The Living World Part 4: Life cycles

Classes don’t always go the way the teacher plans them. I was so pleased with the children’s interest in our rainforest model the previous week. This week I had geared myself up for them spending a whole session designing and making the model, just like the mum here:

(This is about 8 hours work sped up and edited to give a 14 min video.)

I had been in touch with the volunteers at Stony Range and they confirmed for me that the rainforest gully there has plants like a sub-tropical rainforest:

Looking at the definition of a subtropical rainforest on the Royal Botanic Garden web-site it seems to cover our rainforest which has a mixed composition of many tree species with no obvious domination by any one species, trees of large to medium size with a range of leaf forms with palms, figs, large vines and large epiphytes growing in an environment of fertile soil and high rainfall (in our case with the use of the installation of a regular watering system)

Our rainforest was developed in the early years of the Range along a creek line that was covered in lantana and privet and planted with rainforest species such as Red Cedar, Coachwood, Hoop Pine, Lilly Pilli, ferns and palms.

In 1988 the southern end of the Rainforest was planted with Proteaceae species from North Queensland rainforests as a gift from the Sydney Royal Botanic Garden.

I prepared some information on the various plants and animals in the rainforest, so that our model could be authentic. I printed off pictures of the different layers of a rainforest and set myself up for a morning of drawing and painting.

However, none of the children wanted to make the model! Luckily I had also prepared some salt dough so we could make life cycle models instead. I thought we could make silkworm life cycles like these ones available commercially, but I left it to the children to choose what creature’s life cycle they wanted to make. The children settled down to make models and it was lovely to see the older boys working as a team.

Silkworm life cycle models from Insect Lore (now discontinued)
crocodile lifecycle cropped for blog
Crocodile life cycle model created by 8-10 year olds in a Nurture Learning class.

Both groups made life cycle models, but in the older group we also discussed how organisms can change their life cycle depending on environmental conditions. This is in the NSW syllabus. I had to research this in preparation for the class. I found it quite interesting as it wasn’t something I had really thought about before.

I asked the children to think about the factors, or variables, that might change in the environment. They came up with a few and I added some others. Here is our list, which is pretty comprehensive:

Temperature, water levels/humidity, wind-speed, earth movement (e.g. due to earthquakes), dissolved chemicals in the soil or water (e.g. due to leaching, volcanic action or pollution), other species present (leading to competition).

How do PLANTS change their life cycle in response to environmental conditions?

The seed stage of plants is generally the least vulnerable stage of their life cycle. Plants may delay germination until the conditions right. This handout about growing native plants (from the Australian Plants Society NSW) tells you what you have to do to pre-treat seeds to get them to germinate.

Some Australian native plants are very hard to propagate in nurseries due to requiring extreme conditions before germination, e.g. the Eremophila maculata shrub has extremely hard seed shells, almost like a rock. In natural conditions these require fire, cycling wet and dry conditions, and abrasion by soil before the seed starts to germinate.

Eremophila maculata flowers (taken from

If conditions change, some species may become dominant where before they were not, e.g. higher temperatures may make annuals flower before perennials and then annuals take over.

How can ANIMALS change their life cycle in response to environmental triggers?

Just like plants, there are environmental triggers that will cause an animal to go to the next stage of its life cycle.

Caterpillars can change the amount of time they spend in each stage of their life-cycle. Several of us have been looking after silkworms this springtime, and were interested to learn that you don’t have to feed silkworms every day, but if you feed them less frequently, they remain as larvae (‘worms’) for longer before pupating. (This could lead to an interesting experiment for another year.)

Some animals may not reproduce if conditions are bad, e.g. not enough food, or lack of specific triggering conditions. For the Trout Cod in NSW, spawning is triggered by increasing day length and increasing water temperature. The Trout Cod is now threatened by what is known as cold water pollution. Large volumes of cold water, released into the rivers where the Trout Cod lives (for example, from dams) may mean the temperatures never reach the right level for the cod to spawn and therefore reproduce.

For some fish, spawning  will depend on levels of certain chemicals dissolved in the water. Chemical pollution, just as with the cold water pollution, may mean they do not spawn.

Mini-beast hunt

The older group also had about 20 mins to go out in the garden to look for mini-beasts and think of questions about these creatures. The questions were meant to lead into experiments they could design themselves. They really enjoyed this part of the class and came up with some wonderful questions!

Hunting for minibeasts
Hunting for minibeasts

Due to time limitations they didn’t get to design and carry out their own experiments. In future years I would like to start this part of the course earlier on in the term and allow far more time for the children to plan, carry out and analyse their own experiments.

I feel that science – learning about science and doing science – is far less about learning facts, and far more about the way that you approach learning. I hope that children coming to my classes end up with an understanding of the scientific method, and of scientists as social creatures who work in groups and collaborate with other scientists, rather than working in isolation and coming up with wonderful discoveries.

If you want to explore this idea as a parent, teacher or student, with or without your child, I think the University of Berkeley Understanding Science site is wonderful. I have linked to it before but it might not be easy to find on the blog, so here is another link:

There’s also the idea of failure and of null results to consider. I’ve touched on that before. It’s a hard one to cover because many people (myself included) are perfectionists and find it hard to conceptually deal with the idea of failure being a positive thing.

I love teaching children all about different areas of science, but what I really want to do is to help them to become little scientists themselves – to investigate questions they want to investigate, design and carry out the experiments themselves, alter the experiments based on what happens, and assess how well the experiments went or what conclusions they can reach. I am hoping to run a course next year that is not based on the NSW syllabus or any particular scientific discipline, but solely for the purpose of exploring the scientific method. I’m quite excited about this one as it will reach to the core of my philosophy about science and about teaching. I hope to have positive results to report right here when the course is over!

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