This resource tackles the learning objective “Only areas of the plant with chloroplasts can make starch in photosynthesis”. This is activity 11 in the ‘Photosynthesis: A Survival Guide’ scheme and follows up from activity 10, 'What are chloroplasts'.
Students carry out a starch test on a variegated leaf to demonstrate that only the parts containing chloroplasts are able to synthesise starch.
This resource is designed for 11-14 pupils but could be extended for use with older students as appropriate.
Ethanol is highly flammable; harmful if swallowed.
Do not allow students access to ethanol whilst the Bunsen burner is still lit. Using boiling water from a kettle can overcome this hazard. In this case, use caution in distributing and pouring the boiling water.
Learning Objective
“Only areas of the plant with chloroplasts can make starch in photosynthesis”
Misconceptions
When testing a leaf for the presence of starch in traditional photosynthesis experiments many pupils think that the iodine solution is simply staining the green area of the leaf. If a starch test is carried out on a variegated leaf it needs to be made very clear that the chlorophyll is being dissolved out of the leaf in order to show where the starch is. Pictures of chloroplasts containing starch grains can help to overcome this.
Suggested approaches
Pupils carry out a standard starch test on a variegated leaf. See the accompanying student sheet and Powerpoint presentation
Science & Plants for Schools: www.saps.org.uk
Which parts of a leaf produce starch : p.
1
This document may be photocopied for educational use. Revised 2013.

For a fun activity for an open evening or a science day, you can prepare ‘secret messages’ or hidden images on all-green pelargonium leaves for students to reveal by testing for starch, as shown in the video below.
Video
You may wish to use this video clip, showing 19 th century scientist Julius von Sachs' pioneering research into how plants form starch from the BBC's 'Botany: A Blooming History series, available from the SAPS website. http://www.saps.org.uk/secondary/teaching-resources/796-video-clip-chloroplasts-and-starch
Equipment and materials required for each working group:
• A leaf from a variegated pelargonium 1
• One 250 cm 3 beaker
• One boiling tube
• A Bunsen burner (or access to a kettle of boiling water, if pouring water directly into the boiling tube)
• Heatproof mat
• Tripod and gauze
• One white tile
• Iodine solution in dropping bottle
• A pair of forceps
Materials to be shared:
500cm 3 ethanol (industrial alcohol) – Approximately 25 cm 3 to be given out to each group by the teacher.
Notes:
1 Place the variegated plant under bright light for at least 24 hours prior to the practical. Make sure it has been well watered to enable maximum photosynthesis. If the plant is not actively photosynthesising, this practical will not work. See the SAPS guide to Plants in the Science
Curriculum (www.saps.org.uk/growplants) on pelargoniums for additional guidance on keeping plants in the classroom.
This resource is based on an original by Debbie Eldridge in Photosynthesis: A Survival Guide
(2009).
Science & Plants for Schools: www.saps.org.uk
Which parts of a leaf produce starch : p.
2
This document may be photocopied for educational use. Revised 2013.

Science & Plants for Schools: www.saps.org.uk
Which parts of a leaf produce starch : p.
3
This document may be photocopied for educational use. Revised 2013.