Required Practical: Dissecting Mass Transport Systems (AQA A Level Biology): Revision Note

Required practical: dissection of mass transport system

• It is possible to dissect parts of organisms, e.g. the heart, to better understand form and function

• Dissecting the mammalian heart allows us to observe chambers, valves, and associated vessels

Safety

• Wear a lab coat, gloves, and eye protection to prevent contamination with biological material

• Use dissection tools safely, e.g.:

  • cut away from the body

  • keep fingers away from blades

Apparatus

• Dissection board

• Scalpel

• Dissecting scissors

• Forceps / tweezers

• Pins

• Mounted needle

• Biological specimen, e.g. pig or sheep heart

• Disinfectant and disposal container

Dissection method

1. Place the specimen on a dissection board with the front facing upwards

   • The front of the heart can be identified by the location of the coronary arteries, which cross the front of the heart between the left and right ventricles as shown in the image above

2. Observe external features that are visible, e.g.:

   • coronary arteries

   • fatty deposits

   • left and right atria; these are small flaps at the top of the heart

   • some of the major blood vessels, e.g. aorta, pulmonary artery

3. Make two vertical cuts through the centre of the left and right ventricles and atria

   • This may be easier to accomplish using scissors than a scalpel

4. Use forceps, fingers or a mounted needle to gently open out the muscle tissue

5. Pin back the outer sides of the ventricles to expose internal features

6. Identify the following internal structures:

   • left and right ventricle walls; you should be able to compare the muscle thickness

   • the thin muscle walls of the atria

   • the septum

   • atrioventricular valves

   • the entrances to the major blood vessels

Limitations

• Dead tissue may not accurately reflect the appearance or flexibility of living organs, e.g.:

  • sometimes the atria and blood vessels are removed during the butchering process

  • older tissue, or tissue that has been frozen, may become dry or stiffened

• Smaller structures, such as valve flaps, may be difficult to locate

• Dissecting only one specimen may limit the reliability of observations

Ethical considerations

• Specimens should always come from reputable sources

• Biological waste must be disposed of responsibly

• Some students may have ethical concerns about animal use, or religious beliefs that may prevent participation in a dissection practical