Understanding Of Photosynthesis Research Articles

Cuticular analysis of late Pleistocene, Middle Holocene, and modern Nothofagus dombeyi leaves from Chile: Implications for understanding changes in plant function at different atmospheric CO2 concentrations

How will forests respond to increases in atmospheric CO2 concentrations over the next century? This question is the subject of intensive research, and is based mostly on the results of greenhouse experiments, landscape-level experiments and modeling. In this paper, we examined leaf morphological and physiological characteristics of Nothofagus dombeyi populations exposed to different atmospheric CO2 levels by analyzing leaf cuticle from a Late Pleistocene (~15,500–13,200 cal yr BP) fossil site, a Middle Holocene (~6700–4900 cal yr BP) fossil site, and a modern (2016) collection in mid-latitude Chile. Atmospheric CO2 concentrations were inferred as ~230 ppm, ~270 ppm and ~ 400 ppm based on a comparison with icecore and instrumental records. Our findings show that as atmospheric CO2 concentrations increased by 74% during the transition from late glacial to modern conditions, stomatal density decreased by 24% and maximum stomatal conductance decreased by 42%. In contrast, we observed a 10% increase in stomatal size, a 195% increase in intrinsic water use efficiency, and an increase in leaf nitrogen content. Carbon discrimination decreased as CO2 levels increased contrary to our expectations underscoring that additional factors such as water availability and nutrients can affect carbon discrimination. We also tested the paleo-CO2 method of Franks that performed well under high CO2 conditions (~400 ppm) but failed under low levels (~230 ppm) of atmospheric CO2 indicating the need for a better understanding of photosynthesis during glacial times.

The effect of the ‘Predict-Observe-Explain (POE)’ strategy in teaching photosynthesis and respiration concepts to pre-service science teachers

ABSTRACT The aim of this research is to examine the effects of laboratory activities based on the predict-observe-explain (POE) strategy on the understanding of photosynthesis and respiration concepts of pre-service science teachers, and their attitudes towards biology science and course and biology laboratory. Pre- and post-test designs with an experimental and a control group were used in the research. The research was implemented with participation of 64 the pre-service science teachers. For this purpose, the experimental and the control groups were randomly determined. The same laboratory activities were carried out using POE in the experimental group and utilising a traditional approach in the control group. For the data collection, a two-tier concept test, The Biology as a Science and Course Attitude Scale and the Biology Laboratory Attitude Scale were applied before and after the applications. The results indicated that the pre-service science teachers who were taught using laboratory activities based on the POE strategy had significantly higher scores in terms of achievement and attitude towards biology laboratory than those taught by the traditional approach. In this context, we recommend using and expanding laboratory activities based on active learning methods, such as POE in biology courses.

Emissive Platinum(II) Macrocycles as Tunable Cascade Energy Transfer Scaffolds.

Developing artificial light-harvesting scaffolds with a cascade energy transfer process is significant for better understanding of photosynthesis. Here, we report [3+3] self-assembled PtII fluorescent macrocycles (3 a and 3 b) as light-harvesting platforms with cascade energy transfer. The PtII macrocycles aggregate into nanospheres and show emission-enhancement characteristics upon increasing water content in acetone medium. These aggregates (3aa and 3ba ) serve as energy donors when mixed with the hydrophobic dye Eosin-Y (ESY). In the presence of a second dye, Nile Red (NiR), an unusual sequential two-step energy transfer takes place from the macrocycles to NiR. In this case, ESY acts as a bridge in the relay mode. Additionally, a unique strategy to control such an energy transfer process by tuning the chain length of the alkyl group attached to the periphery of the macrocycles is demonstrated.

Emissive Platinum(II) Macrocycles as Tunable Cascade Energy Transfer Scaffolds

AbstractDeveloping artificial light‐harvesting scaffolds with a cascade energy transfer process is significant for better understanding of photosynthesis. Here, we report [3+3] self‐assembled PtII fluorescent macrocycles (3 a and 3 b) as light‐harvesting platforms with cascade energy transfer. The PtII macrocycles aggregate into nanospheres and show emission‐enhancement characteristics upon increasing water content in acetone medium. These aggregates (3aa and 3ba) serve as energy donors when mixed with the hydrophobic dye Eosin‐Y (ESY). In the presence of a second dye, Nile Red (NiR), an unusual sequential two‐step energy transfer takes place from the macrocycles to NiR. In this case, ESY acts as a bridge in the relay mode. Additionally, a unique strategy to control such an energy transfer process by tuning the chain length of the alkyl group attached to the periphery of the macrocycles is demonstrated.

Understanding photosynthesis in a spatial-temporal multiscale: The need for a systemic view.

In October 2020, at the peak of the COVID-19 pandemic, a group of young Brazilian photosynthesis researchers organized the 1st Brazilian Symposium on Photosynthesis. The event was free and online, with the presence of important guest speakers from all over the world, who discussed their recent works on topics related to the future and perspectives of photosynthesis research. Summarizing the expectations of this symposium we highlighted the importance of adopting a systemic perspective for a better understanding of photosynthesis as a complex and dynamic process. Plants are modular and self-regulating presenting metabolic redundancy and functional degeneration. Among the various biological processes, photosynthesis plays a crucial role in promoting the direct conversion of light energy into carbon skeletons for support growth and productivity. In the past decades, significant advances have been made in photosynthesis at the biophysical, biochemical, and molecular levels. However, this myriad of knowledge has been insufficient to answer crucial questions, such as: how can we understand and eventually increase photosynthetic efficiency and yield in crops subjected to adverse environment related to climate-changing? We believe that a crucial limitation to the whole comprehension of photosynthesis is associated with a vastly widespread classic reductionist view. Moreover, this perspective is commonly accompanied by non-integrative, simplistic, and descriptive approaches to investigate a complex and dynamic process as photosynthesis. Herein, we propose the use of new approaches, mostly based on the Systems Theory, which certainly comes closer to the real world, such as the complex systems that the plants represent.

Powered by Nature

Developing sustainable energy solutions is a multifaceted problem and requires a breadth of research ranging from the fundamental insights of materials for energy applications to the economic feasibility of technologies. Joule brings together research that spans scales as well as fields in order to highlight real-world solutions to the challenge of developing sustainable energy. Joule is a part of Cell Press, which has a long history of publishing outstanding life-science research, and bridges both the physical and life sciences toward solving global energy challenges. Sustainable energy has many standing challenges, such as the generation and storage of renewable energy and the capture, conversion, and utilization of CO2. Often, the methods taken to address the aforementioned challenges focus on the development of new materials for batteries, CO2 capture or reduction catalysts, low-carbon hydrogen production, solar cells, and other human-engineered approaches. Even though these strategies have yielded impressive results that have already become integral in our daily lives, such as Li-ion batteries or Si solar cells, in many cases, nature has already evolved solutions to these problems. For instance, plants and some microbes utilize sunlight to capture and convert CO2 into molecules that are useful for the organisms. By taking inspiration from nature or modifying organisms or molecules found in nature, solutions to some of the main challenges in energy research have been developed. Often, these approaches taken from nature can have inherent advantages of being more sustainable, limited in toxicity, scalable, operational under mild conditions (pH, temperature, and pressure), lower in initial costs, and smaller in physical footprint, and subsequently present viable solutions to the challenges that energy research aims to address. Like many of the other promising technologies, these approaches have their own downsides. However, renewable energy is a critical challenge facing the world that will require a variety of approaches, each with their own upsides and shortcomings, that will inevitably include biological and bio-inspired solutions as well as batteries and solar cells. In this issue of Joule, we are highlighting innovation at the biology-energy interface, spanning a range of topics and approaches. To begin with, Lenz and coauthors in their Perspective show how the conditions that nature creates lead to the degradation of solar cells. Meanwhile, Brudvig and coworkers provide insights into Photosystem II, which allows for a better understanding of photosynthesis and helps to pave the way for bio-inspired photosynthetic systems. Similarly, Wang and coauthors highlight the potential to improve the energy conversion of NAD(P)H, a co-factor that plays an important role in O2 photosynthesis, and how NAD(P)H can be used for photocatalytic energy conversions in reactors. Barstow and colleagues outline the possibilities of using electricity to power microbes for CO2 reduction. Meanwhile, Howe and coauthors highlight the potential of microbes to generate electricity. Gu and coworkers take a slightly different approach, using microbial photoelectrochemical systems to generate syngas from CO2 while simultaneously treating wastewater. Erşan and Park, meanwhile, discuss the potential of non-photosynthetic microbial reduction of CO2. Finally, Rieth and Nocera argue for a hybrid inorganic-biological approach that utilizes inorganic semiconductors for the solar parts of photosynthesis and then uses biological components to perform the conversion of CO2 to higher valued chemicals. This selection of papers demonstrates the rich potential of nature to address today’s energy challenges and hopefully inspires readers to look to nature for solutions and envision biotechnology as part of the future’s sustainable energy solutions.

Coping with branch excision when measuring leaf net photosynthetic rates in a lowland tropical forest

AbstractMeasuring leaf gas exchange from canopy leaves is fundamental for our understanding of photosynthesis and for a realistic representation of carbon uptake in vegetation models. Since canopy leaves are often difficult to reach, especially in tropical forests with emergent trees up to 60 m at remote places, canopy access techniques such as canopy cranes or towers have facilitated photosynthetic measurements. These structures are expensive and therefore not very common. As an alternative, branches are often cut to enable leaf gas exchange measurements. The effect of branch excision on leaf gas exchange rates should be minimized and quantified to evaluate possible bias. We compared light‐saturated leaf net photosynthetic rates measured on excised and intact branches. We selected branches positioned at three canopy positions, estimated relative to the top of the canopy: upper sunlit foliage, middle canopy foliage, and lower canopy foliage. We studied the variation of the effects of branch excision and transport among branches at these different heights in the canopy. After excision and transport, light‐saturated leaf net photosynthetic rates were close to zero for most leaves due to stomatal closure. However, when the branch had acclimated to its new environmental conditions—which took on average 20 min—light‐saturated leaf net photosynthetic rates did not significantly differ between the excised and intact branches. We therefore conclude that branch excision does not affect the measurement of light‐saturated leaf net photosynthesis, provided that the branch is recut under water and is allowed sufficient time to acclimate to its new environmental conditions.

Diffuse light and wetting differentially affect tropical tree leaf photosynthesis.

Most ecosystems experience frequent cloud cover resulting in light that is predominantly diffuse rather than direct. Moreover, these cloudy conditions are often accompanied by rain that results in wet leaf surfaces. Despite this, our understanding of photosynthesis is built upon measurements made on dry leaves experiencing direct light. Using a modified gas exchange setup, we measured the effects of diffuse light and leaf wetting on photosynthesis in canopy species from a tropical montane cloud forest. We demonstrate significant variation in species-level response to light quality independent of light intensity. Some species demonstrated 100% higher rates of photosynthesis in diffuse light, and others had 15% greater photosynthesis in direct light. Even at lower light intensities, diffuse light photosynthesis was equal to that under direct light conditions. Leaf wetting generally led to decreased photosynthesis, particularly when the leaf surface with stomata became wet; however, there was significant variation across species. Ultimately, we demonstrate that ecosystem photosynthesis is significantly altered in response to environmental conditions that are ubiquitous. Our results help to explain the observation that net ecosystem exchange can increase in cloudy conditions and can improve the representation of these processes in Earth systems models under projected scenarios of global climate change.

Organelle Studies and Proteome Analyses of Mitochondria and Plastids Fractions from the Diatom Thalassiosira pseudonana.

Diatoms are unicellular algae and evolved by secondary endosymbiosis, a process in which a red alga-like eukaryote was engulfed by a heterotrophic eukaryotic cell. This gave rise to plastids of remarkable complex architecture and ultrastructure that require elaborate protein importing, trafficking, signaling and intracellular cross-talk pathways. Studying both plastids and mitochondria and their distinctive physiological pathways in organello may greatly contribute to our understanding of photosynthesis, mitochondrial respiration and diatom evolution. The isolation of such complex organelles, however, is still demanding, and existing protocols are either limited to a few species (for plastids) or have not been reported for diatoms so far (for mitochondria). In this work, we present the first isolation protocol for mitochondria from the model diatom Thalassiosira pseudonana. Apart from that, we extended the protocol so that it is also applicable for the purification of a high-quality plastids fraction, and provide detailed structural and physiological characterizations of the resulting organelles. Isolated mitochondria were structurally intact, showed clear evidence of mitochondrial respiration, but the fractions still contained residual cell fragments. In contrast, plastid isolates were virtually free of cellular contaminants, featured structurally preserved thylakoids performing electron transport, but lost most of their stromal components as concluded from Western blots and mass spectrometry. Liquid chromatography electrospray-ionization mass spectrometry studies on mitochondria and thylakoids, moreover, allowed detailed proteome analyses which resulted in extensive proteome maps for both plastids and mitochondria thus helping us to broaden our understanding of organelle metabolism and functionality in diatoms.

Transcription factors involved in the regulatory networks governing the Calvin-Benson-Bassham cycle.

Transcription factors (TFs) play crucial roles in the regulation of photosynthesis; elucidating these roles will facilitate our understanding of photosynthesis and thus accelerate its improvement for enhancing crop yield. Promoter analysis of 52 nuclear-encoded Populus tomentosa Carr. genes involved in the Calvin-Benson-Bassham (CBB) cycle revealed 706 motifs and 326 potentially interacting TFs. A backward elimination random forest (BWERF) algorithm reduced the number of TFs to 40, involved in a three-layer gene regulatory network (GRN) including 46 photosynthesis genes (bottom layer), 25 TFs (second layer) and 15 TFs (top layer). Phenotype-genotype association identified 248 single-nucleotide polymorphisms (SNPs) within 72 genes associated with 11 photosynthesis traits. Of the regulatory pairs identified by the BWERF (202 pairs), 77 TF-target combinations harbored SNPs associated with the same trait, supporting similar mechanisms of phenotype modulation. We used expression quantitative trait nucleotide (eQTN) analysis to identify causal SNPs affecting gene expression, identifying 1851 eQTN signals for 50 eGenes (genes whose expressions are regulated by eQTNs). Distribution patterns identified 14 eQTNs from seven TFs associated with eight expression levels of their downstream targets (defined in the GRN), whereas seven TF-target pairs were also identified by phenotype-genotype associations. To further validate the roles of TFs at the metabolic level, we selected 6764 SNPs from 55 genes (identified by GRN-association or GRN-eQTN pairs or both) for metabolic association, identifying variants within 10 TFs affecting metabolic processes underlying the CBB cycle. Our study provides new insights into the photosynthesis pathway in poplar and may facilitate understanding of processes underlying photosynthesis improvement.

What is global photosynthesis? History, uncertainties and opportunities

Quantifying global terrestrial photosynthesis is essential to understanding the global carbon cycle and the climate system. Remote sensing has played a pivotal role in advancing our understanding of photosynthesis from leaf to global scale; however, substantial uncertainties still exist. In this review, we provide a historical overview of theory, modeling, and observations of photosynthesis across space and time for decadal intervals beginning in the 1950s. Then we identify the key uncertainties in global photosynthesis estimates, including evaluating light intercepted by canopies, biophysical forcings, the structure of light use efficiency models and their parameters, like photosynthetic capacity, and relationships between sun-induced chlorophyll fluorescence and canopy photosynthesis. Finally, we review new opportunities with big data and recently launched or planned satellite missions.

Multispectral multidimensional spectrometer spanning the ultraviolet to the mid-infrared.

Multidimensional spectroscopy is the optical analog to nuclear magnetic resonance, probing dynamical processes with ultrafast time resolution. At optical frequencies, the technical challenges of multidimensional spectroscopy have hindered its progress until recently, where advances in laser sources and pulse-shaping have removed many obstacles to its implementation. Multidimensional spectroscopy in the visible and infrared (IR) regimes has already enabled respective advances in our understanding of photosynthesis and the structural rearrangements of liquid water. A frontier of ultrafast spectroscopy is to extend and combine multidimensional techniques and frequency ranges, which have been largely restricted to operating in the distinct visible or IR regimes. By employing two independent amplifiers seeded by a single oscillator, it is straightforward to span a wide range of time scales (femtoseconds to seconds), all of which are often relevant to the most important energy conversion and catalysis problems in chemistry, physics, and materials science. Complex condensed phase systems have optical transitions spanning the ultraviolet (UV) to the IR and exhibit dynamics relevant to function on time scales of femtoseconds to seconds and beyond. We describe the development of the Multispectral Multidimensional Nonlinear Spectrometer (MMDS) to enable studies of dynamical processes in atomic, molecular, and material systems spanning femtoseconds to seconds, from the UV to the IR regimes. The MMDS employs pulse-shaping methods to provide an easy-to-use instrument with an unprecedented spectral range that enables unique combination spectroscopies. We demonstrate the multispectral capabilities of the MMDS on several model systems.

Genetic variation in transcription factors and photosynthesis light-reaction genes regulates photosynthetic traits.

Transcription factors (TFs) play crucial roles in regulating the production of the components required for photosynthesis; elucidating the mechanisms by which underlying genetic variation in TFs affects complex photosynthesis-related traits may improve our understanding of photosynthesis and identify ways to improve photosynthetic efficiency. Promoter analysis of 96 nuclear-encoded Populus tomentosa Carr. genes within this pathway revealed 47 motifs responsive to light, stress, hormones and organ-specific regulation, as well as 86 TFs that might bind these motifs. Using phenotype-genotype associations, we identified 244 single-nucleotide polymorphisms (SNPs) within 105 genes associated with 12 photosynthesis-related traits. Most (30.33%) of these SNPs were located in intronic regions and these SNPs explained 18.66% of the mean phenotypic variation in the photosynthesis-related traits. Additionally, expression quantitative trait loci (eQTL) mapping identified 216 eQTLs associated with 110 eGenes (genes regulated by eQTLs), explaining 14.12% of the variability of gene expression. The lead SNPs of 12.04% of the eQTLs also contributed to phenotypic variation. Among these, a SNP in zf-Dof 5.6 (G120_9287) affected photosynthesis by modulating the expression of a sub-regulatory network of eight other TFs, which in turn regulate 55 photosynthesis-related genes. Furthermore, epistasis analysis identified a large interacting network representing 732 SNP-SNP pairs, of which 354 were photosynthesis gene-TF pairs, emphasizing the important roles of TFs in affecting photosynthesis-related traits. We combined eQTL and epistasis analysis and found 32 TFs harboring eQTLs being epistatic to their targets (identified by eQTL analysis), of which 15 TFs were also associated with photosynthesis traits. We therefore constructed a schematic model of TFs involved in regulating the photosynthetic light reaction pathway. Taken together, our results provide insight into the genetic regulation of photosynthesis, and may drive progress in the marker-assisted selection of desirable P. tomentosa genotypes with more efficient photosynthesis.

A tribute to Ulrich Heber (1930-2016) for his contribution to photosynthesis research: understanding the interplay between photosynthetic primary reactions, metabolism and the environment.

The dynamic and efficient coordination of primary photosynthetic reactions with leaf energization and metabolism under a wide range of environmental conditions is a fundamental property of plants involving processes at all functional levels. The present historical perspective covers 60years of research aiming to understand the underlying mechanisms, linking major breakthroughs to current progress. It centers on the contributions of Ulrich Heber who had pioneered novel concepts, fundamental methods, and mechanistic understanding of photosynthesis. An important first step was the development of non-aqueous preparation of chloroplasts allowing the investigation of chloroplast metabolites ex vivo (meaning that the obtained results reflect the in vivo situation). Later on, intact chloroplasts, retaining their functional envelope membranes, were isolated in aqueous media to investigate compartmentation and exchange of metabolites between chloroplasts and external medium. These studies elucidated metabolic interaction between chloroplasts and cytoplasm during photosynthesis. Experiments with isolated intact chloroplasts clarified that oxygenation of ribulose-1.5-bisphosphate generates glycolate in photorespiration. The development of non-invasive optical methods enabled researchers identifying mechanisms that balance electron flow in the photosynthetic electron transport system avoiding its over-reduction. Recording chlorophyll a (Chl a) fluorescence allowed one to monitor, among other parameters, thermal energy dissipation by means of 'nonphotochemical quenching' of the excited state of Chl a. Furthermore, studies both in vivo and in vitro led to basic understanding of the biochemical mechanisms of freezing damage and frost tolerance of plant leaves, to SO2 tolerance of tree leaves and dehydrating lichens and mosses.

Prospective elementary science teachers’ understanding of photosynthesis and cellular respiration in the context of multiple biological levels as nested systems

In this study, Turkish prospective elementary science teachers’ understanding of photosynthesis and cellular respiration has been analysed within the contexts of ecosystem knowledge, organism knowledge and interconnection knowledge (IK). In the analysis, concept maps developed by 74 prospective teachers were used. The study was carried out with prospective teachers in their final year who were enrolled in the special teaching methods course. The results show that prospective teachers’ understanding of photosynthesis, cellular respiration, energy flow and matter cycling is quite different from one another’s. In addition, the present study revealed that prospective elementary science teachers showed weak understanding of energy flow and matter, cycling and cellular respiration concepts and IK category but they had strong understanding of photosynthesis concept. Prospective teachers also experience difficulties in understanding connections between macro- and microbiological systems. The study concludes with suggestions for more meaningful biology education.

Photosynthesis-related characteristics of the midrib and the interveinal lamina in leaves of the C3-CAM intermediate plant Mesembryanthemum crystallinum.

Leaf veins are usually encircled by specialized bundle sheath cells. In C4 plants, they play an important role in CO2 assimilation, and the photosynthetic activity is compartmentalized between the mesophyll and the bundle sheath. In C3 and CAM (Crassulacean acid metabolism) plants, the photosynthetic activity is generally attributed to the leaf mesophyll cells, and the vascular parenchymal cells are rarely considered for their role in photosynthesis. Recent studies demonstrate that enzymes required for C4 photosynthesis are also active in the veins of C3 plants, and their vascular system contains photosynthetically competent parenchyma cells. However, our understanding of photosynthesis in veins of C3 and CAM plants still remains insufficient. Here spatial analysis of photosynthesis-related properties were applied to the midrib and the interveinal lamina cells in leaves of Mesembryanthemum crystallinum, a C3-CAM intermediate plant. The midrib anatomy as well as chloroplast structure and chlorophyll fluorescence, diurnal gas exchange profiles, the immunoblot patterns of PEPC (phosphoenolpyruvate carboxylase) and RubisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase), H2O2 localization and antioxidant enzyme activities were compared in the midrib and in the interveinal mesophyll cells in leaves of C3 and CAM plants. Leaf midribs were structurally competent to perform photosynthesis in C3 and CAM plants. The midrib chloroplasts resembled those in the bundle sheath cells of C4 plants and were characterized by limited photosynthetic activity. The metabolic roles of midrib chloroplasts differ in C3 and CAM plants. It is suggested that in leaves of C3 plants the midrib chloroplasts could be involved in the supply of CO2 for carboxylation, and in CAM plants they could provide malate to different metabolic processes and mediate H2O2 signalling.

Photon flux density and temperature-dependent responses of photosynthesis and photosystem II performance of apple leaves grown in field conditions.

The process of photosynthesis depends on the light, and is modulated by leaf temperature and their interaction is important to understand how climate affects photosynthesis. Photosynthetic and PSII light responses at a range of leaf temperatures were measured on leaves of apple (Malus domestica Borkh. cv. Red Gala) trees growing in field conditions. The objective was to assess the interaction between photon flux density (PFD) and temperature on these processes. Results showed leaf temperature strongly modulated the PFD-dependent response of photosynthesis and PSII performance. An interaction on photosynthesis occurred, with temperature affecting saturated rates as well as PFDs saturating photosynthesis. The efficiency of PSII electron transport (operating and maximum in light) universally declined with increasing PFD but temperature strongly influenced the response. Rates of PSII electron transport at saturating PFDs were affected by temperatures. Both photochemical quenching and non-photochemical quenching also responded strongly to temperature but at high PFDs, photochemical quenching increased linearly with decreasing temperatures while non-photochemical quenching increased curvilinearly with increasing temperatures. Modelling revealed changes in photosynthesis were positively correlated with rates of electron transport. These results greatly enhance our understanding of photosynthesis and the underpinning processes and their responses to temperature and PFD.

CHALLENGES IN UNDERSTANDING PHOTOSYNTHESIS IN A UNIVERSITY INTRODUCTORY BIOSCIENCES CLASS

University students’ understanding of photosynthesis was examined in a large introductory biosciences class. The focus of this study was to first examine the conceptions of photosynthesis among students in class and then to investigate how a certain type of text could enhance students’ understanding of photosynthesis. The study was based on pre- and post-test designs, in which students’ prior knowledge of photosynthesis was measured with ten open-ended questions. The test measured the students’ systemic and factual levels of understanding. After students read either a text that systematically pointed out how typical misconceptions contradict scientific concepts (a refutational text) or a traditional text (a non-refutational text), the students’ knowledge was tested again with the same test instrument. Results showed that students’ prior knowledge and understanding of photosynthesis varied considerably, but both texts seemed to support effective learning. The study revealed several common systemic and factual misconceptions students hold concerning photosynthesis. The knowledge of students majoring in biology was higher than that of non-major students, especially concerning the systemic understanding of photosynthesis. The refutational text appeared to help the students who had weak prior knowledge. Thus, science educators should be aware of the heterogeneity of students concerning their levels of prior knowledge and should design instruction accordingly. We suggest that tools, such as refutational texts, can support students at the university level who have weaker prior understanding.

Promoting the Understanding of Photosynthesis Among Elementary School Student Teachers Through Text Design

The purpose of this study was to investigate elementary school pre-service teachers’ understanding of photosynthesis and to examine if a refutational text can support understanding of photosynthesis better than a non-refutational text. A total of 91 elementary school pre-service teachers read either a refutational or a non-refutational text concerning photosynthesis and then answered open-ended questions. Our results indicate that there are critical problems associated with student teachers learning about the process of photosynthesis, even after it has been systematically taught in teacher education. However, the results positively indicate that refutational science texts seem to foster effective conceptual change among student teachers. The results interestingly showed that students who read a refutational text improved their systemic and factual understanding of photosynthesis more than did those who read a non-refutational text. Especially students who had naïve prior understanding regarding photosynthesis benefitted more from a refutational text. Thus, a refutational text may act as an effective facilitator of conceptual change. These results have implications for teacher education, where conceptual mastery of the most important science phenomena, such as photosynthesis, should be achieved. A refutational text is an easy and effective way to support conceptual change in higher education. Thus, this study highlights the importance of domain-specific science education in teacher programmes.

David Alan Walker. 18 August 1928 — 13 February 2012

David Alan Walker was born in Kingston upon Hull, England. He entered King’s College, Newcastle, then part of the University of Durham, where he received his BSc, and subsequently his PhD under Meirion Thomas FRS in 1958. Later, in 1968 he was awarded a DSc at the University of Newcastle in recognition of his exceptional contributions of published work in his field. In 1991 he received a Humboldt Research Prize, and in 2004 the inaugural Communications Award from the International Society of Photosynthesis Research. He was the author of more than 230 publications, including several books. He made important contributions to the understanding of photosynthesis, in particular the fixation of carbon dioxide by the biochemical transformations of the Benson–Calvin cycle in the stroma of chloroplasts of higher plants. Based on the meticulous attention to detail and technical prowess derived from his earlier training as an enzymologist, his work prompted totally new thinking about how this cycle was regulated and how it interfaced with the synthesis of ATP and NADPH in the light reactions of photosynthesis. Later, he was one of a very small group of people to recognize that this regulation was observable in whole leaves through the changes in chlorophyll fluorescence, helping to open the door to one of the most widely used tools in plant physiology. After periods at Newcastle, Purdue, Cambridge, Queen Mary College and Imperial College, London, he spent the largest part of his academic career as a professor at the University of Sheffield. There he established a world-renowned photosynthesis research group that grew into one of the university’s first semi-autonomous research institutes, the Research Institute for Photosynthesis, later renamed the Robert Hill Institute. This legacy persists more than 30 years later. He also distinguished himself in the wider aspects of being a scientist: long before it became fashionable, he wrote about the issues of food, energy and global change in his 1992 book Energy, plants and man . His enthusiasm for communicating both the joy of science and these serious issues led to many other imaginative schemes and endeavours, again long before the need for greater ‘public understanding of science’ became recognized.