PAG 2: Dissection

Question 1

Health and safety:

Answer 1

● Take care when using the sharp dissecting instruments.

● Wear non-latex gloves to protect hands from harmful chemicals (e.g. disinfectant) and
potentially harmful bacteria

● Wear goggles to protect eyes from harmful chemicals

● Wear an apron

● Dispose of waste responsibly and safely

Question 2

Heart dissection - external examination

Answer 2

2. Place your fingers inside the 4 chambers to feel the differences in the thicknesses of
   the walls. Identify the left and right atria, and left and right ventricles (the left will be
   thicker than the right, and the ventricles will be thicker than the atria). Do not make
   any cuts at this stage.
3. Identify the four main vessels attached to the heart. Arteries are thick and rubbery, whereas veins are thinner.
4. Identify the coronary artery on the external surface. Locate where the coronary artery connects to the aorta.
5. Draw a sketch of the external structure and label it.

Question 3

Internal examination of heart:

Answer 3

6. Using a clean scalpel, carefully cut along lines to look inside the left ventricle, and
   use scissors to cut through the wall of the left atrium. Follow the cut down to the apex
   of the left ventricle.
7. Open up the left atrium and left ventricle to examine them. Look for tendinous cords
   (heart strings), observe how they are attached to the atrioventricular valve.
8. Look at the atrioventricular (AV) and semilunar (SL) valves. The AV valve has
   two flaps so is called the bicuspid valve. The SL valve has a half-moon shape, hence
   its name.
9. Make a similar cut down the right side of the heart to open up the right atrium and
   ventricle. Examine the wall and internal structures.
10. Look for the AV valve on this side. It has three flaps so is called the tricuspid valve.
    Look for the SL valve.
11. Use a ruler to measure the thicknesses of the walls of the left and right ventricles and
    atria.
12. Draw a scientific annotated drawing to show all the identified structures. Include
    detail about each structure beside each label (see PAG1 – drawings for how to draw a
    scientific drawing).

Question 4

Plant dissection:

Answer 4

1. On a white tile, use a scalpel to cut a cross-section of a stem. Cut the sections as
   perpendicular to the length of the stem as possible and as thinly as possible.
2. Use tweezers to gently place the transverse sections in tap water for 2 minutes (or
   until it’s time to use them). This stops them from drying out.
3. Set up the microscope as shown in PAG 1.
4. Use tweezers to lift the sections of stem into a watch glass containing a stain (such as
   toluidine blue) and leave them in the stain for 1 minute.
5. Use tweezers to transfer the sections back into tap water to rinse off excess stain.
6. Place a transverse section on a microscope slide, add a drop of water and a coverslip.
   Repeat for the three thinnest transverse sections.
7. View under light microscope under the lowest magnification (x4 objective lens) (see
   PAG 1 for how to use a microscope).
8. Position so you can clearly see a variety of structures and draw an annotated scientific
   diagram (see PAG 1).
9. View under a higher magnification (x10 objective lens) and find the clearest view of
   one vascular bundle.
10. Produce an annotated scientific diagram.
11. You could repeat these steps to view a longitudinal section as well.

Question 5

What can be seen using Toluidine blue stain:

Answer 5

● Phloem – red
● Xylem – green/blue-green
● Sclerenchyma – blue-green/sometimes green
● Collenchyma – red-purple
● Parenchyma – red-purple