A.) Differentiate between ovum, morula, blastula and gastrula.
B.) Discuss neurulation and state the significance.
C.) Describe the functions of the extra-embryonic membranes.
D.) List tissue that results from each germ layer.
E.) View the two diagrams that illustrate the early development of the 72-hour chick embryo and the 7-mm (~32 – 36 days) human embryo. Compare the diagrams. What are some similarities? What are some differences?
F.) How would you differentiate between a pre-metamorphic, prometamorphic, and a metamorphic tadpole?
The Correct Answer and Explanation is:
Sure! Here’s a complete breakdown of your questions on embryonic development and metamorphosis:
A.) Differentiate between ovum, morula, blastula, and gastrula
| Stage | Description |
|---|---|
| Ovum | The unfertilized female gamete (egg cell); it is haploid and ready for fertilization by a sperm. |
| Morula | A solid ball of cells resulting from early cleavage divisions of the zygote (16–32 cells), resembling a mulberry. |
| Blastula | A hollow ball of cells formed from the morula; contains a fluid-filled cavity called the blastocoel. |
| Gastrula | A stage following the blastula, where cells begin to migrate inward forming the three germ layers (ectoderm, mesoderm, endoderm) via gastrulation. |
B.) Discuss neurulation and state the significance
Neurulation is the process during embryonic development in which the neural tube forms from the ectoderm. It typically follows gastrulation.
- Steps:
- The notochord induces the overlying ectoderm to form the neural plate.
- The neural plate folds to form the neural groove.
- The edges (neural folds) fuse to form the neural tube.
- Significance:
- The neural tube becomes the brain and spinal cord (central nervous system).
- It marks the beginning of organogenesis.
- Errors in neurulation can result in serious birth defects (e.g., spina bifida).
C.) Describe the functions of the extra-embryonic membranes
- Amnion – Forms a fluid-filled sac (amniotic fluid) that cushions and protects the embryo.
- Chorion – Participates in gas exchange and forms part of the placenta in mammals.
- Yolk sac – Supplies nutrients in early development and forms the first blood cells.
- Allantois – Stores nitrogenous waste and contributes to the umbilical cord and placenta development in mammals.
D.) List tissue that results from each germ layer
| Germ Layer | Derived Tissues |
|---|---|
| Ectoderm | Skin, nervous system, eyes, hair, nails, enamel of teeth. |
| Mesoderm | Muscles, bones, cardiovascular system, kidneys, gonads, connective tissues. |
| Endoderm | Lining of the digestive and respiratory tracts, liver, pancreas, thyroid, urinary bladder. |
E.) Compare the diagrams of a 72-hour chick embryo and 7-mm human embryo
Similarities:
- Both show pharyngeal arches, neural tube, somites, and a tail-like structure.
- Both exhibit curved body shape due to rapid growth.
- Early organ systems are beginning to form in both.
Differences:
- The chick embryo develops outside the mother’s body (in an egg), while the human embryo develops in utero.
- The chick’s yolk sac is larger due to yolk nutrition, while in humans, the placenta is developing.
- The number and position of somites and limb buds differ due to timing and species-specific development.
- Chick embryos retain more avian-specific structures, such as the allantois protruding toward the shell.
F.) Differentiate between pre-metamorphic, prometamorphic, and metamorphic tadpoles
Correct Answer:
| Stage | Key Characteristics |
|---|---|
| Pre-metamorphic | Lacks hindlimbs; primarily focused on growth; dependent on aquatic lifestyle. |
| Prometamorphic | Hindlimbs appear; tail remains; internal changes begin; still aquatic. |
| Metamorphic (Climax) | Forelimbs emerge, tail resorbs; lungs become functional; transition to terrestrial life begins. |
300-word Explanation:
Tadpole metamorphosis is a complex process involving major morphological, physiological, and behavioral changes as an aquatic larva transforms into a terrestrial or semi-aquatic adult frog. This process is typically divided into three stages: pre-metamorphic, prometamorphic, and metamorphic.
In the pre-metamorphic stage, the tadpole is largely focused on feeding and growth. It lacks visible limbs and possesses a long tail used for swimming. Its body is entirely adapted to an aquatic environment, with gills for respiration and a herbivorous digestive system. Hormone levels, particularly thyroid hormones, are low during this phase.
The prometamorphic stage is marked by the appearance of hindlimbs, indicating the beginning of significant anatomical restructuring. During this time, the tadpole still retains its tail and gills but starts developing lungs and other adult organs. This stage is crucial for preparing the organism for a shift in habitat and behavior. Endocrine changes, especially a rise in thyroid hormones, drive internal and external transformations. As development proceeds, the tail becomes shorter and the mouth structure begins changing.
The metamorphic climax represents the final and most dramatic stage. Forelimbs emerge, the tail undergoes rapid resorption, and the tadpole shifts from an aquatic to a semi-terrestrial mode of life. The digestive system restructures for a carnivorous diet, lungs fully develop for air-breathing, and the skin thickens to reduce water loss. These changes allow the organism to survive on land. This phase is hormonally regulated and rapid, making it critical for survival.
Understanding these stages highlights the role of hormones in amphibian development and reflects evolutionary adaptations that enable amphibians to exploit both aquatic and terrestrial environments.
