3 times for each conc of yeast solution and complete for 5 conc

Calculations- initial rate= grad of steepest point on graph of vol against time for each conc

As conc of enzyme increases, rate of reaction increase until plateau point where all enzymes have metabolised all substrate

Eval- loss of gas when attaching syringe, reaction going too quickly to read

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Effect of Different Antibiotics

IV= antibiotic                DV= diameter of inhibition zone

CV= conc antibiotic, vol antibiotic, disc size, bacterial species, temp, ruler, no contamination, age of bacteria

Method:

  • Prepare agar plate seeded with bacteria and label petri dish with type of bacteria
  • Flame forceps and pick up antibiotic disc and place in centre of agar in petri dish
  • Tape with two pieces to form a cross and keep upsidedown in icubator (30 degrees) for 2 days
  • Measure diameter of inhibition zone
  • Repeat for other antibiotics

All in aspectic conditions- flame forceps,disinfect surfaces, work in undraught

Depend on bacterical species used (gram + or -). Larger the inhibition zone the more effective the antibiotic against that species

Eval- ensure discs evenly placed on petri dish, aseptic techniques to avoid contamination

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Respirometer

CV= no of organisms, temo, time, amount of soda lime

Method:

  • Place 5g maggots into tube and replace bung
  • Add drop of dye into glass tube and open 3 way tap to move drop to convinient place
  • Matk starting position and close connection to syringe and amosphere. Start timing
  • Mark position of fluid every minute for 5 mins
  • Measure distance travelled each min and calculate mean

Calulation- vol of oxygen= Pi x r^2 x distance travelled

Can work out rate using time

Eval- doesnt allow reset, needs control tube alongside. measurement less accurate

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Observing Mitosis

DV= chromosomes stained blue using orcein ethanoic stain

Method:

  • Place test tube of 2cm3 of 1M HCl into 60 degree waterbath
  • Cut off 1-2cm of root tip from garlic root
  • Put in watchglass containing 5cm3 of cold distilled water and leave for 5mins the remove and dry
  • Place tips in heated HCl for 5mins then repeat process
  • Transfer 1 tip to microscope slide and gently break up with mounting needle
  • Add a drop of orcein ethanoic stain and leave for 2 mins
  • Add coverslip and blot with filter paper
  • View under microscope and identify stages of mitosis

Calculations- % cells in each mitosis stage

Mitotic index= no of cells containing visible chromosomes/ total no of cells in field of view

Eval- resolution of microscope, human error with counting

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Identify Vascular Bundle

Method:

  • Place a small piece of rhubarb on a watch glass
  • Use forceps to pick out one or two vascular bundles from this block of tissue and place them on a microscope slide
  • Use mounting needle to tease the vascular bundles apart
  • Cover the tissure with a drop of methlene blue and leave for 5 mins
  • Draw off extra stain with filter paper
  • Place a drop of dilute glycerol on the fibres and mount under a coverslip
  • Examine under low, medium and high magnification
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Measuring Vit C Content in Juice

IV= fruit juice             DV= vol juice to decolourise 1cm3 of DCPIP

CV= temp, conc DCPIP solution (1%), amount of shaking tube, end point colour

Method:

  • Pipette 1cm3 DCPIP into test tube
  • Use burette to add 1% Vit C solution (control) drop by drop and shake gently after each drop
  • Continue until blue colour just disappears
  • Record vol of solution needed to decolourise DCPIP
  • Repeat 2 times and calculate mean
  • Repeat procedure with different fruit juices

Calculations- mass of Vit C= 10mg x vol

Eval- difficulty controlling temp, end point difficult to judge

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Effect of Caffeine on Daphnia HR

IV= caffeine conc                  DV= heart rate

CV= temp, vol of solutions, stress of daphnia, size of daphnia, time of acclimatisation

Method:

  • Remove 1 daphnia and place on cavity slide
  • Remove pondwater and replace with distilled water (control)
  • Leave for 5 mins to acclimatise then observe HR under mircroscope for 30secs
  • Repeat with 2 more daphnia
  • Repeat for 5 conc of caffeine

As caffeine increases HR increases

Calculation- HR= bpm so if timed for 30sec x2

Eval- light from microscope increases temp=increased HR, high conc of caffeine kills daphnia, counting HR can be inaccurate (human error)

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Spirometer

Method:

  • Tank of water with air-filled chamber suspended. Set up so adding air makes chamber rise and removing air makes chamber fall. Movements are recorded
  • Tubes run from chamber to mouthpiece and back again
  • Calibrated so movement corresponds to given vol
  • Soda lime canister between mouthpiece and chamber to absorb CO2
  • Person tested wears noseclip and need time to acclimatise
  • Trace will move move as person breathes

Tidal vol= vol person breathes in and out at rest

Vital capacity= max vol air that can be breathed in and out

BR= no of breaths per min

Minute Ventilation= tidal vol x breathing rate

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Habituation

IV= no of stimuli          DV= retraction time

CV= replication of stimuli, snails approx same size and age, equal handling history, drying out

Method:

  • Place snail on clean and firm surface and allow to acclimatise
  • Dampen cotton bud wiht water and touch snail between eye stalks and start timing
  • Measure length of time between touch and snail beig fully exposed from shell again
  • Repeat procedure for 10 touches

As no of stimuli increases, time taken to re-emerge decreases. With repeated stimuli Ca channels become less responsive so less Ca crosses membrane= less NT released = less likely to result in action potential= less response

Eval- snails handled before may not react same way, hard to determine when fully emerged, lack of moisture encourages snail to stay in shell

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Effect of Temp on Enzyme Reaction

IV= temp                 DV= vol of gas collected

CV= vol hydrogen peroxide, mass of peas, time period, room temp, age of peas, variety of peas

Method:

  • Grind known mass of peas in a known vol of distilled water
  • Measure a known quality of this solution into a boiling tube
  • Add 5cm3 of hydrogen peroxide to solution
  • Reconnect boilign tube to apparatus (ensure gas-tight)
  • Place the syringe over end of delivery tube and measure oxygen produced while timing
  • Measure vol of oxygen produced at regular intervals
  • Repeat at range of temps

Calculation- Q10= rate at temp +10 degrees/. rate at temp

Eval- errors of waterbath temp, change in room temp, time limitations

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Effect of Temp on Hatching (Brine Shrimp)

IV= temp                   DV= no of hatched brine shrimp

CV= light intensity, pH, salt content, presence of Cl from tap water, oxygen conc

Method:

  • Place 2g of seasalt into a 100cm3 beaker of dechlorinated water and stir until all dissolved
  • Label the beaker with seasalt and temp it will be incubated
  • Place a pinch of egg cysts onto a large sheet of white paper and wet graph paper with saltwater to pick approx 40 eggs up with
  • Put the paper in beaker upsidedown and after 5mins remove paper ensuring eggs washed off
  • Incubate at a range of temps from 5 degrees to 35 degrees
  • Next day count the no of hatched larvae using a bright light and catching the shrimps wiht a fine glass pipette

Majority hatch between 25-30 degrees

Eval- ethics of hatching in different conditions, use of animals, not accurate salt or egg measurements, human error, some eggs wont hatch

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Photosynthesis on Isolated Chloroplasts

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