Osmosis and diffusion are essential foundation concepts for first-year biology students as they are a key to understanding much of the biology curriculum. However, mastering these concepts can be challenging due to their interdisciplinary and abstract nature. Even at their simplest level, osmosis and diffusion require the learner to imagine processes they cannot see. In addition, many students begin university with flawed beliefs about these two concepts which will impede learning in related areas. The aim of this study was to explore misconceptions around osmosis and diffusion held by first-year cell biology students at an Australian regional university. The 18-item Osmosis and Diffusion Conceptual Assessment was completed by 767 students. From the results, four key misconceptions were identified: approximately half of the participants believed dissolved substances will eventually settle out of a solution; approximately one quarter thought that water will always reach equal levels; one quarter believed that all things expand and contract with temperature; and nearly one third of students believed molecules only move with the addition of external force. Greater attention to identifying and rectifying common misconceptions when teaching first-year students will improve their conceptual understanding of these concepts and benefit their learning in subsequent science subjects.
An immersive 320° 3D experience of osmosis was perceived by cell biology students to be fun, useful, and educational. Performance of all students improved on a multiple-choice exam question, and those students with moderate to high base-level knowledge also performed better on short-answer questions.
In this study on decapod crustaceans, we examined the Ca2+- and Sr2+-activation properties of skeletal muscle fibres from an identified proprioceptor, the thoracic coxal muscle receptor organ (TCMRO) and its extrafusal promotor muscle fibres. Proprioceptors and extrafusal muscles were isolated from a walking leg from the crayfish (Cherax destructor) and the rear swimming leg of the mud crab (Scylla serrata). The crayfish and mud crab TCMROs had very low Hill coefficient (nCa) values (1.86 +/- 0.08 and 1.64 +/- 0.03, respectively). In comparison to other skeletal muscle fibre types these low Hill coefficients would enable the length of the receptor muscles to be finely controlled over a wide range of [Ca2+]. Maximum force was found to be significantly lower in the TCMROs (crayfish: 5.76 +/- 0.98; crab: 4.80 +/- 0.56 Ncm(-2)), compared to their associated extrafusal promotor muscle fibres (crayfish: 10.69 +/- 1.63; crab: 20.07 +/- 1.98 Ncm(-2)), which is consistent with their sensory role. The muscle fibres of the crayfish TCMRO had faster contractile properties than the mud crab TCMRO, we discuss how these contractile properties relate to the type of locomotion undergone by each leg. The mud crab 'red' promotor and all crayfish promotor fibres were characterised as slow with low Hill coefficients (nCa: crayfish: 3.22 +/- 0.29; crab: 3.34 +/- 0.29) and a contractile apparatus with a high sensitivity to Ca2+ (pCa50: crayfish: 6.42 +/- 0.03; crab: 6.18 +/- 0.03). In contrast the 'white' mud crab promotor fibres from the swimming leg had contractile properties that were characteristic of fast fibres with a high mean Hill coefficient (nCa: 5.27 +/- 0.76) and a lower Ca2+ sensitivity (pCa50: 6.03 +/- 0.03). The sensitivity of the contractile apparatus to Sr2+ was very low (range of mean pSr50: 4.23 +/- 0.03-3.48 +/- 0.06) and low force levels were produced in comparison to that produced with Ca2+. The results of this study show that the muscle fibres of the sensory receptor, produce less force and have been adapted to enable the length of the receptor to be finely set in relation to the length of the extrafusal muscle. We discuss how the striated fibres of the receptor have been adapted to perform a sensory role and how this is related to the type of locomotion undergone by the legs. We also discuss how the fibre types of the extrafusal muscle have adapted to the mode of locomotion.
Using confocal laser scanning and conventional light microscopy, the morphology and organization of the muscle fibres in a proprioceptor, the thoracic coxal muscle receptor organ (TCMRO), and the associated ‘extrafusal’ promotor muscle were investigated in two species of decapod crustacea, the crayfish Cherax destructor and the mud crab Scylla serrata. The diameter of the TCMROs was shown to increase distally, with an increase up to 350% recorded for the crayfish. The tapered shape of the crayfish TCMRO was demonstrated to amplify movements mechanically at the transducer region where the afferent nerves attach. Serial sectioning of the TCMROs, showed that the fibre number increased in the proximal to distal direction from 14 to 30 fibres in the crayfish and from 7 to 20 in the crab. Optical sectioning with the laser scanning confocal microscope revealed that the increase in fibre numbers was the result of muscle fibres branching in the distal third section of the TCMRO. The percentage of muscle tissue in the cross‐sectional area in the TCMRO was found to be only 35.2% and 64.6% in the crayfish and crab, respectively. Longitudinal sectioning using laser scanning confocal microscopy revealed the average sarcomere length of the TCMRO muscle fibres of both species to be in the intermediate range for crustacean muscle fibres (4.1 ± 0.1 µm and 4.55 ± 0.34 µm for the crayfish and crab) compared with the long sarcomere muscle fibres in the associated promotor muscles (7.87 ± 0.2 and 10.6 ± 0.6 µm). The distinct morphology of the TCMRO muscle fibres – smaller diameter, intermediate sarcomere length and branching of fibres compared to the larger, long sarcomere promotor fibre muscle fibres – suggest that the TCMRO muscle fibres are specialized in their role of proprioception.
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