What is a cell?Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cells also contain the bodys hereditary material and can make copies of themselves.Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell.

The cell constituents are:

NucleusA part of the cell containing DNA and RNA and responsible for growth and reproduction

Cell Membranethin, flexible barrier around a cell; regulates what enters and leaves the cell

NucleolusThe organelle where ribosomes are made, synthesized and partially assembled, located in the nucleus (contains RNA)

Nuclear Envelopesurrounds and protects the nucleus

Cytoplasmjellylike fluid inside the cell in which the organelles are suspended; separates nucleus from cells; aids in cell movement and shape of cell

MitochondriaPowerhouse of the cell, converts nutrients into energy

Vacuoleregulates amount of pressure in the cell, stores nutrients, waste products and water with out it the cell would dry out.

ChloroplastConverts energy from the sun into chemical energy through photsynthesis

RibosomesFound on rough ER and throughout cytoplasm; synthesizes proteins

LysosomesOrganelle containing digestive enzymes

Golgi Apparatusstack of membranes in the cell that modifies, sorts, and packages proteins from the endoplasmic reticulum

Types of Cells Cells can be subdivided into the following subcategories:1. Prokaryotes: Prokaryotes are relatively small cells surrounded by the plasma membrane, with a characteristic cell wall that may differ in composition depending on the particular organism.Prokaryotes lack anucleus(although they do have circular or linearDNA) and other membrane-boundorganelles(though they do containribosomes). Theprotoplasmof a prokaryote contains the chromosomal region that appears asfibrousdeposits under the microscope, and thecytoplasm.[16]BacteriaandArchaeaare the twodomainsof prokaryotes.2. Eukaryotes: Eukaryotic cells are also surrounded by the plasma membrane, but on the other hand, they have distinct nuclei bound by anuclear membraneor envelope. Eukaryotic cells also contain membrane-bound organelles, such as (mitochondria,chloroplasts,lysosomes, rough and smoothendoplasmic reticulum,vacuoles).In addition, they possess organized chromosomes which store genetic material