1) How would you test an unknown solution for: (a) sugar (b)fat (c) starch (d) p
ID: 6815 • Letter: 1
Question
1) How would you test an unknown solution for: (a) sugar (b)fat (c) starch (d) protein?2) Although pepsin is an enzyme that breaks down protein, a test for peptides is negative. Why?
3)How much larger than normal does an object appear with a low-power objective?
4) A test tube contains albumin and pepsin, a test for peptides is negative. Why?
5) Why is necessary to shake an oil and vinegal salad dressing before adding it to salad?
6) A test tube contains starch, pancreatic amylase, and water. The biuret test is negative. After 30 minutes, the Benedict's test is positive. What substance is present?
7) What purpose is served when a test is done using water instead of a sample substance?
8) Predict the microscopic appearance of cells in the leaf tissue of a wilted plant
9) A test tube contains red blood cells and a salt solution. When the test tube is held up to a page, you can see the print. With reference to a concentration of 0.9% sodium chloride (NaCl), how concentrated is the salt solution?
Explanation / Answer
1). A test for unknown solution done by using:a)sugar - Benedicts test is performed.
b) fat - Brown paper test
c) starch - using iodine and check for colour change
d) protein - biuret test
2) Although pepsin is an enzyme that breaks down protein, a test for peptides is negative -- it depends on the amino acids present in the polypeptide. pepsin is specific for aromatic amino acids. Absence of them may give negative result.
3). How much larger than normal does an object appear with a low-power objective?
--10 times.
4). A test tube contains albumin and pepsin, a test for peptides is negative. Why?
-- The action of these two enzymes depends on the amino acids present in the polypeptide. And albumin binds to fatty acids and cations in the peptide which may mask the cleavage. 5) Why is necessary to shake an oil and vinegal salad dressing before adding it to salad?
--It is due the polar nature of vinegar and non polar nature of vegetable oil which needs them shaking to get mixed up. 6) A test tube contains starch, pancreatic amylase, and water. The biuret test is negative. After 30 minutes, the Benedict's test is positive. What substance is present?
- It is due to the action of amylase on starch which cleaved it into smaller sub units. These units will react with benedict reagent and gave positive result.(reducing sugars). At first biuret is negative as the enzyme binds with starch and its reactive groups are masked, so negative result given. 7) What purpose is served when a test is done using water instead of a sample substance?
-- It acts as control. As water is pure the reaction results will be accurately known and compared. 8) Predict the microscopic appearance of cells in the leaf tissue of a wilted plant ---Cells would be Hypertonic, and they would appear small and shrugged due to a process called crenation. 9) A test tube contains red blood cells and a salt solution. When the test tube is held up to a page, you can see the print. With reference to a concentration of 0.9% sodium chloride (NaCl), how concentrated is the salt solution? --- the solution contains low concentration and this makes it hypotonic. This results in burst of the cells.
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