Asking Questions in Biology: Discovery versus Knowledge

Life Cycles

The three main life cycles I will focus on for this unit are the butterfly, frog and chicken. I selected these three animals because we will be able to physically have them in our room to personally witness the changes each animal makes in going through their individual life cycles. It is important to note that I have made sure that not only can I have these animals in my classroom but I understand what will happen with them as we complete our unit of study. Please check with your local regulations on the ability to obtain or release any animal you may wish to study in your classroom.

In an effort to fully meet the goals of encouraging my students to ask questions and inquire about our world we will be studying other animal life cycles based on student's interest and their personal research. I am open to the idea of having other animals in my room but it will be up to the students to research all the necessary facts about care and shelter and what to possibly do with the animal at the end of our school year and over breaks. This will not only give students a personal stake in their learning but help them to see that scientists must look to effects of their experiments as well and the consequences they may or may not have on the environment and to themselves personally. I will be keeping the frogs in my class until they complete their life cycle in death and the chickens will be going home with me to live.

Not everyone will be able to have animals in their classroom for students to experience firsthand the life cycle. If that is the case there are many books available, free videos on youtube and teachertube, and other videos are available for purchase and posters with illustrated and live photos. The teacher resources section of this unit is a sample of what is readily available.

Butterflies

I selected butterflies for several reasons; one being they are simply the easiest to care for. I will be using the Painted Lady Butterfly. They look similar to the Monarch and are available for purchase with or without a habitat online. They can be ordered and arrive as larva, if you are lucky one may still be in the egg. They are left in the container they arrive in along with their food until they go into their pupa stage and form a chrysalis. Then you simply move them to the larger habitat and provide sugar water for them to eat. They can be kept or released into the wild. Butterflies are insects: they have three body parts consisting of a head, thorax and abdomen. They also have 3 sets of jointed legs and most insects have wings and antennae. Butterflies have all these characteristics and they go through a complete metamorphosis, meaning they pass through four distinctive stages of development; egg, larva, pupa and finally adult. This makes them especially dramatic for students to observe and document.

The first stage of a butterfly life cycle is the egg. They are very small and can be round, oval or cylindrical in shape. Some butterfly eggs are so transparent you are able to see the embryo move inside. This will not be observable in the classroom as they normally arrive already in their larval stage; however there are video clips available that show the larva eating its way out of its egg. In nature butterflies will usually lay their eggs on or near plants to give the larva the food source they will need to grow. The eggs are sticky so they will be secure and stay on the plant they are laid on.

The second stage is called larva or more commonly for butterflies caterpillar. The main job of a caterpillar is to eat. In fact that is almost all they do; they will eat their way out of their egg, eat the leaf their egg was on and move on to more leaves. The caterpillar will need to store energy from the food to get it through its metamorphosis phase and then continue on to reproduce. Butterflies only live a short time, many just a month but some can live up to a year. So they must mature and reproduce quickly. As the caterpillar grows it will "molt" or shed the outer layer of soft exoskeleton several times. This stage will only last a week or so. Some caterpillars will create silk webbing to protect it and to assist in movement.

The third stage is the pupa or chrysalis. Once the caterpillar has completed its growth, it will suspend itself from a leaf or branch using silk thread and molt one last time. As the last molting is removed the chrysalis is left. This is the moment of metamorphosis. The tissue, limbs and organs of the caterpillar are all going through a change. It moves from being a converter of food to energy to being a reproductive butterfly. This transformation can take anywhere from 10 days to several months, and some species of butterfly will spend the winter in the chrysalis form.

The final stage is that of the adult butterfly. As the butterfly emerges its wings will be soft and folded against its body. It will take a little time for them to extend and harden. If you are using Painted Lady butterflies you will notice red drops coming off of them; it is simply the excess color from the chrysalis stage that will give the wings their brightness. This can take three or four hours to complete; however, you will see movement of the wings soon to get them to dry and fully spread out. Once the adult is able to fly it will be ready for sugar water, or nectar in the wild. It will also be ready to reproduce. If you have a large enough holding area and the right environment you may be able to see the entire life cycle from birth to rebirth of the butterfly. This is much more difficult for other animals.

Frogs

It may surprise you to discover that a toad is a frog. There are many fun and strange facts available about frogs and toads. In the teacher resource portion of this unit you will find a list of books and websites for you and your students. Although I am sure my student's questions will lead us to compare and contrast not only frogs and toads but also different types of frogs and toads, as well as where they live and all the crazy facts that can be found. I will not be including them in the body of this unit. I encourage you to use the list of resources I have provided for your personal research as well as that of your students.

For this unit I will be focusing on a few main facts. Frogs are an amphibian which means two lives. During their life cycle they go through what is called an incomplete metamorphosis. This means they do not go through a pupal stage during their life cycle. Frogs begin as eggs in the water; however, as adults they can live on land breathing air with lungs. It is believed that there are over 4,000 different types of amphibians. Frogs are cold-blooded; this means that they are the same temperature as the environment they are in. They will seek out shade or water to cool off or the sun to warm up. This also means that more frogs tend to live in warmer climates. However, frogs can be found in every part of the world with the exception of Antarctica. As frogs begin their life in water they will tend to be found near any form of fresh water, but they prefer water that is still such as lakes, ponds and marshes.

We will utilize five main stages in the frog life cycle. First, eggs which are laid in the water by a female frog. The eggs which are covered with a jelly like substance to protect them from predators; this can be called frog spawn or egg masses. These "egg masses" can contain up to 4,000 eggs. After they hatch from the egg the second stage is called a tadpole or polliwog, they remain in the water where they swim, eat and grow. At this stage they very much resemble fish and use gills to breathe and, like fish, a tail to move. The third stage is a tadpole with legs, they will develop legs first (arms will develop later near the end of this third stage). The head will also become more distinct. They are still breathing with gills and remain underwater. The fourth stage is called a froglet. The most drastic change is the addition of lungs and the ability to breathe outside of water. The froglet resembles an adult frog with the exception of a tail and smaller overall size. Finally the fifth stage is the adult frog, where the tail will be absorbed into the body and the frog will now breathe exclusively with lungs. It should be noted that there are always various adaptations to these stages some tadpoles have lungs and need air to breath and some frogs live their entire life under water without the need to go on dry land.

There seem to be two main types on frogs that are easily available for online purchase and classroom use. One is the African Dwarf Frog (also known as the African Water Frog), which lives underwater its entire life. I am interested in utilizing this particular frog to show how adaptations are found in many animals and insects. They do have lungs so they need to surface for air. Their complete metamorphosis can be experienced in 8 weeks. However, they are very small and can be difficult to view. They will live 5 to 18 years and should not be released into the wild. The other popular frog is the Leopard frog which has approximately a 12 to 16 week time span for metamorphosis and a life span of about 5 years. These frogs will need land or a dry area as they near the froglet stage. I should also caution you that frogs will eat tadpoles as well as other frogs. It will be important to take these habits into consideration prior to bringing them into your room.

I have noted a few online purchasing resources in my materials section. From what I can tell both of these frogs are small and it can be difficult to see all the changes during a life cycle. In contrast the bull frog is much larger and the stages of metamorphosis can easily be seen. However, it can take up to 2 years to progress from egg to adult frog. Bullfrog tadpoles are also available online. If they are purchased as tadpoles the expectation is they will take 8 to 12 months to mature depending on your school year it is quite a commitment but could be well worth it for the student's ability to observe the stages. I plan to buy mine before the school year begins in early August so that by June when we are out they should be able to see the most exciting changes if not the whole metamorphosis. It should be noted that the part of the country I live in bull frogs are safe to release into the wild. This is not true of all areas. Please check with your local environment and be sure it is safe to allow any animals you have raise in your room to be released into your local environment.

Chickens

A chicken is a bird. Birds are distinct for being the only animals with feathers. Although not all birds fly, they do all have wings. Bird eggs come in a variety of colors and sizes as well. A study of bird eggs alone can be fascinating from the tiny egg of a humming bird that is about the size of a jellybean to the large melon-sized egg of an ostrich. For this unit we will focus on three main stages of the chicken's life cycle. However, we will utilize videos and pictures to help students see the development that occurs inside of the egg. Although we will not be experimenting with the fertilized eggs we will do a few experiments with unfertilized eggs as well. I have a list of some experiments in the activities section and some resources noted later as well. This will again bring the inquiry into our activities and allow students to continue to further develop their scientific thinking and the use of the scientific method.

A female chicken called a hen will lay eggs in a nest. The eggs that have been fertilized by a male chicken called a rooster will contain an embryo. Eggs that have not been fertilized will not contain an embryo; these are what we eat for breakfast. The fertilized egg contains a yolk, amniotic fluid (egg white) and a blood spot. The blood spot is small and is where the embryo will develop. It takes about 21 days for the embryo to grow into a chick. During the 48 hours prior to hatching the yolk will be pulled into the abdomen of the chick and used as food for the first few days after hatching from the egg. The hard outer shell of the egg protects the growing chick. As the chick develops they have a special growth on their beak called an egg tooth. They will use this tooth to break open the egg when it is time to hatch. It can take up to a full day for a chick to fully hatch from its egg.

The second stage is the chick. Once they have escaped the egg, chickens will be wet and scrawny. The egg tooth they developed will soon disappear. As they dry and their down feathers fluff out they will start to look more like the cute little chicks we all know and love. Chicks will be able to walk almost from the moment they fight their way out of the egg. They will eat seeds, bugs and worms as well as the food that you provide. We will take this time to compare and contrast baby birds, baby mammals and even baby amphibians. How they have developed so far, what they need to continue to grow and develop and how they will continue to change in appearance. After about 4 weeks new feathers will have grown in, and the down feathers will have all fallen out. Chicks will also begin to develop a comb on the top of their head and a wattle under their beak. It is also good to note that from the time a chick emerges from its egg it resembles its parent. As they grow they will continue to develop traits found in their parents such as size and feather color.

The third stage in a chicken's life cycle is adulthood. It takes a chicken about six months to become an adult. The female hen will begin to lay eggs at or near this time. Most hens can lay two eggs a day through the spring and summer this will slow over the fall and they may not lie any over the winter. However, some chickens have been bred to produce a larger amount of eggs. Eggs come in a variety of colors from white, brown, green, blue and even some are speckled. The size can vary as well based on the breed of chicken. Chickens can live up to 12 years depending on the breed. Chickens don't chew their food nor do they even have teeth. They will swallow their food whole, where it goes into a gizzard that holds tiny stones and is then ground up before it makes its way to the stomach. If you have chicks in your room you will need to be sure and provide these "stones" that can be purchased along with the food.

I will get my eggs from Oklahoma State University's local agricultural site. They provide the eggs and incubator along with assistance on care, feeding and raising. I will then be taking the chickens home with me and will then utilize them for their egg production for later school years and personal use. I would encourage you to contact your local agricultural department or even Four H Club to see what resources they may have valuable for use in schools. If you are not able to utilize a local organization to acquire eggs and borrow an incubator it can be quite expensive. However, you can order chicks online or get them from a local farm. It is not quite as exciting as seeing them hatch form an egg but the growth and development is also exciting to watch and can be documented by students.