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Biology; Chemistry; Physics: Post your doubts here!

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http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s13_qp_12.pdf
Question 3?
And in question 4 why does the iodine test give black colour when we have BOILED amylase which means that the enzyme got denatured. Thus the enzyme wont act on it and the colour should be yellow.No?
Look at the chloride ion uptake. It is irrespective of the oxygen conc. whatsoever. Thus it is not move by active transport. Nitrate ions do however

4. Bioled amylase will mean no reducing sugars will be present (ie. starch will be there), and thus there is a postive test for starch
 
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Look at the chloride ion uptake. It is irrespective of the oxygen conc. whatsoever. Thus it is not move by active transport. Nitrate ions do however

4. Bioled amylase will mean no reducing sugars will be present (ie. starch will be there), and thus there is a postive test for starch

Oh righttt. You mean that active transport needs oxygen as for active transport to take place, energy is required and which is obtained in the presence of oxygen. (Aerobic respiration) Its needed for active transport.
Right?
 
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Can someone please explain questions 1 and 24?
Rinsing with distilled water removes all impurities making it suitable for re-use so B.
In 24th the test tube initially contains air which has almost 21% oxygen in it. So the oxygen in the air reacts with the steel forming rust. Water level at the beginning of experiment is at D so it will reach C approximately when 21% of the tube contents have reacted.
 
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http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_s13_qp_12.pdf
Question 3?
And in question 4 why does the iodine test give black colour when we have BOILED amylase which means that the enzyme got denatured. Thus the enzyme wont act on it and the colour should be yellow.No?
For chloride ions see the graph is constant. The uptake occurs even when the oxygen from respiration is zero. Though the rate of uptake of nitrate ions increases with oxygen showing that it is an energy dependent process.
 
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