Cell Organelles

The studies of Robert Hooke 1665 into a plant material would allow the determination of a pore like regular structure surrounded by a wall of which he called 'cells' this in itself unbeknownst to him, was the discovery of the fundamental unit of all living things.

In 1838 a botanist called Schleiden derived the theory 'The basic unit of structure and function of all living organisms is the cell.' Over 150 years later this can be regarded as one of the most familiar and important facts within the biological fields.

Drawing of cork cells published by Robert Hooke 1665

The Cell itself and use of Cytology:

The cell can be thought of as a bag in which the chemistry of life is allowed to occur, partially separated from the environment outside the cell, it exists within all living organisms as its basic structure.

The study of cells is made possible through the use of 'cytology' the preparation of materials for examination through microscopes as an average animal cell exists on a scale of 10 microns roughly one hundredths of a millimetres. Originally light microscopy was used in this field but with the advancement of knowledge scientists were restricted to 200nm magnification, or 2 tenths of a micron. Realising the existence of cell organelles within the cell structure, allowing the function of the cell itself to occur; It was necessary to increase magnification by utilising an alternate source radiation (alternate to light).The result was the electron microscope, whereby the short wavelength and negative charge of electrons when supplied with energy allowed for greater focusing with electromagnetism. This method bends the path of the beam in the manner of a lens to light.

Cell Organelles and the variation between Plant and Animal Cells:

We have already determined the cell to be the foundation to all organisms, however the term cell is associative and categorises a wide variation.

Every animal cell has a specified function whether it be the production of hair, mucus, or the process of other chemicals ( multiple reactions occur within a cell for other purposes i.e. creation of ATP, protein manufacture etc.) So from this we must examine the cell in more detail and determine what it is within the cell that creates it specialised function and separates it as an individual type.

Plant cells vary from animal through the existence of certain organelles.

Organelles are the substances that provide a cell with the ability to produce (a production line) and exist within the cells boundaries.

Typical Animal Cell.(Fig.1)

A plant cell requires a cell wall spanning the perimeter of the cells surface membrane and allocating a more defined form. This wall being rigid in nature embodies the pressure within the cell caused by the contained water (Large central Vacuole non existent within animal cells and surrounded by a Tonoplst membrane controlling the exchange between the vacuole and the cytoplasm.) This prevents the cell from bursting when more water enters through Osmosis. It is also recognised that Plasmodesmata links plant cells to neighbouring plant cells. These are fine strands of cytoplasm which pass through pore like structures in the walls of the neighbour.

Typical Plant Cell.(Fig.2)

Finally the plant cells required for photosynthesis contain chloroplasts these exist within the plastids family of organelles. Chloroplasts are relatively large green organelles that house chlorophyll necessary in collecting and processing sunlight.

Prokaryotes and Eukaryotes:

Eventually it was determined that cells could also be categorised into to two fundamental groups pro, and eukaryotes.

Organisms that lack nuclei are recognised as Prokaryotes ( Pro meaning before and karyote meaning nucleus). These cells all can be regarded as bacteria and exist at a magnification upto 10,000 times smaller than animal cells.

Eukaryote (Eu meaning true) these cells such as plant, animal and fungi all contain the DNA information stored within a nucleus and subsequently contain the ability to divide and replicate.

Organelles within Animal Cell The Nucleus:

The nucleus controls the cell's activities and is the most noticeable organelle in a eukaryotic cell. Division of the nucleus precedes cell division the process in which cells multiply to create tissues, organs, and finally organisms (mitosis, meiosis).

Chromatin is contained within the nucleus this being the loosely coiled form of chromosomes (see later) and these exist within the nuclear plasma, which is contained via the nuclear membrane/envelope.

The Nucleus(Fig.3)

The nuclear plasma is the substance that acts as an atmosphere within the nucleus (similar to the cytoplasm within the cell.) This carries various materials whether it be for transportation to the exterior of the nuclei or just storage.

The nuclear membrane allows for the exchange of substances through pore like openings around its perimeter (nuclear pores) and grants access to these into the opposing cytoplasm.

Chromosomes:

Chromosomes are the carriers of DNA the substance which is eventually organised into genes and furtherly control the specialised function of the cell and its inheritance. DNA is a complex molecule carrier of the information determining cell processes it is associated with histone proteins and can resultantly be called chromatin.

The Nucleolus:

The large body central to the nuclei and used in the production of ribosome's is known as the nucleolus.

The nucleolus is made up of closely formed loops of DNA.

Cytoplasm:

This is the aqueous material , varying in consistency from fluid to jelly-like. The cytoplasm is the unit of containment to all the organelles within the cell and makes up the major part of the cells form.

Ribosomes: