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Functions of cell organelles.

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BY01 - Functions of cell organelles Cell Surface Membrane The cell surface membrane (plasma membrane) is a thin selective cell barrier, which can select what can enter and leave the cell. In addition to the transport of nutrients and respiratory gases, membranes are also receptors and message senders. The membrane receives and dispatches specific messages such as nerve impulses, antibodies and hormones. Nucleus The nucleus is the largest organelle within the eukargotic cell, so large that it is easily observed by light microscopy. It is spherical in structure or avoid in structure and is 10-20pm in diameter. The nucleus is surrounded by a double membrane which is perforated by many pores. The nucleus encloses the chromosomes. These are only visible at times of cell division and are otherwise dispersed as a diffuse network called chromatin. The chromosomes contain the genetic information and are replicated prior to nuclear and cell division. ...read more.


Golgi Apparatus The golgi apparatus consists of a stack of flattened membranous sacs. This organelle is present in all cells, but most prominent in those that are metabolically active. The golgi apparatus is the site of the synthesis of biochemicals; these are packaged into swellings at the margin of the sac which become pinched off as vesicles. The golgi apparatus also collects proteins and lipids made in the ER by the fusion of vesicles pinched off from the ER with its own flattened sacs. In the golgi apparatus, additional substances are added and the products are repackaged into fresh vesicles which then cut off and move to other parts of the cell where the secrets are discharged and deposited. Lyosomes Lyosomes are small spherical vesicles, 0.2-0.5pm in diameter or larger (Particularly in plant cells). The lyosome is bounded by a single membrane and contains a concentrated mixture of hydrochloric digestive enzymes. If these digestive enzymes were not kept enclosed in a membranous sac they would attack other cell organelles. ...read more.


Mitochondria occur in all cells in very large numbers, possibly more than a thousand of them in a cell that is metabolically very active. They vary in size within the range 0.5-1.5pm wide and 3.0-10pm long. Each mitochondrion is bounded by a double membrane, the outer being a smooth continuous boundary. The inner membrane is infolded to form partitions called cristae, which partially divide the interior. Chloroplasts Chloroplasts are members of a group of organelles known as plastids. Plastids normally contain pigments such as chlorophylls and carotenoids. Photosynthesis occurs in chloroplasts in all green plants. They are 4-10pm long and 2-3pm wide. The chloroplast os bounded by a double membrane. The outer membrane is a smooth continuous boundary; the inner gives rise to strands of branching membranes called lamellae or thylakoids extending throughout the organelle. The interior of the chloroplast is divided into the grana, which are surrounded by stroma. In the grana the thylakoids are stacked in flat, circular piles and contain photosynthetic pigments. In the stroma the thylakoids criss-cross loosely, suspended in an aqueous matrix containing ribosomes, liquid droplets and small starch grains. ...read more.

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