The purpose of this dissection is to revise the theory behind tissues and apply it to actual tissues.
Investigation: Knowing more about tissues – Dissection of animal tissue
The aim of this dissection is for you to revise the theory behind tissues and apply your knowledge to actual tissues.
You will be working in pairs. Instructions for this activity will be written in italics.
- At the end of the practical you should:
- Know and be able to use dissecting instruments correctly, especially insertion and removal of blades.
- Be able to recognise and use ether responsibly
- Be familiar with apparatus: petri dish, dissecting tray.
- Use a scale: zero (calibrate) and record mass
- Perform simple mathematical calculations: percentage
- Be able to read a vernier calliper.
- Clean and dry thoroughly and appropriately.
- 1 piece filter paper
- dissecting tray
- petri dish
- chicken wing
- 1 ml Ether
- roller towel
Before you begin, look at the external appearance of the chicken wing.
Weigh the entire wing and record its mass in the table on the last page.
- Insert the scalpel blade onto the handle.
- Lie the wing upside down on the dissecting board.
- Cut with scissors from the severed end towards the wingtip along the midline of the wing.
- Remove as much of the skin as you can by freeing it from the underlying tissue with a blunt instrument or pulling with your fingers.
- Carefully observe the tissue that you are breaking.
- Is skin a tissue or an organ?
- Why is there a ‘web’ of skin between the joints?
- What are the ‘bumps’ on the skin?
- How easily does the skin come off between the joints?
- Where is the skin most firmly attached?
- Record the mass of the skin in a table as shown on the last page.
- Skin is an organ.
- To increase the surface area for the attachment of feathers and to help hold them together.
- The bumps are feather follicles.
- Easily – it is loosely attached on the muscle between the joints.
- At the joints.
- Optional – You can record mass if scales are available.
2. Connective tissue
The skin is held to the underlying pink tissue by a type of connective tissue.
Name this particular type of connective tissue.
Give two adjectives that accurately describe it.
- Areolar connective tissue.
- Soft, flexible, thin, elastic, transparent.
3. Fatty tissue
Look at the underside of the skin you have removed. You should see clumps of yellow material. This is fat, or adipose tissue. It is also a type of connective tissue.
Take a small amount of this fatty tissue and squash it gently in a small beaker with some ether.
- Pour some of this solution onto a piece of filter paper.
- Dry the filter paper by waving it in the air.
This oily stain is known as a translucent stain.
- From now on collect all the fatty material you find — you will need it later (place in a separate beaker).
What do you think the function of connective tissue is here?
What do you notice? There is an oily stain on the paper after the ether has evaporated.
- To store reserve food in the form of lipids and to insulate the body against heat loss.
- There is an oily stain on the paper after the either has evaporated, indicating that this substance is fat.
Muscle is the pinky-orange tissue you can see under the skin. The muscles were most likely severed when the chicken was dismembered in the butchery. Muscles are all arranged in ‘antagonistic pairs’. In an antagonistic pair, the action of one muscle (e.g. contraction) causes the opposite action to occur in the paired muscle (flexion).
Hold the wing in your left hand.
- Grip the end of one of the muscles with forceps. Pull it.
Describe what happens and name the type of action it caused.
Let go and pull various other muscles.
Can you get one to cause the opposite movement?
Carefully dissect out a single muscle in FULL. Remove it from the wing completely.
What type of tissue lies between the muscles?
- Draw the wing muscle.
- You need to follow the convention of drawing diagrams by:
- providing a heading or title.
- adding labels (tendon, muscle, epimysium, fat tissue).
- labelling on the right hand side of the diagram.
- providing a scale bar.
- When the upper muscle is pulled, the wing flexes / bends at the elbow. When the lower muscle is pulled, the wing straightens.
5. Blood vessels
The smallest vessels you will be able to see are small arteries (arterioles) and small veins (venules). Capillaries are the very smallest blood vessels — so narrow in fact that erythrocytes can only fit through in single file. It is ONLY between these vessels and the surrounding tissues where diffusion of substances occurs. Capillaries will not be visible to the naked eye.
As you work, look out for blood vessels.
- The darker vessels are venules; the redder ones are arterioles.
- In the cut end of thicker vessels you may be able to see the lumen and vessel wall.
- If you find one, work the blunt end of the threader into it and down the vessel and see where it leads.
Name two substances that will diffuse into the tissues and out of the tissues in this wing.
- Oxygen and food will diffuse from the blood to the wing tissues. Carbon dioxide and other wastes will diffuse from the tissues to the blood.
- Keep a look out for nerves.
- Nerves are hard to see but when soaked in ethanol they become white (If possible check with your teacher if he or she can do this for you).
Muscles are attached to bones by means of tendons. Tendons are made of a type of connective tissue that contains lots of white fibres made of collagen. It is this collagen that gives the connective tissue its properties.
Your task now is to remove all the muscles neatly from the bones.
- As you do so, try and pull one or two off the bone using your fingers or forceps; remove the rest using scissors or the scalpel.
Look carefully at how the tendon joins the muscle.
- If necessary dissect into the muscle tissue.
Collect ALL the muscles you remove.
- You should now have a pile of fat and a pile of muscle.
- Weigh and record the mass of subcutaneous fat and muscle in the table where you recorded the mass of the wing.
How firmly are the muscles attached to bones?
Approximately how many muscles did you remove?
Describe how the tendon and muscle join.
Write down four adjectives to describe collagen from what you can observe.
- Muscles are VERY firmly attached to bone by tendons. It is not possible to just pull them off using fingers or forceps. They have to be cut off.
- Learner dependent answer. Most groups manage to remove one or two at least.
- Tendons are attached directly to the bone and gradually become muscle – the two are intermeshed at the start.
- White, strong, inelastic, flexible, firm, fibrous, occurs in bundles.
You should now be left with some bones joined together with skin, muscles and ‘proper’ connective tissue removed.
Use the miniature hacksaw to cut a bone in half.
Describe what you see after sawing the bone in half.
Use the vernier calliper to measure the thickness of the bone wall.
The bones of most birds are hollow. Why are hollow bones an advantage for a bird?
- If learners do not have miniature hacksaws available, the bone can be broken by hand. Learners should be able to see red bone marrow and a marrow cavity inside.
- Use the vernier callipers if they are available for measurements.
- Being hollow makes bones lighter, so it’s easier for the bird to fly. BUT chickens can’t fly, so their bones are not hollow, they contain bone marrow.
Ligaments look similar to tendons and have a very similar histology with lots of collagen fibres. Ligaments join bone to bone, and also form protective capsular ligaments around synovial joints by for instance, keeping in the lubricating synovial fluid.
- Cut through and carefully remove the capsular ligament of a large joint using your scissors.
Can you see internal ligaments?
Write down three observable characteristics of the ligament you cut.
- When they have cut through the ligament capsule around the elbow joint, learners may be able to see internal ligaments – they look like white ‘strings’ holding the bones of the elbow together.
- Learners may use words like narrow, white, strong, etc to describe them, but many learners may not find them at all – they have destroyed them already.
Look at the end of a bone and find the cartilage (it is pearly white in colour).
Try to remove it from the bone. Then try to scratch it first with your nail and, then with something very hard and sharp.
Describe what you observe.
What type of cartilage is this?
What do you think the function of cartilage is?
What common, man-made material is closest in its properties to cartilage?
- It cannot be removed easily by just scratching it. The cartilage is very firmly joined to the end of the bones and forms a smooth, glassy surface on the bone.
- Hyaline cartilage, but it can also be called articular cartilage.
- The cartilage makes the end of the bone smooth, to reduce friction when the bones are moved by muscles.
- It is similar to plastic.
Data (show all working)
|Tissue||Mass, correct to 1 decimal place (g)|
- Muscle is eaten for its protein. Muscle is made of protein. What percentage of this wing is muscle?
- What total percentage of this wing was made up of fat?
- Calculate the total fat-to-muscle ratio as a percentage.
- Look at the price per kilo for these wings. Assuming the wings have the same mass, and there are six per pack, how much does one wing cost?
- You are paying the above price only to really eat the muscle (protein), what is the actual price per kilo you are paying for the meat (protein) in this case?
Tidy and clean the work station thoroughly after each session. Wash instruments in hot soapy water with a sponge/scourer, rinse in the cold sink (NOT under running water) and dry with a cloth. Replace apparatus in the correct containers. Scalpel blades are to be removed, cleaned, dabbed dry with roller-towel and returned to their envelopes.