Frog Life Cycle

In this lesson, students observe and compare patterns of growth and development as organisms move through their life cycles. Students focus on the phenomena surrounding how a frog’s internal and external structures change as it moves through its life cycle. These changes allow the frog to survive in the water during the first part of its life and on land during the final part of its life.  

• A life cycle is the series of developmental stages an organism passes through on its way from birth to death. It describes how an organism is born, grows, and reproduces, producing a new organism that will go through the same series of developmental stages. It is a cycle because it is predictable and continuous.  
• Some animals undergo metamorphosis—a life cycle with distinct stages of change from an immature form to an adult form.
• Frogs go through metamorphosis because their bodies when they are first born are completely different from their bodies as adults. Frogs undergo a complete transformation of most of their internal and external structures during metamorphosis.
• Frogs have certain requirements they have to meet in order to complete their full life circle.
  
  

• How can tadpoles survive underwater?
• Why is reproduction an important part of a life cycle?
• How is the frog life cycle different from a dog’s life cycle?
• Why do frogs undergo metamorphosis?
• How are all life cycles similar?
• What external structure allows tadpoles to move around?  
• What internal structure allows tadpoles to access energy?
• What has to change in a tadpole so that adult frogs can spend most of their time on land?  
• Why might a frog not be able to complete its life cycle?  
• What would happen if no frogs survived long enough to reproduce?
  
  

Misconception: An organism is not a system.

Fact: All organisms are systems because they are made up of smaller structures that have a specific function and work together to help the organism survive.

Animal:  a living thing that eats other organisms for energy, breathes oxygen, and undergoes growth and reproduction

Change:  to make something different from what it is now

Function:  the normal action of something or how something works

Life cycle:  the series of developmental stages an organism passes through on its way from birth to death

Metamorphosis: a life cycle with a change from an immature form to an adult form

Reproduction:  the ability of a mature organism to have offspring

Structure:  the way in which parts are put together to form a whole

Amphibians of the Pantanal

Some organisms have life cycles that are connected to the cycling wet and dry seasons in the Pantanal. For example, during the rainy season, many different kinds of amphibians grow in the wetlands environment. Amphibians are animals such as frogs, toads, and salamanders. They live the first part of their life in the water and the last part of their life on land.

There are at least 40 different kinds of amphibians in the Pantanal, including the South American horned frog. This frog has a powerful, sticky tongue that can catch prey up to half of its body size, including insects, fish, and other amphibians.

The South American horned frog is found in wetlands because it survives in shallow water, as well as moist soil.

A Frog’s Life Cycle

The South American horned frog, like all amphibians, changes its entire body during its life cycle. To change means to make something different from what it is now. This change from an immature form to an adult form is called metamorphosis. The frog’s internal and external structures change to help it survive in its environment.

An adult female frog can lay hundreds of eggs in the water. Frog eggs are also called embryos. They are surrounded by a jelly-like fluid and are food for many predators. Laying large numbers of eggs means that at least a few will survive.

Once the eggs hatch, they turn into tadpoles. Tadpoles are fish-like creatures that breathe underwater using gills and their skin. They grow tails, which they use to swim. They also develop a mouth, which they use to eat algae. Most tadpoles are herbivores, eating only plant matter. Internally, they have a long intestine but no stomach for digesting food.

Those tadpoles that aren’t eaten by other animals begin a complete transformation. During this stage, they are called froglets. Some body parts disappear. Other body parts are formed. For example, tadpoles begin to lose their tail and to grow legs. They begin to breathe on land as skin grows over the gills and lungs develop. A froglet has tiny teeth that help it eat. With enough energy and nutrients, the froglet will turn into an adult frog. Adult frogs lose their tail and develop a full set of lungs, as well as powerful back legs. This means they can spend most of their time on land. A frog can go in the water, but it needs to hold its breath to swim. Frogs also have large, bulging eyes.

Adult frogs are carnivores. They eat mostly insects. Because of this, the adult frog develops a larger mouth with a strong, wide jaw, teeth, and a tongue for capturing insects. The long intestine of the tadpole decreases in size and a stomach forms. After a year or so, adult frogs return to the water to lay eggs, starting the life cycle over again.

In this lesson, students observe how the internal and external structures of frogs function to support their growth and development as they move through their life cycle. Students observe frogs and develop a diagram of each frog in the tank every two weeks for eight weeks as the frogs move through their life cycle, including internal and external structures in each diagram. Students make observations about the frogs to produce data that will serve as evidence to explain how the internal and external structures of frogs function to support their growth and development. Students compare their observations with other student teams, and then use their observations to make an argument about the observed patterns in the stages of the frog’s life cycle.