Once a sperm and egg unite to form a fertilized egg, a baby starts to develop. This early stage of life has a funny name: it's called a zygote. This is true for most living things (even plants!). This zygote then has all the information inside of it that it needs to develop into a embryo and, eventually, a new plant or animal. This zygote (which is just one cell) quickly starts to divide, so that one cell becomes two, two cells becomes four, four cells become eight, etc. At this point, the zygote becomes an embryo. The rest of what I am going to discuss is specific to mammals.

It this early stage the embryo looks like a ball of cells with all the cells pretty much the same and could probably fit on the head of pin. As the embryo starts to grow, it needs access to oxygen and nutrients, a way to remove the wastes it produces (carbon dioxide) and physical protection. So after about a week, the embryo attaches itself to the lining of the womb and a protective sac (the placenta) starts to develop around it and a chord grows (the umbilical chord) anchoring it to the mother. Blood is transfered from the mother to the embryo though the chord, and this is how the embryo receives the oxygen and nutrients that it needs, and also is how wastes are removed from the placenta.

As the initial ball of cells grows larger and larger, the cells begin to become different from each other, and take on special functions (for example, some cells will grow to form the skin, or the stomach or the brain). There are many stages in the development of an embryo, and the names are complicated so I won't list them, but basically things happen to that initial ball of cells roughly in this order: the mouth forms, the gut forms
(stomach and anus), the neural system forms (the spinal chord, brain and eyes), the circulatory system forms (blood vessels and a beating heart), lungs form (even though the embryo gets oxygen from the mother and not from its own lungs), and arms, legs, hands and feet begin to develop and eventually bones form within them. At this stage, the embryo looks like a miniature human being and is called a fetus. Each of the new, growing cells are programmed to perform a function and in this way the fetus develops all the things it will need to live once it leaves the mother's womb. All this happens very rapidly...within the first three months after fertilization of the egg!

During the next 3 months the fetus continues to grow, the arms and legs get longer and the fingers, toes and face begin to form. In the last 3 months the fetus is still growing but doesn't change much physically. The fetus may become active (kicking, moving its arms, sucking its thumb) and there is evidence that its brain goes though stages of being asleep and awake, just like our brians do. The fetus is now ready to be born and become a baby!

If you want to find out more about all the processes that lead to cell development during the early stages of the embryo, you should look in an encyclopedia under "human development", "development", "cellular development" or "reproduction". You could also try to find a copy of a textbook on introductory biology (try the public library). The textbooks I used in college and which might be good for you to read were "Life: The Science of Biology" by W. K. Purves, G. H. Orians and H. C. Heller and also
"Biology" by Neil A. Campbell. I haven't found any good web pages on the subject yet, though I am sure they are out there! A lot of the chemical signals and information that is responsible for telling each cell what to do or how to develop are not yet well understood by scientists. You now know about as much as I do on the subject. Good luck finding out more!

Hello! You have asked a very wonderful question! Although we know many things about how an animal or plant develops from an egg, there are still many more things that we don't know or understand. All humans start out as a tiny egg (about the size of a dust speck) that is in the mother. After the father's sperm fertilizes the egg, the new embryo has many, many cell divisions to create a larger number of cells. But, as you read this, consider that you once were a tiny egg, then a tiny ball of cells but now you are a specialized, fantastic creature that has a complex nervous system and muscles and bones and a heart! A tiny ball of similar cells somehow grew into a large, organized collection of groups of specialized cells! How did that happen? During development, groups of cells take on specific "jobs" such that some will become heart cells, other nerves and so on and so on. These groups of cells have to arrange themselves relative to one another, too, so that the arm is built in the right place and the heart goes on the left, for example. It's amazing! Anyway, we know a little bit about how the embryo/fetus does this but we have lots more to discover.

You can find out all about developmental biology of all kinds of creatures, including humans, by going to a big website that is maintained by a group of scientists that belong to the Society for Developmental Biology. This website will link you to all kinds of other websites on this topic. The address is:
http://sdb.bio.purdue.edu

You can also link directly to a fantastic site called "Virtual Embryo" at
http://www.ucalgary.ca/UofC/eduweb/virtualembryo
This website has lots of movies that you can download so that you can watch different animals and plants develop.

I hope that you have fun discovering more about how humans and other animals develop. It's really a miraculous process!

I just watched a really good program on the Discovery channel about the human body, and part of that was about how a baby develops in the mother's body. (Tell your teacher to email me, and I can send him a copy of the program, if he thinks you guys would like to watch it. ).

The program talked showed the growth of the baby inside the mother's womb actually pushing the mother's organs out of the way to make room for the fetus. The small intestines and the stomach and the bladder are moved out of their usual places and swished! The pregnant mother had to go to the bathroom to relieve herself more often than usual because of the increased pressure of the womb (placenta) and baby on that organ. The heart of the mother was under more stress because it also got pushed upwards as the baby matured, and also because the mother had to deliver food to and remove wastes from the baby in addition to herself! Lots of changes happen when a women gets pregnant, wow!

Hope this helps!

The process of getting from two cells to a newborn baby is pretty fascinating.
It is difficult to imagine how it all happens. Here's a quick version of the story. We all started out as an egg cell from our mother and a sperm cell from our father. These two cells got together to form a fertilized egg. The egg (and embryo and fetus) are not actually in the stomach, but in the uterus.
Your teacher can probably find you a textbook with a picture of this. But back to the egg, it is now one cell. Inside the nucleus of that cell is all of the information it will take to make a human. The recipes for making a human, are stored in the DNA. Half the DNA came from the mother, half from the father.
Now the egg divides to make 2 identical cells. Now each cell will divide again
a few times. Now the embryo is a ball of cells, with each cell exactly like every other cell. This doesn't seem to be making a human in a hurry does it?
But here comes the tricky part. Now the cells "specialize". Each cell still has all the same recipes, but now they only use a few of the recipes. Some cells ignore one part of the DNA, other cells ignore other parts. It's like organizing a group of people to do a job.
Say your class wanted to do a big project. You and your teacher planned it all out. Mr. Foote gave directions to the whole class, but then he told your group to do one part of the project and had your friend's group do another part. You would be specializing in one thing and your friend would be specializing in another part of the job, even though you all had the same list of instructions.

Now some cells specialize to be parts of the nervous system (brain, eyes, spinal cord, etc.). Other parts become part of the digestive system, other cells become part of your muscles or bones. Gradually, the parts organize themselves. By about week 10, most of the major parts are in place. At this point we say this is a fetus. There are still a lot of things that need to happen to produce a healthy baby, but the big step from a bunch of identical cells to specialized cells organized in a particular way has happened. A baby who has a healthy first "trimester" or first 12 weeks is usually going to be free of most major birth defects. That is why it is so important for a pregnant woman to take good care of herself, especially early in the pregnancy. Sometimes a woman won't know she's pregnant until some important steps have happened so it is very important for a woman who may get pregnant to eat well and stay away from drugs, including tobacco and alcohol.

The last 6 months, the fetus gets bigger and better developed. Each cell now only uses a small fraction of the 80,000 DNA recipes in each cell, but all of the recipes are still in each cell.

Thanks for asking

Actually the fetus grows inside the mother's uterus which is a totally different organ than the stomach. It is located below the stomach in the center of the body. Imagine how much the uterus has to stretch in order to hold the growing baby!
Look at this web site:
http://www.ama-assn.org/insight/gen_hlth/atlas/newatlas/changes6.htm.

View with a little more detail some of the many organs your body is packed with on this web site (NOTE: click on red buttons to find out what's what!)
http://www.ama-assn.org/insight/gen_hlth/atlas/newatlas/torsof.htm,

then compare the stomach to the uterus by viewing this website:
http://www.ama-assn.org/insight/gen_hlth/atlas/newatlas/femorg.htm

A really great website that takes you step by step through the development of a human baby is : http://www.visembryo.com/baby/hp.html
Click on each of the numbers in the colored coil leading to a baby in the center (I suggest you start with #1 and then click the next button at the upper right corner).

For learning about the details surrounding the first steps in pregnancy and the growing fetus, check out this website: http://w-cpc.org/Fetal.html

Here's a question for you: How many cells did we all start out as?
Good Luck!