AIR CIRCULATION: 

• Warm air expands (density decreases) and rises up leaving an area of low pressure.
• When air goes up through upper layers of the atmosphere cools down (se enfria). 
• Cold air contracts going down into the atmosphere, generating a high-pressure area.
• From high pressure area, air flows near Earth’s surface to low pressures, warming up. 
• The circuit which air flows continuously: convective cell.
• If Earth were motionless, air circulation would follow convective cells that would extend

1.Ecosystems and environmental factors.Ecosystem:is a system formed by a group of organisms of different species(or biocenosis),the environment in which they live and its physical/chemical characteristics(or biotope) and the interactions.Types of environmental factors.Abiotic factor:are the physical/chemical components of an ecosystem(temperature,light,water).Biotic factors:interactions produced in the biocenosis(wolves when they hunt as a pack).Tolerance ranges and limiting factors:an environmental

DNA Structure: Phos Group gives DNA acid props. | DNA written 5′ to 3′ | Comp pairing pu-py so constant width, A(pu)-T(py) 2 H-bonds, G(pu)-C(py) 3 H-bonds | Backbone antiparallel, sugars upside down for pairing to occur, helix shields hydrophobic bases, 10 B.P. for rotation | Packages 3 bil B.P., 2 meters | Chromosomes 23 pairs, same genes differ in inherited sequence (diff. traits), condensed chromatin fiber loops | Histones allow wrapping of DNA, +Lysine/Argininebind with negative backbone