Links to GCSE: Structure of animal & plant cells Using a microscope

Hooke’s compound microscope

Hooke’s view of cork

Generalised (a) plant cell and (b) animal cell as seen under the light Week 1 Generalised (a) plant cell and (b) animal cell as seen under the light microscope © Pearson Education Ltd 2008 This document may have been altered from the original

Standard light microscope

Answers!

Using the light microscope 1: To carry the microscope grasp the microscopes arm with one hand. Place your other hand under the base. 2. Place the microscope on a table with the arm toward you. 3. Turn the coarse adjustment knob to raise the body tube. 4. Revolve the nosepiece until the low-power objective lens clicks into place. 5. Adjust the diaphragm. While looking through the eyepiece, also adjust the mirror until you see a bright white circle of light. 6. Place a slide on the stage. Center the specimen over the opening on the stage. Use the stage clips to hold the slide in place. 7. Look at the stage from the side. Carefully turn the coarse adjustment knob to lower the body tube until the low power objective almost touches the slide. 8. Looking through the eyepiece, VERY SLOWLY the coarse adjustment knob until the specimen comes into focus. 9. To switch to the high power objective lens, look at the microscope from the side. CAREFULLY revolve the nosepiece until the high-power objective lens clicks into place. Make sure the lens does not hit the slide. 10. Looking through the eyepiece, turn the fine adjustment knob until the specimen comes into focus.

Cross sectioning: Longitudinal: cut along the long axis of a structure. The opposite of a cross section. Transverse: cut perpendicular to the longitudinal axis

Images of specimens seen under the light microscope

Explain the difference between magnification and resolution. Week 1 State the resolution and magnification that can be achieved by a light microscope. Explain the difference between magnification and resolution. Explain the need for staining samples in light microscopy. © Pearson Education Ltd 2008 This document may have been altered from the original

Key definitions Magnification: the degree to which the size of an image is larger than the object itself. Numerically, it is the image size divided by the actual size of the object, measured using the same units. It is usually expressed as x10, x1.5. Resolution: is the degree to which it is possible to distinguish between 2 objects that are very close together. The higher the resolution the greater the detail that can be seen

Low resolution image

High resolution image

Andromeda at low resolution

Andromeda at high resolution

Week 1 Calculate the linear magnification of an image such as a photomicrograph or electron micrograph. © Pearson Education Ltd 2008 This document may have been altered from the original

Units of measurement Unit Symbol Equivalent in metres Fraction of a metre Metre m 1 One Decimetre dm 0.1 One tenth Centimetre cm 0.01 One hundredth Millimetre mm 0.001 One thousandth Micrometre µm 0.000 001 One millionth nanometre nm 0.000 000 001 One thousand millionth

Key definitions: A micrometre is equal to one millionth of a metre (10ˉ6) and is the standard unit for measuring cell dimensions. A nanometre is one thousandth of a micrometre (10ˉ3). It is therefore a thousand millionth of a metre (10ˉ9). It is useful for measuring the sizes of organelles within cells and large molecules

Limits of resolution Human eye: 100µm Light microscope 200nm Electron microscope 0.20nm

Week 1 Eyepiece graticule and stage micrometer at (a) x40 magnification and (b) x100 magnification Please note that magnification sizes are subject to variation on different screens © Pearson Education Ltd 2008 This document may have been altered from the original

Calibrating the eyepiece graticule A microscopic ruler on a slide (stage micrometer) is placed on the microscope stage. This ruler is 1mm long and divided into 100 divisions. Each division is 0.01mm OR 10 µm. With a x4 objective lens and x10 eyepiece (magnification x40), 40 epu (eyepiece units) = 1mm (1000 µm). Therefore 1 epu = 1000/ 40 = 25µm. With a x10 objective lens (magnification x100) 100 epu = 1000 µm. So 1 epu = 10µm.

An amoeba seen under a light microscope; (a) with a x10 objective Week 1 An amoeba seen under a light microscope; (a) with a x10 objective (b) with a x40 objective Please note that magnification sizes are subject to variation on different screens © Pearson Education Ltd 2008 This document may have been altered from the original

Magnification of eyepiece lens Magnification of objective lens Total magnification Value of one eyepiece division/µm X 10 X 4 X 40 25 X 100 10 X 400 2.5 X 100 (oil immersion) X 1000 1.0

Worked example In figure 1a the length on the nucleus is 3.2 epu At X100 magnification, one epu = 10µm We have 3.2 all worth 10µm So the length of this nucleus is 32.0µm In figure 1b the length of the nucleus is 13 epu At X 400 magnification, one epu = 2.5 µm So the length of this nucleus is 32.5 µm

IMA triangle Week 1 © Pearson Education Ltd 2008 This document may have been altered from the original

Calculations of actual size from magnification given Week 1 Calculations of actual size from magnification given Please note that magnification sizes are subject to variation on different screens © Pearson Education Ltd 2008 This document may have been altered from the original

Explain the need for staining samples for use in electron microscopy. Week 1 State the resolution and magnification that can be achieved with the electron microscope. Explain the need for staining samples for use in electron microscopy. © Pearson Education Ltd 2008 This document may have been altered from the original

Transmission electron micrograph

Electron microscope in outline Week 1 Electron microscope in outline © Pearson Education Ltd 2008 This document may have been altered from the original

Electron Microscopes Transmission Scanning

Advantages & disadvantages of electron microscopes Resolution is 0.1nm (2000x more than LM) Produces detailed images of internal cell organelles SEM produces 3D images Electron beams are deflected by molecules in the air, samples are placed in a vacuum Expensive Operators are highly skilled and trained

Comparing LM to EM Both allow us to see a magnified image of a small object Both use a radiation beam focused using lenses to generate an image LM are easier to use, portable and can be used to observe living specimens EM need training and skill to prepare specimens, and it has to be placed in a vacuum. It is not possible to observe living specimens It is not possible to see colours of an EM EM has much greater resolution and give greater magnification with a clear image

Images of specimens seen under a scanning electron microscope

Topic outcomes revisited State the resolution and magnification that can be achieved by a light microscope. Explain the difference between magnification and resolution. Explain the need for staining samples in light microscopy. Calculate the linear magnification of an image such as a photomicrograph or electron micrograph. State the resolution and magnification that can be achieved with the electron microscope. Explain the need for staining samples for use in electron microscopy.