Exercises

Examining an egg

Cover your workspace with newspaper or tissue paper before getting started.


1. Take an unfertilized chicken egg and gently crack the egg crosswise on the plate or a tray. Separate the two halves of the eggshell as you would to put an egg in a frying pan. Allow the contents of the egg to drop into the plate or a tray.
2. Examine the outside of the eggshell. Place the eggshell to the side for later examination. Describe the texture of the eggshell in your reports section.
3. Examine the internal structures of the chicken egg. On the surface of the yolk, locate a small white round dot. This dot is the germinal disk from which an embryo would form after fertilization. Use a metric ruler to find the diameter of the germinal disk in mm. Record this measurement in your results. 
4. Find two dense white cord-like structures. These structures are called the chalazae (singular chalaza). Gently pull on one of the chalazae (use a fork for example). To which egg structure are the chalazae attached? 
The white of the egg contains water and a protein called albumen. Notice that the egg white surrounds the yolk and is thick.
5. Observe the yolk. The yolk of the egg contains fats, minerals and vitamins. These materials, which come from the liver of the hen, pass to the ovary and become part of the egg. Touch the yolk gently. Note that a membrane called the vitelline membrane surrounds it.
6. Examine the inside of the shell and the membranes attached to it. Try to locate an air space between the membranes and shell. The chick uses the air space only when it is ready to hatch. At which end of the egg, the blunt or the pointed end, is the air space located?  
7. Properly dispose the chicken egg and the shell. Make sure to wash your hands thoroughly with soap and warm water.

Egg examination analysis

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a) Names of the group members

b) What purpose does the eggshell of a bird’s egg serve?

c) If the shell membranes are removed from the shell and water is added, the water will seep out of the shell. What characteristic of the shell would allow this to occur?

d) What is the likely function of the chalazae?

e) What might the egg white provide for the developing embryo?

f) What might the yolk provide for the developing embryo?

g) In the developing human, there is no albumen or yolk serving as a source of nutrients. How does the human embryo obtain nutrients for growth and development?

h) A chick embryo develops in 21 days but a human embryo develops in about 266 days. Why are longer periods of development possible in humans and other mammals?

i) Candling is a process by which egg processors look at an egg through a light source to determine whether the egg has been fertilized. Why is “candling” of chicken eggs important to egg processors?

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10/1. Bird adaptations

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a) How have birds adapted to flying?

b) Describe the ways in which mallards have adapted to life in water ecosystems.

c) Why are almost all duck species migrating birds?

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10/2. Pair assignment

Make a pair presentation on a single bird species that can be found in or near water ecosystems. Teacher will give you one.

Include the following information:
- characteristics (how to identify)
- nutrition and nesting (what it eats and what kind of nest in has)
- aquatic bird group it belongs to (how do you know?)
- adaptations to aquatic environment or living in a shore
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