Equipment;
Method of dissection;
There are a few safety issues in this experiment;
It is important to cut away from your body so that you do not cut yourself
It is also important to wear safety googles to prevent locust bodily fluids entering the eyes.
- Scalpel
- Scissors
- Tweezers
- Pins
- Light Microscope
- Monocular microscope
- Watch glass
- Slide
- A dead locust
Method of dissection;
- Fix a dead adult locust to the stage of a monocular microscope and examine the abdominal and thoracic spiracles more closely.
- Record the location of the spiracles on a simple outline sketch or digital photograph for future reference. Place the dead locust in its normal resting position in the centre of a cork board.
- Fix it by means of pins through the legs and thorax.
- Cut off the wings if they get in the way.
- Pull back the tip of the abdomen with forceps, stretching it slightly, and insert a pin to hold it back and down.
- Cut down between the segments on one side and then continue the incision forward to the head along the dotted line shown. As you cut, let the lower blade of your scissors pull the locust up slightly. Make a similar cut on the other side and carefully remove the strip of exoskeleton from the animal so that you can see the organs inside.
- Flood the dissection with water.
- Examine the many silver threads (tracheae) and the associated organs with the aid of a monocular microscope and a light microscope. Pull the mid-gut upwards gently and look at the air-filled tracheae from the side.
There are a few safety issues in this experiment;
It is important to cut away from your body so that you do not cut yourself
It is also important to wear safety googles to prevent locust bodily fluids entering the eyes.
The Respiratory system The picture on the right shows the trachae in the insect with the walls structured with chitin. The chitin forms a spiracle shape which maintains its structure if it is stretched by the insect. Insects have very irregular pattern of gas exchange, with their spiracles opening and closing seemingly randomly. There have been a few hypotheses put forward to explain this phenomenon. To reduce water loss from the insect is one such example. Resources used; http://www.nuffieldfoundation.org/practical-biology/dissection-ventilation-system-locust Edexcel AS Biology B book 1 pub. 2015 Ann Fullick pages 232-233 |