paper 2 required practicals Flashcards
describe the method for the reaction time RP:
- person 1 is getting their reaction time measured. person 2 is measuring person 1’s reaction time
- person 1 sits on a stool with a good, upright posture. they then place the forearm of their dominant arm across the table, with their hand overhanging the edge
- person 2 holds a ruler vertically, and the 0cm mark should be between person 1’s thumb and first finger
- person 2 drops the ruler at a random time. person 1 has to catch it with their thumb and first finger as quickly as possible when it drops
- person 2 records the measurement on the ruler that is level with the top of person 1’s thumb
- person 1 has a short rest, and the test is repeated multiple times, and a mean is calculated
- person 1 and person 2 then switch places, to see whether the two people have different reaction times
what do the reaction time practical results tell us?
- convert our results to a reaction time
- use a conversion table
what is the independent, dependent, and control variable in the reaction time practical?
independent:
- the person having their reaction time tested (most common)
- the effect of practice - they catch it multiple times, does their reaction time change depending on the number of tries?
- the hand catching the ruler - dominant vs non-dominant hand?
- certain chemicals (e.g. caffeine) affecting reaction time - drink measured amount of cola half an hour before experiment
dependent: reaction time
control: starting distance between thumb and forefinger, measure the ruler at the top of the thumb, keep the room conditions the same (lighting, level of background noise)
what are the problems with testing certain chemicals to see if they affect reaction time?
- could be some other chemical in the cola, which is affecting reaction time
- to check this, carry out the test using a caffeine-free cola
- ## compare this reaction time to their normal reaction time
- must be certain giving our subject something to drink is safe
- check no medical issue that could be affected by caffeine (e.g. allergy, heart condition)
what are the independent, control and dependent variables in the plant responses required practical?
independent: light intensity
dependent: height of the seedlings
control: volume of water, type of seed, number of seedlings
describe the method pt.1 for the plant responses RP:
- place cotton wool in three petri dishes, soak them with equal volumes of water
- place 10 mustard seeds in each dish
- leave the dishes in a warm place, allow the seeds to germinate. water the seeds with the same volume of water every day
- after a few days, the seeds will germinate
- ensure the 3 dishes have the same number of seedlings
- use a ruler to measure the height of each seedling (hold the stem to ensure they’re straight, but ensure you don’t damage the seedlings)
describe the method pt.2 for the plant responses RP:
- place the three dishes in different conditions
- one dish is placed in full sunlight (e.g. on a very bright windowsill)
- one dish is placed in partial light (e.g. back of a lab)
- last dish placed in darkness (e.g. cupboard)
- measure the height of each seedling every day, for at least 5 consecutive days, and record the results
- calculate a mean seedling height
what are the typical results for the plant responses experiment?
- the height of the seedlings is similar for both full sunlight and partial light, as chlorophyll is very efficient at absorbing light energy. plants don’t need full sunlight to grow
- ## seeds have grown towards the light source, due to phototropism (auxins)
- the seedlings in the dark will have grown the longest
- seeds usually germinate underground, and grow rapidly to reach the light
- keeping seedlings in the dark means they continue to grow rapidly, seeking out light
- the leaves are also small and yellow, as once the seedlings have used all of their energy stores, they can’t carry out photosynthesis in the dark
what do auxins inhibit in roots?
GRAVITROPISM
- cell growth
- gravity causes auxins to build up on the lower side of the root, causing it to grow more slowly than the upper side, and therefore in the direction of gravity
describe the method of sampling organisms:
- place 2 tape measures at right angles, around 20m in length
- take two bags, each bag contains the numbers 1-20. student 1 removes a number from the bag. student 2 does the same. place a quadrat on the ground at this coordinate
- record the number of daisies in this quadrat
- repeat this process 9 more times
how do you use the data from the sampling organisms required practical?
total population size = (total area/area sampled) x number of organisms of that species counted in that sample
- this is an estimate, and this may not represent the entire area
- there may be regions with a much higher or lower number of daisies than the average
- to counter this, increase the number of quadrat throws, to increase the area sampled
how do you measure the effect of a factor on the distribution of a species?
- e.g. large field of daisies, containing a tree in the corner. measuring effect of light intensity
- place a tape measure at the tree, extending diagonally out across the field
- use a quadrat to count the number of daisies at the start of the transect
- record the light intensity at this point (e.g. using lightmeter/app)
- move the quadrat 1m down the transect, repeat the measurements
- continue doing this all the way down the transect
- may see greater number of daisies as we move further away from the tree, as under the tree there’ll be a lower light intensity
- plants need light for photosynthesis
- the tree will also absorb a lot of water and minerals from the soil, so light intensity may not be the only abiotic factor that’s affecting the number of daisies
why does milk go sour after a few days at room temperature?
- bacteria in the milk start the decay process
- they use enzymes to produce acidic molecules, and that’s why sour milk tastes acidic
what is the problem with the decay practical?
- decay is a slow process, so hard to observe in a lesson
- model decay by using the enzyme lipase, so what’s actually happening isn’t strictly decay, but should give results that approximate what we would see with decay
describe the method pt.1 for the decay RP:
- label a test tube ‘lipase’
- use a pipette solution to place 5cm^3 of of lipase solution into the test tube
- label another test tube ‘milk’, and add 5 drops of the indicator cresol red. add 5cm^3 of milk and 7cm^3 of sodium carbonate solution to this test tube
- at this point, the solution should be purple, as sodium carbonate is alkaline, and cresol red is purple in alkaline conditions
- place a thermometer into the milk test tube
- place both test tubes into a beaker of water at the first chosen temperature, e.g. room temp. (20 degrees celsius)
describe the method pt.2 for the decay RP:
- wait until the temperatures of the solutions is the same as the water in the beaker
- use a pipette to transfer 1cm^3 of lipase solution to the test tube containing milk, and stir the solution, start a timer
- enzyme lipase will start to break down fat molecules in the milk, releasing fatty acids, causing the milk solution to become acidic
- in acidic conditions, the indicator cresol red will turn yellow, so once the solution turns yellow, we stop timing, and record the results
- repeat the experiment at a range of different temperatures
what are the independent, dependent, and control variables in the decay RP?
independent: temperature
dependent: time taken for the milk solution to turn yellow
control: volumes of the different solutions
name some important points about the decay RP:
- use a clean test tube for the milk solution for each experiment, as any traces of lipase from the previous experiment can trigger the reaction before we’re ready
- as we’re looking for a change of colour, it can be difficult to know the exact point to stop the timer. reduce the effect of this by sharing data with other groups and calculating a mean
what results can you expect from the decay RP?
- at low temperatures, the reaction is slow, as enzymes are working slower
- at a certain temperature, the reaction is taking place at its fastest rate, which is the optimum temperature
- in conditions warmer than the optimum temperature, the reaction slows down and may even stop completely, as the enzymes denature at higher temperatures
