chemical composition of cells

At this point, the tubes all contain unknown solutions and amylase that has reacted for 30 minutes. You added Benedict reagent, and the unknown solutions are still light blue, indicating no simple sugars are present. Which of the following is/are possible reason(s) for a negative result in this case?Select all that apply.

all unknown solutions are water the samples are not heated unknown solutions were mixed incorrectyly

Which reagent is used to detect the presence of protein?

biuret

which solution is the negative control?

distilled water

When Benedict reagent is added to a solution containing simple sugars, the solution turns green, orange, or red. In the absence of simple sugars, the solution is blue. Benedict reagent was added to solutions that may or may not contain simple sugars. The data can be seen in the table below. The contents of the unknown solutions would be considered the

independent variable.

glucose and starch are both carbohydrates. why does glucose produce a negative result when testing using iodine?

iodine only test for polysaccharides, and glucose is a monosaccharide

a substance that causes emulsification that you might encounter in everyday life?

soap

Benedict test

test for the presence of simple sugars such as maltose and glucose. A positive result for the Benedict test occurs anytime the reagent changes from its original blue color. The reaction requires heat to take place.

When biuret reagent is added to a solution containing protein, the solution turns pink or purple. In the absence of protein, the solution is blue. Biuret reagent was added to solutions that may or may not contain protein. The data can be seen in the table below. What is the dependent variable in this experiment?

the color change from blue to purple

Oligosaccharide

A carbohydrate made up of more than two sugar molecules linked together.

Disaccharide

A carbohydrate made up of two sugar molecules linked together.

Maltose

A disaccharide consisting of two glucose molecules bound together.

Biuret reagent

A light blue reagent that tests for protein.

Fatty acids

Long chains of carbon with hydrogen attached, making them nonpolar molecules.

Simple sugar

Monosaccharides and disaccharides.

which solution is the positive control?

starch solution ex.Since iodine tests for the presence of starch, you can verify that a positive result turns purple by using a solution of starch.

which tube do you predict contains emulsifier?

the tube that has bubbles contains an emulsifier, oil and water mixed with bubbles

what is the purpose of testing distilled water in tube 3?

to eliminate the possibility that the water portion if the potato and onion solutions causes a positive result explination. Since iodine tests for the presence of starch, you need to rule out water to test the potato and onion specifically.

How to interpret the paper test:

A positive result for a lipid will result in an evenly distributed oily stain remaining on paper after 15 minutes. Water will completely evaporate, and nonlipid substances mixed with water will leave a circular stain.

Polysaccharide

A carbohydrate made up of hundreds to thousands of sugar molecules linked together.

Phospholipid

A lipid made up of a three-carbon glycerol molecule with a phosphate group and two fatty acids attached.

Glycogen

An animal-based polysaccharide.

Monosaccharide

One individual molecule of sugar; the building blocks of carbohydrates.

Why does the procedure use a graduated cylinder and not simply have you put 2 mL of unknown solution directly into the test tube?

accuracy is important in the labotary. there is not a way to accurately put 2ml into a test tube without first measuring 2ml in the graduated cylinder

When testing for starch within the potato and onion, the test tube containing potato turned purple while the test tube containing onion turned orange. What can you conclude about the amount of starch in these two vegetables?

The potato contained a higher concentration of starch than the onion.

Unsaturated fatty acid

A chain of carbon atoms that contain one (monounsaturated) or more (polyunsaturated) double bonds between carbons with hydrogen atoms attached to the carbon atoms.

Saturated fatty acid

A chain of carbon atoms using only single carbon-to-carbon bonds with hydrogen atoms attached to the carbon atoms.

Benedict reagent

A light blue solution that tests for many types of simple sugars, including maltose and glucose. Benedict reagent goes through a series of color changes to indicate the amount of simple sugars present. Light blue (original color) = no simple sugars. The color then progresses through green, yellow, orange, red, and brown as the amount of simple sugars increases.

Triglyceride

A lipid made up of a three-carbon glycerol molecule with three fatty acid chains attached to it.

- Cholesterol

A lipid with a structure containing over 20 carbon atoms configured into four rings.

Lipid

A macromolecule made up of dozens to hundreds of molecules of mostly carbon and hydrogen.

Starch

A plant-based polysaccharide. Starch is a storage form of carbohydrates in plants. As a food source, starch is vital to survival. Testing for starch content helps you more clearly understand food choices.

How to interpret the tests for emulsifiers:

A positive result for an emulsifier will result in oil and water mixing much better than without an emulsifier.

Benedict test for sugar

A positive result for the Benedict test occurs anytime the reagent changes from its original blue color. Relative concentration of simple sugar can be determined by color. Blue represents the lack of simple sugars. The color then progresses through green, orange, and red as the amount of simple sugars increases.

How to interpret the Benedict test:

A positive result for the Benedict test occurs anytime the reagent changes from its original blue color. The reaction requires heat to take place.

How to interpret the starch test:

A positive test result for starch occurs when iodine turns color. Orange is a small amount of starch, blue indicates a medium amount of starch, and purple indicates a large amount of starch. A negative test result for starch occurs when iodine stays yellow.

Glucose

A small, six-carbon sugar molecule found in starch and glycogen. A common monosaccharide.

Polymer

A substance made up of many units of a common chemical attached to each other.

Emulsifier

A substance that has a polar and nonpolar component that can disperse fat into smaller particles in water or other polar solutions.

Monomer

A substance that is the smallest unit of a category of substances. For example, an amino acid is a monomer of a protein.

Nonpolar

A type of covalent bonding that produces a molecule without any charge. This is common when many of the same or similar atoms are bonded.

Polar

A type of covalent or ionic bond that produces a molecule with electrical charges. This is common when atoms that are very dissimilar are bonded.

Negative control

Any procedure that is known to NOT produce the desired result. A negative test result means what you are looking for is NOT present.

Positive control

Any procedure that is known to produce the desired result. A positive test result means what you are looking for is present.

The unknown solutions contain starch or water.

As a control, each unknown solution could be tested for simple sugars prior to being digested with amylase. Each unknown solution will then be treated with amylase so that any starch that is present will be digested.

A student is testing for the presence of protein, simple sugars, starch, and lipids using the tests summarized in the table below. The student tests an unknown solution using each of the tests and observes that the solution turns blue-black when he tests for protein. Which of the following conclusions can the student make?

No conclusion can be drawn; the student made an error.

Proteins are a very diverse group of molecules with many important functions.

Proteins are the most functionally diverse group of macromolecules in living systems. It is important to be able to test for the presence of proteins in solutions.

While testing an unknown solution a student adds Benedict's reagent and watches as the contents of the test tube turn green. The student then added amylase and heats the test tube. This causes the contents to turn red. Which of the following conclusions could the student make?

The solution has both simple sugars and starch.