Testing leaves

Testing leaves

Pencil and paper
Overview
Connecting to the Curriculum
Marking Student Responses
Working with Students
Read the information below about testing a leaf with iodine solution.
 

Put the leaf in boiling water for 30 seconds. Carefully remove the leaf from the water and put it into a boiling tube which contains methylated spirits. Heat the boiling tube in a water bath for 5 minutes. Then wash the leaf and spread it onto a petri dish. Add a few drops of iodine solution.
 
 
a) Draw a line from each step of testing a leaf with iodine solution, to the purpose of that step. One of the purposes is not needed.
 

Step       Purpose
 
i) Leaf in hot water
  •  
  
  •  
 
Remove the methylated spirits
 
ii) Leaf into methylated spirits
  •  
  
  •  
 
Remove any proteins
 
iii) Wash the leaf
  •  
  
  •  
 
Remove the chlorophyll
     
  •  

Break down the cell walls
 
b) 
 
If the iodine solution turned blue-black, what substance is present in the leaf? ____________________
 
 
c)
 
A leaf was removed from a plant and left beside the plant for a week. Explain what would happen if this leaf was now tested with iodine solution.

______________________________________________________________________

 

______________________________________________________________________

 

Level:
5
Curriculum info: 
Science, Knowledge, Living World
Keywords: 
Life processes, leaves, photosynthesis, starch test
Description of task: 
Students are provided with some information about testing leaves for starch. They are required to match the steps in the process with their purpose, and to explain what substance is present that turns iodine blue-black.
Curriculum Links: 
Science capabilities
The capabilities focus is brought about by the conversations you have and the questions you ask.

Capability: Gather and interpret data
This resource provides opportunities to discuss methodology in investigations.
Science capability: Gather and interpret data (TKI)
Science capabilities: 
Gather and interpret data
Answers/responses: 

 

Y10 (11/02)
a)

i)
ii)
iii)

Break down the cell walls.
Remove the chlorophyll.
Remove the methylated spirits.

moderate
difficult
easy
b)   starch moderate
c)   Any 1 of:

  • No starch.
  • No blue-black.
  • It stays brown because no photosynthesis has occurred.
  • Respiration has used the starch.
  • Any other acceptable answer.
 difficult

 

Diagnostic and formative information: 
  Common error
a) i)
    ii) 		 29% of students indicated that the purpose was to 'remove the chlorophyll'.
31% stated that the purpose was to 'break down the cell walls'.