Paper 2 practical's Flashcards
(10 cards)
Reaction time
First, person one sits upright on a stool with good upright posture.
Person one then places the forearm of their dominant arm across the table, with their hand overhanging the edge.
Now person two holds a ruler vertically.
The 0 cm mark should be between person one’s thumb and first finger.
Person two then tells person one to prepare to catch the ruler.
Person two now drops the ruler at a random time.
Person one has to catch the ruler with their thumb and first finger as quickly as possible when it drops.
Person two records the measurement on the ruler that is level with the top of person one’s thumb.
At this point, person one has a short rest.
The test is repeated several times and the mean distance is calculated.
From these experiments, we can convert our results into a reaction time using a conversion table (many can be found online).
At the end, the two people switch places, with person one testing the reaction time of person two.
This allows us to see if the two people have different reaction times.
Variables in Reaction time + extra notes
Independent variable:
The person having their reaction time tested.
Dependent variable:
The reaction time (measured by how far the ruler falls before being caught).
Control variables:
The starting distance between the first finger and thumb should be kept constant.
Always measure the ruler at the top of the thumb.
Keep conditions in the room the same (e.g. lighting, noise, temperature).
+
Using a reaction time conversion chart, we can turn the distance the ruler falls into an approximate reaction time in seconds.
This practical helps show how quickly the nervous system responds to a stimulus.
This method avoids using stopwatches, which can introduce human error due to delay in starting/stopping the timer.
Testing for other Variables of the reaction time test
Same idea but testing for
- Does practice improve reaction time
- Does the dominant hand have a faster reaction time then the non-dominant hand
- Do certain chemicals effect reaction time e.g cafine (drink a fixed volume of cola) issue other chemicals + use caffeine free cola + check if they have medical issues. Carry out in lab where non hazardous chemicals are used
Plant response
- First we place cotton wool in three petri dishes then soak them with equal volumes of water (the volume of water is a control variable)
- We then place ten mustard seeds in each dish (Type of mustard seed is a control variable)
- Next we leave the dishes in a warm place and allow the seeds to germinate
- We need to water the seed every day with the same volume of water
- After a few days the seeds will germinate
- At this point, we need to make sure the three dishes have the same number of seedlings (Number of seedlings control variable)
- Imagine only 8 seeds germinate in one of the dishes, but ten seeds germinate in both of the other dishes.
- In this case we would need to remove seedlings from two of the dishes – so that all three of the dishes contain 8 seedlings
- Next we use a ruler to measure the height of each seedling
- We need to hold the stems to make sure they are straight
- However, we need to be careful not to damage the seedlings
- Now we place the three dishes in different conditions
- One dish is placed in full sunlight, for example on a very bright windowsill.
- One dish is placed in partial light, for example at the back of a lab.
- And finally the last dish is placed in darkness, for example in a cupboard.
- We then measure the height of each seedling every day for eight consecutive days
- Record results in a table
- When the experiment is finished we calculate a mean seedling height for each day
- We should also draw diagrams to show the effects of different light intensities on the seedlings
- Height of seedlings should be similar for complete sunlight and partial sunlight since chlorophyl is very efficient in absorbing light, so plants do not need full sunlight to grow
- However seedlings have grown towards the light source because of phototropism
- Auxin concentrates on side of seedling furthers away from side of the seedling causing it to grow faster
- Seedlings in the dark have grown the longest, (because seeds germinate from the underground and grow rapidly to reach the light) so when grow them in dark they grow rapidly trying to reach light
- Leaves are small and yellow, since once seeds have used all their energy stores, they cannot carry out photo synthesis in the dark
Gravity
Gravity
Sampling Organisms
- To estimate the population of daises in a field we need to use random sampling
- We use a quadrat of 0.5m to 0.5m
- First we place two tape measures at right angles
- These tape measures should be 20m in length
- Then we need two bags with each bag containing numbers 1 to 20
- In this practical students work in groups of three
- The first student removes a number from the bag
- Imagine this number is eight, this student now moves to the eight meter point on one of the tape measures
- The second student now selects a number from their bag, and moves to that point of the other tape measure
- Imagine they have the number 12, they go to the twelfth meter on the other tape measure
- Now the third student places the quadrat on the 8 meter 12 meter point
- Now the students record the number of daisies in the first quadrat
- The students now return the numbers back to the bags and repeat this process nine more times for a total of 10 samples
- Now imagine the students counted three hundred daises across the ten quadrats
- We now need to estimate the total population of daisies in the whole field
- To do that we use equation Total population size = Total area/ area sampled x number of organisms of that species counted in the sample
- This is a estimate, it means that our ten quadrates do not represent the whole area
- Could be regions in the area with a much higher or lower number of daises than average
- If you think that is the case you should increase the number of quadrat throws to cover a greater percentage of the area
Effect of a factor on a distribution of a species
- There is a tree on the quadrat
- We need to use a transect line to see how number of daisies changes from the tree outwards
- To do this we place a tape measure at the tree
- We then use a quadrat to count the number of daisies at the start of the transect
- We also need to measure the light intensity at this point, we can use a light meter
- Then move quadrat 1 meter down the tape measure and repeat the measurements
- Continue doing this all the way down the tape measure
- Likely to see a greater number of daisies as we move further away from the tree
- This is because under the tree lower light intensity, and tree absorbs water and minerals from the soil
- So light intensity may not be the only factor that is effecting the number of daisies
Decay
- Start by labeling tube “lipase”
- We then use a pipette to place 5cm^3 of lipase solution into the test tube
- We now label another test tube “milk”
- Add five drops of the indicator Cresol red
- We now add 5 cm^3 of milk and 7cm^3 of sodium carbonate solution to the milk test tube
- At this point the solution should be purple
- This is because sodium carbonate is alkaline, and cresol red is purple in alkaline conditions
- At this point we place a thermometer into the test tube containing milk
- Now we place both of the test tubes into a beaker of water at our first chosen temperature
- We will start with 20 degrees Celsius (about room temp)
- At this point we need to wait until the temperature of our solutions is the same as the water in the beaker
- Now we use the beaker containing lipase solution to the test tube containing milk and stir the solution
- At the same time we start a timer
- At this point lipase will start to break down fat molecules in the milk
- This realses fatty acids and this causes the milk solution to go acidic
- In acidic contions the indicator cresol red goes changes to yellow
- So once the solution turns yellow we stop recording the results we stop recording the time and record the results
- We need to repeate the experiment with a range of differet temps
- The indepedet variable is the temperature of the experiment
- Dependant variable is the time taken for the milk to go yellow
- Control variables is the volumes of the different solutions (make sure they are the same)
- At end of experiment plot graph for results
Key points for Decay
- It is very important to clean the test tube for the milk solution for each experiment, because any traces of lipease from the previous experiment would trigger a reaction before we were ready
- Because we are looking for a change in colour it can be difficult to determine a specific point to look for to stop the timer
- We can reduce the effect of this by sharing data with other groups and calculating a mean
Graph of decay
- At low temperatures the reaction is slow, this is because enzymes work slowly at lower temp
- At certain temperature the reaction takes time in its fastest rate (optimum temp)
- In conditions warmer then the optimum temperatures slow the reaction down or even stop it. Because denature
