Lesson 2.2 - Starch Investigation

You have learned that plants will convert excess glucose into starch and store it in this form.  How can you test this to see if it is true? 

Read the investigation How Do Plants Store Energy from the Sun on pages 240 and 241 so that you understand what was done in the investigation.  Then, use the sample data below to answer the questions about the investigation.

When a student performed the investigation, the following observations were recorded.

  • The part of the leaf that was covered by the paper turned orange-red when the iodine was added.  I could see clearly the shape of the paper on the leaf.
  • The part of the leaf that was not covered by the paper and was exposed to the sunlight turned a dark blue-black colour.  

Now, answer the following questions.

 

Question 1. Write out your hypothesis.

Question 2. Answer questions 1 to 7 in the Analyze, Conclude and Apply, and Extend Your Knowledge on page 241.

Question 3. Answer Check Your Understanding questions 1, 2, and 3 on page 241.

 

Check your answers with those that follow.

 

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. Write out your hypothesis.

You could hypothesize such as the following:

        1. The amount of sunlight a leaf on a growing plant gets affects the amount of starch present in the leaf.  The more sunlight, the more starch in the leaf.

        2. The amount of sunlight a leaf on a growing plant gets does not affect the amount of starch present in the leaf.  The amount of starch in the leaf will stay the same regardless of the amount of sunlight.

Question 2. Answer questions 1 to 7 in Analyze, Conclude and Apply, and Extend Your Knowledge on page 241.

Analyze

        1. Yes, starch was present in the leaf.  Iodine turns blue-black in the presence of starch.
        2. The starch must have come from excess glucose.  You know that plants produce glucose by the process of photosynthesis.  The glucose is used by plant cells for their life processes.  Only excess glucose is converted to starch.  There was more starch in the part of the leaf that was exposed to sunlight where photosynthesis could take place.

Conclude and Apply

        1. If you hypothesized that the amount of sunlight affects the amount of starch in a leaf, then your hypothesis is supported by the results of the student. If you hypothesized that the amount of sunlight does not affect the amount of starch in a leaf, then your hypothesis is rejected by the results of the student.
        2. The iodine is used to test for starch.  Iodine turns blue-black in the presence of starch.
        3. The hot alcohol dissolves the green chlorophyll from the leaf so that the iodine test produces observable colour changes.

Extend your Knowledge

        1. A leaf kept in the dark for three days would not have very much starch in it.  If there was very little starch left after only one day in this experiment, three days should be enough time to have used up most of the starch.
        2. The experimental design would require that you take two healthy plants of the same type, place one in a room where it would receive no sunlight for three days, place the other plant in sunlight for three days.  Then perform the iodine starch test on a leaf from each plant. 

 

Question 3. Answer Check Your Understanding questions 1, 2, and 3 on page 241.

        1. Plants get the chemical energy they need from glucose which they make using the energy from the Sun.
        2. Plants store excess chemical energy in the leaves and roots for use by their cells when conditions are not right for photosynthesis to occur, such as at night or when it is too cold or too dry.
        3. The source of chemical energy for animals is plants or other animals that are eaten as food.

 


Now, do Assignment 12B. Page forward to access it.