studying cells microscopes

Question 1

1. Describe how to produce a scientific
   diagram

Answer 1

No sketched or hanging or crossing lines or shading; It must look similar to the image; must be correctly labelled, without overlapping lines; Correct scale calculated and stated;

Question 2

2. Describe how to measure an object
   using an eyepiece graticule in an optical
   microscope.

Answer 2

Calibrate the graticule using the stage micrometer. Count the number of divisions in the graticule to measure the image. Multiply the number of divisions by the calibrated measurement of each division.

Question 3

3. Give the magnification equation.

Answer 3

Magnification = size of image Size of the real object

Question 4

4. Describe and explain how to prepare a
   specimen for a light microscope.

Answer 4

Slice the specimen very thinly (e.g. single layer of cells) so light can pass through. Add a drop of stain to the specimen to increase contrast between different cellular components. Add the coverslip ensuring there are no air bubbles.

Question 5

5. Give two safety precautions that must
   be taken when cutting specimens

Answer 5

Cut onto a hard surface e.g. a tile Cut away from the body

Question 6

6. Why do you press down lightly on the
   coverslip but not push it sideways

Answer 6

Push down to create a monolayer of cells Do not push sideways as it may roll cells on top of oneanother.

Question 7

7. Describe the principles of a light microscope.

Answer 7

Light microscopes use light transmitted through the specimen to form an image. They have a maximum resolution of 0.2μm (low resolution), this means they are unable to see ribosomes, ER and lysosomes. The maximum magnification is about x1500 (low magnification).

Question 8

8. Give the difference between
   magnification and resolution.

Answer 8

Magnification is how much bigger an image looks compared to the object. Resolution is the shortest distance between two points on a specimen that can still be distinguished as separate by the observer.

Question 9

9. Describe the principles of a
   transmission electron microscope

Answer 9

Transmission electron microscopes (TEM) use a beam of electrons through the specimen to form an image. Electrons don’t pass as easily through denser parts. The image is therefore 2D. They have a high resolution of 0.1nm. The maximum magnification is about x500000. Samples need to be dead, thinly sliced and in a vacuum. The images are black and white.

Question 10

10. Describe the principles of a scanning
    electron microscope.

Answer 10

Scanning electron microscopes (SEM) use a beam of electrons to reflect off the specimen. The electrons are then scattered on to the reciever. The image is then built by a computer to be 3D. They have a high resolution of 0.1nm. The maximum magnification is about x100000. Samples need to be dead. The images are black and white. The images are 3d.

Question 11

11. Contrast how an optical microscope
    and a transmission electron microscope
    work and contrast the limitations of their
    use when studying cells

Answer 11

TEM use electrons and optical use light; TEM allows a greater resolution; So with TEM smaller organelles can be observed and in greater detail; TEM view only dead and optical can view live specimens; TEM does not show colour and optical (can); TEM requires thinner specimens; TEM requires a more complex and time consuming preparation; TEM focuses using magnets and optical uses glass lenses

Question 12

12. An electron microscope can see more
    detail and smaller organelles than a light
    microscope.

Answer 12

Electron microscopes have a much higher resolution than light microscopes, so can distinguish details that are closer together.