Reproduction and Development

​I start this unit asking students which of the cells in the first slide of their note packet they think is reproducing.  We discuss student's observations about the characteristics of these dividing cells.

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​I explain why cells can't continue to grow indefinitely.  We then demonstrate this mathematically using an imaginary cube shaped cell. Students note that, as the cell size increases, the cell's volume increases more dramatically than does its surface area. Therefore, the cell's cytoplasm and organelles within cannot receive the necessary water, nutrients, and oxygen to conduct their activities, nor can the cell membrane rid the cell of the wastes it produces if it grows too large.

​The class then completes the LAB Limits to Cell Size in which a model large cell (hard boiled egg) and model small cell ("cube" cut from the white of a hard boiled egg) are used to demonstrate the relationship of surface area and volume on the relative sizes of cells.

​​Students next learn about the cell cycle.  I spend some time talking about the phonetically similar terms chromatin, chromatid, sister chromatid, centromere, and chromosome.  I clarify the vocabulary to students.

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​I explain that we will focus on asexual reproduction first and get to sexual reproduction a bit later.  But I clarify the main differences in the number of parents, and the similarity or lack of similarity of the offspring.

​I go over the phases of mitosis and make sure that students can identify the phases using cell diagrams in each phase.  I tell students that plant cells that undergo mitosis do so without centrioles and have a cell plate in telophase.

I clarify the terms haploid, diploid, and homologous chromosomes.  I also explain that most diagrams showing mitosis will have only 2 or 4 chromosomes for simplification, but human cells contain 46, which replicate during interphase to produce 92, but when the chromatid pairs separate each daughter cell winds up with 46, the same as the parent.

​There are several cell cycle and mitosis activities that I used to reinforce those concepts.  I also discuss special kinds of mitosis such as binary fission, budding, sporulation, regeneration, and vegetative propagation.  I talk about some specific organisms which reproduce asexually.

​I talk about the proteins known as cyclins, which regulate the timing of the cell cycle in eukaryotic cells.   I tell students that cancer is the disorder in which body cells have lost the ability to regulate their own cell cycles. I give examples of typical cell life spans of cells indifferent parts of the human body. 

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​​Moving on to sexual reproduction, students complete a Diagramming Meiosis LAB.   I discuss sexual reproduction in plants.  Students learn reproductive structures in flowers, pollination, and germination.  I spend some extra time on the parts of the bean seed in my discussion about germination.  The class follows with a Bean Seed LAB in which they dissect a Lima bean.

​​Next, I talk in more detail about meiosis and gametogenisis in humans.  I discuss crossing-over, disjunction, non-disjunction and compare internal fertilization vs external fertilization done by some other organisms.

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​I use diagrams on slides in the PowerPoint, as well as reproductive system models to discuss human reproductive structures.  In terms of the male system, I explain the functions of the urethra and ​vasa deferentia.  I talk about the passage of sperm, seminal fluid, the functions of the epididymus, Cowper's gland, and prostate, as well as the implications of the vasectomy.  I go over specialized structures of sperm.

I terms of the female system, I explain the location of the urethra in females, as compared to males.  Many students, even at the high school level, have inaccurate ideas about the orifices of females in relation to urination, menstruation, and deification!  I enlighten them.  ​

I talk about the differences in the timing of oogenesis, compared to spermatogenesis.  I compare the timing of fertility of females to that of males and I briefly touch on ovulation (which I discuss more later).  I discuss the differences between the female egg and the male sperm.

I discuss ovulation in more detail when I cover the menstrual cycle.  I talk about the relevant hormones that are associated with the female menstrual cycle and mention testosterone as the main hormone associated with male reproductive structures and traits.  After I describe what happens if pregnancy does not occur, I move on to if pregnancy does occur.  I describe the process of fertilization and embryonic development. 

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Finally, I end the unit by talking about some specialized processes and situations:  amniocentesis, artificial insemination, sperm and egg banks, and multiple births.  Students complete a LAB on Embryological Development.  I also have students compare and contrast mitosis and meiosis to review.

The Presentation and Student Notes files are available here.