This essay will outline the functions of the main cell components, these consist of the nucleus, nuclear membrane, mitochondria, lysosomes, Golgi apparatus, cell membrane, ribosomes, cytoplasm and endoplasmic reticulum both rough and smooth. Images:  Every human body has billions of microscopic units called cells. Cells carry out numerous of chemical reactions and processes that make up the essence of life. The structure of cells varies in size and shape and has different functions.
There are four main features with in a cell and these consist of the cell membrane also known as the plasma, the cell nucleus which contains mature red blood cells, the cytoplasm and the organelles which is a “various component of a cell with a distinct structure and their own functions and can be likened to miniature organs. Organelles include mitochondria, the endoplasmic reticulum the Golgi apparatus and lysosomes”  The nucleus is usually the largest structure inside the cell which contains chromosomes which contains deoxyribonucleic acid (DNA), this is the genetic coding material which determines difference characteristics.
The nucleus main function is to contain instructions for growth, work and maintenance of the cell, it controls nearly all the activities of the cell. “A smaller, darker sphere is often visible, the nucleolus, this is a source of ribonucleic acid (RNA) one of the nucleic acids” . When a cell is not dividing (known as resting) this is called the chromatin network and the nuclear material appears like a thick, triangle mass. When a cell is in the process of dividing, the chromatin network separates into distinct black threads known as chromosomes and there are 23 pairs of chromosomes in a human cell. The nuclear membrane is made up of 2layers, each composed of a lipid bilayer. It has holes all over which are called nuclear pores, to facilitate and regulate the exchange of materials, for example, proteins and RNA, between the nucleus and cytoplasm. The outer membrane is continuous with the endoplasmic reticulum. The inner membrane is linked with a network of intermediate filaments called nuclear lamina acts as a site of attachment for chromosomes. It also acts as a shield for the nucleus”.  The mitochondria are rod shaped or spherical shaped, they are very energy active cells.
Each mitochondrion has a double layered membrane but the inner layer is folded at intervals, producing a series of ridges known as cristae which is where the enzymes responsible for the end stages of cell respiration. “The energy released from glucose is stored until it is needed by a chemical battery called adenosine triphosphate (ATP). When energy is required for building complex molecules or doing work like contracting muscles, ATP breaks down to adenosine diphosphate (ADP), releasing energy to build chemical bonds.
The ADP is recycled, to be built up once more into ATP, using the energy released from glucose. “ The number of mitochondria in a cell depends on the amount of energy it needs to perform its function, for example the muscle cell will have a large amount because it needs a lot of energy. Images:  Lysosomes are very small vesicles produced by part of the Golgi apparatus. They contain powerful enzymes that destroy bacteria, protein, nucleic acids, carbohydrates, lipids and other foreign materials and they release it outside the cells. ysosomes travel freely within the cell and by releasing their contents they can destroy old or damaged organelles and in some cases entire cells, like the clean-up crew of the cell that eliminate anything that has outlived their usefulness. The Golgi apparatus packages protein to deliver to other organelles or outwards from the lysosomes. This appears to look flattened, fluid filled sacs which are stacked upon each other. Images:  “The cell membrane is a thin semi-permeable membrane that surrounds the cytoplasm of a cell, enclosing its contents.
Its function is to protect the integrity of the interior of the cell by allowing certain substances into the cell” (for example, gases and liquids), “while keeping other substances out” . The cytoplasm is semi-fluid, gel like substance that gives shape to the cell. This where metabolism takes place and this accommodates cell organelles such the mitochondria and the endoplasmic reticulum. There are two types of endoplasmic reticulum (ER), rough and smooth.
The rough ER is studded with tiny black bodies called ribosomes and its functions are to manufacture cell proteins and act as a temporary storage area. Sometimes sugars are added to protein (glycoprotein) in secretions like mucus. The smooth ER has no attached ribosomes and is involved in the metabolism. “Smooth ER is important in the synthesis of lipids and membrane proteins. Rough ER is important in the synthesis of other proteins. Information coded in DNA sequences in the nucleus is transcribed as messenger RNA. Messenger RNA exits the nucleus through small pores to enter the cytoplasm.
At the ribosomes on the rough ER, the messenger RNA is translated into proteins. These proteins are then transferred to the Golgi in “transport vesicles” where they are further processed and packaged into lysosomes, peroxisomes, or secretory vesicles”  The reticulum network fills the cell interior and channels passage ways for transporting materials to and from parts of the cell. Images:  Ribosomes what are studded all over rough ER. “A ribosome is a biological molecule made of ribonucleic acid (RNA) and proteins (ribosomal proteins).
The structure of a ribosome is complex, and it is responsible for making the millions of proteins that are needed by cells. Think of a ribosome as a small protein biosynthetic factory that translates the DNA genetic information into an amino acid sequence (the primary structure of proteins). ”  A ribosome may be located in many places within the cell. Some are in the cytosol and others are bound to cellular membranes. Membrane-bound ribosomes are responsible for the characteristic roughness of the endoplasmic reticulum when seen under a microscope.
Reference: Images: 1. Anon. (undated) http://www. cellsalive. com/cells/er. htm [online] 2. Anon. (undated) http://micro. magnet. fsu. edu/cells/golgi/golgiapparatus. html [online] 3. Anon. (undated) http://scienceaid. co. uk/biology/cell/structure. html [online] 4. Michael W. Davidson (2000) http://micro. magnet. fsu. edu/cells/mitochondria/mitochondria. html [online] Books and internet: 1. Stretch B. (2010) Health & Social Care Level 3 Book 1: Anatomy and physiology for health and social care 2. Stretch B. 2010) Health & Social Care Level 3 Book 1: Anatomy and physiology for health and social care 3. Stretch B. (2010) Health & Social Care Level 3 Book 1: Anatomy and physiology for health and social care 4. Anon. (2008) www. biology-online. org/dictionary/Nuclear_membrane [online] 5. Anon. (undated) www. cellsalive. com/cells/er. htm [online] 6. Regina Bailey (2012) www. biology. about. com/od/biologydictionary/g/cell-membrane. htm [online] 7. Paul Arnold (2009) www. brighthub. com/science/genetics/articles/22938. aspx [online]