Essential Science for Teachers: Life Science
Animal Life Cycles Animal Life Cycles: Children’s Ideas
Children’s Ideas About Animal Life Cycles
Below are common ideas children in grades K-6 have about this topic, compiled from research on children’s ideas about science (see the Session 3 Children’s Ideas Bibliography). Consider what evidence might refute this idea, and why a child would be likely to believe this?
1. Young children do not volunteer reproduction as a criterion for life.
Reproduction is a characteristic that defines life. Reproduction, however, is not an immediate observation that young children are likely to make of living things. Once they have enough experience observing the production of offspring by parents and see themselves as a part of this pattern, they are more likely to add this to their definition of life.
2. Reproduction is synonymous with mating.
Children probably hold this idea because they are most familiar with an animal model for reproduction – where mating involves the act of copulation. Not all life forms mate to reproduce. Even life forms that involve the union of male and female sex cells do not necessarily mate – plants are a good example. And, there are even animals that don’t mate. Female fish and frogs, for example, deposit their eggs in the water where the males fertilize them externally. And many aquatic invertebrates – for example, sponges, jellyfish, starfish, and clams – shed sex cells into open water where fertilization occurs.
3. Eggs contain a whole baby in miniature form or the parts of a whole baby that somehow get assembled.
In sexually reproducing organisms, life begins as a single cell – a fertilized egg. The fertilized egg begins to divide, and the incredibly complex and not well-understood process of development into a baby begins. Most children have ample experience observing the progression of development that occurs after birth through adulthood – they can see themselves as part of this progression. In this sense, babies can be seen as “miniatures” that grow into an adult form. So it is reasonable to think that before birth, an even smaller baby exists, especially since the cellular nature of sexual reproduction – including development of an embryo into a baby – is not something a child can directly observe.
4. Babies are “already present” but are waiting for a cue to be born.
In sexually reproducing organisms, a baby is the product of the union of sperm and egg. Before this union, no baby exists. Children may hold this idea because their only experience with babies – including themselves – is that they emerge from a mother already formed. If they don’t understand the process of sexual reproduction, then it is reasonable that they believe a baby is already present – it can’t come from nowhere, so it must already be there. A different version of this is that babies are “put there” from an external source.
5. The father provides help with care but doesn’t play a role in reproduction.
Males donate half the hereditary material to the offspring via sperm – females donate the other half via eggs. Because only females are associated with birth, however, children may assume that they are solely responsible for reproduction.
6. The role of sperm is to “trigger” the egg to begin to develop.
In a sense, sperm do trigger eggs to begin to develop, but this occurs because they deliver the male half of the hereditary material to the egg, where it joins with the female half. Once all of the hereditary material – the complete genome – is present, development can begin.
7. Eggs are not alive but can give rise to chicks.
All living things arise from other living things. A fertilized egg is a living cell that arises from the union of two other living cells – sperm and egg. These cells themselves arise from living cells – there is no discontinuity in this process. A fertilized egg demonstrates all the characteristics of life: it’s made of cells, it has a life span, it uses matter and energy, it responds to its environment, and it carries DNA.
8. “Nature” makes offspring resemble parents.
Offspring resemble their parents because each parent contributes hereditary information – DNA – that is used to create that offspring. Before children understand that parents transfer hereditary information via a physical structure – the molecule DNA – they are unlikely to be able to account for what causes offspring to resemble parents although they observe it to happen.
9. Inheritance is not directly connected to reproduction.
This idea may arise because children don’t connect mating with the transfer of hereditary material and, subsequently, the observation of inherited traits. However, reproduction and inheritance can’t be separated. Reproduction by definition involves the replication and transfer of hereditary material from parent to offspring. This holds true for both asexually and sexually reproducing organisms.
10. The mother provides the main contribution to the inheritance of traits.
Females contribute half of the hereditary material to the offspring and males contribute the other half. This idea may arise because mothers are observed to carry and give birth to an offspring so they seem to have a greater “share” in its creation.
Children's Ideas Bibliography
The Children’s Ideas listed in this section of the Web site were compiled from the following research:
- Carey, S. (1985). Conceptual change in childhood. Cambridge, MA: The MIT Press
- Driver, et al. (1992). Life and living processes. Leeds National Curriculum Support Project, Part 2. Leeds City Council and the University of Leeds, UK.
- Kargbo, D. et al. (1980) Student beliefs about inherited characteristics. Journal of Biological Education, 14(2): 137-146.
Session 1 What Is Life?
What distinguishes living things from dead and nonliving things? No single characteristic is enough to define what is meant by "life." In this session, five characteristics are introduced as unifying themes in the living world.
Session 2 Classifying Living Things
How can we make sense of the living world? During this session, a systematic approach to biological classification is introduced as a starting point for understanding the nature of the remarkable diversity of life on Earth.
Session 3 Animal Life Cycles
One characteristic of all life forms is a life cycle — from reproduction in one generation to reproduction in the next. This session introduces life cycles by focusing on continuity of life in the Animal Kingdom. In addition to considering what aspects of life cycles can be observed directly, the underlying role of DNA as the hereditary material is explored.
Session 4 Plant Life Cycles
What is a plant? One distinguishing feature of members of the Plant Kingdom is their life cycle. In this session, flowering plants serve as examples for studying the plant life cycle by considering the roles of seeds, flowers, and fruits. A comparison to animal life cycles reveals some surprising similarities and intriguing differences.
Session 5 Variation, Adaptation, and Natural Selection
What causes variation among a population of living things? How can variation in one generation influence the next generation? In this session, variation in a population will be examined as the "raw material" upon which natural selection acts.
Sessions 6 Evolution and the Tree of Life
Why are there so many different kinds of living things? Comparing species that exist today reveals a lot about their relationships to one another and provides evidence of common origins. This session explores the theory of evolution: change in species over time.
Session 7 Energy Flow in Communities
Communities are populations of organisms that live and interact together. The structure of a community is defined by food web interactions. The process of energy flow is the focus of this session as the interactions between producers, consumers, and decomposers are examined.
Session 8 Material Cycles in Ecosystems
Studying an ecosystem involves looking at interactions between living things as well as the nonliving environment that surrounds them. Life depends upon the nonliving world for habitat, as well as energy and materials. In this session, material cycles will be explored as critical processes that sustain life in an ecosystem.