Natural or Artificial?

 

 

Experiment A


 

Introduction

Anhydrous copper sulfate is an indicator for the presence of the chemical substance H2O (water).

Aim

To see if apples contain any H2O molecules.

Method

  1. Place some anhydrous copper sulfate on a freshly cut piece of apple.

  2. Observe any changes.


Results

A1) Before starting the experiment, what color is the anhydrous copper sulfate?

A2) What do you observe when the anhydrous copper sulfate is placed on the apple?

A3) What information does this reaction give us about apples?

A4) Which of these foods would NOT give a positive reaction in this experiment? (You may write more than one possible answer)

  • milk

  • vegetable oil

  • orange juice

  • Perrier

  • mayonnaise

Photo of experiment:  



Experiment B


Introduction

The pH of a substance measures the presence of H+ ions. A substance with many of these ions is said to be acidic. Any pH measurement under 7 is considered acidic. 7 is neutral on the pH scale.

Aim

To see if apples contain any H+ ions. In other words, to see if they are acidic or not by measuring the pH.

Method

  1. Cut up a small piece of apple into a mortar and pistil. Grind it into a pulp.

  2. Place a strip of pH indicator paper on the apple pulp.

  3. Observe any changes in the color of the strip.

  4. Compare the color to the standard colors in order to measure the pH number.

  5. When you are finished, put the used pH paper in the bin.


Results


B1) What color does the pH paper become?

B2) On the pH scale of 1 to 14, what is the pH of apples?

B3) In order to get a color change, a chemical reaction has to happen. Which two chemicals are interacting in this experiment?

B4) Which of the following foods would give similar results as apples (in other words ±2 points on the pH scale).

  • Kiwi fruit

  • Oranges

  • Evian

  • sodium bicarbonate (baking powder)

Photo of experiment:



Experiment C


Introduction

Fehling's solution (or Benedict's solution) is a chemical indicator for simple sugars such as fructose: C6H12O6. Unlike some other indicators, Fehling's solution does not work a room temperature - it must be heated first.

Aim

To see if apples contain sugar.

Method

  1. Cut up a small piece of apple into a mortar and pistil. Grind it into a pulp.

  2. Carefully pour 1 cm3 of the pulp into a test tube.

  3. Add 5 drops of Fehling's solution.

  4. Heat in a water bath for 3 to 5 minutes.

  5. Observe any changes in the color of the liquid (not the chunks of apple).

  6. When you are finished, clean out the test tube and the mortar & pistil for the next group.


Results


C1) Before starting the experiment, what color is Fehling's solution?

C2) What are we looking for in this experiment?

C3) Once it is heated, what is the color of the liquid?

C4) What does that tell us about apples?

C5) Would we get similar results if we tested all different species of apples?

C6) From a biological point of view, what is the apple tree's reason for putting such a valuable energetic molecule such as fructose in a fruit which will only fall off its branches?


Photo of experiment:


Experiment D


Introduction

Iodine solution is an indicator for a molecule called starch. Starch is a huge molecule made up of hundreds of simple sugar molecules (such as glucose) connected to each other.

Aim

To see if apples contain starch.

Method

  1. Place some iodine solution on a small freshly cut piece of apple (~2 x 2 cm).

  2. Observe any changes.

  3. When you are finished, clean up the table for the next group.


Results


D1) Before starting the experiment, what color is the iodine solution?

D2) What happened when you put some on the apple?

D3) What does that tell us about apples?

D4) List two other foods with starch in them.


Photo of experiment:




Experiment E


Introduction

Pigments are chemicals which give color to certain things. When you buy jeans, for example, they have a blue pigment added to the cotton. Black jeans have a black pigment and white jeans have no pigment added.

Aim

To see if apples have pigments in their skin.

Method

  1. Peel off some skin from an apple and cut it up into small pieces into a mortar. Be careful with the knife, please.

  2. Cover the pieces of skin in the mortar with dichloromethane (a solvent).

  3. Using the pistil, grind the skin for a minute or two, mixing it with the solvent.

  4. Observe any changes.


Results


E1) What is the biological name for the microscopic “bricks” that apple skin is made of - In other words, what is the smallest unit of an apple which would permit us to identify it?

E2) In order to get the pigments out of the skin, we need to grind it. What is the purpose of this? In other words, what are we doing to the microscopic “bricks” mentioned in question E1?

E3) What happens to the liquid between the beginning and the end of the experiment?

E4) From a biological point of view, what is the advantage for the apple tree to put red pigments in the skin of its apples?

Photo of experiment:


© A.W. Damon 2003

 

Last modification: 2004-01-30