A set of quasi-quantitative experiments are described to relate volume and pressure variations associated to the phase changes of the main components of the air. The processes are promoted by variation of temperature using liquid nitrogen to refrigerate the air and get liquid oxygen, traces of dry ice and ice. The changes in volume and pressure associated to oxygen phase changes are used to discuss and rationalize phenomena as different as the effects of intermolecular forces on the properties of substances, industrial accidents resulting from a sudden pressure increase due to undesired reactions or even rationalize how popcorns are made. The ludic character of some of the experiments aims to promote the interest and curiosity of youngsters on scientific issues.

Metalloids have characteristics between metals and non-metals which give them, in some cases, specific properties. At least two of this chemical elements, boron and silicon, are essential to a significant number of living organisms and since some years ago it has been observed that the same metalloids may be involved in the synthesis and stabilization of some molecules relevant to the origin of life.

It is still frequently referred, even in reference text-books, that the D-enantiomers of amino acids are not present in living organisms, which is not right. In the present revision/informative paper we describe a large number of D-amino acids that are present in all forms of organisms, from bacteria to human beings, in the free state, in peptides and in proteins, and give a short overview of their characteristics, physiological interaction and roles.