Dissecting the Gas Exchange System (AQA A Level Biology): Revision Note

Dissection of a gas exchange system

• Gas exchange system structure can be examined during dissection

• Dissection involves the use of equipment such as:

  • scalpel: a sharp blade used for precise cutting

  • dissecting scissors: small, sharp scissors used for lower-precision tasks or separating layers of tissue

  • tweezers/forceps: useful for manipulating the specimen during dissection

  • dissecting pins: may be useful for pinning sections of a specimen in place while working

• Care should be taken during dissection practical work, including:

  • safety, e.g.:

    • a lab coat, gloves and eye protection should be worn to avoid contamination with biological material

    • sharp, clean blades should be used for ease and accuracy of cutting

    • scalpel blades should cut away from the body

    • fingers should be kept away from blade edges

  • responsible use of biological materials

    • Any biological specimen used for dissection should be from a reputable source and should be disposed of in the correct manner

Dissecting mammalian lungs

• The key structures that can be seen during a dissection of mammalian lungs include:

  • trachea, supported by c-shaped rings of cartilage

    • Scissors may be needed to cut through the tough cartilage of the trachea

  • bronchi branching into each lung

  • bronchioles

• Smaller structures, such as the alveoli, can be hard to distinguish in a dissected lung, though the 'spongy' texture of lung tissue indicates that lungs contain many air-filled sacs

Dissecting bony fish gills

• The gills of a fish are located on either side of the head, beneath a bony flap known as the operculum

• The key structures that can be seen with the eye during a dissection of fish gills include:

  • the gill arch; this can be cut to remove the gill from the fish

  • the gill filaments, which have a feathery appearance

• The lamellae are too small to view by eye but can be examined under a microscope

Dissecting an insect tracheal system

• It is possible to dissect large insects, such as grasshoppers, in the classroom as follows:

  • attach insect to a dissecting board using pins

  • cut the exoskeleton along the length of the abdomen

  • add a saline solution to the abdomen to highlight the location of the tracheae, which will show as silvery tubes

• Tracheae can be removed and viewed under a microscope