Joseph Rohrig 10-2-09 AP Biology Cell Wall and Chloroplasts The Cell Wall is found in plants. It has many functions. It provides tensile strength and limited plasticity. The thick walled cells provide mechanical support. Cells Walls are tubes for long distance transport. They prevent water loss. They also provide mechanical protection for insects and pathogens. When cell division occurs, it needs a cell wall. When a cell enlarges, it includes changes in the cell wall. Also, when a cell differentiates, it includes changes in the cell wall. The Cell Wall has a very unique structure. The structure of a cell wall has three layers: the middle lamella, the primary wall, and the secondary wall. The middle lamella is formed during cell division. It makes up the outer wall of the cell and is composed of protein and pectic compounds. The primary wall occurs after the middle lamella and is composed of a rigid skeleton of cellulose microfibrils embedded in a matrix composed of hemicelluloses, pectic compounds, and glycoproteins. The secondary wall occurs after cell enlargement. It is rigid and provides compression strength. It is layered and made up of hemicelluloses, cellulose, and lignin. Chloroplasts are found in plants and protists . Chloroplasts have a unique structure. They are bounded by a double membrane called the chloroplast envelope. It has a third internal membrane called the thylakoid membrane. The Outer membrane contains porins which make it permeable to small molecules. The Inner membrane is impermeable to ions and metabolites. The structure of chloroplasts allow for many functions as well. Chloroplasts have many functions. The membranes of Chloroplasts have similar functions to mitochondria because it gives roles to organelles in chemiosmotic generation of ATP. Chloroplasts are generally larger than mitochondria. Both chloroplasts and mitochondria function to generate metabolic energy. Chloroplasts are organelles responsible for photosynthesis. Chloroplasts were also evolved by endosymbiosis which allows them to replicate by division. They are responsible for the photosynthetic conversion of CO2 to carbohydrates. They synthesize amino acids, fatty acids, and lipid components in their own membranes. The reduction of Nitrite to Ammonia also occurs in Chloroplasts. It is an essential step in the incorporation of nitrogen to organic compounds.