Cells and Microscopes

Cells are the fundamental units of life, making up all organisms.
Each cell is enclosed by a cell membrane which controls what enters and leaves the cell.
The interior of the cell is filled with cytoplasm, a jelly-like substance where the cell’s metabolic reactions occur.
Within the cytoplasm lies the nucleus, the control centre of the cell which contains the genetic material (DNA).
Some cells also contain organelles, specialised structures that perform various functions such as energy production (mitochondria) or protein synthesis (ribosomes).

There are two main types of cells: prokaryotes and eukaryotes.
Prokaryotic cells, like bacteria, are simpler and smaller. They do not have a nucleus, but instead a circular DNA molecule that floats freely in the cytoplasm.
Eukaryotic cells, found in animals, plants and fungi, are larger and more complex. They have a nucleus and other organelles, all surrounded by membranes.

Most organisms start life as a single cell, then grow and develop by cell division.
Over time, these cells specialise and become differentiated, taking on specific roles within the organism.
For example, some cells may become nerve cells, others might become muscle cells, and so on.

Cells are typically too small to see with the naked eye, so we use microscopes to study them.
A basic light microscope works by passing light through a specimen, and uses lenses to magnify the image.
More advanced microscopes like the electron microscope use a beam of electrons instead of light. These can magnify objects much more, allowing us to see the structure of cells in much greater detail.
When preparing a sample to be observed under a microscope, a thin slice of the specimen is often required. This is to allow the light or electron beam to pass through.
The image seen under the microscope is often enhanced or colourised, as cell components can look very similar and hard to distinguish under a natural view.

Staining is a technique used to enhance contrast in micrograph images, making features of the cell more visible.
Use of fluorescent dyes and UV light in fluorescence microscopy allows specific structures within the cell to be highlighted.
Transmission electron microscopy (TEM) provides highly detailed images of ultra-thin sections of cells, revealing internal structures.
Scanning electron microscopy (SEM) visualises the surface of specimens, giving a 3D view of the cell. However, it cannot provide information about the internal structure of cells.