Currently our understanding of both system and phytoplankton metabolism in large rivers is somewhat limited. Knowledge of the metabolic balance in such systems is necessary not only for proper management of the river itself, but also for the lakes into which they discharge. The River Continuum Concept proposes that the deep, turbid waters of large rivers have a poor light climate which leads to heterotrophic conditions (respiration > photosynthesis) yet this idea has been challenged. Similarly, it has been predicted that phytoplankton growth in large rivers is limited to areas of unusually favourable light climate and water retention (e.g. margins, backwaters), but the evidence is limited. Through longitudinal and diel measurements of Chl a, nutrient concentrations, dissolved oxygen and stable oxygen isotopes it was shown in this study that the lower Grand River was autotrophic during the two successive summers but either balanced or heterotrophic in other seasons. This implies that large rivers such as the Grand can be a transition zone for nutrients and a phytoplankton source, depending on season. Experimental incubations to measure oxygen production under varying irradiance demonstrated that phytoplankton could indeed grow (i.e., achieve positive net production) in the main river channel. Comparison of system and plankton metabolic rates further indicated that the phytoplankton were responsible for the major portion of the system production, but much less of the respiration. Sediment oxygen demand probably accounted for much of the additional respiration, but interactions with marginal and upstream habitats was probably an additional influence on both consumption and production of oxygen. The results further showed that stable oxygen isotope dynamics did not conform to the steady state model commonly used to infer metabolic patterns from environmental isotope data. A non-steady model was more successful and largely supported independent assessments of metabolism.

Currently our understanding of both system and phytoplankton metabolism in large rivers is somewhat limited. Knowledge of the metabolic balance in such systems is necessary not only for proper management of the river itself, but also for the lakes into which they discharge. The River Continuum Concept proposes that the deep, turbid waters of large rivers have a poor light climate which leads to heterotrophic conditions (respiration > photosynthesis) yet this idea has been challenged. Similarly, it has been predicted that phytoplankton growth in large rivers is limited to areas of unusually favourable light climate and water retention (e.g. margins, backwaters), but the evidence is limited. Through longitudinal and diel measurements of Chl a, nutrient concentrations, dissolved oxygen and stable oxygen isotopes it was shown in this study that the lower Grand River was autotrophic during the two successive summers but either balanced or heterotrophic in other seasons. This implies that large rivers such as the Grand can be a transition zone for nutrients and a phytoplankton source, depending on season. Experimental incubations to measure oxygen production under varying irradiance demonstrated that phytoplankton could indeed grow (i.e., achieve positive net production) in the main river channel. Comparison of system and plankton metabolic rates further indicated that the phytoplankton were responsible for the major portion of the system production, but much less of the respiration. Sediment oxygen demand probably accounted for much of the additional respiration, but interactions with marginal and upstream habitats was probably an additional influence on both consumption and production of oxygen. The results further showed that stable oxygen isotope dynamics did not conform to the steady state model commonly used to infer metabolic patterns from environmental isotope data. A non-steady model was more successful and largely supported independent assessments of metabolism.

According to previous research, students show difficulties in understanding photosynthesis and respiration, and basic ecological concepts like energy flow in ecosystems. There are successful teaching units accomplished in this area and many of them can be described as inquiry-based teaching. One definition of inquiry-based teaching is that it involves everything from finding problems, investigating them, debating with peers and trying to explain and give solutions. Accordingly students need to be confronted with challenging questions and empirical data to reason about and teachers need to implement student-generated inquiry discussion since students often stay silent and do not express their thoughts during science lessons. This thesis will focus on young peoples’ understanding of the functioning of plants, students’ participation during biology lessons, and how biology teaching is accomplished in primary and secondary school. Two school classroom projects focusing on teaching about plants and ecology are described. Four teachers and their 4th, 5th and 6th grade classes plus two science teachers and their three 8th grade classes collaborated. Photosynthesis and respiration were made concrete by using tasks where plants, plant cells, germs, seeds and the gas exchange were used. The aim was to listen to students’ reasoning in both teaching and interview situations. Learning outcome, as described by students’ reasoning in the classrooms and in individual interviews but also by their test results, is especially focused. Student-student and student-teacher interactions have been analysed with an ethnographic approach in the classroom context. The plant tasks encouraged the students’ in primary school to develop scientific reasoning and the interviews confirmed that the students had learned about photosynthesis. The ecology teaching in secondary school showed a substantial understanding confirmed both by students’ oral and written reasoning. Analyses of test results and understanding as presented in interviews did not always correspond. The interviews showed the importance of letting students try to explain concepts and to correct themselves. Primary students’ reasoning and understanding about photosynthesis were in the interviews almost the same as the secondary students’. The secondary students’ questioning during the lectures showed wonderments and interest for ecology from a broader view than in the content presented by the teachers and the textbooks, but the large classes and disruptive students stole too much time from the teachers’ management in the classroom. Students’ knowledge was underestimated and their interest in ecology faded away. / Tidigare forskning visar att elever har svårigheter att förstå processer som fotosyntes, cellandning och ekologiska samband, såsom energiflöden i ekosystem. Lyckosamma undervisningsprojekt inom det här området kan ofta beskrivas som ”inquiry-based”. Ett sätt att definiera ”inquiry-based” är att det innefattar allt ifrån att hitta problem, undersöka dem, debattera med andra elever och till att försöka förklara och ge lösningar. Utifrån detta visas att elever behöver bli konfronterade med utmanande frågor och empiriska data att resonera utifrån. Lärarna behöver också arbeta med att föra in studentdiskussioner eftersom det visat sig att många elever ofta är tysta och inte uttrycker sina tankar och spekulationer under NO-lektionerna. Den här avhandlingen fokuserar på elevernas förståelse av växternas funktion, elevernas deltagande under biologilektionerna och på hur biologiundervisning genomförs i mellan- och högstadiet. Två skolprojekt med fokus på växter och ekologi beskrivs. Fyra klasslärare och deras klasser i årskurs 4, 5 och 6, plus två NO-lärare och deras tre klasser i årskurs 8 samarbetade. Fotosyntes och cellandning konkretiserades med hjälp av växter, växtceller, groddar, frön och några gas-utbytesreaktioner. Syftet var att lyssna på vad eleverna resonerade om, både i undervisningssituationer och vid intervju. Elevernas förståelse utifrån deras resonerande men också utifrån deras testresultat fokuserades. Elev-elev- och elev-lärarinteraktioner analyserades med hjälp av en etnografisk ansats i klassrums-kontexten. Uppgifterna med konkret växtmaterial uppmuntrade mellanstadieeleverna att utveckla ett naturvetenskapligt resonerande och intervjuerna bekräftade att eleverna hade lärt sig om fotosyntes. Ekologiundervisningen på högstadiet resulterade i en påtaglig förståelse, som bekräftades utifrån elevernas muntliga och skriftliga resonerande. Analysen av förståelse visad i provresultat och vid intervju överensstämde inte alltid. Intervjuerna visade betydelsen av att låta eleverna både få förklara begrepp och att rätta sig själva i sina förklaringar. I intervjusituationen visade det sig att mellanstadieelevernas resonerande och förståelse av fotosyntes gott kunde mäta sig med högstadieelevernas. Elevernas sätt att ställa frågor under lektionsgenomgångarna visade på funderingar och ett intresse för ekologi, som hade en större bredd än det innehåll som lärare och lärobok presenterade, men stora klasser och störande elever stal alldeles för mycket av lärarens tid för att det skulle vara möjligt att genomföra bra undervisning i klassrummet. Elevernas kunskaper underskattades och deras intresse tonade bort.

The purpose of this study was to identify the relative predictive influences of prior knowledge, meaningful learning orientation, formal reasoning ability and mode of instruction on understanding in photosynthesis and respiration in plants concepts. Two hundred thirty three 8th grade students from six classes of one elementary school in Ankara participated in this study. The study was carried out during the 2004-2005 Fall semester. Students in the experimental group (N=117) received conceptual change instruction, and the students in the control group (N=116) received traditional instruction. Two-tier multiple choice diagnostic test, &ldquo / Photosynthesis and Respiration in Plants Concept Test&rdquo / developed by Haslam and Treagust (1987), was used to determine students&rsquo / understanding of photosynthesis and respiration in plants concepts. The test was administered to the sample prior to the treatment as pre-test, and after the treatment as post-test. The pre-test scores were used as prior knowledge of students. Students&rsquo / reasoning abilities were measured by the &ldquo / Test of Logical Thinking&rdquo / and their learning orientations were measured by &ldquo / Learning Approach Questionnaire&rdquo / . The results of the study indicated that students held several misconceptions concerning photosynthesis and respiration in plants concepts. Significant differences between the experimental group and control group with respect to understanding of the concept were found in favor of experimental group. The main predictor of achievement in the experimental group was students&rsquo / prior knowledge, while it was reasoning ability in the control group. Meaningful learning orientation accounted for a small amount of variance in the experimental group but it did not contribute to understanding on post-test scores in traditional group.