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An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail.
An electron microscope has much higher magnification and resolving power than a light microscope. This means that it can be used to study cells in much finer detail.
Why are microscopes so important? What if they weren't invented?
Why are microscopes so important? What if they weren't invented?
Overview of mini topic - Cell theory and Discovery
Overview of mini topic - Cell theory and Discovery
Study the following tasks at your own pace in class and at home. Your teacher will guide you through the activities as well.
- Task 1.1 Using a microscope - Learn how use a light microscope correctly and calculate magnifications (40 mins)
- Task 1.2 Learn the differences between light and electron microscopes (20 mins)
- Task 1.3 Learn how to calculate cell sizes and convert units (40 mins)
- Retrieval Practice - revisit the work again in one week and then in a month. Complete: Recall questions, Exam questions, Test each other, Write a summary... (Retrieval practice is such an effective revision technique because it requires you to recall previously learnt knowledge, which creates stronger memory traces). Doing it more than once helps you to remember.
Task 1.1 Using a microscope (40 mins)
Task 1.1 Using a microscope (40 mins)
LO: Use a light microscope correctly and calculate total magnification.
LO: Use a light microscope correctly and calculate total magnification.
Close your eyes and picture a brick wall. What is the basic building block of that wall? A single brick, of course. Like a brick wall, your body is composed of basic building blocks, and the building blocks of your body are cells.
Your body has many kinds of cells, each specialised for a specific purpose. Just as a home is made from a variety of building materials, the human body is constructed from many cell types. For example, epithelial cells protect the surface of the body and cover the organs and body cavities within. Bone cells help to support and protect the body. Cells of the immune system fight invading bacteria. Additionally, blood and blood cells carry nutrients and oxygen throughout the body while removing carbon dioxide. Each of these cell types plays a vital role during the growth, development, and day-to-day maintenance of the body.
Attribution: “Introduction ” from Unit 2: The Cell by OpenStax College, Biology, CC BY 3.0
Microscopy practical (30 mins) - Observing plant and animal cells
Microscopy practical (30 mins) - Observing plant and animal cells
In this experiment, you are going to use a light microscope to observe, draw, and label a selection of plant and animal cells and include a scaled magnification.
Before you start, watch the video tutorial and then follow the visual method so that you can carry it out successfully. You need to draw what you can see clearly. Drawings should be labelled with the specimen name and magnification.
Attribution: CC-BY-NC-SA 4.0 @LouiseCass @BiologyRachProject ; www.biologycorner.com Thank you:)
Task 1.2 Light & electron microscopes (20 mins)
Task 1.2 Light & electron microscopes (20 mins)
LO: Describe the advantages and disadvantages of using a light and an electron microscope.
LO: Describe the advantages and disadvantages of using a light and an electron microscope.
Introduction video
Introduction video
Light microscope
Light microscope
Electron microscope
Electron microscope
Read about the history
Read about the history
Leeuwenhoek's early microscope was called a simple microscope because it only used one lens. This kind of simple microscope was much like a magnifying glass that you might use to look at an insect or picture. This way of looking at things is limited and is what enticed people to create the compound microscope, which uses more lenses. The word Microscope is the combination of two words; "micro" meaning small and "scope" meaning view.
Leeuwenhoek was not the first person to build a microscope, but the microscopes that he did build were the best ones for that time period. Leeuwenhoek was the first person to describe bacteria and helped to prove the theory of blood circulation. He gained much of his inspiration from reading Robert Hooke's book, Micrographia. Hooke was the person who discovered and named cells.
Questions to answer
Questions to answer
1. What does ‘micro’ and ‘scope’ mean?
2. What was Leeuwenhoek famous for?
3. What was Robert Hooke famous for?
Light vs Electron microscopes
Light vs Electron microscopes
Cells are too small to be seen with the naked eye. Instead microscopes have to be used.
The first light microscopes were made in the 17th century. They use a beam of light to form an image of an object and can only reach magnifications of x2000. They are relatively cheap, easy to use and can magnify live specimens. The invention of electron microscopes in the 1930’s allowed scientists to see cells in more detail and discover new sub cellular structures.
Electron microscopes have a higher magnification and resolution. They use a beam of electrons and can magnify up to 2 000 000. Electron microscopes are large, very expensive, have to be kept in special conditions and cannot use live specimens. Resolution is the ability to distinguish between two objects as separate points. Magnification of a light microscope can be calculated very easily.
Total magnification = eyepiece lens magnification x objective lens magnification
Questions to answer
Questions to answer
4. Describe how a light microscope works.
5. Describe how an electron microscope works.
6. Evaluate the advantages and disadvantages of an electron microscope vs. a light microscope (6 marks). Include the terms magnification and resolution (for help use the slideshow).
7. Look carefully at the images of the objects below to get the idea of what can be seen by the naked eye, a light microscope, and an electron microscope.
8. Then play with Cell Size & Scale Animation.
Image: Studying cells by OpenStax College, Biology, CC BY 3.0 https://cnx.org/contents/GFy_h8cu@9.87:pOpVdIwp@11/Prokaryotic-Cells
Task 1.3 Calculating cell size (40 mins)
Task 1.3 Calculating cell size (40 mins)
LO: Use the formula: magnification = image size / real size of object
LO: Use the formula: magnification = image size / real size of object
Teacher explanations
Teacher explanations
Learn how to carry out calculations based on magnification.
There are rarely many opportunities in your biology exam where you will be able to use a formula to calculate an answer. The magnification equation however is one of those times, it is relatively easy to use. The Equation as well as the rearrangements are as follows;
- magnification = image size / real size
- image size = magnification x real size
- real size = image size / magnification
The main area that you need to focus on when using the above equations is ensure that both the image size and real size magnitudes are both in the same units. For example if a question asks for the object size in micrometres, you need to ensure that the image size you input into the equation is also in micrometres. This is the most common mistake seen in all magnification equation type questions.
Attribution: @teamscience
When studying, you should try to work it out on your own first and then discuss with your partner so that you really get it. Do as many examples as you can to build your confidence in being able to use the equations and converting the units.
B1.1 Explain - How to calculate cell sizesWorked examples
Worked examples
B1.1 AIM calculations SLOP.docxPractice calculations 1
Practice calculations 1
B1.1 AIM calculations SLOP answers.pdfAnswers
Answers
B1.1 Calculating cell magnification from images.docxPractice calculations 2
Practice calculations 2
Attribution: GCSE Biology Mastery Booklet, @CommonBrewer @Mr_Badham @BioRachProject Thank you:)
Retrieval practice (20-30 mins)
Retrieval practice (20-30 mins)
Retrieval practice is the act of retrieving something from your memory (often with the help of a cue).
What does the evidence tell us?
Recent research has shown that retrieval is critical for robust, durable, long-term learning. Every time a memory is retrieved, that memory becomes more accessible in the future. Retrieval also helps us create coherent and integrated mental representations of complex concepts, the kind of deep learning necessary to solve new problems and draw new inferences.
Recall 1 - Techniques for using a light microscope (10 mins)
Recall 1 - Techniques for using a light microscope (10 mins)
- Why does the tissue sample need to be stained before looking at it under the microscope?
- Which objective lens should we start using?
- What is the function of the diaphragm of the light microscope?
- Which focus knob should be used during low and medium power magnification?
- Which focus knob should be used during high power magnification?
- Why must we not use the coarse focus knob during high power magnification?
- It is acceptable to draw sketchy and feathery lines for biological drawing. True or false?
- Biological drawings must always be labelled. True or false?
- Biological drawings must occupy at least half the size of the space provided. True or false?
- Colouring and shading is allowed in biological drawings. True or false?
- What is the function of a scale bar?
*Check your answers on the slideshow.
Recall 2 - Calculations and units (10 mins)
Recall 2 - Calculations and units (10 mins)
Microscopy
What is magnification?
How do you calculate magnification?
How do you convert mm to μm?
How do you convert μm to mm?
What is the advantage of an electron microscope?
Exam Questions - Calculations (10 mins)
Exam Questions - Calculations (10 mins)
Reference: Retrieval practice https://teacherhead.com/2019/03/03/10-techniques-for-retrieval-practice/
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