So What's a Cell?

Would you believe that a chicken egg or an ostrich egg is a cell?

But these eggs are not typical of the cells in our body. The relative sizes are shown below:

The dot that represents a human cell should be smaller, but you might have trouble seeing it. In addition to the size difference , these eggs are actually sex cells. So, how do sex cells differ from other kinds?

A main difference is that sex cells only contain half of the genetic material needed to form a baby. When the female sex cell and the male sex cell combine, they create a new cell that has complete genetic instructions. This new cell can then divide, each daughter cells divides, and each of those daughter cells divide, and so on to make an embryo, fetus, and finally, a baby.

So what do you see when you break open a chicken egg? If it has not been fertilized by a rooster, you won't see a baby chick (embryo) growing. You see:

one cell that is specialized for reproduction.
dark yellow yolk, which is actually a membrane "bag" filled with nutrients for a growing embryo (remember, a chick embryo is trapped inside the shell and can't get food from the outside).
a little spot on the yolk, called the "germ spot," which contains the genetic material.
lots of white substance outside the yolk, most of which is a pure protein, called albumin.
a thin membrane, called the cell membrane, that surrounds the white material, which is equivalent to the cell membrane.

Next time you have an egg for breakfast, take a close look before it is cooked!

Enough about eggs. It is time to learn about your own cells.

This diagram shows what is inside a cell. (MTOC stands for microtubule organizing center, which makes tubules to guide cell division, help transport chemicals, and provide structure).

We suggest that you pick Unit 1 first. After that, the order doesn't much matter.