plant responses REQUIRED PRACTICAL

Question 1

what is the independent variable in this investigation:

investigating the effect of light intensity on the height of seedlings

DAIRY MILK ICE CREAM

Answer 1

independent variable- light intensity

Question 2

what is the dependent variable in this investigation:

investigating the effect of light intensity on the height of seedlings

Answer 2

the height of the seedlings

Question 3

method for investigating the effect of light intensity on the height of seedlings

Answer 3

• first place cotton wool in petri dishes
• soak them with equal volumes of water
  (the volume of water is a control variable)
• place 10 mustard seeds in each dish
  ( the type of seed is a control variable)
• leave the petri dishes in a warm place to allow the seeds to germinate
• water the seeds everyday with the same volume of water
• when the seeds have germinated (after a few days) make sure all the dishes have the same number of seedlings (number of seedlings is a control variable)
• remove seedlings so number in each dish is the same
• use a ruler to measure the height of each seedling
• place the 3 petri dishes in different conditions
• 1 petri dish is placed on full sunlight (on a very bright window sill)
• 1 petri dish is placed in partial light (at the back of the laboratory)
• the last petri dish is placed in darkness in a cupboard
• measure the height of each seedling each day for 5 days
• record the results in a table
• calculate a mean seedling height for each day
• draw diagrams to show effects of different light intensities on the seedling

Question 4

can also investigate the effects of gravity on seedlings

Answer 4

• a dish of seedlings is placed on it’s side in the dark
• the shoots will grow upwards against the direction of gravity
• the roots will grow downwards towards the direction of gravity

Question 5

what are the typical results for investigating the effect of light intensity on the height of seedlings

Answer 5

the height of the seedlings grown in full sunlight is very similar to partial light
because, chlorophyll is very efficient at absorbing light energy so plants do not need full sunlight to grow
the seedlings grow towards the light source due to PHOTOTROPISM

the seedlings in the dark have grown the longest due to seeds usually germinate underground so grow rapidly to reach the light. if we keep seedlings in the dark they continue to grow rapidly trying to reach light. the leaves of the seedling are small and yellow as once the seedlings have used all of their energy stores they cannot carry out photosynthesis in the dark