A2.2 Cell Theory & Microscopy

Cryogenic Microscopy

Is used in researching the structure of proteins. Analyses proteins at the instant moment in time when they freeze. Reconstructs its 3D shape.

Freeze-Fracture Microscopy

Is used to produce images of surfaces within cells. It rapid freezes cells and the subsequent fracturing allows the cell to be broken along the lines of weakness, including the centre of membranes.

Immunofluorescence

Uses antibodies equipped with fluorescent markers to bind to specific targets and produce fluorescent images.

Metal Staining

Dense tissue absorbs electrons and appears darker; less dense tissue allows electrons to pass and appears lighter.

Scanning Electron Microscope (SEM)

Scans the outside of a sample to create a 3D image of surface shape and texture. It has a lower resolution and magnification than TEM. Samples must be stained and fixed by using harsh chemicals, otherwise, images produced are only black and white. Samples are killed in the process of the shooting of electrons. Electrons are reflected off the surface of the specimen.

Transmission Electron Microscope (TEM)

Shoots electrons straight through a thin sample to show inner details and creates a 2D image. It has a much higher resolution than SEM. Image produced is black and white, so sample material is stained using heavy metal ions.

Resolution

The ability to distinguish between two objects very close together, limited by the wavelength of the radiation source.

Light Microscope Advantages

It is cheap; images can be viewed directly and often don't need harsh sample preparation. Samples can be alive and specimens are often naturally coloured.

Electron Microscope Advantages

High resolution and high magnification; it allows for 3D viewing of the specimen. Has a greater depth of field and allows very small sample sizes to be viewed. The samples can be biological or nonbiological.

Methylene Blue

A positively charged dye that binds to negatively charged DNA/RNA to visualize genetic material or the nucleus.

Eyepiece Graticule

A transparent scale embedded in the eyepiece lens, superimposed on an object for measurement.

Stage Micrometer

Used to calibrate eyepiece graticules, featuring minor divisions of 0.01 mm and major divisions of 0.1 mm.

First Pillar of Cell Theory

All living organisms consist of cells (multicellular or unicellular). Multicellular organisms have a number of specialised cells.

Second Pillar of Cell Theory

Cells are the smallest unit of life. Cell components cannot survive alone. Organelles carry out various metabolic functions in the cell.

Third Pillar of Cell Theory

Cells arise from pre-existing cells. Cells multiply from division. All cells descended from simpler common ancestors.

Light Microscope

Doesn’t have very high resolution and only allows cells or bigger structures to be visualised. Uses the wavelength of light to view the specimen. It has a convex lens that focuses light on to the specimen. Cells observed are alive and show their natural composition, colours, movement and appearance.

Cell Membrane

Thin and has a partially permeable layer of phospholipids. It controls the entry and exit of substances. It pumps substances in and out by active transport. It is made out of lipids and proteins. It also acts as a barrier and protects the inner components of a cell.

Genetic Material

Is in the form of DNA, is the hereditary set of information, which holds coded instructions for all the building blocks required by a cell. It can be located inside the nucleus or freely in the cytoplasm of cells (Eg. bacteria).

Cytoplasm

Allows the dissolution of substances in the cells. It is important for all types of biochemical reactions to occur. It is important because it allows the transport of materials within a cell.