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Harvey and the search for ova

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  • Harvey and the search for ova

This lesson includes annotation of reproductive organ diagrams just as biologists, Aristotle, Harvey and de Graaf did in history in their quest to discover the function of the ovary and the existence of ova and sperm cells in mammalian sexual reproduction. Students will participate in a balloon debate and compare each biologist's work, notably the work of William Harvey, who advanced the idea "ex ovo omnia" all life originates from an egg.

Lesson Description

Guiding Question

The greatest reward of the scientific investigator, that no matter what his success or failure, he knows that he can serve by merely keeping on asking questions; if he cannot answer them someone else will, and in the end truth is achieved, and mankind advanced a little farther toward the light.

Activity 1 - Balloon debate

You are part of a group of ten eminent biologists from the history of embryology on a wonderful hot air balloon trip.

Unfortunately the balloon's gas supply has run out and you are being blown towards a mountain by the wind.

The only way to survive is to make the balloon lighter so it rises above the cliffs. One of you will have to jump out.

The fairest way to decide who will jump is for each of you to present details of your contributions to the biological search to understand sexual reproduction in mammals and the hunt for the mammalian ovum.

Then you will vote. Those with fewest votes will jump.

To do

  1. Each student is given one (double sided) page from the balloon debate 'talking heads' worksheet.
  2. Students have just 5 minutes to read their sheet and look up anything they don't understand
  3. Students then prepare a little speech to the whole class.
  4. They present their "speech" using the photo as a mask.
    Start with Aristotle and progress chronologically to end with von Baer.
  5. Students can ask questions after each presentation.
    They should take a few notes about each biologist as each one is presented.
  6. Students discuss details with a partner for 2 minutes and decide their top 3 biologists.
  7. Final vote, everyone has 3 votes to cast, take the votes one biologist at a time. The biologist with the fewest votes is thrown out of the balloon.

This activity is likely to be a lively discussion.
Students should answer the following questions at the end. 
There is an IB style questions student worksheet of these questions too.

IB Style questions

William Harvey investigated sexual reproduction in deer for several years.  In his writings he proposed a new doctrine ex ovo omnia, meaning that all life originates from an egg. Regarding the mechanism of reproduction, he concluded that the male semen doesn’t reach the uterus but sends up an “effluvium” which stimulates the uterus to secrete an egg. First this is something with no body, then it becomes a filamentous web and finally it forms into an embryo.

Which scientist(s) work did he disprove?

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How did Harvey's methods and conclusions help or hinder the work of later scientists?

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The microscope was invented 17 years after Harvey's death.
If Harvey had used a microscope suggest how his conclusions could have been different? Explain why.

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Click the eye icon to display some suggested answers

IB Style questions

William Harvey investigated sexual reproduction in deer.

Which scientist(s) work did he disprove?

Harvey denounced the theory of 'spontaneous generation' of Aristotle and Galen,
and he also contested Aristotle's idea that the embryo comes from the menstrual blood and the male semen.

Harvey was convinced that the embryo came from an egg, although his conclusions about the non-material early stages of embryo development were wrong.

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How did Harvey's methods and conclusions help or hinder the work of later scientists

Harvey's rigorous scientific methods based on experiment and observation inspired the work of later biologists, who repeated his methods.

His idea that the male semen sends an "effluvium" to the uterus and the concept that the egg at first has no body may have dissuaded some biologists from looking for ova.

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The microscope was invented 17 years after Harvey's death.
If Harvey had used a microscope how might his conclusions have been different? Explain why.

Had Harvey had a hand lens or a microscope he would have probably seen the ova in the filaments which he observed in the uterus.

He might have seen sperm cells in the uterus

Many biological discoveries follow the development of new apparatus.

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Activity 2 - Structure of human reproductive organs

As activity 1 shows the importance of anatomical study to biology label the following simple diagrams of the human reproductive organs with their structure and function. Record your annotations on this worksheet shown below​.

Activity 3 - Oestrogen, progesterone and testosterone hormones.

Hormones which lead to the development of prenatal development of male and female reproductive organs and secondary sexual characteristics were discovered later. They influence the ovulation of an ova from its ovary, and the successive implantation of the blastocyst in the uterus lining. This information about the functions of these hormones is also important in IB Biology.

Study the flashcards below then take an online test here.

Teacher's notes

In activity 1: The balloon debate is a nice way to get everyone to read and hear about he early days of embryology.

Students research ten biologists from Aristotle to de Graaf using the balloon debate 'talking heads' worksheet - they find out a little about each of their methods and their findings. The aim is to illustrate the scientific method, how international collaboration helps the advance of science and how the study of anatomy can lead to an understanding of biological processes. 

An alternative for activity 1 would be to organise the ideas about reproduction in a chronological timeline.

  • Students write about their biologist on a post it, answering the questions above.
  • Then as a group they read each others, organise them into a timeline and then group them into similar methods.
  • Identify those who showed ingenuity / creativity / resilience etc.

Activities 2 & 3 are very simple, but important parts of the IB guide.

For further information the following links are useful.

Harvey's book (in latin) Exercitationes de generatione animalium

and Harvey's book translated into English

See more here and in the Embryo project encyclopedia

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For more on balloon debates take a look at this great blog: Tarr's toolbox