Dissecting Gas Exchange

Question 1

Why must you do the lung dissection with a lab coat?

Answer 1

It will get messy

Question 2

Why shoud your dissecting tool (e.g scapels, dissecting scissors) be all clean , sharp and free from rust?

Answer 2

Blunt tools don’t cut well

Can be dangerous

Question 3

What should you be able to see when first laying the lung on the cutting board?

Answer 3

See the trachea and two bronchi going into the lungs

Question 4

How to practically see the lungs inflate?

Answer 4

1. Attach a piece of rubber tubing to the trachea and pump air into the lungs using foot/bicycle pump
2. Lungs will deflate by themselves because of the elastin in the walls of alveoli

Question 5

Why should you not blow down the tube to inflate the lungs?

Answer 5

You could end up sucking stale air from the lungs into the mouth

Pop the lungs into a clear plastic bag before you start

this stops the bacteria inside the lungs from being released into the room

Question 6

Seeing different tissue types in the lungs

What is the trachea supported by?

Answer 6

C-rings of the cartilage

Question 7

Diagram of a cross-section of trachea

Answer 7

Question 8

How do you practically open up the trachea?

Answer 8

• Since cartilage is tough, open the trachea by cutting it lengthways down the gap in the C-shaped rings
• Use dissecting scissors/scalpel to make the cut
• Continue cutting down one of the bronchi
• Able to see the bronchioles branching off
• Cut off a piece of lung - tissue feel spongy because of air trapped in alveoli

Question 9

Why should you be careful to cut the cartilage in trachea?

Answer 9

• You need to wear goggles to protect your eyes
• If use scalpel cut downwards ( not towards you) and don’t apply too much pressure to the blade

Question 10

What are the safety problems from lungs from butcher?

Answer 10

• It is safe
• But may contain bacteria cause food poisoning
• Wash your hands after dissection and disinfect work surfaces

Question 11

What is the safety procedures for dissecting fish?

Answer 11

• Wear apron or lab coat

Question 12

Where should you place your fish?

Answer 12

In dissection tray or cutting board

Question 13

Practical instructions to dissect fish gills in bony fish

Answer 13

1. Gills located on either side of fish’s head. They are protected by bony flap called operculum and supported by gill arches
2. To remove gills , push back operculum and use scissors to carefully remove gills
3. Cut each gills arch through the bone at the top and bottom
4. You can see the gill filaments

Question 14

What type of insects do you need to use?

Answer 14

• Big insects like grasshopper or cockroaches
• Easier to handle
• Need to use one that is humanely killed fairly recently

Question 15

Instructions to dissecting insect:

Answer 15

1. Fix insect onto dissecting board using dissecting pins to hold legs in place
2. Examine trachea , need to carefully cut and remove piece of exoskeleton (hard outer shell) from along the length of insect’s abdomen
3. Use syringe to fill abdomen with saline solution - seeing network of thin , silvery-grey tubes , these are trachea
4. Examine the trachea under an optical microscope using a temporary mount slide

Question 16

Why in insect they still look silver?

Answer 16

Filled with air

Question 17

What will you be able to see observing trachea under optical microscope?

Answer 17

Trachea appear silver-grey

Rings of chitin in the walls of trachea - support (like rings of cartilage in trachea)

Question 18

Why should you be careful like live insects e.g grasshoppers to be handled carefully?

Answer 18

• They can cause allergic reactions in some people

Question 19

1st ethical issue

Some people think it is morally wrong to kill animals for dissection as it is unnecessary killing

Contradicting point:….

Answer 19

• Many dissections that are carried out in schools involve animals that have already been killed for their meat
  
  • E.G Sheet lung dissection
• Some people disagree with killing animals altogether

Question 20

2nd ethical issue

Concerns using animals for dissections are not raised in a humane way

Answer 20

• Subject to overcrowding , extremes of temperature or lack of food
• May not be killed in a humane way either*
• Animals raised in school for dissection:
  
  • Make sure they are looked after properly and killed humanely to minimise any suffering or distress

Question 21

Explain why she shouldn’t inflate the lungs by blowing into them

Answer 21

She could end up sucking the stale air from the inside of lungs into her mouth

Question 22

Give one another safety precaution the student should take while inflating the lungs

Answer 22

Put the lungs in a plastic bag while inflates them

Prevents the bacteria released into the air

Question 23

Once the lungs are inflated , the student stops pumping air into them. Describe and explain what the student would expect to see next

Answer 23

Lungs deflate by themselves because of the elastin in the walls of alveoli

Question 24

Describe how the student would cut the trachea?

Answer 24

Lengthways , down the gaps in the C-shaped rings of the cartilage

Question 25

How can you make sure your dissecting tools are safe to use?

Answer 25

Check they are sharp and free from rust

clean

Question 26

A student is examining grasshopper trachea under the microscooe

Grasshopper was killed in some time ago and kept in a liquid preservative

Trachea do not appear silver under the microscope

Instead they are dark grey

Suggest why this is the case

Answer 26

Liquid preservative has entered the grasshopper trachea

no longer filled with air

e.g appear silver in colour if they are filled with air

Question 27

The student cuts off a piece of lung tissue and drops in a beaker of water

The lung tissue floats in water

Explain why it floats

Answer 27

Alveoli still contains some air

Question 28

Give on safety precaution the student should take when carrying out this lung dissection

Answer 28

Make sure dissecting tools clean, sharp, free from rust

Carry out dissection on cutting board

Wash hands/disinfect work surfaces after carrying out dissection