Welcome to WHAT BIOLOGISTS DO. These five page contain information on the science behind how biologists know what they know. From microscopes to DNA sequencing, scientists have technologies to measure and analyse almost anything they want. Each technique, however, can only give certain types of information and only by using lots of different methods can we know things for certain.
WHAT BIOLOGISTS DO
Fun fact: The famous book and film 'Gulliver's Travels' was likely inspired by some of the pictures Robert drew
Imaging = producing an exact picture of something by scanning or detecting it
Resolution = the smallest distance between two spots that can be seen through a microscope
Scanning electron microscopy = imaging the surface of something by shooting a concentrated beams of electrons at it
Fluorescent microscopy = imaging samples by using fluorescent LED or laser illumination in different colours
Fluorescent tag/label = something fluorescent that you chemically stick to the thing you want to look at
LOOKING AT THINGS
Almost every lab will have some kind of microscope, and they come in all different shapes and sizes.
Cells were discovered through the use of one of the first microscopes ever built (see if you can spot it from the lineup above). Robert Hooke (1635-1703) was looking at cork down this microscope and saw lots of tiny boxes filling the whole material that looked like the small rooms that monks live in called cells (maybe today more people would think of a prison cell).
A page from Robert's book 'Micrographia' shows what he saw down the microscope when he discovered cells. Before the invention of the camera, scientists would look down microscopes and draw what they saw. Many scientists were pretty artistic and books like Micrographia were published with amazingly detailed drawings of tiny things like insects.
Since the invention of the microscope, there have been huge advancements in the technology of microscopy, or as it is commonly called 'imaging'. Now we don't have to look at cells as blurry small boxes as microscopes have the resolution to see things that are much smaller than a cell. The latest Guinness World Record for the highest resolution microscope was in June 2018 with a microscope that can see things that are 0.039 nanometers apart! Check out this video from the World Science Festival that puts 1 nanometer into perspective:
Microscopy means looking at things not only with visible light but with scanning probes that feel the surface of things (like electron beams). These different technologies give very different-looking images, have different resolutions and can be used for different samples.
Scanning electron microscope image of the surface of a corn plant leaf made by Louisa Howard at Dartmouth college
Fluorescent microscopy image of the 46 human chromosomes made by Hesed Padilla-Nash and Thomas Ried at the NIGMS Image Gallery
Samples that you want to look at under a microscope can be anything from a whole animal (like a fly), a bit of an animal (like the eye of a mouse) to cells themselves. The type of sample you are looking at will be important when you decide what kind of microscope to use, and of course what you are looking for will also be important!
Fluorescent microscopy makes colourful images which show the location of things you are looking for in cells. To do this, you need to label the thing you want to see with a fluorescent tag to make it glow under the microscope.
These pictures are of developing sperm in the testes of a Drosophila (fly). Fluorescent tags were added to 2 different proteins, so you can see 2 different colours. The green tag was added to a protein called Mozart. Mozart is a fairly newly discovered protein - and before this experiment we didn't know what it did. When Mozart is removed in flies the males are less fertile whilst females are not affected. This picture was taken to try to understand if Mozart is doing something important in sperm development in the fly. By labelling Mozart as well as another protein that we know plays a specific role in sperm development, we can infer Mozart's role because it is found in the same location.
Live imaging / making a time-lapse = taking a photo at certain time intervals (e.g. every second) to create a video
Quantitative = measuring something in a way to get numbers e.g. "it was 10 decibels louder as measured by a sound level meter" rather than "it sounded louder"
Image analysis = turning pictures into meaningful information by quantification
Microscopes are not only used to take images, but videos too! This is called live imaging and the videos are often called time-lapses. Videos are not only cool to look at but also give a dynamic view instead of a snapshot of whats happening.
This is an amazing time-lapse of a salamander growing from just a single cell - made by Jan van IJken
Imaging is cool, but scientists love numbers as well as pictures. Numbers, or quantitative results make it easier for scientists to share their results and compare what they've found. It's possible to get numbers from images (or quantify images) by using image analysis. Image analysis is something you can do on your computer and can be anything from measuring how bright a pixel is to tracking moving objects and telling you their speed.
Example of how image analysis might be used. Two different drugs are given to some cells. The cells are then coloured using a fluorescent dye for DNA and dead cells. Image analysis can count the number of cells that are blue and red. A table of numbers makes it much easier to say for certain what effect the drugs are having, and to share with other scientists to see if they get the same results.