Life Cycle - Human Biology (6A)

  • Plotting human growth during pregnancy.
  • Analyzing the different stages of human growth.
  • chromosome
  • egg cell
  • fertilization
  • fetus
  • pregnancy
  • sperm cell
  • fetus growth chart
  • ruler
  • chart on organ development

Students measure the stages of a growing fetus.


Babies grow within the womb of their mothers. The sperm of the father unites with the egg of the mother to start the creation of life. The medical profession divides all pregnancies into three trimesters - a period of three months. This division is useful because various events, signs, and developments tend to appear in different trimesters. From a length of three inches and a weight of one ounce, the fetus grows to some 14 inches and a weight of two and quarter pounds at the end of the second trimester. Movements of the fetus become noticeable at about 20 weeks or midway through the second trimester. The mother's weight gain is the most rapid during these three months, averaging close to a pound a week. 

Within the first week, three layers of cells form which will later be the start of all organs. The outer layer produces the nervous system, skin, nails, hair, and tooth enamel. The middle layer produces the bones, muscles, kidneys, and circulatory system. The inner layer produces the respiratory and digestive system and the glands. 

The genetic material directs the number of cells at a given time in the growing baby. Two cells (the original egg and sperm) divide into the 6 trillion cells of a newborn baby. In this lab we want the students to look at the development of the fetus. All children are curious about what is going on within a woman who is pregnant, it is something obvious, natural, and all of us have gone through it ourselves. Question from children are natural and remember that this is not a morality issue, it is a fact of life. Describing and explaining pregnancy in a factual method, will make these students confident of what is going on.  

  1. This lab looks at the development of the baby in the mother's womb.  Students need to measure the fetus during selected periods of growth.  On the lab sheet graph, students need to obtain the following information: number of weeks of growth; the size of the fetus at that time; the difference between the last growth and the new growth; the rate of growth (growth/time); and the percent of growth.  
  2. We suggest that you use a calculator and measure in centimeters because it makes the math much easier.  The answers are below.  Please note that the precision of the fetus growth is simplified.
  # Weeks Size cm Growth cm Growth Rate % Growth
5th week 5 .1 .1 .02 2%
8th week 3 .8 .7 .23 23%
12th week 4 2 1.2 .3 30%
18th week 6 3.6 1.6 .26 26%
22nd week 4 5 2.4 .60 60%
26th week 4 6 1 .25 25%
30th week 4 7 1 .25 25%
34th week 4 7.3 .3 .075 7.5%
36th week 4 7.4 .1 .025 2.5

The rate of growth is greatest between the 18th and 22nd week (4th-5th months).  The baby turns around because its head must come out first.  The baby turns until it gets into that position.

  1. 4th week
  2. 5th week
  3. 7th month, 5th month
  4. 6th month
  5. 7th month 
  1. Students may ask about abortion, but just refrain from your views and tell students that is a moral issue, and not part of this science lesson.  

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