dissections Flashcards
what must you wear during a lung dissection
a lab coat
describe dissecting tools
scalpels, dissecting scissors
they should all be clean, sharp and free from rust
blunt tools do not cut well and could be dangerous
when you lay your lungs down onto the cutting board what should u see first
the trachea and the two bronchi going into the lungs
how do we see the lungs inflate
attach a peice of rubber tubing into the trachea and punp air into the lungs using a foot or bicycle pump
the lungs will deflate by themselves because of the elastin in the walls of the alveoli
why should we never blow down the tube to inflate the lungs
you could end up sucking up stale air from inside the lungs into your mouth
pop the lungs in a clear plastic bag before you start to stop bacteria inside the lungs from being released into the room
when do we start to examine the different tissue types in the lungs
when the lungs have inflated
describe how we open up the trachea
cut the cartliage lengthways, down the gap in the c-shaped rings.
use dissecting scissors or a scalpel to make the cut.
if using a scalpel cut downwards and dont apply too much pressure to the blade
why does the tissue feel spongy when u cut off a piece of the lung
the tissue will feel spongy because of the air trapped in all the alveoli
describe where the gills are located on the fish head
the gills are located on either side of the fish head.
they’re protected on each side by a bony flap called an operculum and supported by gill arches
how do we dissect the gills
to remove the gills, push back the operculum and use scissors to carefully remove the gills.
cut each gill arch through the bone at the top and the bottom
if you look closely you will see the gill filaments
what types of insects are best for dissecting
big insects like grasshoppers are cockroaches are usually best for dissecting because they are easier to handle
for dissection, u need to use an insect thats been humanely killed fairly recently
describe how to perform a dissection on an insect
place insect on dissecting board and put dissecting pins through its legs to hold it in place
to examine the tracheae, cut and remove a piece of exoskeleton from along the length of the insects abdomen
use a syringe to fill the abdomen with saline solution. you should be able to see a network of tracheae
they look silvery because they are filled with air
how can we examine the trachea
under an optical microscope using a temporary mount slide
again, the trachea will appear silver or grey.
you should also be able to see rings of chitin in the walls of the tracheae- these are there for support
ethical issues involved in dissecting animals
its morally wrong to kill animals just for dissections, as its unnecessary killing
however many dissections involve animals that have already been killed for their meat
animals used for dissections are not always raised in a humane way
describe gas exchange in plants
When the guard cells are turgid (full of water) the stoma remains open allowing air to enter the leaf
The air spaces within the spongy mesophyll layer allows carbon dioxide to rapidly diffuse into cells
The carbon dioxide is quickly used up in photosynthesis by cells containing chloroplasts - maintaining the concentration gradient
No active ventilation is required as the thinness of the plant tissues and the presence of stomata helps to create a short diffusion pathway
how to prepare a slide with a liquid specimen
Add a few drops of the sample to the slide using a pipette
Cover the liquid/smear with a coverslip and gently press down to remove air bubbles
Wear gloves to ensure there is no cross-contamination of foreign cells
Preparing a slide using a solid specimen:
Use scissors to cut a small sample of the tissue
Peel away or cut a very thin layer of cells from the tissue sample to be placed on the slide (using a scalpel or forceps)
Some tissue samples need be treated with chemicals to kill/make the tissue rigid
Gently place a coverslip on top and press down to remove any air bubbles
A stain may be required to make the structures visible depending on the type of tissue being examined
Take care when using sharp objects and wear gloves to prevent the stain from dying your skin
why do we always start with the lowest objective lens when using an optical microscope
It is easier to find what you are looking for in the field of view
This helps to prevent damage to the lens or coverslip incase the stage has been raised too high
how do we prevent the dehydration of tissue
Adding a drop of water to the specimen (beneath the coverslip) can prevent the cells from being damaged by dehydration
how do we get rid of unclear or blurry images
Switch to the lower power objective lens and try using the coarse focus to get a clearer image
Consider whether the specimen sample is thin enough for light to pass through to see the structures clearly
There could be cross-contamination with foreign cells or bodies
how do we use an eyepiece graticule on an optical microscope
As a graticule has no fixed units it must be calibrated for the objective lens that is in use.
This is done by using a scale engraved on a microscope slide (a stage micrometer)
By using the two scales together the number of micrometers each graticule unit is worth can be worked out
After this is known the graticule can be used as a ruler in the field of view
describe the mamalian gas exchange system under the optical microscope
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
what do we expect to see when viewing fish under the optical microscope
The gill arch resembles a backbone for the gills
The different filaments are shown with many of the lamellae visible
