core practicals

microscopy practical aim

investigate biological specimens using microscopes

microscopy practical safety points

safety goggles when handling iodine

broken glass risk

microscopy practical method

1. peel off an onion layer (forceps)

2. place onto slide with a drop of water (pipette)

3. two drops of iodine solution

4. place cover slip

5. remove excess stain (paper towel)

6. place the slide on the stage

7. microscope focus: start low, focus, then move up

8. make a labelled drawing

enzyme and pH practical aim

calculate the rate of enzyme activity at different pH values

enzyme and pH practical safety points

avoid contact with iodine → irritant

be careful with hot water

enzyme and pH practical controlled variables

temp

volume and concentration of starch or amylase solutions

time interval between testing

enzymes and pH practical method

1. on a tile, label each tile with time

2. add one drop of iodine each

3. starch, amylase, buffer solutions in water bath at 25 degrees for a few minutes

4. add 2cm³ of buffer solution (and mark pH) and amylase and starch to the test tube

5. start timing

6. put a drop of the mixture onto each well every thirty seconds until iodine remains brown (instead of turning black)

7. repeat steps 1 - 6 and take a mean time

8. calculate rate of enzyme reaction → 1/time taken

9. repeat steps 1 - 8 with buffer solutions of different pHs

10. plot a graph for the rate of reaction against pH

test for starch method

1. some food sample into test tube

2. add a few drops of iodine

iodine test for starch positive result

brown → blue-black

benedict’s test aim

test for reducing sugars

benedict’s test method

1. add an equal volume of benedict’s solution to the food sample

2. place in a hot water bath

benedict’s test positive result

red (present) → blue (no sugar present)

test for protein method

1. add a few drops of Biuret’s reagent to the food sample

2. shake

test for protein positive result

blue → purple

test for lipids method

1. a few cm³ of ethanol to the food sample

2. add equal volumes of distilled water

test for lipids positive result

a white emulsion forms on the surface

emulsion test aim

test for lipids

food tests safety precautions

tie hair back

wear safety goggles

biuret solution may be corrosive

ethanol is flammable

osmosis practical aim

immerse plant tissue in a range of concentrations to investigate osmosis

osmosis method

1. cut potato cylinders (cork borer)

2. trim them to 3 cm

3. measure and record the mass

4. 10cm³ of 1.0 sugar solution into a boiling tube and label

5. repeat step 4 for the other concentrations

6. add one potato cylinder to each boiling tube

7. leave for 15 minutes

8. remove and blot dry

9. measure the change in mass

10. calculate percentage change

11. plot change in mass against conc (x-intercept is the concentration of sugar that is isotonic to the potato)

osmosis controlled variables

• temperature

• type of potato

• age of potato

osmosis source of error

different parts of the potato may have different water potentials

osmosis risk

cork borer and sharp knife

microbiology practical aim

investigate the effect of different antiseptics or antibiotics on bacterial growth

microbiology method

1. disinfect

2. mark the agar plate with 3 segments with dots in the middle, initials and date

3. wash your hands

4. add the bacteria with a sterilised inoculation loop

5. place the different antiseptics onto different filter paper discs

6. place each filter paper onto the dots and note the antiseptic

7. tape the lid loosely

8. incubate at 25 degrees for 48 hours

9. measure the diameter of the clear zones (do twice and take a mean)

10. calculate zone of inhibition → (pi)r²

microbiology controlled variables

species of bacteria

area of filter paper disk

microbiology source of error

contamination

area of the clear zone may be irregular

microbiology safety precautions

wash hands/sterilise

wear safety goggles with disinfectant

photosynthesis aim

investigate the effect of light intensity on the rate of photosynthesis

photosynthesis method

1. place 20 algal balls and same amount of indicator solution and replace screw top with correct distance

2. check the colour of the indicator against the colour chart to measure start pH

3. leave for hour

4. record final pH and distance

5. repeat for more distances

photosynthesis method results

light intensity decreases → rate of photosynthesis decreases → rate of change in pH decreases

photosynthesis controlled variables

• temperature

• amount of carbon dioxide

• volume of indicator solution

photosynthesis hazards

boiling water

respiration practical aim

investigate the rate of respiration in living organisms using a simple respirometer

respiration practical setup

respiration method

1. set up as in the diagram

2. weight the organisms and place in boiling tube

3. open the connection between the syringe and the respirometer

4. draw the fluid to the end of the scale

5. leave in a water bath for 5 minutes

6. mark the start point of the fluid

7. close the tap to make it airtight and start the timer

8. record the position of the fluid at one minute intervals for at leave five mins

9. calculate distance travelled by the fluid per minute

respiration practical controlled variables

mass of soda lime

temperature

time allowed for measuring

respiration practical sources of error

animals may be affected by stress

quadrats aim

estimate the population size of a plant species

transects aim

investigate the effect of variation in a factor on the distribution of plant species

quadrats type of sampling

random sampling

transects type of sampling

continuous sampling

method for quadrats

1. set up two tape measures on the perimeter of the area

2. use a random number generator to get two coordinates

3. place the quadrat at the coordinates

4. count the number of required plant species

5. repeat 9 times

6. population size = total area / area of quadrat x mean number of individuals in a quadrat

method of transects

1. write down a hypothesis of the effect of a change in an abiotic factor on the distribution of plant species

2. lay down a tape measure from the base of a tree to an open area

3. place the quadrat on the 0 end of the tape measure and count the plants

4. repeat at 5 meter intervals

5. plot number of plants against the ecological gradient that is observed on the transect line

field investigations controlled variables

size of quadrats

number of repetitions

coordinate system at each site

field investigations sources of error

certain species may be too small to see