Paper 2 Practicals Flashcards
How do you measure a person’s reaction time?
Need 2 people
Person 2 measures reaction time of Person 1
1- Person 1 sits on stool, placing the forearm of their dominant hand across the table, with hand over the edge
2- Person 2 holds ruler vertically, 0cm mark between the thumb and first finger of Person 1’s hand
3- Person 2 tells Person 1 to prepare to catch
4- Person 2 drops ruler at random time, Person 1 has to catch ruler as quickly as possible
5- Person 2 records measurement level with Person 1’s thumb
6- Person 1 has a short rest, then repeat experiment and find mean distance, using a conversion table to convert this to find reaction time
7- Person 1 and 2 switch places, and repeat the experiment to find Person 2’s reaction time (then can compare results)
Reaction time: What is the independent, dependant and control variables for the experiment?
Independent: The person having their reaction time tested
Dependent: The reaction time of the person
Control: starting distance between thumb and first finger, measure ruler at the top of thumb, room conditions (background noise, lighting)
Reaction time: What else can this practical be used to measure?
The effect of practice:
- a person catches the ruler, then keeps trying
- see if there is a change in reaction time depending on the amount of tries (more practice)
The effect of the hand catching the ruler:
- carry out the practical with the dominant hand and the non-dominant hand
- measure the difference in reaction time
The effect of chemicals (caffeine):
-test subject drinks half a can of cola (contains caffeine) before the experiment
- compare the results with caffeine to the ones without
(could be another chemical in the cola, so test a caffeine free cola as well to compare with normal reaction time)
-check subject have no medical issue with cola
How do you investigate the effect of light intensity on the height of seedlings?
1- Place cotton wool in 3 petri dishes, soaking them in water (equal volumes)
2- Place 10 mustard seeds in each dish, leaving the dishes in warm places to allow the seeds to germinate. Water the seeds every day with the same volume of water
3- Once the seeds have germinated after a few days, make sure the 3 dishes have the same number of seedlings (if there’s only 8 seeds in one, the others have to become 8)
4- Use a ruler to measure the height of each seedling, hold the stems to make sure they are straight.
5- Place the 3 dishes in different conditions. 1- Full sunlight (windowsill), 2- Partial sunlight (back of lab), 3- Darkness (cupboard)
6- Measure height of each seedling every day (for at least 5 days), recording results in a table
7- Calculate mean seedling height for each day, draw diagrams to show effect of different light intensities,
Light intensity effect on seedlings: What are the Independent, Dependent and Control variables?
Independent: Light intensity
Dependent: Height of the seedlings
Control: Volume of water, type of seed, number of seedlings
Light intensity: Why are the leaves left in the dark yellow?
Plants in the dark grow rapidly to reach the light source (think they are under the ground), so they grow rapidly in the cupboard. Once they use all their energy stores growing, they cannot carry out photosynthesis due to the lack of light, so the leaves turn yellow.
How can you investigate the effect of gravity on seedlings?
1- Dish of seedlings is placed on its side in the dark
2- shoots grow up, roots grow down (gravitropism)
How do you measure the population size of a common species in a habitat?
1- Place 2 tape measures of 20m length at right angles
2- Use dice or a random number generator to pick random coordinates ie 8, 10 or 12, 7
3- 1 student moves to one number on the tape measure, and another student moves to the other number on the other tape measure, meeting at the coordinate.
4- They then place a quadrat (0.5m by 0.5m) on the coordinate and count the amount of daisies in the quadrat
5- Repeat the process of the random number generator and counting the daisies in the quadrat 10 times
6-
Species in a habitat sampling: What equation do you use to estimate the number of the species in the area?
Total Population Size=
Total area number of
—————- x species counted
Area sampled overall in
sample
Species in a habitat sampling: Why the results of the experiment only an estimate/ How can the results be inaccurate?
- There could be areas with more or less than the average daisies per quadrat
- Areas with higher amounts of the species could have been measured (inaccurate estimation)
- Areas with lower amounts of the species could have been measured (inaccurate estimation)
Species in a habitat sampling: How can we make the results more accurate?
- Take more quadrat readings/throws (covers greater percentage)
Species in a habitat sampling: How do you measure the effect of a factor on a species?
(light intensity on daisies)
From an area shade (tree)
Use a transect line to measure from the tree outwards
1- Place a tape measure at the tree going out, use a quadrat to count the number of daisies at the start of the transect, also recording light intensity (light meter)
2- Move the quadrat 1m along and repeat recording the measurements
3- Continue this all the way down the tape measure
- Possible there will be more daisies further from the tree, as the light intensity under the tree is low (less light for photosynthesis
- Trees provide water and minerals in the soil, can be beneficial. (more beneficial abiotic factors)
How does the effect of temperature affect the rate of decay of fresh milk?
(measure pH)
Problem- Decay is slow, hard to observe
1- Label a test tube ‘lipase’, then use a pipette to add 5cm^3 of lipase solution
2- Label another test tube ‘milk’, then add 5 drops of indicator Cresol Red.
3- Add 5cm^3 of milk and 7cm^3 of Sodium Carbonate to the milk test tube (purple solution- NaCO3= alkaline)
4- Place a themometer in the milk solution, then place both test tubes in a beaker of a chosen temperature (ie 20 degrees C), wait until the solutions become the same temp as the water
5- Use a pipette to add 1cm^3 of the lipase solution to the milk solution and stir, at same time start a timer (lipase breaks down fat in milk, releasing fatty acids, makes solution acidic, turning indicator yellow)
6- Once there is a colour change (to yellow), stop timing and record the results
7- repeat the experiment at a range of different water bath temperatures
Effect of temperature on the decay of milk: What are the Independent, Dependent and Control variables?
Independent: temperature of the milk solution
Dependent: Time taken for milk solution to turn yellow
Control: Volumes of different solutions (lipase, milk etc),
Effect of temperature on the decay of milk: What are Important points about this practical?
- Clean test tube for milk solution for each experiment: lipase will trigger reaction
- Calculate mean, share data with other groups OR repeat experiments
