Required practical: effect of light/ gravity on growth

Question 1

Aim of this experiment

Answer 1

Investigate how auxin controls growth of newly germinated seedlings

Question 2

First experiment

Answer 2

How light intensity effects height of seedlings

Question 3

FE independent variable

Answer 3

Light intensity

Question 4

FE dependent variable

Answer 4

Height of seedlings

Question 5

FE control variable

Answer 5

Volume of water on cotton wool
Type of seed
Number of seedlings in each dish

Question 6

FE step 1

Answer 6

Cotton wool in 3 petrol dishes
Soaked with equal volume of water

Question 7

FE step 2

Answer 7

10 mustard seeds in each petri dish with cotton wool

Question 8

FE step 3

Answer 8

Leave seeds to germinate into seedlings by watering them with same volume of water

Question 9

FE step 4

Answer 9

Look at Petri dishes after a few days that have seeds germinated into seedlings
Make sure same number of seeds in each dish if some didn’t germinate

Question 10

FE step 5

Answer 10

Measure height of each seedling with ruler, carefully not to damage but also no damage

Question 11

FE step 6

Answer 11

Place each dish in different light intensity conditions
1 = full sunlight on windowsill
2 = partial light eg back of lab
3 = darkness in cupboard

Question 12

FE step 7

Answer 12

Record length of each seedling every day for at least 5 days

Question 13

FE step 8

Answer 13

Calculate mean seedling length for each condition every day
Plot graph showing this

Question 14

Results of experiment

Answer 14

Full sunlight = green, grown straight up
Partial = green, same height as full sunlight but curves off towards light
Darkness = yellow, grown rapidly higher upwards

Question 15

What do the results tell us in first experiment?

Answer 15

Ones with light grew well because chlorophyll efficient at absorbing light energy (not need full sunlight)
Seedlings grow towards light source
Seedlings germinate underground so with ni light they continue upwards
Yellow = all energy put in growing upwards so none to make chlorophyll

Question 16

Second experiment

Answer 16

Investigating effect of gravity on seedlings

Question 17

SE step 1

Answer 17

Repeat steps to germinate seedlings

Question 18

SE step 2

Answer 18

Place Petri dish on its side in the dark

Question 19

SE results

Answer 19

Shoots grow upwards against gravity and roots go downwards

Question 20

What do Second experiment results tell us?

Answer 20

Auxin builds up on lower side of root to inhibit its growth so grows down as it grows slower
Auxin builds up on lower side of shoot to increase growth