An egg becomes a chick.

[Music] these are chicken eggs and what I'd like you to do is compare the eggs on the left with the eggs on the right is there any difference are these a little larger no they're not there isn't any real difference they look pretty much alike let's open them now any difference between theg eggs on the left and the ones on the right are some of the ones on the left a little lighter I'm not sure maybe some of them are well I can't see any difference just looking at them there's very little difference but eggs like the ones on the left cannot become chickens eggs like the ones on the right can grow into chickens the difference is that these have a tiny white dot on one side of the yolk and that means they've been fertilized by a rooster a male hens are females that can lay eggs a rooster and a hen can mate to produce fertile eggs then the hen sits on her eggs to keep them warm and moist while the babies grow inside them how warm do the eggs have to be the thermometer reads slightly more than 38° Centigrade we can keep the same temperature in a machine an artificial incubator used to hatch eggs the temperature is 38° Centigrade that's about 100° f a little warmer than your body water in the incubator keeps the the eggs moist Like A Hen's body does now what do you think would happen if we keep the eggs at 38° Centigrade but we put them in water instead of out in the air they'll spoil won't they they won't hatch well let's see look at an eggshell it's not not so smooth is it take a very close look with a powerful microscope it looks like a pile of stones like it's full of cracks and holes yes there are holes tiny microscopic holes that air passes in and out of without air the baby chicken would die that's why there are holes in an incubator to let air in and out and there's another thing when we hatch eggs in an incubator we turn them over every day a hen does the same thing when she hatches her own eggs in either case under a hen or in an incubator it takes 3 weeks for a chick to grow and hatch what do you think is happening inside the egg draw some pictures to show me what you think is happening well what I think is that the yolk is the part of the egg that gets to be a chicken the white spot on the yolk is the eye then in 3 weeks the yolk gets to look more and more like a chicken the beak gets pointed and the chicken moves around and cracks open the shell I don't think that's right I think part of the egg white sticks to the yolk and gets to be feathers then the Yol and the white all together get to be a chicken wait I've changed my mind now what I think is that you start with the yolk but the yolk doesn't change right into a chicken first it grows a heart and veins and it gets to have blood but even then it doesn't get to be a chicken right away first it looks like a fish or a seahorse with his tail all curled up and with feathers starting to grow it looks more like a bird is that right yes and no all your explanations are partly right let's study a fertilized egg you tell me what you see as we watch it for several days well I see the spot on the Yol the egg is one day old now the spot is bigger now now it's 2 days old the spot is bigger a lot bigger now it's 3 days old those dark lines they look like veins like a web of veins is something moving I think I see something moving it's 4 days old yes something is moving that must be its heartbeating wow I didn't think that much would happen in Just 4 days it does remember what it looked like 4 days ago this living growing chicken we call it an embryo this embrio with its Beating Heart with blood with life was only a little spot on one side of the Yol of an egg Nothing But the spot is alive so you see the spot is the embryo that becomes a chicken while the embryo is changing you may wonder what's happening to the Yol and white of the egg well even after 4 days when we have a living embryo with a beating heart the Yol is still there and so is the white the embryo is still small the blood vessels of the embryo cover part of the Yol but the shape of the yolk doesn't change much in 4 days what's in the Shell is mostly yolk and white the blood vessels are spread out on the yolk a microscope shows that blood flowing through the vessels picks up tiny drops of yolk drops of white mix with the blood too it looks as though the yolk and white may be food for the embryo food that is used up as the chicken grows we can do a demonstration to help us watch the growing embryo we'll look at it under a microscope first I'll carefully cut the embryo from the Yol the embryo is on the thin membrane is it still alive well we're going to see the membrane with the embryo can be picked up in a spoon now I'll transfer it to a glass dish food is dissolved in the water in the dish food that is a lot like the material in the yolk and white now let's look at the embryo through a microscope the tail the spinal column the Beating Heart the embryo is still living kept Alive by the food we put in the dish in the egg the yolk and white provide its food in 3 weeks the egg hatches the chick is old enough to live outside the egg it's using its bill