Chemical properties are the changes in composition undergone by a substance when it is subjected to various conditions. The various changes may be physical and chemical. The physical properties are temporary. In a chemical change the composition of the substance is changed and new products are formed. Chemical properties are permanent.
It is useful to classify materials as solid, liquid or gas (though water, for example, exists as solid (ice), as liquid (water) and as gas (water vapour). The changes of state described by the terms solidify (freeze), liquify (melt), va—pourise (evaporate) and condense are examples of physical changes. After physical change there is still the same material. Water is water whether it is solid, liquid or gas. Also, there is still the same mass of material. It is usually easy to reverse a physical change.
New words
matter – материя
mass – масса
sense – чувство
organ – орган
steam – пар
to undergo – подвергать
variety – разнообрзие
change – перемена
physical – физический
chemical – химический
natural – природный
transformation – трансформация
colour – цвет
taste – вкус
odour – запах
density – плотность
hardness – твердость
solubility – растворимость
ability – возможность
to conduct – проводить
permanent – постоянный
The components of the skeletal system are derived from mesenchymal elements that arise from mesoderm and neural crest. Mesenchymal cells differentiate into fibroblasts, chondroblasts, and osteoblasts, which produce connective tissue, cartilage, and bone tissue, respectively. Bone organs either develop directly in mesenchymal connective tissue (intramembranous ossification) or from preformed cartilage models (endochondral ossification). The splanch nic meso—derm gives rise to cardiac and smooth muscle.
The skeletal system develops from paraxial mesoderm. By the end of the fourth week, the sclerotome cells form embryonic connective tissue, known as mesenchyme. Mesenchyme cells migrate and differentiate to form fibro—blasts, chondroblasts, or osteoblasts.
Bone organs are formed by two methods.
Flat bones are formed by a process known as intra—membinous ossification, in which bones develop directly within mesenchyme.
Long bones are formed by a process known as en—dochondral ossification, in which mesenchymal cells give rise hyaline cartilage models that subsequently become ossified.