Whilst we may take specific notice to particular regions and functions of our bodies when analysing fitness and health we must not forget the basis of all life. Our human bodies are made up of millions of living cells, and at a basic platform form the basis of life. It is interesting to take a look at the construction of a generalised cell.

Structure of the plasma membrane
The plasma membrane is essentially the outer layer of a cell, which both separates two types of fluid, and helps house the organelles inside the cell structure.

Its body- according to the fluid mosaic model- consists of a double layer structure which contains both lipid molecules and the larger protein molecules.

Protein molecules consists of peripheral proteins (attached head facing outward), integral proteins (attached head facing inward) and glycoproteins. The remaining structure of the bi-layer (double layer) is mainly fabricated of phospholipids, with cholesterol and glycolipids making up the remaining structure.

The phospholipids have a stem with a round shaped head – and are water loving (hydrophilic), with the tail being opposed and non water loving. The head is charged while the tail is not. Due to the tails not liking water they will face inward of the plasma membrane to avoid fluid both sides.

The plasma membrane has finger like extensions named microvilli which enlarge the size of the plasma membrane and are primarily found in absorptive cells such as intestinal and kidney tubule cells.

How materials move across the plasma membrane
The plasma membrane is very selective as to which substances are allowed entry into the cell, selecting only what is required and blocking the unwanted. It will also dispose of waste products.

Primarily materials move across the plasma membrane in two ways: passively or actively.

In the passive process substances do not require an energy source from the cell to cross the plasma membrane. The passive process is produced by either diffusion- primarily, and filtration. Alternatively the active process requires energy in the form of Adenosine Triphosphate (ATP) from the cell to allow it to cross the plasma membrane.

Diffusion involves the spread of substances (Ions) from a concentrated area to a more non-concentrated area, done so on an evenly spread basis.

Filtration will involve the transport of water or solutes by using pressure to move from a high-pressure area to a low-pressure area.

Structure and functions of major organelles of a generalised cell
A cell consists of various units of workers termed organelles, which exist in the watery internal environment called the cytoplasm.

There will be some organelles which will not have membranes, such as cytoskeleton and ribosomes, although most organelles are housed by a membrane similar to that of the plasma membrane. It is vital that the appropriate organelles are packaged by a membrane so that enzymes can be used and stored in the applicable areas.

Mitochondria
Mitochondria are the powerhouse of a cell providing the majority of ATP. They are long and sausage like in structure, and regularly changing shape by elongating and shortening. The mitochondria has a double layered membrane, with the outside membrane being smooth and featureless in structure, and the inside version folding inwards creating shelf like crests. The mitochondria have their own DNA, separate to that of the cells nucleus.

The amount of mitochondria in a cell will reflect the energy requirements of that particular cell- busy cells like kidney, liver and of course muscle are plentiful of mitochondria.

The primary role of mitochondria is to convert organic materials into cellular energy in the form of ATP, however mitochondria also plays a part in many metabolic tasks, such as apoptosis- programmed cell death, glutamate- mediated exitotoxin neuronal injury, cellular proliferation, regulation of cellular redox state, heme synthesis and steroid synthesis. The way in which ATP is produced by mitochondria is by oxidating the two main players in glycolysis: pyruvate and NADH . The internal enzymes of the mitochondria process the oxidative reactions of cellular respiration.

Ribosomes
Ribosomes area structured with two subunit of RNA and proteins, which come together like an acorn. Ribosomes may move around freely, or can be attached to part of a separate organelle called the (rough) endoplasmic reticulum. Ribosomes can also be found inside mitochondria.

The role of ribosomes is to facilitate protein synthesis. Free ribosomes which are moving freely throughout the cytoplasm on the inside of a cell make soluble proteins, whilst membrane bound ribosomes role is to synthesise proteins for either placement in cell membranes, or exportation from the cell.

Endoplasmic Reticulum
Endoplasmic reticulum is a united formation of tubular like membranes with fluid filled cavities that curls and twists through the cells internal fluid. Endoplasmic reticulum is divided into two separate formats: rough and smooth variations. Endoplasmic reticulum is joined to the nucleus membrane of a generalised cell.

The roles of endoplasmic reticulum vary from its rough to smooth area.

Rough endoplasmic reticulum is the site of attached ribosomes, and as such these ribosomes manufacture all proteins secreted by cells. Rough endoplasmic reticulum is also the manufacture of membranes due to integral proteins and phospholipids being stationed there.

Smooth endoplasmic reticulum does not contain ribosomes and does not play a role in proteins syntheses, however it has an important role in metabolic functions, such as: lipid metabolism, cholesterol syntheses, syntheses of steroid based hormones, processing of fats and detoxification of drugs.

Golgi apparatus
Golgi apparatus are a group of stacked and flattened membranous sacs known as cristernae, along with associated small membranous vesicles which are spherical in shape.

The role of Golgi apparatus is a demonstration as to how truly marvellous the processes are within biological life forms.

Golgi apparatus main job is to sort and package different macromolecules required for life by receiving small vesicles from the rough endoplasmic reticulum, making the required adjustments, and then sending out in three types of vesicles (Excocytotic, Secretory and Lysosomal) from the Trans face to various locations for usage. Golgi apparatus is also responsible for producing Lysosomes.

Lysosomes
The structure of a Lysosome consists of a membranous and spherical like organelle.

With so much action going on in a cell there is a requirement for an organelle which cleans out and digests worn out organelles, as well as food particles, viruses and unwanted bacteria, and such is the job of Lysosomes.

Peroxisomes
Peroxisomes consist of a double layered membrane organelle which helps store proteins vital for transportation across a cell, and separates its contents from the cytosol.

Peroxisomes role is to clean a cell of toxic substances by neutralising free radicals. Peroxisomes work in a way that the more you need them, the more they work.

Cytoskeleton
Cytoskeleton is effectively the scaffolding (like human bone skeleton) structure which holds are protects the cell and its organelles.

There are three types of cytoskeleton: microfilament, intermediate filament and microtubule. Microfilaments are the thinnest rods on the cytoskeleton structure, with intermediate filaments the second largest, and microtubule being the largest.

Role of the nucleus as the cells control centre
The cell nucleus is the control centre of a cell, likewise to that of the brain of a human body. The cell nucleus is primarily made up of three regions: the nuclear envelope, nucleoli and chromatin.

The nuclear envelope is similar in structure to that of the mitochondrial membrane in that it has a double layered membrane. Both layers can fold onto each other to form pours, which distribute substances into the cytoplasm for organelle distribution.

The nucleoli are spherical shaped bodies that lie inside the wall of the nucleus. Usually there will be one nucleoli, but some cells will have multiple amounts. Nucleoli are the site where ribosomal subunits are assembled. These subunits will leave the nucleus through pours placed in the nuclear envelope.

Chromatin consists of bumpy threads which weave their way through the nucleoplasm. Chromatin is made of 30% DNA, 60% globular histone proteins and about 10% RNA chains.