Practical: Dissection of Gas Exchange Surfaces in Fish & Insects (OCR AS Biology)

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Practical: Dissection of Gas Exchange Surfaces in Fish & Insects

  • 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

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)
    • A scalpel enable 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

Dissection of gas exchange surfaces

  • 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

Gas exchange under the microscope

  • The gas exchange surfaces of different organisms can be observed using microscopes
  • They often appear very different in photomicrographs than they do in the diagrams found in textbooks
  • It is important to be able to identify the gas exchange surface and the key structures present

Mammal gas exchange

  • A section of stained lung tissue can be seen in the image below
  • The alveoli are of different sizes and shapes
    • This is because they are no longer inflated as they would be in a living lung

  • The nuclei are shown as dark dots
  • Blood vessels can found in between the alveoli
  • Sometimes white blood cells are present in tissue samples

Alveoli Photomicrograph, downloadable AS & A Level Biology revision notes

Image showing a section of stained lung tissue

Fish

  • A section of stained fish gills taken from a dogfish are shown in the image below
  • The gill arch resembles a backbone for the gills
  • The different filaments are shown with many of the lamellae visible

Fish Gills Photomicrograph, downloadable AS & A Level Biology revision notes

Image showing a section of fish gills taken from a dogfish

Insect

  • As insects are very small obtaining a clear image of their gas exchange system can be difficult
  • Electron microscopes can take clear images of the spiracle structures found on the surface of insects, like the one shown below

Spiracle Electronmicrograph, downloadable AS & A Level Biology revision notes

Image showing a spiracle found in the wall of a caterpillar

Examiner Tip

You may be asked to suggest a method of dissection for a particular organ. Make sure you name the specific tools (e.g. scissors and forceps) that should be used in order to get the marks.

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Lára

Author: Lára

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.