This family, friendly lab covers the egg inside the shell. It is to be used with The Anatomy of an Eggshell, Part I. Please make sure to complete part 1, first.
Wait! Have you printed your lab sheet from Anatomy of an Eggshell, Part 1? If not, here is another link! Make sure you complete the shell section first!
In this lab, we will look at the anatomy of an egg. Assuming that you still have the egg contents from The Anatomy of an Eggshell, Part 1, lab, take a good look at the inside egg contents with your magnifying glass. You should be able to see three distinct sections.
Eggs look pretty simple, right? But they are actually a very small world inside a shell! The inside of the egg is all a chick needs to develop before birth.
Anatomy of the Egg
There are three visible sections of an egg.
The egg whites are called the Albumin which comes from the Latin word, Albus, that means, ‘white’. There are actually four layers of egg whites but in this elementary section, we will discuss the egg as having two layers. The egg whites carry 40 different proteins, plus water, and has two parts that look visibly different.
1. The Thin Layer of Albumin
The thin layer of egg white protects the yolk. Because it is thin, and contains water, it tends to spread out more than the thicker albumin. The thin layer of albumin contains most of the protein found in the whites.
2. The Thick Layer of Albumin
2. The thick part of the egg white is called the Chalaziferous White. It is the central layer around the yolk. The thick, jelly like consistency stabilizes the yolk’s movements and keeps the yolk in the center of the egg. Otherwise, if there was a baby chick growing inside it might feel like it was on a roller coaster when the hen decided it was time to roll the egg over! If the Chalaziferous White didn’t exist, you might find your eggs automatically scrambled when your parents brought them home from the store. The Chalaziferous White is important to the well being of the egg.
3. The Anatomy of the egg yolk
The yolk, or the yellow center gets its color from the type of food that the hen eats. Farm fresh eggs will look strangely orange if you aren’t use to seeing a fresh egg. The yolk has fats, proteins, and essential nutrients. The yolk provides food for the baby chick while it is growing in the shell. This is the part of the egg from which the baby chick develops.
The yolk has a clear membrane, similar to the membrane we saw in the egg shell. This thin skin, or membrane, is called the ‘Vitelline Membrane“. It is an invisible boundary that holds the yolk together.
The yolk has a small white spot on it called the egg cell or germinal disc. This is the part of the egg from which the baby chick develops. If the egg were fertilized this little spot would be much larger.
Chalaza
The Chalazae ropes can be seen along the side of the egg. They are not umbilical cords like many people think, instead, these little ropes are anchors. They holds the yolk in the center and attach it to the membrane of the eggshell. (By the way, chalaza is singular and chalazae is a plural noun)
Vocabulary
Albumin – The egg whites
Membrane – A membrane is a thin flexible layer around the cells of all living things. It separates cells on the inside from the outside cells.
Chalazae Ropes – Anchors that keep the egg yolk tethered to the center and shell membrane.
Tethered – Attached
Air Cell – Pillow of air behind the membrane at the large end of the shell.
Germinal Disc – Small indent or pale white spot on the yolk. The area in which fertilization begins.
Yolk – The yellow center made up of fats, proteins, and essential nutrients.
Vitelline Membrane – The thin, lining that covers the yolk.
Here are a few questions my science students have asked.
Students ask great questions. Here’s just a few from my past egg anatomy classes.
My Grandma doesn’t refrigerate her eggs, but my Mom does. Why?
Remember the coating that is on the egg shell to keep bacteria from penetrating the pores? Here is an interesting tid-bit: Farm fresh eggs can be kept on the counter, but once eggs have been refrigerated they have to stay refrigerated. If eggs are left out and condensation (moisture) forms on the warming shell it will allow bacteria to penetrate to the inside. All commercial eggs need to remain refrigerated.
Why isn’t there a chick inside all eggs? When I eat an egg, am I eating a baby chick?
Great questions! Thanks to Mark and Patty for asking these two questions!
Eggs can be fertilized or unfertilized. Commercial eggs are unfertilized meaning they are laid by hens who most likely have never seen a rooster before. Therefore the eggs would not be fertile and not be able to produce a chick.
A fertilized egg happens when the rooster and the hen mate. Then there’s a big possibility that the eggs will be able to produce a chick.
Parents: if you want to go further into this subject with your children here’s a site for Curious Kids that answers this in full detail.
Curious Kids: Why do hens still lay eggs when they don’t have a mate?
What part of the egg is not healthy?
Andrew asked this complicated question. Egg yolks are high in vitamins and are high in fat. Most of the fat, are Omega 3s which are healthy for us because our bodies can’t produce this type of fat. It is also high in cholesterol and that’s where the problem comes in. Scientists still argue whether eggs are good, or bad, for us. The cholesterol that is in an egg is a natural cholesterol not like cholesterol found in processed foods. My motto: It is all about moderation!
Why are eggs different colors?
I love this question from Meredith!
What kind of food the hen eats can determine what the egg tastes like and what color the yolk will be. The shell color is dependent on the hen’s genes. All shells, of any color, are made of calcium carbonate. The most uncomplicated answer is that different types of hens lay different types of eggs. Some hens lay white shell eggs and some lay brown eggs. There are also blue, green, and speckled eggs.
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