The introduction of the concept of the variable represents a critical point in the arithmetic-algebraic transition. This concept is complex because it is used with different meanings in different situations. Its management depends on the particular way of using it in problem-solving. The aim of this paper was to analyse whether the notion of "unknown" interferes with the interpretation of the variable "in functional relation" and the kinds of languages used by the students in problem-solving. We also wanted to study the concept of the variable in the process of translation from algebraic language into natural language. We present two experimental studies. In the first one, we administered a questionnaire to 111 students aged 16-19 years. Drawing on the conclusions of this research we carried out the second study with two pairs of students aged 16-17 years.

SummaryIn the present paper we applied confocal microscopy and fluorescence technologies for studying the distribution and the oxidative activity of sea urchin (Paracentrotus lividus) mitochondria during development, by in vivo incubating eggs and embryos with cell-permeant MitoTracker probes. We calculated, by a mathematical model, the intensity values, the variations of intensity, and the variation index of incorporated fluorochromes. Data demonstrate that mitochondrial mass does not change during development, whereas mitochondrial respiration increases. In addition, starting from 16 blastomeres stage, some regions of the embryo contain organelles more active in oxygen consumption.

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Preface VI students as it is shown in discussion and analysis of the Chinese particular system of graphemic fixation and specific characteristics of Chinese writing. The charts and tables of the participant demographic information were very helpful and informative, and the statistical illustration in writing used various figures and tables, which organizes the information of the study in a visually meaningful way and provides readers with a deep understanding of the study.The authors used rigorous and unique methods to analyze and draw conclusions from the data by structuring data analysis in different types and chapters. More commendable, treating cultural diversity as an opportunity in mathematics by deeply studying Chinese mathematics from the arithmetic to the algebraic content in the historical aspect-cultural puzzle, is excellent approach in culture-related studies.The book provides strong evidence that research on the cognitive processes, from arithmetic thought to algebraic thought, should take into consideration the socio-cultural context. It is an important contribution to the literature on linguistic structure in comparative studies related to Chinese student mathematics learning.This book not only makes a great contribution to research in mathematics education, but the findings of this study also addressed insightful approaches and thoughts of understanding the development of algebraic thinking in cultural contexts for classroom teachers. Using written Chinese language from different theoretical references provided wonderful approaches for understanding student algebra cognitive development in a different way and calls educators to pay special attention to an epistemological and linguistic view of algebraic development. The findings inform classroom teachers that the cultural context plays an important role in student learning mathematics. A typical analysis of the cognitive dimension involved in some in the historical and cultural contexts is a great resource for classroom teachers.

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