Primary Connections: Linking science with literacy

Life cycles A: General stages - Butterflies and frogs

Life cycle stages

Butterflies

Frogs

Life cycle stages
The life cycle of all organisms usually involves some variation of each of these stages:

Mature adults produce gametes (sperm and eggs in animals; pollen and ovules in flowering plants).
In animals, adults attract a mate of the same species but opposite sex using sounds (frog calls), scents (dogs on heat), visual appearance (breeding plumage in birds), and courtship rituals (lyrebird dance, sea gull displays). This ensures the fittest individuals breed at the best time to aid survival of the species.
Mating occurs to bring gametes together (pollination in flowers is helped by insects, birds, and wind).
Fertilisation of gametes occurs to form the zygote, the first cell of the new individual. This may occur externally as in fish, or internally in land animals as the sperm must swim to the eggs.
The zygote starts dividing to form an embryo which continues to develop (in shelled eggs, or internally inside the mother).
Adults build a nest (or the female's womb develops) to protect developing embryos.
The young hatch from eggs, or are born.
Parents protect the young and help development of survival skills through learning and instinct.
The young grow and develop to reproductive maturity.

Any long-term disruption of any stage can result in extinction.

Some life cycles studied in Primary Schools: Butterflies and frogs.

Butterflies
This life cycle involves the adult male detecting a female by smell, brief courtship display, and mating (sperm enters female and fertilises eggs). The female lays eggs on a plant. The embryo develops into a caterpillar using food stored in the egg. The caterpillar (larva) hatches, eats the eggshell and then the plant. As it grows, it moults and grows new skin several times to accommodate increased size. It increases in birth weight by approximately 3000 times. Finally, it spins a cocoon in which the pupa (chrysalis) changes drastically (metamorphosis) into the emerging adult butterfly. The role of the short-lived adult is to fly to a new area, mate and lay more eggs.

Frogs
Adult frogs locate and attract mates by "singing" a call recognised only by that species. This prevents the loss of time, energy and gametes in mating with other species resulting in no offspring.

The male grips onto the female's back and deposits sperm as he squeezes out her jelly-covered eggs into the water. The jelly surrounding the eggs protects against germs, sticks them together, and absorbs warmth from the Sun, but it is not a food source. Over 14 days, the developing tadpole uses the egg's food and grows rapidly, then it escapes. It uses its sucker mouth to attach first to the jelly sac and later to weeds which it eats. In many common species, hind leg buds appear at 5 weeks, and by 8 weeks they are fully developed. At 3 months a complete body change occurs (metamorphosis). It casts its skin, gills disappear, forelimbs grow, the tail is absorbed as a food supply, and the froglet is formed. It now eats insects, breathes with lungs, and grows to sexual maturity.

Copyright owned by the State of Victoria (Department of Education and Early Childhood Development). Used with Permission.


	FAQ:
			What conditions are needed to keep pet tadpoles? Why do animals mate? Why don't animals of different species mate (e.g. goat with a horse)?


	Related Topics:
			Life cycles B: Chicks, roos and more.. Plant Systems C: Reproduction. flowering plants Human reproduction A: The female system Human reproduction B: The male system and contraception Populate or perish Too late: Extinctions Inheritance Species and evolution


	Quiz:
			Question 1 Question 2 Question 3


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	Glossary

		Gamete Zygote Embryo Instinct Cocoon