Basic Components of Living Systems

2.1. Microscopy

Cell Theory:

(1) All living things are made up of cells

(2) Cells are basic units of structure

(3) Cells only develop from existing cells

• Cells contain and pass on hereditary information during cell division
• All cells are relatively the same in relation to chemical composition and metabolic activity

How light travels through a microscope:

Light from bulb/mirror -> Condenser lens focuses the light onto the specimen -> Light passes through specimen and objective lens -> Objective lens contributes the most to enhancing detail -> Lights travels through the objective lens, through the body piece to the eyepiece lens -> Eyepiece lens magnifies the image made by the objective lens -> Light from specimen enters eye.

Sample Preparation:

• Dry mount - used to view solid specimens. They are sectioned and placed in the centre of the slide, with a cover slip placed over the sample. E.g. hair, pollen and muscle tissue.
• Wet mount - the specimen is suspended in a liquid such as water or an immersion oil. A cover slip is placed on top at an angle. E.g. aquatic samples and living organisms. 
• Squash slides - a wet mount is prepared, then a lens tissue is used to gently press down the cover slip. To avoid damage, the sample can be squashed between two slides. E.g. root tips.
• Smear slides - the edge of a slide is used to smear the sample, creating a thin, even coating on another slide. A cover slip is then placed on the sample. E.g. blood. 

Using staining:

Stains increase contrast as different components within a cell take on stains to different degrees. This increase, in contrast, allows components to become visible so they can be identified. 

• To prepare a sample for staining it is first placed on a slide and allowed to air dry.
• This is then heat-fixed by passing through a flame.
• The specimen will adhere to the microscope slide and will then take up stains. 

Differential staining - can distinguish between two types of organisms that would otherwise be hard to identify. Can also differentiate between different organelles of a single organism within a tissue sample. E.g. gram stain technique ad acid-fast technique. 

Stages in the production of slides:

1.   Fixing – chemicals are used to preserve the specimen to keep it as close to a natural state as possible

2.   Sectioning – specimens dehydrated with alcohols and then placed in a mould with wax. This can be sliced thinly with a knife called microtome.

3.   Staining – specimens are stained with multiple chemicals to sow different structures 

4.   Mounting – the specimen is then put on a microscope slide and a cover slip is put on top.

Many of the chemicals used to stain are toxic/irritants.

2.2. Magnification and calibration

Magnification = how many…