Biological and social evolutionary processes, along with social and cultural developments, have allowed humans to separate procreation from pleasurable/recreational sexual activity. As a class learning project, an alternative, hypothetical reproductive scenario is presented: “What if humans were biologically ready to conceive only during one period each year?” Discussion is followed by small-group or individual research on the possible effects of this scenario on human reproductive response and its further effects on human life, society, and civilization. An important purpose of the activity is to stimulate active learning through small-group interaction, communication, and research.

In this guided inquiry, students explore the complex hormonal regulation of the female reproductive cycle using inexpensive ovulation and pregnancy detection hits that are readily available over the counter. This hands-on activity engages students in the practice of doing science as highlighted by the National Science Education Standards. The laboratory approach described is an effective alternative or complement to traditional lecture presentations of this challenging topic. The laboratory activities described are appropriate for both college and high school students, as reproductive physiology is covered in a wide variety of curricula.

The growth of a pine tree is examined by preparing “tree cookies” (cross-sectional disks) between whorls of branches. The use of Christmas trees allows the tree cookies to be obtained with inexpensive, commonly available tools. Students use the tree cookies to investigate the annual growth of the tree and how it corresponds to the number of whorls on the tree. Height—diameter and height—age relationships are also investigated. While aimed at high school classes, the procedure can be adapted for younger students.

We describe a technique for removing and growing chick embryos in culture that utilizes relatively inexpensive materials and requires little space. It can be readily performed in class by university, high school, or junior high students, and teachers of any grade level should be able to set it up for their students. Students will be able to directly observe the chick's development from 3 days post-fertilization to the point at which it would normally hatch. Observing embryonic development first hand, including the chick embryos' natural movements, gives students a full appreciation for the complexity and wonder of development. Students can make detailed observations and drawings, and gain understanding of important principles in developmental biology. Finally, we suggest various ways in which this project can be adapted to allow students in advanced classes to design and implement their own projects for investigating teratogenic effects on development using the ex ovo model of chick development.

Embryonic development offers a unique perspective on the function of many biological processes because of embryos' heightened sensitivity to environmental factors. This hands-on lesson investigates the effects of elevated vitamin A on the morphogenesis of chicken embryos. The active form of vitamin A (retinoic acid) is applied to shell-less (ex ovo) cultured chick embryos, which are highly accessible and intrinsically spawn inquiry. The student activities mirror the scientific research process, including review of scientific literature, hypothesis formation, experimental design, interpretation of data, and re-evaluation of the initial hypothesis. This exercise supports instruction on developmental biology, biophysics, animal research, and experimental design and is motivated by a clinically relevant health issue.

This simple role-play exercise involves the whole class in learning about the function of hormones in promoting homeostasis and the value of negative feedback, using the example of regulation of calcium ions by parathyroid hormone.

In species that reproduce sexually, an individual's fitness depends on its ability to secure a mate (or mates). Although both males and females are selected to maximize their reproductive output, the mating strategies of the two sexes can differ dramatically. We present a classroom simulation that allows undergraduates to actively experience how differences in parental investment lead to differences in reproductive behavior. Students will understand why males generally compete for mates whereas females generally choose among mates. The activity provides a foundation for exploring advanced topics in animal behavior, or it can be adapted for introductory biology courses.