Biology Extended Essay - Illuminance as a Mechanism for Anthocyanin Biosynthesis and Expression in Hibiscus Rosa-Sinensis (Chinese Hibiscus)

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Biology Extended Essay
May, 2011

Illuminance as a mechanism for anthocyanin biosynthesis and expression in Hibiscus rosa-sinensis (Chinese Hibiscus) Name: Scott Joel Heng Candidate session number: 003400-023 Supervisor: Dr Jensen Hjorth Institution: SJI International, Singapore

Word count : 3990 words Total number of pages in this document: 54 pages

Scott Joel Heng, Candidate session number: 003400-023, Biology Extended Essay

Abstract
Hibiscus rosa-sinensis does not emit perfume, relying on visual attraction for pollination1/2. Studies show that hummingbirds are responsible approximately 98% of its pollination, suggesting a mutualistic relationship between the two18. It is possible that, illuminance levels are important for pollination in plants like H. rosa-sinensis as lower levels could mean that they will not be spotted by hummingbirds. Given that H. rosa-sinensis is solely dependent on visual attraction2, and mostly one pollinator for pollination, I was interested to see if H. rosa-sinensis displayed an adaptive response to changes in illuminance levels to increase pollination chances. This led me to a research question, “How do different levels of illuminance affect anthocyanin biosynthesis and expression in Hibiscus rosasinensis (chinese hibiscus) flowers?” H. rosa-sinensis plants were exposed to illuminance levels that corresponded to that of their natural habitat, achieved through the wattage of cool fluorescent bulbs. Plants were exposed to illuminance levels for 10 hours daily for 10 days, with flower blossoms snipped off and stored in a freezer. After 10 days, floral anthocyanins were extracted with acidified methanol, and analysed using a Vernier Spectrophotometer. Absorption spectrums were analysed to examine absorbance levels at different wavelengths for each illuminance level. My experimental results showed that decreased illuminance levels resulted in increased total absorbance, suggesting increased anthocyanin biosynthesis. Two maximas in the blue and green region were observed. My results showed that the ratio of blue to green absorbance increased as illuminance levels decreased. It is my suggestion in this essay that a greater contrast achieved through changes in anthocyanin, increases the flower’s chances of being spotted by hummingbirds and hence being pollinated under lower illuminance levels. My results may give rise to optimum illuminance levels required for commercial production of anthocyanins3.

Word count : 295

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Scott Joel Heng, Candidate session number: 003400-023, Biology Extended Essay

Contents Table
Content
About Myself Acknowledgments 1. Introduction 1.1 Description of H. rosa-sinensis 1.2 Anthocyanins, and their role in creating colours in flowers 1.3 Hummingbirds and pollination of H. rosa-sinensis 1.3.1 Colour vision and the concept of illuminance 1.3.2 Recognition of H. rosa-sinensis by hummingbirds 1.4 Plant response and illuminance (H. mutabilis) 1.5 This investigation 1.5.1 Research Question 1.5.2 Hypothesis 1.6 Brief outline of the experiment 9 9 10 7 7-8 8 8-9 9 9

Page(s)
5 6

2. Method and materials
2.1 Background information (Plant growth phases) 2.2 Independent, dependent and controlled variables 2.2.1 Independent variable 2.2.2 Dependent variable(s) 2.2.3 Controlled variables 2.3 Varying illuminance levels 2.4 H. rosa-sinensis plant samples 2.5 Experimental set up and procedure 2.5.1 Set up and materials 2.5.2 Procedure 2.5.3 Anthocyanin extraction 2.6 Analysis of anthocyanins 2.6.1 Total amount of anthocyanin biosynthesized 10 11 11 11 11 11 - 12 12 13 13 14 14 14 14

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Scott Joel Heng, Candidate session number: 003400-023, Biology Extended Essay

Content
2.6.2 Anthocyanin expression

Page(s)
15

3. Results and discussion
3.1 Results 3.1.1 Primary data 3.1.1.1 Anthocyanin expression trends 3.1.1.2 Absorbance trends (absorption maximas) 3.1.1.3 Anthocyanin biosynthesis 3.1.2 Accessory data 3.1.2.1 Qualitative observations 3.2...
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