Module 4 Lesson 2 - 3 (Lab)

Lab - Comparing Embryonic Structures

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Introduction

Looking at various images, whether they be real or diagrams, will help you understand the differences of the various stages of embryonic development and the structures that support the embryo. In the following lab investigation, you will examine microscope slides of various stages of embryonic development in a sea urchin, and you will compare the support structures of an embryonic chick and an embryonic human.

Early embryonic development is similar in many species. In the beginning, formation of the embryonic cells and the supporting structure cells cannot be distinguished among various species of organisms.

In this investigation, you will compare embryonic stages of development using microscopy (scientific term for objects viewed by a microscope). Images of a sea urchin embryo, a chicken embryo, and a human embryo will be compared. 

Problem

How do embryonic structures of humans and other animals compare?

Materials

• blank paper
• pencil
• microscopy images of stages of embryo development (provided below)

Procedure

Part 1: Observing Embryonic Structures

1. View the microscopy images of the various stages of embryonic development. Be aware of the magnification power given and the name of the development stage.
   
   
2. Sketch the main features that you observe in the cleavage at the 4-cell stage, the blastula stage, and gastrula stage. Add labels to identify all the features that you recognize.

The source of the microscopy images is http://www.new.learnalberta.ca. The use of these materials is done without any affiliation with or endorsement by the Government of Alberta.

Part 2:  Comparing Extra-embryonic Structures

1. Examine the diagrams of extra-embryonic membranes of an embryonic chick and an embryonic human below.
   
   
2. Make notes on which extra-embryonic membranes the human and the chicken embryos have in common.
   
   
3. What similarities and differences do you observe in the structures of these membranes?  Describe or sketch your observations.

Observations

When you have completed examining the microscopy slides of the various stages of embryonic development, you should have completed three diagrams with appropriate labels and titles for each diagram. From your examination of these slides and the diagrams of the chick and human embryos, you should now be able to identify structures that support the embryo during its prenatal development.

Analysis

1. On which slide or slides do you observe evidence that cleavage has occurred?


2. Identify changes in the embryo that indicate that a blastocyst has formed.


3. Identify changes that indicate a gastrula has formed.


4. In birds, the extra-embryonic membranes have the following functions:
   
   • allantois: In combination with the chorion, the allantois transports oxygen to the embryo and removes carbon dioxide produced by the embryo. It stores nitrogenous wastes and absorbs calcium from the shell to make it available for bone formation.
   • amnion: This fluid-filled sac provides protection from physical shock and enables the embryo to move freely and safely.
   • chorion: See allantois.
   • yolk sac and yolk: The yolk sac stores nutrient-rich yolk and absorbs nutrients from it so that they are available for nourishing the embryo by means of blood vessels in the sac membrane.


5. How do the functions of the extra-embryonic membranes in birds compare with their functions in humans?
   
   1. Think about the place (the environment or location) in which human development occurs. Based on the place (environment or location) in which the following animals develop, predict whether they would form a placenta. Give reasons to justify your prediction.
      • Frog
      • Turtle
      • Sea star
      • Pike (fish)
      • Crow
   
   
   2. Identify the extra-embryonic membranes from which the placenta forms and explain how their function, which is modified in humans, relates to their function for chicken embryos.

Conclusions

In this lab, you should have been able to distinguish characteristics that identify the zygote, cleavage, morula, blastula, and gastrula stages of development of a sea urchin embryo. You should now be capable of comparing the embryonic supporting structures of a human and a chicken embryo.

Real World Applications (Going Beyond)

Many cells and tissues support the developing embryo. How do you think this changes if the mother is a litter-bearing animal such as cat, dog, or mouse? Find this answer by doing some research on your own.