Required practicals

Question 1

What are the general tips that need to be considered for every method question?

Answer 1

Always state equipment used
Safety
State how to reduce errors/uncertainties
Carry out repeats and calculate a mean

Question 2

What are valid results?

Answer 2

Results that are repeatable and reproducible

Question 3

How can you see if your results are valid?

Answer 3

Repeat experiment with same method and see if you get very similar results] Repeatable
Repeat experiment with new equipment and or new method and see if you get very similar results] Reproducible

Question 4

What is precision?

Answer 4

How large the spread of data/results are

Question 5

What is accuracy?

Answer 5

How close the recorded value is to the actual value

Question 6

What are some examples of safety considerations?

Answer 6

Goggles when working with springs/acids
Stand up when working with hot water/acids
Avoid touching hot surfaces

Question 7

Microscopy practical.

Answer 7

Peel a one-cell layer of skin from an onion using a scalpel and tweezers
Place this on a microscope slide, and add a drop of iodine to stain the cells
Place a cover slip on top, and make sure there aren’t any air bubbles
Place slide onto stage and place clips on top to hold it in place
Turn on the light
Use lowest magnification on objective lens
Use the coarse and fine focus knobs to focus
Increase magnification and refocus if needed
Use the graticule on the slide to measure length of cell

Question 8

Osmosis practical.

Answer 8

Cut equal size cylinders from potato and remove any skin because it is non permeable
Remove excess water from surface by drying it and measure mass using top pan mass balance
Place each cylinder in a test tube with different concentrations of sugar/salt solution and leave for 24 hours
Water will move in/out of cells via osmosis
Remove cylinders and dab off excess water
Re-measure and calculate % change in mass using equation: …..
Plot this against concentration (x)
Where the LOBF cuts x-axis is the concentration in potato where there would be no net water movement, which is also the sugar/salt concentration of the cells

Question 9

Enzyme practical.

Answer 9

Independent variable: Temperature/pH
Dependent variable: Time for substrate to be broken down
Measure out enzyme and substrate (e.g. starch and amylase)
Place separately in a water bath
Add buffer solution to change pH if needed
Prepare a spotting tile with indicator (e.g. Benedicts/iodine) drops
Mix reactants together and start a timer
Every 10 seconds, use a pipette to remove a drop of the mixture and put in a dimple
If +VE result is achieved (e.g. iodine goes black), substrate has been broken down
Repeat for different temperatures or pH
Plot times (y) against temperature/pH (x) and draw a line of best fit
The optimum condition lies between the two lowest points

Question 10

Reaction time experiment.

Answer 10

Hold a ruler between a person’s thumb and index finger, lined up with 0 mark
Drop without warning, and record distance dropped before caught
Calculate reaction time using conversion graph or t = sqrt 2s/a where a is gravity and s is distance
Carry out repeats and calculate mean, bet the person will likely improve over time
Add a variable such as with/without distraction or stimulant like sugary drimk

Question 11

Food tests.

Answer 11

Make a solution of the food by grinding food in a mortar and pestle and mix with distilled water
Starch turns iodine solution from orange to blue/black
Sugars turn Benedicts solution from blue to green, yellow, orange, brick red when heated to 75 degrees C in water bath
Protein turns biuret solution from blue to purple
When lipids are added to cold ethanol, then mixed and shaken with water, the solution will turn cloudy
(Alternatively, add to Sudan III solution, if lipids present, solution will form 2 layers, and the top will be brick red in colour).

Question 12

Photosynthesis practical

Answer 12

Independent variable: Distance between plant and light source
Dependent variable: Rate of photosynthesis
Put pond weed in a test tube and add sodium hydrogen carbonate in water to promote oxygen release
Place test tube upside down in a beaker with water and sodium hydrogen carbonate
Carry out investigation in dark room
Position light source at a distance measured by a ruler
Wait one minute for the plant to acclimatise to the light intensity
Start the stopwatch and count how many bubbles are produced or the volume of oxygen produced in one minute
Change distance and repeat

Question 13

Germination practical.

Question 13

Microbiology practicals.

Answer 13

Sterilise equipment every time they are used to avoid contamination
Open petri dish towards flame to move airborne microbes away from dish
Add drops of different bacteria cultures onto agar or spread culture across whole plate if comparing antibiotics
(Add drops or paper discs of antibiotic onto the ‘lawn’ of bacteria)
Label dish with date and type of bacteria/antibiotics
Seal dish with tape but make sure to leave gaps for oxygen
Turn upside down
Leave for a few days
Measure diameter of bacterial colony or area of inhibition

Question 13

Quadrat practical.

Answer 13

Place 1 m^2 quadrat in random grid positions in an area using random number generator and count organisms
Take at least 10 readings of organism count around area
Calculate mean number of organisms per m^2
Multiple by total area in m^2 to estimate the total population

Question 14

Germination practical (phototropism)

Answer 14

Take three identical shoe boxes
In one make a hole on the top
In another make a hole on the left side
In the other make a hole on the right side
In each box place a petri dish with wet cotton wool and 8 mustard seeds
Put the lids of the boxes on and leave them in similar conditions for 2-3 days
In 2-3 days, the seeds in the first box will have grown upwards toward the light and the others will have grown toward their light source too

Question 15

Germination practical (geotropism)

Answer 15

Take 4 broad bean seeds and place them on moist cotton wool so that the four seeds are lying in four different positions
Leave them all in a warm room
Observe them over a few days and keep the wool moist
When the shoots and roots appear, the shoots will grow upwards and the roots will grow downwards
Turn them all 180 degrees
Leave for a few days and observe
The shoots will bend around so that they are growing upwards, and vice versa for the roots

Question 16

Decay practical.

Answer 16

Independent variable: Temperature
Dependent variable: Time to decay/time for certain pH to be reached
Measure volume of whole milk or milk using measuring cylinder
Put in a test tube and add sodium carbonate
Add test tube to water bath and add thermometer
Wait until desired temperature is reached
Add phenolphthalein indicator which turns pink for a pH over 8.3
Add lipase and start stopwatch
Record the time taken for the indicator to turn white
Repeat for different temperatures
An increase in temperature will increase the rate of decay up to the point at which the enzyme denatures
Plot graph
Optimum temperature is between two lowest times