Week 1 Ideas

FEATHERS

Feathers are among the most complex integumentary appendages found in vertebrates and are formed in tiny follicles in the epidermis, or outer skin layer, that produce keratin proteins. The β-keratins in feathers, beaks and claws — and the claws, scales and shells of reptiles — are composed of protein strands hydrogen-bonded into β-pleated sheets, which are then further twisted and crosslinked by disulfide bridges into structures even tougher than the α-keratins of mammalian hair, horns and hoof. (R. Schor and S. Krimm (1961). "Studies on the Structure of Feather Keratin II. A β-Helix Model for the Structure of Feather Keratin". Biophys J. 1 (6): 489–515. doi:10.1016/S0006-3495(61)86904-X. PMID 19431311. ^ Linus Pauling and Robert B. Corey (1951). "The Structure of Feather Rachis keratin". Proceedings of the National Academy of Sciences of the United States of America 37 (5): 256–261. doi:10.1073/pnas.37.5.256. PMID 14834148)

 CRYSTALS

The process of forming a crystalline structure from a fluid or from materials dissolved in the fluid is often referred to as the crystallization process. In the old example referenced by the root meaning of the word crystal, water being cooled undergoes a phase change from liquid to solid beginning with small ice crystals that grow until they fuse, forming a polycrystalline structure. The physical properties of the ice depend on the size and arrangement of the individual crystals, or grains, and the same may be said of metals solidifying from a molten state.

CAVES

The formation and development of caves is known as speleogenesis. Caves are formed by various geologic processes. These may involve a combination of chemical processes, erosion from water, tectonic forces, microorganisms, pressure, atmospheric influences, and even digging.

Most caves are formed in limestone by dissolution.