AQA A Level Biology复习笔记3.2.2 Dissecting the Gas Exchange System

• Dissections are a vital part of scientific research
• They allow for the internal structures of organs to be examined so that theories can be made about how they function
• There are ethical concerns surrounding dissections
  • People worry about how the animals for dissections are raised and killed
  • It goes against the religious beliefs of some individuals

   

• The biological specimen used for dissection should be from a reputable source and should be disposed of in the correct manner
• If multiple specimens are being dissected then they should be taken from individual organisms of the same species and roughly the same age

Image showing a heart dissection. The pencil passes through the right ventricle into the right atrium via the tricuspid valve. Remember that just like in diagrams the right ventricle appears on the left side of the heart. You can distinguish between the left and right ventricles also by looking at their size; the left ventricle is much larger than the right.

Apparatus

• Scissors
• Scalpel
• Tweezers / Forceps
• Dissection board
• Paper towels
• Biological specimen
• Pins

Method

• A lab coat, gloves and eye protection should be worn
  • To avoid contamination with biological material (which could cause an allergic reaction)

   

• Place the specimen on the dissecting board
• Use the tools to access the desired structure
  • When using the scalpel cut away from your body and keep your fingers far from the blade to reduce the chance of cutting yourself
  • Scissors can be used for cutting large sections of tissue (cuts do not need to be precise)
  • Scalpel enables finer, more precise cutting and needs to be sharp to ensure this

   

• Use pins to move the other sections of the specimen aside to leave the desired structure exposed

Limitations

• It can be hard to see some of the smaller, finer structures within organs
• The specimens do not reflect how the tissue would look in a living organism
• If only a single specimen is dissected then anomalies found within that specimen may be ignored or glossed over

• The main structures of the gas exchange systems in mammals and fish can be revealed in dissections
• The much smaller gas exchange systems of organisms such as insects can be more difficult to examine by dissection

Mammalian lungs

• The key structures that can be seen from a dissection of mammalian lungs are shown in the image below
  • Trachea
  • Bronchi
  • Bronchioles

   

• The smaller structures such as the alveoli can be hard to distinguish in a dissected lung

Image showing the visible structures of the lungs after dissection.

Bony fish gills

• The key structures that can be seen from a dissection of fish gills are shown in the image below
  • Gill arch
  • Filaments

   

• The smaller structures such as the lamellae can be hard to distinguish in a dissected fish

Image showing the visible structures of the gills after dissection.

Insect tracheal system

• Due to the small size of insect tracheal systems specialised equipment and skills are sometimes required to dissect them
• Microscopes are also needed to observe the structures