mircoscope

Question 1

Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure.

Answer 1

iples:

1. Electrons pass through / enter (thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;

Principles:

Allow maximum of 3 marks

Limitations:

5. Cannot look at living material / Must be in a vacuum;
6. Specimen must be (very) thin;
7. Artefacts present;
8. Complex staining method / complex / long preparation time;
9. Image not in 3D / only 2D images produced.

Question 2

The student cut a thin section of the tissue. Explain why it was important that the section was thin.

Answer 2

Need a single layer of cells / only a few cells thick / not too many layers / detail obscured by cells underneath;

Light must be able to pass through;