Stages in a life cycle

What is a life cycle?

As mentioned above, a life cycle is a repeated pattern in the life of an organism.

All living things undergo stages of growth in their life.

Some organisms, such as plants may start out as seeds, spores, or buds on the adult plant.
Other organisms such as animals, start out their life cycle as an egg.

*We would like to note that even though all animals, including Humans originally form from a fertilized egg, we want to make a differentiation between Egg-laying and Live-bearing animals. Therefore, we will NOT consider the egg stage as one of the stages in life-bearing animals.

*E.g. Human = Young –> Adult   NOT   Egg –> Young –> Adult

*[The life cycles of non-flowering plants, plants that reproduce through budding, fungi and bacteria and fish are not the the P4 syllabus.]

Stages in a Life Cycle

In the growing up phase of an organism, it undergoes certain changes. We call these specific periods in the life of an organism a stage.

Some animals have 2 stages (all live bearing animals, most mammals except spiny anteater and Platypus)
Some animals have 3 stages (3 different types of 3 stage life cycles will be explored later)
Some animals have 4 stages (animals that have 4 stages undergo a pupa stage where it does not eat or drink during that stage)

A life cycle can only repeat itself if the adult reproduces before it dies. This ensures the survival and continuity of its kind.

Different Types of Life Cycles

2 Stage Life cycle                                                                                                                

Life Cycle of a Cat   The young of the cat is called a Kitten The stages in the life cycle of a cat are the Young and Adultstage, not the kitten and adult stage.

Life Cycle of a Human

The young and adult stage in that of a Cat looks similar.

The young and adult stage in that of a Human looks similar.

For Mammals, the young of the animal looks very similar to that of the adult.

3 Stage Life Cycles                                                                      

Egg-laying Mammals/Birds Platypus   Another egg-laying mammal with 3 stages in its life cycle is the spiny anteater. Spiny Anteater   One thing I hope you noticed is that both the young of the Platypus and the Spiny anteater feed on milk (which is the main characteristic of mammals) Chicken   The young of a chicken is known as achick. The three stages are: Egg, Young and Adult All other birds have 3 stages in their life cycle.

Insects (without Pupa Stage) Cockroach   The cockroach nymph is very similar to the adult cockroach but just smaller in size. It has also not yet developed wings to fly. Grasshopper   The grasshopper nymph is very similar to the adult grasshopper but just smaller in size. It has also not yet developed wings to fly as you can notice in the picture above. These young of these two insects, in the nymph stage, look very similar to the adult. But there is one insect in the nymph stage that looks different from the adult. That is the Dragonfly. The three stages of these insects are: Egg, Nymph and Adult Dragonfly   The young of the dragonfly, its nymph stage, looks different from the adult. The egg and nymph stage is in water while the adult lives on land. Click the link below for more information on the dragonfly.   DRAGONFLY

Amphibians Frog   The life cycle of the frog, toad, salamander and other amphibians are largely similar. They all consist of 3 stages: Egg, Tadpole and Adult The young tadpole looks different from the adult. The growth of a frog from egg to adult can be seen listed below. We call this process Metamorphosis Egg is covered in Jelly-like substance. Tadpole breathes through gills. Tadpole develops hind(back) legs. Tadpole develops fore(front) legs. Tadpole’s tail shortens. Tadpole develop lungs and gills disappear Tadpoles become young frog. Newts and Salamanders do not lose their tail and spend most of their life completely submerged in water. For more information about salamanders/newts, click the button below. (this is not in the P4 syllabus but just for you to know)   SALAMANDER

4 Stage Life cycles

The four stage life cycles are different from the other stages such that their young definitely do not look like the adult at all. They also have a larva and pupa stage wherein the animal changes from a worm-like creature(larva) to a pupa which doesn’t eat or drink at all until it emerges as an adult. This process is also known as Metamorphosis which describes an animal that undergoes great changes to its physical structure and appearance from the time it hatches from its egg.

You can click on the link below to learn more about Metamorphosis.

 

METAMORPHOSIS

 

Darkling Beetle (Mealworm Beetle)   The Darkling Beetle has 4 stages in its life cycle: Egg, Larva, Pupa and Adult. The name of the animal in the Larva stage is the Mealworm During the Larva stage, the Mealwormmoults several times, getting larger each time. When it is ready to undergo metamorphosis, it moults one more time and turns into a Pupa. During this stage, the pupa does not eat or drink. Inside the exoskeleton, it is changing into a beetle. When metamorphosis is complete, the animal emerges from its case as an adult Darkling Beetle.

Butterfly/Moth   The Butterfly/Moth has 4 stages in its life cycle: Egg, Larva, Pupa and Adult. The eggs of the butterfly/moth are usually laid on the underside of the leaves which the larva feeds on. The name of the animal in the larva stage is the Caterpillar *The pupa stage is also known as theChrysalis. (not in syllabus) During the Larva stage, the caterpillarmoults several times, getting larger each time. When it is ready to undergo metamorphosis, it finds a branch of a plant and attaches its abdomen to it. Then it moults one last time to become a Pupa. During this period, the Pupa does not eat or drink. Inside the exoskeleton, it is changing into a butterfly/moth. When metamorphosis is complete, the animal emerges from its case as an adult butterfly/moth.

Mosquito   The Mosquito has 4 stages in its life cycle: Egg, Larva, Pupa and Adult. The eggs of the mosquito are laid at the water surface. The name of the animal in the larva stage is the Wriggler. This is because it moves about by wriggling. The Larva lives in the water and breathes through a breathing tube at the bottom of its abdomen. *The pupa stage is also known as theTumbler (not in syllabus) because it tumbles about in the water. The Pupa stays close to the surface of the water to breathe with breathing tubes. During the Larva stage, the wrigglermoults several times, getting larger each time. When it is ready to undergo metamorphosis, it moults one more time and turns into a Pupa. When it emerges as an adult mosquito, the male mosquito feeds on nectar of flowers and the female feeds on blood.

All three of these insects have 4 stages in their life cycle. Egg, Larva, Pupa and Adult. All three of them have a Pupa stage where the animal does not eat or drink. One main difference is that the Mosquito larva spends its egg, larva and pupa stage in water. As we can observe, the young of these three animal looks very different from its adult.