6' Snails and Pondweed

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6. Snails and Pondweed

• Scientific Enquiry Question

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• Read the questions carefully, look at the
  information and the diagrams closely.
• Hydrogen carbonate indicator solution changes
  colour when the amount of carbon dioxide
  dissolved in it changes. The different colours
  are shown in the table.

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• Five test tubes were set up as shown below.
• Normal air was bubbled through hydrogen
  carbonate indicator solution.
• The solution was then poured into each test
  tube.
• The test tubes were left in sunlight for two
  hours.

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• (a). What this experiment trying to find out?
• ______________________________________
• ______________________________________
• (b). For the results of the experiment to be
  valid it should be a fair test.
• (i). What can you see from the diagrams that
  make the experiment a fair test?
• ______________________________________
• ______________________________________
• (ii). What else has been done that might not be
  exactly fair? _________________________
• ______________________________________

The affect of light on carbon dioxide production
Same volume of dye, snail size and number, mass,
healthy organisms, amount of pondweed
Amount of pondweed
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• (c) (i). What colour would the indicator be in
  all of the tubes to start the experiment?
• ______________________________________
• (ii). Use the information in the table to help
  you, predict the indicator colours that would
  likely be seen in tubes A, B, C and D after 2
  hours
• Tube A ___________________________
• Tube B ___________________________
• Tube C ___________________________
• Tube D ___________________________

Reddish orange
yellow
purple
reddish orange
yellow
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• (d). Think about the indicator colours you have
  predicted. Recall the sorts of life processes
  that occur in plants and animals.
• Use your scientific knowledge and understanding
  to explain what caused the indicators to change
  colour. __________________________________________
  _
• ___________________________________________
• ___________________________________________
• (e) Tube E was labeled as the "control"
• (i). What was the purpose of this part of the
  experiment? ________________________________
• __________________________________________
• (ii). The colour of the indicator solution in
  tube C did not change. Explain why.
  ______________________
• __________________________________________

More photosynthesis than respiration then less
carbon dioxide so turns purple. Less
photosynthesis than respiration then more carbon
dioxide so turns yellow.
Makes sure the changes are due to the respiration
or photosynthesis of the pondweed.
The rate of photosynthesis and respiration are
the same.
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• (f). Tube D is wrapped to keep the light out. It
  contains waterweed but no snails.
• After twenty four hours in the dark what would
  be the colour of the indicator solution in tube
  D? Select from Reddish orange, Yellow or Purple.
  Explain giving a reason your choice of colour.
• Colour of Indicator _______________
• This is because _______________
• _______________________________

yellow.
Photosynthesis has stopped but the pondweed is
still respiring.