Introduction All living things need to reproduce in order for the species to survive. If no offspring are reproduced from any of the members in a population, the species will not have replacements for those organisms that died; meaning that eventually the species will go extinct. Humans are sexual organisms, which means that in order to make an offspring, a male and female is needed. Human reproductions takes place inside the female. An egg is released from one of the two ovaries. This egg travels down a tube called the fallopian tubes. It is here where it is fertilized by a sperm cell. Sperm cells come from the male and are deposited in the female during sexual intercourse. When the egg becomes fertilized it becomes a zygote. The zygote continues to move down the fallopian tubes. While doing so, the single celled zygote beings to divide; first into two cells and then into four. This cellular division continues until a blastocyte (a ball of identical cells) is formed. Once the blastocyte is formed, the cells continue to divide but they are no longer identical; they become specialized or unique. These cells eventually become tissue, organs and then organ systems. This process of identical cells becoming specialized in known as differentiation. Has the cells in the blastocyte become more specialized and begin to develop tissues and organs, the blastocyte becomes a fetus. Complete development of a human fetus takes about 38 weeks. Increase in size and mass are two of the many changes that the fetus undergoes. Many factors can affect the birth size of a human baby, such as the amount of nutrient that the mother is consuming or the types of medicines or drugs the mother may take. But no matter what the weight of the fetus is, there is an average length standard for each stage of the baby's development. The approximate age of a fetus can be determined from its mass and length. Objective:
Students must calculate the length of a human fetus at various stages of development.
Graph the length of a developing human fetus.
Graph the mass of a developing fetus.
Determine the period of development during which the greatest change in mass and length occurs.
Procedure PART A - Development of a human Fetus The diagram below shows various stages of a developing human fetus. Each fetus in the picture is not drawn to scale and is approximately 40% smaller the an actual fetus at that stage of development.
Mitosis A cell spends most of its time doing what cells do: their normal cell functions.
1) ________________________
1. Measure each fetus using a metric ruler. Record your data in spaces provided in the table on the next page. Use the lines on the 38 week fetus to guild you on the following measurements: a. Body length - measured from the rump (butt) to the top of the head. b. Thigh length - measured from the rump to the knee. c. Leg length - measured from the heel to the knee. 2. Once the table is complete, add the body length, the thigh length and the leg length and fill in column (d) of the table. 3. Multiply the total length by 2.5 to give a figure that is close to the actual size of the fetus at each stage and fill in the last column of the table .
Data Table Length of Developing Fetus Age of fetus
(a) Body
(b) Thigh
(c) Leg Length
(d) Total Length
Actual
Times
in weeks
Length (cm)
Length (cm)
(cm)
(cm) (a+b+c)
Length (cm)
Actual
2.5 X (d)
length by 10
2 9 16 20 24 32 38 PART B - Graphing the Length of the developing Fetus 1) Make a line graph of the actually length (the last column) from the table above. Each plot must be circled and connected to each other. The first plot starts at "0", the time of fertilization.
PART C - Graphing the Mass of a Developing Fetus 1. Make a line graph use the data from the table below. Each plot must be circled and connected to each other. The first plot starts at "0", the time of fertilization. Mass of a Developing Fetus Time (weeks)
Mass (grams)
Time (weeks)
Mass (grams)
4
0.5
24
650
8
1
28
1100
12
15
32
1700
16
100
36
2400
20
300
38
3300
Analysis 1. What is the actual length of the fetus at week 9? _______________________________________ 2. How much mass does the fetus gain from 0 to 8 weeks? __________________________________ 3. Look at the graph of the length and the graph of the mass for the halfway point in development at week 19. a) Is the fetus half of its full length at this time? ________________ b) Is the fetus half of its full mass at this time? _________________ 4. Why was the total length of each fetus multiplied by 2,5 to obtain the actual length?_________________ _____________________________________________________________________________ 5. At what week does the fetus reach a) Half its full length? ____________ b) Half its full mass? ______________ 6. If a premature baby is born with a mass of a) 2200 grams, how old is the fetus? _________________ b) 1800 grams, how old is the fetus? __________________ 7. Based on this lab and your own knowledge, list 3 factors that can affect the birth weight of a developing human baby? ___________________________________________________________________ 8. Using the graph, what would you predict the length of the baby would be if the baby was born on the 40th week? ________________________________________________________________________ 9. The tranquilizer thalidomide was once prescribed for pregnant women. When the drug was used between the third and sixth week after fertilization, serious deformities in the fetus occurred as the fetus developed. State why thalidomide would have a greater effect on development when used between weeks 3 and 6 than when used in late pregnancy. (Hint: think about what is going on early in the pregnancy) _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________ _____________________________________________________________________________
