Study Sheet

1. Know the parts of the microscope

Eyepiece Lens:the lens at the top that you look through.  They are usually 10X or 15X power. 

Tube:  Connects the eyepiece to the objective lenses

Arm:  Supports the tube and connects it to the base

Base:  The bottom of the microscope, used for support

Illuminator:  A steady light source used in place of a mirror.  If your microscope has a mirror, it is used to reflect light from an external light source up through the bottom of the stage.

Stage:  The flat platform where you place your slides.  Stage clips hold the slides in place.  If your microscope has a mechanical stage, you will be able to move the slide around by turning two knobs.  One moves it left and right, the other moves it up and down.

Revolving Nosepiece or Turret:  This is the part that holds two or more objective lenses and can be rotated to easily change power.

Objective Lenses:  Usually you will find 3 or 4 objective lenses on a microscope.  They almost always consist of 4X, 10X, 40X and 100X powers.  When coupled with a 10X (most common) eyepiece lens, we get total magnifications of 40X (4X times 10X), 100X , 400X and 1000X.  To have good resolution at 1000X, you will need a relatively sophisticated microscope with an Abbe condenser.  

Rack Stop:  This is an adjustment that determines how close the objective lens can get to the slide.  It is set at the factory and keeps students from cranking the high power objective lens down into the slide and breaking things.  You would only need to adjust this if you were using very thin slides and you weren’t able to focus on the specimen at high power. 

Condenser Lens:  The purpose of the condenser lens is to focus the light onto the specimen.  Condenser lenses are most useful at the highest powers (400X and above).  Microscopes with in stage condenser lenses render a sharper image than those with no lens (at 400X).  I

Diaphragm or Iris:Many microscopes have a rotating disk under the stage.  This diaphragm has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide.  There is no set rule regarding which setting to use for a particular power.   Rather, the setting is a function of the transparency of the specimen, the degree of contrast you desire and the particular objective lens in use+

2.  If I give you data about absorbance readings over time for an enzyme experiment, plot the absorbance.  Data will be for the reactions run at different temperatures and/or different pHs. Be above to plot the absorbance of a solution and know which is the optimal pH and temperature.

-Optimal pH and temperatures are those that exemplify consistent changes over time

3.  Know the basics of osmosis and how free water molecules will move into or out of a dialysis tube, based on differences in the concentration of the solution. If I show you the setup for an osmosis experiment, with a beaker filled with a certain % solution, and dialysis bags filled with % solutions, placed into the beakers, you will have to predict whether each dialysis bag will gain weight or lose weight.

-Osmosis: the passing of molecules through a semipermeable membrane from an area of low concentrations of free water molecules to an area of high concentration, thus equalizing everything.

-If the dialysis bag has more % of a solutions than the % in the beaker, the dialysis bag will most likely lose weight

4.  Know the tests for reducing sugars, starch, and proteins and what a positive reaction is for each test.  Understand the difference between a positive test and positive control. In an experiment to test for biomolecules, 5 test tubes will be set up.  Be able to tell me which is the negative control and which is the positive control?

-Glucose and fructose are both reducing sugars

-Benedict’s solution is used to test reducing sugars (turns purple when positive)

-Iodine is a positive test for starches (turns black when positive)

-Biuret’s the test for proteins (turns purple when positive)

-Negative control for carbohydrates is water

-Positive control for carbohydrates is reducing sugar

-Negative control for starches is water

-Positive control for starches is iodine

-Positive controls test to make sure the experiment is going to work; known response is expected

-Negative control is something that is not expected to give a response

5.  Know what homeostasis is, and what buffers do for homeostasis. There are three solutions tested to determine which is the best buffer.  We add acid to each drop by drop, to look at pH change.  You need to determine which solution is the best buffer.  You may need to plot change in pH for the three solutions.

-Homeostasis: The tendency of the body to maintain equilibrium between interdependent elements within its internal environment in the presence of external changes

-Buffers will move the equilibrium in order to oppose the change of pH

6.  If I give you one or two sets of weights, be able to calculate the mean, median, and standard deviation for each of the sets.  Then compare the means and standard deviations and come to some conclusion.

Standard Deviation steps:

– Workout the mean (the average of all numbers added together and divided by the amount of items)

– Then for each number subtract the mean and square the result

– Workout the mean of those squared differences

Take the square root of that and you’re done

7. Know how to calculate the amount of solute to put into a solvent for a % solution and for a molar solution.

8.  Know the definition for acid and for base. 

-Acid: Has a pH of lower than 7; A compound that forms hydrogen ions (H+) in a solution

-Base: Has a pH of higher than 7; A compound that produces hydroxide ions (OH-) in a solution