3A - Dissecting gas exchange systems Flashcards
What gaseous exchange systems in animals can we dissect?
Lungs, gills, insects.
Describe the procedure to dissect lungs
Wear a lab coat.
Make sure the dissecting tools (scalpels, scissors etc.) are clean, sharp and free from rust.
Lay the lungs on a cutting board - you should be able to see the trachea and 2 bronchi going into the lungs.
To see the lungs inflate, attach a piece of rubber tubing to the trachea and pump air into the lungs using a foot or bicycle pump. The lungs will deflate by themselves because of the elastin in the walls of the alveoli.
Examine the tissue: The trachea is supported by C-shaped rings of cartilage. which is tough so if you want to open it up, cut it lengthwise, down the gap in the ring.
Continue cutting down one of the bronchi so you can see the bronchioles branching off.
Cut off a piece of lung - it will feel spongy because of the air trapped in the alveoli.
Afterwards, wash hands and disinfect work surfaces to get rid of the bacteria that could cause food poisoning.
Describe the procedure to dissect fish gills in bony fish
Wear a lab coat/apron.
Place fish is a dissection tray/on a cutting board.
Gills are located on either side of the fish’s head, protected by a bony flap on each side called an operculum and supported by gill arches.
To remove the gills, push back the operculum and use scissors to carefully remove the gills. Cut each gill arch through the bone at the top and bottom.
If you look closely, you should be able to see the gill filaments.
Describe the procedure to dissect an insect
Fix insect to a dissecting board using dissecting pins through its legs.
To examine the tracheae, you need to carefully cut and remove a piece of exoskeleton from along the length of the insect’s abdomen.
Use a syringe to fill the abdomen with saline solution. You should be able to see a network of very thin, silvery-grey tubes (the tracheae). They look silver as they are filled with air.
You can examine the tracheae under an optical microscope using a temporary mount slide. Again, the tracheae will appear silver or grey. You should also be able to see rings of chitin in the walls of the tracheae which provide support (like the rings of cartilage in the human trachea).
What are some ethical issues associated with dissecting animals?
Some people argue that it is morally wrong to kill animals just for dissections as it is unnecessary killing. However, most dissections involve animals that have already been killed for their meat.
There are concerns that the animals used for dissections are not always raised in a humane way - they may be subject to overcrowding, extremes of temperature or lack of food - and they may not be killed humanely either. (If insects are raised in schools for dissection, it is important to make sure they are looked after properly and killed humanely to minimise any suffering or distress).
Why is it important that dissecting tools are sharp?
As blunt tools don’t cut well and can be dangerous.
