Practical Skills

Rennin and Cheese making- an old practicum Example of enzymes Rennin (AKA Rennet, chymosin) – Enzyme found in the stomachs of young mammals Rennin’s substrate is casein (protein found in milk) Video - Cheese making

Lab Practical Skills In papers 21 and 31 (esp. 31), you will be expected to demonstrate mastery of collecting, organizing, and displaying data Plotting points Creating a table Measuring Drawing

Plotting points Independent var.: x-axis Variable being manipulated (ex: temperature, concentration, pH) Dependent (response) var.: y-axis Variable being measured (ex: reaction rate, products formed) D I

Plotting points (see Link here) Always plot points with a small x or small dot inscribed in a circle Always connect data points with a ruler Different data sets should use different points OR different lines (solid, dashed, dotted)

Creating a table ALWAYS USE A RULER!!! Tables should be drawn in pen only Units go on column headings First column = always independent

Units of Measurement Kilometer (km) 103 Meter (m) 1 Centimeter (cm) 10-2 Millimeter (mm) 10-3 Micrometer (µm) 10-6 Nanometer (nm) 10-9 Picometer (pm) 10-12

Units of measurement Important for measuring cells! BIG to SMALL: decimal to the right SMALL to BIG: decimal to the left 1. Convert 10 μm to mm 2. Convert 10 µm to nm

We will cover this in more detail in Chapter 1! Drawing – Cells We will cover this in more detail in Chapter 1!

Drawing different tissues: Drawing Cells Do’s Don’ts pencil only Clear, continuous lines Accurate proportions Tissues completely enclosed by lines Label all tissues Correctly identified parts Representative portions or cells Scale bar Shading Textbook versions Individual cells on low power Nucleus as a solid blob on high power Drawing different tissues: Shape, Size, and Shading

Visualizing Animal and Plant Cells Every plant and animal cell is surrounded by a very thin cell surface membrane (aka plasma membrane) All have a nucleus which is very large and stains very darkly (especially chromatin) The nucleolus located within the nucleus stains even more deeply (variable amount, can be ~1-5)

Visualizing Animal and Plant Cells The most numerous organelles seen with light microscopes are usually mitochondria (single mitochondrion) Golgi apparatus can only be seen with silver containing stains

Plant Cells Only Usually larger than animal cells All surrounded by cell wall Linked to neighboring cells by plasmodesmata (single plasmodesma)

Plant Cells Only Large central vacuole, surrounded by tonoplast Chloroplasts: show grana (single granum) at high magnification

I=observed size of the image Light Microscopes There is a limit to how much can be seen w/light Magnification is the number of times larger an image is, compared with the real size of the object. 𝒎𝒂𝒈𝒏𝒊𝒇𝒊𝒄𝒂𝒕𝒊𝒐𝒏= 𝒐𝒃𝒔𝒆𝒓𝒗𝒆𝒅 𝒔𝒊𝒛𝒆 𝒐𝒇 𝒕𝒉𝒆 𝒊𝒎𝒂𝒈𝒆 𝒂𝒄𝒕𝒖𝒂𝒍 𝒔𝒊𝒛𝒆 Or 𝑴= 𝑰 𝑨 I=observed size of the image A= actual size

Magnification I M × A

Check Your Understanding This length of the displayed lymphocyte is 36mm. The actual length of the lymphocyte is 6µm. What is the magnification?

Check Your Understanding This length of the displayed lymphocyte is 36mm. The actual length of the lymphocyte is 6µm. What is the magnification? 1.) Convert mm → µm 2.) Use the equation 𝑴= 𝑰 𝑨 to calculate magnification (M=magnification, I= image size, A=actual size)

Check Your Understanding This length of the displayed lymphocyte is 36mm. The actual length of the lymphocyte is 6µm. What is the magnification? 1.) Convert mm → µm 𝟑𝟔𝒎𝒎=𝟑𝟔×𝟏𝟎𝟎𝟎𝝁𝒎=𝟑𝟔,𝟎𝟎𝟎𝝁𝒎 2.) Use the equation 𝑴= 𝑰 𝑨 to calculate magnification (M=magnification, I= image size, A=actual size) 𝑴= 𝟑𝟔,𝟎𝟎𝟎𝝁𝒎 𝟔𝝁𝒎 = 6000 x 𝑀=×6,000

Measuring Cells

Measuring Cells Cells and organelles can be measured with a microscope by means of an eyepiece graticule This is a transparent scale with 100 divisions that is placed in the eyepiece so it can be seen at the same time and the sample on the slide

Using an eyepiece graticule This figure shows the scale over a human cheek epithelial cell. The cell lies between 40 and 60 on the scale, therefore we say it measures 20 eyepiece units in diameter We will not know the actual size of the cell until the eyepiece graticule scale is calibrated

Calibrating an eyepiece graticule scale What is the value of 1 epu? To calibrate the eypiece graticule scale, a miniature transparent ruler called a stage micrometer scale is placed on the microscope stage and is brought into focus This scale may be etched onto a glass slide or printed on transparent film It commonly has subdivisions of 0.1 and 0.01 mm The images can then be super imposed to calibrate the graticule 8 cm ?? cm

Complete the Calibration problem and paste in notebook!

Calibrating an eyepiece graticule scale In the eyepiece graticule shown, 100 units measure 0.25 mm. Hence, the value of each eyepiece unit is 0.25 100 =0.0025 mm. Converting mm to µm: 0.0025𝑚𝑚× 1000𝑚𝑚 1𝜇𝑚 =𝟐.𝟓𝝁𝒎 for each epu

Calibrating an eyepiece graticule scale The diameter of the cell measures 20 eyepiece units, so the actual diameter is 20×2.5𝜇𝑚=50𝜇𝑚

Find the size of the nucleus

Nucleus measures 10 eyepiece units (from 40 to 50) In the eyepiece graticule shown, 100 units measure .25mm. Hence, the value of each eyepiece unit is 0.25 100 =0.0025 mm. The diameter of the nucleus measures 10 eyepiece units, so the actual diameter is 𝟏𝟎 𝐞𝐩𝐮×0.0025 mm= 0.025 mm 𝟎.𝟎𝟐𝟓 𝐦𝐦 𝒙 𝟏𝟎𝟎𝟎= 𝟐𝟓𝝁𝒎

Solution Distance between X and Y is approximately 27 eyepiece units (epu) 27 units x 0.0025 mm = 0.0675 mm 0.0675 mm x 1000 = 67.5 𝝁𝒎