paper 2 practicals

Question 1

method - reaction time practical

Answer 1

• person 1 sits on a stool with a good upright posture
• person 1 then places the forearm of their dominant arm across the table, with their hand overhanging the edge
• person 2 holds a metre ruler vertically. the 0cm mark should be between person 1’s thumb and first finger
• person 2 then tells person 1 to prepare to catch the ruler
• person 2 drops the ruler at a random time
• 1 had to catch the ruler with their thumb and first finger as quickly as they can when it drops
• 2 then records the measurement on the ruler that is level with the top of person 1s thumb
• repeat test and find mean
• use a conversion table to find reaction time
• switch turns

Question 2

what is the independent variable in the reaction time practical

Answer 2

the person having their reaction time tested

Question 3

what is the depended variable in the reaction time practical

Answer 3

reaction time

Question 4

what are the control variables in the reaction time practicals

Answer 4

• starting distance between the thumb and first finger
• ruler placement
• lighting of room
• level of background noise

Question 5

how can we adjust the reaction practical using different independent variables

Answer 5

• the effect of practise - get one person to catch the ruler a large number of times and see if the reaction time changes depending on the number of tries
• investigate whether the reaction time depends on the hand catching the ruler- get the person to catch the ruler with their dominant then non dominant hand
• whether certain chemicals such as caffeine affect reaction time - test subject drinks a measured amount of cola half an hour before the experiment, compare this reaction time with their normal

Question 6

what is a problem using cola for the reaction time practical

Answer 6

• there could be some other chemical in the cola which is affecting reaction time
• to fix, use a caffeine free cola

Question 7

what else do we need to consider when using drinks in the reaction time practical

Answer 7

• make sure the drink is safe, person doesn’t have any conditions or allergies
• carry out the test in a lab where hazardous chemicals are not normally used

Question 8

how to investigate effects of light intensity on the growth of newly germinated seedlings

Answer 8

1. place cotton wool in three petri dishes and then soak them with equal volumes of water
2. place 10 mustard seeds in each dish
3. leave the seeds in a warm place and allow them to germinate
   
   • water the seeds every day with the same volume of water
4. after the seeds germinate, make sure that the three dishes have g same number of seedlings
5. use a ruler to measure the height of each seedling
6. place the three dishes in different conditions, one in full sunlight, one in partial light, and one in darkness
7. measure the height of each seedling every day for at least 5 consecutive days and record results in a table
8. calculate a mean seedling height for each day
   - draw diagrams

Question 9

independent dependent variables and control of light intensity seedling practical

Answer 9

IV - light intensity
DV - height of seedlings
CV - volume of water added to petri dish, type of seedlings, number of seedlings

Question 10

how do we make the stem straight

Answer 10

by holding it

Question 11

why are the heights of the seedlings left in full light and partial light similar

Answer 11

because chlorophyll is very efficient at absorbing light energy, so plants do not need full sunlight to grow
- they both grow towards the light source due to phototropism

Question 12

why do the seeds left in the darkness grow the fastest

Answer 12

because seeds usually germinate underground and they grow rapidly to reach the light

if we keep seedlings in the dark, they continue to grow rapidly, trying to reach light

Question 13

why did the leaves from the seedlings left in dark turn yellow

Answer 13

because once the seedlings have used all their energy stores, they can’t carry out photosynthesis in the dark

Question 14

how to investigate the effect of gravity on seedlings

Answer 14

• a dish of seedlings is placed on its side in the dark
• shoots grow upwards, against the direction of gravity
• roots grow downward, towards the direction of gravity
• gravity causes auxin to build up on the lower side of the root
• lower side grows more slowly than upper side ,making the root grow in the direction of gravity