Essay Paper Assignment Help-Biology

Microscope, Cells, & the Cell Cycle Lab

Objectives:

Identify and describe the function of the main parts of the microscope.

Describe the proper use and care for the microscope.

Describe the relationship between magnification, field of view, and resolution.

Draw and label cellular structures observed under the microscope.

Compare the size and identify key structures of various cell types, including prokaryotic and eukaryotic cells.

Background:

Microscopes are designed to make objects visible that are too difficult or too small to see with the human eye.  All types of scientists use microscopes.  Different kinds of microscopes are designed to visualize various magnifications and types of specimens.

This week’s lab will introduce you to the compound microscope, and give you an opportunity to use this type of microscope to observe various cell types up close (we’ll use a virtual one!).  As we are also learning about cell structure, be sure to look to your notes to help you identify organelles and other cell structures, when applicable.

There are 3 parts to today’s lab:  Part 1 introduces you to the parts and associated functions of the microscope, Part 2 gets you using the virtual microscope by looking at slides, and Part 3 has you looking at mitotically dividing cells under the virtual microscope. 

For all parts of today’s lab, you will be using NC Community Colleges BioNetwork’s interactive Virtual Microscope.  It will take a few moments to load at first, so be patient and give your computer time to completely load before you start. 

Part 1: Microscope Basics

In Part 1 of today’s lab, the goal is to familiarize yourself with the parts of the microscope and how to care for the microscope. 

Click on the “Guide” button along the bottom of the screen. Read and click through the ‘chapters’ from the Introduction to Microscope Care. All of the ‘chapters’ except the Introduction are made up of several pages that you need to click through (e.g., the Overview page has 12 short pages for you to read and click through). Take notes and answer the numbered questions below.You do not need to upload your notes for this assignment.

  1. Define the function for each of the following parts of the microscope:

Arm, Base, & Body of the Microscope

Coarse Focus Knob

Fine Focus Knob

Diaphragm

Eyepiece

Objectives

Immersion Oil Lens

Immersion Oil

Lens Paper/Tissue

Nosepiece

On/Off Switch

Stage

Condenser Lens

  • Define the following terms:

field of view

micrometer

paracentered

parfocal

resolution

When you are finished, click the “Close” button at the top, right of the reference guide.

Click on the “Learn” button along the bottom of the screen. NOTE: There are 4 pages to this interactive click-through. Be sure to complete and answer all the questions below before moving on to the next page as you will NOT be able to go back.

The microscope presented on the first screen is very similar to the microscopes we have in our labs at CCSF.  You will need to click through all the 16 different parts before moving on to the next part of this “Learn” module.  As you work through these microscope parts, be sure to complete the following before moving on:

Compare your notes from the previous section with what you read about here. Include any information that you might have missed from the last section. You do not need to upload your notes for this assignment. Answer the numbered questions below.

  • Define the function for each of the following items:

Stage Adjustment Knob

KimWipes

Slides

  • Identify where the parts of the microscope are located (click on them to see).  List the parts of the microscope where the path of light goes through, from the illuminator (located right under the stage) to when it reaches your eye, in order.

You will next go through the various lenses of the microscope.  The eyepiece, scanning (4x, red), low power (10x, yellow), high power (40x, blue), and oil immersion (100x, white) lenses all have a nosepiece thread, color band, and magnification listed on the objective. As you click through each of these lenses, answer the following numbered questions:

  • What is a useful feature of each lens?:

eyepiece

scanning

low power

high power

immersion oil

Click “Main” at the bottom left of the lens window to return to the main page. Then click “Explore” to move to the next section.

You will next see how the differentlenses can magnify specimens.  Click the ? to open the slide box and then click on Animal Slides and Spider Leg to view that slide. Bring the specimen into focus at 4X using the course focus, fine focus and light adjustment. Then, answer the numbered questions below.

  • Draw the specimen at 4X.

Select the 10X objective, and make the necessary adjustments to bring the specimen into focus.

  • Draw your specimen at 10X.

Select the 40X objective, and make the necessary adjustments to bring the specimen into focus.

  • Draw your specimen at 40X.

Select the 100X objective, and make the necessary adjustments to bring the specimen into focus.

  • What additional steps did you need to take to use the 100X objective? (HINT: The tools you need are indicated by a ? mark in the image.)
  1. Draw your specimen at 100X.
  1. Did you try using the coarse adjustment while looking through the 100X objective? What happened? If you didn’t try it, try it now and record what happens.

Put your slide away and clean the microscope.

Next, let’s calculate the magnifications we just viewed. 

  1. At CCSF, our eyepieces are 10x.  If we were looking through our 4x, 10x, 40x, and 100x objectives, what would the total magnification be for each?

The equation is total magnification = objective magnification x eyepiece magnification

            4X total magnification

            10X total magnification

            40X total magnification

            100X total magnification

Click “Main” at the bottom left of the lens window to return to the main page.

OPTIONAL: Click “Test” to test your understanding of what you’ve learned so far.

Part 2: Observing Specimens Under the Microscope

You should now have a good understanding of the various microscope parts and their functions, as well as how to care for the microscope.  In Part 2 of today’s lab, we will learn how to use the microscope.

Generally, here are the steps of using a “real” microscope:

Getting started

Plug in and turn on light source (lamp);

Clip slide you want to observe on the stage and center it over the light;

Raise the stage with the coarse focus as far as it can go.

Initial focus

ALWAYS start with the short scanning lens (4x objective);

Turn the coarse focus down until the image is clear (I suggest even turning it even a bit further than this and then back again to find the sharpest image possible);

Re-center the slide and adjust the light (including the diaphragm) if needed.

Higher magnification

Watching from the side, rotate to the low power lens (10x objective) SLOWLY (so lens DOES NOT hit the slide – if it looks like it will hit, then STOP and start over from the steps under initial focus);

Sharpen image with the fine focus; the coarse focus may not be necessary;

Re-center slide and adjust the light if needed;

Repeat for high power lens (40x objective). The coarse focus should not be used at 40X or above.

Oli immersion lens

If a higher magnification is necessary, rotate the oil immersion lens almost into the place. BEFORE clicking the oil immersion lens into place, however, place a drop of oil directly on top of the center of your slide;

SLOWLY slide your oil immersion lens into place, making sure that the lens does not hit the slide as before.  Once in place, the lens should be in the oil itself;

Sharpen image with the fine focusonly;

Once done, be sure to clean the slide and lens with lens paper.

Ok, are you ready?  Let’s finally look at some slides!

Click on the “Explore” button along the bottom of the screen.  Click to open the slide box and notice all the choices of specimens that you can look at.  As you observe specimens today, follow these general guidelines:

Label your drawings.  Whenever you make a drawing from what you see in a microscope, always include the name of the specimen, label any visible structures, and include the total magnification.

Take note of the size of your drawing.  Your drawings should always be about ~7cm (almost 3 inches) in length and in width so that you can provide enough detail in what you are observing.  Use the provided Microscope & Cells Lab Assignment sheet to guide you on your drawings if needed.

Find the sharpest image possible.  Always try to find the clearest image using the coarse focus first, and then the fine focus.

Always start at the 4x objective.  This compound microscope is parfocal.  So, always remember to focus as well as you can at the 4x objective first.  If you do this correctly, as you move higher in magnification, all you will need to do is to toggle the fine focus and light.  Never use the coarse focus on high magnification and never skip an objective (don’t jump from 4X to 40X, for example).

  1. There are 5 specimens that I want you to draw today (listed below). Draw the 5 specimens at the magnification indicated and answer the related questions. Remember to label your drawings as indicated above (specimen name, label structures, total magnification).


The letter “e” (in the ‘Sample Slides’ deck) 10x.  As you increase in magnification, can you see less or more of the letter “e”?

Plant cells (in the ‘Plant Slides’ deck) at 40x.  Be sure to label the nucleus, chloroplasts, cytoplasm, cell wall, and cell membrane.

Stratified Squamous Epithelium (in the ‘Human Slides’ deck) at 40x.  Be sure to label the visible cell structures here.  How are these cells similar and different from the plant cells?

Gram Stain Mix (in the Bacteria Slides’ deck) at 40x AND 100x (2 drawings).  Label the rod-shaped bacteria (Bacillus subtilis) from the cocci (round)-shaped bacteria (Neisseria subflava).  At which magnification is it easier to distinguish the bacteria’s shape?  How are these cells different from the eukaryotic cells you just observed?

One more additional slide of your choice in the ‘Human Slidesdeck.  Look through the different slides that are available to you to look at.  Pick one to view and draw – be sure to use an appropriate magnification and label any structures that you can identify.  How are these cells different from the squamous epithelium cells you observed above?

Part 3: Observing Mitosis Under the Microscope

Mitosis is the process in which somatic (non-sex) cells divide.  Since the main purpose of mitosis is for growth and repair, the resulting cells that are produced (known as daughter cells) through mitosis are exactly the same as the original (parent) cell.  Think about it:  If your body needs to repair and replace the skin cells on your finger after a papercut, mitosis will enable your body to produce the same type of skin cells to maintain its original function. 

Similarly, mitosis occurs in other organisms besides us.  In plants, a common place where we would see mitotic growth is at the onion root tip:  Cells are constantly dividing in this region as the root elongates and moves deeper into the soil.  In Part 3 of today’s lab, you will observe the various stages of mitosis at an onion root tip.  Please have your book and notes on mitosis to help you identify the various stages under the microscope.  

After clicking on the “Explore” button of the Virtual Microscope, click on the box of slides and go into the ‘Plant Slides’ deck.  From here, click on the Onion Root Tip slide and use the microscope to focus up to the 40x objective (starting with 4X, of course!).  After scanning this field of view, complete the following:

  1. Draw a representative onion root tip cell in interphase. Repeat this for a cell in prophase, metaphase, and anaphase.  You should have a total of 4 cell drawings.  For each drawing, label any structures you can identify (nuclear membrane, chromosomes, spindle fibers, cell wall). Write down a brief description of what is happening in each of your cells above (e.g., the chromosomes are aligned along the center of the cell). Don’t forget to label each of your drawings with a specimen name, label structures, and total magnification.

interphase

prophase

metaphase

anaphase

  1. Next, look at the Whitefish Metaphase slide (in the ‘Animal Slides’ deck) at 40x.  Identify a cell(s) in interphase, prophase, metaphase, and anaphase?  You can click and drag on the specimen to move it around in the field of view.

interphase

prophase

metaphase

anaphase

  1. How are these dividing cells different and/or similar to the dividing cells in the onion root tip?
  1. You were not able to see a clear image of telophase and cytokinesis in these slides.  How is this stage of mitosis different in a plant cell versus an animal cell?
  1. Below is another image of the onion root tip cell from a different microscope slide. Indicate that you can identify cells in interphase, prophase, metaphase, anaphase, and telophase by drawing an arrow to each with a label.

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