OCR AS Biology

Revision Notes

1.2.3 Practical: Dissection of Gas Exchange Surfaces in Fish & Insects

Practical: Dissection of Gas Exchange Surfaces in Fish & Insects

The safe use of instruments for the dissection of an animal or plant organ

  • Dissections are a vital part of scientific research
  • They allow for the internal structures of organisms and organs to be examined so that theories can be made about how they function
    • For example, dissections can be performed on fish to expose and study their gills (the gas exchange surface in fish) or on insects to expose and study their spiracles, tracheae and tracheoles (the gas exchange system in insects)
  • 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
  • Safety is a priority when conducting dissection experiments with sharp tools like scalpels and scissors
  • The method below outlines some precautions that should be taken in the interest of safety

Apparatus

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

Method

  • A lab coat, gloves and eye protection should be worn
    • This is done 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 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
  • Dissection instruments (scissors and scalpel) should be sharp to give good clean cuts with as little damage as possible – blunt instruments are dangerous (as more force is required to cut) and will not give precise cuts making internal structures harder to distinguish

Exam 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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