Climate Zones Objectives: 1. Describe Earth's major climate zones. 2. Explain how climate zones are characterized. Notes: According to the three cell convection model of each hemisphere the Earth neatly separates itself into three distinct climate zones; the polar, temperate, and the tropical zones.limate Zones Objectives: 1. Describe Earth's major climate zones. 2. Explain how climate zones are characterized. Notes: According to the three cell convection model of each hemisphere the Earth neatly separates itself into three distinct climate zones; the polar, temperate, and the tropical zones.
The nucleus is a large roundish organelle. It is bounded by a double membrane which has numerous pores. Inside the nucleus are chromosomes and a dark region called a nucleolus which makes ribosomes. (Ribosomes are necessary for protein synthesis.)
Ribosomes are found in the cytoplasm of a cell. They are either free floating or bound to the endoplasmic reticulum. Groups of ribosomes stuck together are called polysomes. Most cells contain thousands of ribosomes, while a few specialized cells contain millions. Brain cells and the cells of the pancreas contain large concentrations of ribosomes since they produce a large amount of protein. slide 2 of 6. The Structure of Ribosomes Although ribosomes are called organelles, they don't have a membrane that holds the contents of the ribosome in one cohesive structure. Ribosomes are composed of ribosomal RNA (rRNA) and protein. Sixty percent of the structure is rRNA and 40 percent is protein. There are two subunits: a large subunit and a small subunit. They are labeled as 60s and 40s after the Svedberg values. The subunits of ribosomes are produced in the nucleolus, which is located in the nucleus of the cell. Ribosomal proteins enter the nucleolus and combine with four rRNA strands to produce the two subunits. The subunits leave the nucleus through the nuclear pores and combine in the cytoplasm.