Principles of Biology Lab Homework Questions 3

Biuret reagent contains ________ ions which react with peptide bonds under the alkaline conditions of the reagent and produce the color change associated with the presence of protein.

Copper

An unknown liquid sample is tested for chemical composition. You receive the following results: iodine test = yellow; biuret test = purple; Benedict's test = red; and paper lipid test = clear. Which of the following are present in this sample? (Select all that apply)

Protein, sugar

Which molecule is hydrolyzed (digested) by amylase?

Starch

The positive control for the Iodine test was the

Starch solution

An unknown liquid sample is tested for chemical composition. You receive the following results: iodine test = purple/black; biuret test = purple; Benedict's test = blue; and paper lipid test = clear. Which of the following are present in this sample? (Select all that apply)

Starch, protein

Polysaccharides are polymers composed of

Sugars

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.

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.

Select from the tubes numbered above those that show positive for starch.

Tube 2, 3, 5

Carbohydrates like glycogen and cellulose are polymers. What is a polymer?

a chain of similar building blocks called subunits, or monomers

What are the building blocks of proteins?

amino acids

Which of the following are functions of proteins? (Select all that apply)

catalytic (enzymatic) activity, transport of molecules/ions through blood and across plasma membranes

Emulsifiers are

molecules with a polar end and a nonpolar end that can be used to disperse lipids into polar liquids such as water.

Which of the following are functions of lipids? (Select all that apply)

storage of energy, membrane structure, signaling molecules (such as hormones or neurotransmitters)

Which of the following are functions of carbohydrates? (Select all that apply)

storage of energy, structural support

Liz is interested in the relative sugar concentration of her favorite sodas. She mixes a standard amount of each soda with a standard amount of the reagent, heats the samples in boiling water for five minutes, and observes the color reactions. Place the soda brands in order of increasing sugar concentration (lowest to highest).

1. Brand D (Blue reaction color) 2. Brand C (Green reaction color) 3. Brand M (Yellow reaction color) 4. Brand X (Red reaction color)

From the figures above where is emulsification demonstrated? Mark all that apply.

1A in Tube A, Microscope image Figure 3

To prove that starch is made up of building blocks called sugar you could treat it with _____, then test with Benedict's solution.

Amylase

Which of the following tests requires heating prior to observing results?

Benedict's

Which reagent is used to detect the presence of simple sugars?

Benedict's

Which reagent is used to detect the presence of protein?

Biuret

Which of the following tests is best suited for the detection of fat and oils?

Brown paper

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 color change that occurs is considered the

Dependent variable

A negative control is a sample that you know will give you a negative result. You are testing for the presence of proteins, simple sugars, starch, and lipids in various foods. What would be the best negative control for this experiment?

Distilled water, because it does not contain any of the molecules you are testing for.

During the paper test, solution 2 left a faint stain behind and was determined to be milk while solution 4 left a very definite and greasy stain behind and was determined to be oil. What can be concluded about the lipid content of milk?

It contains a lower concentration of lipids than oil.

The image shows a iodine test to determine the presences of starch. Is it positive or negative?

Negative

The image shows a Biuret test for protein. Is it positive or negative?

Positive

The image shows a paper test for lipids. Is it positive or negative?

Positive