Subject: Type of Lesson: Grade: CSEC OBJ: Term: UNIT: 5 Duration: Lesson: 10 Week: 4 Objectives Prerequisite Student Knowledge Important Points

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1 Subject: Biology Type of Lesson: Practical work; Discussion; Q & A Grade: 10. CSEC OBJ: Students should be able to carry out simple controlled investigations to demonstrate that light and chlorophyll are necessary conditions for photosynthesis, delete this text and type. Term: Easter UNIT: 5 Nutrition - Photosynthesis Duration: 2 x 40 mins Lesson: 10 Conditions and materials for photosynthesis Week: 4 Objectives As a result of this lesson, you will be able to: 1) carry out controlled experiments to demonstrate the need for light in photosynthesis. 2) carry out controlled experiments to demonstrate the need for chlorophyll in photosynthesis. 3) identify the control in each experiment. 4) work cooperatively with other group members in carrying out the practical activities. Prerequisite Student Knowledge You should be familiar with: 1) basic information about photosynthesis. 2) structure of plant leaf and its adaptations for photosynthesis. Important Points Important points in this lesson: 1) In the earlier lesson on photosynthesis it was noted that chlorophyll was one of the conditions necessary for photosynthesis. 2) How could we test if this is really true? Could we use one plant with chlorophyll and another without? We would have a problem there, as without chlorophyll a plant cannot survive. 3) Fortunately nature has provided for us some plants with leaves that are variegated. These leaves have green parts and also parts without chlorophyll as shown below in Figure Such leaves may be used to illustrate the need for chlorophyll and the need for light in order for plants to photosynthesize.

2 Figure 10.1: An example of variegated leaves. Key Terms Variegated De-starched Translocated Challenge Areas Write a paragraph on A world without photosynthesis, including the implications for humans. Equipment/Material Needed 1) Leaves of a plant with variegated leaves that are green and white as shown in Figure ) Apparatus and materials for doing the test for starch in leaves test tubes, beaker, alcohol, Bunsen burner/source of heat, iodine, white tile, water. 3) Pencil,ruler, eraser, drawing paper 4) You will need for the investigation on light a. A well watered potted plant that has been kept in a dark cupboard for two days. Such a plant is said to be destarched as starch previously made would have been translocated/removed from the leaves. b. black cartridge paper or aluminium foil about 3 cm X 7 cm ( wide enough to go across the width of your leaf) c. knife or razor blade d. four paper clips

3 Note to Student 1) There is a need for a control when carrying out investigations which could be affected by more than one factor. 2) For example, if you are investigating the need for light; we cannot just remove light from one plant and accept the results we get from this. It is necessary to compare this plant with one that is as similar to the other as possible, but which is receiving light. It is better still if the same plant or the same leaf can be used. 3) You will be heating alcohol today, so you must be careful. It might be best if your teacher heated the alcohol and you brought your leaf to the front to be dipped. 4) If you plan to carry out both tests in one class, begin with the plant with variegated leaves. For the test for light you will have to put the stencils on the leaves before putting them to photosynthesize. While you wait on these, you could carry out the test using the variegated leaves so long as these have already been exposed to light.

Introduction 1) Introductory Activity: Applying real life experience to the practical that will be carried out. a. The need for chlorophyll in plants. Look at the variegated leaves.

Have you ever noticed that the grass does not grow well under those big trees outside? That mostly there are no plants underneath?

4 Introduction 1) Introductory Activity: Applying real life experience to the practical that will be carried out. a. The need for chlorophyll in plants. Look at the variegated leaves. You notice that there is no green in some parts. What does this mean? Do you think that we could use a leaf like this to find out if chlorophyll is needed for photosynthesis? How? b. Have you ever noticed that the grass does not grow well under those big trees outside? That mostly there are no plants underneath? Have you ever noticed if you left a piece of board on your lawn, that the grass below it eventually gets yellow and dies? What might have caused the death of this grass? Is it light? How could you test to determine if light is needed for this plant? Body of Lesson 1) Demonstrating the need for light in the process of photosynthesis a. In your group, use Worksheet 10.1 to do the investigation. b. Answer the questions at the end of the worksheet. Check with your teacher about the answers. c. Notice below the findings of an investigation like this one. Warning Caution is needed when working with hot alcohol. Its vapours can easily catch fire. Use the work station that is set up by your teacher for this part of the investigation Figure 10.2: A leaf with stencil removed and starch test completed i. Can you explain why only the two ends of the leaf and the L showed starch when the test was carried out? ii. Where on the leaf acted as the control? 2) Demonstrating the need for chlorophyll in the process of photosynthesis a. Look at this plant in Figure 10.3

5 Figure 10.3: Photograph of plant showing green and white leaves b. Now look at the one your teacher has, which has been outside in the sunshine. Notice that some parts of some leaves are white in colour and do not appear to have chlorophyll, whereas other parts are green coloured. c. Draw one of the leaves, showing on the sketch the areas that are white, and those that are green or have other colours (use stippling/striping for this). d. Now carry out a starch test on the leaf, and compare the results with the sketch you did earlier. The results should look like the photo below in Figure Expected Results

6 Figure 10.4: The results of the starch test on a green and white variegated leaf a. Consider: i. Why the starch was found only in these sections. ii. What do these two tests tell about the need for light and chlorophyll for photosynthesis? 3) Review of photosynthesis a. Can you remember what you already know about photosynthesis? Write down the important points. b. Now, summarize the process by answering the following questions: i. What is needed for it to occur? ii. What does the plant make from photosynthesis? iii. What happens to these products? iv. Why do we test the leaf for starch and not for sugar? Closure In-Class Assignments 1 ) Plan and design an investigation to test EITHER A. If leaves that are purple can photosynthesize. OR B. If purple or red leaves photosynthesize faster than green leaves. Write it up in your books, with a hypothesis, and a method for doing this investigation, the control to be used and expected problems to be encountered.

7 Out-of-Class Assignment 1 ) Do research to discover if the following factors affect how efficiently photosynthesis occurs in a green plant: a. temperature b. time of day, e.g., early morning/.late afternoon/mid-day c. amount of light, e.g., cloudy day or bright sunny day. Supplemental Glossary of Terms Variegated De-starched Water bath Translocation Adjective describing multi coloured sections of a leaf. Plant/leaf that has been kept in the dark for at least one day, in order for the starch/sugar made in photosynthesis to be removed from the leaves, and transported to other areas of the plant A large container kept at a constant temperature, in order to help keep warm/boiling a smaller container inside it. Word used to describe the removal of starch or glucose sugar that was made in the plant leaves to another part of the plant. CSEC Questions 1. Although the photosynthesis equation shows sugar as a product, a leaf is not usually tested for sugar in order to show that photosynthesis has taken place. Suggest a reason for this practice. (3 marks) Before an experiment was set up, the plants were placed in a dark cupboard for about 24 hours. This was necessary to a) reduce the quantity of sugar produced during photosynthesis b) allow the plant to get its store of carbon dioxide c) ensure that any starch produced was removed from the leaves d) stop further reduction of carbon dioxide to carbohydrates. (Specimen paper 2004)

8 Recommended Materials 1. Worksheet 10.1: Demonstrating the need for light in order for photosynthesis to occur. 2. The following is a helpful website. where you can use either gardening with children or go directly to dna/h2g2/a Bibliography Atwaroo-Ali, L. (2003). CXC Biology. Oxford, UK: Macmillan Caribbean Publishers Campbell, N. A. (1996). Biology (4 th Edition.) San Francisco, California, USA: The Benjamin /Cummings Publishing Company, Inc Carrington, C., Agard, M., Sealy, L. (1995). Biology Skills for Excellence. Harlow, UK: Longman Caribbean Chinnery, L., Glasgow, J., Jones, M., Jones, G. (2001). CXC Biology. London: Cambridge University Press. Roberts, M. B. V. & Mitchelmore, J. (1985). Biology for CXC. Cheltenham, UK: Thomas Nelson and Sons, Ltd. Worksheet Worksheet 10.1: Demonstrating the need for light in order for photosynthesis to occur. 1) Materials: 2) Procedure: a. Use the razor blade or knife to make a stencil out of the black paper or foil. You could cut out a figure like a star or just use your initial. The size of the whole piece of paper should be enough to cover the width of the leaf you will use. b. Prepare the stencil and place it on the leaf of a well watered plant that has been kept in the dark for the previous 24 hours. Stick it on with a paper clip or two. c. Leave the plant with the stenciled leaf outside in the sun for about half

9 an hour. Bring it back inside and then remove the stencil carefully. d. Remove the leaf from the plant and test it for starch with iodine. Figure 10.4: A leaf with stencil before starch test. 3) Answer the questions below: a) Why was the plant kept in the dark for 24 hours before doing any experimenting? Expected answer: Allow any starch previously formed to leave leaf. b) After half an hour in the sunlight, did the leaf have any starch present? Why? Expected answer: Yes, photosynthesis occurred. c) Was starch present throughout the leaf? Were there any areas that had no starch? Why? Expected answer: Present only in areas exposed to light. d) Was there a part of the leaf which was a control? What other kind of control could you have used? Expected answer: Areas not exposed to light/keep another similar plant in dark for same time period.

Answers Expected Results Figure 10.3: The results of the starch test on a green and white variegated leaf Worksheet 10.

10 Answers Expected Results Figure 10.3: The results of the starch test on a green and white variegated leaf Worksheet ) Answer the questions below: a) Why was the plant kept in the dark for 24 hours before doing any experimenting? Expected answer: Allow any starch previously formed to leave leaf. b) After half an hour in the sunlight, did the leaf have any starch present? Why? Expected answer: Yes, photosynthesis occurred. c) Was starch present throughout the leaf? Were there any areas that had no starch? Why? Expected answer: Present only in areas exposed to light. d) Was there a part of the leaf which was a control? What other kind of control could you have used? Expected answer: Areas not exposed to light/keep another similar plant in dark for same time period.

Conditions necessary for photosynthesis

Conditions necessary for photosynthesis This practical can be used to easily assess Scientific enquiry standards 1, 3 and 4. Relevant biology standards: 11A 7.1 & 8.4 and 12F 7.1 & 8.4 Materials: For setting