Dissection of Animal Tissue

This is an example practical investigation on tissues. You do not have to perform the experiment, but going through the investigation procedure could help better understand how life scientists learn about tissues.

Investigation: Dissection of Animal Tissue

Aim

The aim of this dissection is for you to revise the theory behind tissues and apply your knowledge to actual tissues.

Instructions

You will be working in pairs. Instructions for this activity will be written in italics.

At the end of the practical you should:
1. Know and be able to use dissecting instruments correctly, especially insertion and removal of blades.
2. Be able to recognise and use ether responsibly
3. Be familiar with apparatus: petri dish, dissecting tray.
4. Use a scale: zero (calibrate) and record mass
5. Perform simple mathematical calculations: percentage
6. Be able to read a vernier calliper.
7. Clean and dry thoroughly and appropriately.

Materials

1 piece filter paper
scissors
forceps
threader
pointer
scalpel
blade
dissecting tray
petri dish
chicken wing
1 ml Ether
cloths
roller towel

Method

1. Skin

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 in the way you were shown. 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 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.

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.

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 as 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.

4. Muscle

This 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.

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 by referring to the notes on levers on the side bench. The wing flexes / bends at the elbow joint when the muscle is pulled. This action is called FLEXION. (bending a limb)

Let go and pull various other muscles.

Can you get one to cause the opposite movement?

Muscles are all arranged in 'antagonistic pairs' where the action one muscle does the opposite to its partner.

Carefully dissect out a single muscle in FULL. Remove it from the wing completely.

Draw the wing muscle. You need to follow the convention of drawing diagrams by i) providing a heading or title ii) adding labels (tendon, muscle, epimysium, fat tissue). All labels should be on the right hand side of the diagram. iii) providing a scale bar.

What type of tissue lies between the muscles?

5. Blood vessels

As you work, look out for blood vessels. 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.

The smallest vessels you will be able to see are small arteries (arterioles) and small veins (venules). The darker ones 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.

6. Nerves

Also keep a look out for nerves. Nerves are bundles of neurons enclosed in a membrane rather like a piece of electrical flex. 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). They tend to be deep in the tissues for protection.

7. Tendons

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 s/s scissors or the scalpel.

Look carefully at how the tendon joins the muscle. If necessary dissect into the muscle tissue.

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.

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.

8. Bone

You should now be left with some bones joined together with skin, muscles and 'proper' connective tissue removed. The bones of most birds are hollow.

Why are hollow bones an advantage for a bird?

Use the miniature hacksaw to cut a bone in half.

Describe what you see.

Use the vernier calliper to measure the thickness of the bone wall.

Label the following parts of the bird

upper arm
Forearm
Wingtip

9. Ligaments

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 s/s scissors.

Can you see internal ligaments?

Write down three observable characteristics of the ligament you cut.

10. Cartilage

Look at the end of a bone and find the cartilage it is pearly white in colour.

What type of cartilage is this?

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 do you think the function of cartilage is?

What common, man-made material is closest in its properties to cartilage?

Questions

Data (show all working)

Tissue	Mass, correct to 1 decimal place (g)
Entire wing
Skin
Muscle
Subcutaneous Fat

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 6 per pack, how much does one wing cost? You are paying the above price only to really eat the protein, what is the actual price per kilo you are paying for the meat in this case.

Cleaning

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.